AUTOMOTIVE AIR CONDITIONER

Abstract

An automotive air conditioner which is capable of efficiently disposing an internal heat exchanger, and enabling the air conditioner to perform an efficient operation. A thermostatic expansion valve is accommodated in a casing directly connected to the refrigerant outlet of an evaporator. The inlet of the expansion valve and a pipe for receiving high-pressure liquid refrigerant are connected to each other within the casing. The outlet of the expansion valve and the refrigerant inlet of the evaporator are connected to each other within the casing. The internal heat exchanger for performing heat exchange between high-pressure refrigerant delivered to the inlet of the expansion valve and low-pressure refrigerant returning to a compressor is connected between the casing and a pipe joint disposed in a firewall.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY

This application claims priority of Japanese Application No. 2006-338152 filed on Dec. 15, 2006, entitled “AUTOMOTIVE AIR CONDITIONER”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an automotive air conditioner, and more particularly to an automotive air conditioner which is capable of performing an efficient operation with component elements on a vehicle compartment side in compact arrangement.

2. Description of the Related Art

In general, an automotive air conditioner comprises a compressor driven by an automotive engine, a condenser for condensing refrigerant compressed by the compressor, a receiver for separating the condensed refrigerant into gas and liquid phases and storing the liquid refrigerant, an expansion valve for throttling and expanding high-temperature, high-pressure refrigerant into atomized low-temperature, low-pressure refrigerant, and an evaporator for evaporating the atomized refrigerant by heat exchange between the atomized refrigerant and air in the vehicle compartment and then returning the evaporated refrigerant to the compressor. As the expansion valve, there is widely used a thermostatic expansion valve which controls the flow rate of refrigerant delivered into the evaporator by sensing the temperature and pressure of refrigerant at the refrigerant outlet of the evaporator.

In the automotive air conditioner constructed as above, the compressor, the condenser, and the receiver are arranged in an engine room which accommodates the automotive engine, while the evaporator is disposed in the vehicle compartment. Further, the expansion valve is disposed between the evaporator and the compressor and between the evaporator and the receiver. It is also known to dispose the expansion valve in a firewall separating the engine room from the vehicle compartment such that the body block of the expansion valve is also used as a pipe joint for connecting between the evaporator in the vehicle compartment and the compressor and the receiver in the engine room (see e.g. Japanese Unexamined Patent Publication No. 2001-235259 (FIGS. 11, 17 and 18)). To configure the expansion valve such that the body block thereof also plays the role of the pipe joint can be said to be very rational from the viewpoint of construction since operations for assembling component elements to the automotive vehicle are performed separately for those in the engine room and those in the vehicle compartment, and finally it is necessary to install piping in the firewall for connection via the expansion valve between the compressor and the receiver in the engine room and the evaporator in the vehicle compartment.

Further, in a supercritical refrigeration cycle using carbon dioxide as refrigerant, for improvement of efficiency, that is, the coefficient of performance and the cooling power thereof, it is known to provide an internal heat exchanger and cause heat to be exchanged between refrigerant flowing from a gas cooler to an expansion device and refrigerant returning from an evaporator to a compressor (see e.g. Japanese Unexamined Patent Publication No. 2001-108308).

The above idea is expected to be also applicable to a refrigeration cycle which uses chlorofluorocarbon (HFC-134a), generally used as refrigerant, or a gas having a physical property equivalent or similar to that of chlorofluorocarbon, to improve the efficiency thereof.

However, the idea suffers from the problem that when the internal heat exchanger is disposed in the refrigeration cycle, it is necessary to newly install piping to the refrigerant inlet and outlet of the heat exchanger, which makes the construction of the refrigeration cycle complicated, thereby making it difficult to perform operations for assembling the component elements to the automotive vehicle. Further, the internal heat exchanger returns refrigerant leaving the evaporator to the compressor after superheating the refrigerant by refrigerant sent from the condenser to the expansion valve, and hence when refrigeration load is low, the efficiency of the refrigeration cycle can be improved, whereas when the refrigeration load is high, the temperature of refrigerant returned to the compressor tends to become too high, which makes lubricating oil for the compressor liable to undergo thermal deterioration.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above points, and an object thereof is to provide an automotive air conditioner which is capable of efficiently disposing an internal heat exchanger, and enabling the air conditioner to perform an efficient operation.

To attain the above object, the present invention provides an automotive air conditioner. The automotive air conditioner is characterized in that a thermostatic expansion valve having an inlet to which is connected a pipe for receiving high-pressure refrigerant and an outlet to which is connected a refrigerant inlet pipe of an evaporator is accommodated in a casing directly connected to a refrigerant outlet of the evaporator, an internal heat exchanger for performing heat exchange between the high-pressure refrigerant and low-pressure refrigerant returning from the casing to a compressor is connected to the casing, and a pipe joint for connecting a high-pressure pipe extending from a receiver and a low-pressure pipe extending to the compressor independently of each other is connected to an end of the internal heat exchanger on the side opposite to the side where the casing is connected.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of a refrigeration cycle for an automotive air conditioner according to the present invention.

