Abstract:
A compressor has a refrigerant gas passage selectively connected to and disconnected from a refrigerant circuit apart from the compressor. A swash plate is supported on a drive shaft for integral rotation with inclining motion with respect to the drive shaft to drive the pistons. The swash plate is moveable between a maximum inclined angle and a minimum inclining angle. A disconnecting member disconnects the refrigerant circuit from the refrigerant gas passage when the swash plate is at the minimum inclined angle.

Description:
This application is a continuation of application Ser. No. 08/255,043, filed Jun. 7, 1994 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a swash plate type compressor that uses no electromagnetic clutch. 
     2. Description of the Related Art 
     A clutchless type compressor, as disclosed in Japanese Unexamined Patent Publication No. 3-37378, does not use any electromagnetic clutch for either the transmission or cutting of power from an external driving source to the drive shaft of the compressor. The external driving source is coupled directly to the drive shaft. 
     Not using a clutch with direct connection between the driving source and drive shaft effectively eliminate-shocks caused by the ON/OFF action of the clutch. This tends to improve the comfort level of the driver during the vehicle&#39;s operation. The clutchless structure also contributes to a reduction in the overall weight and the cost of the cooling system. 
     In such a clutchless systems the compressor runs even when no cooling is needed. With such type of compressors, it is important that when cooling is unnecessary, the discharge displacement be reduced as much as possible in order to prevent the evaporator from undergoing frosting. Likewise, under these conditions, it is also important to stop the circulation of the refrigerant gas through the compressor, and its external refrigerant circuit. 
     The compressor described in Japanese Unexamined Patent Publication No. 3-37378, for example, is designed to block the flow of gas into the compressor&#39;s suction chamber from the external refrigerant circuit by the use of an electromagnetic valve. This valve selectively allows for the circulation of the gas through the external refrigerant circuit and the compressor. When gas circulation is blocked the pressure in the suction chamber drops and the control valve responsive to that pressure opens fully. The full opening of the control valve allows the gas in the discharge chamber to flow into the crank chamber, which in turn raises the pressure inside the crank chamber. The gas in the crank chamber is then supplied to the suction chamber. Accordingly, a short circulation path in formed which passes through the cylinder bores, the discharge chamber, the crank chamber, the suction chamber and back to the cylinder bores. 
     As the pressure in the suction chamber decreases, the suction pressure in the cylinder bores falls, causing an increase in the difference between the pressure in the crank chamber and the suction pressure in the cylinder bores. This pressure differential in turn minimizes the inclination of the swash plate which reciprocates the pistons. As a result, the compressor&#39;s discharge displacement, driving torque and power loan are minimized during times when cooling is unnecessary. 
     The aforementioned electromagnetic valve performs a simple ON/OFF action to instantaneously stop the gas flow from the external refrigerant circuit into the suction chamber. Naturally, when the valve is off, the amount of gas supplied into the cylinder bores from the suction chamber decreases drastically. This rapid decrease in the amount of gas flowing into the cylinder bores likewise causes a rapid decrease in the discharge displacement and discharge pressure. Consequently, the driving torque needed by the compressor is drastically reduced over a short period of time. 
     When the electromagnetic valve switches to an on position the amount of gas supplied to the cylinder bores from the suction chamber quickly increases as does the discharge displacement and discharge pressure. Consequently, the driving torque needed by the compressor undergoes a rapid rise over a short period of time. 
     This variation in torque, however, obstructs the suppression of shocks caused by the ON/OFF action that is the primary purpose of the clutchless system. 
     In the compressor disclosed in Japanese Unexamined Patent Publication No. 3-37378, the control valve controls the displacement of the compressor in response to the suction pressure. In this respect, the control valve is located downstream of the electromagnetic valve with the suction chamber disposed therebetween. 
     When the electromagnetic valve is closed to block the gas flow into the suction chamber, the gas pressure in the suction chamber remains low. Such a low gas pressure is an unreliable indicator of the cooling load. 
