EXPANSION VALVE

Abstract

An expansion valve is configured such that a shaft, a first valve, a second valve, a compression coil spring, and an adjustment screw are coaxially arranged within a body exactly below a power element, and the first valve and the second valve control the flow rate in an interlocked manner. A second valve seat of the second valve is press-fitted into the body, and an amount of press-fitting of the second valve seat into the body is adjusted such that when the first valve is in a closed state in which a first valve element is seated on a first valve seat, the second valve is in a closed state in which a second valve element is seated on the second valve seat.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-055616, filed on Mar. 14, 2011, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to an expansion valve.

BACKGROUND

In an automotive air conditioning system, a refrigeration cycle is formed by piping between a compressor that compresses refrigerant, a condenser that condenses refrigerant, a receiver that separates gas-liquid mixture refrigerant, an expansion valve that adiabatically expands refrigerant, and an evaporator that evaporates refrigerant, into a loop. The expansion valve that expands refrigerant is generally implemented e.g. by a thermostatic expansion valve configured to control a flow rate of refrigerant to be supplied to the evaporator according to the temperature and pressure of refrigerant at an outlet of the evaporator.

The evaporator that performs heat exchange between refrigerant and air in a vehicle compartment is installed in the vehicle compartment, and hence the evaporator is demanded to be compact. For this reason, an evaporator has been generally used which is formed by disposing two heat exchangers each having a reduced thickness in an air passing direction in a laminated manner and allows refrigerant to serially flow through these heat exchangers.

In the evaporator described above, respective passages of the heat exchangers through which refrigerant flows are narrowed due to the reduced thickness of each heat exchanger, and what is more, the total length of the passages is made longer due to serial connection of the passages of the heat exchanges. For this reason, in the evaporator having the above-described arrangement, a pressure loss generated in the passages through which refrigerant flows increases, which lowers the efficiency of the refrigeration cycle.

To solve this problem, there has been proposed an evaporator configured such that two heat exchangers are independently provided, and refrigerant is supplied in parallel to the heat exchangers (see e.g. Japanese Laid-Open Patent Publication No. 2010-38455 (FIGS. 5 and 6) and International Publication Pamphlet NO. WO2010/131918 (FIG. 3)). According to this evaporator, a pressure loss generated when refrigerant flows through the heat exchangers is reduced, and a net loss is reduced which is caused when the whole refrigeration cycle is considered, whereby it is possible to improve cooling power.

An expansion valve used in such an evaporator described above has also been proposed in Japanese Laid-Open Patent Publication No. 2010-38455 and International Publication Pamphlet NO. WO2010/131918. This expansion valve includes two valves each capable of adiabatically expanding refrigerant independently of each other, and is configured to control the two valves in an interlocked manner according to temperature and pressure of refrigerant joined after flowing out of the heat exchangers, which are detected at an outlet of the evaporator.

However, both of the configurations of the disclosed expansion valves are theoretical ones, and are not specifically illustrated. If refrigerant leakage flow through the expansion valve occurs when the automotive air conditioning system is stopped, this generates a considerably large noise of flow of the refrigerant, which is perceived as a untoward noise by the sense of hearing of occupants, and hence it is necessary to close the expansion valve. The expansion valve having two valves also has the same problem, and in this case, it is important to simultaneously close the two valves.

SUMMARY

According to an aspect of the invention, there is provided an expansion valve including a first valve having a first valve element and a first valve seat, a second valve having a second valve element and a second valve seat, and a power element configured to control lifts of the first valve element and the second valve element in an interlocked manner, wherein the second valve seat of the second valve is a movable valve seat which is adjustable in a direction toward or away from the second valve element.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a refrigeration cycle to which an expansion valve according to embodiments is applied;

FIG. 2 is a central vertical cross-sectional view of an expansion valve according to a first embodiment;

FIG. 3 is a central vertical cross-sectional view of the expansion valve according to the first embodiment, as viewed at right angles to a plane of FIG. 2; and

FIG. 4 is a central vertical cross-sectional view of an expansion valve according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be explained below with reference to the accompanying drawings, wherein like reference numerals refer to like elements throughout.

FIG. 1 illustrates a refrigeration cycle to which an expansion valve according to the present embodiments is applied.