FIG. 2 is a cross-sectional view of a first embodiment of a unit disposed in a vehicle compartment.

FIG. 3A is an enlarged cross-sectional view of essential parts of an expansion valve.

FIG. 3B is a cross-sectional view taken on line a-a of FIG. 3A.

FIG. 4 is a cross-sectional view of a pipe connected to an inlet of the expansion valve, taken along a plane passing through a center line of the pipe.

FIG. 5 is an end view of a pipe joint.

FIG. 6A is an enlarged cross-sectional view of essential parts of an expansion valve according to a second embodiment of the present invention.

FIG. 6B is a cross-sectional view taken on line b-b of FIG. 6A.

FIG. 7 is a view of a differential pressure valve according to a third embodiment of the present invention.

FIG. 8A is a partial perspective view of an end of an example of the internal heat exchanger.

FIG. 8B is a partial cross-sectional perspective view of an example of a high-pressure forward pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in detail with reference to the drawings showing a preferred embodiment thereof.

FIG. 1 is a system diagram of a refrigeration cycle for an automotive air conditioner according to the present invention.

In the automotive air conditioner, a compressor 1 for compressing refrigerant, a condenser 2 for condensing the compressed refrigerant by heat exchange between the refrigerant and the outside air, and a receiver 3 for separating the condensed refrigerant into gas and liquid phases and storing surplus refrigerant within the refrigeration cycle are arranged in an engine room. On the other hand, an internal heat exchanger 4 for performing heat exchange between high-temperature, high-pressure refrigerant flowing from the receiver 3 and low-temperature, low-pressure refrigerant returning to the compressor 1 are disposed in a vehicle compartment. The outlet of the internal heat exchanger 4 on the high-pressure side is connected to the inlet of a thermostatic expansion valve 5, and the outlet of the thermostatic expansion valve 5 is connected to the refrigerant inlet of an evaporator 6. The refrigerant outlet of the evaporator 6 opens into a casing 7 accommodating the thermostatic expansion valve 5. The casing 7 is connected to the inlet of the compressor 1 via the internal heat exchanger 4. Further, disposed within the casing 7 is a differential pressure valve 8 connecting the outlet of the expansion valve 5 and the inlet of the internal heat exchanger 4 on the low-pressure side. Furthermore, a pipe joint 9 is disposed in a firewall 10 separating the engine room from the vehicle compartment, for connecting between pipes to the compressor 1 and the receiver 3 in the engine room and the internal heat exchanger 4 in the vehicle compartment.

The expansion valve 5 includes a temperature-sensing section for sensing the temperature and pressure of refrigerant leaving the evaporator 6, and controls the flow rate of refrigerant sent to the evaporator 6 according to the temperature and pressure of the refrigerant, sensed by the temperature-sensing section. The whole expansion valve 5 is accommodated in the casing 7 directly connected to the refrigerant outlet of the evaporator 6. Therefore, connection between the inlet of the expansion valve 5 and a pipe for receiving liquid refrigerant from the internal heat exchanger 4, and connection between the outlet of the expansion valve 5 and a pipe to the refrigerant inlet of the evaporator 6 are both performed within the casing 7, and moreover the casing 7 forms part of a low-pressure return pipe for returning refrigerant from the evaporator 6 to the compressor 1. For this reason, even when a minute amount of refrigerant leaks from the sealing portions of the inlet and outlet of the expansion valve 5, the refrigerant leaks only into the casing 7, i.e. only into the low-pressure return pipe, and hence is prevented from leaking to the outside of the refrigeration cycle.

The internal heat exchanger 4 includes a high-pressure forward pipe 4a for allowing high-temperature, high-pressure refrigerant to flow to the expansion valve 5, and a low-pressure return pipe 4b for allowing low-temperature, low-pressure refrigerant to flow to the compressor 1, and performs heat exchange between the high-temperature, high-pressure refrigerant flowing through the high-pressure forward pipe 4a and the low-temperature, low-pressure refrigerant flowing through the low-pressure return pipe 4b.

In the automotive air conditioner configured as above, the compressor 1 is driven by an automotive engine, for sucking and compressing refrigerant to discharge the same. In doing this, the displacement of the compressor 1 is controlled such that refrigerant is discharged at a predetermined flow rate, irrespective of the rotational speed of the engine. Refrigerant compressed by the compressor 1 into high-temperature, high-pressure refrigerant is sent to the condenser 2, in which the refrigerant is condensed by heat exchange with the outside air to be sent to the receiver 3. Liquid refrigerant obtained by gas/liquid separation in the receiver 3 is sent via the internal heat exchanger 4 to the expansion valve 5, where the liquid refrigerant is throttled and expanded into atomized low-temperature, low-pressure refrigerant. The atomized refrigerant is sent to the evaporator 6, where the refrigerant exchanges heat with air in the vehicle compartment to evaporate. As the atomized refrigerant evaporates in the evaporator 6, it cools air in the vehicle compartment by depriving the air of latent heat of vaporization.

