# Patent

## Title
Double-headed piston type swash plate compressor

## Abstract

A double-headed piston type swash plate compressor includes a swash plate, a double-headed piston, a control pressure chamber, a discharge pressure region, a suction pressure region, a supplying passage, which extends from the discharge pressure region to the control pressure chamber, a narrowing portion, which narrows an opening degree of the supplying passage, and a displacement control valve. The displacement control valve controls a pressure in the control pressure chamber. The displacement control valve includes a driving force transmission rod, a valve chamber, a guide wall, and a back pressure chamber. The back pressure chamber is in communication with the valve chamber through a clearance between the guide wall and the driving force transmission rod. The narrowing portion has a passage cross-sectional area that is larger than a passage cross-sectional area of the clearance.

## Background
BACKGROUND OF THE INVENTION
The present invention relates to a double-headed piston type swash plate compressor including a double-headed piston that engages with a swash plate and reciprocates with a stroke according to an inclination angle of the swash plate.
Japanese Laid-open Patent Publication H1-190972 teaches one example of a double-headed piston type swash plate compressor having a crank chamber. The crank chamber in this publication does not function as a control pressure chamber for varying an inclination angle of a swash plate. This differs from a variable displacement type swash plate compressor including a single-headed piston in which a crank chamber functions as a control pressure chamber. For this reason, the double-headed piston type swash plate compressor has a movable body that is connected with the swash plate to vary the inclination angle of the swash plate. The movable body moves in an axial direction of a rotation shaft when a control pressure chamber formed in a housing is supplied with a control gas to change a pressure inside the control pressure chamber. The movement of the movable body in the axial direction of the rotation shaft changes the inclination angle of the swash plate. The double-headed piston type swash plate compressor further includes a displacement control valve for controlling a pressure in the control pressure chamber.
The control pressure chamber defines a smaller space than the crank chamber. Accordingly, the response characteristic of the displacement control valve for controlling the pressure in the control pressure chamber is likely to affect the variability of the inclination angle of the swash plate. It is desirable that the response characteristic of the displacement control valve be improved.
SUMMARY OF THE INVENTION
The objective of the present invention is to provide a double-headed piston type swash plate compressor that improves the response characteristic of a displacement control valve.
To achieve the foregoing objective, a double-headed piston type swash plate compressor according to one aspect of the present invention includes a housing, a rotation shaft, a swash plate, a crank chamber, a double-headed piston, a movable body, a control pressure chamber, a discharge pressure region, a suction pressure region, a supplying passage, a narrowing portion, an exhaust passage, and a displacement control valve. The swash plate is rotated by a driving force of the rotation shaft. The swash plate is configured to vary an inclination angle with respect to the rotation shaft. The crank chamber is formed in the housing and accommodates the swash plate. The double-headed piston engages with the swash plate. The double-headed piston reciprocates with a stroke according to the inclination angle of the swash plate. The movable body is connected with the swash plate to vary the inclination angle of the swash plate. The control pressure chamber is arranged in the housing and defined by the movable body. The control pressure chamber is configured to move the movable body in an axial direction of the rotation shaft when the control pressure chamber is supplied with a control gas to change a pressure inside the control pressure chamber. The supplying passage extends from the discharge pressure region to the control pressure chamber. The narrowing portion narrows an opening degree of the supplying passage. The exhaust passage extends from the control pressure chamber to the suction pressure region. The displacement control valve controls a pressure in the control pressure chamber. The displacement control valve includes an electromagnetic solenoid, a part of the exhaust passage, a driving force transmission rod, a valve chamber, a pressure sensing chamber, a pressure sensing mechanism, a guide wall, a back pressure chamber, and a communication passage. The driving force transmission rod includes a valve body that adjusts an opening degree of the exhaust passage. The driving force transmission rod is driven by the electromagnetic solenoid. The valve chamber accommodates the valve body. The pressure sensing chamber is in communication with the suction pressure region. The pressure sensing mechanism is accommodated in the pressure sensing chamber. The pressure sensing mechanism is configured to expand and contract along a movement direction of the driving force transmission rod in accordance with a pressure in the suction pressure region so as to adjust an opening degree of the valve body. The guide wall guides the driving force transmission rod to move along the movement direction. The back pressure chamber is arranged between the electromagnetic solenoid and the valve chamber. The back pressure chamber is in communication with the valve chamber through a clearance between the guide wall and the driving force transmission rod. The back pressure chamber communicates with the pressure sensing chamber through the communication passage. The narrowing portion has a passage cross-sectional area that is larger than a passage cross-sectional area of the clearance.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:
FIG. 1 is a side cross-sectional view showing a double-headed piston type swash plate compressor according to one embodiment of the present invention;
FIG. 2 is a cross-sectional view of a displacement control valve of FIG. 1 when an inclination angle of a swash plate is at a minimum;
FIG. 3 is a cross-sectional view of a displacement control valve of FIG. 1 when an inclination angle of a swash plate is at a maximum; and
FIG. 4 is a side cross-sectional view showing a double-headed piston type swash plate compressor of FIG. 1 when an inclination angle of a swash plate is at a maximum.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereafter, discussion will be made on one embodiment that embodies the present invention according to FIGS. 1 to 4.
