HEAT EXCHANGER

Abstract

A flow inlet and a flow outlet are provided at one lateral end of a core. A second communication passage is provided at the other lateral end of the core to communicate between an interior of a downstream side lower tank, which is connected to a furthermost downstream side passage row that is furthermost from the flow inlet, and an interior of an upstream side lower tank, which is connected to a furthermost upstream side passage row that is furthermost from the flow outlet. The second communication passage is placed at a location that projects from a body of the core in a lateral direction or a top-to-bottom direction of the core.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2007-336862 filed on Dec. 27, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat exchanger.

2. Description of Related Art

For example, Japanese Unexamined Patent Publication No. JP2005-291659A discloses an evaporator as a heat exchanger. This evaporator has a core (a heat exchanging unit) that includes an upstream side row of tubes and a downstream side row of tubes, which are placed one after another in a direction of an air flow. In each row, the tubes extend in a top-to-bottom direction of the core and are stacked one after another in a lateral direction of the core. An upper tank is provided at upper ends of the tubes, and a lower tank is provided at lower ends of the tubes. A partition plate is placed in an interior of the upper tank.

In this evaporator, refrigerant is supplied into the interior of the upper tank through a refrigerant inlet, which is provided at one lateral end of the upper tank. Then, the refrigerant flows from the interior of the upper tank through the downstream side row of the tubes and the lower tank and makes a U-turn. Thereafter, the refrigerant is supplied into the upstream side row of the tubes. Next, the refrigerant flows through the upstream side row of the tubes and the lower tank and makes a U-turn. Thereafter, the refrigerant is outputted from a refrigerant outlet, which is provided next to the refrigerant inlet at the same side of the core. When the refrigerant flows through the tubes, the refrigerant exchanges the heat with the air, which flows outside of the tubes. Thereby, the refrigerant is evaporated.

In the above heat exchanger, the refrigerant distribution in the direction of the air flow at the core poses the following disadvantage. That is, at a further portion of the core, which is apart from the refrigerant inlet, the refrigerant, which is discharged from the tank, tends to enter the downstream side row of the tubes. Therefore, the supply of the refrigerant is biased to the downstream side. As a result, the desirable refrigerant performance cannot be achieved.

SUMMARY OF THE INVENTION

The present invention addresses the above disadvantage. Thus, it is an objective of the present invention to provide a heat exchanger, which alleviates biasing of a refrigerant flow that tends to enter a downstream side flow passage at a further portion of a core, which is apart from a refrigerant inlet.

To achieve the objective of the present invention, there is provided a heat exchanger that includes a core, a plurality of downstream side header tanks, a plurality of upstream side header tanks, a refrigerant inlet, a refrigerant outlet, at least one downstream side partition wall and at least one upstream side partition wall. The core includes a plurality of downstream side flow passage rows and a plurality of upstream side flow passage rows. Each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row. The downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant. Each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row. The upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow. Each downstream side header tank supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows. The plurality of downstream side header tanks includes at least one downstream side upper tank and at least one downstream side lower tank. Each downstream side upper tank is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows. Each downstream side lower tank is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows. Each upstream side header tank supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows. The plurality of upstream side header tanks includes at least one upstream side upper tank and at least one upstream side lower tank. Each upstream side upper tank is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows. Each upstream side lower tank is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows. The refrigerant inlet is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows. The refrigerant outlet is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows. Each downstream side partition wall is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall. Each upstream side partition wall is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall.

In one instance, a communicating means may be provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet. The communicating means is for communicating between an interior of each corresponding one of the downstream side header tanks, which is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of each corresponding one of the upstream side header tanks, which is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core. The communicating means is placed at a location that projects from a body of the core in one of the lateral direction and the up-to-bottom direction of the core. A portion of the refrigerant in a furthermost one of the downstream side header tanks, which is furthermost from the refrigerant inlet in the lateral direction of the core, is conducted toward the upstream side of the air flow into a furthermost one of the upstream side header tanks located on an upstream side thereof in the direction of the air flow after flowing through the communicating means and then flows through the furthermost one of the upstream side flow passage rows into an opposed one of the upstream side header tanks, which is opposed to the furthermost one of the upstream side header tanks in the top-to-bottom direction of the core. A rest of the refrigerant, which remains in the furthermost one of the downstream side header tanks, flows through the furthermost one of the downstream side flow passage rows into an opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks where the rest of the refrigerant is merged with the portion of the refrigerant supplied through the communicating means.

In another instance, a lower communication passage may be provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet. The lower communication passage communicates between an interior of a furthermost one of the at least one downstream side lower tank, which is furthermost from the refrigerant inlet in the lateral direction of the core and is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side lower tank, which is furthermost from the refrigerant outlet in the lateral direction of the core and is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, to conduct a portion of the refrigerant in the furthermost one of the at least one downstream side lower tank into the furthermost one of the upstream side flow passage rows. The portion of the refrigerant from the furthermost one of the at least one downstream side lower tank flows into the furthermost one of the at least one upstream side lower tank through the lower communication passage and then flows into the furthermost one of the at least one upstream side upper tank after flowing upwardly thorough the furthermost one of the upstream side flow passage rows. A rest of the refrigerant, which remains in the furthermost one of the at least one downstream side lower tank, flows upwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side upper tank and then flows into the furthermost one of the at least one upstream side upper tank and is merged with the portion of the refrigerant in the furthermost one of the at least one upstream side upper tank. The refrigerant inflow opening of the lower communication passage is an inlet of the lower communication passage and opens to an interior of the furthermost one of the at least one downstream side lower tank at a location that is below lower end openings of the downstream side tubes of the furthermost one of the downstream side flow passage rows in the vertical direction.

In a further instance, an upper communication passage may be provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet. The upper communication passage communicates between an interior of a furthermost one of the at least one downstream side upper tank, which is furthermost from the refrigerant inlet in the lateral direction of the core and is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side upper tank, which is furthermost from the refrigerant outlet in the lateral direction of the core and is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, to conduct a portion of the refrigerant in the furthermost one of the at least one downstream side upper tank into the furthermost one of the upstream side flow passage rows. The portion of the refrigerant from the furthermost one of the at least one downstream side upper tank flows into the furthermost one of the at least one upstream side upper tank through the upper communication passage and then flows into the furthermost one of the at least one upstream side lower tank after flowing downwardly thorough the furthermost one of the upstream side flow passage rows. A rest of the refrigerant, which remains in the furthermost one of the at least one downstream side upper tank, flows downwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side lower tank and then flows into the furthermost one of the at least one upstream side lower tank and is merged with the portion of the refrigerant in the furthermost one of the at least one upstream side lower tank. A refrigerant inflow opening of the upper communication passage is an inlet of the upper communication passage and opens to an interior of the furthermost one of the at least one downstream side upper tank at a location that is above upper end openings of the downstream side tubes of the furthermost one of the downstream side flow passage rows in the vertical direction.

In a further instance, a communicating means may be provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet. The communicating means is for communicating between an interior of each corresponding one of the downstream side header tanks, which is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of each corresponding one of the upstream side header tanks, which is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core. The core has an upstream side lateral plane and a downstream side lateral plane, which are located on the upstream side and the downstream side, respectively, in the direction of the air flow. The core is tilted toward the upstream side in the direction of the air flow such that the upstream side lateral plane is closer to an imaginary horizontal plane, which is placed vertically below the at least one upstream side lower tank, in comparison to the downstream side lateral plane. A portion of the refrigerant in a furthermost one of the downstream side header tanks, which is furthermost from the refrigerant inlet in the lateral direction of the core, is conducted toward the upstream side of the air flow into a furthermost one of the upstream side header tanks located on an upstream side thereof in the direction of the air flow after flowing through the communicating means and then flows through the furthermost one of the upstream side flow passage rows into an opposed one of the upstream side header tanks, which is opposed to the furthermost one of the upstream side header tanks in the top-to-bottom direction of the core. A rest of the refrigerant, which remains in the furthermost one of the downstream side header tanks, flows through the furthermost one of the downstream side flow passage rows into an opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks where the rest of the refrigerant is merged with the portion of the refrigerant supplied through the communicating means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a perspective view showing an evaporator (an example of a heat exchanger) according to a first embodiment of the present invention;

FIG. 2 is a partial perspective enlarged view showing a portion of a core of the evaporator;

FIG. 3 is a schematic view showing a structure and a refrigerant flow of the evaporator according to the first embodiment;

FIG. 4 is an exploded view showing a structure of a communication passage forming member of the evaporator according to the first embodiment;

FIG. 5 is a schematic view showing a structure and a refrigerant flow of an evaporator according to a second embodiment of the present invention;

FIG. 6 is a schematic diagram seen in a direction opposite from an X-direction, showing a positional relationship of a communication passage inlet and a communication passage outlet relative to a downstream side flow passage row and an upstream side flow passage row according to the second embodiment;

FIG. 7 is a schematic view showing a structure and a refrigerant flow of an evaporator according to a third embodiment of the present invention;

FIG. 8 is a schematic view showing a structure and a refrigerant flow of an evaporator according to a fourth embodiment of the present invention;

FIG. 9 is a schematic view showing a structure and a refrigerant flow of an evaporator according to a fifth embodiment of the present invention;

FIG. 10 is a schematic view showing a structure and a refrigerant flow of an evaporator according to a sixth embodiment of the present invention;

FIG. 11 is a schematic diagram seen in an X direction, showing a positional relationship of a communication passage inlet and a communication passage outlet relative to a downstream side flow passage row and an upstream side flow passage row according to the sixth embodiment;

FIG. 12 is a schematic view showing a structure and a refrigerant flow of an evaporator according to a seventh embodiment of the present invention;

FIG. 13 is a schematic view seen from a direction opposite from a Z-direction, showing a relationship of communication holes relative to a downstream side flow passage row and an upstream side flow passage row according to the seventh embodiment;

FIG. 14 is a schematic view showing a structure and a refrigerant flow of an evaporator according to an eighth embodiment of the present invention;

FIG. 15 is a schematic view seen from a direction opposite from a Z-direction, showing a relationship of communication holes relative to a downstream side flow passage row and an upstream side flow passage row according to the eighth embodiment;

FIG. 16 is a schematic view showing a structure and a refrigerant flow of an evaporator (a case where the number of refrigerant flow paths is six) according to a ninth embodiment of the present invention;

FIG. 17 is a schematic view showing a structure and a refrigerant flow of an evaporator (a case where the number of refrigerant flow paths is five) according to a tenth embodiment of the present invention;

FIG. 18 is a schematic view showing a structure and a refrigerant flow of an evaporator (a case where the number of refrigerant flow paths is five) according to an eleventh embodiment of the present invention;

FIG. 19 is a schematic view showing a structure and a refrigerant flow of an evaporator (a case where the number of refrigerant flow paths is four) according to a twelfth embodiment of the present invention;

FIG. 20 is a schematic view showing a structure and a refrigerant flow of an evaporator (a case where the number of refrigerant flow paths is three) according to a thirteenth embodiment of the present invention;

FIG. 21 is a side view showing a positioning state of an evaporator according to a fourteenth embodiment of the present invention;

FIG. 22 is a partial schematic side view showing an interior of an upper header tank at a furthermost portion of the evaporator and a refrigerant flow quantity relationship in an interior of a core of the evaporator according to the fourteenth embodiment;

FIG. 23 is a partial schematic side view showing an interior of a lower header tank at a furthermost portion of the evaporator and a refrigerant flow quantity relationship in an interior of the core of the evaporator according to the fourteenth embodiment;

FIG. 24 is a partial side view showing an upper header tank of an evaporator according to a fifteenth embodiment of the present invention;

FIG. 25 is a partial front view seen from an X-direction, showing a flow inlet at the upper header tank of FIG. 24;

FIG. 26 is a graph showing a result of a computation obtained under a predetermined condition for a relationship between a tank outer diameter and a pressure loss in an interior of the tank according to the fifteenth embodiment;

FIG. 27 is a schematic diagram for designing an appropriate condition of a flow quantity of refrigerant, which flows in an upstream side flow passage row, and a flow quantity of a refrigerant, which flows in a downstream side flow passage row, according to a sixteenth embodiment of the present invention;

FIG. 28 is a diagram showing a result of a computation of a ratio between a total passage cross sectional area of a branching passage and a total passage cross sectional area of a merging passage for various numbers of refrigerant flow paths according to the sixteenth embodiment;

FIG. 29 is a schematic view showing a structure and a refrigerant flow of an evaporator according to a seventeenth embodiment of the present invention;

FIG. 30 is a schematic diagram showing a modification of the evaporator of FIG. 29;

FIG. 31 is a schematic front view showing a relationship between communication passage forming member and a core of an evaporator according to an eighteenth embodiment of the present invention;

FIG. 32 is a schematic partial front view showing a modification of the evaporator of FIG. 31; and

FIG. 33 is a schematic partial front view showing another modification of the evaporator of FIG. 31.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, similar components are indicated by the same reference numerals and will not be redundantly described to simply the description. Furthermore, it should be noted that any one or more components of one or more of the following embodiments may be freely combined with any one or more components of any other one or more of the following embodiments as long as there is no reason that hinders implementation of such a combination.

First Embodiment

A first embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a schematic perspective view showing an entire structure of an evaporator 1 according to the first embodiment. FIG. 2 is a partial enlarged perspective view of a core 100, which is a heat exchanging unit of the evaporator 1. FIG. 3 is a schematic diagram showing the structure of the evaporator 1 and a flow of refrigerant therein according to the present embodiment.

The evaporator 1 of the present embodiment is a component of a refrigeration cycle, which is installed in a vehicle air conditioning system. The evaporator 1 serves as a heat exchanger. In this refrigeration cycle, the refrigerant is compressed by a compressor and becomes the high temperature and high pressure refrigerant. Thereafter, the refrigerant is cooled through a radiator and is depressurized through an expansion device to become the low temperature and low pressure refrigerant. The refrigerant is then supplied to the evaporator 1 and is evaporated therethrough. In the present embodiment, R134a (one of hydro-fluoro-carbon refrigerants) is used as the refrigerant. The radiator serves as a condenser, which condenses the refrigerant discharged from the compressor.

As shown in FIG. 1, the evaporator 1 includes a core 100, an upper header tank (forming corresponding upstream side and downstream side upper tanks described below) 3 and a lower header tank (forming corresponding upstream side and downstream side lower tanks described below) 4. As shown in FIG. 2, the core 100 includes a plurality of tubes 20, a plurality of outer fins 26 and side plates 28. The tubes 20 and the outer fins 26 are alternately staked in one direction (hereinafter, referred to as a stacking direction). Each of the side plates 28 is placed on an outer side of a corresponding one of opposed outermost outer fins 26 in the stacking direction. The outer fins 26 serve as heat exchanging fins. In FIGS. 1 and 2, an X-direction is the stacking direction (lateral direction), along which the tubes 20 are placed one after another. Furthermore, a Z-direction is a flow direction of the air, and a Y-direction is a longitudinal direction (extending direction) of the respective tubes and corresponds to a top-to-bottom direction of the core 100. In FIG. 1, a width W of the core 100 is measured in the X-direction, and a height H of the core 100 is measured in the Y-direction. Also, a thickness T of the core 100 is measured in the Z-direction.

In the core 100 of the evaporator 1, the vertically extending tubes 20 are arranged in a plurality of rows, each of which extends in the X-direction. The rows of the tubes 20 include at least two rows (an upstream side row and a downstream side row) of tubes 20, which are placed one after another in the Z-direction, i.e., the direction of the air flow (hereinafter, also simply referred to as the air flow direction). The air serves as an external fluid, which exchanges the heat with the refrigerant that flows through the tubes 20. Each tube 20 is formed, for example, by bending a thin aluminum strip plate into a generally flat tubular member that has a generally planar cross section, which is generally planar in a direction perpendicular to the longitudinal direction (internal fluid passage direction) of the tubular member. Inner fins (not shown) are provided in the interior of the tube 20 and are joined to an inner surface of the tube 20.