The refrigerant evaporated in the evaporator 6 returns to the compressor 1 via the casing 7 and the internal heat exchanger 4. At this time, in the casing 7, the temperature-sensing section of the expansion valve 5 accommodated in the casing 7 senses the temperature and pressure of the refrigerant leaving the evaporator 6, and the expansion valve 5 controls the flow rate of refrigerant supplied to the evaporator 6 such that the refrigerant leaving the evaporator 6 has a predetermined degree of superheat. In the internal heat exchanger 4, when the refrigerant leaving the evaporator 6 returns to the compressor 1 via the low-pressure return pipe 4b, the refrigerant is further superheated by high-temperature, high-pressure refrigerant flowing through the high-pressure forward pipe 4a toward the expansion valve 5, whereby it is possible to enhance the efficiency of the refrigeration cycle.

Further, the differential pressure valve 8 operates by sensing the differential pressure between the pressure at the refrigerant inlet and the pressure at the refrigerant outlet of the evaporator 6. When pressure loss in the evaporator 6 increases, the differential pressure valve 8 opens to cause refrigerant at the outlet of the expansion valve 5 to bypass to the low-pressure return pipe 4b of the internal heat exchanger 4. This increases refrigeration load to increase the flow rate of refrigerant circulating through the refrigeration cycle, and when the pressure loss of the evaporator 6 exceeds a predetermined value, the differential pressure valve 8 opens to supply refrigerant which is throttled and expanded by the expansion valve 5 into atomized low-temperature, low-pressure refrigerant. As described above, when refrigeration load is high, moist refrigerant is supplied to the low-pressure return pipe 4b of the internal heat exchanger 4, to thereby prevent the temperature of refrigerant returned to the compressor 1 from becoming too high, for preventing thermal deterioration of lubricating oil for the compressor 1.

Next, a description will be given of examples of the constructions of the internal heat exchanger 4, the expansion valve 5, the evaporator 6, and the pipe joint 9.

FIG. 2 is a cross-sectional view of a first embodiment of a unit disposed in the vehicle compartment. FIG. 3A is an enlarged cross-sectional view of essential parts of the expansion valve, and FIG. 3B is a cross-sectional view taken on line a-a of FIG. 3A. FIG. 4 is a cross-sectional view of a pipe connected to the inlet of the expansion valve, taken along a plane passing through the center line of the pipe. FIG. 5 is an end view of the pipe joint. It should be noted that component elements in FIGS. 2 to 5 identical or similar to those shown in FIG. 1 are designated by identical reference numerals.

The evaporator 6 has a refrigerant inlet 11 and a refrigerant outlet 12 formed in the same end face thereof, for introducing refrigerant and for discharging refrigerant, respectively. An inlet pipe 13 is joined to the refrigerant inlet 11, and a hollow cylindrical connecting part 14 is joined to an end face of the evaporator 6 in a manner enclosing the refrigerant inlet 11 and the refrigerant outlet 12. Preferably, the inlet pipe 13 and the connecting part 14 are integrally formed with the evaporator 6 by being welding to the evaporator 6 together when the evaporator 6 is formed by furnace brazing.

A hollow cylindrical casing 7 having a closed end is hermetically joined to the connecting part 14 via an O ring, and accommodates the expansion valve 5. The expansion valve 5 has a body 18 made e.g. of a resin material. The body 18 is integrally formed with an inlet port 16 for introducing high-pressure refrigerant and an outlet port 17 for discharging low-pressure refrigerant. The body 18 has a passage formed therethrough for communication between the inlet port 16 and the outlet port 17, and a valve seat 19 is inserted in an intermediate portion of the passage.

A valve element 20 is disposed on the downstream side of the valve seat 19 in a manner movable to and away from the valve seat 19. The valve element 20 is disposed in a state urged by a spring 21 in the valve-closing direction. The spring 21 is received by an adjustment screw 22 screwed into the outlet port 17, and the load of the spring 21 is adjusted by the screwing amount of the adjustment screw 22 into the body 18, whereby the set point of the expansion valve 5 is adjusted.

