Control apparatus for variable displacement compressor

Abstract: A swash plate tiltably supported on a drive shaft is controlled by adjusting the pressure in a crank chamber. When an electromagnetic valve is de-excited, the high-pressure refrigerant gas in a discharge chamber is supplied to the crank chamber so that the inclination angle of the swash plate is shifted to its minimum inclination from its maximum inclination. An open/close mechanism located in a suction passage opens or closes the suction passage in accordance with the differential pressure between the pressure in the external refrigeration circuit located upstream the open/close mechanism and the pressure in a suction chamber. When the inclination angle of the swash plate is minimized, the open/close mechanism closes the suction passage. It is therefore possible to prevent frosting while also suppressing rapid changes in load torque.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a displaceable compressor according to the preamble of claim 1. Description of the Related Art Ordinary compressors have a clutch, e.g., an electromagnetic clutch, provided between the drive shaft and an external driving source to permit or block power transmission. Recently, a clutchless variable displacement type rocking swash plate compressor which uses no electromagnetic clutch has been proposed. This type of compressor, particularly when mounted on a vehicle, removes shocks produced by the ON/OFF action of the electromagnetic clutch, thus eliminating passenger discomfort. This clutchless structure also reduces the overall weight and cost. Such a clutchless compressor, however, fails to cope with a change in discharge displacement when no cooling is needed and with the occurrence of frosting in the evaporator in the external refrigeration circuit. To overcome those problems, the circulation of the refrigerant gas through the external refrigeration circuit should simply be stopped when no cooling is needed. Japanese Unexamined Patent Publication No. Hei 3-37378 discloses a compressor which is designed to block the flow of refrigerant gas into the suction chamber from the external refrigeration circuit, thereby stopping the circulation of the refrigerant in the external refrigeration circuit. When the circulation of the gas from the external refrigeration circuit to the suction chamber in this compressor is blocked, the pressure in the suction chamber drops and the displacement 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 reduced pressure in the suction chamber also reduces the suction pressure in the cylinder bores. Therefore, the difference between the pressure in the crank chamber and the suction pressure in the cylinder bores increases to minimize the inclination of the swash plate. As a result, the discharge displacement becomes minimum. At this time, the driving torque needed by the compressor is minimized, thus reducing power loss as much as possible when no cooling is needed. The flow of the refrigerant gas toward the suction chamber in the compressor from the external refrigeration circuit is blocked by closing an electromagnetic valve. This electromagnetic valve performs a simple ON/OFF action, and the checking of the gas flow from the external circuit to the suction chamber is executed spontaneously. Accordingly, the amount of gas led into the cylinder bores from the suction chamber decreases drastically. The rapid reduction in the amount of gas led into the cylinder bores quickly reduces the discharge displacement, causing the discharge pressure to fall sharply. Consequently, the torque needed by the compressor varies in a short period of time. Further, the gas flow from the external circuit to the suction chamber restarts also instantaneously when the electromagnetic valve is opened. The amount of gas supplied into the cylinder bores from the suction chamber increases rapidly. This sharp increase in the amount of refrigerant gas promptly increases the discharge displacement, raising the discharge pressure. Consequently, the torque needed by the compressor sharply rises in a short period of time, causing shock. US-A-5 074 123 discloses a generic displaceable compressor which comprises a suction port and a discharge port, said suction port and said discharge port being connectable with each other by way of a refrigeration fluid passage to suck fluid introduced into the refrigeration fluid passage through the suction port and to discharge compressed fluid from the discharge port to the refrigeration fluid passage, wherein the refrigeration fluid passage has external refrigeration circuit elements, wherein the fluid circulating in the refrigeration fluid passage changes pressure thereof. US-A-5 173 032 discloses a similar displaceable compressor. It is the object of the present invention suppressing a variation in torque in a displaceable compressor. According to the invention, this problem is solved by the displaceable compressor having the features of claim 1. The invention is further developed as it is defined in the dependent claims. 