In the core 100, the rows of the tubes 20 are divided into a predetermined number of downstream side flow passage rows 21 of the tubes 20 (these tubes 20 will be hereinafter referred to as tubes 20a) placed on the downstream side in the air flow direction and a predetermined number of upstream side flow passage rows 22 of the tubes 20 (these tubes will be hereinafter referred to as tubes 20b) placed on the upstream side in the air flow direction with respect to the downstream side flow passage rows 21 of the tubes 20a. In each downstream side flow passage row 21, the tubes 20a are placed one after another in the X-direction (lateral direction) to form a plurality of flow passages. Also, in each upstream side flow passage row 22, the tubes 20b are placed one after another in the X-direction (lateral direction) to form a plurality of flow passages. The downstream side flow passage rows 21 and the upstream side flow passage rows 22 are respectively placed on the downstream side and the upstream side in the air flow direction and are integrated together to form the core 100. Here, the number of the downstream side flow passage rows 21 and the number of the upstream side flow passage rows 22 are determined based on a pattern of the refrigerant flow (hereinafter, referred to as a refrigerant flow pattern) in the core 100. Furthermore, with reference to FIG. 2, a thickness Ta of the downstream side flow passage row 21, which is measured in the direction of the air flow, is set to be generally the same as a thickness Th of the upstream side flow passage row 22, which is measured in the direction of the air flow, in this embodiment.

In each downstream side flow passage row 21, the refrigerant in each of the tubes 20a flows in a common direction. Furthermore, the downstream side flow passage rows 21 are communicated with each other through downstream side header tanks 11 (the downstream side upper tank of the upper header tank 3 and the downstream side lower tank of the lower header tank 4). In each upstream side flow passage row 22, the refrigerant in each of the tubes 20b flows in a common direction. Furthermore, the upstream side flow passage rows 22 are communicated with each other through upstream side header tanks 12 (the upstream side upper tank of the upper header tank 3 and the upstream side lower tank of the lower header tank 4).

The outer fins 26 are corrugate fins and have, for example, louvers (not shown) formed on the surfaces of the outer fins 26 to increase the heat exchange efficiency. The outer fins 26 are joined to the outer surfaces of the tube 20 (tubes 20a, 20b) by brazing.

The side plates 28 serve as reinforcing members, which reinforce the structural strength of the core 100. Each side plate 28 is formed through a press working process of an aluminum plate. Each of two opposed longitudinal end portions of each side plate 28 is configured into a flat plate form, and the rest of the side plate, which is other than the longitudinal end portions, is configured into a generally U-shaped form, which opens toward the outer side in the stacking direction of the tubes 20 (20a, 20b). Furthermore, the side plate 28 is fixed to the corresponding outer fin 26 by brazing.

The downstream side header tanks 11 include the downstream side upper tank (downstream side upper tank portion) 31 and the downstream side lower tank (downstream side lower tank portion) 41. The downstream side upper tank 31 is connected to upper ends of the tubes 20a of the downstream side flow passage rows 21, and the downstream side lower tank 41 is connected to lower ends of the tubes 20a of the downstream side flow passage rows 21. These upper and lower tanks 31, 41 form chambers (interior spaces), to which the refrigerant from the tubes 20a of the downstream side flow passage rows 21 is supplied and from which the refrigerant is distributed into the tubes 20a of the downstream side flow passage rows 21.

A connector 5 in a form of a block is fixed to a left side end (an end in a direction opposite from the X-direction) of the downstream side upper tank 31 by brazing. The connector 5 has a flow inlet 51, which serves as a refrigerant inlet that is communicated with the interior of the downstream side header tank 11 to conduct the refrigerant into the core 100. The flow inlet 51 is communicated with a left end of the downstream side lower tank 41 (an end in the direction opposite from the X-direction) through a side flow passage 2 defined in, for example, the interior side of the side plate 28.

The upstream side header tanks 12 include the upstream side upper tank 32 and the upstream side lower tank 42. The upstream side upper tank 32 is connected to upper ends of the tubes 20b of the upstream side flow passage rows 22, and the upstream side lower tank 42 is connected to lower ends of the tubes 20b of the upstream side flow passage rows 22. These upper and lower tanks 32, 42 form chambers (interior spaces), to which the refrigerant from the tubes 20a of the upstream side flow passage rows 22 is supplied and from which the refrigerant is distributed into the tubes 20a of the upstream side flow passage rows 22.

The connector 5 in the form of the block is fixed to a left side end (an end in a direction opposite from the X-direction) of the upstream side upper tank 32 by brazing. The connector 5 has a flow outlet 52, which serves as a refrigerant outlet that is communicated with the interior of the upstream side header tank 12 to conduct the refrigerant out of the core 100 toward the external device in the refrigerant cycle. As discussed above, the flow inlet 51 and the flow outlet 52 are respectively provided to the end of the downstream side header tank 11 and the end of the upstream side header tank 12 on the common lateral side of the core 100.

The upper header tank 3 is divided into two halves, which are referred to as a tank header and a plate header, in the longitudinal direction (the extending direction, the internal fluid passage direction) of the tubes 20 (20a, 20b). The tank header is placed on the side opposite from the tubes 20 (20a, 20b), and the plate header is placed on the side where the tubes 20 (20a, 20b) are located. Each corresponding longitudinal end opening of the upper header tank 3 is closed with a cap. The upper header tank 3 includes the downstream side upper tank (downstream side upper tank portion) 31 and the upstream side upper tank (upstream side upper tank portion) 32. Each of the tank header and the plate header has a cross section that includes two semi-spherical parts or two semi-rectangular parts, which are connected side-by-side. Furthermore, each of the tank header and the plate header is formed through a press working process of an aluminum plate. The tank header and the plate header are engaged with each other and are securely brazed together to form a tubular body, in which the two interior spaces are placed one after another in the air flow direction to form the downstream side upper tank 31 and the upstream side upper tank 32. The cap, which is formed through a press working of an aluminum plate, is brazed to each corresponding longitudinal end opening of the downstream side upper tank 31 and of the upstream side upper tank 32 to close the same.

A plurality of separators (see FIG. 3) is fixed by brazing in the upper header tank 3 to divide each of the two internal spaces into two parts in the X-direction (the lateral direction). Specifically, the interior of the upstream side upper tank 32 is divided by the separator (upstream side upper partition wall) 32a into two spaces in the lateral direction of the core 100. Also, the interior of the downstream side upper tank 31 is divided by the separator (downstream side upper partition wall) 31a into two spaces in the lateral direction of the core 100.

The downstream side flow passage rows 21 include downstream side flow passage rows 21a, 210 (serving as upflow passage rows) and a downstream side flow passage row 21b (serving as a downflow passage row). The separator 31a is provided in the downstream side upper tank 31 in such a manner that one of the downstream side flow passage rows 21a, 210 is placed adjacent to the separator 31a on one lateral side thereof, and the downstream side flow passage row 21b is placed adjacent to the separator 31a on the other lateral side thereof, thereby dividing between the upflow and the downflow. The, upstream side flow passage rows 22 include upstream side flow passage rows 22a, 220 (serving as upflow passage rows) and an upstream side flow passage row 22b (serving as a downflow passage row). The separator 32a is provided in the upstream side upper tank 32 in such a manner that one of the upstream side flow passage rows 22a, 220 is placed adjacent to the separator 32a on one lateral side thereof, and the upstream side flow passage row 22b is placed adjacent to the separator 32a on the other lateral side thereof, thereby dividing between the upflow and the downflow.

In the right side region of the downstream side upper tank 31, which is located on the right side of the separator 31a (the side of the separator 31a in the X-direction) in FIG. 3, a plurality of communication holes 300 is provided to communicate between the right lateral side space of the downstream side upper tank 31 and the right lateral side space of the upstream side upper tank 32.

The communication holes 300 are formed through a partition wall, which partitions the tank interior at the other lateral side, which is opposite from the lateral side wherein the flow inlet 51 and the flow outlet 52 are provided. The communication holes 300 serve as a communicating means for communicating between the interior of the furthermost downstream side upper tank 311 (also referred to as a furthermost downstream side upper tank portion, a furthermost downstream side upper tank interior, or a furthermost downstream side upper tank chamber of the downstream side upper tank 31), which is connected to the downstream side flow passage row 210 that is furthermost from the flow inlet 51 (hereinafter, also referred to as a furthermost downstream side flow passage row 210 at the furthermost portion of the core 100, which is furthermost from the flow inlet 51 and the flow outlet 52 in the X-direction), and the interior of the furthermost upstream side upper tank 321 (also referred to as a furthermost upstream side upper tank portion, a furthermost upstream side upper tank interior, or a furthermost upstream side upper tank chamber of the upstream side upper tank 32), which is connected to the upstream side flow passage row 220 that is furthermost from the flow outlet 52 (hereinafter, also referred to as a furthermost upstream side flow passage row 220 at the furthermost portion of the core 100). The communication holes 300 also form a part of a first communication passage 33, through which the refrigerant in the furthermost downstream side upper tank 311 flows toward the upstream side of the air flow and finally into the furthermost upstream side upper tank 321.

The first communication passage 33 is an upper communication passage, which communicates between the interior of the furthermost downstream side upper tank 311, which is furthermost from the flow inlet 51 in the lateral direction, and the furthermost upstream side upper tank 321, which is furthermost from the flow outlet 52 in the lateral direction. The interior of the downstream side upper tank 311 is the furthermost one of the two partitioned spaces, which are partitioned from each other in the lateral direction by the separator 31a, with respect to the flow inlet 51. The interior of the upstream side upper tank 321 is the furthermost one of the two partitioned spaces, which are partitioned from each other in the lateral direction by the separator 32a, with respect to the flow outlet 52.

The lower header tank 4 is similar to the upper header tank 3 and thereby includes the tank header and the plate header to form the tubular body. Caps are provided to longitudinal end portions, respectively, of the tubular body. The lower header tank 4 includes the downstream side lower tank 41 and the upstream side lower tank 42.

A plurality of separators (see FIG. 3) is fixed by brazing in the lower header tank 3 to divide each of the two internal spaces into two parts in the X-direction (the lateral direction). Specifically, the interior of the upstream side lower tank 42 is divided by the separator (downstream side lower partition wall) 42a into two spaces in the lateral direction of the core 100. Also, the interior of the downstream side lower tank 41 is divided by the separator (downstream side lower partition wall) 41a into two spaces in the lateral direction of the core 100.

The separator 41a is provided in the downstream side lower tank 41 in such a manner that one of the downstream side flow passage rows 21a, 210 is placed adjacent to the separator 41a on one lateral side thereof, and the downstream side flow passage row 21b is placed adjacent to the separator 41a on the other lateral side thereof, thereby dividing between the upflow and the downflow. The separator 42a is provided in the upstream side lower tank 42 in such a manner that one of the upstream side flow passage rows 22a, 220 is placed adjacent to the separator 42a on one lateral side thereof, and the upstream side flow passage row 22b is placed adjacent to the separator 42a on the other lateral side thereof, thereby dividing between the upflow and the downflow.

In the right side region of the downstream side lower tank 41, which is located on the right side of the separator 41a (the side of the separator 41a in the X-direction) in FIG. 3, a second communication passage 43 is provided to communicate between the right lateral side space of the downstream side lower tank 41 and the right lateral side space of the upstream side lower tank 42.

The second communication passage 43 is a lower communication passage (a communicating means), which communicates between the interior of the furthermost downstream side lower tank 411 (a furthermost downstream side lower tank portion, a furthermost downstream side lower tank interior, or a furthermost downstream side lower tank chamber of the downstream side lower tank 41), which is furthermost from the flow inlet 51 in the lateral direction, and the furthermost upstream side lower tank 421 (a furthermost upstream side lower tank portion, a furthermost upstream side lower tank interior, or a furthermost upstream side lower tank chamber of the upstream side lower tank 42), which is furthermost from the flow outlet 52 in the lateral direction. The interior of the downstream side lower tank 411 is the furthermost one of the two partitioned spaces, which are partitioned from each other in the lateral direction by the separator 41a, with respect to the flow inlet 51. The interior of the upstream side lower tank 421 is the furthermost one of the two partitioned spaces, which are partitioned from each other in the lateral direction by the separator 42a, with respect to the flow outlet 52.

The second communication passage 43 is formed in an interior of a communication passage forming member 44. A communication passage inlet 441a of the second communication passage 43, through which the refrigerant is supplied into the second communication passage 43, includes one or more holes that extend through in the X-direction (the lateral direction) to communicate between the interior of the furthermost downstream side lower tank 411 and the interior of the communication passage forming member 44. A communication passage outlet 441b of the second communication passage 43, through which the refrigerant is outputted from the second communication passage 43, includes one or more holes that extend through in the X-direction (the lateral direction) to communicate between the interior of the communication passage forming member 44 and the interior of the furthermost downstream side lower tank 421.

The communication passage forming member 44 is a separate component, which is formed separately from the downstream side lower tank 411 and the upstream side lower tank 421 and is integrally fixed to the downstream side lower tank 411 and the upstream side lower tank 421 by, for example, brazing. The communication passage forming member 44 is placed at a location, which projects laterally from the body of the core 100 (the body of the core 100 being made by the refrigerant conducting tubes 20 and the fins 26). In the present embodiment, the communication passage forming member 44 is configured into a box shape that projects laterally from the furthermost downstream side lower tank 411. Furthermore, the communication passage forming member 44 is made of the material that is similar to or is the same as that of the furthermost downstream side lower tank 411.

FIG. 4 is an exploded view showing the communication passage forming member 44. As shown in FIG. 4, the communication passage forming member 44 includes a planar member 441 and a dome member 44b. The planar member 441 has the communication passage inlet 441a and the communication passage outlet 441b and is joined to the downstream side lower tank 411 and the upstream side lower tank 421. The dome member 44b is joined to the planar member 441 and has a projecting portion 44a, which projects in the X-direction (lateral direction) away from the planar member 441 to define a predetermined space therein and thereby to define the second communication passage 43.

The communication passage forming member 44 may be assembled as follows. First, the planar member 441 is joined to the downstream side lower tank 411 and the upstream side lower tank 421 by, for example, brazing, such that the communication passage inlet 441a and the communication passage outlet 441b are respectively aligned with a lateral side end opening 411a of the downstream side lower tank 411 and a lateral side end opening 421a of the upstream side lower tank 421. Then, the dome member 44b is joined to the planar member 441 by, for example, brazing, such that the communication passage inlet 441a and the communication passage outlet 441b are opposed to a recess, which is formed inside of the projecting portion 44a.

With the above construction, a portion of the refrigerant in the furthermost downstream side lower tank 411 is supplied into the second communication passage 43 through the communication passage inlet 441a and flows toward the upstream side of the air flow to enter the furthermost upstream side lower tank 421 through the communication passage outlet 441b. Then, this refrigerant in the furthermost upstream side lower tank 421 flows upwardly through the furthermost upstream side flow passage row 220 and then flows into the furthermost upstream side upper tank 321, which is opposite from the furthermost upstream side lower tank 421 in the top-to-bottom direction of the core 100. The remaining refrigerant (the rest of the refrigerant) in the furthermost downstream side lower tank 411 flows upwardly through the furthermost downstream side flow passage row 210 and is supplied into the furthermost downstream side upper tank 311, which is opposite from the furthermost downstream side lower tank 411 in the top-to-bottom direction of the core 100. Then, this refrigerant flows toward the upstream side of the air flow and enters into the upstream side upper tank 321 where this refrigerant is merged with the branched portion of the refrigerant, which has passed through the second communication passage 43.

Tube insertion inlets and side plate insertion inlets are provided at generally equal pitches in the longitudinal direction in a wall surface of each of the upper and lower header tanks 3, 4. The longitudinal end portions of each tube 20 and the longitudinal end portions of each side plate 28 are received into and are joined to the corresponding tube insertion inlets and the corresponding side plate insertion inlets by, for example, brazing. In this way, the tubes 20 are communicated with the interior space of each of the upper and lower header tanks 3, 4, and the longitudinal end portions of each side plate 28 are supported by the upper and lower header tanks 3, 4.