The valve element 20 is rigidly fixed to a shaft 23. As shown in detail in FIG. 3, the shaft 23 includes a large-diameter portion 23a which is supported by the body 18 in a manner movable in the opening and closing directions of the valve element 20, and a small-diameter portion 23b which extends through a valve hole of the valve seat 19. The shaft 23 has the valve element 20 fixed to the small-diameter portion 23b thereof. The large-diameter portion 23a of the shaft 23 has a groove circumferentially formed in the periphery thereof. An O ring 24 is fitted in the groove to thereby prevent high-pressure refrigerant introduced into the inlet port 16 from leaking into the casing 7 through a clearance between the body 18 and the large-diameter portion 23a of the shaft 23.

Here, the large-diameter portion 23a of the shaft 23 is configured to have a back pressure cancelling structure in which the large-diameter portion 23a has an outer diameter equal to the inner diameter of the valve hole of the valve seat 19 such that the force of high pressure introduced into the inlet port 16 acting on the valve element 20 in the valve-opening direction and the force of the high pressure acting on the large-diameter portion 23a in the valve-closing direction are set to be substantially equal to each other to prevent the valve element 20 from being adversely affected by the high pressure introduced into the inlet port 16. Since the outer diameter of the large-diameter portion 23a and the inner diameter of the valve hole of the valve seat 19 are set to be equal to each other, the shaft 23 cannot be incorporated in the expansion valve 5 via the valve hole of the valve seat 19 from the outlet port side, with the O ring 24 fitted on the large-diameter portion 23a. Therefore, the shaft 23 is inserted from a side opposite to the outlet port 17, and the valve element 20 is fitted from the outlet port side onto the small-diameter portion 23b of the shaft 23 extending through the valve hole of the valve seat 19, whereby the shaft 23 and the valve element 20 are assembled with each other.

Further, the valve element 20 has a tapered portion 20a which can be seated on a tapered portion 19a formed on the inner periphery of the valve seat 19 on the downstream side thereof. Further, a portion inward of the tapered portion 20a is integrally formed with three guides 20b which are arranged at circumferentially equal intervals and projecting radially outward. The guides 20b move in the opening or closing direction of the valve element 20 while sliding along the inner wall of the valve hole, whereby it is possible to secure passages through which refrigerant passes, between adjacent ones of the guides 20b, and guide the opening or closing operation of the valve along the valve hole while positioning the valve element 20 in the center of the valve hole. This prevents the valve element 20 from rolling in which the valve element 20 radially vibrates.

The body 18 has a power element 25 mounted on an end thereof opposite from the outlet port 17. The power element 25 comprises an upper housing and a lower housing, each made of thick metal, a diaphragm 26 made of a flexible thin metal plate and disposed in a manner partitioning a space enclosed by the upper and lower housings, and a center disk 27 for transmitting the displacement of the diaphragm 26 to the shaft 23. The space enclosed by the upper housing and the diaphragm 26 forms a temperature-sensing chamber, which is filled with refrigerant gas and the like. The lower housing has several gas-passing holes formed so as to introduce refrigerant passing through the casing 7 into space on the center disk side. The amount of refrigerant to be introduced is adjusted by changing the size or number of the gas-passing holes. Further, a heat-insulating cover 28 made e.g. of resin is attached to the power element 25 in a manner covering the same. The heat-insulating cover 28 also serves as a fixing element for fixing the power element 25 to the body 18.

The expansion valve 5 has the differential pressure valve 8 provided in the body 18 thereof. The differential pressure valve 8 is configured such that a passage for causing a space accommodating the spring 21 to communicate with the outside of the expansion valve 5 is formed through the body 18, and a valve element for opening and closing the passage is urged by a spring from the outside of the expansion valve 5 such that the valve element closes the passage. As a result, when the pressure at the outlet port 17 of the expansion valve 5 becomes higher than the pressure outside the expansion valve 5 (i.e. the interior of the casing 7) by a value exceeding a predetermined value, the differential pressure valve 8 acts to open. The predetermined value is set by adjusting the load of the spring urging the valve element in the valve-closing direction.

The outlet port 17 of the expansion valve 5 is fitted on the inlet pipe 13 of the evaporator 6 and is sealed by an O ring 29. On the other hand, the inlet port 16 of the expansion valve 5 and the casing 7 are directly connected to the internal heat exchanger 4. The internal heat exchanger 4 is formed as a double pipe in which the low-pressure return pipe 4b is disposed outside the high-pressure forward pipe 4a in coaxial relation thereto, so that one end of the high-pressure forward pipe 4a and one end of the low-pressure return pipe 4b are connected to the inlet port 16 of the expansion valve 5 and the casing 7, respectively. More specifically, the high-pressure forward pipe 4a is fitted in the inlet port 16 of the expansion valve 5 and is sealed by an O ring 30. As to the casing 7, as shown in FIG. 4, a hollow cylindrical connecting pipe 31 is brazed to a side surface thereof, and the low-pressure return pipe 4b is fitted in the connecting pipe 31 and is sealed by an O ring 32.

