Slant plate type compressor with variable displacement mechanism

Abstract: A variable capacity type slant plate compressor including a crank chamber, a suction chamber 241 and a discharge chamber 251 is disclosed. The slant plate is disposed in the crank chamber at a variable slant angle. The slant angle varies in dependence on the crank chamber pressure. The crank chamber is linked by a first communication path (400a) to the suction chamber, and is linked by a second communication path (500a) to the discharge chamber. A first valve control mechanism (400) is disposed within the first communication path. A second valve control mechanism (500) is disposed within the second communication path. The slant angle may be varied by operation of the first valve control mechanism which controls an open and close of the first communication path so that the suction chamber pressure is adjusted at a predetermined constant value. The second communication path is compulsorily opened by operation of the second valve control mechanism so as to compulsorily minimize the capacity of the compressor when the energy consumed in operation of the compressor is demanded to be reduced. A throttling device (249a) is disposed within the second communication path between the discharge chamber and the second valve control mechanism so that the capacity of the compressor is compulsorily quickly minimized without damage of the internal component parts of the compressor.

Description: The present invention generally relates to a refrigerant compressor and, more particularly, to a slant plate type compressor, such as a wobble plate type compressor, with a variable displacement mechanism suitable for use in an automotive air conditioning system. A wobble plate type compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system is disclosed in Japanese Utility Model Application Publication No 64-27487. The compressor includes a variable displacement mechanism which comprises a first communication path communicating a crank chamber and a suction chamber, and a second communication path communicating the crank chamber and a discharge chamber. A first valve control mechanism controlling an open and close of the first communication path is disposed within the first communication path. A second valve control mechanism controlling an open and close of the second communication path is disposed within the second communication path. The first communication path is provided with a first valve seat formed at one portion thereof. The second communication path is provided with a second valve seat formed at one portion thereof. The first valve control mechanism includes a first valve member which is received on and left from the first valve seat. The second valve control mechanism includes a second valve member which is received on and left from the second valve seat. The first and second valve members are linked through a rod member so that the first valve member is received on and left from the first valve seat while the second valve member is left from and received on the second valve seat. The first valve control mechanism includes a pressure sensing device, such as a diaphragm for sensing the pressure in the suction chamber. In operation of the variable displacement mechanism, the first valve member is received on and left from the first valve seat so as to close and open the first communication path while the second valve member is left from and received on the second valve seat so as to open and close the second communication path in response to the changes in the sensed pressure in the suction chamber so that the pressure in the suction chamber is adjusted at a predetermined constant value. The adjusted constant value of pressure in the suction chamber is shifted downwardly and upwardly in response to the changes in an amount of a demand for energy which is derived from an engine of a vehicle to drive the vehicle. When the amount of the demand for energy which is derived from the engine of the vehicle to drive the vehicle is large, the adjusted constant value of pressure in the suction chamber is shifted upwardly with a great amount so that the displacement of the compressor is compulsorily minimized. Therefore, the energy which is derived from the engine to be consumed in operation of the compressor is compulsorily minimized. Accordingly, the energy derived from the engine of the vehicle is effectively used for driving the vehicle. When the first valve member is received on the first valve seat so as to close the first communication path while the second valve member is left from the second valve seat so as to open the second communication path, an amount of the refrigerant gas which flows from the discharge chamber to the crank chamber is substantially regulated by a value of a substantial opening area of the second valve seat. However, in an usual manufacturing process of the compressor, it is difficult to set up a certain value of the substantial opening area of the second valve seat so as to regulate the amount of the refrigerant gas which flows from the discharge chamber to the crank chamber at a demanded value. Especially, in a stage of compulsorily minimizing the displacement of the compressor, if the value of the substantial opening area of the second valve seat is large, an amount of the refrigerant gas which flows from the discharge chamber to the crank chamber is regulated so that the pressure in the crank chamber is quickly increased to thereby quickly reduce the displacement of the compressor while the pressure in the crank chamber is maintained at an excessive high value which causes damage of the internal component parts of the compressor. On the other hand, if the value of the substantial opening area of the second valve seat is small, an amount of the refrigerant gas which flows from the discharge chamber to the crank chamber is regulated so that the pressure in the crank chamber is slowly increased to thereby slowly reduce the displacement of the compressor while the pressure in the crank chamber is maintained at a certain value which does not cause damage of the internal component parts of the compressor. An object of the present invention is to provide a variable slant plate type compressor in which the capacity of the compressor can be compulsorily quickly minimized without damage of the internal component parts of the compressor. US-A-4606705 discloses a slant plate type compressor including a compressor housing enclosing a crank chamber, a suction chamber and a discharge chamber therein the compressor housing comprising a cylinder block having a plurality of cylinders, a piston slidably fitted within each of the cylinders, a drive means coupled to the pistons for reciprocating the pistons within the cylinders, the drive means including a drive shaft rotatably supported in the housing, coupling means for drivingly coupling the pistons with the drive shaft and for converting rotary motion of the drive shaft into reciprocating motion of the pistons, the coupling means including a slant plate having a surface disposed at a slant angle relative to a plane perpendicular to the drive shaft, the slant angle changing in response to a change in pressure in the crank chamber relative to the suction pressure to change the capacity of the compressor, a first communication path, linking the crank chamber with the suction chamber, a first valve control mechanism disposed within the first communication path, the first valve control mechanism controlling the opening and closing of the first communication path in response to changes in pressure in the suction chamber, a second communication path linking the crank chamber with the discharge chamber, a second valve control mechanism disposed within the second communication path, the second valve control mechanism responding to an external signal and opening the second communication path to increase the pressure in the crank chamber to thereby minimize the capacity of the compressor, and according to the present invention such a compressor is characterised by a throttling means disposed within the second communication path between the discharge chamber and the second valve control mechanism so as to regulate the quantity of fluid which flows from the discharge chamber to the crank chamber when the second valve control mechanism opens the second communication path and wherein the first and the second valve control mechanisms operate independently. In the accompanying drawings:- Figure 1 illustrates a longitudinal sectional view of a wobble plate type compressor in accordance with a first embodiment of the present invention. Figure 2 illustrates an enlarged fragmentary longitudinal sectional view of a valve control mechanism shown in Figure 1. Figure 3 illustrates a longitudinal sectional view of a wobble plate type compressor in accordance with a second embodiment of the present invention. Figure 4 illustrates an enlarged fragmentary longitudinal sectional view of a valve control mechanism shown in Figure 3. Figure 5 illustrates a longitudinal sectional view of a wobble plate type compressor in accordance with a third embodiment of the present invention. Figure 6 illustrates an enlarged fragmentary longitudinal sectional view of a valve control mechanism shown in Figure 5. In Figures 1-6, identical reference numerals are used to denote identical elements. Additionally, although the present invention is described below in terms of a wobble plate type compressor, it is not limited in this respect. The present invention is broadly applicable to slant plate type compressors. Furthermore, for purposes of explanation only, the left side of Figures 1-6 will be referenced as the forward end or front and the right side of the drawings will be referenced as the rearward end. The term "axial" refers to a direction parallel to the longitudinal axis of the drive shaft, and the term "radial" refers to the perpendicular direction. Of course, all of the reference directions are made for the sake of convenience of description