As shown in FIG. 1, a housing 11 of a double-headed piston type swash plate compressor 10 includes a first cylinder block 12 and a second cylinder block 13 connected to each other. The double-headed piston type swash plate compressor 10 further includes a front housing 14, which is connected with the first cylinder block 12 located toward a front (one side) and a rear housing 15, which is connected with the second cylinder block 13 located toward a rear (the other side).
A first valve/port formation body 16 is disposed between the front housing 14 and the first cylinder block 12. A second valve/port formation body 17 is disposed between the rear housing 15 and the second cylinder block 13.
A suction chamber 14a and a discharge chamber 14b are defined between the front housing 14 and the first valve/port formation body 16. The discharge chamber 14b is arranged radially outside the suction chamber 14a. A suction chamber 15a and a discharge chamber 15b are defined between the rear housing 15 and the second valve/port formation body 17. A pressure adjustment chamber 15c is arranged in the rear housing 15. The pressure adjustment chamber 15c is arranged at a central portion of the rear housing 15. The suction chamber 15a is arranged radially outside the pressure adjustment chamber 15c. The discharge chamber 15b is arranged radially outside the suction chamber 15a. The discharge chambers 14b and 15b are in communication with each other through a discharge passage, which is not shown. The discharge passage is connected with an outer refrigerant circuit, which is not shown. The discharge chambers 14b and 15b serve as a discharge pressure region.
The first valve/port formation body 16 is formed with a suction port 16a, which is in communication with the suction chamber 14a and a discharge port 16b, which is in communication with the discharge chamber 14b. The second valve/port formation body 17 is formed with a suction port 17a, which is in communication with the suction chamber 15a and a discharge port 17b, which is in communication with the discharge chamber 15b. A suction valve mechanism, which is not shown, is arranged in each of the suction ports 16a and 17a. A discharge valve mechanism, which is not shown, is arranged in each of the discharge ports 16b and 17b. 
A rotation shaft 21 is supported in the housing 11 to be rotatable. A front end portion of the rotation shaft 21 is inserted into a shaft hole 12h, which extends through the first cylinder block 12. The front end portion of the rotation shaft 21 is a portion of the rotation shaft 21 closer to a first end of the rotation shaft 21 in a direction along which a central axis L extends (i.e., an axial direction of the rotation shaft 21). The front end portion of the rotation shaft 21 is located toward a front side (one side) of the housing 11. A front end of the rotation shaft 21 is arranged inside the front housing 14. A rear end portion of the rotation shaft 21 is inserted into a shaft hole 13h, which extends through the second cylinder block 13. The rear end portion of the rotation shaft 21 is a portion of the rotation shaft 21 closer to a second end of the rotation shaft 21 in the direction along which the central axis L extends (i.e., the axial direction of the rotation shaft 21). The rear end portion of the rotation shaft 21 is located toward a rear side (the other side) of the housing 11. A rear end of the rotation shaft 21 is arranged inside the pressure adjustment chamber 15c. 
The front end portion of the rotation shaft 21 is supported to be rotatable by the first cylinder block 12 through the shaft hole 12h. The rear end portion of the rotation shaft 21 is supported to be rotatable by the second cylinder block 13 through the shaft hole 13h. A shaft seal device 22 of a lip seal type is disposed between the front housing 14 and the rotation shaft 21. The front end of the rotation shaft 21 operably connects with a vehicle engine E, which serves as an external driving source through a driving force transmission mechanism PT. In the present embodiment, the driving force transmission mechanism PT is a clutch-less mechanism (for example, a combination of a belt and a pulley), which is an always transmitting type.
A crank chamber 24 is arranged in the housing 11 and defined by the first cylinder block 12 and the second cylinder block 13. The crank chamber 24 accommodates a swash plate 23, which is rotated by a driving force of the rotation shaft 21 and is inclined with respect to the rotation shaft 21 in the axial direction. The swash plate 23 is formed with an insertion hole 23a into which the rotation shaft 21 is inserted. The rotation shaft 21 is inserted into the insertion hole 23a so that the rotation shaft 21 connects with the swash plate 23.