As described above, the expansion valve 5, the casing 7 accommodating the expansion valve 5, and the high-pressure forward pipe 4a and the low-pressure return pipe 4b of the internal heat exchanger 4 are connected to each other by a clamp device 33. As clearly shown in FIG. 4, the clamp device 33 includes a first holding member 33a formed in a manner covering a half of a side surface of the casing 7, a second holding member 33b formed in a manner covering the remaining half of the side surface of the casing 7 including the connecting pipe 31, and fixing pins 33c for connecting the first holding member 33a and the second holding member 33b. The first holding member 33a and the second holding member 33b have restricting portions for covering respective fitting portions of the connecting part 14 and the casing 7 where they are fitted to each other, from outside along the whole circumference thereof, such that the restricting portions restrict the motions of the connecting part 14 and the casing 7 in the fitting direction. The second holding member 33b has an engaging portion engaged with a rib formed in the vicinity of a foremost end of the low-pressure return pipe 4b of the internal heat exchanger 4, in addition to the restricting portion, such that when the first holding member 33a and the second holding member 33b are connected to each other by the fixing pins 33c, a state of the rib of the low-pressure return pipe 4b being pressed against the connecting pipe 31 is maintained. At this time, since the high-pressure forward pipe 4a and the low-pressure return pipe 4b are connected to each other such that they maintain the coaxial arrangement thereof, the connected state of the high-pressure forward pipe 4a and the inlet port 16 of the expansion valve 5 is also maintained. It should be noted that the closed end of the casing 7 is configured to hold the power element 25 when the casing 7 is fitted in the connecting part 14, which causes the connection between the outlet port 17 of the expansion valve 5 and the inlet pipe 13 of the evaporator 6 to be also maintained.

As described above, the expansion valve 5 is accommodated in the low-pressure return pipe of the evaporator 6, and the expansion valve 5 and the internal heat exchanger 4 are connected to each other in the low-pressure return pipe, and hence the connecting portion connecting between the inlet port 16 and the high-pressure forward pipe 4a is the only connecting portion of a high-pressure system in the vehicle compartment, from which refrigerant can leak out. Moreover, since the connecting portion is within the low-pressure return pipe, even if a minute amount of high-pressure refrigerant leaks via the O ring 30, the refrigerant remains in the low-pressure return pipe without leaking out into the atmosphere.

The pipe joint 9 is disposed on a side of the internal heat exchanger 4, opposite from the side where the casing 7 is disposed. The pipe joint 9 has a first connecting hole 9a in which the low-pressure return pipe 4b is fitted, and a second connecting hole 9b which is disposed in the first connecting hole 9a coaxially therewith, for having the high-pressure forward pipe 4a fitted therein, on an end face thereof on the internal heat exchanger side. The low-pressure return pipe 4b fitted in the first connecting hole 9a is fixed to the pipe joint 9 by inwardly swaging the outer periphery of the first connecting hole 9a such that it is entirely circumferentially engaged with a rib formed in the vicinity of the foremost end of the low-pressure return pipe 4b.

Further, as shown in FIG. 5, the pipe joint 9 has a third connecting hole 9c and a fourth connecting hole 9d formed in parallel in an end face thereof on the engine room side, for communication with the first connecting hole 9a and the second connecting hole 9b, respectively. It should be noted that in the present embodiment, the pipe joint 9 has an expanding hole 9e formed in the end face, for expanding a passage between the first connecting hole 9a and the third connecting hole 9c. Furthermore, screw holes 9f and 9g are formed adjacent to the third connecting hole 9c and the fourth connecting hole 9d in the end face of the pipe joint 9, respectively. The screw hole 9f is provided for screwing a fixing plate provided in the vicinity of the foremost end of a low-pressure pipe after the low-pressure pipe extending to the refrigerant inlet of the compressor 1 is fitted in the third connecting hole 9c from the engine room side. The screw hole 9g is provided for screwing a fixing plate provided in the vicinity of the foremost end of a high-pressure pipe after the high-pressure pipe extending from the receiver 3 is fitted in the fourth connecting hole 9d from the engine room side.

Next, a description will be given of the operation of the unit which is constructed as described above, and is disposed in the vehicle compartment. First, when the automotive air conditioner is not in operation, gas filling the temperature-sensing chamber of the power element 25 is condensed, so that the pressure of the gas is low. Therefore, as shown in FIG. 2, the diaphragm 26 is displaced toward the temperature-sensing chamber, and the displacement of the diaphragm 26 is transmitted to the valve element 20 via the shaft 23, whereby the expansion valve 5 is placed in the fully closed state.