The refrigerant flow pattern in the evaporator 1 of the present embodiment is constructed from three downstream side flow passage rows and three upstream side flow passage rows. The three downstream side flow passage rows include one downstream side flow passage row 21b (the refrigerant upflow portion), one downstream side flow passage row 21b (the refrigerant downflow portion) and one furthermost downstream side flow passage row 210. The three upstream side flow passage rows include one furthermost upstream side flow passage row 220, one upstream side flow passage row 22b (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion).

In this instance, the number of the refrigerant flow paths is counted in the following manner. Specifically, the refrigerant flow in the furthermost downstream side flow passage row 210 and refrigerant flow in the furthermost upstream side flow passage row 220 are collectively counted as one refrigerant flow path. Furthermore, the number (two in this instance) of the other downstream side flow passage rows 21a, 21b, which are other than the furthermost downstream side flow passage row 210, and the number (two in this instance) of the other upstream side flow passage rows 22a, 22b, which are other than the furthermost upstream side flow passage row 220, are also counted. Therefore, the number of the refrigerant flow paths in the core 100 is five in the present embodiment. Furthermore, the refrigerant flow pattern in the evaporator 1 is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 200 (the portion where the branched flow of the refrigerant, which is branched from the downstream side to the upstream side, flows upwardly in the top-to-bottom direction of the core 100). These numbers are written one after another according to the flow order of the refrigerant in the evaporator 1 and are thereby expressed as a 2-1-2 refrigerant flow pattern in this instance.

Next, the flow of the refrigerant in the evaporator 1 will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction) through the upper flow inlet 51 and the side flow passage 2. Then, the refrigerant flows upwardly through the downstream side flow passage row 21a (the first path). Next, the flow direction of this refrigerant is reversed in the interior of the downstream side upper tank 31, which is the space on the left lateral side of the separator 31a (the side of the separator 31a, which is opposite from the X-direction), and thereafter the refrigerant flows downwardly through the downstream side flow passage row 21b (the second path). Thereafter, this refrigerant is supplied into the interior of the furthermost downstream side lower tank 411.

Then, a portion of the refrigerant in the downstream side lower tank 411 is branched into the second communication passage 43. Then, in the second communication passage 43, the branched portion of the refrigerant flows in the X-direction and then flows toward the upstream side of the air flow (the side opposite from the Z-direction), and thereafter the branched portion of the refrigerant flows in the direction opposite from the X-direction and is supplied into the upstream side lower tank 421. Thereafter, this branched portion of the refrigerant flows upwardly through the furthermost upstream side flow passage row 220 (the third path, the full-path portion 200) into the upstream side upper tank 321.

In contrast, the remaining refrigerant (the rest of the refrigerant) in the downstream side lower tank 411, which is other than the branched portion of the refrigerant, flows upwardly through the furthermost downstream side flow passage row 210 (the third path, the full-path portion 200) and then flows from the interior of the downstream side upper tank 311 toward the upstream side of the air flow into the upstream side upper tank 321 through the communication holes 300 in the first communication passage 33. Then, this refrigerant is merged with the above branched portion of the refrigerant, which is supplied through the furthermost upstream side flow passage row 220 after flowing upwardly therethrough. That is, the refrigerant in the furthermost downstream side flow passage row 210 and the refrigerant in the furthermost upstream side flow passage row 220 flow upwardly parallel to one another.

The flow direction of the merged refrigerant, which is merged in the interior of the upstream side upper tank 321, is reversed, and this refrigerant flows downwardly through the upstream side flow passage row 22b (the fourth path). Then, the flow direction of this refrigerant is reversed once again in the upstream side lower tank 42, and thereby the refrigerant flows upwardly through the upstream side flow passage row 22a (the fifth path). Thereafter, this refrigerant flows to the outside of the core 100 from the upstream side upper tank 32 through the flow outlet 52.

Normally, the evaporator has the function of cooling the air by taking the heat of vaporization from the air at the time of vaporization of the liquid phase refrigerant (hereinafter, referred to as the liquid refrigerant). Therefore, in the evaporator, the refrigerant is in the two-phase (gas phase and liquid phase) state. In the operating state of the evaporator, a gas-liquid density ratio is about 80 to 95 times (i.e., liquid phase density:gas phase density=80-95:1) in the case of the R134a refrigerant and is about 8 to 9 times in the case of the carbon dioxide refrigerant. Therefore, the gas/liquid separation substantially occurs. Furthermore, an enlarged flow passage cross sectional area is provided at the tank as a refrigerant pressure loss reducing means. However, when this measure is taken, the refrigerant flow velocity at the tank is reduced, so that the gas/liquid separation is further promoted, thereby causing a reduced performance. Furthermore, there is a strong market demand for an evaporator having a simple structure, in which the refrigerant flow passage is simplified.

The evaporator of the present embodiment addresses the above demand and has the following structure. The evaporator has the flow inlet 51 and the flow outlet 52, which are provided at the one lateral end portion of the evaporator on the same lateral side. The second communication passage 43 (the lower communication passage) is provided to the opposite lateral side of the core 100, which is opposite from the side where the flow inlet 51 and the flow outlet 52 are located, to communicate between the interior of the downstream side lower tank 411, which is connected to the furthermost downstream side flow passage row 210 that is furthermost from the flow inlet 51, and the interior of the upstream side lower tank 421, which is connected to the furthermost upstream side flow passage row 220 that is furthermost from the flow outlet 52. The second communication passage 43 conducts the portion of the refrigerant in the furthermost downstream side lower tank 411, which is furthermost from the flow inlet 51, into the upstream side lower tank 421 to supply the refrigerant into the furthermost upstream side flow passage row 220. The second communication passage 43 is placed at the location that projects laterally or vertically (or in the top-to-bottom direction) from the body of the core 100.

The refrigerant, which has passed through the multiple downstream side flow passage rows 21 upwardly and downwardly multiple turns in the S-shaped path, gets the inertial force and reaches the furthermost downstream side lower tank 411. With the above structure, the refrigerant flows through the second communication passage 43 (the lower communication passage), which is placed at the location that projects laterally from the body of the core 100. Thus, the refrigerant can get the additional inertial force, and thereby the refrigerant in the downstream side lower tank 411 can be supplied in the greater amount to the furthermost upstream side flow passage row 220. The above effect is more prominent in the evaporator that has the thickness (the thickness in the air flow direction) T of the core 100, which is equal to or less than 70 mm.

The heat exchanger, which has the above structure, can reduce or alleviate the transitional period temperature distribution (transitional period temperature difference) between an on-time and an off-time of the compressor. When this heat exchanger is applied as the evaporator of the vehicle air conditioning system, the comfortableness of the occupant of the vehicle can be improved. Furthermore, the anti-frost performance of the evaporator can be improved to improve the cooling performance of the air conditioning system.

Furthermore, in the case where the refrigerant flow quantity is relatively small at the time of, for example, a low load operation, even in the upstream side flow passage, the flow of the refrigerant, which has passed through the second communication passage 43, is biased toward the downstream side of the air flow. Therefore, when the entire furthermost part of the core 100 is viewed, the condition of the refrigerant inflow in the core width direction is reversed between the downstream side part of the furthermost portion of the core 100 and the upstream side part of the furthermost portion of the core 100, so that they can be compensated with each other to implement the self adjusting function.

Furthermore, in the case of the evaporator 1 where the flow inlet 51 and the flow outlet 52 are provided together at the one lateral side of the core 100 in the lateral direction of the core 100, the adjacent area of the upstream side flow passage row 22, which is adjacent to the flow outlet 52, serves as a refrigerant superheating area. Therefore, the portion of the core 100, in which the refrigerant tends to be stagnated, is the furthermost downstream side flow passage row, which is placed furthermost from the flow inlet 51 and the flow outlet 52 and contacts with the cooler air. In the evaporator 1 of the present embodiment, the occurrence of the stagnation of the liquid refrigerant can be reduced or alleviated.

Furthermore, the evaporator 1 has the second communication passage 43 (the lower communication passage), which communicates between the interior of the furthermost downstream side lower tank 411 and the interior of the furthermost upstream side lower tank 421, and the first communication passage 33 (the upper communication passage), which communicates between the interior of the furthermost downstream side upper tank 311 and the interior of the furthermost upstream side upper tank 321. In this structure, the remaining refrigerant in the furthermost downstream side lower tank 411 flows upwardly through the furthermost downstream side flow passage row 210 and then flows toward the upstream side of the air flow through the first communication passage 33 and finally into the upstream side upper tank 321 where the remaining refrigerant is merged with the branched refrigerant, which has flown upwardly through the furthermost upstream side flow passage row 220 upon passing through the second communication passage 43 (the lower communication passage).

With the above structure, it is possible to limit the flow tendency of the refrigerant in the furthermost downstream side lower tank 411 into the downstream side flow passage row 210. Thereby, it is possible to supply the greater amount of the refrigerant into the upstream side flow passage row 220.

The refrigerant pressure loss of the evaporator 1 gets bigger toward the evaporator outlet side. Therefore, it is desirable to have the refrigerant, which has completed the heat exchange, at the location adjacent to the flow outlet 52. Since the flow outlet 52 is provided to the end portion of the upstream side upper tank 32, it is desirable that the upstream side flow passage row 22a, which conducts the final refrigerant flow in the upstream side flow passage rows 22, is the refrigerant upflow portion. Furthermore, since the furthermost upstream side flow passage row 220 (the third path), which is furthermost from the flow outlet 52, is also the refrigerant upflow portion, it is desirable that the upstream side flow passage row 22b (the fourth path) is the refrigerant downflow portion.

Second Embodiment

The evaporator 1 according to a second embodiment of the present invention is a modification of the first embodiment and will be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic diagram showing the structure of the evaporator 1 and the flow of refrigerant therein according to the present embodiment. FIG. 6 is a schematic diagram showing a positional relationship of the communication passage inlet 441a and the communication passage outlet 441b relative to the downstream side flow passage row 210 and the upstream side flow passage row 220.

In the present embodiment, the first communication passage 33 (the upper communication passage) of the evaporator 1 of FIG. 3 is modified and is thereby placed at a location, which projects laterally from the body of the core 100 in the X-direction (the lateral direction) in a manner similar to the second communication passage 43. Other than this point, the evaporator of the present embodiment is the same as the evaporator 1 of FIG. 3 and provides the same effects and the same advantages as those of the evaporator 1 of FIG. 3.

The first communication passage 33 is formed in an interior of a communication passage forming member 34. A communication passage inlet 341a of the first communication passage 33, through which the refrigerant is supplied into the first communication passage 33, includes one or more holes that extend through in the X-direction (the lateral direction) to communicate between the interior of the furthermost downstream side upper tank 311 and the interior of the communication passage forming member 34. A communication passage outlet 341b of the first communication passage 33, through which the refrigerant is outputted from the first communication passage 33, includes one or more holes that extend through in the X-direction (the lateral direction) to communicate between the interior of the communication passage forming member 34 and the interior of the furthermost upstream side upper tank 321.

The communication passage forming member 34 is a separate component, which is formed separately from the downstream side upper tank 311 and the upstream side upper tank 321 and is integrally fixed to the downstream side upper tank 311 and the upstream side upper tank 321 by, for example, brazing. The communication passage forming member 34 is placed at the location, which projects laterally from the body of the core 100. In the present embodiment, the communication passage forming member 34 is configured into a box shape that projects laterally from the furthermost downstream side upper tank 311. Furthermore, the communication passage forming member 34 is made of the material that is similar to or the same as that of the furthermost downstream side upper tank 311.

As shown in FIG. 6, the communication passage inlet 441a (a refrigerant inflow opening) is opened to the interior of the furthermost downstream side lower tank 411 and is located on a lower side of lower end openings 210a of the tubes 20a of the furthermost downstream side flow passage row 210 in the vertical direction (gravitational direction).

For the comparative purpose, it is now assumed that the refrigerant in the furthermost flow passage rows 210, 220 form the upflow, and the refrigerant inflow opening of the second communication passage opens in the furthermost downstream side lower tank only on an upper side of the lower end openings of the tubes of the furthermost flow passage rows 210, 220 in the vertical direction. In such a case, the lower end openings of the tubes of the furthermost flow passage row are closer to the liquid surface of the refrigerant in the tank in comparison to the refrigerant inflow opening of the second communication passage, so that the refrigerant tends to flow into the furthermost downstream side flow passage row 210, and thereby the refrigerant cannot easily flow into the first communication passage through the refrigerant inflow opening. With the above structure of the present embodiment, it is possible to limit the flow tendency of the refrigerant in the furthermost downstream side lower tank into the downstream side flow passage row, and thereby it is possible to supply the greater amount of the refrigerant into the upstream side flow passage row. As a result, the heat exchange performance of the evaporator can be improved.

Furthermore, it is desirable that an upper end of the opening of the communication passage inlet 441a (the refrigerant inflow opening) is located on the lower side of the lower end openings 210a of the tubes 20a of the furthermost downstream side flow passage row 210.

Third Embodiment

The evaporator 1 according to a third embodiment of the present invention is a modification of the evaporator 1 of the first embodiment and will be described with reference to FIG. 7. FIG. 7 is a schematic diagram showing the structure of the evaporator 1 and the flow of refrigerant therein according to the present embodiment.

The present embodiment differs from that of FIG. 3 such that the second communication passage 43 (the lower communication passage) of the evaporator 1 of FIG. 3 is modified and is thereby placed at a location, which projects downwardly from the body of the core 100 in the vertical direction (the direction opposite from the Y-direction). Other than this point, the evaporator of the present embodiment is the same as the evaporator 1 of FIG. 3 and provides the same effects and the same advantages as those of the evaporator 1 of FIG. 3.

In the case of the present embodiment, the communication passage forming member 44A, which forms the second communication passage 43, is provided integrally with the lower surfaces of the furthermost downstream side lower tank 411 and the furthermost upstream side lower tank 421, which are located at the lateral end portion of the core 100 in the X-direction. The communication passage forming member 44A is placed inward of two lateral ends of the core 100 in the lateral direction of the core 100. In this way, a dead space is reduced to effectively use the installation space for placing the heat exchanger, and the size of the core 100 in the width direction can be increased. Thus, it is possible to implement the design that improves the effective heat exchange surface area of the core 100.

The communication passage inlet 441a of the second communication passage 43, through which the refrigerant is supplied into the second communication passage 43, includes one or more holes that extend through a lower surface of the furthermost downstream side lower tank 411 and an upper surface of the communication passage forming member 44A in the Y-direction (the vertical direction) to communicate between the interior of the furthermost downstream side lower tank 411 and the interior of the communication passage forming member 44A. The communication passage outlet 441b of the second communication passage 43, through which the refrigerant is outputted from the second communication passage 43, includes one or more holes that extend through a lower surface of the furthermost upstream side lower tank 421 and an upper surface of the communication passage forming member 44A in the Y-direction (the vertical direction) to communicate between the interior of the communication passage forming member 44A and the interior of the furthermost downstream side lower tank 421.

The communication passage forming member 44A is a separate component, which is formed separately from the downstream side lower tank 411 and the upstream side lower tank 421 and is integrally fixed to the downstream side lower tank 411 and the upstream side lower tank 421 by, for example, brazing.

In the evaporator of the present embodiment, the second communication passage 43 is placed at the location, which projects downwardly from the body of the core 100 in the vertical direction (or in the top-to-bottom direction of the core 100). The refrigerant, which has passed through the multiple downstream side flow passage rows 21 upwardly and downwardly multiple turns in the S-shaped path, gets the inertial force and reaches the furthermost downstream side lower tank 411. This refrigerant flows through the second communication passage 43 (the lower communication passage), which is placed at the location that projects downwardly from the body of the core 100 in the vertical direction. Thus, the refrigerant can get the additional inertial force by the gravity to promote the vertically downward flow of the refrigerant, and thereby the refrigerant in the downstream side lower tank 411 can be supplied in the greater amount to the furthermost upstream side flow passage row 220.