The first cylinder block 12 is formed with a plurality of first cylinder bores 12a, which are arranged around the rotation shaft 21. FIG. 1 shows one of the first cylinder bores 12a. Each of the first cylinder bores 12a extends through the first cylinder block 12 in the axial direction. Each of the first cylinder bores 12a is in communication with the suction chamber 14a through the suction port 16a and is in communication with the discharge chamber 14b through the discharge port 16b. The second cylinder block 13 is formed with a plurality of second cylinder bores 13a, which are arranged around the rotation shaft 21. FIG. 1 shows one of the second cylinder bores 13a. Each of the second cylinder bores 13a extends through the second cylinder block 13 in the axial direction. Each of the second cylinder bores 13a is in communication with the suction chamber 15a through the suction port 17a and is in communication with the discharge chamber 15b through the discharge port 17b. The first cylinder bores 12a and the second cylinder bores 13a are arranged at the front and the rear to form respective pairs. A double-headed piston 25 is accommodated in each cylinder bore including the first cylinder bore 12a and the second cylinder bore 13a to be reciprocable in a front and rear direction.
Each double-headed piston 25 engages with a radially outer portion of the swash plate 23 through a pair of shoes 26. Rotational movement of the swash plate 23 by the rotation of the rotation shaft 21 is converted to a reciprocable linear movement of the double-headed piston 25 through the shoes 26. The double-headed piston 25 and the first valve/port formation body 16 define a first compression chamber 20a in each first cylinder bore 12a. The double-headed piston 25 and the second valve/port formation body 17 define a second compression chamber 20b in each second cylinder bore 13a. 
The first cylinder block 12 is formed with a first large diameter hole 12b, which is continuous with the shaft hole 12h and has a larger diameter than the shaft hole 12h. The first large diameter hole 12b is in communication with the crank chamber 24. The crank chamber 24 is in communication with the suction chamber 14a through a suction passage 12c, which extends through the first cylinder block 12 and the first valve/port formation body 16.
The second cylinder block 13 is formed with a second large diameter hole 13b, which is continuous with the shaft hole 13h and has a larger diameter than the shaft hole 13h. The second large diameter hole 13b is in communication with the crank chamber 24. The crank chamber 24 is in communication with the suction chamber 15a through a suction passage 13c, which extends through the second cylinder block 13 and the second valve/port formation body 17.
The second cylinder block 13 has a peripheral wall that is formed with a suction port 13s. The suction port 13s is connected with the outer refrigerant circuit. Refrigerant gas drawn into the crank chamber 24 through the suction port 13s from the outer refrigerant circuit is drawn into the suction chambers 14a and 15a through the suction passages 12c and 13c. The suction chambers 14a and 15a and the crank chamber 24 serve as a suction pressure region and have pressures substantially the same to each other.
The rotation shaft 21 has a flange portion 21f that projects from the rotation shaft 21 and is arranged in the first large diameter hole 12b. A first thrust bearing 27a is disposed between the flange portion 21f and the first cylinder block 12 in the axial direction of the rotation shaft 21. A support member 39 having a circular tube shape is press-fitted to the rear end portion of the rotation shaft 21. The support member 39 has a radially outer surface having a circular flange portion 39f that projects from the radially outer surface and is arranged in the second large diameter hole 13b. A second thrust bearing 27b is disposed between the flange portion 39f and the second cylinder block 13 in the axial direction of the rotation shaft 21.
A fixed body 31 having a circular ring shape is fixed to a portion of the rotation shaft 21 located between the rear side of the flange portion 21f and the front side of the swash plate 23. The fixed body 31 is rotatable integrally with the rotation shaft 21. A movable body 32 is arranged between the flange portion 21f and the fixed body 31. The movable body 32 has a circular tube shape having a bottom. The movable body 32 is movable with respect to the fixed body 31 in the axial direction of the rotation shaft 21.
The movable body 32 includes a bottom portion 32a, which is formed to be a circular ring shape having an insertion hole 32e to which the rotation shaft 21 is inserted and a circular tube portion 32b, which extends from a radially outer edge of the bottom portion 32a in the axial direction of the rotation shaft 21. A radially inner surface of the circular tube portion 32b contacts with a radially outer edge of the fixed body 31 in a slidable manner. The movable body 32 is rotatable integrally with the rotation shaft 21 through the fixed body 31. A seal member 33 is arranged between the radially inner surface of the circular tube portion 32b and the radially outer edge of the fixed body 31 to seal therebetween. A seal member 34 is arranged between the insertion hole 32e and the rotation shaft 21 to seal therebetween. The fixed body 31 and the movable body 32 define a control pressure chamber 35 therebetween.
The rotation shaft 21 includes a first internal passage 21a that is arranged inside the rotation shaft 21 and extends in the axial direction of the rotation shaft 21. A rear end of the first internal passage 21a opens toward the pressure adjustment chamber 15c. The rotation shaft 21 further includes a second internal passage 21b that is arranged inside the rotation shaft 21 and extends in a radial direction of the rotation shaft 21. The second internal passage 21b has a first end, which is in communication with a distal end of the first internal passage 21a and a second end, which opens toward the control pressure chamber 35. The control pressure chamber 35 is in communication with the pressure adjustment chamber 15c through the first internal passage 21a and the second internal passage 21b. 
A lug arm 40 is disposed between the swash plate 23 and the flange portion 39f in the crank chamber 24. The lug arm 40 shaped to be a substantially L-shaped, has a first end and a second end. A weighted portion 40a is arranged in the first end of the lug arm 40. The lug arm 40 extends through a groove 23b so that the weighted portion 40a is arranged in front of the swash plate 23.
A first pin 41 extends through the groove 23b transversely. The first pin 41 connects a portion of the lug arm 40 that is closer to the first end of the lug arm 40 with a portion of the swash plate 23 that is closer to an upper end of the swash plate 23 (an upper portion in FIG. 1). The swash plate 23 supports the portion of the lug arm 40 that is closer to the first end of the lug arm 40 to be swingable about an axis of the first pin 41. The axis of the first pin 41 serves as a first swing center M1. A second pin 42 connects a portion of the lug arm 40 that is closer to the second end of the lug arm 40 with the support member 39. The support member 39 supports the portion of the lug arm 40 that is closer to the second end of the lug arm 40 to be swingable about an axis of the second pin 42. The axis of the second pin 42 serves as a second swing center M2.
A distal end of the circular tube portion 32b of the movable body 32 has a connecting portion 32c that projects toward the swash plate 23. The connecting portion 32c is formed with a movable body side insertion hole 32h into which a third pin 43 is inserted. A portion of the swash plate 23 closer to an lower end of the swash plate 23 (a lower portion in FIG. 1) is formed with a swash plate side insertion hole 23h into which the third pin 43 is inserted. The third pin 43 connects the connecting portion 32c with the portion of the swash plate 23 closer to the lower end of the swash plate 23.
The second valve/port formation body 17 is formed with a narrowing portion 36a. The narrowing portion 36a extends through the second valve/port formation body 17 and is in communication with the discharge chamber 15b. An end face of the second cylinder block 13 closer to the second valve/port formation body 17 is formed with a communication portion 36b that depresses from the end face of the second cylinder block 13 and communicates the pressure adjustment chamber 15c with the narrowing portion 36a. The discharge chamber 15b is in communication with the control pressure chamber 35 through the narrowing portion 36a, the communication portion 36b, the pressure adjustment chamber 15c, the first internal passage 21a and the second internal passage 21b. Accordingly, the narrowing portion 36a, the communication portion 36b, the pressure adjustment chamber 15c, the first internal passage 21a and the second internal passage 21b serve as a supplying passage that extends from the discharge chamber 15b to the control pressure chamber 35. The narrowing portion 36a narrows an opening degree of the supplying passage. A displacement control valve 50 of an electromagnetic type is arranged in the rear housing 15 to control a pressure in the control pressure chamber 35. The displacement control valve 50 communicatively connects electrically with a control computer, which is not shown.
As shown in FIG. 2, a valve housing 51 of the displacement control valve 50 includes a first housing 51a, which accommodates an electromagnetic solenoid 52, a second housing 51b, which has a tube shape and is attached to the first housing 51a, and a lid portion 51c, which has a plate shape and is located at a portion of the valve housing 51 opposite to the first housing 51a to close an opening of the second housing 51b. A dividing wall 51s is arranged in the second housing 51b. The dividing wall 51s divides an internal space of the second housing 51b into a valve chamber 55 and a pressure sensing chamber 56.
The electromagnetic solenoid 52 includes a fixed iron core 52a and a movable iron core 52b. A coil 52c is supplied with a current and is excited so that the movable iron core 52b is attracted to the fixed iron core 52a. The control computer controls the current to be supplied to the electromagnetic solenoid 52 (a duty ratio control).
A driving force transmission member 53 having a circular column shape is attached to the movable iron core 52b so that the driving force transmission member 53 is movable integrally with the movable iron core 52b. A back pressure chamber 55k is formed between the electromagnetic solenoid 52 and the valve chamber 55. The driving force transmission member 53 extends from an inside of the first housing 51a to the back pressure chamber 55k. A valve body formation member 54 having a circular column shape is arranged in the valve chamber 55 and the back pressure chamber 55k. The valve body formation member 54 includes a valve body 54v, which is accommodated in the valve chamber 55. The valve body 54v has an outer diameter that is greater than a shaft diameter of the valve body formation member 54.
A projecting portion 54a having a circular column shape is arranged on an end surface of the valve body 54v that is closer to the pressure sensing chamber 56. The projecting portion 54a extends through a valve hole 51h of the dividing wall 51s and projects into the pressure sensing chamber 56. A flange portion 54f having a circular ring shape is arranged in and projected from an end portion of the valve body formation member 54 that is located closer to the driving force transmission member 53. A biasing spring 55b is disposed in the back pressure chamber 55k and biases the flange portion 54f toward the driving force transmission member 53.
The valve body 54v come into and out of contact with the dividing wall 51s to open and close the valve hole 51h. An electromagnetic force of the electromagnetic solenoid 52 biases the valve body 54v against a spring force of the biasing spring 55b toward a position at which the valve body 54v closes the valve hole 51h. The driving force transmission member 53 and the valve body formation member 54 serve as a driving force transmission rod 60 that is driven by the electromagnetic solenoid 52. The electromagnetic solenoid 52, the back pressure chamber 55k, the valve chamber 55 and the pressure sensing chamber 56 are arranged in this order along an axial direction of the driving force transmission rod 60. A guide wall 61 having a circular tube shape guides the driving force transmission rod 60 in the valve chamber 50 along a movement direction of the driving force transmission rod 60.
The valve body formation member 54 (valve body 54v) is formed of a material (for example, aluminum), which is lighter than the driving force transmission member 53 in weight. The valve body formation member 54 (valve body 54v) has a surface that is subjected to a surface treatment such as a coating so as to have an excellent wear resistance.
The pressure sensing chamber 56 accommodates a pressure sensing mechanism 57. The pressure sensing mechanism 57 includes a bellows 58, a pressure receiving body 59a, which connects with an end portion of the bellows 58 that is closer to the lid portion 51c, a connection body 59b, which connects with an end portion of the bellows 58 that is closer to the projecting portion 54a, and a spring 59c, which is disposed in the bellows 58 to bias the pressure receiving body 59a and the connection body 59b in a direction to separate to each other. The projecting portion 54a has an end portion closer to the connection body 59b that connects with the connection body 59b in a manner as to come into and out of contact with the connection body 59b. 
The pressure sensing chamber 56 is in communication with the suction chamber 15a through a passage 67. The valve chamber 55 is in communication with the pressure adjustment chamber 15c through a passage 68. Accordingly, the second internal passage 21b, the first internal passage 21a, the pressure adjustment chamber 15c, the passage 68, the valve chamber 55, the valve hole 51h, the pressure sensing chamber 56 and the passage 67 serve as an exhaust passage that extends from the control pressure chamber 35 to the suction chamber 15a. 
The bellows 58 expands and contracts in the movement direction of the driving force transmission rod 60 in accordance with a pressure in the pressure sensing chamber 56. Specifically, the bellows 58 is configured to expand and contract when the bellows sensed a pressure in the suction chamber 15a that acts on an end surface of the connection body 59b that is closer to the projecting portion 54a. The expansion and contraction of the bellows 58 is used for determining the position of the valve body 54v. This contributes to the adjustment for a valve opening degree by the valve body 54v. The valve opening degree of the valve body 54v is determined by a balance of the electromagnetic force generated in the electromagnetic solenoid 52, the biasing force of the biasing spring 55b, and the biasing force of the pressure sensing mechanism 57.
The valve body 54v adjusts the opening degree (passage cross-sectional area) of the exhaust passage. The valve body 54v closes the exhaust passage when contacting with the dividing wall 51s. The valve body 54v opens the exhaust passage when separating from the dividing wall 51s. 
The pressure in the control pressure chamber 35 is adjusted by introducing the refrigerant gas from the discharge chamber 15b to the control pressure chamber 35 through the narrowing portion 36a, the communication portion 36b, the pressure adjustment chamber 15c, the first internal passage 21a and the second internal passage 21b, and by exhausting the refrigerant gas from the control pressure chamber 35 to the suction chamber 15a through the second internal passage 21b, the first internal passage 21a, the pressure adjustment chamber 15c, the passage 68, the valve chamber 55, the valve hole 51h, the pressure sensing chamber 56 and the passage 67. Accordingly, the refrigerant gas introduced to the control pressure chamber 35 serves as a control gas that adjusts the pressure in the control pressure chamber 35. The movable body 32 moves with respect to the fixed body 31 along the axial direction of the rotation shaft 21 in accordance with a pressure difference between the control pressure chamber 35 and the crank chamber 24.
In the double-headed piston type swash plate compressor 10 configured as discussed above, as shown in FIG. 3, when reducing the valve opening degree of the valve body 54v, a flow amount of the refrigerant gas exhausted from the control pressure chamber 35 to the suction chamber 15a through the second internal passage 21b, the first internal passage 21a, the pressure adjustment chamber 15c, the passage 68, the valve chamber 55, the valve hole 51h, the pressure sensing chamber 56, and the passage 67 is reduced. The refrigerant gas is introduced from the discharge chamber 15b to the control pressure chamber 35 through the narrowing portion 36a, the communication portion 36b, the pressure adjustment chamber 15c, the first internal passage 21a and the second internal passage 21b. The pressure in the control pressure chamber 35 becomes generally the same as the pressure in the discharge chamber 15b. 
As shown in FIG. 4, when the pressure difference between the control pressure chamber 35 and the crank chamber 24 becomes larger, the movable body 32 moves to separate the bottom portion 32a of the movable body 32 from the fixed body 31 . This enables the swash plate 23 to swing about the first swing center M1. This swing movement of the swash plate 23 enables the two ends of the lug arm 40 to swing about the first swing center M1 and the second swing center M2, respectively so that the lug arm 40 separates from the flange portion 39f of the support member 39. This increases the inclination angle of the swash plate 23 and increases the stroke of the double-headed piston 25 so as to increase the discharge displacement. The movable body 32 contacts with the flange portion 21f when the inclination angle of the swash plate 23 reaches a maximum inclination angle θ max. The contact between the movable body 32 and the flange portion 21f maintains the inclination angle of the swash plate 23 at the maximum inclination angle θ max.
As shown in FIG. 2, when increasing the valve opening degree of the valve body 54v, the flow amount of the refrigerant gas exhausted from the control pressure chamber 35 to the suction chamber 15a through the second internal passage 21b, the first internal passage 21a, the pressure adjustment chamber 15c, the passage 68, the valve chamber 55, the valve hole 51h, the pressure sensing chamber 56, and the passage 67 is increased. The pressure in the control pressure chamber 35 becomes generally the same as the pressure in the suction chamber 15a. 
As shown in FIG. 1, when the pressure difference between the control pressure chamber 35 and the crank chamber 24 becomes smaller, the movable body 32 moves so that the bottom portion 32a of the movable body 32 approaches the fixed body 31. This enables the swash plate 23 to swing about the first swing center M1 in a direction opposed to a swing direction when increasing the inclination angle of the swash plate 23. This swing movement of the swash plate 23 enables the two ends of the lug arm 40 swing about the first swing center M1 and the second swing center M2, respectively in the direction opposed to a swing direction when increasing the inclination angle of the swash plate 23 so that the lug arm 40 approaches the flange portion 39f of the support member 39. This reduces the inclination angle of the swash plate 23 and reduces the stroke of the double-headed piston 25 so as to reduce the discharge displacement. The lug arm 40 contacts with the flange portion 39f of the support member 39 when the inclination angle of the swash plate 23 reaches a minimum inclination angle θ min. The contact between the lug arm 40 and the flange portion 39f maintains the inclination angle of the swash plate 23 at the minimum inclination angle θ min.
As shown in FIG. 2, a clearance 61a is defined between the guide wall 61 and the driving force transmission rod 60. The back pressure chamber 55k is in communication with the valve chamber 55 through the clearance 61a. The narrowing portion 36a has a passage cross-sectional area that is larger than a passage cross-sectional area of the clearance 61a. The second housing 51b is formed with a communication passage 62 through which the back pressure chamber 55k is in communication with the pressure sensing chamber 56.
Next, discussion will be made on the operation of the present embodiment.
The clearance 61a is formed between the guide wall 61 and the driving force transmission rod 60. The clearance 61a enables the driving force transmission rod 60 and the valve body 54v to move smoothly. In addition, the clearance 61a enables the refrigerant gas to flow from the control pressure chamber 35 to the back pressure chamber 55k through the clearance 61a. In the present embodiment, the narrowing portion 36a has the passage cross-sectional area that is larger than the passage cross-sectional area of the clearance 61a. This enables an amount of the refrigerant gas that flows to the back pressure chamber 55k through the clearance 61a to be smaller compared to a structure in which the narrowing portion 36a has the passage cross-sectional area that is smaller than the passage cross-sectional area of the clearance 61a. This eliminates the necessity to increase the amount of the refrigerant gas to be introduced from the discharge chamber 15b to the control pressure chamber 35 by an amount corresponding to the reduced amount of the refrigerant gas from the control pressure chamber 35 to the back pressure chamber 55k through the clearance 61a. 
Further, the communication passage 62 enables the back pressure chamber 55k to communicate with the pressure sensing chamber 56 so that the pressure in the back pressure chamber 55k approaches the pressure in the suction chamber 15a. This prevents the pressure in the back pressure chamber 55k to be the same as the pressure in the control pressure chamber 35. This suppresses the effect on the valve opening degree of the valve body 54v that is adjusted by the pressure sensing mechanism 57.
The present embodiment has the advantages described below.
(1) The displacement control valve 50 includes the guide wall 61, the back pressure chamber 55k, and the communication passage 62. The guide wall 61 guides the driving force transmission rod 60 to move along the movement direction. The back pressure chamber 55k is arranged between the electromagnetic solenoid 52 and the valve chamber 55. The back pressure chamber 55k is in communication with the valve chamber 55 through the clearance 61a between the guide wall 61 and the driving force transmission rod 60. The back pressure chamber 55k communicates with the pressure sensing chamber 56 through the communication passage 62.
According to this configuration, the clearance 61a is formed between the guide wall 61 and the driving force transmission rod 60. The clearance 61a enables the driving force transmission rod 60 and the valve body 54v to move smoothly. In addition, the narrowing portion 36a has the passage cross-sectional area that is larger than the passage cross-sectional area of the clearance 61a. This enables an amount of the refrigerant gas that flows to the back pressure chamber 55k through the clearance 61a to be smaller compared to a structure in which the narrowing portion 36a has the passage cross-sectional area that is smaller than the passage cross-sectional area of the clearance 61a. This eliminates the necessity to increase the amount of the refrigerant gas to be introduced from the discharge chamber 15b to the control pressure chamber 35 by an amount corresponding to the reduced amount of the refrigerant gas from the control pressure chamber 35 to the back pressure chamber 55k through the clearance 61a. Further, the communication passage 62 enables the back pressure chamber 55k to communicate with the pressure sensing chamber 56 so that the pressure in the back pressure chamber 55k approaches the pressure in the suction chamber 15a. This prevents the pressure in the back pressure chamber 55k to be the same as the pressure in the control pressure chamber 35. This suppresses the effect on the valve opening degree of the valve body 54v that is adjusted by the pressure sensing mechanism 57. As a result, the present invention improves the response characteristic of the displacement control valve 50.
(2) The electromagnetic solenoid 52, the back pressure chamber 55k, the valve chamber 55 and the pressure sensing chamber 56 are arranged in this order along the axial direction of the driving force transmission rod 60. According to this configuration, the pressure sensing chamber 56 is arranged at an end portion of the driving force transmission rod 60 in the axial direction. This allows for the arrangement of the pressure sensing mechanism 57 to be easier compared to a structure in which the pressure sensing chamber 56 is arranged between the electromagnetic solenoid 52 and the valve chamber 55 in the axial direction. The present invention is preferable in manufacturability of the displacement control valve 50.
(3) The larger the diameter of the valve hole 51h is, the larger a flow amount of the refrigerant gas exhausted from the control pressure chamber 35 to the suction chamber 15a is. The present invention shorten the time necessary for the pressure in the control pressure chamber 35 to be generally the same as the pressure in the suction chamber 15a. However, enlargement of the diameter of the valve hole 51h requires an outer diameter of the valve body 54v that opens and closes the valve hole 51h to be larger. Enlargement of the outer diameter of the valve body 54v enlarges a passage cross-sectional are of the clearance 61a. This increases the amount of the refrigerant gas to flow from the control pressure chamber 35 to the back pressure chamber 55k through the clearance 61a. In the present embodiment, the narrowing portion 36a has the passage cross-sectional area that is larger than the passage cross-sectional area of the clearance 61a. This reduces an amount of the refrigerant gas that flows to the back pressure chamber 55k through the clearance 61a. This eliminates the necessity to increase the amount of the refrigerant gas to be introduced from the discharge chamber 15b to the control pressure chamber 35 by an amount corresponding to the reduced amount of the refrigerant gas from the control pressure chamber 35 to the back pressure chamber 55k through the clearance 61a. 