When the automotive air conditioner is started in this state, refrigerant is sucked by the compressor 1, and hence pressure within the low-pressure return pipe 4b of the internal heat exchanger 4 drops. The power element 25 senses this, so that the diaphragm 26 is displaced outward to lift the valve element 20 via the shaft 23. On the other hand, refrigerant compressed by the compressor 1 is condensed by the condenser 2, and liquid refrigerant obtained by gas/liquid separation in the receiver 3 is supplied to the inlet port 16 of the expansion valve 5 through the high-pressure forward pipe 4a of the internal heat exchanger 4.

The high-temperature, high-pressure liquid refrigerant supplied to the inlet port 16 is throttled and expanded while passing through the expansion valve 5 and flows out as low-temperature, low-pressure gas-liquid mixture refrigerant from the outlet port 17. The refrigerant is supplied to the evaporator 6 through the inlet pipe 13, and is evaporated in the evaporator 6 to flow out from the refrigerant outlet 12. The refrigerant having returned from the evaporator 6 returns to the compressor 1 via the casing 7, the low-pressure return pipe 4b of the internal heat exchanger 4, the pipe joint 9, and the low-pressure pipe.

The space enclosed by the diaphragm 26 of the power element 25 and the lower housing of the same communicates with the inside of the casing 7 via the gas-passing holes, so that while refrigerant having returned from the evaporator 6 is passing through the casing 7, some of the refrigerant is introduced into the space within the power element 25, and the temperature of the introduced refrigerant is detected by the power element 25. In the early stage of the start of the automotive air conditioner, the temperature of the refrigerant returning from the evaporator 6 is high due to heat exchange with high-temperature air in the compartment, and the power element 25 senses the temperature of the refrigerant, so that the pressure within the temperature-sensing chamber becomes high. This causes the diaphragm 26 to be largely displaced toward the valve element 20, and this displacement is transmitted to the valve element 20 via the shaft 23, whereby the expansion valve 5 is fully opened.

As the temperature of refrigerant from the evaporator 6 becomes lower, the pressure within the temperature-sensing chamber also becomes lower. Accordingly, the diaphragm 26 is displaced in a direction away from the valve element 20, whereby the expansion valve 5 moves in the valve-closing direction to control the flow rate of refrigerant passing therethrough. At this time, the expansion valve 5 operates to detect the temperature of refrigerant having flowed from the evaporator 6, and controls the flow rate of refrigerant supplied to the evaporator 6 such that the refrigerant maintains a predetermined degree of superheat. As a consequence, refrigerant in a superheated state is always returned to the compressor 1, which enables the compressor 1 to perform an efficient operation.

When refrigeration load is high as when the outside air temperature is very high, the expansion valve 5 continues to allow refrigerant to flow at a large flow rate. At this time, the temperature of refrigerant having passed through the expansion valve 5 is not lowered, and the evaporation temperature of the refrigerant in the evaporator 6 is high. Moreover, the refrigerant is further superheated in the internal heat exchanger 4 while the refrigerant is returning from the evaporator 6 to the compressor 1. When the flow rate of refrigerant is large as described above, the differential pressure between the pressure at the inlet and the pressure at the outlet of the evaporator 6 becomes large, and hence the differential pressure valve 8 detects the differential pressure to open itself. As a result, part of the atomized refrigerant expanded into low-temperature refrigerant is mixed with superheated refrigerant flowing out from the evaporator 6 and flowing into the low-pressure return pipe 4b of the internal heat exchanger 4. This causes the temperature of the superheated refrigerant to become lower, and the refrigerant lowered in temperature comes to contain moisture. Such refrigerant is evaporated and superheated by heat exchange with high-temperature refrigerant flowing from the receiver 3 in the internal heat exchanger 4, and is then sucked by the compressor 1. This prevents the temperature of refrigerant sucked by the compressor 1 from becoming too high, and therefore the temperature of refrigerant compressed by the compressor 1 is also prevented from becoming too high, which prevents thermal deterioration of lubricating oil for the compressor 1, circulating through the refrigeration cycle together with refrigerant.

FIG. 6A is an enlarged cross-sectional view of essential parts of an expansion valve according to a second embodiment of the present invention, and FIG. 6B is a cross-sectional view taken on line b-b of FIG. 6A. It should be noted that component elements in FIGS. 6A and 6B identical or similar to those shown in FIGS. 3A and 3B are designated by identical reference numerals.

The expansion valve 5a according to the present embodiment is modified in valve structure thereof, and further the shape of the guides 20b integrally formed with the valve element 20, for preventing rolling of the valve element 20, is changed. More specifically, in the expansion valve 5a, a guide for the O ring 24 is formed by fitting two rings 34a and 34b axially away from each other onto the shaft 23 having a straight shape. Further, the valve seat 19 of the expansion valve 5a includes the tapered portion 19a which forms a seating surface where the valve element 20 is seated, a valve hole 19b which forms an annular space between the same and the tapered portion 20a of the valve element 20, and a guide-holding portion which has an inner diameter smaller than that of the valve hole 19b, and has an inner wall surface forming a sliding surface along which the guides of the valve element 20 slide.