A refrigeration cycle of an automotive air conditioning system comprises a compressor 1, a condenser 2, an expansion valve 3, and an evaporator 4, which are connected by piping between them into a loop. The compressor 1 compresses refrigerant circulating through the refrigeration cycle and delivers the compressed refrigerant to the condenser 2. The condenser 2 is configured such that a cooling fan 5 causes outside air to pass through the condenser 2, and condenses high-temperature, high-pressure refrigerant compressed by the compressor 1 by performing heat exchange with outside air. A receiver (not illustrated) that temporarily stores the condensed refrigerant is disposed at an outlet of the condenser 2, and liquid refrigerant obtained by gas/liquid separation performed in the receiver is supplied to the expansion valve 3.

The expansion valve 3 is a thermostatic expansion valve including a first valve 3a and a second valve 3b, which adiabatically expands liquid refrigerant. The evaporator 4 includes a first heat exchanger 4a and a second heat exchanger 4b, which are disposed in a laminated manner within an air blowing passage on a downstream side of a fan 6. Adiabatically expanded vapor refrigerant is supplied from the first valve 3a of the expansion valve 3 to the first heat exchanger 4a disposed on a side toward the fan 6, and adiabatically expanded vapor refrigerant is supplied from the second valve 3b to the second heat exchanger 4b disposed on an air outlet port side. The refrigerant is evaporated by heat exchange with air blown by the fan 6. Refrigerant flowing out of the first heat exchanger 4a and refrigerant flowing out of the second heat exchanger 4b are joined and the joined refrigerant is returned to the compressor 1 through the expansion valve 3. When the refrigerant returning from the evaporator 4 passes through the expansion valve 3, the expansion valve 3 monitors the temperature and pressure of the refrigerant, i.e. a degree of superheat of the refrigerant at the outlet of the evaporator, and controls the flow rate of refrigerant supplied from the first valve 3a and the second valve 3b according to the degree of superheat.

In the evaporator 4, the first heat exchanger 4a disposed on the side toward the fan 6 performs heat exchange with higher-temperature air, and the second heat exchanger 4b disposed on the air outlet port side performs heat exchange with air cooled by the first heat exchanger 4a. Therefore, the flow rate of refrigerant supplied from the first valve 3a to the first heat exchanger 4a is set to be higher than the flow rate of refrigerant supplied from the second valve 3b to the second heat exchanger 4b, and in the present embodiment, the flow rate ratio between the first valve 3a and the second valve 3b is set to 2:1.

FIG. 2 is a central vertical cross-sectional view of an expansion valve according to a first embodiment, and FIG. 3 is a central vertical cross-sectional view of the expansion valve according to the first embodiment, as viewed at right angles to a plane of FIG. 2.

The expansion valve according to the first embodiment includes a rectangular parallelepiped body 11 having a high pressure inlet port 12 formed in a lower portion, as viewed in FIG. 3, of one side surface thereof (right side surface, as viewed in FIG. 3). High-pressure liquid refrigerant is supplied to the high pressure inlet port 12. The body 11 has a first low-pressure outlet port formed in a central portion of a side surface (left side surface, as viewed in FIG. 2) adjacent to the one side surface formed with the high pressure inlet port 12. The first low-pressure outlet port 13 is connected to the first heat exchanger 4a disposed on the side toward the fan 6. Further, the body 11 has a second low-pressure outlet port 14 formed in a lower portion than the central portion where the first low-pressure outlet port 13 is formed, as viewed in FIG. 2. The second low-pressure outlet port 14 is connected to the second heat exchanger 4b disposed on the air outlet port side. Also, the body 11 has a returning refrigerant inlet port 15 formed in an upper portion than the central portion where the first low-pressure outlet port 13 is formed, as viewed in FIG. 2. Further, the body 11 has a returning refrigerant outlet port 16 formed in an upper portion of the one side surface formed with the high pressure inlet port 12 as viewed in FIG. 3.

A power element 17 that senses a degree of superheat of refrigerant returning from the evaporator 4 is screwed into an upper end surface of the body 11. A shaft 18, the first valve 3a, the second valve 3b, a compression coil spring 19, and an adjustment screw 20 are coaxially arranged within the body 11 exactly below the power element 17. The shaft 18, the first valve 3a, and the second valve 3b are separately disposed such that they operate independently of each other, and are configured to be capable of smoothly operating in an axial direction even when they are disposed with the center of the axis slightly displaced.

The first valve 3a includes a first valve element 21 and a first valve seat 22 formed in the body 11, and the first valve seat 22 is formed with a first valve hole 23 communicating with the first low-pressure outlet port 13. The second valve 3b includes a second valve element 24 and a second valve seat 25 press-fitted into the body 11, and the second valve seat 25 is formed with a second valve hole 26 having a smaller port diameter than that of the first valve hole 23.