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 best be understood by reference to the following description of the presently preferred embodiment together with the accompanying drawings in which: Fig. 1 is a side cross-sectional view showing the overall structure of a clutchless variable displacement compressor according to a first embodiment of the present invention; Fig. 2 is a cross-sectional view taken along the line 2-2 in Fig. 1; Fig. 3 is a cross-sectional view taken along the line 3-3 in Fig. 1; Fig. 4 is a side cross-sectional view of the whole variable displacement compressor whose swash plate is at the minimum inclined angle; Fig. 5 is an enlarged side cross-sectional view of the essential parts of the compressor whose swash plate is at the maximum inclined angle; Fig. 6 is an enlarged side cross-sectional view of the essential parts of the compressor whose swash plate is at the minimum inclined angle; Fig. 7 is an enlarged side cross-sectional view of the essential parts of another embodiment; Fig. 8 is a side cross-sectional view of the essential parts of a different embodiment; Fig. 9 is a side cross-sectional view of the essential parts of a further embodiment; Fig. 10 is a side cross-sectional view showing the overall structure of a clutchless variable displacement compressor according to a still further embodiment; Fig. 11 is a side cross-sectional view of the essential parts of the compressor whose swash plate is at the minimum inclined angle; Fig. 12 is a side cross-sectional view showing the overall structure of a variable displacement compressor with a clutch according to yet another embodiment; and Fig. 13 is a side cross-sectional view of the essential parts of yet another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the present invention will be now described with reference to Figs. 1 through 6. As shown in Fig. 1, a front housing 12 is secured to the front end of a cylinder block 11, which is a part of the housing of the compressor. A rear housing 13 is secured to the rear end of the cylinder block 11 via a valve plate 14, valve-forming plates 15 and 16, and a retainer-forming plate 17. The front housing 12 and the cylinder block 11 define a crank chamber 12-1 which serves as a control pressure chamber. A drive shaft 18 is rotatably supported between the front housing 12 and the cylinder block 11. The front end of the drive shaft 18 protrudes outside the crank chamber 12-1, with a driven pulley 19 secured to,this front end. The driven pulley 19 is coupled to a vehicle's engine (not shown) via a belt 20. The engine serves as the driving source for supplying the rotational driving force to the compressor. The driven pulley 19 is supported on the front housing 12 via an angular bearing 21. Between the front end of the drive shaft 18 and the front housing 12 is a lip seal 22 which prevents the pressure leakage from the crank chamber 12-1. A rotational support 23 is attached to the drive shaft 18 on which a swash plate 24 is supported in such a way as to be slidable and tiltable in the axial direction of the drive shaft 18. As shown in Fig. 2, stays 25 and 26 are secured to the swash plate 24, with a pair of guide pins 27 and 28, respectively, secured to the stays 25 and 26. Guide balls 27-1 and 28-1 are formed at the distal ends of the guide pins 27 and 28. A support arm 23-1 extends from the rotational support 23. The support arm 23-1 has a pair of guide holes 23-2 and 23-3 in which the guide balls 27-1 and 28-1 are slidably fitted. As shown in Figs. 1, 4 and 5, a support hole 29 is formed in the center portion of the cylinder block 11 in the axial direction of the drive shaft 18. One end of the drive shaft 18 is rotatably supported in the support hole 29 via a radial bearing 30. The coupling of the support arm 23-1 and the guide pin pair 27 and 28 allows the swash plate 24 to incline in the axial direction of the drive shaft 18 and rotate together with the drive shaft 18. The inclination of the swash plate is determined by the support arm 23-1, the guide pins 27 and 28 and the drive shaft 18. The minimum inclined angle of the swash plate 24 is slightly greater than zero degrees. This minimum inclination state is established by the abutment of the swash plate 24 against a position restricting ring 31 which serves as minimum inclination restricting means. The maximum inclined angle of the swash plate 24 is restricted by the abutment of an inclination restricting projection 23-4 of the rotational support 23 on the swash plate 24. A plurality of cylinder bores 11-1 which communicate with the crank chamber 12-1 are formed through the cylinder block 11, and single-headed pistons 32 are retained in the respective cylinder bores 11-1. Rotational motion of the swash plate 24 is converted to forward and backward movement of the single-headed pistons 32 via shoes 33, so that the pistons reciprocate in the associated cylinder bores 11-1. As shown in Figs. 1 and 3, a suction chamber 13-1 and a discharge chamber 13-2 are defined in the rear housing 13. Suction ports 14-1 and discharge ports 14-2 are formed in the valve plate 14. Suction valves 15-1 are formed on the valve-forming plate 15, and discharge valves 16-1 on the valve-forming plate 16. As the single-headed pistons 32 move backward, the refrigerant gas in the suction chamber 