and are not intended to limit the invention in any way. Figure 1 illustrates the overall construction of a wobble plate type refrigerant compressor with a variable displacement mechanism in accordance with a first embodiment of the present invention. With reference to Figure 1, compressor 10 includes cylindrical housing assembly 20 including cylinder block 21, front end plate 23 disposed at one end of cylinder block 21, crank chamber 22 enclosed within cylinder block 21 by front end plate 23, and rear end plate 24 attached to the other end of cylinder block 21. Front end plate 23 is secured to one end of cylinder block 21 by a plurality of bolts 101. Rear end plate 24 is secured to the opposite end of cylinder block 21 by a plurality of bolts 102. Valve plate 25 is disposed between rear end plate 24 and cylinder block 21. Opening 231 is centrally formed in front and plate 23 for supporting drive shaft 26 by bearing 30 disposed therein. Inner end portion of drive shaft 26 is rotatably supported by cylinder block 21 through bearing 31. Bore 210 extends to a rear end surface of cylinder block 21 and includes a thread portion (not shown) formed at an inner peripheral surface of a central region thereof. Adjusting screw 220 having a hexagonal central hole 221 is screwed into the thread portion of bore 210. Circular disc-shaped spacer 230 having central hole 231 is disposed between the inner end of drive shaft 26 and adjusting screw 220. Axial movement of adjusting screw 220 is transferred to drive shaft 26 through spacer 230 so that all three elements move axially within bore 210. The construction and functional manner of adjusting screw 220 and spacer 230 are described in detail in U.S. Patent No. 4,948,343 to Shimizu. Cup-shaped member 211 is fixedly disposed at a rear portion of bore 210. Filter member 212 is fixedly disposed in hole 213 which is centrally formed at a bottom end of cup-shaped member 240. Axial hole 262 is axially formed through drive shaft 26. One end of axial hole 262 opens to central hole 231 of spacer 230, and the other end of axial hole 262 is located at a position which is the forward of cylinder block 21. Radial hole 263 is radially formed through drive shaft 26 so as to link the other end of axial hole 262 to crank chamber 22. O-ring seal element 214 is disposed between the outer peripheral surface of rear end portion of cup-shaped member 211 and the inner peripheral surface of the rear portion of bore 210. Cam rotor 40 is fixed on drive shaft 26 by pin member 261 and rotates therewith. Thrust needle bearing 32 is disposed between the inner end surface of front end plate 23 and the adjacent axial end surface of cam rotor 40. Cam rotor 40 includes arm 41 having pin member 42 extending therefrom. Slant plate 50 is disposed adjacent cam rotor 40 and includes opening 53 through which drive shaft 26 passes. Slant plate 50 includes arm 51 having slot 52. Cam rotor 40 and slant plate 50 are coupled by pin member 42 which is inserted in slot 52 to form a hinged joint. Pin member 42 slides within slot 52 to allow adjustment of the slant angle of slant plate 50, that is, the angle of the surface of slant plate 50 with respect to a plane perpendicular to the longitudinal axis of drive shaft 26. Wobble plate 60 is mounted on slant plate 50 through bearings 61 and 62 such that slant plate 50 may rotate with respect thereto. Balance weight ring 80 of substantial mass is disposed on a nose of hub 501 of slant plate 50 in order to balance the slant plate 50 under dynamic operating conditions. Balance weight ring 80 is held in place by means of retaining ring 81. Bias spring 33 is compressedly mounted on drive shaft 26 at a portion between annular ridge 26a and snap ring 34. Fork shaped slider 63 is attached to the outer peripheral end of wobble plate 60 and is slidably mounted on sliding rail 64 disposed between front end plate 23 and cylinder block 21. Fork shaped slider 63 prevents rotation of wobble plate 60. Wobble plate 60 nutates along rail 64 when cam rotor 40 and slant plate 50 rotate. Cylinder block 21 includes a plurality of peripherally located cylinder chambers 70 in which pistons 71 reciprocate. Each piston 71 is coupled to wobble plate 60 by a corresponding connecting rod 72. Rear end plate 24 includes peripherally positioned annular suction chamber 241 and centrally positioned discharge chamber 251. Valve plate 25 is located between cylinder block 21 and rear end plate 24 and includes a plurality of valved suction ports 242 linking suction chamber 241 with respective cylinders 70. Valve plate 25 also includes a plurality of valved discharge ports 252 linking discharge chamber 251 with respective cylinders 70. Suction ports 242 and discharge ports 252 are provided with suitable reed valves as described in U.S. Patent No. 4,011,029 to Shimizu. Suction chamber 241 includes an inlet portion (not shown) which is connected to an evaporator of an external cooling circuit (not shown). Discharge chamber 251 is provided with an outlet portion (not shown) connected to a condenser of the cooling circuit (not shown). Gaskets 27 and 28 are positioned between cylinder block 21 and the inner surface of valve plate 25 and the outer surface of valve plate 25 and rear end plate 24, respectively. Gaskets 27 and 28 seal the matting surface of cylinder block 21, valve plate 25 and rear end plate 24. Gaskets 27 and 28 and valve plate 25 thus form valve plate assembly 200. Passage 150 is formed at the rear end of cylinder block 21. One end of passage 150 is open to the rear end portion of bore 210 and the other end of passage 150 is open to hole 151 which is bored through valve plate assembly 200. Conduit 18 is axially bored through cylinder block 21 so as to link crank chamber 22 to discharge chamber 251 through hole 181 which is axially bored through valve plate assembly 200. A throttling device, such as, orifice tube 182 is fixedly disposed within conduit 18. Filter member 183 is disposed in conduit 18 at the rear of orifice tube 182. Accordingly, a portion of the discharged refrigerant gas in discharge chamber 251 always flows into crank chamber 22 with a reduced pressure generated by orifice tube 182. The above-mentioned construction and functional manner are described in detail in Japanese Patent Application Publication No. 1-142277. Axially extending first cylindrical cavity 243 is formed in a central portion of rear end plate 24 at a rear of discharge chamber 251. First cylindrical cavity 243 includes large diameter portion 243a and small diameter portion 243b extending from a front end of large diameter portion 243a. Annular projection 244 projecting from a central region of a rear end surface of rear end plate 24 defines a rear portion of first cylindrical cavity 243. First valve control mechanism 400 is fixedly disposed in first cylindrical cavity 243. Radially extending second cylindrical cavity 247 is formed in rear end plate 24 at a rear of suction chamber 241 and a part of discharge chamber 251. Second cylindrical cavity 247 includes large diameter portion 247a and small diameter portion 247b extending from a radial inner end of large diameter portion 247a. Second valve control mechanism 500 is fixedly disposed in second cylindrical cavity 247. With reference to Figure 2 additionally, the construction of first and second valve control mechanisms 400 and 500 is described in detail below. First valve control mechanism 400 includes cylindrical member 401 which comprises front annular flange 401a outwardly extending from a front end thereof and rear annular flange 401b also outwardly extending from a rear end thereof. Front annular flange 401a is positioned at a rear half of small diameter portion 243b of first cylindrical cavity 243. Rear annular flange 401b is positioned at a mid region of large diameter portion 243a of first cylindrical cavity 243. O-ring seal element 402 is disposed at an outer peripheral surface of front annular flange 401a to seal the mating surfaces between the inner peripheral surface of small diameter portion 243b of first cylindrical cavity 243 and the outer peripheral surface of front annular flange 401a. O-ring seal element 402 sealingly insulates a front hollow space of small diameter portion 243b of cavity 243 from a front hollow space of large diameter portion 243a of cavity 243. Axially extending cylindrical cavity 403 is formed in cylindrical member 401. Cylindrical cavity 403 extends from the rear end surface of cylindrical member 401 and terminates at a position which is the rear of front annular flange 401a. Axially extending cylindrical cavity 404 of which diameter is smaller than a diameter of cylindrical cavity 403 extends from a front end of cylindrical cavity 403 and terminates at a position which is adjacent to the front end of cylindrical member 401. Annular ridge 408 functioning as a first valve seat is formed at the boundary between cylindrical cavities 403 and 404. Axial hole 405 is centrally formed at the front end portion of cylindrical meter 401 so as to link cylindrical cavity 404 to the front hollow space of small diameter portion 243b of cylindrical cavity 243. A plurality of radial holes 406 are formed at the side portion of cylindrical member 401 so as to link the front hollow space of large diameter portion 243a of cavity 243 to cylindrical cavity 403. Cylindrical valve member 407 is axially movably disposed in cylindrical cavity 403. Cylindrical valve member 407 includes truncated cone shaped portion 407a formed at the front end thereof and spherically shaped convex portion 407b formed at the rear end thereof. Truncated cone shaped portion 407a of cylindrical valve member 407 is received by first valve seat 408 when cylindrical valve member 407 moves forwardly. Annular ring member 409 is fixedly disposed at an outer peripheral side surface of a mid region of cylindrical valve member 407 so as to guide cylindrical valve member 407 along an inner peripheral surface of cylindrical cavity 403 when cylindrical valve member 407 axially moves in cylindrical cavity 