The first valve element 21 of the first valve 3a is disposed in a valve chamber 27 communicating with the high pressure inlet port 12, in a manner movable to and away from the first valve seat 22. For this purpose, the first valve element 21 is integrally formed with two guides 28 which slide along an inner wall of the valve chamber 27, on respective sides toward the first valve seat 22 and the second valve 3b.

The guides 28 are each formed with a plurality of communication passages 29 for guiding liquid refrigerant introduced into the valve chamber 27 toward the first valve seat 22 and toward the second valve 3b. The communication passages 29 may be three arc-shaped openings formed through each guide 28 in a concentric arrangement at equally-spaced intervals. The guides 28 on the respective sides toward the first valve seat 22 and the second valve 3b have different axial lengths such that when liquid refrigerant flows through the communication passages 29, respective forces are cancelled out by which the first valve element 21 is pulled toward the first valve seat 22 and the second valve 3b, due to viscosity of refrigerant. In the present embodiment, the distribution ratio between the flow rate of refrigerant supplied from the first valve 3a and the flow rate of refrigerant supplied from the second valve 3b is set to 2:1, and hence a ratio between the axial length of the guide 28 toward the first valve seat 22 and that of the guide 28 toward the second valve 3b is set to 1:2.

Further, the first valve 3a has a structure in which the first valve element 21 is disposed on a upstream side of the first valve seat 22, whereby high-pressure liquid refrigerant acts on the first valve element 21 in a valve-closing direction. With this structure, the first valve 3a has high-pressure-dependent characteristics that although there is a proportional relationship between pressure of liquid refrigerant on a primary side and pressure of vapor refrigerant of a secondary side when the first valve 3a is fully open, when the valve opening becomes smaller than a predetermined opening, as the pressure on primary side increases, the pressure on the secondary side decreases.

The second valve 3b is disposed in a space formed within the body 11, which communicates between the valve chamber 27 and the second low-pressure outlet port 14 and is formed coaxially with the valve chamber 27. The second valve seat 25 is fixed to the body 11 by press fitting, and the second valve element 24 is disposed in a manner movable to and away from the second valve seat 25. The second valve element 24 has an axially extending portion 30 integrally formed thereon such that the axially extending portion 30 extends through the second valve hole 26 of the second valve seat 25 toward the first valve 3a. An end face of the axially extending portion 30 is constantly brought into contact with the first valve element 21 by an urging force of the compression coil spring 19.

Further, the second valve 3b has a structure in which the second valve element 24 is disposed on a downstream side of the second valve seat 25, and high-pressure liquid refrigerant acts on the second valve element 24 in a valve-opening direction. Therefore, the present expansion valve is configured to have high-pressure-dependent characteristics that the expansion valve is operated in the valve-closing direction according to a balance between the port diameter of the first valve hole 23 and the port diameter of the second valve hole 26.

The compression coil spring 19 is received by the adjustment screw 20 screwed into the body 11. Load of the compression coil spring 19 is adjusted by adjusting a screwing amount of the adjustment screw 20. This adjustment corresponds to the setting of the superheat degree to be controlled by the expansion valve. A portion where the adjustment screw 20 is screwed into the body 11 is hermetically sealed by an O ring 31.

The power element 17 is screwed into a fitting hole formed in an upper surface of the body 11, as viewed in FIGS. 2 and 3. The fitting hole for fitting the power element 17 communicates with a refrigerant returning passage 32 formed between the returning refrigerant inlet port 15 and the returning refrigerant outlet port 16, and enables refrigerant flowing through the refrigerant returning passage 32 to be introduced into the power element 17.

The power element 17 is formed by sandwiching a diaphragm 33 between an upper housing 34 and a lower housing 35, and welding together the outer peripheries of these. A hermetically sealed space enclosed by the diaphragm 33 and the upper housing 34 is filled with gas having characteristics similar to refrigerant, and forms a temperature sensing chamber. The lower housing 35 is provided with a disk 36 which transmits the displacement of the diaphragm 33 to the first valve 3a and the second valve 3b. The disk 36 is fitted on an upper end of the shaft 18 held by a holder 37, and has its center positioned by the shaft 18 within the lower housing 35.