Fourth Embodiment

The evaporator 1 according to a fourth embodiment of the present invention is a modification of the evaporator 1 of the first embodiment and will be described with reference to FIG. 8. FIG. 8 is a schematic diagram showing the structure of the evaporator and the flow of refrigerant therein according to the present embodiment.

The evaporator of the present embodiment differs from the evaporator 1 of FIG. 3 with respect to the following points. That is, the refrigerant flow pattern is different from that of FIG. 3, and the flow of the refrigerant in the furthermost flow passage row is the downflow. Furthermore, the first communication passage 33A is placed at a location, which projects laterally from the body of the core 101. In FIG. 8, components similar to those of FIG. 3 will be indicated by the same reference numerals. Other than this point, the evaporator of the present embodiment is the same as the evaporator 1 of FIG. 3 and provides the same effects and the same advantages as those of the evaporator 1 of FIG. 3.

The refrigerant flow pattern in the evaporator 1 of the present embodiment is constructed from two downstream side flow passage rows and two upstream side flow passage rows. The two downstream side flow passage rows include one downstream side flow passage row 21a (the refrigerant upflow portion) and one furthermost downstream side flow passage row 211 (the refrigerant downflow portion). The two upstream side flow passage rows include one furthermost upstream side flow passage row 221 (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion).

In this instance, the number of the refrigerant flow paths is three. Furthermore, the refrigerant flow pattern in the evaporator 1 is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 201 (the portion where the branched flow of the refrigerant from the downstream side to the upstream side flows downwardly). These numbers are written one after another according to the flow order of the refrigerant in the evaporator 1 and are thereby expressed as a 1-1-1 refrigerant flow pattern in this instance.

The first communication passage 33A is formed in the interior of the communication passage forming member 34A. A communication passage inlet 341a of the first communication passage 33A, through which the refrigerant is supplied into the first communication passage 33A, includes one or more holes that extend through in the X-direction (the lateral direction) to communicate between the interior of the furthermost downstream side upper tank 311 and the interior of the communication passage forming member 34A. A communication passage outlet 341b of the first communication passage 33A, through which the refrigerant is outputted from the first communication passage 33A, includes one or more holes that extend through in the X-direction (the lateral direction) to communicate between the interior of the communication passage forming member 34A and the interior of the furthermost upstream side upper tank 321.

The communication passage forming member 34A is a separate component, which is formed separately from the downstream side upper tank 311 and the upstream side upper tank 321 and is integrally fixed to the downstream side upper tank 311 and the upstream side upper tank 321 by, for example, brazing. The communication passage forming member 34A is placed at the location, which projects laterally from the body of the core 101. In the present embodiment, the communication passage forming member 34A is configured into a box shape that projects laterally from the furthermost downstream side upper tank 311. Furthermore, the communication passage forming member 34A is made of the material that is similar to or the same as that of the furthermost downstream side upper tank 311. In the evaporator of the present embodiment, a separator is not provided in the downstream side upper tank 31. Therefore, the furthermost downstream side upper tank 311 is the downstream side upper tank 31 itself.

With the above construction, a portion of the refrigerant in the furthermost downstream side upper tank 311 is supplied into the first communication passage 33A through the communication passage inlet 341a and flows toward the upstream side of the air flow to enter the furthermost upstream side upper tank 321 through the communication passage outlet 341b. Then, this refrigerant in the furthermost upstream side upper tank 321 flows downwardly through the furthermost upstream side flow passage row 221 and then flows into the furthermost upstream side lower tank 421, which is opposite from the furthermost upstream side upper tank 321 in the top-to-bottom direction of the core. The remaining refrigerant in the furthermost downstream side upper tank 311 flows downwardly through the furthermost downstream side flow passage row 211 and is supplied into the furthermost downstream side lower tank 411, which is opposite from the furthermost downstream side upper tank 311 in the top-to-bottom direction of the core. Then, this refrigerant flows toward the upstream side of the air flow and enters into the upstream side lower tank 421 where this refrigerant is merged with the branched portion of the refrigerant, which has passed through the first communication passage 33A.

Next, the flow of the refrigerant in the evaporator will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction) through the upper flow inlet 51 and the side flow passage 2. Then, the refrigerant flows upwardly through the downstream side flow passage row 21a (the first path) and is supplied into the downstream side upper tank 311.

Then, a portion of the refrigerant in the downstream side upper tank 311 is branched into the first communication passage 33A. Then, in the first communication passage 33A, the branched portion of the refrigerant flows in the X-direction and then flows toward the upstream side of the air flow (the side opposite from the Z-direction), and thereafter the branched portion of the refrigerant flows in the direction opposite from the X-direction and is supplied into the upstream side upper tank 321. Thereafter, this branched portion of the refrigerant flows downwardly through the furthermost upstream side flow passage row 221 (the second path, the full-path portion 201) into the upstream side lower tank 421.

In contrast, the remaining refrigerant in the downstream side upper tank 311, which is other than the branched portion of the refrigerant, flows downwardly through the furthermost downstream side flow passage row 211 (the second path, the full-path portion 201) and then flows from the interior of the downstream side lower tank 411 toward the upstream side of the air flow into the upstream side lower tank 421 through the communication holes 400 in the second communication passage 43. Then, this refrigerant is merged with the above branched portion of the refrigerant, which is supplied through the furthermost upstream side flow passage row 221 after flowing downwardly therethrough, in the upstream side lower tank 421. That is, the refrigerant in the furthermost downstream side flow passage row 211 and the refrigerant in the furthermost upstream side flow passage row 221 flow downwardly parallel to one another. The flow direction of the merged refrigerant, which is merged in the upstream side lower tank 421, is reversed, and this refrigerant flows upwardly through the upstream side flow passage row 22a (the third path). Thereafter, this refrigerant flows to the outside of the core from the upstream side upper tank 32 through the flow outlet 52.

In the evaporator of the present embodiment, the first communication passage 33A is placed at the location, which projects laterally from the body of the core 101. The refrigerant, which has passed through the multiple downstream side flow passage rows 21 upwardly and downwardly multiple turns in the S-shaped path, gets the inertial force and reaches the furthermost downstream side upper tank 311. This refrigerant flows through the first communication passage 33A (the upper communication passage), which is placed at the location that projects laterally from the body of the core 101. Thus, the refrigerant can get the additional inertial force to promote the flow of the refrigerant toward the upstream side of the air flow, and thereby the refrigerant in the downstream side upper tank 311 can be supplied in the greater amount to the furthermost upstream side flow passage row 221.

Fifth Embodiment

The evaporator according to a fifth embodiment of the present invention is a modification of the evaporator of the fourth embodiment and will be described with reference to FIG. 9. FIG. 9 is a schematic diagram showing the structure of the evaporator 1 and the flow of refrigerant therein according to the present embodiment. In the present embodiment, the second communication passage 43 (the lower communication passage) of the evaporator is modified from that of the evaporator 1 of FIG. 8 in a manner similar to the first communication passage 33A. Thus, the second communication passage 43 is placed at a location, which projects laterally from the body of the core 101 in the X-direction (the lateral direction). Other than this point, the evaporator of the present embodiment is the same as the evaporator 1 of FIG. 8 and provides the same effects and the same advantages as those of the evaporator 1 of FIG. 8.

Sixth Embodiment

The evaporator according to a sixth embodiment of the present invention is a modification of the evaporator of the fifth embodiment and will be described with reference to FIGS. 10 and 11. FIG. 10 is a schematic diagram showing the structure of the evaporator and the flow of refrigerant therein according to the present embodiment. FIG. 11 is a schematic diagram showing a positional relationship of the communication passage inlet 341a and the communication passage outlet 341b relative to the downstream side flow passage row 211 and the upstream side flow passage row 221.

The evaporator of the present embodiment is different from the evaporator of FIG. 9 with respect to the refrigerant flow pattern, the structure of the core 102, the number of the downstream side flow passage rows and the number of the upstream side flow passage rows. In FIG. 10, components similar to those of FIG. 9 will be indicated by the same reference numerals. Other than the above points, the evaporator of the present embodiment is the same as the evaporator of FIG. 9 and provides the same effects and the same advantages as those of the evaporator of FIG. 9.

The refrigerant flow pattern in the evaporator of the present embodiment is constructed from three downstream side flow passage rows and two upstream side flow passage rows. The three downstream side flow passage rows include one downstream side flow passage row 21b (the refrigerant downflow portion), one downstream side flow passage row 21a (the refrigerant upflow portion) and one furthermost downstream side flow passage row 211 (the refrigerant downflow portion). The two upstream side flow passage rows include one furthermost upstream side flow passage row 221 (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion). Furthermore, the evaporator of the present embodiment does not have the side flow passage.

In this instance, the number of the refrigerant flow paths is four. Furthermore, the refrigerant flow pattern in the evaporator is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 201 (the portion where the branched flow of the refrigerant from the downstream side to the upstream side flows downwardly). These numbers are written one after another according to the flow order of the refrigerant in the evaporator 1 and are thereby expressed as a 2-1-1 refrigerant flow pattern in this instance.

With the above construction, a portion of the refrigerant in the furthermost downstream side upper tank 311 is supplied into the first communication passage 33A through the communication passage inlet 341a and flows toward the upstream side of the air flow to enter the furthermost upstream side upper tank 321 through the communication passage outlet 341b. Then, this refrigerant in the furthermost upstream side upper tank 321 flows downwardly through the furthermost upstream side flow passage row 221 and then flows into the furthermost upstream side lower tank 421, which is opposite from the furthermost upstream side upper tank 321 in the top-to-bottom direction of the core. The remaining refrigerant in the furthermost downstream side upper tank 311 flows downwardly through the furthermost downstream side flow passage row 211 and is supplied into the furthermost downstream side lower tank 411, which is opposite from the furthermost downstream side upper tank 311 in the top-to-bottom direction. Thereafter, this refrigerant flows into the second communication passage 43 through the communication passage inlet 441a and flows toward the upstream side of the air flow in the second communication passage 43. Then, this refrigerant flows into the upstream side lower tank 421 through the communication passage outlet 441b. In the upstream side lower tank 421, this refrigerant is merged with the branched portion of the refrigerant, which has passed through the first communication passage 33A.

Next, the flow of the refrigerant in the evaporator will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the downstream side upper tank 31, which is the space on the left lateral side of the separator 31a (the side of the separator 31a, which is opposite from the X-direction) through the upper flow inlet 51. Then, the refrigerant flows downwardly through the downstream side flow passage row 21b (the first path). Next, the flow direction of this refrigerant is reversed in the interior of the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction), and thereafter the refrigerant flows upwardly through the downstream side flow passage row 21a (the second path) and is supplied into the interior of the furthermost downstream side upper tank 311.

Then, a portion of the refrigerant in the downstream side upper tank 311 is branched into the first communication passage 33A. Then, in the first communication passage 33A, the branched portion of the refrigerant flows in the X-direction and then flows toward the upstream side of the air flow (the side opposite from the Z-direction), and thereafter the branched portion of the refrigerant flows in the direction opposite from the X-direction and is supplied into the upstream side upper tank 321. Thereafter, this branched portion of the refrigerant flows downwardly through the furthermost upstream side flow passage row 221 (the third path, the full-path portion 201) into the upstream side lower tank 421.

In contrast, the remaining refrigerant in the downstream side upper tank 311, which is other than the branched portion of the refrigerant, flows downwardly through the furthermost downstream side flow passage row 211 (the third path, the full-path portion 201) and then flows from the interior of the downstream side lower tank 411 into the second communication passage 43. Then, in the second communication passage 43, the refrigerant flows in the X-direction and then flows toward the upstream side of the air flow (the side opposite from the Z-direction), and thereafter the refrigerant flows in the direction opposite from the X-direction and is supplied into the upstream side lower tank 421 where this refrigerant is merged with the branched portion of the refrigerant, which has flown downwardly through the furthermost upstream side flow passage row 221. That is, the refrigerant in the furthermost downstream side flow passage row 211 and the refrigerant in the furthermost upstream side flow passage row 221 flow downwardly parallel to one another. The flow direction of the merged refrigerant, which is merged in the upstream side lower tank 421, is reversed, and this refrigerant flows upwardly through the upstream side flow passage row 22a (the fourth path). Thereafter, this refrigerant flows to the outside of the core from the upstream side upper tank 32 through the flow outlet 52.

As shown in FIG. 11, the communication passage inlet 341a (the refrigerant inflow opening) is opened to the interior of the furthermost downstream side upper tank 311 and is located on an upper side of upper end openings 211a of the tubes 20a of the furthermost downstream side flow passage row 211 in the vertical direction.

For the comparative purpose, it is now assumed that the refrigerant in the furthermost flow passage row forms the downflow, and the refrigerant inflow opening of the first communication passage opens in the furthermost downstream side upper tank only on a lower side of the upper end openings of the tubes of the furthermost flow passage row in the vertical direction. In such a case, the refrigerant tends to flow into the furthermost downstream side flow passage row of the core, and thereby the refrigerant cannot easily flow into the first communication passage through the refrigerant inflow opening. With the above structure of the present embodiment, it is possible to limit the flow tendency of the refrigerant in the furthermost downstream side upper tank into the downstream side flow passage row, and thereby it is possible to guide the refrigerant into the communication passage inlet 341a (the refrigerant inflow opening) and thereby to supply the greater amount of the refrigerant into the upstream side flow passage row. As a result, the heat exchange performance of the evaporator can be improved.

Furthermore, it is desirable that the lower end of the opening of the communication passage inlet 341a (the refrigerant inflow opening) is located on the upper side of the upper end openings 211a of the tubes 20a of the furthermost downstream side flow passage row 211.

Furthermore, in the evaporator of the present embodiment, the number of the downstream side flow passage rows 21 and the number of the upstream side flow passage rows 22 are set as follows. That is, the number of the other downstream side flow passage rows 21a, 21b other than the furthermost downstream side flow passage row 211 is two, and the number of the other upstream side flow passage row 22a other than the furthermost upstream side flow passage row 221 is one. Therefore, the number of the other downstream side flow passage rows 21a, 21b other than the furthermost downstream side flow passage row 211 is greater than the number of the other upstream side flow passage row 22a other than the furthermost upstream side flow passage row 221. With the above structure, in the case of the heat exchanger, in which the dryness of the refrigerant is larger on the downstream side in comparison to the upstream side, it is possible to reduce the pressure loss.

Seventh Embodiment

The evaporator according to a seventh embodiment of the present invention is a modification of the evaporator of the sixth embodiment and will be described with reference to FIGS. 12 and 13. FIG. 12 is a schematic diagram showing the structure of the evaporator and the flow of refrigerant therein according to the present embodiment. FIG. 13 is a schematic diagram showing the positional relationship of the communication holes 300 relative to the downstream side flow passage row 211 and the upstream side flow passage row 221. Although the downstream side flow passage row 211 is not shown in FIG. 13, it should be understood that the downstream side flow passage row 211 is placed at the same position in the Y-direction (the same vertical position), which is the same as that of the upstream side flow passage row 221.

The evaporator of the present embodiment is the same as the evaporator of FIG. 10 with respect to the refrigerant flow pattern and the structure of the core 102 except that the communication passage forming members 34A, 44A are not provided separately from the rest of the core 102 to project laterally. In FIG. 12, components similar to those of FIG. 10 will be indicated by the same reference numerals. Other than the above point, the evaporator of the present embodiment is the same as the evaporator of FIG. 10 and provides the same effects and the same advantages as those of the evaporator of FIG. 10.