13-1 forces the suction valves 15-1 open through the suction ports 14-1 and enters the cylinder bores 11-1. As the pistons 32 move forward, the refrigerant gas in each cylinder bore 11-1 forces the associated discharge valve 16-1 open through the associated discharge port 14-2 and enters the discharge chamber 13-2. As each discharge valve 16-1 abuts on a retainer 17-1 on the retainer-forming plate 17, the amount of opening of the associated discharge port 14-2 is restricted. A thrust bearing 34 is located between the rotational support 23 and the front housing 12. This thrust bearing 34 receives the compressive reaction force from the cylinder bores 11-1 that acts on the rotational support 23 via the single-headed pistons 32, shoes 33, the swash plate 24, the stays 25 and 26 and the guide pins 27 and 28. The drive shaft 18 has a pressure release passage 35 formed inside, which communicates with the crank chamber 12-1 and the support hole 29. The support hole 29 and the suction chamber 13-1 communicate with each other via a restriction passage 36. As shown in Figs. 1 and 4, the discharge chamber 13-2 and the crank chamber 12-1 communicate with each other via a pressure supply passage 37 in which an electromagnetic valve 38, which forcibly restricts the inclination of the swash plate, is located. The electromagnetic valve 38 has a solenoid 38-1 and a valve body 38-2. When the solenoid 38-1 is excited, the valve body 38-2 closes a valve hole 38-3, and when the solenoid 38-1 is de-excited, the valve body 38-2 opens the valve hole 38-3. That is, the electromagnetic valve 38 opens and closes the pressure supply passage 37 that allows the discharge chamber 3-2 and the crank chamber 12-1 to communicate with each other. A suction passage 39 for leading the refrigerant gas into the suction chamber 13-1 is connected to a discharge passage 11-2 for discharging the refrigerant gas from the discharge chamber 13-2 by an external refrigeration circuit 40. Located in the external refrigeration circuit 40 are a condenser 41, an expansion valve 42 and an evaporator 43. The expansion valve 42 controls the flow of the refrigerant gas in accordance with the gas pressure on the outlet side of the evaporator 43. A temperature sensor 44 is provided in the vicinity of the evaporator 43 to sense the temperature in the evaporator 43. The information on the detected temperature is sent to a control computer C. The control computer C, which is the refrigerant circulation controller, controls the excitation and de-excitation of the solenoid 38-1 based on the temperature detected by the temperature sensor 44. When the detected temperature falls to or below a set temperature, the control computer C instructs the de-excitation of the solenoid 38-1 while an air-conditioner activation switch 45 is set ON. The set temperature is set on the reflection of the situation where frosting may occur in the evaporator 43. An open/close mechanism 46 is provided in the suction passage 39. A valve body 46-2 in a valve housing 46-1 is urged in the direction to close a valve hole 46-4 by means of an adjusting spring 46-3. The valve body 46-2 separates the interior of the valve housing 46-1 into a compression-sensing chamber 46-5 and a leading chamber 46-6. The compression-sensing chamber 46-5 communicates with the suction chamber 13-1, and the leading chamber 46-6 communicates with the external refrigeration circuit 40. The pressure inside the compression-sensing chamber 46-5 and the elastic force of the adjusting spring 46-3 are applied to the compression-sensing chamber (46-5) side of the valve body 46-2, and the pressure inside the leading chamber 46-6 is applied to the leading chamber (46-6) side of the valve body 46-2. The valve body 46-2 opens or closes the valve hole 46-4 in accordance with the pressure difference between the urging force on the compression-sensing chamber (46-5) side and the urging force on the leading chamber (46-6) side. As shown in Figs. 1 and 5, when the solenoid 38-1 is excited, the pressure supply passage 37 is closed. Therefore, the high-pressure refrigerant gas is not supplied to the crank chamber 12-1 from the discharge chamber 13-2, and the refrigerant gas inside the crank chamber 12-1 flows out to the suction chamber 13-1 via the pressure release passage 35 and the restriction passage 36. As a result, the pressure in the crank chamber 12-1 approaches the pressure inside the suction chamber 13-1 or the suction pressure, and the inclination of the swash plate 24 is kept maximum to ensure the maximum discharge displacement. The pressure in the leading chamber 46-6 which communicates with the external refrigeration circuit 40 located upstream the suction passage 39 is greater than the pressure in the compression-sensing chamber 46-5 which communicates with the suction chamber 13-1 located downstream the suction passage 39. The greater the discharge displacement becomes, the greater the amount of refrigerant gas flowing in the external refrigeration circuit 40 becomes and the larger the difference between the pressure in the external refrigeration circuit 40 located upstream the suction passage 39 and the pressure in the suction chamber 13-1 located