The holder 37 has an upper portion disposed in the fitting hole of the power element 17, and accommodates a compression coil spring 38 in the upper portion thereof so as to apply a lateral load to the shaft 18, as illustrated in FIG. 3. The shaft 18 is limited in axial motion by having the lateral load applied thereto, and hence even when liquid refrigerant introduced into the high pressure inlet port 12 fluctuates in pressure, the first valve element 21 is prevented from vibrating in the axial direction to generate untoward noise. Further, the holder 37 hangs down through the refrigerant returning passage 32, and a lower end of the holder 37 retains an O ring 39 disposed around the shaft 18 between the first low-pressure outlet port 13 and the refrigerant returning passage 32. The O ring 39 blocks refrigerant from leaking from the first low-pressure outlet port 13 into the refrigerant returning passage 32 without flowing toward the first heat exchanger 4a of the evaporator 4.

The power element 17 is covered with a cap 40, and is thereby thermally insulated from the environment so as not to be affected by the temperature of the environment in which the expansion valve is disposed. Further, a throttle passage member 41 having an annular shape is fitted in the first low-pressure outlet port 13. The throttle passage member 41 has a through hole formed through a central portion thereof, which has a predetermined opening area, and throttles the flow of refrigerant flowing from the first low-pressure outlet port 13 to thereby prevent bubbles from being generated and reduce noise generated when refrigerant passes through the expansion valve.

According to the expansion valve constructed as above, during the stoppage or the minimum capacity operation of the compressor 1, the pressure in the refrigerant returning passage 32 is high, and in the power element 17 which has sensed the high pressure, the diaphragm 33 is displaced toward the temperature sensing chamber. As a result, since the first valve element 21 and the second valve element 24 are urged by the compression coil spring 19 in the valve-closing direction, the first valve 3a and the second valve 3b are in a closed state.

When the compressor 1 starts compression of refrigerant, the pressure in the refrigerant returning passage 32 decreases, whereby the diaphragm 33 of the power element 17 is displaced toward the first valve 3a and the second valve 3b, and high-pressure refrigerant is introduced into the high pressure inlet port 12. Before long, the first valve 3a and the second valve 3b are opened by the power element 17, whereby the liquid refrigerant condensed by the condenser 2 is introduced into the high pressure inlet port 12. The liquid refrigerant introduced into the valve chamber 27 is adiabatically expanded by the first valve 3a to form low-temperature, low-pressure vapor refrigerant, and is delivered from the first low-pressure outlet port 13 to the first heat exchanger 4a of the evaporator 4. Further, the liquid refrigerant in the valve chamber 27 is adiabatically expanded by the second valve 3b to form low-temperature, low-pressure vapor refrigerant, and is delivered from the second low-pressure outlet port 14 to the second heat exchanger 4b of the evaporator 4.

In the evaporator 4, the vapor refrigerant introduced into the first heat exchanger 4a and the vapor refrigerant introduced into the second heat exchanger 4b are evaporated by heat exchange with air blown by the fan 6, and then are joined together to be returned to the returning refrigerant inlet port 15. The air having passed through the evaporator 4 is dehumidified and cooled, and is then blown out into the vehicle compartment after being adjusted to appropriate temperature.

The refrigerant introduced into the returning refrigerant inlet port 15 flows through the refrigerant returning passage 32, and is then returned from the returning refrigerant outlet port 16 to the compressor 1. When the refrigerant returning from the evaporator 4 flows through the refrigerant returning passage 32, the degree of superheat of the refrigerant is sensed by the power element 17, and valve lifts of the first valve 3a and the second valve 3b are controlled according to the degree of superheat. This controls the flow rate of refrigerant flowing through the first valve 3a and that of refrigerant flowing through the second valve 3b, whereby refrigerant is supplied to the first heat exchanger 4a and the second heat exchanger 4b of the evaporator 4 at a predetermined distribution ratio. The first valve 3a and the second valve 3b are thus feedback-controlled according to the degree of superheat of the refrigerant detected at the outlet of the evaporator 4, and hence the present expansion valve controls the flow rate of vapor refrigerant to be delivered to the evaporator 4 such that the refrigerant at the outlet of the evaporator maintains the degree of superheat set by the compression coil spring 19.