With the above construction, a portion of the refrigerant in the furthermost downstream side upper tank 311 flows through the communication holes 300 in the first communication passage 33 toward the upstream side of the air flow and is supplied into the upstream side upper tank 321. Thereafter, this refrigerant flows downwardly through the furthermost upstream side flow passage row 221 and is supplied into the upstream side lower tank 421, which is opposite from the furthermost upstream side upper tank 321 in the top-to-bottom direction of the core. The communication holes 300 also serve as a branching passage, which is provided between the furthermost downstream side upper tank 311 and the furthermost upstream side upper tank 321, so that a portion of the refrigerant in the furthermost downstream side upper tank 311 flows toward the upstream side of the air flow and is supplied into the upstream side upper tank 321 through this branching passage.

In contrast, the remaining refrigerant in the furthermost downstream side upper tank 311 flows downwardly through the furthermost downstream side flow passage row 211 and is supplied into the furthermost downstream side lower tank 411, which is opposite from the furthermost downstream side upper tank 311. Then, this refrigerant flows toward the upstream side of the air flow through the communication holes 400 in the second communication passage 43 and is supplied into the upstream side lower tank 421 where this refrigerant is merged with the branched portion of the refrigerant, which has passed through the first communication passage 33. The second communication passage 43, which includes the communication holes 400, also serves as a merging passage, which is provided between the furthermost downstream side lower tank 411 and the furthermost upstream side lower tank 421, so that the remaining refrigerant in the furthermost downstream side lower tank 411 flows toward the upstream side of the air flow and is supplied into the upstream side lower tank 421 through the communication holes 400 in the second communication passage 43 to merge with the branched portion of the refrigerant at the interior of the upstream side lower tank 421.

The communication holes 300 are opened to the interior of the furthermost downstream side upper tank 311, and the openings of the communication holes 300 are placed on an upper side of the upper end openings 211a of the tubes 20a of the furthermost downstream side flow passage row 211 and the upper end openings 221a of the tubes 20b of the furthermost upstream side flow passage row 221 in the vertical direction.

For the comparative purpose, it is now assumed that the refrigerant in the furthermost flow passage row forms the downflow, and the communication holes in the interior of the furthermost downstream side upper tank, which are communicated with the interior of the upstream side upper tank, open only on a lower side of the upper end openings of the tubes of the furthermost flow passage row in the vertical direction. In such a case, the refrigerant tends to flow into the furthermost downstream side flow passage row of the core. With the above structure of the present embodiment, it is possible to limit the flow tendency of the refrigerant in the furthermost downstream side upper tank into the downstream side flow passage row, and thereby it is possible to supply the greater amount of the refrigerant into the upstream side flow passage row. As a result, the heat exchange performance of the evaporator can be improved.

Furthermore, it is desirable that the lower ends of the openings of the communication holes 300 are located on the upper side of the upper end openings 211a of the tubes 20a of the furthermost downstream side flow passage row 211.

Eighth Embodiment

The evaporator according to an eighth embodiment of the present invention is a modification of the evaporator of FIG. 3 of the first embodiment and will be described with reference to FIGS. 14 and 15. FIG. 14 is a schematic diagram showing the structure of the evaporator and the flow of refrigerant therein according to the present embodiment. FIG. 15 is a schematic diagram showing the positional relationship of the communication holes 400 relative to the downstream side flow passage row 210 and the upstream side flow passage row 220. Although the downstream side flow passage row 210 is not shown in FIG. 15, it should be understood that the downstream side flow passage row 210 is placed at the same position in the Y-direction (the same vertical position), which is the same as that of the upstream side flow passage row 220.

The evaporator of the present embodiment is the same as the evaporator of FIG. 3 with respect to the refrigerant flow pattern and the structure of the core except that the communication passage forming member 44 is not provided separately from the rest of the core to project laterally. Here, the second communication passage 43 is formed between the interior of the downstream side lower tank 411 and the interior of the upstream side lower tank 421. In FIG. 14, components similar to those of FIG. 3 will be indicated by the same reference numerals. Other than the above point, the evaporator of the present embodiment is the same as the evaporator of FIG. 3 and provides the same effects and the same advantages as those of the evaporator of FIG. 3.

With the above construction, a portion of the refrigerant in the furthermost downstream side lower tank 411 flows through the communication holes 400 in the second communication passage 43 toward the upstream side of the air flow and is supplied into the upstream side lower tank 421. Thereafter, this refrigerant flows upwardly through the furthermost upstream side flow passage row 220 and is supplied into the upstream side upper tank 321, which is opposite from the furthermost upstream side lower tank 421 in the top-to-bottom direction of the core. The second communication passage 43, which includes the communication holes 400, also serves as a branching passage, which is provided between the furthermost downstream side lower tank 411 and the furthermost upstream side lower tank 421, so that a portion of the refrigerant in the furthermost downstream side lower tank 411 flows toward the upstream side of the air flow and is supplied into the upstream side lower tank 421 through the communication holes 400 in the second communication passage 43.

In contrast, the remaining refrigerant in the furthermost downstream side lower tank 411 flows upwardly through the furthermost downstream side flow passage row 210 and is supplied into the furthermost downstream side upper tank 311, which is opposite from the furthermost downstream side lower tank 411 in the top-to-bottom direction of the core. Then, this refrigerant flows toward the upstream side of the air flow through the communication holes 300 in the first communication passage 33 and is supplied into the upstream side upper tank 321 where this refrigerant is merged with the branched portion of the refrigerant, which has passed through the second communication passage 43. The communication holes 300 also serve as a merging passage, which is provided between the furthermost downstream side upper tank 311 and the furthermost upstream side upper tank 321, so that the remaining refrigerant in the furthermost downstream side upper tank 311 flows toward the upstream side of the air flow and is supplied into the upstream side upper tank 321 through the communication holes 300 in the first communication passage 33 to merge with the branched portion of the refrigerant at the interior of the upstream side upper tank 321.

The communication holes 400 are opened to the interior of the furthermost downstream side lower tank 411, and the openings of the communication holes 400 are placed on a lower side of the lower end openings 210a of the tubes 20a of the furthermost downstream side flow passage row 210 and the lower end openings 220a of the tubes 20b of the furthermost upstream side flow passage row 220 in the vertical direction.

For the comparative purpose, it is now assumed that the refrigerant in the furthermost flow passage row forms the upflow, and the communication holes in the interior of the furthermost downstream side lower tank, which are communicated with the interior of the upstream side lower tank, open only on an upper side of the lower end openings of the tubes of the furthermost flow passage row in the vertical direction. In such a case, the refrigerant tends to flow into the furthermost downstream side flow passage row of the core. With the above structure of the present embodiment, it is possible to limit the flow tendency of the refrigerant in the furthermost downstream side lower tank into the downstream side flow passage row, and thereby it is possible to supply the greater amount of the refrigerant into the upstream side flow passage row. As a result, the heat exchange performance of the evaporator can be improved.

Furthermore, it is desirable that the lower ends of the openings of the communication holes 400 are located on the upper side of the lower end openings 210a of the tubes 20a of the furthermost downstream side flow passage row 210.

Ninth Embodiment

In a ninth embodiment of the present invention, a modification (a case of six paths of refrigerant flow) of the evaporator of the eighth embodiment will be described with reference to FIG. 16. FIG. 16 is a schematic diagram showing the structure of the evaporator and the flow of refrigerant therein in the case where the number of the refrigerant flow paths is six.

The evaporator of the present embodiment is different from the evaporator of FIG. 14 with respect to the refrigerant flow pattern (six paths in this embodiment), the structure of the core 103 and the elimination of the side flow passage. Other than the above points, the evaporator of the present embodiment is the same as the evaporator of FIG. 14 and provides the same effects and the same advantages as those of the evaporator of FIG. 14.

The refrigerant flow pattern in the evaporator of the present embodiment is constructed from four downstream side flow passage rows and three upstream side flow passage rows. The four downstream side flow passage rows include two downstream side flow passage rows 21b (the refrigerant downflow portion), one downstream side flow passage row 21a (the refrigerant upflow portion) and one furthermost downstream side flow passage row 210 (the refrigerant upflow portion). The three upstream side flow passage rows include one furthermost upstream side flow passage row 220 (the refrigerant upflow portion), one upstream side flow passage row 22b (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion).

Therefore, the number of the refrigerant flow paths in the core 103 is six in the present embodiment. Furthermore, the refrigerant flow pattern in the evaporator is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 200 (the portion where the branched flow of the refrigerant from the downstream side to the upstream side flows upwardly). These numbers are written one after another according to the flow order of the refrigerant in the evaporator and are thereby expressed as a 3-1-2 refrigerant flow pattern in this instance.

Next, the flow of the refrigerant in the evaporator will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the downstream side upper tank 31, which is the space on the left lateral side of the separator 31a (the side of the separator 31a, which is opposite from the X-direction) through the upper flow inlet 51. Then, the refrigerant flows downwardly through the downstream side flow passage row 21b (the first path). Next, the flow direction of this refrigerant is reversed in the interior of the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction), and thereafter the refrigerant flows upwardly through the downstream side flow passage row 21a (the second path). Thereafter, this refrigerant is supplied into the downstream side upper tank 31, which is the space between the separator 31b and the separator 31a, and the flow direction of this refrigerant is reversed in the interior of the downstream side upper tank 31. Then, this refrigerant flows downward through the downstream side flow passage row 21b (the third path) and is supplied into the furthermost downstream side lower tank 411.

A portion of the refrigerant in the downstream side lower tank 411 is branched and flows toward the upstream side of the air flow (the side opposite from the Z-direction) through the communication holes 400 in the second communication passage 43. Then, this refrigerant is supplied into the upstream side lower tank 421. Then, this refrigerant flows upwardly through the upstream side flow passage row 220 (the fourth path, the full-path portion 200) and is supplied into the upstream side upper tank 321.

In contrast, the remaining refrigerant in the downstream side lower tank 411, which is other than the branched portion of the refrigerant, flows upwardly through the furthermost downstream side flow passage row 210 (the fourth path, the full-path portion 200) and then flows from the interior of the downstream side upper tank 311 toward the upstream side of the air flow into the upstream side upper tank 321 through the communication holes 300 in the first communication passage 33. Then, this refrigerant is merged with the above branched portion of the refrigerant, which is supplied through the furthermost upstream side flow passage row 220 after flowing upwardly therethrough. That is, the refrigerant in the furthermost downstream side flow passage row 210 and the refrigerant in the furthermost upstream side flow passage row 220 flow upwardly parallel to one another.

The flow direction of the merged refrigerant, which is merged in the interior of the upstream side upper tank 321, is reversed, and this refrigerant flows downwardly through the upstream side flow passage row 22b (the fifth path). Then, the flow direction of this refrigerant is reversed once again in the upstream side lower tank 42, and thereby the refrigerant flows upwardly through the upstream side flow passage row 22a (the sixth path). Thereafter, this refrigerant flows to the outside of the core from the upstream side upper tank 32 through the flow outlet 52.

Furthermore, in the evaporator of the present embodiment, the number of the downstream side flow passage rows 21 and the number of the upstream side flow passage rows 22 are set as follows. That is, the number of the other downstream side flow passage rows 21a, 21b other than the furthermost downstream side flow passage row 210 is three, and the number of the other upstream side flow passage row 22a, 22b other than the furthermost upstream side flow passage row 220 is two. Therefore, the number of the other downstream side flow passage rows 21a, 21b other than the furthermost downstream side flow passage row 210 is greater than the number of the other upstream side flow passage row 22a, 22b other than the furthermost upstream side flow passage row 220. With the above structure, in the case of the heat exchanger, in which the dryness of the refrigerant is larger on the downstream side in comparison to the upstream side, it is possible to reduce the pressure loss.

Tenth Embodiment

In a tenth embodiment of the present invention, a modification (a case of five paths of refrigerant flow) of the evaporator of the ninth embodiment will be described with reference to FIG. 17. FIG. 17 is a schematic diagram showing the structure of the evaporator and the flow of refrigerant therein in the case where the number of the refrigerant flow paths is five.

The evaporator of the present embodiment is different from the evaporator of FIG. 16 with respect to the refrigerant flow pattern (five paths in this embodiment) and the structure of the core 104 and the location of the flow inlet 51 (the lower side in this embodiment). Other than the above point, the evaporator of the present embodiment is the same as the evaporator of FIG. 16 and provides the same effects and the same advantages as those of the evaporator of FIG. 16.

The refrigerant flow pattern in the evaporator of the present embodiment is constructed from three downstream side flow passage rows and three upstream side flow passage rows. The three downstream side flow passage rows include one downstream side flow passage row 21a (the refrigerant upflow portion), one downstream side flow passage row 21b (the refrigerant downflow portion) and one furthermost downstream side flow passage row 210 (the refrigerant upflow portion). The three upstream side flow passage rows include one furthermost upstream side flow passage row 220 (the refrigerant upflow portion), one upstream side flow S passage row 22b (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion).

Therefore, the number of the refrigerant flow paths in the core 100 is five in the present embodiment. Furthermore, the refrigerant flow pattern in the evaporator is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 200 (the portion where the branched flow of the refrigerant from the downstream side to the upstream side flows upwardly). These numbers are written one after another according to the flow order of the refrigerant in the evaporator and are thereby expressed as a 2-1-2 refrigerant flow pattern in this instance.

Next, the flow of the refrigerant in the evaporator will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction) through the lower flow inlet 51. Then, the refrigerant flows upwardly through the downstream side flow passage row 21a (the first path). Next, the flow direction of this refrigerant is reversed in the interior of the downstream side upper tank 31, which is the space on the left lateral side of the separator 31a (the side of the separator 31a, which is opposite from the X-direction), and thereafter the refrigerant flows downwardly through the downstream side flow passage row 21b (the second path). Thereafter, this refrigerant is supplied into the interior of the furthermost downstream side lower tank 411.

A portion of the refrigerant in the downstream side lower tank 411 is branched and flows toward the upstream side of the air flow (the side opposite from the Z-direction) through the communication holes 400 in the second communication passage 43. Then, this refrigerant is supplied into the upstream side lower tank 421. Then, this refrigerant flows upwardly through the upstream side flow passage row 220 (the third path, the full-path portion 200) and is supplied into the upstream side upper tank 321.

In contrast, the remaining refrigerant in the downstream side lower tank 411, which is other than the branched portion of the refrigerant, flows upwardly through the furthermost downstream side flow passage row 210 (the third path, the full-path portion 200) and then flows from the interior of the downstream side upper tank 311 toward the upstream side of the air flow into the upstream side upper tank 321 through the communication holes 300 in the first communication passage 33. Then, this refrigerant is merged with the above branched portion of the refrigerant, which is supplied through the furthermost upstream side flow passage row 220 after flowing upwardly therethrough. That is, the refrigerant in the furthermost downstream side flow passage row 210 and the refrigerant in the furthermost upstream side flow passage row 220 flow upwardly parallel to one another.

The flow direction of the merged refrigerant, which is merged in the interior of the upstream side upper tank 321, is reversed, and this refrigerant flows downwardly through the upstream side flow passage row 22b (the fourth path). Then, the flow direction of this refrigerant is reversed once again in the upstream side lower tank 42, and thereby the refrigerant flows upwardly through the upstream side flow passage row 22a (the fifth path). Thereafter, this refrigerant flows to the outside of the core from the upstream side upper tank 32 through the flow outlet 52.

Eleventh Embodiment

An eleventh embodiment of the present invention is a modification (a case where the refrigerant flow pattern is 3-1-1 pattern) of the evaporator of the tenth embodiment and will be described with reference to FIG. 18. FIG. 18 is a schematic diagram showing the structure of the evaporator and the refrigerant flow therethrough in the case where the refrigerant flow pattern is 3-1-1 according to the present embodiment.

In the evaporator of the present embodiment, the number of the refrigerant flow paths is five, which is the same as that of the evaporator of FIG. 17. However, the evaporator of the present embodiment is different from the evaporator of FIG. 17 with respect to the refrigerant flow pattern (3-1-1 pattern in the present embodiment) and the flow direction of the refrigerant in the furthermost portion (the refrigerant downflow portion in this embodiment) of the core 105. Other than the above points, the evaporator of the present embodiment is the same as the evaporator of FIG. 17 and provides the same effects and the same advantages as those of the evaporator of FIG. 17.