downstream the suction passage 39 becomes. With a large discharge displacement, the pressure in the leading chamber 46-6 is greater than the sum of the pressure in the compression-sensing chamber 46-5 and the elastic force of the adjusting spring 46-3, so that the valve body 46-2 opens the valve hole 46-4. When the electromagnetic valve 38 is excited, the circulation of the refrigerant gas in the external refrigeration circuit 40 is permitted. When the swash plate 24 keeps the maximum inclination with a low cooling load to effect the discharging action, the temperature in the evaporator 43 approaches the level at which frosting occurs. The temperature sensor 44 has sent the information of the detected temperature in the evaporator to the control computer C. When the detected temperature becomes equal to or lower than the set temperature, the control computer C instructs the de-excitation of the solenoid 38-1. When the solenoid 38-1 is de-excited, the pressure supply passage 37 is open, connecting the discharge chamber 13-2 to the crank chamber 12-1. Therefore, the high-pressure refrigerant gas in the discharge chamber 13-2 is supplied via the pressure supply passage 37 to the crank chamber 12-1, raising the pressure inside the crank chamber 12-1. This pressure increase shifts the swash plate 24 toward the minimum inclination position. When the swash plate 24 abuts on the position restricting ring 31, as shown in Figs. 4 and 6, the inclination angle of the swash plate 24 becomes minimum. Under this minimum inclination status, the discharge displacement becomes minimum and so does the amount of refrigerant gas flowing in the external refrigeration circuit 40. With the minimum flow rate of the refrigerant gas, the difference between the pressure in the compression-sensing chamber 46-5 and the pressure in the leading chamber 46-6 becomes slight and the sum of the pressure in the compression-sensing chamber 46-5 and the spring force of the adjusting spring 46-3 exceeds the pressure in the leading chamber 46-6. As a result, the valve body 46-2 closes the valve hole 46-4. When the electromagnetic valve 38 is de-excited, therefore, the circulation of the refrigerant gas in the external refrigeration circuit 40 is inhibited. In other words, the excitation instruction from the control computer C means the sending of a refrigerant-circulation instructing signal, and the electromagnetic valve 38, when excited, permits the circulation of the refrigerant gas in the external refrigeration circuit 40. The de-excitation instruction from the control computer C means the disabling of the refrigerant-circulation instructing signal, and the electromagnetic valve 38, when de-excited, inhibits the circulation of the refrigerant gas in the external refrigeration circuit 40. As the minimum inclination angle of the swash plate 24 is not zero degrees, the refrigerant gas is discharged to the discharge chamber 13-2 from each cylinder bore 11-1 even with this minimum inclination angle. The refrigerant gas discharged to the discharge chamber 13-2 from each cylinder bore 11-1 flows through the pressure supply passage 37 to the crank chamber 12-1. The refrigerant gas in the crank chamber 12-1 flows through the pressure release passage 35 and the restriction passage 36 to the suction chamber 13-1. The refrigerant gas in the suction chamber 13-1 is drawn into the cylinder bores 11-1 to be discharged to the discharge chamber 13-2. That is, with the minimum inclination angle of the swash plate 24, the circulation passage connecting the discharge chamber 13-2, the pressure supply passage 37, the crank chamber 12-1, the pressure release passage 35, the restriction passage 36, the suction chamber 13-1 and the cylinder bores 11-1 is formed in the compressor, and the lubricating oil which flows together with the refrigerant gas lubricates the interior of the compressor. Differential pressures are produced among the discharge chamber 13-2, the crank chamber 12-1 and the suction chamber 13-1. When the cooling load increases from the state shown in Fig. 6, this increase in cooling load appears as a rise in temperature in the evaporator 43 so that the temperature detected by the temperature sensor 44 exceeds the set temperature. Based on this change in detected temperature, the control computer C instructs the excitation of the solenoid 38-1. Consequently, the solenoid 38-1 is excited to close the pressure supply passage 37, so that the pressure in the crank chamber 12-1 is released through the pressure release passage 35 and the restriction passage 36 to become lower. This pressure reduction shifts the swash plate 24 toward the maximum inclination position from the minimum inclination position. When the inclination of the swash plate 24 increases, the amount of refrigerant gas drawn into the cylinder bores 11-1 from the suction chamber 13-1 increases, rapidly reducing the pressure in the suction chamber 13-1. Consequently, the pressure in the compression-sensing chamber 46-5 also drops so that the pressure in the leading chamber 46-6 becomes greater than the sum of the pressure in the compression-sensing chamber 46-5 and the spring force of the adjusting spring 46-3. As a