     Consequently, with compressors having the above construction, should the need for cooling arise or should the suction pressure undergo a rise in response to the cooling load, the control valve can not adequately respond. To overcome this shortcoming, a pressure sensor for detecting the suction pressure is used between the evaporator and the electromagnetic valve in the conventional compressor. In response to the cooling load, the pressure sensor provides a signal to the valve assembly, causing the electromagnetic valve to open. 
     The conventional compressor however requires the above described pressure sensor an well as its interconnections in order for the compressor to operate properly. This requirement effectively increases the conventional compressor&#39;s complexity as well as its price. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary objective of the present invention to suppress shocks caused by variation in driving torque needed by a compressor. 
     It is another objective of this invention to ensure adequate lubrication in a compressor. 
     It is a further objective of this invention to provide a compressor having a simple structure. 
     It is a still further objective of this invention to provide a compressor whose discharge displacement can be accurately regulated. 
     A compressor has a coolant gas passage selectively connected and disconnected with a coolant circuit apart from the compressor. A swash plate is supported on a drive shaft for integral rotation with inclining motion with respect to the drive shaft to drive the pistons. The swash plate is moveable between a maximum inclined angle and a minimum inclined angle. A disconnecting member disconnects the coolant circuit from the coolant gas passage when the swash plate is at the minimum inclined angle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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 beat be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIGS. 1 through 8 illustrate a first embodiment of the present invention. 
     FIG. 1 is a side cross-sectional view of an overall compressor according to the first embodiment; 
     FIG. 2 is a cross section taken along the line 2--2 in FIG. 1; 
     FIG. 3 is a partial cross-sectional view showing the interior of a rear housing; 
     FIG. 4 is a side cross-sectional view of the whole compressor with its swash plate at the minimum inclined angle; 
     FIG. 5 is an enlarged fragmentary cross-sectional view showing the essential portions with a spool located at an open position; 
     FIG. 6 is an enlarged fragmentary cross-sectional view showing the essential portions with the spool located at a closed position 
     FIG. 7 is an enlarged fragmentary cross-sectional view of the essential portions, showing the spool located at the closed position with a deactivated solenoid; 
     FIG. 8A is a graph showing the results of an experiment on a variation in torque in the compressor of the present invention; and 
     FIG. 8B is a graph showing the results of an experiment on a variation in torque when the flow of a refrigerant gas into the compressor from an external refrigerant circuit is instantaneously stopped. 
     FIGS. 9 through 12 illustrate a second embodiment of the present invention. 
     FIG. 9 is a side cross-sectional view of an overall compressor according to the second embodiment; 
     FIG. 10 is a cross section taken along the line 10--10 in FIG. 9; 
     FIG. 11 is an enlarged fragmentary cross-sectional view showing the essential portions with a spool at an open position; and 
     FIG. 12 is an enlarged fragmentary cross-sectional view showing the essential portions with the spool at a closed position. 
     FIG. 13 is an enlarged fragmentary cross-sectional view showing the essential portions of another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A swash plate type variable displacement compressor according to a first embodiment of the present invention will now be described referring to FIGS. 1 through 8. 
     As shown in FIGS. 1 and 4, a front housing 2 and a rear housing 3 are secured to a cylinder block 1. The cylinder block 1, front housing 2 and roar housing 3 constitute a housing 60 of the compressor. Secured between the cylinder block 1 and the roar housing 3 are a first plate 4, a second plate 5c, a third plate 5d and a fourth plate 6. A crank chamber 2a in defined in the front housing 2 between the cylinder block 1 and the front housing 2. 
     A ball bearing 7 is attached inside the front housing 2. A drive plate 8 is supported by the inner race of the ball bearing 7, and a drive shaft 9 is secured to the drive plate 8. By means of the drive plate 8, the ball bearing 7 receives the thrust load and radial load which act on the drive shaft 9. 
     The drive shaft 9 protrudes outside the front housing 2, with a pulley 10 fixed to the protruding portion. The pulley 10 is coupled to a vehicle&#39;s engine (not shown) via a belt 11. No electromagnetic clutch intervenes between the pulley 10 and the engine. A lip seal 12 is located between the drive shaft 9 and the front housing 2 to prevent a pressure leak from the crank chamber 2a. 