Here, the inner diameter of a cylinder 18a of the body 18 for holding the rings 34a and 34b of the shaft 23 in a manner movable in the valve opening and closing directions is set to be approximately equal to the diameter of a circle forming a boundary between the tapered portion 19a of the valve seat 19 and an end face thereof toward the outlet port 17, and the outer diameter of the rings 34a and 34b on the shaft 23 is set to be approximately equal to the diameter of a circle forming a boundary between the tapered portion 19a and the valve hole 19b of the valve seat 19. Thus, the effective pressure-receiving area of the valve element 20 for receiving high pressure in the valve-opening direction, and the effective pressure-receiving area of the ring 34a (O ring 24) on the shaft 23 for receiving high pressure in the valve-closing direction can be made substantially equal to each other. This enables even the power element 25 which operates with a small power and is made compact in size so as to be accommodated in the casing 7 to accurately control the valve element 20 without being adversely affected by the high pressure.

Further, as shown in FIG. 6B, in the present embodiment, four guides 20b integrally formed with the valve element 20 are circumferentially arranged for guiding the valve element 20 in the valve opening and closing directions while positioning the valve element 20 in the center of the guide-holding portion of the valve seat 19.

FIG. 7 is a view of a differential pressure valve according to a third embodiment of the present embodiment. It should be noted that component elements in FIG. 7 identical or similar to those shown in FIG. 2 are designated by identical reference numerals.

In the third embodiment, there is modified the construction of the differential pressure valve 8 for delivering moist refrigerant at the outlet of the expansion valve 5 to the low-pressure return pipe 4b of the internal heat exchanger 4 by bypassing the evaporator 6. More specifically, in this differential pressure valve 8, a hollow cylindrical portion 35 is connected to a position away from the power element 25 but close to the inlet of the low-pressure return pipe 4b, that is, the outside of the body 18 of the expansion valve 5 in the vicinity of a position where the adjustment screw 22 is screwed, and an opening 36 is formed in the body 18 located at a position eccentric from the center line of the hollow cylindrical portion 35. A portion of the body 18 located on the center line of the hollow cylindrical portion 35 is formed with a valve seat 37 having a flat surface, and a hollow cylindrical valve element 38 is disposed in a manner movable to and away from the valve seat 37. The valve element 38 is supported by a central portion of a diaphragm 39 disposed in a manner partitioning the interior of the hollow cylindrical portion 35, and is urged by a spring 40 in the direction in which the valve element 38 is seated on the valve seat 37. Further, an orifice 41 for limiting the flow rate of refrigerant is formed within the hollow cylindrical valve element 38.

According to the differential pressure valve 8 configured as above, the differential pressure between the pressure at the refrigerant inlet 11 of the evaporator 6 and the pressure at the refrigerant outlet 12 of the same is sensed by the diaphragm 39 having a large pressure-receiving area. As a result, even with the evaporator 6 which is small in pressure loss and hence generates only a small differential pressure, the diaphragm 39 having a large pressure-receiving area senses the small differential pressure, whereby it is possible to obtain a sufficient actuating force to open and close the valve element 38.

When the automotive air conditioner is not in operation, or when it is operating with low refrigeration load, the valve element 38 is seated on the valve seat 37 by the urging force of the spring 40 in the valve-closing direction to close the differential valve 8. When the automotive air conditioner is operating with high refrigeration load, refrigerant flows through the evaporator 6 at a large flow rate, and hence the differential pressure between the pressure at the refrigerant inlet 11 and the pressure at the refrigerant outlet 12 is increased, and when the differential pressure becomes larger than a predetermined value, the differential pressure valve 8 is opened. As a consequence, low-temperature moist refrigerant having been just throttled and expanded flows via the hollow cylindrical valve element 38 to flow into the low-pressure return pipe 4b of the internal heat exchanger 4, and is mixed with refrigerant from the evaporator 6. At this time, the flow rate of the refrigerant is limited by the orifice 41 formed in the valve element 38. The moist refrigerant is completely evaporated by the internal heat exchanger 4, and is then sucked by the compressor 1. Since the temperature of the refrigerant becomes lower during evaporation thereof, the refrigerant from the evaporator 6 is cooled, whereby the temperature of refrigerant compressed by the compressor 1 and discharged is prevented from becoming too high, to prevent thermal deterioration of lubricating oil.

FIG. 8A is a partial perspective view of an end of an example of the internal heat exchanger. FIG. 8B is a partial cross-sectional perspective view of an example of the high-pressure forward pipe.