The refrigerant flow pattern in the evaporator of the present embodiment is constructed from four downstream side flow passage rows and two upstream side flow passage rows. The four downstream side flow passage rows include two downstream side flow passage rows 21a (the refrigerant upflow portions), one downstream side flow passage row 21b (the refrigerant downflow portion) and one furthermost downstream side flow passage row 211 (the refrigerant downflow portion). The two upstream side flow passage rows include one furthermost upstream side flow passage row 221 (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion).

Therefore, the number of the refrigerant flow paths in the core 105 is five in the present embodiment. Furthermore, the refrigerant flow pattern in the evaporator is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 200 (the portion where the branched flow of the refrigerant from the downstream side to the upstream side flows upwardly). These numbers are written one after another according to the flow order of the refrigerant in the evaporator and are thereby expressed as a 3-1-1 refrigerant flow pattern in this instance.

Next, the flow of the refrigerant in the evaporator will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction) through the lower flow inlet 51. Then, the refrigerant flows upwardly through the downstream side flow passage row 21a (the first path). Next, the flow direction of this refrigerant is reversed in the interior of the downstream side upper tank 31, which is the space on the left lateral side of the separator 31a (the side of the separator 31a, which is opposite from the X-direction), and thereafter the refrigerant flows downwardly through the downstream side flow passage row 21b (the second path). Thereafter, the flow direction of this refrigerant is reversed in the interior of the downstream side lower tank 41, which is the space defined between the separator 41a and the separator 41b. Then, this refrigerant flows upwardly through the downstream side flow passage row 21a (the third path) and is supplied into the interior of the furthermost downstream side upper tank 311.

A portion of the refrigerant in the downstream side upper tank 311 is branched and flows toward the upstream side of the air flow (the side opposite from the Z-direction) through the communication holes 300 in the first communication passage 33. Then, this refrigerant is supplied into the upstream side upper tank 321. Then, this refrigerant flows downwardly through the upstream side flow passage row 221 (the fourth path, the full-path portion 201) and is supplied into the upstream side lower tank 421.

In contrast, the remaining refrigerant in the downstream side upper tank 311, which is other than the branched portion of the refrigerant, flows downwardly through the furthermost downstream side flow passage row 211 (the fourth path, the full-path portion 201) and then flows from the interior of the downstream side lower tank 411 toward the upstream side of the air flow into the upstream side lower tank 421 through the communication holes 400 in the second communication passage 43. Then, this refrigerant is merged with the above branched portion of the refrigerant, which is supplied through the furthermost upstream side flow passage row 221 after flowing downwardly therethrough, in the upstream side lower tank 421. That is, the refrigerant in the furthermost downstream side flow passage row 211 and the refrigerant in the furthermost upstream side flow passage row 221 flow downwardly parallel to one another.

Next, the flow direction of the merged refrigerant, which is merged in the upstream side lower tank 421, is reversed, and this refrigerant flows upwardly through the upstream side flow passage row 22a (the fifth path) and is supplied into the upstream side upper tank 32, which is the space on the left lateral side of the separator 32a (the side of the separator 32a, which is opposite from the X-direction). Thereafter, this refrigerant flows to the outside of the core from the upstream side upper tank 32 through the flow outlet 52.

Furthermore, in the evaporator of the present embodiment, the number of the downstream side flow passage rows 21 and the number of the upstream side flow passage rows 22 are set as follows. That is, the number of the other downstream side flow passage rows 21a, 21b other than the furthermost downstream side flow passage row 211 is three, and the number of the other upstream side flow passage row 22a, 22b other than the furthermost upstream side flow passage row 221 is one. Therefore, the number of the other downstream side flow passage rows 21a, 21b other than the furthermost downstream side flow passage row 211 is greater than the number of the other upstream side flow passage row 22a, 22b other than the furthermost upstream side flow passage row 221. With the above structure, in the case of the heat exchanger, in which the dryness of the refrigerant is larger on the downstream side in comparison to the upstream side, it is possible to reduce the pressure loss.

Twelfth Embodiment

In a twelfth embodiment of the present invention, a modification (a case of four paths of refrigerant flow) of the evaporator of the eleventh embodiment will be described with reference to FIG. 19. FIG. 19 is a schematic diagram showing the structure of the evaporator and the refrigerant flow therethrough in the case where the refrigerant flow pattern is 2-1-1 according to the present embodiment.

The evaporator of the present embodiment is different from the evaporator of FIG. 18 with respect to the number of the paths (four paths in this embodiment) and the refrigerant flow patter (2-1-1 pattern in this embodiment). Other than the above point, the evaporator of the present embodiment is the same as the evaporator of FIG. 18 and provides the same effects and the same advantages as those of the evaporator of FIG. 18.

The refrigerant flow pattern in the evaporator of the present embodiment is constructed from three downstream side flow passage rows and two upstream side flow passage rows. The three downstream side flow passage rows include one downstream side flow passage row 21b (the refrigerant downflow portion), one downstream side flow passage row 21a (the refrigerant upflow portion) and one furthermost downstream side flow passage row 211 (the refrigerant downflow portion). The two upstream side flow passage rows include one furthermost upstream side flow passage row 221 (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion).

Therefore, the number of the refrigerant flow paths in the core 102 is four in the present embodiment. Furthermore, the refrigerant flow pattern in the evaporator is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 201 (the portion where the branched flow of the refrigerant from the downstream side to the upstream side flows downwardly). These numbers are written one after another according to the flow order of the refrigerant in the evaporator and are thereby expressed as a 2-1-1 refrigerant flow pattern in this instance.

Next, the flow of the refrigerant in the evaporator will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the downstream side upper tank 31, which is the space on the left lateral side of the separator 31a (the side of the separator 31a, which is opposite from the X-direction) through the upper flow inlet 51. Then, the refrigerant flows downwardly through the downstream side flow passage row 21b (the first path). Next, the flow direction of this refrigerant is reversed in the interior of the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction), and thereafter the refrigerant flows upwardly through the downstream side flow passage row 21a (the second path) and is supplied into the interior of the furthermost downstream side upper tank 311.

A portion of the refrigerant in the downstream side upper tank 311 is branched and flows toward the upstream side of the air flow (the side opposite from the Z-direction) through the communication holes 300 in the first communication passage 33. Then, this refrigerant is supplied into the upstream side upper tank 321. Then, this refrigerant flows downwardly through the furthermost upstream side flow passage row 221 (the third path, the full-path portion 201) and is supplied into the upstream side lower tank 421.

In contrast, the remaining refrigerant in the downstream side upper tank 311, which is other than the branched portion of the refrigerant, flows downward through the furthermost downstream side flow passage row 211 (the third path, the full-path portion 201) and then flows from the interior of the downstream side lower tank 411 toward the upstream side of the air flow into the upstream side lower tank 421 through the communication holes 400 in the second communication passage 43. Then, this refrigerant is merged with the above branched portion of the refrigerant, which is supplied through the furthermost upstream side flow passage row 221 after flowing downwardly therethrough, in the upstream side lower tank 421. That is, the refrigerant in the furthermost downstream side flow passage row 211 and the refrigerant in the furthermost upstream side flow passage row 221 flow downwardly parallel to one another.

Next, the flow direction of the merged refrigerant, which is merged in the upstream side lower tank 421, is reversed, and this refrigerant flows upwardly through the upstream side flow passage row 22a (the fourth path) and is supplied into the upstream side upper tank 32, which is the space on the left lateral side (the side of the separator 32a, which is opposite from the X-direction). Thereafter, this refrigerant flows to the outside of the core from the upstream side upper tank 32 through the flow outlet 52.

Thirteenth Embodiment

In a thirteenth embodiment of the present invention, a modification (a case of three paths of refrigerant flow) of the evaporator of the twelfth embodiment will be described with reference to FIG. 20. FIG. 20 is a schematic diagram showing the structure of the evaporator and the refrigerant flow therethrough in the case where the refrigerant flow pattern is 1-1-1 according to the present embodiment.

The evaporator of the present embodiment is different from the evaporator of FIG. 19 with respect to the structure of the core 106, the number of refrigerant flow paths (three in this embodiment), the refrigerant flow pattern (1-1-1 pattern in this embodiment) and the location of the flow inlet 51 (lower side in this embodiment). Other than the above points, the evaporator of the present embodiment is the same as the evaporator of FIG. 19 and provides the same effects and the same advantages as those of the evaporator of FIG. 19.

The refrigerant flow pattern in the evaporator 1 of the present embodiment is constructed from two downstream side flow passage rows and two upstream side flow passage rows. The two downstream side flow passage rows include one downstream side flow passage row 21a (the refrigerant upflow portion) and one furthermost downstream side flow passage row 211 (the refrigerant downflow portion). The two upstream side flow passage rows include one furthermost upstream side flow passage row 221 (the refrigerant downflow portion) and one upstream side flow passage row 22a (the refrigerant upflow portion).

Therefore, the number of the refrigerant flow paths in the core 106 is three in the present embodiment. Furthermore, the refrigerant flow pattern in the evaporator is expressed by the number of path(s) in the downstream side flow passage rows 21, the number of path(s) in the upstream side flow passage row 22 and the number of path(s) of the full-path portion 201 (the portion where the branched flow of the refrigerant from the downstream side to the upstream side flows downwardly). These numbers are written one after another according to the flow order of the refrigerant in the evaporator and are thereby expressed as a 1-1-1 refrigerant flow pattern in this instance.

Next, the flow of the refrigerant in the evaporator will be sequentially described. The refrigerant from the external constituent component of the refrigeration cycle is supplied into the interior of the downstream side lower tank 41, which is the space on the left lateral side of the separator 41a (the side of the separator 41a, which is opposite from the X-direction) through the lower flow inlet 51. Then, the refrigerant flows upwardly through the downstream side flow passage row 21a (the first path) and is supplied into the downstream side upper tank 311.

A portion of the refrigerant in the downstream side upper tank 311 is branched and flows toward the upstream side of the air flow (the side opposite from the Z-direction) through the communication holes 300 in the first communication passage 33. Then, this refrigerant is supplied into the upstream side upper tank 321. Then, this refrigerant flows downwardly through the upstream side flow passage row 221 (the second path, the full-path portion 201) and is supplied into the upstream side lower tank 421.

In contrast, the remaining refrigerant in the downstream side upper tank 311, which is other than the branched portion of the refrigerant, flows downwardly through the furthermost downstream side flow passage row 211 (the second path, the full-path portion 201) and then flows from the interior of the downstream side lower tank 411 toward the upstream side of the air flow into the upstream side lower tank 421 through the communication holes 400 in the second communication passage 43. Then, this refrigerant is merged with the above branched portion of the refrigerant, which is supplied through the furthermost upstream side flow passage row 221 after flowing downwardly therethrough, in the upstream side lower tank 421. That is, the refrigerant in the furthermost downstream side flow passage row 211 and the refrigerant in the furthermost upstream side flow passage row 221 flow downwardly parallel to one another.

Next, the flow direction of the merged refrigerant, which is merged in the upstream side lower tank 421, is reversed, and this refrigerant flows upwardly through the upstream side flow passage row 22a (the third path) and is supplied into the upstream side upper tank 32, which is the space on the left lateral side of the separator 32a (the side of the separator 32a, which is opposite from the X-direction). Thereafter, this refrigerant flows to the outside of the core from the upstream side upper tank 32 through the flow outlet 52.

Fourteenth Embodiment

In a fourteenth embodiment of the present invention, the positioning state of the evaporator (the state where the core is tilted relative to the horizontal direction), which is applicable to all of the embodiments of the present invention, will be described with reference to FIG. 21. FIG. 21 is a schematic side view of the positioning state of the evaporator according to the present embodiment. FIG. 22 is an enlarged partial cross sectional side view showing the relationship between the interior of the upper header tank 3 and the refrigerant quantities (the refrigerant quantity in the upstream side and the refrigerant quantity in the downstream side) in the core 100 at the furthermost portion thereof. FIG. 23 is an enlarged partial cross sectional side view showing the relationship between the interior of the lower header tank 4 and the refrigerant quantities (the refrigerant quantity in the upstream side and the refrigerant quantity in the downstream side) in the core 100 at the furthermost portion thereof.

With reference to FIG. 21, the core 100 has an upstream side lateral core surface (upstream side lateral plane) 100b and a downstream side lateral core surface (downstream side lateral plane) 100a, which are generally parallel to each other and are located on the upstream side and the downstream side, respectively, in the air flow direction. The evaporator of the present embodiment is tilted such that the upstream side lateral core surface 100b of the core 100 is closer to an imaginary horizontal plane L indicated by a dot-dash line in FIG. 21 (a plane that is placed vertically below the upstream side lower tank 42 and is parallel to the Z-direction) in comparison to the downstream side lateral core surface 100a of the core 100. The core 100 is placed and is held at a tilt angle (specifically, a tilt angle of the upstream side lateral core surface 100b) θ relative to the imaginary horizontal plane (the imaginary horizontal line) L. Other than this point, the evaporator of the present embodiment is the same as the evaporator 1 of the first embodiment and provides the same effects and the same advantages as those of the evaporator 1 of the first embodiment.

With this structure, due to the aid of the gravity, a portion of the refrigerant in the furthermost downstream side header tank 11 (e.g., the furthermost downstream side upper tank 311 in the case of FIG. 22 and the furthermost downstream side lower tank 411 in the case of FIG. 23) flows in the greater amount in comparison to the first embodiment through the communicating means (the first communication passage 33 or 33A in the case of FIG. 22 and the second communication passage 43 or 43A in the case of FIG. 23) toward the upstream side of the air flow and is supplied into the furthermost upstream side header tank 12 (e.g., the furthermost upstream side upper tank 321 in the case of FIG. 22 and the furthermost upstream side lower tank 421 in the case of FIG. 23). At this time, the refrigerant is under the influence of the gravity, so that the refrigerant tends to flow through the communicating means toward the upstream side flow passage row 220, 221 rather than the furthermost downstream side flow passage row 210, 211 due to the fact that the upstream side flow passage row 220, 221 is placed at the lower side of the furthermost downstream side flow passage row 210, 211 in the vertical direction. Furthermore, the portion of the refrigerant, which is supplied into the upstream side header tank 12 (e.g., the furthermost upstream side upper tank 321 in the case of FIG. 22 and the upstream side lower tank 421 in the case of FIG. 23) flows through the furthermost upstream side flow passage row 220, 221 toward the opposite upstream side header tank 12 (e.g., the furthermost upstream side lower tank 421 in the case of FIG. 22 and the furthermost upstream side upper tank 321 in the case of FIG. 23), which is opposite from the above upstream side header tank 12 (e.g., the furthermost upstream side upper tank 321 in the case of FIG. 22 and the upstream side lower tank 421 in the case of FIG. 23) in the top-to-bottom direction of the core 100.

In contrast, the rest of the refrigerant, which remains in the furthermost downstream side header tank 11 (e.g., the furthermost downstream side upper tank 311 in the case of FIG. 22 and the furthermost downstream side lower tank 411 in the case of FIG. 23) flows through the furthermost downstream side flow passage row 210, 211 toward the opposite furthermost downstream side header tank 11 (e.g., the furthermost downstream side lower tank 411 in the case of FIG. 22 and the furthermost downstream side upper tank 311 in the case of FIG. 23), which is opposite from the above downstream side header tank 11 (e.g., the furthermost downstream side upper tank 311 in the case of FIG. 22 and the furthermost downstream side lower tank 411 in the case of FIG. 23) in the top-to-bottom direction of the core 100. Then, this refrigerant flows toward the upstream side of the air flow into the upstream side header tank 12 (e.g., the furthermost upstream side lower tank 421 in the case of FIG. 22 and the upstream side upper tank 321 in the case of FIG. 23) where this refrigerant is merged with the branched portion of the refrigerant, which has passed through the communicating means.