403. Coil spring 410 is resiliently disposed between the front bottom surface of cylindrical cavity 404 and the flat front end surface of truncated cone shaped portion 407a of cylindrical valve member 407 so that cylindrical valve member 407 is urged rearwardly by the restoring force of coil spring 410. First valve control mechanism 400 further includes cup-shaped casing 421 which houses annular electromagnetic coil 422, annular cylindrical member 423 forcibly inserted within annular electromagnetic coil 422, cylindrical pedestal 424 of magnetic material fixedly disposed within a rear portion of annular cylindrical member 423, and cylindrical member 425 of magnetic material axially slidably disposed within a front portion of annular cylindrical member 423. Cylindrical member 425 includes cylindrical hollow space 425a formed at a rear end surface thereof and spherically shaped convex portion 425b formed at the front end thereof. Coil spring 426 is resiliently disposed between the front end surface of pedestal 424 and the front bottom surface of cylindrical hollow space 425a of cylindrical member 425 so that cylindrical member 425 is urged forwardly by the restoring force of coil spring 426. Annular plate member 427 is disposed at a front opening end of cup-shaped casing 421. Annular plate member 427 and a front portion of cup-shaped casing 421 is fixedly disposed in large diameter portion 243a of first cylindrical cavity 243 by forcible insertion. Diaphragm 428 is disposed between the rear, annular flange 401b of cylindrical member 401 and the annular plate member 427. An outer periphery of diaphragm 428 is fixedly sandwiched by rear annular flange 401b and annular plate member 427. O-ring seal element 429 is disposed at the inner peripheral surface of a mid region of large diameter portion 243a of cavity 243 so as to seal the mating surfaces between the inner peripheral surface of large diameter portion 243a of cavity 243 and the outer peripheral surface of rear annular flange 401b of cylindrical member 401. O-ring seal element 429 sealingly insulates the front hollow space of large diameter portion 243a of cavity 243 from the atmosphere of outside compressor 10. Second valve control mechanism 500 includes cylindrical member 510 and annular electromagnetic coil 520 which is located at a radial outer side of cylindrical meter 510. Cylindrical member 510 comprises annular flange 511 outwardly extending from a radial outer end thereof. Annular flange 511 is located at a mid region of second cylindrical cavity 247. A radial inner end region of cylindrical member 510 is fixedly inserted to a position which is approximate two-thirds of the length of small diameter portion 247b of second cylindrical cavity 247. O-ring seal element 512 is disposed at an outer peripheral surface of the radial inner end region of cylindrical member 510 to seal the mating surfaces between the outer peripheral surface of cylindrical member 510 and the inner peripheral surface of small diameter portion 247b of cavity 247. O-ring seal element 512 sealingly insulates a radial inner hollow space of large diameter portion 247a of cavity 247 from a radial inner hollow space of small diameter portion 247b of cavity 247. Radially extending circular hole 513 is formed in cylindrical member 510. Circular hole 513 extends from the radial inner end of cylindrical member 510 and terminates at a position which is approximate one-third of the length of cylindrical member 510. Circular hole 513a of which diameter is smaller than the diameter of circular hole 513 extends from the upper end of circular hole 513 and terminates at a position which is approximate one half of the length of cylindrical member 510. A diameter of circular hole 513a is designed so as to allow a large amount of the refrigerant gas to flow through circular hole 513a even though a later-mentioned rod 524a is located in circular hole 513a. Annular ridge 513b functioning as a second valve seat is formed at the boundary between circular holes 513 and 513a. Snap ring 514 is fixedly disposed at an inner peripheral surface of the radial inner end region of cylindrical member 510. Coil spring 514a is disposed upon snap ring 514, and resiliently supports ball valve member 530 which is radially movably disposed in hole 513. Ball valve member 530 is received on second valve seat 513b when ball valve member 530 moves upwardly. A plurality of holes 515 are formed at a side portion of cylindrical member 510 so as to link an inner hollow space of circular hole 513 to a radial inner hollow space of large diameter portion 247a of cavity 247. O-ring seal element 516 is disposed at an outer peripheral surface of annular flange 511 of cylindrical member 510 to seal the mating surfaces between the outer peripheral surface of annular flange 511 and the inner peripheral surface of large diameter portion 247a of cavity 247. O-ring seal element 516 sealingly insulates the radial inner hollow space of large diameter portion 247a of cavity 247 from the atmosphere of outside compressor 10. Second valve control mechanism 500 further includes cup-shaped casing 521 which houses annular electromagnetic coil 520, annular cylindrical member 522 forcibly inserted within annular electromagnetic coil 520. A radial inner end portion of annular cylindrical member 522 is forcibly inserted within circular depression 517 which is formed at a radial outer end surface of cylindrical member 510. Cylindrical pedestal 523 of magnetic material is fixedly disposed within a radial outer portion of annular cylindrical member 522. Cylindrical member 524 of magnetic material is radially slidably disposed within a radial inner portion of annular cylindrical member 522. Rod 524a radially extending from a radial inner end surface of cylindrical member 524 is radially slidably disposed in hole 518 which is radially formed through cylindrical member 510. A radial inner end of rod 524a projects into hole 513 and terminates at a position which is adjacent to ball valve member 530. Cylindrical member 524 includes cylindrical hollow space 524b formed at a radial outer end surface thereof. Coil spring 525 is resiliently disposed between the radial inner end surface of pedestal 523 and the radial inner bottom end surface of cylindrical hollow space 524b of cylindrical member 524 so that cylindrical member 524 is urged radially inwardly by the restoring force of coil spring 525. Conduits 245, 246 and 248 are formed in rear end plate 24. Conduit 245 links suction chamber 241 to the front hollow space of large diameter portion 243a of cavity 243. Conduit 246 links hole 151 to the front hollow space of small diameter portion 243b of cavity 243. Conduit 248 links the radial inner hollow apace of small diameter portion 247b of second cylindrical cavity 247 to the front hollow space of small diameter portion 243b of first cylindrical cavity 243. Hole 249 is also formed in rear end plate 24, and links the radial inner hollow space of large diameter portion 247a of cavity 247 to discharge chamber 251. A throttling device, such as, orifice tube 249a is fixedly disposed in hole 249. In the first embodiment of the present invention, first communication path 400a communicating suction chamber 241 to crank chamber 22 is formed by conduit 245, the front hollow space of large diameter portion 243a of cylindrical cavity 243, radial holes 406, cylindrical cavities 403 and 404, axial hole 405, the front hollow space of small diameter portion 243b of cylindrical cavity 243, conduit 246, hole 151 and passage 150, bore 210, hole 221, hole 231, axial hole 262 and radial hole 263. Every portion of first communication path 400a is designed so as to cause a negligible pressure reduction thereat. First valve control mechanism 400 is disposed within first communication path 400a. Second communication path 500a communicating discharge chamber 251 to crank chamber 22 is formed by hole 249, the radial inner hollow space of large diameter portion 247a of cylindrical cavity 247, holes 515, circular holes 513a and 513, the radial inner hollow space of small diameter portion 247b of cylindrical cavity 247, conduit 248, the radial front hollow space of small diameter portion 243b of cylindrical cavity 243, conduit 246, hole 151 and passage 150, bore 210, hole 221, hole 231, axial hole 262 and radial hole 263. Every portion of second communication path 500a is designed so as to cause a negligible pressure reduction thereat except for hole 249 in which orifice tube 249a is fixedly disposed. Second valve control mechanism 500 is disposed within second communication path 500a at the downstream side of hole 249. During operation of compressor 10, drive shaft 26 is rotated by the engine of the vehicle (not shown) through electromagnetic clutch 300. Cam rotor 40 rotates with drive shaft 26, causing slant plate 50 to rotate as well. The rotation of slant plate 50 causes wobble plate 60 to nutate. The nutating motion of wobble plate 60 reciprocates pistons 71 in their respective cylinders 70. As pistons 71 are reciprocated, refrigerant gas introduced into suction chamber 241 through the inlet portion is drawn into cylinders 70 through suction ports 242 and subsequently compressed. The compressed refrigerant gas is discharged from cylinders 70 to discharge chamber 251 through respective discharge ports 252 and then into the cooling circuit through the outlet portion. Some of the partially compressed refrigerant gas in cylinders 70 is blown into crank chamber 22 from cylinders 70 through gaps between respective pistons 71 and cylinders 70 during the compression stroke of pistons 71. (This gas is known as blow-by gas.) In operation of first valve control mechanism 400, the refrigerant gas conducted from suction chamber 241 to the front hollow space of large diameter portion 243a of cavity 243 via conduit 245 flows into cylindrical cavity 403 via holes 406. Therefore, a front surface of diaphragm 428 receives pressure in suction chamber 241. On the other hand, a rear surface of diaphragm 428 receives pressure in the atmosphere which passes through the gap created between the outer peripheral surface of cup-shaped casing 421 and the inner peripheral surface of annular projection 244, and the gap created between the outer peripheral surface of annular plate member 427 and the inner peripheral surface of annular projection 244. Hence, the rear surface of diaphragm 428 always receives the constant value of pressure. A first force rearwardly acting on diaphragm 428 is the sum of the restoring force of coil spring 410 and the force generated by the suction pressure which is received on the front surface of diaphragm 428. A second force forwardly acting on diaphragm 428 is the sum of the restoring force of coil spring 426 and the force generated by the atmospheric pressure which is received on the rear surface of diaphragm 428. Since the value of the restoring force of each of coil springs 410 and 426 are constant when coil springs 410 and 426 have once selected, diaphragm 428 is bent forwardly and rearwardly in response to the changes in the pressure in suction chamber 241. Accordingly, truncated cone shaped portion 407a of cylindrical valve member 407 moves forwardly and rearwardly so as to be received on and left from first valve seat 408 in response to the changes in the pressure in suction chamber 241. That is, first communication path 400a is blocked and communicated by cylindrical valve member 407 in response to the changes in the pressure in suction chamber 241 so that the pressure in suction chamber 241 is adjusted at a predetermined constant value. A first electric current received by electromagnetic coil 422 as a first signal represents a value which is obtained by subtracting the predetermined set value from the measured value of the temperature of air leaving from the evaporator. Hereafter, the above-mentioned value is simply described by "the subtracted value" for an explanation only. The subtracted value is correspondingly transformed to the magnitude of amperage of the first electric current in a process in a micro computer (not shown). The magnitude of amperage of the first electric current is directly proportional to the subtracted value. When electromagnetic coil 422 receives the first electric current from the micro computer through a wire (not shown), magnetic attraction force rearwardly attracting cylindrical member 425 against the restoring force of coil spring 426 is generated. The magnitude of the magnetic attraction force is varied in response to the changes in the magnitude of amperage of the first electric current. Therefore, an axial position of cylindrical member 425 is varied in response to the changes in the magnitude of amperage of the first electric current. The adjusted constant value of the pressure in suction chamber 241 is shifted in response to the changes in the axial position of cylindrical member 425. Therefore, the adjusted constant value of the pressure in suction chamber 241 is shifted in response to the changes in the magnitude of amperage of the first electric currant, i.e., the changes in the subtracted value. For example, when the subtracted value is zero which is represented by a first magnitude of amperage of the first electric current, cylindrical member 425 is located at a first position so that the pressure in suction chamber 241 is adjusted at a first constant value. If the subtracted value is changed from zero to a positive large value, the magnitude of amperage of the first electric current is changed from the first magnitude to a second magnitude which is greater than the first magnitude by a great amount. Therefore, the magnitude of attraction force rearwardly attracting cylindrical member 425 against the restoring force of coil spring 426 is increased with a great amount. Therefore, an axial location of cylindrical member 425 is changed from the first position to a second position which is rearwardly away from the first position with a long distance. Accordingly, the adjusted constant value of the pressure in suction chamber 241 is shifted from the first constant value to a second constant value which is smaller than the first constant value by a great amount. On the other hand, if the subtracted value is changed from zero to a negative large value, the magnitude of amperage of the first electric current is changed from the first magnitude to a third magnitude which is smaller than the first magnitude by a great amount. Therefore, the magnitude of attraction force rearwardly attracting cylindrical member 425 against the restoring force of coil spring 426 is decreased with a great amount. Therefore, the axial location of cylindrical member 425 is changed from the first position to a third position which is forwardly away from the first position with a long distance. Accordingly, the adjusted constant value of the pressure in suction chamber 241 is shifted from the first constant value to a third constant value which is greater than the first constant value by a great amount. In operation of second valve control mechanism 500, the step amount of the accelerator pedal of the vehicle is correspondingly transformed to the magnitude of amperage of a second electric current, which is received by electromagnetic coil 520 as a second signal, in the process of the micro computer. When the step amount of the accelerator pedal is below a predetermined value, that is, when the engine of the vehicle is not demanded to be derived a large amount of energy therefrom, the second electric current of which amperage can generate the magnetic attraction force sufficiently attracting cylindrical member 524 upwardly against the restoring force of coil spring 525 is sent to electromagnetic coil 520 from the micro computer through a wire (not shown). Therefore, ball valve member 530 moves upwardly so as to be received on second valve seat 513b. Therefore, second communication path 500a communicating discharge chamber 251 to crank chamber 22 is blocked. Accordingly, the capacity of compressor 10 is substantially controlled by only operation of first valve control mechanism 400. On the other hand, when the step amount of the accelerator pedal is equal to or exceeds the predetermined value, that is, when the engine of the vehicle is demanded to be derived a large amount of energy therefrom, such as a stage of accelerating the vehicle or a stage of driving the vehicle in an ascent, the second electric current of which amperage is zero is sent to electromagnetic coil r520 from the micro computer through the wire so that no magnetic attraction force is generated by electromagnetic coil 520. Therefore, cylindrical member 524 is urged downwardly by the restoring force of coil spring 525 so that ball valve member 530 moves downwardly so as to be left from second valve seat 513b. Therefore, second communication path 500a is communicated with disregarding operation of first valve control mechanism 400. Accordingly, the capacity of compressor 10 is quickly minimized by operation of second valve control mechanism 500. At the time immediately after changing from the blocking stage to the communicating stage of second communication path 500a, the refrigerant gas in the radial inner hollow space of large diameter portion 247a of cavity 247 maintained at the discharge chamber pressure quickly flows into crank chamber 22 via holes 515, circular holes 513a and 513, the radial inner hollow space of small diameter portion 247b of cylindrical cavity 247, conduit 248, the front hollow space of small diameter portion 243b of cylindrical cavity 243, conduit 246, hole 151 and passage 150, bore 210, hole 221, hole 231, axial hole 262 and radial hole 263. However, once second communication path 500a has been communicated, the refrigerant gas in discharge chamber 251 flows into the radial inner hollow space of large diameter portion 247a of cavity 247 with pressure reduction thereof by virtue of the throttling effect of orifice tube 249a, and then flows into crank chamber 22 via holes 515, circular holes 513a and 513, the radial inner hollow space of small diameter portion 247b of cylindrical cavity 247, conduit 248, the radial front hollow space of small diameter portion 243b of cylindrical cavity 243, conduit 246, hole 151 and passage 150, bore 210, hole 221, hole 231, axial hole 262 and radial hole 263. Accordingly, pressure in crank chamber 22 is quickly increased, but is maintained at a certain blue which can make slant plate 50 be positioned in the minimum slant angle, that is, the capacity of the compressor be minimized, without causing damage of the internal component parts of the compressor. In the event, when the engine of the vehicle is demanded to be derived a large amount of energy therefrom, second communication path 500a is communicated by virtue of operation of second valve control mechanism 500 in order to compulsorily quickly minimize the capacity of the compressor. Therefore, the energy which is derived from the engine to be consumed in operation of the compressor is compulsorily minimized without causing damage of the internal component parts of the compressor. Accordingly, the energy derived from the engine of the vehicle is effectively used for accelerating the vehicle or driving the vehicle in the ascend. Figure 3 illustrates the overall construction or a wobble plate type refrigerant compressor with a variable displacement mechanism in accordance with a second embodiment of the present invention. With reference to Figure 3, compressor 10' is provided with valve retainer 253 of rigid member firmly fixed to a rear end surface of valve plate assembly 200 by bolt 254 and nut 255. One end portion of valve retainer 253 locates upon each of discharge ports 252, and is gradually bent rearwardly in order to prevent an excessive bend of the reed valve annexed to discharge port 252 when the compressed refrigerant gas passes through discharge port 252 during the compression stroke of piston 71. Bolt 254 includes head section 254a which is located in the rear end portion of central bore 210, and shaft section 254b which penetrates through valve plate assembly 200 and valve retainer 253. Shaft section 254b of bolt 254 is screwed into nut 255 so that valve retainer 253 is firmly fixed to valve plate assembly 200. A rear portion of shaft section 254b of bolt 254 is inserted into circular depression 256 which is formed at a central region of an inner surface of rear end plate 24. The rear end of shaft section 254b is located at a position which is approximate two-thirds of the depth of circular depression 256. O-ring seal element 257 is disposed at an inner peripheral surface of circular depression 256 so as to seal the mating surfaces between the outer peripheral surface of shaft section 254b of bolt 254 and the inner peripheral surface of circular depression 256. O-ring seal element 257 sealingly insulates a rear hollow space of circular depression 256 from discharge chamber 251. Conduit 258 is axially bored through bolt 254 so as to link central bore 210 to the rear hollow space of circular depression 256. Radially extending cylindrical cavity 340 is formed in rear end plate 24 at a rear of suction and discharge chambers 241 and 251 along the approximate length of diameter of rear end plate 24. Cylindrical cavity 340 includes large diameter portion 341, intermediate portion 342 extending from an upper end of large diameter portion 341, and small diameter portion 343 extending from an upper end of intermediate portion 342. In the length of diameter, the value is steppedly decreased in order of larger intermediate and small diameter portions 341, 342 and 343. Intermediate diameter portion 342 includes lower section 342a and upper section 342b extending from an upper end of lower section 342a. A diameter of lower section 342a is greater than a diameter of upper section 342b. Valve control device 600 is fixedly disposed in cylindrical cavity 340. With reference to Figure 4 additionally, the construction of valve control device 600 is described in detail below. Valve control device 600 includes cylindrical member 610 which comprises large, intermediate and small diameter regions 611, 612 and 613. Large, intermediate and small diameter regions 611, 612 and 613 of cylindrical member 610 are generally disposed in large, intermediate and small diameter portions 341, 342 and 343 of cavity 340, respectively. An upper end of small diameter region 613 of cylindrical member 610 is located at a position which is approximate one-fourth of the length of small diameter portion 343 of cavity 340. A lower end portion of large diameter region 611 of cylindrical member 610 projects from a side wall of rear end plate 24. Cylindrical member 610 is provided with cylindrical cavity 620 formed therein. Cylindrical cavity 620 comprises large, intermediate and small diameter sections 621, 622 and 623. Cylindrical cavity 620 extends from the lower end surface of cylindrical member 610 in order of large, intermediate and small diameter sections 621, 622 and 623. An upper end of small diameter section 623 of cavity 620 terminates at a position which is approximate two-thirds of the length of intermediate diameter region 612 of cylindrical member 610. An upper end of large diameter section 621 of cavity 620 terminates at a position which is approximate five-sixths of the length of large diameter region 611 of cylindrical member 610. An upper end of intermediate diameter section 622 of cavity 620 terminates at a position which is approximate half way of the length of intermediate diameter region 612 of cylindrical member 610. A lower end of small diameter section 623 of cavity 620 and the upper end of intermediate diameter section 622 of cavity 620 are linked by truncated cone section 622a which functions as a first valve seat. Annular ridge 621a is formed at the boundary between large and intermediate diameter sections 621 and 622. Annular electromagnetic coil 630 is fixedly disposed in large diameter section 621 of cavity 620. First annular cylindrical member 631 of magnetic material having outwardly extending annular flange 631a at its upper end is forcibly inserted into an upper portion of annular electromagnetic coil 630. A lower end of first annular cylindrical member 631 terminates at a position which is approximate half way of the length of annular electromagnetic coil 630. Annular flange 631a is sandwiched between annular ridge 621a and the upper end surface of annular electromagnetic coil 630. Second annular cylindrical member 632 of magnetic material is radially slidably disposed in a lower portion of annular electromagnetic coil 630. Second annular cylindrical member 632 is provided with cylindrical depression 632a formed at a lower end surface thereof. Annular disc member 633 is fixedly disposed at a lower end of coil 630 by inwardly bending a lower end of cylindrical member 610. O-ring seal element 633a is disposed at an outer peripheral surface of annular disc member 633 to seal the mating surfaces between the outer peripheral surface of annular disc member 633 and the inner peripheral surface of large diameter section 621 of cavity 620. Adjusting screw 634 having cylindrical depression 634a formed at an upper end surface thereof is screwed into a threaded inner peripheral surface 633b of annular disc member 633. Central hole 634b is formed through adjusting screw 634. Coil spring 635 is resiliently disposed between the upper bottom surface of cylindrical depression 632a and the lower bottom surface of cylindrical depression 634a. The value of the restoring force of coil spring 635 is adjusted by changing in a radial position of adjusting screw 634. Bellows valve 636 having bellows 636a and valve member 636b fixedly connected to an upper end of bellows 636a is disposed in intermediate diameter section 622 of cavity 620. A lower end of bellows 636a is fixedly and hermetically connected to an upper end surface of annular flange 631a of first annular cylindrical member 631. First rod 636c is disposed in an inner hollow space of bellows valve member 636. An upper end of first rod 636c is fixedly connected to valve member 636b. First rod 636c slidably penetrates through first annular cylindrical member 631. A lower end portion of first rod 636c is screwed into a threaded inner peripheral surface 632b of second annular cylindrical member 632 so that the lower end portion of first rod 636c is firmly connected to second annular cylindrical member 632. Coil spring 637 is disposed in the inner hollow space of bellows 636a with surrounding first rod 636c. Coil spring 637 is resiliently disposed between valve member 636b and annular flange 631a of first annular cylindrical member 631. An interior space of bellows 636a is linked to the atmosphere of the outside compressor via axial hole 634b of adjusting screw 634, cylindrical depressions 634a and 632a, a gap created between the outer peripheral surface of rod 636c and the threaded inner peripheral surface 633b of annular disc member 633, and a gap created between the outer peripheral surface of rod 636c and the inner peripheral surface of first annular cylindrical member 631. Therefore, the interior space of bellows 636a is maintained at the atmospheric pressure having a substantial constant value. O-ring seal element 631b is disposed at an outer peripheral surface of the first annular cylindrical member 631 to seal the mating surfaces between the outer peripheral surface of first annular cylindrical member 631 and the inner peripheral surface of annular electromagnetic coil 630. O-ring seal element 638 is disposed at an outer peripheral surface of an upper end portion of large diameter region 611 of cylindrical member 610 to seal the mating surfaces between the outer peripheral surface of large diameter region 611 of cylindrical member 610 and the inner peripheral surface of large diameter portion 341 of cylindrical cavity 340. O-ring seal element 638 sealingly insulates an upper hollow space of large diameter portion 341 of cavity 340 from the atmosphere outside compressor 10'. A plurality of holes 639 are formed in a lower portion of intermediate diameter region 612 of cylindrical member 610 so as to link intermediate diameter section 622 of cylindrical cavity 620 to the upper hollow space of large diameter portion 341 of cylindrical cavity 340. Hole 344 is formed in rear end plate 24 so as to link the upper hollow space of large diameter portion 341 of cavity 340 to suction chamber 241. A plurality of holes 640 are formed in an approximately mid portion of intermediate diameter region 612 of cylindrical member 610 so as to link small diameter section 623 of cylindrical cavity 620 to an upper hollow space of lower section 342a of intermediate diameter portion 342 of cavity 340. O-ring seal element 641 is disposed at an outer peripheral surface of an outwardly extending annular flange 612a which is formed at an outer peripheral surface of intermediate diameter region 612 of cylindrical member 610, between holes 639 and holes 640, so as to seal the mating surfaces between the outer peripheral surface of annular flange 612a and the inner peripheral surface of lower section 342a of intermediate diameter portion 342 of cavity 340. O-ring seal element 641 sealingly insulates the upper hollow space of lower section 342a of intermediate portion 342 of cavity 340 from the upper hollow space of large diameter portion 341 of cavity 340. Conduit 345 is formed in rear end plate 24 so as to link the upper hollow space of lower section 342a of intermediate diameter portion 342 of cavity 340 to one end of hole 153 which is formed through valve plate assembly conduit 200. The other end of hole 153 is linked to one end of 152 which is formed through cylinder block 21. The other end of conduit 152 is opened to crank chamber 22. Small diameter region 613 of cylindrical member 610 is provided with cylindrical cavity 650 formed therein. Cylindrical cavity 650 includes large diameter section 651 extending from an upper end surface of small diameter region 613 of cylindrical member 610 and small diameter section 652 extending from the lower end of large diameter section 651. Small diameter section 652 of cavity 650 terminates at a position which is a lower end of small diameter region 613 of cylindrical member 610. Annular ridge 652a is formed at the boundary between large and small diameter sections 651 and 652 of cavity 650 so as to function as a second valve seat. A diameter of small diameter section 652 of cylindrical cavity 650 is designed so as to allow a large amount of the refrigerant gas to flow through small diameter section 652 of cavity 650 even though a later-mentioned small diameter portion 636e of second rod 636d is located in small diameter section 652 of cavity 650. Circular disc member 660 is received on annular ridge 651a formed at an inner peripheral surface of upper portion of large diameter section 651 of cavity 650. Circular disc member 660 is firmly secured to annular ridge 651a by inwardly bending an upper end of small diameter region 613 of cylindrical member 610. Circular disc member 660 includes annular projection 660a downwardly projecting from a lower end surface of an outer peripheral portion of circular disc member 660. Circular disc member 660 includes hole 660b formed therethrough so as to link an upper hollow space to a lower hollow space of large diameter section 651 of cylindrical cavity 650 with respect thereto. Cylindrical valve member 661 having truncated cone portion 661a formed at a lower end thereof is radially movably disposed in large diameter section 651 of cavity 650. Valve member 661 further includes cylindrical depression 661b formed at a lower end surface of truncated cone portion 661a. Coil spring 662 is resiliently disposed between the lower end surface of circular disc member 660 and the upper end surface of cylindrical valve member 661 so that cylindrical valve member 661 is urged downwardly by the restoring force of coil spring 662. Truncated cone portion 661a of cylindrical valve member 661 is received on second valve seat 652a when cylindrical valve member 661 moves downwardly. Bellows valve 636 is provided with second rod 636d of which one end is firmly secured to a top portion of valve member 636b of bellows valve 636. Second rod 636d extends upwardly and slidably penetrates through intermediate diameter region 612 of cylindrical member 610 so that the other end of second rod 636d projects into small diameter section 652 of cylindrical cavity 650. Second rod 636d includes smaller diameter portion 636e which upwardly extends from the other end of second rod 636d. Smaller diameter portion 636e of second rod 636d terminates at a position which is adjacent to an upper bottom surface of cylindrical depression 661b of valve member 661. O-ring seal element 663 is disposed at an outer peripheral surface of an upper portion of intermediate diameter region 612 of cylindrical member 610 so as to seal the mating surfaces between the outer peripheral surface of intermediate diameter region 612 of cylindrical member 610 and the inner peripheral surface of upper section 342b of intermediate diameter portion 342 of cavity 340. O-ring seal element 663 sealingly insulates an upper hollow space of upper section 342b of intermediate diameter portion 342 of cavity 340 from the upper hollow space of lower section 342a of intermediate diameter portion 342 of cavity 340. O-ring seal element 664 is disposed at an outer peripheral surface of small diameter region 613 of cylindrical member 610 so as to seal the mating surfaces between the outer peripheral surface of small diameter region 613 of cylindrical member 610 and the inner peripheral surface of small diameter portion 343 of cavity 340. O-ring seal element 664 sealingly insulates the upper hollow space of upper section 342b of intermediate diameter portion 342 of cavity 340 from an upper hollow space of small diameter portion 343 of cavity 340. A plurality of holes 665 are formed in small diameter region 613 of cylindrical member 610 between O-ring seal elements 663 and 664, so as to link the upper hollow space of small diameter section 652 of cavity 650 to the upper hollow space of upper section 342b of intermediate diameter portion 342 of cavity 340. Hole 346 is formed in rear end plate 24 so as to link the upper hollow space of upper section 342b of intermediate diameter portion 342 of cavity 340 to the rear hollow space of circular depression 256. Hole 347 is formed in rear end plate 24 so as to link discharge chamber 251 to the upper hollow space of small diameter portion 343 of cavity 340. A throttling device, such as, orifice tube 347a is fixedly disposed in hole 347. In the second embodiment of the present invention, valve control device 600 includes first and second valve control mechanisms 600a and 600b. First valve control mechanism 600a is substantially formed by electromagnetic coil 630, second annular cylindrical member 632, first rod 636c, bellows valve 636 and first valve seat 622a. First communication path 600c communicating suction chamber 241 to crank chamber 22 is formed by hole 344, the upper hollow space of large diameter portion 341 of cylindrical cavity 340, holes 639, intermediate diameter, truncated cone and small diameter sections 622, 622a and 623 of cylindrical cavity 620, holes 640, the upper hollow space of lower section 342a of intermediate diameter portion 342 of cylindrical cavity 340, conduit 345, hole 153 and conduit 152. Every portion of first communication path 600c is designed so as to cause a negligible pressure reduction thereat. First valve control mechanism 600a is disposed within first communication path 600c. Second valve control mechanism 600b is substantially formed by electromagnetic coil 630, second rod 636d, valve member 661 and second valve seat 652a. Second communication path 600d communicating discharge chamber 251 to crank chamber is formed by hole 347, the upper hollow space of small diameter portion 343 of cylindrical cavity 340, the upper hollow space or large diameter section 651 of cylindrical cavity 650, hole 660b, the lower hollow space of large diameter section 651 of cylindrical cavity 650, small diameter section 652 of cylindrical cavity 650, holes 665, the upper hollow space of upper section 342b of intermediate diameter portion 342 of cylindrical cavity 340, hole 346, the rear hollow space of circular depression 256, conduit 258, bore 210, hole 221, hole 231, axial hole 262 and radial hole 263. Every portion of second communication path 600d is designed so as to cause a negligible pressure reduction thereat except for hole 347 in which orifice tube 347a is fixedly disposed. Second valve control mechanism 600b is disposed within second communication path 600d at the downstream side of hole 347. In the second embodiment of the present invention, an operational manner of compressor 10' is substantially similar to the operational manner described in the first embodiment of the present invention without an operational manner of valve control device 600. Therefore, only the operational manner of valve control device 600 is described in detail below. In operation of first valve control mechanism 600a, the refrigerant gas conducted from suction chamber 241 to the upper hollow space of large diameter portion 341 of cavity 340 via hole 344 flows into intermediate diameter section 622 of cylindrical cavity 620 via holes 639. Therefore, an exterior surface of bellows 636a receives pressure in suction chamber 241 so that a first force tending to radially contract bellows 636a is generated. The contracting motion of bellows 636a moves valve member 636b of bellows valve 636 downwardly. A value of the first force is varied in response to the changes in the pressure in suction chamber 241. A second force tending to move valve member 636b upwardly is the sum of the restoring force of coil spring 637 and the restoring force of coil spring 635. Since the value of the restoring force of each of coil springs 637 and 635 are constant when coil spring 637 has once selected and when the restoring force of coil spring 635 has once adjusted, valve member 636b of bellows valve 636 is moved downwardly and upwardly in response to the changes in the pressure in suction chamber 241. Accordingly, valve member 636b moves upwardly and downwardly so as to be received on and left from first valve seat 622a in response to the changes in the pressure in suction chamber 241. That is, first communication path 600c is blocked and communicated by valve member 636b of bellows valve 636 in response to the changes in the pressure in suction chamber 241 so that the pressure in suction chamber 241 is adjusted at a predetermined constant value. A first electric current received by electromagnetic coil 630 as a first signal represents the subtracted value. A second electric current also received by electromagnetic coil 630 as a second signal represents the step count of the accelerator pedal of the vehicle. The subtracted value is correspondingly transformed to the magnitude of amperage of the first electric current in a process in a micro computer (not shown). The magnitude of amperage of the first electric current is inversely proportional to the subtracted value. The step amount of the accelerator pedal of the vehicle is correspondingly transformed to the magnitude of amperage of the second electric current in the process of the micro computer. When electromagnetic coil 630 receives the first electric current from the micro computer through a wire (not shown), magnetic attraction force upwardly attracting cylindrical member 632, thereby moving upwardly valve member 636b of bellows valve 636 through first rod 636c is generated. The magnitude of the magnetic attraction force is varied in response to the changes in the magnitude of amperage of the first electric current. Therefore, the radial position of cylindrical member 632 is varied in response to the changes in the magnitude of amperage of the first electric current. The adjusted constant value of the pressure in suction chamber 241 is shifted in response to the changes in the radial position of cylindrical member 632. Therefore, the adjusted constant value of the pressure in suction chamber 241 is shifted in response to the changes in the magnitude of amperage of the first electric current, i.e., the changes in the subtracted value. For example, when the subtracted value is zero which is represented by a first magnitude of amperage of the first electric current, cylindrical member 632 is located at a first posttion so that the pressure in suction chamber 241 is adjusted at a first constant value. If the subtracted value is changed from zero to a positive large value, the magnitude of amperage of the first electric current is changed from the first magnitude to a second magnitude which is smaller than the first magnitude by a great amount. Therefore, the magnitude of attraction force upwardly attracting cylindrical member 632 against the first force is decreased with a great amount. Therefore, a radial location of cylindrical member 632 is changed from the first position to a second position which is downwardly away from the first position with a long distance. Accordingly, the adjusted constant value of the pressure in suction chamber 241 is shifted from the first constant value to a second constant value which is smaller than the first constant value by a great amount. On the other hand, if the subtracted value is changed from zero to a negative large value, the magnitude of amperage of the first electric current is changed from the first magnitude to a third magnitude which is greater than the first magnitude by a great amount. Therefore, the magnitude of attraction force upwardly attracting cylindrical member 632 against the first force is increased with a great amount. Therefore, the radial location of cylindrical member 632 is changed from the first position to a third position which is upwardly away from the first position with a long distance. Accordingly, the adjusted constant value of the pressure in suction chamber 241 is shifted from the first constant value to a third constant value which is greater than the first constant value by a great amount Furthermore, in the process of the micro computer, the magnitude of amperage of the first electric current is varied from zero to the predetermined magnitude in response to the changes in the subtracted value. When electromagnetic coil 630 receives the first electric current of which the magnitude of amperage varying from zero to the predetermined maximum magnitude, first valve control mechanism 600a normally operates. In operation of second valve control mechanism 600b, when the step amount of the accelerator pedal is below a predetermined value, that is, when the engine of the vehicle is not demanded to be derived a large amount of energy therefrom, the first signal overrides the second signal in the process of the micro computer. Therefore, electromagnetic coil 630 receives only the first electric current from the micro computer. Accordingly, the capacity of compressor 10' is controlled by operation of first valve control mechanism 600a. On the other hand, when the step amount of the accelerator pedal is equal to or exceeds the predetermined value, that is, when the engine of the vehicle is demanded to be derived a large amount of energy therefrom, such as a stage of accelerating the vehicle or a stage of driving the vehicle in an ascent, the micro computer calculates whether a difference between the magnitude of amperage of the first electric current at a present time and the predetermined maximum magnitude of amperage of the first electric current exceeds a predetermined value. If the above-mentioned difference exceeds a predetermined amount, the first signal is overridden by the second signal in the process of the micro computer so that electromagnetic coil 630 receives the second electric current of which amperage is the predetermined maximum magnitude of amperage of the first electric current from the micro computer through the wire. Therefore, increase in the magnetic attraction force upwardly attracting cylindrical member 632 is large so that cylindrical member 632 is moved upwardly against the first force until valve member 636b of bellows valve 636 is received on first valve seat 622a. Concurrently, cylindrical valve member 661 is moved upwardly against the restoring force of coil spring 662 through first rod 636c, valve member 636b of bellow valve 636 and second rod 636d so that cylindrical valve member 661 is left from second valve seat 652a. Therefore, second communication path 600d communicating discharge chamber 251 to crank chamber 22 is communicated so that the capacity of compressor 10' is quickly minimized. On the other hand, if the above-mentioned difference does not exceed the predetermined amount, the first signal still overrides the second signal in the process of the micro computer. Therefore, the capacity of compressor 10' is still controlled by operation of first valve control mechanism 600a. At the time immediately after changing from the blocking stage to the communicating stage of second communication path 600d, the refrigerant gas in the upper hollow space of small diameter portion 343 of cavity 340 maintained at the discharge chamber pressure quickly flows into crank chamber 22 via the upper hollow space of large diameter section 651 of cavity 650, hole 660b, the lower hollow space of large diameter section 651 of cavity 650, small diameter section 652 of cavity 650, holes 665, the upper hollow space of upper section 342b of intermediate diameter portion 342 of cylindrical cavity 340, hole 346, the rear hollow space of circular depression 256, conduit 258, bore 210, hole 221, hole 231, axial hole 262 and radial hole 263. However, once second communication path 600d has been communicated, the refrigerant gas in discharge chamber 251 flows into the hollow space of small diameter portion 343 of cavity 340 with pressure reduction thereof by virtue of the throttling effect of orifice tube 347a, and then flows into crank chamber 22 via the upper hollow space of large diameter section 651 of cavity 650, hole 660b, the lower hollow space of large diameter section 651 of cavity 650, small diameter section 652 of cavity 650, holes 665, the upper hollow space of upper section 342b of intermediate diameter portion 342 of cylindrical cavity 340, hole 346, the rear hollow space of circular depression 256, conduit 258, bore 210, hole 221, hole 231, axial hole 262 and radial hole 263. Accordingly, pressure in crank chamber 22 is quickly increased, but is maintained at a certain value which can make slant plate 50 be positioned in the minimum slant angle, that is, the capacity of the compressor be minimized, without causing damage of the internal component parts of the compressor. In the event, when the engine of the vehicle is demanded to be derived a large amount of energy therefrom, second communication path 600d is communicated by virtue of operation of second valve control mechanism 600b in order to compulsorily quickly minimize the capacity of the compressor. Therefore, the energy which is derived from the engine to be consumed in operation of the compressor is compulsorily minimized without causing damage of the internal component parts of the compressor. Accordingly, the energy derived from the engine of the vehicle is effectively used for accelerating the vehicle or driving the vehicle in the ascend. Figure 5 illustrates the overall construction of a wobble plate type refrigerant compressor with a variable displacement mechanism in accordance with a third embodiment of the present invention. With reference to Figure 5, compressor 10'' is provided with valve control device 700 disposed within radially extending cylindrical cavity 840 which is formed in rear end plate 24 at a rear of suction and discharge chambers 241 and 251 along the approximate length of diameter of rear end plate 24. Cylindrical cavity 840 includes large diameter portion 841, intermediate portion 842 extending from an upper end of large diameter portion 841, and small diameter portion 843 extending from an upper end of intermediate portion 842. In the length of diameter, the value is steppedly decreased in order of large, intermediate and small diameter portions 841, 842 and 843. With reference to Figure 6 additionally, the construction of valve control device 700 is described in detail below. Valve control device 700 includes cylindrical member 710 having large diameter region 711 and small diameter region 712 which extends from an upper end surface of large diameter region 711. Large and small diameter regions 711 and 712 of cylindrical member 710 are fixedly disposed in large and intermediate diameter portions 841 and 842 of cavity 840, respectively. Cylindrical member 710 is provided with first cylindrical cavity 720 and second cylindrical cavity 730 formed therein. First cylindrical cavity 720 extends from an upper end surface of small diameter region 712 of cylindrical member 710 and terminates at a position which is immediately below an upper end of large diameter region 711 of cylindrical member 710. Second cylindrical cavity 730 extends from a lower end surface of large diameter region 711 of cylindrical member 710 and terminates at a position which is approximate two-thirds of the length of large diameter region 711 of cylindrical member 710. Second cylindrical cavity 730 includes large diameter portion 731 and small diameter portion 732 which extends from an upper end of large diameter portion 731. Annular ridge 731a functioning as a first valve seat is formed at the boundary between large and small diameter portions 731 and 732. Circular plate member 740 located at the lower end side of cylindrical member 710 is fixedly disposed in cylindrical cavity 840. Circular plate member 740 is provided with circular depression 740a formed at an upper end surface thereof. Circular plate member 740 includes cylindrical projection 740b downwardly projects from a lower end surface thereof. Circular hole 741 is formed through cylindrical projection 740b and links