FIG. 4 is a central vertical cross-sectional view of an expansion valve according to a second embodiment. Component elements illustrated in FIG. 4 identical or equivalent to those illustrated in FIG. 2 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion valve according to the second embodiment includes the shaft 18, the first valve 3a, the compression coil spring 19, and the adjustment screw 20, coaxially arranged within the body 11 exactly below the power element 17. The second valve 3b is arranged such that the valve is lifted in a direction orthogonal to an axial direction of the shaft 18, and is screwed into an inner wall of a refrigerant passage 42 formed in a manner extending from the second low-pressure outlet port 14 across the shaft 18. The shaft 18 has a tapered surface 43 having a frustoconical shape formed on an intermediate portion thereof, and the second valve 3b is in constant contact with the tapered surface 43. The O ring 39 fitted around the shaft 18 prevents the high-pressure refrigerant introduced into the high pressure inlet port 12 from leaking into the refrigerant returning passage 32 through a clearance between the shaft 18 and the body 11.

The first valve 3a includes the first valve element 21, which is ball-shaped, and the first valve element 21 is urged by the compression coil spring 19 disposed between a valve element-supporting portion 44 which receives the first valve element 21 and the adjustment screw 20, in the valve-closing direction. With this arrangement, the first valve element 21 is brought into contact with a front end of the shaft 18 extended through the first valve hole 23 of the first valve seat 22. Since the first valve element 21 is ball-shaped, it is preferable to spot-weld the first valve element 21 to the front end of the shaft 18, so as to improve the assembly properties. The valve chamber 27 which accommodates the first valve element 21 communicates with the first low-pressure outlet port 13, and the throttle passage member 41 is fitted in an intermediate portion of the passage communicating between the valve chamber 27 and the first low-pressure outlet port 13.

Further, the first valve 3a has a structure in which that the first valve element 21 is disposed on the 12 downstream side of the first valve seat 22 and is operated by high-pressure liquid refrigerant in the valve-opening direction, whereas the O ring 39 sealing the shaft 18 receives high pressure refrigerant through the clearance between the shaft 18 and the body 11 to thereby operate the shaft 18 in the valve-closing direction. Therefore, the expansion valve is configured to have high-pressure-dependent characteristics that the expansion valve is operated in the valve-closing direction according to a balance between the port diameter of the first valve hole 23 and the sealing diameter of the O ring 39.

The second valve 3b includes a screwing portion 25a by which the second valve seat 25 is screwed into the inner wall of the refrigerant passage 42, and a valve shaft-supporting portion 25b which supports a valve shaft 24a of the second valve element 24, and the valve shaft-supporting portion 25b has a groove communicating with the second valve hole 26, formed in a supporting hole within which the valve shaft 24a is supported. A spring receiver is fitted on the valve shaft 24a, and a compression coil spring 45 is disposed between the spring receiver 50 and the screwing portion 25a of the second valve seat 25, for urging the second valve element 24 in the valve-closing direction, and constantly bringing the front end of the valve shaft 24a into contact with the tapered surface 43 of the shaft 18. With this arrangement, the second valve seat 25 forms a movable valve seat adjustable in a direction toward or away from the second valve element 24 having the valve shaft 24a in contact with the tapered surface 43. This makes it possible to match timing for closing the first valve 3a with timing for closing the second valve 3b by adjusting a screwing amount of the second valve seat 25. A downstream side of the second valve 3b communicates with the second low-pressure outlet port 14, and a throttle passage member 46 is fitted in an intermediate portion of a passage communicating between the second valve 3b and the second low-pressure outlet port 14. Similarly to the throttle passage member 41 of the first valve 3a, the throttle passage member 46 throttles the flow of refrigerant flowing from the second low-pressure outlet port 14 to thereby prevent bubbles from being generated, and reduce noise generated when refrigerant passes through the expansion valve.

According to the expansion valve configured as above, when the first valve 3a is in a closed state, the shaft 18 is at rest in a position in which the valve shaft 24a of the second valve element 24 seated on the second valve seat 25 is just in contact with the tapered surface 43.

When the power element 17 is driven in a direction of lifting the first valve element 21 of the first valve 3a, the tapered surface 43 of the shaft 18 is moved toward the first valve 3a. As a result, the direction of lifting the first valve element 21 is converted into a direction orthogonal thereto by the tapered surface 43, which causes the second valve element 24 to be lifted in a manner interlocked with the lift of the first valve element 21. Therefore, the operation of the present expansion valve is the same as the above-described operation of the expansion valve according to the first embodiment, and hence detailed description of the operation is omitted.

Also in the present expansion valve according to the second embodiment, similarly to the expansion valve according to the first embodiment, the flow rate of vapor refrigerant to be fed to the evaporator 4 is controlled such that the refrigerant at the outlet of the evaporator maintains the degree of superheat set by the compression coil spring 19. Further, the first valve 3a and the second valve 3b operating in an interlocked manner are simultaneously closed, and refrigerant does not leak during valve closing, and hence it is possible to completely prevent flowing noise of refrigerant from being generated by the leakage of refrigerant.