At the evaporator of the present embodiment, in the case where the furthermost flow passage rows (the furthermost upstream side and downstream side flow passage rows) form the refrigerant downflow portions (the full-path portion 201), the quantity of the refrigerant, which flows through the furthermost upstream side flow passage row 221, becomes greater than the quantity of the refrigerant, which flows through the furthermost downstream side flow passage row 211 (see FIG. 22). Furthermore, in the case where the furthermost flow passage rows form the refrigerant upflow portions (the full-path portion 200), the quantity of the refrigerant, which flows through the furthermost upstream side flow passage row 220, becomes larger than the quantity of the refrigerant, which flows through the furthermost downstream side flow passage row 210 (see FIG. 23).

In the evaporator of the present embodiment, the furthermost upstream side flow passage row 220, 221 is placed on the lower side of the furthermost downstream side flow passage row 210, 211, so that the refrigerant in the downstream side header tank 11 tends to flow toward the furthermost upstream side flow passage row 220, 221 due to the gravity. Therefore, it is possible to alleviate the biased flow of the refrigerant, which tends to flow toward the downstream side flow passage row at the furthermost portion of the core that is furthermost from the flow inlet 51 and the flow outlet 52.

Also, in the evaporator, the refrigerant of the gas phase and liquid phase mixture is supplied into the downstream side header tank 11. The liquid phase refrigerant is heavier than the gas phase refrigerant. Thus, in addition to the inertial force, the gravity has the significant influence on the liquid phase refrigerant. Therefore, the liquid phase refrigerant is expected to flow toward the upstream side flow passage row 220, 221, which is placed on the lower side of the downstream side flow passage row 210, 211. Thereby, the refrigerant can be more actively supplied to the upstream side where the temperature of the blown air is relatively high, so that the heat exchange performance can be further improved.

Fifteenth Embodiment

In a fifteenth embodiment of the present invention, the structure of the header tank, which is applicable to the evaporator of all of the embodiments of the present invention, will be described with reference to FIGS. 24 to 26. FIG. 24 is a partial side view showing the upper header tank 3 of the evaporator of the present embodiment. FIG. 25 is a partial cross sectional front view showing the flow inlet 51 of the upper header tank 3 of FIG. 24 seen from the X-direction in FIG. 24. FIG. 26 is a diagram (graph) showing a computed result of a relationship between a tank outer diameter (a total tank outer diameter of the upstream side and downstream side header tanks or a total thickness of the upstream side and downstream side header tanks in the air flow direction) D and a pressure loss in the tank obtained under a predetermined condition.

As shown in FIGS. 24 and 25, the upper header tank 3 and the tubes 20 are formed from a plurality of plate members (constituent members) 50, which are integrally stacked and joined one after another in the lateral direction. The plate member 50 has a through hole and an extending portion. The extending portion of the plate member 50 extends from the through hole of the plate member 50 in the direction opposite from the Y-direction. One side of the through hole of the plate member 50 is configured into a plate form, and the other side of the through hole of the plate member 50 is configured into a tubular form. The upper header tank 3 is formed by alternately directing and stacking the plate members 50 of the above configuration, so that the tubular portion, which extends in the X-direction, and the flow passages, which conduct the refrigerant, are created. Furthermore, it should be noted that although not show in the drawing, the lower header tank 4 is also formed at the undepicted lower ends of the tubes 20 in FIG. 24 in a manner similar to that of the upper header tank 3.

The above tubular portion, which extends in the X-direction, constitutes the tank, and the lateral side end opening of the tubular portion can be used as the flow inlet 51 or the flow outlet 52. When the lateral side end opening of the tubular portion is not used as the flow inlet 51 or the flow outlet 52, the cap is fitted into the lateral side end opening to close the same. The tank interior (the tube interior) is communicated with the flow passages (the interiors of the tubes), which extend in the direction opposite from the Y-direction.

FIG. 26 shows the relationship between the tank outer diameter or the thickness D (mm) and the pressure loss (kPa) in the case of the separate type tank (indicated by a solid line) where separate tubes are joined to the tank. FIG. 26 also shows the relationship between the tank outer diameter D (mm) and the pressure loss (kPa) in the case of the laminate type tank (indicated by a dotted line) where the plate members 50 are stacked. The tank outer diameter D is defined by the following equation 1.

D=2(d+2t)   Equation 1

Here, “t” denotes a wall thickness of the tank. Furthermore, “d” denotes an equivalent inner diameter of the interior of the tank, which is obtained as follows. That is, first, an effective cross sectional area of the interior of the tank is multiplied by 4, and then the thus obtained value (i.e., the product of the effective cross sectional area multiplied by 4) is divided by a circumferential length of the interior of the tank to obtain the equivalent inner diameter of the interior of the tank.

Furthermore, in the case of the separate type tank, the data of FIG. 26 is computed for the corresponding predetermined condition where the wall thickness t of the tank is 1.0 mm (i.e., t=1.0 mm), and a protrusion of the tube into the interior of the tank is minimum of 4 mm. In the case of the laminate type tank, the data of FIG. 26 is computed for the corresponding predetermined condition where the wall thickness t of the tank is 1.0 mm (i.e., t=1.0 mm), and the tank brazing area is 1.5 to 3.0 mm.

In the result of the computation of the above separate type tank and of the laminate type tank, the pressure loss factors are compared by using a square of an inverse (a flow velocity factor) of the effective cross sectional area of the interior of the tank. Furthermore, the comparison is made by using the pressure loss factor in the case of the tank outer diameter D=70 mm as a reference.

As shown in FIG. 26, according to the result of the computation, it is desirable that the thickness D of the both header tanks (the upstream side and downstream side header tanks), which is measured in the air flow direction, is 48 mm or less. In this case, the tank interior space is not large, and thereby the pressure loss in the tank tends to become large. Here, when the present invention is applied to the evaporator, which satisfies the above condition, the more prominent effect for reducing the pressure loss can be expected.

Sixteenth Embodiment

In a sixteenth embodiment of the present invention, an appropriate relationship between a total passage cross sectional area S1 of the branching passage and a total passage cross sectional area S2 of the merging passage, which is applicable to all of the embodiments of the present invention, will be described with reference to FIGS. 27 and 28. FIG. 27 is a schematic diagram for designing the appropriate condition of the flow quantity (hereinafter, also referred to as the upstream side refrigerant flow quantity) GR2 of the refrigerant, which flows in the upstream side flow passage row, and the flow quantity (hereinafter, also referred to as the downstream side refrigerant flow quantity) GR1 of the refrigerant, which flows in the downstream side flow passage row. FIG. 28 is a diagram showing the result of the computation of an appropriate ratio (S1/S2) between the total passage cross sectional area S1 of the branching passage and the total passage cross sectional area S2 of the merging passage computed for each corresponding one of the refrigerant flow paths (3 paths to 6 paths).

As shown in FIG. 27, in the case where the furthermost downstream side flow passage row and the furthermost upstream side flow passage row are refrigerant upflow portions, respectively, the flow quantity of the refrigerant flowing through the furthermost downstream side flow passage row is indicated by “GR1”, and the flow quantity of the refrigerant flowing through the furthermost upstream side flow passage row is indicated by “GR2”. Furthermore, the flow quantity of the refrigerant flowing from the furthermost downstream side upper tank 311 to the furthermost upstream side upper tank 321 is indicated by “GRU”, and the flow quantity of the refrigerant flowing from the furthermost downstream side lower tank 411 to the furthermost upstream side lower tank 421 is indicated by “GRL”.

Furthermore, the number of the refrigerant flow paths in the core is indicated by “N”. At the second communication passage 43 or 43A (the branching passage), which conducts the portion of the refrigerant from the furthermost downstream side lower tank 411 to the furthermost upstream side lower tank 421, the pressure loss is indicated by “ΔPt1”, and the dryness is indicated by “X1”. Also, the specific volume at the second communication passage 43 is indicated by “V1”. In addition, at the first communication passage 33 or 33A (the merging passage), which conducts the remaining refrigerant from the downstream side upper tank 311 to the upstream side upper tank 321 after the remaining refrigerant being supplied from the furthermost downstream side lower tank 411 to the furthermost downstream side upper tank 311 through the furthermost downstream side flow passage row 210, the pressure loss is indicated by “ΔPt2”, and the dryness is indicated by “X2”. Also, the specific volume at the first communication passage 33 is indicated by “V2”.

In comparison between the upstream side portion (the upstream side flow passage row) of the core and the downstream side portion (the downstream side flow passage row) of the core, which are placed one after another in the flow direction of the air, the air around the upstream side portion of the core is warmer. Therefore, the upstream side portion of the core should have the higher performance. In a typical condition (an ideal condition), the good balance of the performance is achieved with the following state. That is, the air to be supplied to the core has the temperature of 27° C. and the relative humidity of 50% RH. Furthermore, the air right after passing through the upstream side portion (the upstream side flow passage row) of the core has the temperature of 14° C. and the relative humidity of 85% RH, and the air right after passing through the downstream side portion (the downstream side flow passage row) of the core has the temperature of 7° C. and the relative humidity of 90% RH.

When the amount of energy is computed for the above state, the ratio between the downstream side refrigerant flow quantity GR1 and the upstream side refrigerant flow quantity GR2 is 4:6. The above balance may vary about ±10% due to the variation in the distribution of the refrigerant in the lateral direction (the width direction) of the core. In view of the above fact, it is desirable to set the ratio of GR1/GR2 to be equal to or greater than 0.55 (=3.6/6.6) but is equal to or less than 0.81 (=4.4/5.4), i.e., 0.55≦GR1/GR2≦0.81.

Next, the result (see FIG. 28) of the computation of the appropriate ratio (S1/S2) between the total passage cross sectional area S1 of the branching passage and the total passage cross sectional area S2 of the merging passage will be described in view of the number of the refrigerant flow paths of the evaporator.

The logic of the computation will now be described. First, it should be understood that the dryness of the refrigerant before entering the core differs from the dryness of the refrigerant after exiting the core. In view of this fact, when the pressure loss ΔPt1 of the branching passage is set to be smaller than the pressure loss ΔPt2 of the merging passage (i.e., ΔPt1<ΔPt2), the refrigerant flow quantity of the downstream side and the refrigerant flow quantity of the upstream side can be balanced.

The refrigerant flow quantity balance and the pressure loss depend on the square of the flow velocity of the refrigerant, so that it is desirable to satisfy the following equation 2.

S1/S2=(V1/V2)²   Equation 2

Furthermore, it is desirable that the refrigerant flow quantity in the upstream side portion of the core is larger than the refrigerant flow quantity in the downstream side portion of the core. Thus, it is desirable to have the value of S1/S2, which is equal to or larger than the corresponding value shown in the column of “ANSWER” in FIG. 28.

As indicated in FIG. 28, it is desirable that the heat exchanger is constructed to satisfy a condition of 0.41≦S1/S2. Furthermore, as discussed above, in the case where the furthermost downstream side flow passage row and the furthermost upstream side flow passage row are refrigerant upflow portions, respectively, the total passage cross sectional area S1 of the branching passage is the total passage cross sectional area S1 of the second communication passage 43, and the total passage cross sectional area S2 of the merging passage is the total passage cross sectional area S2 of the first communication passage 33. Furthermore, in a case where the second communication passage 43 includes a plurality of sub-passages, the total passage cross sectional area S1 is a sum of all of cross sectional areas of the sub-passages of the second communication passage 43. Similarly, in a case where the first communication passage 33 includes a plurality of sub-passages, the total passage cross sectional area S2 is a sum of all of cross sectional areas of the sub-passages of the first communication passage 33. Also, in a case where the second communication passage 43 is made of a single passage, the total passage cross sectional area S1 is the cross sectional area of this single passage. Similarly, in a case where first communication passage 33 is made of a single passage, the total passage cross sectional area S2 is the cross sectional area of this single passage.

In contrast, in the case where the furthermost downstream side flow passage row and the furthermost upstream side flow passage row are refrigerant downflow portions, respectively, the total passage cross sectional area S1 of the branching passage is the total passage cross sectional area S1 of the first communication passage 33, and the total passage cross sectional area S2 of the merging passage is the total passage cross sectional area S2 of the second communication passage 43. Furthermore, in a case where the first communication passage 33 includes a plurality of sub-passages, the total passage cross sectional area Si is a sum of all of cross sectional areas of the sub-passages of the first communication passage 33. Similarly, in a case where the second communication passage 43 includes a plurality of sub-passages, the total passage cross sectional area S2 is a sum of all of cross sectional areas of the sub-passages of the second communication passage 43. Also, in a case where the first communication passage 33 is made of a single passage, the total passage cross sectional area S1 is the cross sectional area of this single passage. Similarly, in a case where second communication passage 43 is made of a single passage, the total passage cross sectional area S2 is the cross sectional area of this single passage.

In addition, as shown in FIG. 28, in the case where the number of the refrigerant flow paths in the core is six, it is desirable to satisfy the condition of 0.71≦S1/S2. Furthermore, in the case where the number of the refrigerant flow paths in the core is five, it is desirable to satisfy the relationship of 0.47≦S1/S2. Furthermore, in the case where the number of the refrigerant flow paths in the core is four, it is desirable to satisfy the relationship of 0.66≦S1/S2. In addition, in the case where the number of the refrigerant flow paths in the core is three, it is desirable to satisfy the relationship of 0.41≦S1/S2.

Seventeenth Embodiment

In a seventeenth embodiment of the present invention, cores, in which the lateral size (lateral extension) of the furthermost upstream side flow passage row 220, 221 and the lateral size (lateral extension) of the furthermost downstream side flow passage row 210, 211 measured in the X-direction (lateral direction of the core) are not identical, will be described with reference to FIGS. 29 and 30. FIG. 30 is a schematic diagram showing a variation of the evaporator of FIG. 29 along with the structure and the refrigerant flow thereof. Here, it should be noted that although FIGS. 29 and 30 do not show the communication passage forming member(s) 34, 44 of the first to sixth embodiments, the present embodiment is equally applicable to the evaporator of any one of the first to sixth embodiments with the communication passage forming member(s) 34, 44. In other words, FIGS. 29 and 30 are only for the purpose of showing the difference between the lateral size (lateral extension) of the furthermost upstream side flow passage row 220, 221 and the lateral size (lateral extension) of the furthermost downstream side flow passage row 210, 211.

FIG. 29 is a schematic diagram showing the structure and the refrigerant flow in the case of the evaporator, in which the lateral size of the furthermost upstream side flow passage row 221 is larger than the lateral size of the furthermost downstream side flow passage row 211. Furthermore, in this evaporator, the furthermost downstream side flow passage row and the furthermost upstream side flow passage row are the refrigerant downflow portions, respectively, and the refrigerant flow pattern is a 1-1-1 refrigerant flow pattern. In addition, the number of the refrigerant flow paths is three.

Next, FIG. 30 is the schematic diagram showing the structure and the refrigerant flow in the case of the evaporator, in which the lateral size of the furthermost downstream side flow passage row 211 is larger than the lateral size of the furthermost upstream side flow passage row 221. Furthermore, in this evaporator, the furthermost downstream side flow passage row and the furthermost upstream side flow passage row are the refrigerant downflow portions, respectively, and the refrigerant flow pattern is a 1-1-1 refrigerant flow pattern. In addition, the number of the refrigerant flow paths is three.

Eighteenth Embodiment

In an eighteenth embodiment of the present invention, a positional relationship between the communication passage forming member and the core, which is applicable to all of the embodiments of the present invention, will be described with reference to FIGS. 31 to 33. FIG. 31 is a partial schematic front view showing the relationship between the communication passage forming member 44 and the core. FIG. 32 is a partial schematic front view showing the relationship between the communication passage forming member 44 and the core in a modification of FIG. 31. FIG. 33 is a partial schematic front view showing the relationship between the communication passage forming member 44 and the core in a further modification of the FIG. 31.