The internal heat exchanger 4 is formed by inserting the high-pressure forward pipe 4a into the low-pressure return pipe 4b. The high-pressure forward pipe 4a has a plurality of baffles 4c radially formed on the outer periphery thereof, and a plurality of protrusions 4d radially formed on inner periphery thereof. The high-pressure forward pipe 4a configured as above is formed by working on a pipe material having the baffles 4c and the protrusions 4d, which is formed by drawing, such that the outer edges of the baffles 4c are bent into wavy shapes along the direction of the length thereof. Further, the foremost end of the high-pressure forward pipe 4a is subjected to rib processing for disposing the O ring 30 after eliminating the protrusions 4d within the foremost end. The rib processing is similarly performed on the foremost end of the low-pressure return pipe 4b so as to dispose the O ring 32.

By arranging the baffles 4c between the high-pressure forward pipe 4a and the low-pressure return pipe 4b, the low-pressure return pipe 4b and the high-pressure forward pipe 4a is held in the coaxial state, and by bending the baffles 4c into the form of a wave, contact areas between refrigerant flowing through the low-pressure return pipe 4b and the baffles 4c are increased to enhance heat transfer efficiency from high-temperature refrigerant flowing through the high-pressure forward pipe 4a to low-temperature refrigerant flowing through the low-pressure return pipe 4b.

The automotive air conditioner according to the present invention is configured such that the evaporator, the expansion valve, and the pipe joint are connected by the internal heat exchanger, whereby improvement of the efficiency of the refrigeration cycle by the installation of the internal heat exchanger is made possible, while dispensing with a special space for disposing the internal heat exchanger. Further, although in the refrigeration cycle having the internal heat exchanger, the temperature of refrigerant discharged from the compressor during high load tends to become too high, refrigerant having been just expanded is mixed in refrigerant returning from the evaporator to the compressor to thereby lower the temperature of the returning refrigerant, which makes it possible to lower the temperature of the discharged refrigerant, thereby making it possible to prevent thermal deterioration of lubricating oil for the compressor.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents.

Claims

1. An automotive air conditioner wherein a thermostatic expansion valve having an inlet to which is connected a pipe for receiving high-pressure refrigerant and an outlet to which is connected a refrigerant inlet pipe of an evaporator is accommodated in a casing directly connected to a refrigerant outlet of said evaporator,

wherein an internal heat exchanger for performing heat exchange between the high-pressure refrigerant and low-pressure refrigerant returning from said casing to a compressor is connected to said casing, and

wherein a pipe joint for connecting a high-pressure pipe extending from a receiver and a low-pressure pipe extending to said compressor independently of each other is connected to an end of said internal heat exchanger on the side opposite to the side where the casing is connected.

2. The automotive air conditioner according to claim 1, wherein said internal heat exchanger is formed by a double pipe in which a low-pressure return pipe for allowing low-pressure refrigerant to flow to said compressor is coaxially disposed outside a high-pressure forward pipe for allowing the high-pressure refrigerant to flow therethrough.

3. The automotive air conditioner according to claim 2, wherein in the double pipe, heat transfer baffles are arranged between the high-pressure forward pipe and the low-pressure return pipe, whereby the state of the low-pressure return pipe and the high-pressure forward pipe being coaxial with each other is held.

4. The automotive air conditioner according to claim 1, wherein said expansion valve has a back pressure cancelling structure in which an area for a valve element to receive pressure of the high-pressure refrigerant introduced into the inlet of said expansion valve in a valve-opening direction and an area for a shaft operating in unison with the valve element to receive the pressure of the high-pressure refrigerant in a valve-closing direction are made substantially equal to each other, the valve element being provided with a guide for guiding the valve element such that the valve element moves along a valve hole during opening and closing operations of said expansion valve.

5. The automotive air conditioner according to claim 1, wherein said expansion valve is provided with a differential pressure valve for causing refrigerant having been just expanded to bypass to the low-pressure return pipe of said internal heat exchanger when a differential pressure between pressure at the refrigerant inlet of said evaporator and pressure at the refrigerant outlet of said evaporator exceeds a predetermined value.

6. The automotive air conditioner according to claim 5, wherein said differential pressure valve includes a diaphragm for sensing the differential pressure, a hollow cylindrical valve element held in a center of said diaphragm, a spring for urging the hollow cylindrical valve element such that the hollow cylindrical valve element is seated on a valve seat having a flat surface, and an orifice disposed in a refrigerant passage within the hollow cylindrical valve element.

7. The automotive air conditioner according to claim 2, wherein the pipe joint has one end face formed with a first connecting hole in which the low-pressure return pipe of the double pipe is fitted, and a second connecting hole which is coaxially disposed in the first connecting hole, for having the high-pressure forward pipe fitted therein, and another end face having a third connecting hole and a fourth connecting hole arranged in parallel for communication with the first connecting hole and the second connecting hole, respectively.

8. The automotive air conditioner according to claim 1, wherein the pipe joint is disposed in a firewall separating an engine room from a vehicle compartment.