     A support 14 having a convex surface is supported on the drive shaft 9 in such a way as to be slidable along the axial direction of the drive shaft 9. The support 14 supplies support to swash plate 15 and allows it to tilt at the center of support 14 where the surface of swash plate 15 is concave. 
     As shown in FIGS. 1 and 2, a pair of stays 16 and 17 are securely attached to the swash plate 15, with pins 18 and 19 respectively secured to the stays 16 and 17. 
     The drive plate 8 has a protruding arm 8a in which a hole 8c is formed extending in the direction perpendicular to the axis of the drive shaft 9. A pipe-shaped connector 20, rotatable about its axis, is inserted in the hole 8c. A pair of holes 20a are formed in the cylindrical wall of the connector 20, and the pine 18 and 19 are slidably fitted in the respective holes 20a. 
     The swash plate 15 rotates together with the drive plate 8 by the coupling of the pine 19 and 19 to the connector 20, i.e., the swash plate 15 rotates with the drive shaft 9. When the swash plate 15 tilts, the connector 20 rotates about its axis and the pins 18 and 19 move in the holes 20a along their axes. 
     As shown in FIGS. 1, 4 and 5, a retainer hole 13 is formed in the center of the cylinder block 1 and extends along the axis of the drive shaft 9. A cylindrical spool 21 in retained slidable in the retainer hole 13. A flange 13a is formed on the inner wall of the retainer hole 13. A step 21c is formed at the outer wall of the spool 21. A spring 36 is disposed between the step 21c and the flange 13a to press the spool 21 toward the support 14. 
     The drive shaft 9 is fitted inside the spool 21. The drive shaft 9 is pressed via a ball 41 by a spring 42 which suppresses the movement of the drive shaft 9 in the thrust direction. A ball bearing 53 is located between the drive shaft 9 and the spool 21. The drive shaft 9 is supported on the inner wall of the retainer hole 13 via the ball bearing 53 and spool 21. The ball bearing 53 has an outer race 53a secured to the inner wall of the spool 21, and has an inner race 53b which is slidable on the outer surface of the drive shaft 9. 
     As shown in FIGS. 5 to 7, a restricting surface 55 is formed at the bottom of the retainer hole 13 of the spool 21. A step 9a (see FIGS. 6 and 7) is formed at the outer surf ace of the drive shaft 9. The spool 21 is movable between the position where it abuts the restricting surface 55 and the position where the inner race 53b of the ball bearing 53 abuts on the step 9a. 
     As shown in FIGS. 1, 3 and 4, a suction chamber 3a and a discharge chamber 3b are defined in the rear housing 3. A suction passage 54 is formed in the center of the rear housing 3 and communicates with the bottom of the retainer hole 13. Because the spool 21 abuts on the restricting surface 55, communication between the suction passage 54 and the retainer hole 13 is obstructed. The suction chamber 3a is connected via a passage 4c to the retainer hole 13. 
     When the spool 21 abuts the restricting surface 55, communication between the passage 4c and the suction passage 54 is obstructed. The suction passage 54, as illustrated is an inlet through which gas is supplied into the compressor. Additionally, when the spool 21 abuts surface 55, communication between the suction passage 54 and the retainer hole 13 is blocked. In case of either obstruction, the spool 21 is located at the downstream portion of the passage 54. 
     A pipe 56 is slidably provided on the drive shaft 9 between the support 14 and the ball bearing 53. An the support 14 moves toward the spool 21, the inner race 53b of the ball bearing 53 is pushed via the pipe 56 as shown in FIGS. 6 and 7. Consequently, the spool 21 moves toward the restricting surface 55 against the force of the spring 36. 
     The minimum inclined angle of the swash plate 15 is determined by the abutment of the spool 21 on the restricting surface 55. The minimum inclined angle of the swash plate 15 in slightly larger than 0 degree with respect to a plane perpendicular to the drive shaft 9. The maximum inclined angle of the swash plate 15 is determined by the abutment of a projection 8b of the drive plate 8 on the swash plate 15. 