The expansion valve configured as above is capable of simultaneously closing the first valve and the second valve operating in an interlocked manner, and hence leakage of refrigerant during valve closing does not occur, which is advantageous in positively preventing noise caused by the leakage of refrigerant.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

Claims

1. An expansion valve comprising a first valve having a first valve element and a first valve seat, a second valve having a second valve element and a second valve seat, and a power element configured to control lifts of the first valve element and the second valve element in an interlocked manner,

wherein the second valve seat of the second valve is a movable valve seat which is adjustable in a direction toward or away from the second valve element.

2. The expansion valve according to claim 1, wherein the power element, the first valve, the second valve, and a spring which urges the first valve element and the second valve element toward the power element are coaxially arranged,

wherein a high pressure inlet port for introducing high-pressure liquid refrigerant is communicated with a flow passage between the first valve and the second valve,

wherein a first low-pressure outlet port for delivering low-pressure vapor refrigerant is communicated with a downstream side of the first valve,

wherein a second low-pressure outlet port for delivering low-pressure vapor refrigerant is communicated with a downstream side of the second valve,

wherein the second valve seat is press-fitted into a body forming the first valve seat, and

wherein an amount of press-fitting of the second valve seat is adjusted such that the first valve and the second valve are simultaneously closed.

3. The expansion valve according to claim 2, wherein the first valve element is axially movably disposed in a valve chamber into which high-pressure liquid refrigerant is introduced, such that a front end of a shaft for transmitting a driving force of the power element is in contact therewith through a first valve hole of the first valve seat, and that an axially extending portion of the second valve element is contact therewith through a second valve hole of the second valve seat.

4. The expansion valve according to claim 3, wherein guides which slide along an inner wall of the valve chamber are integrally formed on respective portions of the first valve element toward the first valve seat and the second valve seat, and the guides have respective communication passages formed therethrough for introducing liquid refrigerant into the first valve hole and the second valve hole.

5. The expansion valve according to claim 4, wherein the first valve element is configured such that a ratio between an axial length of a guide toward the first valve seat and an axial length of a guide toward the second valve seat is made equal to a ratio between a flow rate of the second valve and a flow rate of the first valve.

6. The expansion valve according to claim 1, wherein there are provided high-pressure-dependent characteristics that the expansion valve is operated in a valve-closing direction according to a balance between a port diameter of the first valve through which high-pressure liquid refrigerant acts in the valve-closing direction, and a port diameter of the second valve through which high-pressure liquid refrigerant acts in a valve-opening direction.

7. The expansion valve according to claim 1, wherein a shaft which transmits a driving force of the power element to the first valve, the first valve, and a first spring which urges the first valve element toward the shaft are coaxially arranged,

wherein the second valve is disposed in a direction orthogonal to the axial direction of the shaft,

wherein a valve shaft of the second valve element is brought into contact with a tapered surface having a frustoconical shape and formed on an intermediate portion of the shaft, by an urging force of a second spring, to thereby cause a lift of the second valve element to be interlocked with a lift of the first valve element,

wherein a high pressure inlet port for introducing high-pressure liquid refrigerant is communicated with a flow passage between the first valve and the second valve,

wherein a first low-pressure outlet port for delivering low-pressure vapor refrigerant is communicated with a downstream side of the first valve,

wherein a second low-pressure outlet port for delivering low-pressure vapor refrigerant is communicated with a downstream side of the second valve,

wherein the second valve seat is screwed into a body forming the first valve seat, and

wherein a screwing amount of the second valve seat is adjusted such that the first valve and the second valve are simultaneously closed.

8. The expansion valve according to claim 7, wherein the first valve element is brought into contact with or is welded to a front end of the shaft extended through a first valve hole of the first valve seat.

9. The expansion valve according to claim 7, wherein there are provided high-pressure-dependent characteristics that the expansion valve is operated in the valve-closing direction according to a balance between a port diameter of the first valve through which high-pressure liquid refrigerant acts in the valve-opening direction, and a sealing diameter of an O ring disposed around the shaft at a location where the shaft is supported by the body, via which high-pressure liquid refrigerant acts on the shaft in the valve-closing direction.

10. The expansion valve according to claim 1, further comprising a throttle passage member disposed on a downstream side of at least one of the first valve and the second valve, for preventing bubbles from being generated in refrigerant having passed through the first valve and the second valve.