result, the valve body 46-2 opens the valve hole 46-4 to re-start the circulation of the refrigerant gas in the external refrigeration circuit 40. The opening/closing of the valve hole 46-4 by the valve body 46-2 is accomplished by the shift of the differential pressure in the external refrigeration circuit between the upstream and downstream of the open/close mechanism 46 from the set value that is determined by the spring force of the adjusting spring 46-3. In other words, the opening/closing of the valve hole 46-4, unlike in the electromagnetic opening/closing, is not the ON/OFF action and the cross-sectional area of the valve hole 46-4 through which the refrigerant gas passes changes gradually. Accordingly, the amount of refrigerant gas drawn into the cylinder bores 11-1 from the suction chamber 13-1 increases slowly, and the discharge displacement increases gradually. Consequently, the discharge pressure gradually changes, thus preventing the load torque needed by the compressor from significantly changing in a short period of time. Because the load torque in the compressor does not change rapidly, the shock reduction, which is the primary aim of the clutchless compressor, is accomplished. According to the invention, one of two pressure points in the external refrigeration circuit for controlling the opening/closing of the open/close mechanism 46 is located upstream of this mechanism 46 and the other pressure point is located downstream of the mechanism 46. This pressure-leading structure has such an advantage that the passage for leading the pressure to the open/close mechanism 46 can be made shortest. An embodiment illustrated in Fig. 7 will be now described. In this embodiment, a retaining chamber 47 is formed in the cylinder block 11. The retaining chamber 47 communicates with the external refrigeration circuit 40 via the suction passage 39. The retaining chamber 47 also communicates with the suction chamber 13-1 via a port 48. An open/close mechanism 49 is accommodated in the retaining chamber 47, and a valve body 50 in a valve housing 53. The valve body 50 has a rod portion 51 whose tail portion is slidably inserted in the cylinder block 11. The rod portion 51 has a head 51-2, which is insertable in the port 48, and an axial center portion through which a restriction passage 51-3 is bored. The valve body 50 separates the interior of the valve housing 53 into a compression-sensing chamber 53-1 and a leading chamber 53-2. The compression-sensing chamber 53-1 communicates with the suction chamber 13-1 via the retaining chamber 47, and the leading chamber 53-2 communicates with the suction passage 39. The valve body 50 is urged in the direction to close the port 48 by an adjusting spring 52 located in the compression-sensing chamber 49-1. The differential pressure between the pressure in the suction passage 39 and the pressure in the suction chamber 13-1 changes in accordance with the amount of circulating refrigerant gas. When the electromagnetic valve 38 is excited, the inclination angle of the swash plate 24 becomes maximum as in the first embodiment. When the swash plate 24 is at the maximum inclination angle, the difference between the pressure in the compression-sensing chamber 53-1 and the pressure in the leading chamber 53-2 is large, and the valve body 50 opens the port 48. When the electromagnetic valve 38 is de-excited, the inclination angle of the swash plate 24 is minimized, reducing the differential pressure between the pressure in the compression-sensing chamber 53-1 and the pressure in the leading chamber 53-2. As a result, the valve body 50 closes the port 48 to block the circulation of the refrigerant gas in the external refrigeration circuit 40. Even with the circulation of the refrigerant gas inhibited, the restriction passage 51-3 connects the crank chamber 12-1 to the suction chamber 13-1, so that the refrigerant gas circulates through the passage that links the discharge chamber 13-2, the crank chamber 12-1, the suction chamber 13-1 and the cylinder bores 11-1. When the electromagnetic valve 38 is excited, the inclination angle of the swash plate 24 changes to the maximum angle from the minimum angle, allowing the valve body 50 to open the port 48 as in the first embodiment. This embodiment, like the first embodiment, also executes the opening/closing of the open/close mechanism 49 in accordance with the amount of circulating refrigerant gas, and was the advantage of suppressing the switching-oriented shocks and the advantage of permitting the formation of the shortest passage for leading the pressure to the open/close mechanism 49. An embodiment illustrated in Fig. 8 will be now described. In this embodiment, the compression-sensing chamber 46-5 of the open/close mechanism 46 communicates via a pressure leading pipe 54 to the external refrigeration circuit 40 located downstream the evaporator 43. The leading chamber 46-6 communicates via a pressure leading pipe 55 with the external refrigeration circuit 40 upstream the position where the pressure leading pipe 54 is connected to the external refrigeration circuit 40. The valve body 46-2 of the open/close mechanism 46 opens or closes the suction passage 39. The pressure at the connection between the pressure leading pipe 55 and the external refrigeration circuit 40 is higher than the pressure at the connection between the pressure leading pipe 54 and the external refrigeration circuit 40, and the differential pressure therebetween changes in accordance with a change in the amount of the circulating refrigerant gas. In this embodiment, the opening/closing of the open/close-mechanism 49 is also executed in accordance with the amount of the circulating refrigerant gas, and the advantage of suppressing the switching-oriented shocks can be obtained as in the first embodiment. An embodiment illustrated in Fig. 9 will be now described. In this embodiment, the compression-sensing chamber 46-5 of the open/close mechanism 46 communicates via a pressure leading pipe 56 to the external refrigeration circuit 40 between the condenser 41 and the expansion valve 42. The leading chamber 46-6 communicates via a pressure leading pipe 57 with the external refrigeration circuit 40 upstream the position where the pressure leading pipe 56 is connected to the external refrigeration circuit 40. The valve body 46-2 of the open/close mechanism 46 opens or closes the suction passage 39. The pressure at the connection between the pressure leading pipe 57 and the external refrigeration circuit 40 is higher than the pressure at the connection between the pressure leading pipe 56 and the external refrigeration circuit 40, and the differential pressure therebetween changes in accordance with a change in the amount of circulating refrigerant gas. In this embodiment, the opening/closing of the open/close mechanism 49 is also executed in accordance with the amount of circulating refrigerant gas, and the advantage of suppressing the switching-oriented shocks are obtained as in the first embodiment. An embodiment illustrated in Figs. 10 and 11 will be now described. In this embodiment, the pressure in the crank chamber 12-1 is controlled by a displacement control valve 58. The control valve 58 has a pressure leading port 59 which communicates with the discharge chamber 13-2 and a suction pressure leading port 60 which communicates with the suction passage 39. A pressure supply port 61 communicates with the pressure supply passage 37. The pressure in a suction-pressure detecting chamber 62, which communicates with the port 59, is applied to one side of a diaphragm 63, and the elastic force of an adjusting spring 64 is applied to the other side of the diaphragm 63. The spring force of the adjusting spring 64 is transmitted to a valve body 66 via the diaphragm 63 and a rod 65. The valve body 66 which receives the elastic force of a return spring 67 opens or closes a valve hole 68 in accordance with a change in the suction pressure in the suction-pressure detecting chamber 62 to respectively permit or block the communication between the port 59 and the port 61. The other structure is the same as that of the embodiment shown in Fig. 7, except that no restriction function is given to the passage in the valve body 50 of the open/close mechanism 49. When the suction pressure is high (the cooling load is large) while the solenoid 38-1 of the electromagnetic valve 38 is excited and the pressure supply passage 37 is closed, the amount of opening of the valve body 66 of the displacement control valve 58 becomes smaller, reducing the amount of the refrigerant gas flowing into the crank chamber 12-1 from the discharge chamber 13-2. As a result, the pressure in the crank chamber 12-1 falls to increase the inclination of the swash plate. When the suction pressure is low (the cooling load is small), on the other hand, the amount of opening of the valve body 66 becomes larger, increasing the amount of the refrigerant gas flowing into the crank chamber 12-1 from the discharge chamber 13-2. Consequently, the pressure in the crank chamber 12-1 rises to reduce the inclination of the swash plate. That is, the discharge displacement is controlled variably and continuously. When the electromagnetic valve 38 is de-excited, the valve body 50 of the open/close mechanism 49 closes the port 48, and when the electromagnetic valve 38 is excited, the valve body 50 opens the port 48, as in the embodiment shown in Fig. 7. This embodiment can accomplish the suppression of the switching-oriented shocks at the time the circulation of the refrigerant gas stops or starts while continuously executing the variable control of the discharge displacement. An embodiment illustrated in Fig. 12 will be now described. The compressor according to this embodiment is a variable displacement compressor with a clutch, which has a displacement control valve 58 attached to the rear housing 13. The displacement control valve 58 continuously performs the variable control of the inclination of the swash plate as in the embodiment shown in Fig. 10. Intervened in the discharge passage in the rear housing 13 is an open/close mechanism 69 whose valve body 70 is urged in the direction to close a valve hole 72 by the elastic force of an adjusting spring 71. A through hole 70-1 is formed in the valve body 70. The valve body 70 closes the valve hole 72 when the pressure acting on the valve body 70 from the direction of the discharge chamber 13-2 becomes equal to or smaller than a set value which is slightly higher than the pressure in the crank chamber 12-1 needed to shift the swash plate 24 to the minimum inclination angle from the maximum inclination angle. When the pressure acting on the valve body 70 from the direction of the discharge chamber 13-2 exceeds the set value, the valve body 70 opens the valve hole 72. That is, when the differential pressure between the upstream and downstream sides of the valve body 70 falls to or below a certain set level, the valve hole 72 is closed, and when this differential pressure exceeds the certain set level, the valve hole 72 is opened. Without the open/close mechanism 69, when the inclination angle of the swash plate is shifted to the minimum inclination angle from the maximum inclination angle, most of the refrigerant gas discharged to the discharge chamber 13-2 flows out to the external refrigeration circuit 40. When the inclination of the swash plate becomes small or when the discharge pressure becomes very low, therefore, the pressure in the crank chamber 12-1 does not rise and the inclination angle of the swash plate does not smoothly shift toward the minimum inclination side. According to this embodiment, however, when the inclination angle of the swash plate moves to the minimum inclination side, the open/close mechanism 69 is closed, causing the pressure in the crank chamber 12-1 to surely rise. This ensures the smooth transition of the inclination angle of the swash plate toward the minimum inclination side from the maximum inclination side and thus accomplishes surer displacement control. When the inclination angle of the swash plate is the minimum, the open/close mechanism 69 is closed, and thus no frosting occurs in the evaporator 43. It is possible to avoid the frequency ON/OFF actions of the electromagnetic clutch in the low-load operation, thus preventing the torque from changing by the ON/OFF action of the electromagnetic clutch. Further, because the opening/closing of the open/close mechanism 69 is executed in accordance with a change in pressure in the discharge chamber 13-2, the opening/closing of the valve hole 72, unlike in the electromagnetic opening/closing, is not the ON/OFF action and the cross-sectional area of the valve hole 72 through which the refrigerant gas passes changes gradually. Accordingly, the discharge pressure gradually changes to prevent the load torque in the compressor from changing significantly. An embodiment illustrated in Fig. 13 will be now described. In this embodiment, a compression-sensing chamber 74 in an open/close mechanism 73 communicates via a pressure leading pipe 75 with the external refrigeration circuit 40 located downstream the evaporator 43. A leading chamber 76 communicates via a pressure leading pipe 77 with the external refrigeration circuit 40 located upstream the position where the pressure leading pipe 75 is connected to the external refrigeration circuit 40. A valve body 78 of the open/close mechanism 73 opens or closes a discharge passage 79. An adjusting spring 80 urges the valve body 78 in the direction to close the discharge passage 79. The pressure at the position where the pressure leading pipe 77 is connected to the external refrigeration circuit 40 is higher than the pressure at the position where the pressure leading pipe 75 is connected to the external refrigeration circuit 40, and the differential pressure therebetween varies in accordance with a change in the circulating refrigerant gas. This embodiment also performs the opening/closing of the open/close mechanism 73 in accordance with the amount of the circulating refrigerant gas, and can have the advantage of suppressing the switching-oriented shocks as in the first embodiment. Although seven 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 scope of the invention. Particularly, it should be understood that this invention may be embodied in the following forms. This invention may be adapted for other types of variable displacement compressors which supply the pressure to the control pressure chamber from the discharge pressure area and discharges the pressure to the suction pressure area from the control pressure chamber to vary the displacement. 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. A swash plate tiltably supported on a drive shaft is controlled by adjusting the pressure in a crank chamber. When an electromagnetic valve is de-excited, the high-pressure refrigerant gas in a discharge chamber is supplied to the crank chamber so that the inclination angle of the swash plate is shifted to its minimum inclination from its maximum inclination. An open/close mechanism located in a suction passage opens or closes the suction passage in accordance with the differential pressure between the pressure in the external refrigeration circuit located upstream the open/close mechanism and the pressure in a suction chamber. When the inclination angle of the swash plate is minimized, the open/close mechanism closes the suction passage. It is therefore possible to prevent frosting while also suppressing rapid changes in load torque.

Claims: A displaceable compressor including a suction port (14-1) and a discharge port (14-2), said suction port (14-1) and said discharge port (14-12) being connectable with each other by way of a refrigeration fluid passage (40) to suck fluid introduced into the refrigeration fluid passage (40) through the suction port (14-1) and to discharge compressed fluid from the discharge port (14-2) to the refrigeration fluid passage (40), wherein the refrigeration fluid passage (40) has external refrigeration circuit elements (41, 42, 43), wherein the fluid circulating in the refrigeration fluid passage (40) changes pressure thereof, said compressor being characterized by a mechanism (46, 49, 69, 73) disposed in an area communicable with the refrigeration fluid passage (40) to selectively and gradually open and close the refrigeration fluid passage (40) in accordance with a difference between the pressures of two points respectively positioned upstream and downstream said area, and a valve element (38) for actuating said mechanism (46, 49, 69, 73) to close the refrigeration fluid passage (40) when said pressure difference is smaller than a predetermined value. The compressor as set forth in Claim 1, wherein said mechanism (46) allows the fluid to leak from the upstream point to the downstream point when the fluid passage (40) is closed. The compressor as set forth in Claims 1 or 2, wherein said suction portion (14-1) and discharge portion (14-2) both include passages (39, 11-2) for allowing the fluid to pass therethrough. A displacable compressor as set forth in Claim 3, characterized by that a swash plate (24) is tiltably mounted on a rotary shaft (18) in a crank chamber (12-1) to reciprocally drive a piston (32) in a cylinder bore (11-1), said piston (32) compressing the fluid supplied to the cylinder bore (11-1) from the fluid passage (40) through the suction portion (14-1) and discharges the compressed fluid to the fluid passage (40) through the discharge portion (14-2), wherein difference between the pressures in the crank chamber (12-1) and the cylinder bore (11-1) selectively increases and decreases in accordance with pressure in the crank chamber (12-1) to tilt the swash plate (24) between minimum and maximum angles, wherein an amount of the fluid passing through one of the suction passage (39) and the discharge passage (11-2) is determined to be minimum based on the compression load of said compressor so as to forcibly tilt the swash plate (24) toward the minimum angle, wherein the minimum angle of the swash plate (24) is regulated to be at an angle toward the maximum angle in respect with a plane perpendicular to said rotary shaft (18) to allow the passage of the minimum amount of the fluid in one of the passages (39, 11-2), and whereby one of said suction passage (39) and said discharge passage (11-2) is closed upon the passage of the minimum amount of the fluid therein. The compressor as set forth in Claim 4 characterized by a detector (44) for detecting the compression load of the compressor, wherein said detector (44) outputs a signal based the detected compression load to the determine the minimum amount of the fluid. The compressor as set forth in Claims 4 or 5, characterized by that said crank chamber (12-1) is connected with one of the suction passage (39) and the discharge passage (11-2), whereby the pressure in the crank chamber (12-1) in communication with the discharge passage (11-2) and suction passage (39) respectively increases and decreases, and an electromagnet valve (38) disposed between the crank chamber (12-1) and the discharge passage (11-2) to connect the crank chamber (12-1) with the discharge passage (11-2) when the fluid passes with the minimum amount in one of the suction passage (39) and discharge passage (11-2). The compressor as set forth in Claims 5 or 6, wherein said detector (44) detects the compression load of the compressor based on a temperature in the fluid passage (40).

Inventors: HIBINO SOKICHI, KAWAGUCHI MASAHIRO, KAWAMURA KOJI, KOBAYASHI HISAKAZU, OKUNO TAKUYA, OTA MASAKI, SUITOU KEN, HIBINO, SOKICHI, KAWAGUCHI, MASAHIRO, KAWAMURA, KOJI, KOBAYASHI, HISAKAZU, OKUNO, TAKUYA, OTA, MASAKI, SUITOU, KEN, Hibino, Sokichi, c/o K.K. Toyoda Jidosh. Seisakus., Kawaguchi, Masahiro, c/o K.K. Toy. Jidosh. Seisak., Kawamura, Koji, c/o K.K. Toyoda Jidosh. Seisakusho, Kobayashi, Hisakazu, c/o K.K. Toy. Jidosh. Seisak., Okuno, Takuya, c/o K.K. Toyoda Jidosh. Seisakusho, Ota, Masaki, c/o K.K. Toyoda Jidoshokki Seisakusho, Suitou, Ken, c/o K.K. Toyoda Jidoshokki Seisakusho
Applicants: TOYOTA JIDOSHOKKI KK, KABUSHIKI KAISHA TOYOTA JIDOSHOKKI
Application year: 1995
Main classification: F25B31
IPC codes: F04B49, F04B27