     Pistons 22 are respectively placed in a plurality of cylinder bores 1a formed in the cylinder block 1. A pair of shoes 23 are fitted in a neck 22a of each piston 22. The swash plate 15 is placed between both shoes 23. The undulating movement of the swash plate 15, caused by the rotation of the drive shaft 9 is transmitted via the shoes 23 to each pistons 22. This causes linear reciprocation of the pistons 22. 
     As shown in FIGS. 1 and 3, an inlet port 4a and a discharge port 4b are formed in the first plate 4. An inlet valve 5a is provided on the second plate 5c, and a discharge valve 5b is provided on the third plate 5d. 
     The gas in the suction chamber 3a pushes the inlet valve 5a and enters the cylinder bore 1a through the inlet port 4a in accordance with the backward movement of the piston 22. The gas that has entered the cylinder bore 1a is compressed by the forward movement of the piston 22, and in then discharged to the discharge chamber 3b via the discharge port 4b while pushing the discharge valve 5b. Any excessive opening motion of the discharge valve 5b is inhibited by a retainer 6a on the fourth plate 6. 
     The suction passage 54 and a discharge port 1c, from which the gas from the discharge chamber 3b is discharged, are connected by an external refrigerant circuit 49. Provided in the circuit 49 are a condenser 50, an expansion valve 51 and an evaporator 52. The expansion valve 51 controls the amount of flowing gas in accordance with a change in gas pressure on the outlet side of the condenser 50. The pressure in the passage from the evaporator 52 to the cylinder bores 1a is a low value close to the suction pressure. 
     The inclined angle of the swash plate 15 varies in accordance with the changing pressure differential between the pressure in the crank chamber 2a and the suction pressure in each cylinder bore 1a. As the inclined angle of the swash plate 15 varies, the stroke of the piston 22 changes, thus changing the displacement of the compressor. The pressure in the crank chamber 2a is controlled by a displacement control valve 24 attached to the rear housing 3. The crank chamber 2a is connected to the suction chamber 3a via a passage 1b that has the function of a restriction. 
     The structure of the displacement control valve 24 will be described below with reference to FIGS. 5 through 7. A guide cylinder 27 is fixed to the hollow portion of a bobbin 26 that supports a solenoid 25. A fixed iron core 28 it fixed inside the guide cylinder 27. A movable iron core 29 in placed in the guide cylinder 27. A spring 30 is placed between the fixed core 28 and the movable core 29. The movable core 29 is urged away from the fixed core 28 by the force of the spring 30. 
     A valve housing 31A is secured via a block 32 to the bobbin 26. First and second chambers 61 and 43 are defined in the valve housing 31A, and are connected together by a passage 31d. A spherical valve assembly 33 is placed in the first chamber 61 that has a seat 38 secured thereto. A hole 38a, through which gas passes, is formed in the seat 38. A spring 39 and a seat 40 are provided between the seat 38 and the valve assembly 33. The valve assembly 33 receives the force of the spring 39 that acts in the direction to close the passage 31d. 
     A metal bellows 44, having an air tight interior, is disposed in the second chamber 43, and is fixed to the movable core 29. A plate 45 is fixed to the bellows 44 which in urged to expand by spring 47. A rod 48 is provided between the plate 45 and the valve assembly 33. 
     A first port 31a is formed in the first chamber 61, and a second port 31b is formed in the second chamber 43. A third port 31c is formed in the passage 31d. The first port 31a is connected via a passage 34 to the discharge chamber 3b. The second port 31b 1a connected via a passage 35 to the suction passage 54 at the upstream of the spool 21. The third port 31c is connected via a passage 37 to the crank chamber 2a. 
     The solenoid 25 is controlled by a computer 93. The computer 93 activates the solenoid 25 when an air conditioning switch 57 for activating an air conditioner is turned on or when an accelerator switch 58 is turned off. The computer deactivates the solenoid 25 when the air conditioning switch 57 in turned off or when the accelerator switch 58 is turned on. The accelerator switch 58 is turned on when the acceleration pedal in thrust down to increase the engine speed. The accelerator switch 58 is provided to improve the fuel economy. 