As shown in FIGS. 31 to 33, the communication passage forming member 44 is provided such that at least a portion of the communication passage forming member 44 is placed laterally inward (on the left side in FIGS. 31-33) of the lateral end of the core 100. With this construction, a dead space can be reduced to reduce the lateral size of the core.

In FIG. 31, a longitudinal end portion of the side plate 500, which supports the core, is inserted into the interior of the communication passage forming member 44. Alternatively, a longitudinal end portion of the lateral end tube 20a, which is located at the lateral ends of the core, may be inserted into the interior of the communication passage forming member 44. With this construction, even in the case where the portion of the communication passage forming member 44 is placed laterally inward of the lateral end of the core, it is not required to make any particular adjustment of the longitudinal end portion of the tube 20a or of the side plate 500. Thus, the manufacturing of the heat exchanger can be simplified.

In FIG. 32, a longitudinal end portion of the side plate 500, which supports the core, is bent and is inserted into the interior of the downstream side lower tank 411. Alternatively, a longitudinal end portion of the tube 20a, which is located at the lateral end of the core, may be bent and inserted into the interior of the downstream side lower tank 411. With this construction, even in the case where the portion of the communication passage forming member 44 is placed laterally inward of the lateral ends of the core, the longitudinal end portion of the tube 20a or of the side plate 500 is not placed at the second communication passage 43. Therefore, it is possible to reduce the flow resistance of the refrigerant in the communication passage.

FIG. 33 shows the evaporator, which has the tube 20a, which is placed at the lateral end of the core and does not conduct the refrigerant therethrough. The tube 20a or the side plate 500, which supports the core, has the longitudinal end portion, which is bent and contacts the outer surface of the communication passage forming member 44. With this construction, even in the case where the portion of the communication passage forming member 44 is placed laterally inward of the lateral ends of the core, it is possible to eliminate the need for inserting the longitudinal end portion of the tube 20a or of the side plate 500 into the interior of the tank.

Now, modifications of the above embodiments will be described.

In the above embodiments, the number of the flow passage rows in the direction of the air flow (the Z-direction) is set to be two. However, the present invention is not limited to this. For example, the number of the flow passage rows in the direction of the air flow (the Z-direction) may be alternatively set to be three or more.

Furthermore, the core of the above embodiments may be modified such that the outer fins between the tubes may be eliminated from the core. Furthermore, the core of the above embodiments may be modified such that projections are created (for example by cutting) and bent at the tubes to project between the tubes. In such a case where the core is the finless type, in which the fines are eliminated between the tubes, or the type, in which the fins are joined to only one of the adjacent tubes, a draining performance of the condensed water, which is condensed on the outer surface of the core, can be promoted. Therefore, the accurate temperature measurement of the core is possible, and the good response can be obtained.

Furthermore, in the above embodiments, the refrigerant is the R134a refrigerant. However, the refrigerant of the present invention is not limited to this type of refrigerant. Even when the other refrigerant, such as the carbon dioxide refrigerant or the R152 refrigerant, is used, the advantages similar to the above described ones can be achieved. However, when the R134a refrigerant is used, the above advantages are more prominent.

In the above embodiments, the evaporator is used in the refrigeration cycle of the vehicle air conditioning system. However, the present application is also equally application to a heat exchanger in a refrigeration cycle of any other system, which is other than the vehicle air conditioning system.

In the above embodiments, the upstream side and downstream side header tanks are constructed such that the refrigerant is supplied into or is outputted from the tubes at the interior of the header tank. However, the location, at which the refrigerant is supplied into or is outputted from the tubes, is not limited to the interior of the tank. For example, the location, at which the refrigerant is supplied into or is outputted from the tubes, may be placed on the upstream side or downstream side of the interior of the tank rather than placing it completely in the interior of the tank.

Furthermore, in the above embodiments, the thickness Ta of the downstream side flow passage row 21, which is measured in the direction of the air flow, is set to be generally the same as the thickness Th of the upstream side flow passage row 22, which is measured in the direction of the air flow. Alternatively, the thickness Ta of the downstream side flow passage row 21, which is measured in the direction of the air flow, may be made larger than the thickness Th of the upstream side flow passage row 22, which is measured in the direction of the air flow. In this way, the cross sectional area of the downstream side flow passage, at which the dryness of the refrigerant is relatively large, is increased. Therefore, the pressure loss of the refrigerant can be reduced in the entire heat exchanger.

Furthermore, the evaporator of the above respective embodiments includes the communicating means that communicates between the interior of the furthermost downstream side header tank 11, which is furthermost from the flow inlet 51, and the interior of the furthermost upstream side header tank 12, which is furthermost from the flow outlet 52, and this communicating means is placed at the location, which projects laterally or vertically from the body of the core. In addition to this communication means, it is possible to provide a communication passage, which communicates between the interior of the downstream side header tank 11 and the interior of the upstream side header tank 12.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.

Claims

1. A heat exchanger comprising:

a core that includes: a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow;

a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes: at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows;

a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes: at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows;

a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;

a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;

at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;

at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall; and

a communicating means that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and is for communicating between an interior of each corresponding one of the downstream side header tanks, which is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of each corresponding one of the upstream side header tanks, which is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, wherein:

the communicating means is placed at a location that projects from a body of the core in one of the lateral direction and the up-to-bottom direction of the core;

a portion of the refrigerant in a furthermost one of the downstream side header tanks, which is furthermost from the refrigerant inlet in the lateral direction of the core, is conducted toward the upstream side of the air flow into a furthermost one of the upstream side header tanks located on an upstream side thereof in the direction of the air flow after flowing through the communicating means and then flows through the furthermost one of the upstream side flow passage rows into an opposed one of the upstream side header tanks, which is opposed to the furthermost one of the upstream side header tanks in the top-to-bottom direction of the core; and

a rest of the refrigerant, which remains in the furthermost one of the downstream side header tanks, flows through the furthermost one of the downstream side flow passage rows into an opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks where the rest of the refrigerant is merged with the portion of the refrigerant supplied through the communicating means.

2. The heat exchanger according to claim 1, wherein:

the communicating means includes a lower communication passage that communicates between an interior of a furthermost one of the at least one downstream side lower tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side lower tank, which is furthermost from the refrigerant outlet in the lateral direction of the core;

the heat exchanger further comprises an upper communication passage that communicates between an interior of a furthermost one of the at least one downstream side upper tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side upper tank, which is furthermost from the refrigerant outlet in the lateral direction of the core; and

the rest of the refrigerant, which remains in the furthermost one of the at least one downstream side lower tank, flows upwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side upper tank and then flows into the furthermost one of the at least one upstream side upper tank through the upper communication passage and is merged with the portion of the refrigerant, which flows from the furthermost one of the at least one downstream side lower tank into the furthermost one of the at least one upstream side lower tank through the lower communication passage and then flows into the furthermost one of the at least one upstream side upper tank thorough the furthermost one of the upstream side flow passage rows.

3. The heat exchanger according to claim 1, wherein:

the communicating means includes an upper communication passage that communicates between an interior of a furthermost one of the at least one downstream side upper tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side upper tank, which is furthermost from the refrigerant outlet in the lateral direction of the core;

the heat exchanger further comprises a lower communication passage that communicates between an interior of a furthermost one of the at least one downstream side lower tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side lower tank, which is furthermost from the refrigerant outlet in the lateral direction of the core; and

the rest of the refrigerant, which remains in the furthermost one of the at least one downstream side upper tank, flows downwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side lower tank and then flows into the furthermost one of the at least one upstream side lower tank through the lower communication passage and is merged with the portion of the refrigerant, which flows from the furthermost one of the at least one downstream side upper tank into the furthermost one of the at least one upstream side upper tank through the upper communication passage and then flows into the furthermost one of the at least one upstream side lower tank thorough the furthermost one of the upstream side flow passage rows.

4. The heat exchanger according to claim 1, wherein:

the communicating means includes at least one communication passage forming member that has a communication passage therein; and

each of the at least one communication passage forming member is formed as a separate component, which is separate from the plurality of downstream side header tanks and the plurality of upstream side header tanks and is assembled integrally to a corresponding one of the plurality of downstream side header tanks and the plurality of upstream side header tanks.

5. The heat exchanger according to claim 4, wherein at least a portion of each of the at least one communication passage forming member is placed laterally inward of a lateral end of the core in the lateral direction of the core.

6. The heat exchanger according to claim 5, wherein one of the plurality of downstream side tubes and the plurality of upstream side tubes, which is located at the lateral end of the core, or a side plate, which supports the core, has a longitudinal end portion that is inserted into an interior of a corresponding one of the at least one communication passage forming member.

7. The heat exchanger according to claim 5, wherein one of the plurality of downstream side tubes and the plurality of upstream side tubes, which is located at the lateral end of the core, or a side plate, which supports the core, has a longitudinal end portion that is inserted into an interior of a corresponding one of the plurality of downstream side header tanks and the plurality of upstream side header tanks.

8. The heat exchanger according to claim 4, further comprising a lateral end tube, which is placed at a lateral end of the core and does not conduct the refrigerant therethrough, wherein the lateral end tube or a side plate, which supports the core, has a longitudinal end portion that is bent and contacts a corresponding one of the at least one communication passage forming member.

9. The heat exchanger according to claim 1, wherein at least one communication hole is formed through a wall that partitions between an interior of another furthermost one of the downstream side header tanks and another furthermost one of the upstream side header tanks to communicate therebetween.

10. The heat exchanger according to claim 1, wherein:

the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area SI;

the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area S2; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S1/S2.

11. The heat exchanger according to claim 10, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S1/S2.

12. The heat exchanger according to claim 10, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S1/S2.

13. The heat exchanger according to claim 10, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S1/S2.

14. The heat exchanger according to claim 10, wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three.

15. The heat exchanger according to claim 1, wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows.

16. The heat exchanger according to claim 1, wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core.

17. The heat exchanger according to claim 1, wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm.

18. The heat exchanger according to claim 1, wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows.

19. The heat exchanger according to claim 1, wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows.

20. The heat exchanger according to claim 1, wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows.

21. A heat exchanger comprising:

a core that includes: a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow; a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes: at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows;

a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes: at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows;

a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;

a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;

at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;

at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall;

a lower communication passage that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and communicates between an interior of a furthermost one of the at least one downstream side lower tank, which is furthermost from the refrigerant inlet in the lateral direction of the core and is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side lower tank, which is furthermost from the refrigerant outlet in the lateral direction of the core and is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, to conduct a portion of the refrigerant in the furthermost one of the at least one downstream side lower tank into the furthermost one of the upstream side flow passage rows, wherein:

the portion of the refrigerant from the furthermost one of the at least one downstream side lower tank flows into the furthermost one of the at least one upstream side lower tank through the lower communication passage and then flows into the furthermost one of the at least one upstream side upper tank after flowing upwardly thorough the furthermost one of the upstream side flow passage rows;

a rest of the refrigerant, which remains in the furthermost one of the at least one downstream side lower tank, flows upwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side upper tank and then flows into the furthermost one of the at least one upstream side upper tank and is merged with the portion of the refrigerant in the furthermost one of the at least one upstream side upper tank; and

a refrigerant inflow opening of the lower communication passage is an inlet of the lower communication passage and opens to an interior of the furthermost one of the at least one downstream side lower tank at a location that is below lower end openings of the downstream side tubes of the furthermost one of the downstream side flow passage rows in the vertical direction.

22. The heat exchanger according to claim 21, wherein:

the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area SI;

the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area 52; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S1/S2.

23. The heat exchanger according to claim 22, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S1/S2.

24. The heat exchanger according to claim 22, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S1/S2.

25. The heat exchanger according to claim 22, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S1/S2.

26. The heat exchanger according to claim 22, wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three.

27. The heat exchanger according to claim 21, wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows.

28. The heat exchanger according to claim 21, wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core.

29. The heat exchanger according to claim 21, wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm.

30. The heat exchanger according to claim 21, wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows.

31. The heat exchanger according to claim 21, wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows.

32. The heat exchanger according to claim 21, wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows.

33. A heat exchanger comprising:

a core that includes: a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow;

a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes: at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows;

a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes: at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows;

a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;

a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;

at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;

at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall; and

an upper communication passage that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and communicates between an interior of a furthermost one of the at least one downstream side upper tank, which is furthermost from the refrigerant inlet in the lateral direction of the core and is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side upper tank, which is furthermost from the refrigerant outlet in the lateral direction of the core and is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, to conduct a portion of the refrigerant in the furthermost one of the at least one downstream side upper tank into the furthermost one of the upstream side flow passage rows, wherein:

the portion of the refrigerant from the furthermost one of the at least one downstream side upper tank flows into the furthermost one of the at least one upstream side upper tank through the upper communication passage and then flows into the furthermost one of the at least one upstream side lower tank after flowing downwardly thorough the furthermost one of the upstream side flow passage rows;

a rest of the refrigerant, which remains in the furthermost one of the at least one downstream side upper tank, flows downwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side lower tank and then flows into the furthermost one of the at least one upstream side lower tank and is merged with the portion of the refrigerant in the furthermost one of the at least one upstream side lower tank; and

a refrigerant inflow opening of the upper communication passage is an inlet of the upper communication passage and opens to an interior of the furthermost one of the at least one downstream side upper tank at a location that is above upper end openings of the downstream side tubes of the furthermost one of the downstream side flow passage rows in the vertical direction.

34. The heat exchanger according to claim 33, wherein:

the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area S1;

the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area S2; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S1/S2.

35. The heat exchanger according to claim 34, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S1/S2.

36. The heat exchanger according to claim 34, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S1/S2.

37. The heat exchanger according to claim 34, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S1/S2.

38. The heat exchanger according to claim 34, wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three.

39. The heat exchanger according to claim 33, wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows.

40. The heat exchanger according to claim 33, wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core.

41. The heat exchanger according to claim 33, wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm.

42. The heat exchanger according to claim 33, wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows.

43. The heat exchanger according to claim 33, wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows.

44. The heat exchanger according to claim 33, wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows.

45. A heat exchanger comprising:

a core that includes: a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow;

a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes: at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows;

a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes: at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows;

a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;

a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;

at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;

at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall; and

a communicating means that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and is for communicating between an interior of each corresponding one of the downstream side header tanks, which is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of each corresponding one of the upstream side header tanks, which is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, wherein:

the core has an upstream side lateral plane and a downstream side lateral plane, which are located on the upstream side and the downstream side, respectively, in the direction of the air flow;

the core is tilted toward the upstream side in the direction of the air flow such that the upstream side lateral plane is closer to an imaginary horizontal plane, which is placed vertically below the at least one upstream side lower tank, in comparison to the downstream side lateral plane;

a portion of the refrigerant in a furthermost one of the downstream side header tanks, which is furthermost from the refrigerant inlet in the lateral direction of the core, is conducted toward the upstream side of the air flow into a furthermost one of the upstream side header tanks located on an upstream side thereof in the direction of the air flow after flowing through the communicating means and then flows through the furthermost one of the upstream side flow passage rows into an opposed one of the upstream side header tanks, which is opposed to the furthermost one of the upstream side header tanks in the top-to-bottom direction of the core; and

a rest of the refrigerant, which remains in the furthermost one of the downstream side header tanks, flows through the furthermost one of the downstream side flow passage rows into an opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks where the rest of the refrigerant is merged with the portion of the refrigerant supplied through the communicating means.

46. The heat exchanger according to claim 45, wherein:

the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area S1;

the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area S2; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S1/S2.

47. The heat exchanger according to claim 46, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S1/S2.

48. The heat exchanger according to claim 46, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S1/S2.

49. The heat exchanger according to claim 46, wherein:

the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and

the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S1/S2.

50. The heat exchanger according to claim 46, wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three.

51. The heat exchanger according to claim 45, wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows.

52. The heat exchanger according to claim 45, wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core.

53. The heat exchanger according to claim 45, wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm.

54. The heat exchanger according to claim 45, wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows.

55. The heat exchanger according to claim 45, wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows.

56. The heat exchanger according to claim 45, wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows.