Swash plate type variable displacement compressor

Abstract

 A swash plate type variable displacement compressor includes a crank chamber (16), a rotary shaft (17), a swash plate (23), a piston (29), a supply passage (42) and first and second bleed passages (48,58). The supply passage connecting the crank chamber to a discharge pressure region (39) is provided with a displacement control valve (35). The pressure in the crank chamber is varied by adjusting the opening of the displacement control valve. The first bleed passage (48) connecting the crank chamber to the suction pressure region is provided with a valve (50). The second bleed passage (58) constantly connecting the crank chamber to the suction pressure region (38) is provided with a throttle (59). The valve (50) operates to close the first bleed passage according to the magnitude of centrifugal force generated by the rotation of the rotary shaft.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a variable displacement compressor for use in an automotive air conditioner, and the like.

[0002] Generally, a variable displacement compressor (hereinafter referred to as "compressor") is known as a compressor for use in an automotive air conditioner that is operable to variably control its displacement. This type of compressor uses a displacement control valve for adjusting pressure in a crank chamber to change the inclination angle of a swash plate accommodated in the crank chamber, thereby to adjust the stroke length of pistons and hence to control the displacement of the compressor.

[0003] Japanese Unexamined Patent Application Publication No. 10-54350 discloses the compressor having a valve disposed in a bleed passage connecting the crank chamber to a suction pressure region of the compressor. The valve includes a valve body, a coil spring and a counterweight. The coil spring urges the valve body in the direction that causes the valve body to open a valve hole. When the rotational speed of the rotary shaft reaches a predetermined value, the valve body is moved in the direction that causes the valve body to close the valve hole by centrifugal force acting on the counterweight, which closes the bleed passage and stops the flow of refrigerant gas from the crank chamber into the suction region through the bleed passage. During the compression operation under a large displacement, the valve closes the bleed passage and the pressure in the crank chamber is gradually increased by blow-by gas flowing into the crank chamber. Thus, the displacement of the compressor is decreased so that the compression load is reduced and the contact pressure acting on various sliding surfaces of the compressor is reduced, accordingly.

[0004] However, according to the reference No. 10-54350, the bleed passage is closed by the valve when the rotational speed of the rotary shaft reaches the predetermined value or more, with the result that the amount of refrigerant gas drawn from the crank chamber into the suction pressure region becomes zero. In this operating state, it takes a long time to increase the displacement of the compressor, and the displacement recovery performance of the compressor is deteriorated, because the bleed passage has been closed thereby to prevent the refrigerant gas from being rapidly drawn from the crank chamber.

[0005] The present invention, which has been made in light of the above problems, is directed to a swash plate type variable displacement compressor which ensures the performance to recover displacement of the compressor during the operation at a low rotational speed and to reduce power loss during the operation at a high rotational speed.

SUMMARY OF THE INVENTION

[0006] In accordance with an aspect of the present invention, a swash plate type variable displacement compressor includes a housing including a cylinder block having a cylinder bore formed therein, a crank chamber formed in the housing, a rotary shaft extending through the crank chamber, and a swash plate connected to the rotary shaft. The rotary shaft is rotatably supported by the housing. The swash plate is integrally rotatable with the rotary shaft and inclinable relative to the rotary shaft. The compressor further includes a piston received in the cylinder bore to be reciprocally movable, a discharge pressure region for receiving discharge pressure gas, a suction pressure region for receiving suction pressure gas, a supply passage connecting the crank chamber to the discharge pressure region and first and second bleed passages. The supply passage is provided with a displacement control valve. The pressure in the crank chamber is varied by adjusting the opening of the displacement control valve to change the inclination angle of the swash plate thereby to control the displacement of the compressor. The first bleed passage connecting the crank chamber to the suction pressure region is provided with a valve and the second bleed passage constantly connecting the crank chamber to the suction pressure region is provided with a throttle. The valve operates to close the first bleed passage according to the magnitude of centrifugal force generated by the rotation of the rotary shaft.

[0007] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. 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 longitudinal cross-sectional view of a swash plate type variable displacement compressor according to a first preferred embodiment of the present invention;

Fig. 2 is an enlarged cross-sectional view of a valve used in the compressor according to the first preferred embodiment of the present invention;

Fig. 3 is an enlarged fragmentary cross-sectional view of the compressor according to the first preferred embodiment of the present invention;

Fig. 4 is a schematic block diagram illustrating the compressor according to the first preferred embodiment of the present invention;

Fig.5 is a schematic graph showing a relation between the rotational speed of a rotary shaft of the compressor and the total cross-sectional area of throttle opening in bleed passages of the compressor according to the first preferred embodiment of the present invention;

Fig.6 is an enlarged fragmentary cross-sectional view of the compressor showing the valve according to a second preferred embodiment of the present invention;

Fig. 7 is an enlarged fragmentary cross-sectional view of the compressor showing the valve according to a third preferred embodiment of the present invention, and

Fig. 8 is a schematic view as seen in the direction of the arrow D in Fig.7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The following will describe a swash plate type variable displacement compressor (hereinafter referred to as "compressor") according to the first preferred embodiment of the present invention with reference to Figs. 1 through 5. Referring to Fig. 1, the compressor designated by numeral 10 has a housing 11 forming the outer shell of the compressor 10. The housing 11 includes a cylinder block 12, a front housing 13 joined to the front end of the cylinder block 12, and a rear housing 14 joined to the rear end of the cylinder block 12. The cylinder block 12 has a plurality of cylinder bores 12A formed therein. In Fig. 1, the left side of the drawing corresponds to the front side of the compressor 10, and the right side of the drawing corresponds to the rear side of the compressor 10. The front housing 13, the cylinder block 12 and the rear housing 14 are fastened together in the longitudinal direction of the compressor 10 by a plurality of bolts 15 (only one bolt being shown) inserted through the front housing 13, the cylinder block 12 and the rear housing 14, thus the housing 11 of the compressor 10 is formed thereby.

[0010] The front housing 13 has a crank chamber 16 formed therein, whose rear end is closed by the cylinder block 12. A rotary shaft 17 extends through the center of the crank chamber 16 and is rotatably supported by the front housing 13 and the cylinder block 12 through radial bearings 18, 19, respectively. A shaft seal mechanism 20 is disposed in slide contact with the circumferential surface of the rotary shaft 17 at a position forward of the radial bearing 18 supporting the front part of the rotary shaft 17. The seal mechanism 20 has a lip seal member to prevent refrigerant gas in the crank chamber 16 from leaking out through the clearance between the front housing 13 and the rotary shaft 17. The rotary shaft 17 is connected at the front end thereof to an external drive source (not shown) through a power transmission mechanism (not shown either) so as to be rotated by the external drive source.

[0011] A lug plate 21 is fixedly mounted on the rotary shaft 17 in the crank chamber 16 so as to rotate integrally therewith. A swash plate 23 as a part of displacement changing mechanism 22 of the compressor 10 is provided on the rotary shaft 17 behind the lug plate 21 and supported in such a way that it is slidable in the axial direction of the rotary shaft 17 and inclinable relative to the axis of the rotary shaft 17. A hinge mechanism 24 is interposed between the swash plate 23 and the lug plate 21, through which the swash plate 23 and the lug plate 21 are connected such that the swash plate 23 is integrally rotatable with the lug plate 21 and the rotary shaft 17, while inclinable relative to the rotary shaft 17.

[0012] A coil spring 25 is disposed on the rotary shaft 17 between the lug plate 21 and the swash plate 23. A sleeve 26 is slidably disposed on the rotary shaft 17 and urged rearward by the pressing force of the coil spring 25. The swash plate 23 is urged by the coil spring 25 through the sleeve 26 rearward or in the direction that decreases the inclination angle of the swash plate 23. The inclination angle of the swash plate 23 means an angle between the swash plate 23 and an imaginary plane that is perpendicular to the axis of the rotary shaft 17. The swash plate 23 has a restricting portion 23A projecting from the front end thereof and abutable with the lug plate 21, thereby restricting the maximum inclination angle of the swash plate 23. The rotary shaft 17 has a snap ring 27 fitted thereon behind the swash plate 23. The rear end of the swash plate 23 is abutable with the snap ring 27, thereby restricting the minimum inclination angle of the swash plate 23. Referring to Fig. 1, the swash plate 23 indicated by the solid line represents the position at the maximum inclination angle thereof, and the swash plate 23 indicated by the double-dashed line represents the position at the minimum inclination angle thereof.

[0013] Each cylinder bore 12A of the cylinder block 12 receives therein a reciprocally movable single-headed piston 29. The piston 29 engages at the neck portion thereof with the outer periphery of the swash plate 23 through a pair of shoes 30. As the swash plate 23 is rotated with the rotary shaft 17, each piston 29 is reciprocated in its associated cylinder bore 12A through the pair of shoes 30.

[0014] As shown in Fig. 1, the front end of the rear housing 14 is joined to the rear end of the cylinder block 12 through a valve plate 32. The rear housing 14 has a suction chamber 38 which serves as a suction pressure region formed at a center region thereof. The suction chamber 38 is in communication with a compression chamber 31 defined by the cylinder bore 12A through a suction port 36 formed through the valve plate 32. The rear housing 14 also has a discharge chamber 39 which serves as a discharge pressure region formed at a circumferential region thereof. The discharge chamber 39 and the suction chamber 38 are separated by a partition wall 14A. The valve plate 32 defining the compression chamber 31 with the piston 29 in the cylinder bore 12A has a discharge port 37 formed therethrough in communication with the discharge chamber 39. The suction port 36 and the discharge port 37 for each cylinder bore 12A are provided with a suction valve 33 and a discharge valve 34, respectively.

[0015] When the piston 29 moves toward the bottom dead center from the top dead center thereof, refrigerant gas in the suction chamber 38 is drawn into the compression chamber 31 through the suction port 36 and the suction valve 33. Refrigerant gas drawn into the compression chamber 31 is compressed to a predetermined pressure by the motion of the piston 29 from the bottom dead center to the top dead center thereof, and discharged into the discharge chamber 39 through the discharge port 37 and the discharge valve 34.

[0016] A supply passage 42 is formed in the cylinder block 12 and the rear housing 14 to connect the discharge chamber 39 to the crank chamber 16. An electromagnetic displacement control valve 35 is disposed in the supply passage 42. The displacement control valve 35 is in communication with the suction chamber 38 through a pressure sensing passage 61. The opening of the displacement control valve 35 is adjustable according to the detected pressure in the suction chamber 38 or in response to any external command signals. Adjusting the opening of the displacement control valve 35 varies the flow rate of high-pressure refrigerant gas introduced from the discharge chamber 39 into the crank chamber 16. The pressure differential between the crank chamber 16 and the compression chamber 31 across the piston 29 is varied, thereby changing the inclination angle of the swash plate 23. Accordingly, the stroke length of the piston 29 is varied thereby to control the displacement of the compressor 10.

[0017] The center of the cylinder block 12 has a shaft hole 43 therethrough, and a recess 44 located behind and in communication with the shaft hole 43. The rear end of the rotary shaft 17 is inserted into and supported by the shaft hole 43 through the radial bearing 19. The compressor 10 of the first preferred embodiment includes a first bleed passage 48 and a second bleed passage 58. A passage hole 45 forming a part of the first bleed passage 48 extends in the rotary shaft 17 along its center axis. The front end portion of the passage hole 45 is opened to the crank chamber 16 at a position adjacent to the radial bearing 18 and the shaft seal mechanism 20. The passage hole 45 is closed at the rear end by a plug 60. A valve 50 is mounted on the rotary shaft 17 at the rear end portion thereof in the recess 44. The valve 50 will be described in detail later.

[0018] A thrust bearing 46 and a support spring 47 are interposed between the rear end of the rotary shaft 17 and the valve plate 32. The recess 44 is in communication with the suction chamber 38 through a communication hole 49 formed at the center of the valve plate 32. The communication hole 49 serves as a throttle for restricting flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38. The aforementioned first bleed passage 48 includes the passage hole 45, the recess 44, the valve 50 and the communication hole 49 so as to connect the crank chamber 16 to the suction chamber 38.

[0019] The valve 50 is provided for opening or closing the first bleed passage 48. As shown in Fig. 2, the rotary shaft 17 has plane seating surfaces 51, 52 formed by cutting off the top and bottom of the circumferential surface of the rear end portion of the rotary shaft 17, respectively. A valve hole 53 is formed in the radial direction of the rotary shaft 17, or the compressor 10 so as to provide fluid communication between the seating surfaces 51, 52 and also to be in communication with the passage hole 45. The valve hole 53 is larger in diameter on the side opened to the seating surface 51 than the opposite side opened to the seating surface 52. A valve body 54 is movably mounted on the rotary shaft 17 so as to open or close the valve hole 53. The valve body 54 is disposed on the side of the seating surface 51, and a counterweight 55 connected to the valve body 54 through a connecting portion 56 is disposed on the side of the seating surface 52. A coil spring 57 serving as an urging member is provided between the seating surface 51 and the valve body 54 for urging the valve body 54 toward its opened position.

[0020] A centrifugal force acting on the counterweight 55 is increased with an increase in rotational speed of the rotary shaft 17, with the result that the counterweight 55 is moved away from the axis of the rotary shaft 17. Accordingly, the valve body 54 is moved toward the axis of the rotary shaft 17 against the urging force of the coil spring 57 and brought into contact with the seating surface 51, thereby to close the valve hole 53. On the other hand, the centrifugal force acting on the counterweight 55 is decreased with a decrease in rotational speed of the rotary shaft 17, with the result that the urging force of the coil spring 57 becomes greater than the centrifugal force acting on the counterweight 55. Accordingly, the valve body 54 is moved away from the axis of the rotary shaft 17 by the urging force of the coil spring 57, thereby to open the valve hole 53. Figs. 1 and 2 show the valve 50 in its opened position during compressor operation at a high rotational speed of the rotary shaft 17, and Fig.3 shows the valve 50 in its closed position during compressor operation at a low rotational speed of the rotary shaft 17.

[0021] Referring back to Fig. 1, the second bleed passage 58 connecting the crank chamber 16 to the suction chamber 38 is formed in the cylinder block 12. The second bleed passage 58 has a throttle hole 59 formed in the valve plate 32 which functions as a fixed throttle for throttling the flow rate of the refrigerant gas. The crank chamber 16 is in constant communication with the suction chamber 38 through the second bleed passage 58.

[0022] Referring to Fig. 4 showing a schematic block diagram illustrating the compressor 10 according to the first preferred embodiment, the discharge chamber 39 is in communication with the crank chamber 16 through the supply passage 42 in which the displacement control valve 35 is disposed. The crank chamber 16 is in communication with the suction chamber 38 through the first bleed passage 48 and the second bleed passage 58. The first bleed passage 48 is provided with the valve 50 operable to open or close according to the magnitude of the centrifugal force and the second bleed passage 58 is provided with the throttle hole 59 serving as a fixed throttle.

[0023] Fig.5 is a schematic graph showing a relation between rotational speed N of the rotary shaft 17 of the compressor 10 and total cross-sectional area AS of the throttle opening which is the sum of the cross-sectional areas of the throttle openings formed in the first and second bleed passages 48, 58 according to the first preferred embodiment. In the graph of Fig. 5, the cross-sectional areas of the communication hole 49 provided in the first bleed passage 48 and the throttle hole 59 provided in the second bleed passage 58 are designated by reference symbols AA, AB, respectively. During the operation of the compressor 10 at a low rotational speed, the valve 50 is in its opened position. In this state, the relation among total cross-sectional area AS1 of the throttle opening, the cross-sectional area AA of the communication hole 49 and the cross-sectional area AB of the throttle hole 59 is expressed by AS1=AA+AB. On the other hand, during the operation of the compressor 10 at a high rotational speed, the valve 50 is in its closed position, that is, the first bleed passage 48 is closed and only the second bleed passage 58 is opened. When the rotational speed of the rotary shaft 17 is at or higher than NC1, the relation among total cross-sectional area AS2 of the throttle opening, the cross-sectional area AA of the communication hole 49 and the cross-sectional area AB of the throttle hole 59 is expressed by AS2=AB. The flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38 through the first and second bleed passages 48, 58 is proportional to the total cross-sectional area AS of the throttle opening. Therefore, the flow rate of refrigerant gas during the operation at a low rotational speed that is expressed by AS1 (=AA+AB) is larger than that during the operation at a high rotational speed that is expressed by AS2 (=AB). The cross-sectional areas AA and AB are previously set at any values suitable to ensure both of the displacement recovery and power loss reduction during the operation of the compressor 10. The diameter of the fully opened valve hole 53 is set such that the cross-sectional area of such valve hole 53 is larger than the cross-sectional area AA of the communication hole 49.

[0024] The following will describe the operation of the compressor constructed as described above. As the rotary shaft 17 is rotated by the external drive source such as a vehicle engine, the swash plate 23 is rotated with the rotary shaft 17 through the lug plate 21 and the hinge mechanism 24. Accordingly, the rotational movement of the swash plate 23 is converted into reciprocating movement of the piston 29 by way of the shoes 30. The piston 29 is reciprocated in the cylinder bore 12A, thereby causing refrigerant gas to be drawn from the suction chamber 38 into the compression chamber 31 through the suction port 36 and the suction valve 33. Then the refrigerant gas is compressed in the compression chamber 31 to a predetermined pressure and discharged into the discharge chamber 39 through the discharge port 37 and the discharge valve 34. Most of the high-pressure refrigerant gas discharged into the discharge chamber 39 is delivered to the external refrigeration circuit (not shown), while a part of the high-pressure refrigerant gas in the discharge chamber 39 is drawn into the crank chamber 16 through the supply passage 42 for varying the inclination of the swash plate 23.

[0025] The opening of the displacement control valve 35 provided in the supply passage 42 is adjusted to control the relation between the flow rate of refrigerant gas introduced from the discharge chamber 39 into the crank chamber 16 and the flow rate of refrigerant gas flowing out from the crank chamber 16 into the suction chamber 38 through the first and second bleed passages 48, 58. A crank chamber pressure PC in the crank chamber 16 is determined by this relation of the refrigerant gas. As the opening of the displacement control valve 35 is adjusted to change the crank chamber pressure PC in the crank chamber 16, the pressure differential between the crank chamber 16 and the compression chambers 31 through the piston 29 varies thereby to change the inclination angle of the swash plate 23. Thus, the stroke length of the piston 29 is changed and the displacement of the compressor 10 is changed accordingly.

[0026] When the cooling load is large due to high temperature in the vehicle compartment, a suction pressure PS in the suction chamber 38 is high and there is substantially no pressure differential between the pressures in the compression chambers 31 and the crank chamber pressure PC in the crank chamber 16 through the piston 29. (or PS=PC). In this case, the displacement control valve 35 is controlled to be closed so that the supply passage 42 prevents high-pressure refrigerant gas in the discharge chamber 39 from flowing into the crank chamber 16. Since the crank chamber pressure PC in the crank chamber 16 is substantially the same as the suction pressure PS, refrigerant gas does not flow from the crank chamber 16 through the first and second bleed passages 48, 58 into the suction chamber 38. Thus, as indicated by the solid line in Fig.1, the swash plate 23 is moved to its maximum inclination angle position to increase the stroke of the piston 29, thereby to increase the displacement of the compressor 10. During the maximum displacement operation of the compressor 10, the refrigerant gas does not circulate through the supply passage 42, the first and second bleed passages 48, 58, with the result that the compressor 10 is efficiently operated.

[0027] When the cooling load is decreased due to a decrease of the temperature in the vehicle compartment, the suction pressure PS in the suction chamber 38 is also decreased. In this case, the displacement control valve 35 is controlled to be opened in accordance with the decrease in the suction pressure PS. Accordingly, high-pressure refrigerant gas in the discharge chamber 39 is introduced into the crank chamber 16 through the supply passage 42. As a result, the crank chamber pressure PC in the crank chamber 16 is increased and the pressure differential between the crank chamber 16 and the compression chambers 31 through the piston 29 increases. The inclination angle of the swash plate 23 becomes small in accordance with the increase of the pressure differential, thereby decreasing the displacement of the compressor 10.

[0028] During the variable displacement operation of the compressor 10, in particular, when the rotational speed of the rotary shaft 17 is low, the centrifugal force generated by the rotation of the rotary shaft 17 is small. In this case, the valve body 54 of the valve 50 provided in the first bleed passage 48 is positioned so as to open the valve hole 53, as shown in Fig. 2. The second bleed passage 58 has the throttle hole 59 for constant communication between the crank chamber 16 and the suction chamber 38. That is, the first bleed passage 48 provided with the valve 50 and the second bleed passage 58 provided with the throttle hole 59 are opened. Thus, the refrigerant gas is drawn from the crank chamber 16 into the suction chamber 38 rapidly and, therefore, the displacement of the compressor 10 is controlled appropriately in accordance with a change in the cooling load.

[0029] As the rotational speed of the rotary shaft 17 is increased, the centrifugal force generated by the rotation of the rotary shaft 17 is increased. That is, the centrifugal force acting on the counterweight 55 of the valve 50 is also increased. As shown in Fig.3, the valve body 54 is moved toward the axis of the rotary shaft 17 by the centrifugal force acting against the urging force of the coil spring 57 so as to be brought into contact with the seating surface 51, thereby to close the valve hole 53. The first bleed passage 48 provided with the valve 50 is closed and only the second bleed passage 58 provided with the throttle hole 59 is opened. Thus, the flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38 is decreased. The decrease of the flow rate of refrigerant gas circulating within the compressor means the increase the flow rate of refrigerant gas in the external refrigeration circuit, thus reducing the power loss of the compressor 10.

[0030] As the cooling load is decreased to be nearly zero due to further decrease of the temperature in the vehicle compartment, the suction pressure PS in the suction chamber 38 is further decreased accordingly and the displacement control valve 35 becomes fully opened. In this case, a large amount of high-pressure refrigerant gas is introduced from the discharge chamber 39 into the crank chamber 16 through the supply passage 42, thereby to increase the crank chamber pressure PC in the crank chamber 16. As a result, the pressure differential between the crank chamber 16 and the compression chamber 31 through the piston 29 is increased. As indicated by the double-dashed line in Fig.1, the swash plate 23 is moved to its minimum inclination angle position to decrease the stroke length of the piston 29, thereby to change the displacement of the compressor 10 to the minimum. During the minimum displacement operation (or OFF operation), the displacement of the compressor 10 is not zero. When the compressor 10 is operated at a high rotational speed during the minimum displacement operation, the flow rate of refrigerant gas circulating within the compressor 10 is further decreased thereby to decrease the level of the minimum displacement. Thus, the power loss during the minimum displacement operation is reduced.

[0031] The following will describe the recovery of the compressor 10 from the minimum displacement state. The increase of the displacement of the compressor 10 from the OFF operation is dependent on the rate of refrigerant gas from the crank chamber 16 into the suction chamber 38. When the rotary shaft 17 is rotated at a low speed, the first bleed passage 48 provided with the valve 50 and the second bleed passage 58 provided with the throttle hole 59 are both opened. Therefore, the refrigerant gas is drawn from the crank chamber 16 into the suction chamber 38 rapidly and the crank chamber pressure PC in the crank chamber 16 is decreased accordingly rapidly. Thus, the recovery of the compressor 10 from the minimum displacement state is improved.

[0032] When the rotary shaft 17 is rotated at a high speed, the first bleed passage 48 provided with the valve 50 is closed and only the second bleed passage 58 provided with the throttle hole 59 is opened. Accordingly, the flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38 is decreased. During the high-speed operation of the compressor 10, however, an inertial force acting on the piston 29 and the swash plate 23 is increased so as to principally affect the motion of the piston 29 and the swash plate 23 to change in the direction that increases the compression displacement. Thus, the desired compression displacement is achieved rapidly from the minimum displacement state despite the decrease of the flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38.

[0033] The swash plate type variable displacement compressor 10 according to the first preferred embodiment of the present invention offers the following advantageous effects.

(1) When the rotational speed of the rotary shaft 17 is low and, therefore, the centrifugal force generated by the rotation of the rotary shaft 17 is small, the valve body 54 of the valve 50 provided in the first bleed passage 48 is positioned so as to open the valve hole 53. The second bleed passage 58 has the throttle hole 59 providing constant communication between the crank chamber 16 and the suction chamber 38. That is, the first bleed passage 48 provided with the valve 50 and the second bleed passage 58 provided with the throttle hole 59 are both opened. Thus, the refrigerant gas is drawn from the crank chamber 16 into the suction chamber 38 rapidly and the crank chamber pressure PC is decreased accordingly rapidly, thereby improving the recovery of the compressor 10 from the minimum displacement state.

(2) During the variable displacement operation of the compressor 10, the centrifugal force generated by the rotation of the rotary shaft 17 and acting on the counterweight 55 of the valve 50 is increased with an increase in the rotational speed of the rotary shaft 17. The valve body 54 is moved toward the axis of the rotary shaft 17 by the centrifugal force acting against the urging force of the coil spring 57 so as to be in contact with the seating surface 51, with the result that the valve hole 53 is closed. Since the first bleed passage 48 provided with the valve 50 is closed and only the second bleed passage 58 provided with the throttle hole 59 is opened, the flow rate of the refrigerant gas drawn from the crank chamber 16 into the suction chamber 38 is decreased. Such decreased flow rate of refrigerant gas within the compressor 10 contributes to increasing the flow rate of refrigerant gas in the external refrigeration circuit, thereby to reduce the power loss and improve the operating efficiency of the compressor 10.

(3) During the operation of the compressor 10 at a high rotational speed, the first bleed passage 48 provided with the valve 50 is closed and only the second bleed passage 58 provided with the throttle hole 59 is opened. Thus, the refrigerant gas drawn from the crank chamber 16 into the suction chamber 38 is decreased. In particular, during the OFF operation, the minimum displacement of the compressor is further decreased thereby to reduce the power loss. When the compressor 10 is operated at a high rotational speed, the inertial force acting on the piston 29 and the swash plate 23 is increased so as to affect the increase of the compression displacement. Thus, the decrease of the performance of the compressor 10 to recover the displacement of the compressor 10 from the minimum displacement state is prevented despite the decrease of the flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38.

(4) The valve 50 provided in the first bleed passage 48 formed in the rotary shaft 17 is operable to be opened or closed by utilizing the centrifugal force generated by the rotation of the rotary shaft 17. Further, the throttle hole 59 is easily provided in the second bleed passage 58 formed in the cylinder block 12 separately from the first bleed passage 48 to ensure a constant flow of refrigerant gas therethrough.

(5) The passage hole 45 formed in the rotary shaft 17 along its axis is opened at one end thereof to the crank chamber 16 and has at the other end thereof the valve 50, which allows the valve 50 to be disposed effectively in the cylinder block 12.

(6) The valve 50 includes the valve body 54, the coil spring 57 and the counterweight 55. The coil spring 57 urges the valve body 54 toward its opened position. The centrifugal force generated by the rotation of the rotary shaft 17 and acting on the counterweight 55 causes the valve body 54 to be moved against the urging force of the coil spring 57 and to close the valve hole 53. When the rotational speed of the rotary shaft 17 is increased, the counterweight 55 is moved away from the axis of the rotary shaft 17 by the increasing centrifugal force acting on the counterweight 55 against the urging force of the coil spring 57. As a result, the valve body 54 is moved toward its closed position. On the other hand, when the rotational speed of the rotary shaft 17 is decreased, the urging force of the coil spring 57 becomes greater than the centrifugal force acting on the counterweight 55, so that the valve body 54 is moved to and held at its opened position. The valve 50 is simple in structure as described above and the first bleed passage 48 is opened or closed reliably in accordance with the rotational speed of the rotary shaft 17.

[0034] The following will describe a swash plate type variable displacement compressor according to the second preferred embodiment of the present invention with reference to Fig. 6. The compressor of the second preferred embodiment differs from that of the first preferred embodiment in that the rotary shaft 17 is equipped with the function of the second bleed passage 58 of the first embodiment. That is, the second bleed passage of the second embodiment shares a part of the first bleed passage. The rest of the structure of the compressor according to the second preferred embodiment is substantially the same as that of the first preferred embodiment. For the sake of convenience of explanation, therefore, like or same parts or elements will be referred to by the same reference numerals as those that have been used in the first preferred embodiment, and the description thereof will be omitted.

[0035] As shown in Fig. 6, the rotary shaft 17 of the compressor 10 according to the second preferred embodiment has a throttle hole 70 radially bored therethrough at a position adjacent to the valve 50 for providing fluid communication between the passage hole 45 in the rotary shaft 17 and the recess 44 in the cylinder block 12. The throttle hole 70 functions as a fixed throttle. The diameter D1 of the throttle hole 70 is formed smaller than the diameter D2 of the communication hole 49 (or D1 <D2). As the previously described first preferred embodiment, the relation among the cross-sectional area AA of the communication hole 49, the cross-sectional area AB of the throttle hole 59 and the total cross-sectional area AS1 during the operation at a low rotational speed is expressed by AS1=AA+AB, while the total cross-sectional area AS2 during the operation at a high rotational speed is expressed by AS2=AB. Meanwhile, in the second preferred embodiment, the diameter D1 of the throttle hole 70 and the diameter D2 of the communication hole 49 are set such that D1=AB=AS2 and D2=AA+AB=AS1 respectively.

[0036] When the rotational speed of the rotary shaft 17 is low, the centrifugal force generated by the rotation of the rotary shaft 17 is small, so that the valve body 54 of the valve 50 provided in the first bleed passage 48 is positioned so as to open the valve hole 53. The rotary shaft 17 has the throttle hole 70 for providing constant communication between the crank chamber 16 and the suction chamber 38. In this case, the flow rate of the refrigerant gas drawn from the crank chamber 16 into the suction chamber 38 depends on the diameter D2 of the communication hole 49. As described above, the diameter D1 of the throttle hole 70 is smaller than the diameter D2 of the communication hole 49 (or D1<D2). Therefore, the refrigerant gas in the crank chamber 16 is drawn rapidly into the suction chamber 38 trough the recess 44 and the crank chamber pressure PC in the crank chamber 16 is decreased accordingly rapidly, with the result that the performance of the compressor 10 to recover the displacement of the compressor 10 from the minimum displacement state is improved.

[0037] During high-speed operation of the compressor 10, the centrifugal force generated by the rotation of the rotary shaft 17 acting on the counterweight 55 is increased and the valve body 54 is moved toward the axis of the rotary shaft 17 against the urging force of the coil spring 57 until it is brought into contact with the seating surface 51, thereby to close the valve hole 53. Thus, the first bleed passage 48 provided with the valve 50 is closed and only the throttle hole 70 is opened. Accordingly, the flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38, which depends on the diameter D1 of the throttle hole 70, is decreased. However, during the operation of the compressor 10 at a high rotational speed, the inertial force acting on the piston 29 and the swash plate 23 is increased so as to principally affect the motion of the piston 29 and the swash plate 23 to change in the direction that increases the compression displacement. Thus, the desired compression displacement is achieved rapidly from the minimum displacement state despite the decrease of the flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38. In addition, the decreased flow rate of refrigerant gas circulating within the compressor 10 during its variable displacement operation means the increase of the flow rate of refrigerant gas in the external refrigeration circuit, thereby to reduce the power loss. During the OFF operation, the level of the minimum displacement of the compressor is further decreased. Thus, the power loss during the minimum displacement operation is also reduced. Fig.6 shows the valve 50 in its closed position.

[0038] In the compressor 10 of the second preferred embodiment, the first bleed passage 48 and the throttle hole 70 are both provided in the rotary shaft 17. This structure contributes to reduction in production time and cost as compared with a structure wherein the first bleed passage 48 and the throttle hole 70 are provided separately.

[0039] The following will describe a swash plate type variable displacement compressor according to the third preferred embodiment of the present invention with reference to Figs. 7 and 8. The compressor 10 of the third preferred embodiment differs from that of the second preferred embodiment in that a groove 80 corresponding to the throttle hole 70 of the second preferred embodiment is formed in the valve hole 53 of the valve 50. The rest of the structure of the compressor 10 according to the third preferred embodiment is substantially the same as that of the second preferred embodiment. For the sake of convenience of explanation, therefore, like or same parts or elements will be referred to by the same reference numerals as those which have been used in the first and second preferred embodiments, and the description thereof will be omitted.

[0040] As shown in Fig.7, in the compressor 10 according to the third preferred embodiment, the groove 80 having a certain depth is formed at the opening of the valve hole 53 of the valve 50 on the side of the seating surface 51. When the valve body 54 is in contact with the seating surface 51 by the centrifugal force, the valve body 54 and the groove 80 cooperate to form a groove slit 81. The passage hole 45 is communicated with the recess 44 through the groove slit 81 which functions as a throttle. The cross-sectional area of the groove slit 81 when the valve body 54 is in contact with the seating surface 51 is set smaller than that (D2) of the communication hole 49 and set substantially the same as that (D1) of the throttle hole 70 of the second preferred embodiment.

[0041] When the rotational speed of the rotary shaft 17 is low, the centrifugal force generated by the rotation of the rotary shaft 17 is small and the valve body 54 of the valve 50 provided in the first bleed passage 48 is positioned to open the valve hole 53. In this case, since the groove slit 81 is not formed, the flow rate of the refrigerant gas depends on the diameter D2 of the communication hole 49. Refrigerant gas is drawn from the crank chamber 16 into the suction chamber 38 rapidly and the crank chamber pressure PC in the crank chamber 16 is decreased accordingly rapidly. Thus, the recovery of the compressor 10 from the minimum displacement state is improved.

[0042] As the rotational speed of the rotary shaft 17 is increased, the centrifugal force generated by the rotation of the rotary shaft 17 is increased and the centrifugal force acting on the counterweight 55 of the valve 50 is also increased. The valve body 54 is then moved toward the axis of the rotary shaft 17 by the centrifugal force against the urging force of the coil spring 57 until it is brought into contact with the seating surface 51, thereby to close the valve hole 53. In this case, only the groove slit 81, whose diameter is smaller than that of the communication hole 49, is opened, so that the flow rate of the refrigerant gas drawn from the crank chamber 16 into the suction chamber 38 is decreased. However, during the operation of the compressor 10 at a high rotational speed, the inertial force acting on the piston 29 and the swash plate 23 is increased so as to principally affect the motion of the piston 29 and the swash plate 23 to change in the direction that increases the compression displacement. Thus, the desired compression displacement is achieved rapidly from the minimum displacement state despite the decrease of the flow rate of refrigerant gas drawn from the crank chamber 16 into the suction chamber 38. In addition, the decreased flow rate of refrigerant gas circulating within the compressor 10 during its variable displacement operation means the increase of the flow rate of refrigerant gas in the external refrigeration circuit, thereby reducing the power loss. Further, during the OFF operation, the compression displacement is decreased further than the minimum displacement. Thus, the power loss during the minimum displacement operation is also reduced. Fig.7 shows the valve 50 in its closed position.

[0043] According to the third preferred embodiment, the groove 80 is merely formed at the opening of the valve hole 53 of the valve 50. This contributes to simplified structure and further reduction in the production time and cost of the compressor 10.

[0044] The present invention is not limited to the first through third preferred embodiments, but it may be variously modified within the scope of the invention. For example, the above embodiments may be modified as exemplified below.

[0045] In the second and third preferred embodiments, the throttle hole 70 or the groove slit 81 is provided at one end of the rotary shaft 17 as a throttle. Alternatively, a fixed throttle may be formed through the plug 60 closing rear end of the passage hole 45 so that the passage hole 45 and the recess 44 are in constant communication with each other.

[0046] In the third preferred embodiment, the groove 80 is provided on the side of the seating surface 51 of the valve hole 53. Alternatively, the groove 80 may be provided on the surface of the valve body 54. Further, the valve body 54 may have an elongated hole formed therein as a throttle providing fluid communication between the passage hole 45 and the recess 44.

[0047] In the compressor 10 according to the first through third preferred embodiments, any kind of refrigerant may be used, including preferably fluorocarbon gas or carbon dioxide. Although the compressor 10 according to the foregoing embodiments have been described as a compressor for compressing refrigerant gas, the present invention does not limit the refrigerant only to gaseous refrigerant.

[0048] Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.

[0049] A swash plate type variable displacement compressor includes a crank chamber, a rotary shaft, a swash plate, a piston, a supply passage and first and second bleed passages. The supply passage connecting the crank chamber to a discharge pressure region is provided with a displacement control valve. The pressure in the crank chamber is varied by adjusting the opening of the displacement control valve. The first bleed passage connecting the crank chamber to the suction pressure region is provided with a valve. The second bleed passage constantly connecting the crank chamber to the suction pressure region is provided with a throttle. The valve operates to close the first bleed passage according to the magnitude of centrifugal force generated by the rotation of the rotary shaft.

Claims

1. A swash plate type variable displacement compressor (10) comprising:

a housing (11) including a cylinder block (12) having a cylinder bore (12A) formed therein;

a crank chamber (16) formed in the housing (11);

a rotary shaft (17) extending through the crank chamber (16), the rotary shaft (17) being rotatably supported by the housing (11);

a swash plate (23) connected to the rotary shaft (17), the swash plate (23) being integrally rotatable with and inclinable relative to the rotary shaft (17);

a piston (29) received in the cylinder bore (12A) to be reciprocally movable;

a discharge pressure region (39) for receiving discharge pressure gas;

a suction pressure region (38) for receiving suction pressure gas, and

a supply passage (42) connecting the crank chamber (16) to the discharge pressure region (39), the supply passage (42) being provided with a displacement control valve (35), wherein the pressure in the crank chamber (16) is varied by adjusting the opening of the displacement control valve (35) to change the inclination angle of the swash plate (23) thereby to control the displacement of the compressor (10),

characterized in that
a first bleed passage (48) connecting the crank chamber (16) to the suction pressure region (38), the first bleed passage (48) being provided with a valve (50),
a second bleed passage (58) constantly connecting the crank chamber (16) to the suction pressure region (38), the second bleed passage (58) being provided with a throttle (59, 70, 80),
wherein the valve (50) operates to close the first bleed passage (48) according to the magnitude of centrifugal force generated by the rotation of the rotary shaft (17).

2. The swash plate type variable displacement compressor (10) according to claim 1, wherein the first bleed passage (48) includes a passage hole (45) extending in the rotary shaft (17) along the center axis, one end of the passage hole (45) is opened to the crank chamber (16), the valve (50) is disposed at the other end of the passage hole (45).

3. The swash plate type variable displacement compressor (10) according to claim 1 or 2, wherein the second bleed passage (58) is formed separately from the first bleed passage (48), wherein the throttle (70) of the second bleed passage (58) is a fixed throttle.

4. The swash plate type variable displacement compressor (10) according to claim 1 or 2, wherein the second bleed passage (58) shares at least a part of the first bleed passage (48).

5. The swash plate type variable displacement compressor (10) according to claim 4, wherein the throttle of the second bleed passage (58) is a fixed throttle provided on the rotary shaft (17).

6. The swash plate type variable displacement compressor (10) according to claim 4, wherein the valve (50) has a valve body (54) and a valve seat (51) to contact with the valve body (54), the throttle of the second bleed passage (58) is a groove (80) which is formed on the valve seat (51).

7. The swash plate type variable displacement compressor (10) according to any one of claims 1 through 6, wherein the valve (50) includes a valve body (54), an urging member (57) urging the valve body (54) toward the opened position and a counterweight (55), wherein a centrifugal force generated by the rotation of the rotary shaft (17) acts on the counterweight (55) to move the valve body (54) toward the closed position against the urging force of the urging member (57).

8. The swash plate type variable displacement compressor (10) according to claim 6, wherein a valve hole (53) is formed on the rotary shaft (17) in the radial direction of the rotary shaft (17), wherein the valve body (54) of the valve (50) is mounted on the rotary shaft (17) to open and close the valve hole (53).

9. The swash plate type variable displacement compressor (10) according to claim 7, wherein the urging member (57) is a coil spring.

10. The swash plate type variable displacement compressor (10) according to any one of claims 1 through 9, wherein the displacement control valve (35) is an electromagnetic valve.

Drawing