     In FIGS. 5 and 6, the solenoid 25 is excited. With the solenoid 25 excited, the movable core 29 is attracted to the fixed core 28 against the force of the spring 30, as shown in FIG. 5. In FIG. 7, the solenoid 25 is deactivated, With the solenoid 25 deactivated, the movable core 29 is separated from the fixed core 28 due to the force of the spring 30. 
     With the solenoid 25 activated, the movable core 29 is attracted to the fixed core 28, and the control valve 24 functions as follows. When the suction pressure of the gas, which is supplied via the passage 35 to the second chamber 43 from the suction passage 54, is high the bellows 46 contracts. This occurs when the cooling load is high. The contracting motion is transmitted via the rod 48 to the valve assembly 33 so that the valve assembly 33 moves in a direction that reduces the amount with which the displacement control valve 24 opens. 
     With a small opening of the valve 24, the amount of gas flowing into the crank chamber 2a from the discharge chamber 3b via the passage 34, first port 31a, hole 38a, passage 31d, third port 31c and passage 37 decreased. Consequently, the pressure in the crank chamber 2a falls. 
     When the cooling load is high, the suction pressure in the cylinder bores 1a is high. This decreases the difference between the pressure in the crank chamber 2a and the suction pressure in the cylinder bores 1a. As a result, the inclined angle of the swash plate 15 increases an shown in FIGS. 1 and 5. 
     When the suction pressure is low or the cooling load in low, the bellows 46 expands. Consequently, the valve assembly 33 moves in the opening direction to increase the amount of gas flowing into the crank chamber 2a from the discharge chamber 3b. This raises the pressure in the crank chamber 2a. 
     When the cooling load is low, the suction pressure in the cylinder bores 1a is low so that the difference between the pressure in the crank chamber 2a and the suction pressure in the cylinder bores 1a increases. As a result, the inclined angle of the swash plate 15 becomes smaller. 
     When the suction pressure becomes very low or when the cooling load does not exist, the valve assembly 33 approaches the maximum opening position as shown in FIG. 6. When the air conditioning switch 57 in turned off or the accelerator switch 58 in turned on to deactivate the solenoid 25, the movable core 29 moves away from the fixed core 28 due to the force of the spring 30. This causes the valve assembly 33 to move to the maximum opening position as shown in FIG. 7. 
     In the maximum open state as shown in FIG. 7 or in a state close to the maximum open state as shown in FIG. 6, a large amount of the gas in the discharge chamber 3b flows into the crank chamber 2a. The pressure in the crank chamber 2a therefore rises to the maximum level, and the swash plate 15 moves toward the minimum inclination. 
     As the swash plate 15 moves toward the minimum inclination, the support 14 moves toward the spool 21, causing the pipe 56 to push the inner race 53b of the ball bearing 53. As a result, the spool 21 moves toward the restricting surface 55. 
     The approach of the spool 21 to the restricting surface 55 restricts the area of the gas-passing cross section between the suction passage 54 and the suction chamber 3a. This restriction reduces the amount of gas flowing into the suction chamber 3a from the suction passage 54. The amount of the gas supplied into the cylinder bores 1a from the suction chamber 3a also decreases, thus reducing the discharge displacement. An a result, the discharge pressure falls, reducing the driving torque-needed by the compressor. 
     Even If the valve assembly 33 is moved to the opening position and a large Amount of gas in the discharge chamber 3b enters the crank chamber 2a, there is a certain amount of time that it takes to increase the pressure in the crank chamber 2a. Thus, the swash plate 15 gradually moves toward the minimum inclination. Likewise, the change in the discharge displacement of the compressor will not experience rapid changes and the driving torque needed by the compressor. It is therefore possible to prevent a large change in the compressor&#39;s torque. 
     When the small-diameter portion, 21b, of the spool 21 abuts on the restricting surface 55, the gas flow to the suction chamber 3a from the external refrigerant circuit 49 is blocked and the swash plate 15 moves to a minimum inclined angle. 
     Since the angle of the swash plate 15 is not 0 degrees at this time, the piston 22 reciprocates even in this condition to discharge the gas to the discharge chamber 3b from the associated cylinder bore 1a. With the gas flow to the suction chamber 3a from the external refrigerant circuit 49 so blocked, the gas discharged to the discharge chamber 3b from the associated cylinder bore 1a flows into the crank chamber 2a via the path of the passage 34, port 31a, hole 38a, port 31c and passage 37. The gas in the crank chamber 2a enters the suction chamber 3a via the restricting passage 1b. The gas in the suction chamber 3a is supplied to the cylinder bores 1a and is discharged to the discharge chamber 3b. 
     With the swash plate 15 at a minimum inclined angle, a short gas circulation circuit consisting of the cylinder bore 1a, discharge chamber 3b, passage 34, control valve 24, passage 37, crank chamber 2a, passage 1b, suction chamber 3a and cylinder bore 1a is formed in the compressor. Thus, the movable portions, such as the ball bearings in the compressor, are lubricated with the lubricating oil suspended in the circulating gas, ensuring the adequate continuous operation of the compressor. 
     As the gas circulates through the circulation circuit, having the restrictions explained above, there are pressure differences which are created among the discharge chamber 3b, crank chamber 2a and suction chamber 3a. The gas inside the compressor will not flow out to the external refrigerant circuit 49. Consequently, the frosting of the evaporator 52 is unlikely. 
     Since the pipe 56 is held between the support 14 and the inner race 53b, the pipe 56 rotates with the drive shaft 9. Due to the contact between the pipe 56 and the inner race 53b of the ball bearing 53, the drive shaft 9, support 14, pipe 56 and inner race 53b rotate together, causing no friction among the support 14, pipe 56 and inner race 53b. 
     When the suction pressure rises due to an increase in cooling, load, the increased suction pressure is transmitted to the second chamber 43 via the suction passage 54 and passage 35. Consequently, the bellows 46 contracts and the valve assembly 33 closes the passage 31d. When the air conditioning switch 57 is turned on or the accelerator switch 58 is turned off on the other hand, the solenoid 25 in activated, causing the movable core 29 to be attached to the fixed core 28. The bellows 46 and the rod 48, therefore, move together with the movable core 29, causing the valve assembly 33 to move in the direction to obstruct the passage 31d due to the force of the spring 39. 
     When the valve assembly 33 blocks the passage 31d, the path from the discharge chamber 3b to the crank chamber 2a is closed. Consequently, the pressure in the crank chamber 2a gradually decreases, moving the swash plate 15 to a maximum inclined angle from a minimum inclined angle. 
     The movement of the swash plate 15 causes the support 14 to move in the same direction. Due to the force of the spring 36, the spool 21 moves in response to the movement of the support 14. As a result, the distal end of the spool 21 moves away from the restricting surface 55. 
     The separation of the spool 21 increase the cross sectional area of the passage between the suction passage 54 and the suction chamber 3a. The increased cross-sectional area increases the amount of gas that can flow into the suction chamber 3a from the suction passage 54. Accordingly, the amount of the gas supplied into the cylinder bores 1a from the suction chamber 3a also increases, thus increasing the discharge displacement. As a result, the discharge pressure rises, increasing the driving torque needed by the compressor. 
     Even in this case, the rising of the pressure in the crank chamber 2a taken place gradually, and the swash plate 15 moves toward the maximum inclination gradually. The increase of the discharge pressure changes slowly, thus eliminating the need for quick changes to be made to the torque needed by the compressor. It is therefore possible to prevent shocks caused by a large change in torque from occurring in the compressor. 
     FIG. 8A presents a graph showing the results of an experiment on variations made to the torque of the compressor according to this embodiment. A curve 100 is a torque variation curve, a curve 101 represents a change in pressure in the suction chamber 3a, a curve 102 represents a change in pressure in the discharge chamber 3d, and a curve 103 represents a change in pressure in the crank chamber 2a. The horizontal scale α represents the time, the vertical scale β represents the pressure and the vertical scale γ represents the torque. In this graph, the deactivated solenoid 25 is activated at time η. 
     The graph in FIG. 8B shows the results of an experiment on a variation in torque when the flow of the refrigerant gas into the suction passage 54 from the external refrigerant circuit 49 in the compressor of this embodiment is completely obstructed at time η. 
     The action of restricting the supply of the intake gas in the compressor disclosed in Japanese Unexamined Patent Publication No. 3-37378 in the same as that where the flow of the refrigerant gas into the suction passage 54 from the external refrigerant circuit 49 in completely obstructed. A curve 100&#39; is a torque variation curve, a curve 101&#39; represents a change in pressure in the suction chamber 3a, a curve 102&#39; represents a change in pressure in the discharge chamber 3d, and a curve 103&#39; represents a change in pressure in the crank chamber 2a. 
     It is apparent from the comparison between the two graphs that the change in the discharge pressure curve 102 immediately after time η is smaller and gentler than that in the discharge pressure curve 102&#39;. Likewise, the change in the torque variation curve 100 immediately after time η is smaller and gentler than that in the torque variation curve 100&#39;. 
     It is apparent from the experimental results that the changes in driving torque and shocks originating therefore in compressors according to the present invention is a vast improvement over that of the compressor as disclosed in Japanese Unexamined Patent Publication No. 3-37378. In the No. 3-37378 publication, when the electromagnetic valve is deactivated, the pressure in the suction chamber remains low and the refrigerant gas in the suction chamber is not indicative of the cooling load. A pressure sensor for detecting the suction pressure 1a thus provided between the evaporator and the electromagnetic valve in the conventional compressor. 
     According to this embodiment, by contrast, the suction-pressure introducing position of the displacement control valve 24a, which responds to the suction pressure, is located upstream of the position at which the gas flow is blocked by the spool 21. The control valve 24a can thus always respond to a change in cooling load. When the cooling load is produced and the suction pressure rises, the control valve 24a instantaneously responds to the rise in suction pressure, consequently the inclined angle of the swash plate 15 increases from a minimum inclined angle unless the solenoid 25 is deactivated. 
     In short, the compressor according to this embodiment needs no pressure sensor between the evaporator and the electromagnetic valve and thus has a simpler structure than conventional compressors. 
     A second embodiment of the present invention will now be described referring to FIGS. 9 through 12. 
     The second embodiment does not have the passage 1b provided between the suction chamber 3a and the crank chamber 2a. 
     A passage 59 formed in the axial position of the delve shaft 9, has an inlet port 59a open to the crank chamber 2a in the vicinity of the lip seal 12, and an outlet port 59b open to the area where the spool 21 slides in contact with the drive shaft 9. The opening of the passage 59 at one end of the drive shaft 9 is closed by the ball 41 and spring 42. 
     As shown in FIG. 9, an annular passage 80 is formed in the inner wall of the spool 21, and the outlet port 59b of the passage 59 is always connected to the passage 80 in the spool 21. 
     Formed in the vicinity of the step 21c of the spool 21 is a passage 64 penetrating through the spool 21. The passage 64 allows the passage 80 to communicate with the retainer hole 13. The retainer hole 13 and the passage 4c are connected together via a restricting passage 62. The outlet port of the restricting passage 62 is located downstream of the restricting surface 55. 
     In other words, the crank chamber 2a communicates with the suction chamber 3a via a passage 63 formed by the passages 59, 80, and 64, the retainer hole 13 and the restricting passage 62. The gas in the crank chamber 2a flows out into the suction chamber 3a via the passage 63. The cross-sectional area of the restricting passage 62, which constitutes a part of the passage 63, is smaller than the cross-sectional areas of the passages 59, 80 and 64 The gas flow undergoes a restriction in the restricting passage 62. 
     The outlet port of the control passage 37 is directed to the peripheral portion of the swash plate 15. 
     When the inclined angle of the swash plate 15 is at a minimum, a circulatory system is formed among the cylinder bore 1a, the discharge chamber 3b, the passage 34, the passage in the control valve 24, the passage 37, the crank chamber 2a, the passage 63, the suction chamber 3a, and the cylinder bore 1a. 
     To properly control the inclined angle of the swash plate 15, the pressure in the crank chamber 2a should be set to the proper level. This requires that the amount of gas flowing into the suction chamber 3a from the passage 63 be accurately regulated. The amount of the gas flow is regulated by the restricting passage 62 which is a part of the pressure discharge passage 63. If gas leaks in somewhere in the pressure discharge passage 63, however, the inclined angle of the swash plate 15 cannot be controlled properly. 
     The gas leak from the pressure discharge passage 63 is likely to occur at the clearance between the outer surface of the drive shaft 9 and the inner wall of the spool 21. To prevent the gas leakage, the outer surface of the drive shaft 9 should contact the inner wall of the spool 21 as closely as possible. This structure increases the friction between the drive shaft 9 and the spool 21. In the clutchless compressor, the drive shaft 9 keeps rotating unless the external driving source is stopped. The large friction between the drive shaft 9 and the spool 21 thus causes wearing or burning therebetween. 
     If burning occurs between the drive shaft 9 and the spool 21, the spool 21 cannot slide, disabling the control on the inclined angle of the swash plate 15. If the drive shaft 9 and the spool 21 wear out, the gas leakage from the pressure discharge passage 63 increases no that the inclined angle of the swash plate 15 in turn cannot be accurately controlled. 
     According to the second embodiment, when the spool 21 does not abut the restricting surface 55, the open position, the gas in the crank chamber 2a flows into the suction chamber 3a via the pressure discharge passage 63. When the spool 21 abuts the restricting surface 55, the gas in the discharge chamber 3b circulated through the passage 34, control valve 24, control passage 37, crank chamber 2a, passage 63, suction chamber 3a and cylinder bore 1a and returns to the discharge chamber 3b. The passage 80 which is a part of the passage 63 is located in the slidable area between the drive shaft 9 and the spool 21. This slidable area is lubricated with the lubricating oil that flows together with the gas. 
     Therefore, the wearing or burning of the drive shaft 9 and the spool 21 in prevented. 
     The lubricating oil enters between the drive shaft 9 and the spool 21 to enhance the sealing therebetween, so that the gas leakage from between the drive shaft 9 and the spool 21 is prevented. The adequate lubrication of the slidable area between the drive shaft 9 and the spool 21 contributes to the smooth sliding of the spool 21. This promotes smooth gas flow restriction and increasing of the cross-sectional area of the restricting passage 62. 
     In addition, due to the fact that the retainer hole 13 is a part of the passage 63 and that the slidable area between the spool 21 and the cylinder block 1 is lubricated with oil carried along with the refrigerant gas, the sliding action of the spool 21 becomes smoother. 
     According to the second embodiment, as described above, the wearing or burning of the drive shaft 9 and spool 21 can be prevented and the smooth movement of the spool 21 is enhanced so that the inclined angle of the swash plate 15 can be more accurately controlled. An enhanced compressor displacement control is therefore possible. 
     Since the inlet port 59a of the passage 63 is located near the lip seal 12, the lubricating oil, and refrigerant gas flowing through the passage 63 improves the sealing performance of the lip seal 12. Moreover, since the outlet port of the control passage 37 in directed to the peripheral portion of the swash plate 15, the gas flowing into the crank chamber 2a from the passage 37 hits the sliding portions between the swash plate 15 and the shoes 23. The gas thereby lubricates these sliding portions. 
     Although only two embodiments of the present invention have been described herein, 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 following modes are to be applied. 
     (1) The support and the spool may be integrated. 
     (2) To effect the shifting of the spool between the position where a passage from the external refrigerant circuit to the suction chamber in closed and the position where that passage is opened, the pressure in the crank chamber may directly act on the spool. That is the spool may be shifted in accordance with the difference between the pressure in the crank chamber and the suction pressure, rather than the inclined angle of the swash plate. 
     (3) An embodiment as shown in FIG. 13 may be worked out. In this embodiment, the passage 80 in the inner wall of the spool 21 communicates with the clearance between the outer race 53a and inner race 53b of the ball bearing 53. This allows oil communication without the need of the passage 59 in the drive shaft 9. The gas in the crank chamber 2a flows into the passage 80 through the clearance between the outer race 53a and inner race 53b. The slidable area between the drive shaft 9 and the spool 21 can be lubricated sufficiently as per the previous embodiments, however, this embodiment ensures better lubrication of the ball bearing 53 than the previous embodiments. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention in not to be limited to the details given herein, but may be modified within the scope of the appended claims.