(4) The valve body formation member 54 is formed of a material (for example, aluminum) lighter than the driving force transmission member 53 in weight. This suppresses the displacement control valve 50 to be heavier even when the size of the valve body 54v is larger.
(5) The valve body formation member 54 has a surface that is subjected to a surface treatment such as a coating having an excellent wear resistance. This suppresses the valve body 54v from eroded by a cavitation, which generates when the refrigerant gas flowing through between the valve body 54v and the dividing wall 51s includes a liquefied refrigerant.
(6) The biasing spring 55b is disposed in the back pressure chamber 55k. This facilitates to secure the cross-sectional area of magnetic path generated by the electromagnetic solenoid 52 compared to a structure in which the biasing spring 55b is disposed between the fixed iron core 52a and the movable iron core 52b. 
It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.
In this embodiment, the pressure sensing chamber 56 may be arranged between the electromagnetic solenoid 52 and the valve chamber 55 in the axial direction of the driving force transmission rod 60.
In this embodiment, a supplying passage may be formed between the discharge chamber 14b and the control pressure chamber 35, for example. In other words, the supplying passage needs to be formed between the discharge pressure region and the control pressure chamber 35.
In this embodiment, an exhaust passage may be formed between the control pressure chamber 35 and the suction chamber 14a, for example. In other words, the exhaust passage needs to be formed between the control pressure chamber 35 and the suction pressure region.
In this embodiment, the valve body formation member 54 needs to be formed of a material that is lighter in weight than a material of the driving force transmission member 53. The valve body formation member 54 may be formed of a resin material, for example.
In this embodiment, the valve body formation member 54 may have a surface that is not subjected to a surface treatment such as a coating having an excellent wear resistance.
In this embodiment, the driving force transmission member 53 may be formed integral with the valve body formation member 54.
In this embodiment, the swash plate 23 may receive a driving force from the external driving source through a clutch.

## Claims

1. A double-headed piston type swash plate compressor comprising:
a housing;
a rotation shaft;
a swash plate that is rotated by a driving force of the rotation shaft, wherein the swash plate is configured to vary an inclination angle with respect to the rotation shaft;
a crank chamber that is formed in the housing and accommodates the swash plate;
a double-headed piston that engages with the swash plate, wherein the double-headed piston reciprocates with a stroke according to the inclination angle of the swash plate;
a movable body that is connected with the swash plate to vary the inclination angle of the swash plate;
a control pressure chamber that is arranged in the housing and defined by the movable body, wherein the control pressure chamber is configured to move the movable body in an axial direction of the rotation shaft when the control pressure chamber is supplied with a control gas to change a pressure inside the control pressure chamber;
a discharge pressure region;
a suction pressure region;
a supplying passage that extends from the discharge pressure region to the control pressure chamber;
a narrowing portion that narrows an opening degree of the supplying passage;
an exhaust passage that extends from the control pressure chamber to the suction pressure region; and
a displacement control valve that controls a pressure in the control pressure chamber, wherein the displacement control valve includes:
an electromagnetic solenoid;
a part of the exhaust passage;
a driving force transmission rod including a valve body that adjusts an opening degree of the exhaust passage, wherein the driving force transmission rod is driven by the electromagnetic solenoid;
a valve chamber that accommodates the valve body;
a pressure sensing chamber that is in communication with the suction pressure region;
a pressure sensing mechanism that is accommodated in the pressure sensing chamber, wherein the pressure sensing mechanism is configured to expand and contract along a movement direction of the driving force transmission rod in accordance with a pressure in the suction pressure region so as to adjust an opening degree of the valve body;
a guide wall that guides the driving force transmission rod to move along the movement direction;
a back pressure chamber that is arranged between the electromagnetic solenoid and the valve chamber, wherein the back pressure chamber is in communication with the valve chamber through a clearance between the guide wall and the driving force transmission rod; and
a communication passage through which the back pressure chamber communicates with the pressure sensing chamber;

wherein the narrowing portion has a passage cross-sectional area that is larger than a passage cross-sectional area of the clearance.

2. The double-headed piston type swash plate compressor according to claim 1, wherein the electromagnetic solenoid, the back pressure chamber, the valve chamber and the pressure sensing chamber are arranged in this order along an axial direction of the driving force transmission rod.