to circular depression 740a at its upper end. Diaphragm 742 is fixedly sandwiched between the lower end surface of cylindrical member 710 and the upper end surface of circular plate member 740. An upper surface of a central region of diaphragm 742 faces to a large diameter portion 731 of second cylindrical cavity 730, and a lower surface of a central region of diaphragm 742 faces to circular depression 740a of circular plate member 740. Cylindrical member 743 is radially slidably disposed in circular depression 740a of circular plate member 740. Cylindrical member 743 includes circular projection 743a downwardly extending from a lower end surface thereof. Adjusting screw 744 is screwed into hole 741. Adjusting screw 744 includes circular projection 744a upwardly projecting from an upper end surface thereof. Coil spring 745 is resiliently disposed between cylindrical member 743 and adjusting screw 744 with surrounding projections 743a and 744a. Cylindrical member 743 is urged upwardly by the restoring force of coil spring 745 so that an upper end surface of cylindrical member 743 is in contact with the lower surface of the central region of diaphragm 742. The value of the restoring force of coil spring 745 is adjusted by changing in a radial location of adjusting screw 744. Annular electromagnetic coil 750 is fixedly disposed in first cylindrical cavity 720. Annular cylindrical member 751 is fixedly disposed within annular electromagnetic coil 750. Cylindrical member 752 of magnetic material is radially slidably disposed within a lower half portion of annular cylindrical member 751. Cylindrical member 752 is provided with cylindrical depression 752a formed at a lower end surface thereof. Cylindrical depression 752a extends from the lower end surface of cylindrical member 752 and terminates at a position which is approximate half way of the length of cylindrical member 752. A lower end of cylindrical member 752 projects into circular depression 711a formed at the upper end surface of large diameter region 711 of cylindrical member 710. Cylindrical valve member 760 is radially movably disposed within large diameter portion 731 of second cylindrical cavity 730. Cylindrical valve member 760 includes first truncated cone portion 760a formed at an upper end surface thereof and second truncated cone portion 760b formed at a lower end surface thereof. Lower end surface of second truncated cone portion 760b is in contact with the upper surface of diaphragm 742. First truncated cone portion 760a is received on first valve seat 731a when cylindrical valve member 760 is moved upwardly. Rod 760c upwardly extending from an upper end surface of first truncated cone portion 760a slidably penetrates through large diameter region 711 of cylindrical member 710. A top end of rod 760c projects into cylindrical depression 752a of cylindrical member 752 through circular depression 711a. Cylindrical member 753 radially movably disposed within cylindrical depression 752a is firmly connected to the top end of rod 760c. Cylindrical member 753 includes an outwardly extending annular flange 753a formed at a lower end thereof. Cylindrical member 770 is fixedly disposed in small diameter portion 843 of cylindrical cavity 840. A lower half portion of cylindrical member 770 projects into intermediate diameter portion 842 of cavity 840. A lower end surface of cylindrical member 770 is in contact with an annular upper end surface of electromagnetic coil 750. Cylindrical projection 770a of magnetic material projecting from the lower end surface of cylindrical member 770 is forcibly inserted into annular cylindrical member 751. An outwardly extending annular flange 770b is formed at a lower end of cylindrical member 770. Annular flange 770b is firmly secured to the upper end of cylindrical member 710 by inwardly bending the upper end of cylindrical member 710. Cylindrical member 770 is provided with cylindrical cavity 771 formed therein. Cylindrical cavity 771 extends from an upper end surface of cylindrical member 770 and terminates at a position which is adjacent to a lower end of cylindrical member 770. Cylindrical member 772 is fixedly disposed in cylindrical cavity 771. A lower end of cylindrical member 772 is located at a position which is approximate one-third of the length of cylindrical cavity 771. An upper end of cylindrical member 772 upwardly projects from the upper end surface of cylindrical member 770. Cylindrical member 772 includes first cylindrical depression 772a formed at a lower end surface thereof and second cylindrical depression 772b formed at an upper end surface thereof. A diameter of a lower end portion of second cylindrical depression 772b is gradually decreased in the downward direction so as to form second valve seat 772c. Hole 772d is formed in cylindrical member 772 so as to link first to second cylindrical depressions 772a and 772b. A diameter of hole 772d is designed so as to allow a large amount of the refrigerant gas to flow through hole 772d even though a later-mentioned small diameter portion 773b of rod 773a is located in hole 772d. First circular plate 773 is radially movably disposed in a lower end portion of cylindrical cavity 771. Red 773a projects upwardly from an upper end surface of first circular plate 773. Rod 773a includes small diameter portion 773b extending from an upper end surface thereof. Small diameter portion 773b of rod 773a radially movably penetrates through hole 772d. Coil spring 774 is resiliently disposed between the upper bottom surface of first cylindrical depression 772a of cylindrical member 772 and the upper end surface of first circular plate 773 with surrounding rod 773a. Second circular plate 775 is radially slidably disposed within second cylindrical depression 772b of cylindrical member 772. Second circular plate 775 includes circular projection 775a which upwardly projects from an upper end surface of second circular plate 775, and concave depression 775b which is formed at a lower end surface of second circular plate 775 so as to be able to receive ball valve member 776 therein. A plurality of holes 775c are formed through second circular plate 775 so as to link an upper to a lower hollow space of second cylindrical depression 772b with respect to second circular plate 775. Third circular plate 777 having a central hole 777a is disposed at an upper portion of cylindrical member 772. Third circular plate 777 includes annular projection 777b downwardly projecting from an outer periphery of a lower end surface thereof. Annular projection 777b is received on annular ridge 772e formed at an upper portion of an inner peripheral surface of second cylindrical depression 772b. Third circular plate 777 is firmly secured to the upper portion of cylindrical member 772 by inwardly bending the upper end of cylindrical member 772. Rod 755 radially slidably penetrating through cylindrical projection 770a is fixedly connected to first circular plate 773 at its upper end. A lower end of rod 755 is fixedly connected to an upper end portion of cylindrical member 752. Coil spring 778 is resiliently disposed between the lower end surface of third circular plate 777 and the upper end surface of second circular plate 775 with surrounding circular projection 775a. The restoring force of coil spring 778 urges second circular plate 775 downwardly so that ball valve member 776 is urged downwardly. Coil spring 754 is resiliently disposed between the upper end surface of annular flange 753a of cylindrical member 753 and the upper bottom surface of cylindrical depression 752a. When the restoring force of coil spring 754 is appropriately selected, the upper end surface of annular flange 753a of cylindrical member 753 is maintained to be in contact with a lower end surface of cylindrical member 752 by the restoring force of coil springs 774 and 745. However, when cylindrical member 752 is further moved upwardly in a situation in which first truncated cone portion 760a of cylindrical valve member 760 is received on first valve seat 731a, the lower end surface of cylindrical member 752 is left from the upper end surface of annular flange 753a of cylindrical member 753. Furthermore, when cylindrical member 752 moves downwardly from a situation in which the lower end surface of cylindrical member 752 is left from the upper end surface of annular flange 753a of cylindrical member 753, the lower end surface of cylindrical member 752 can softly contact with the upper end surface of annular flange 753a of cylindrical member 753 through coil spring 754. First and second annular grooves 711b and 711c are formed at an outer peripheral surface of large diameter region 711 of cylindrical member 710. First annular groove 711b is located at the upper side of second annular groove 711c. A plurality of first holes 711d link first annular groove 711b to small diameter portion 732 of second cylindrical cavity 730. A plurality of second holes 711e link second annular groove 711c to large diameter portion 731 of second cylindrical cavity 730. Conduits 154 and 155 are formed in rear end plate 24. Conduit 154 links first annular groove 711b to crank chamber 22 through hole 153 and conduit 152. Conduit 155 links second annular groove 711c to suction chamber 241. First, second and third O-ring seal elements 841a, 841b and 841c are disposed at the outer peripheral surface of large diameter region 711 of cylindrical member 710 to seal the mating surfaces between the outer peripheral surface of large diameter region 711 of cylindrical member 710 and the inner peripheral surface of large diameter portion 841 of cylindrical cavity 840. First O-ring seal element 841a is located at the upper side of first annular grove 711b. Second O-ring seal element 841b is located between first and second annular grooves 711b and 711c. Third O-ring seal element 841c is located at the lower side of second annular groove 711c adjacent to diaphragm 742. First O-ring seal element 841a sealingly insulates an upper hollow space of large diameter portion 841 of cylindrical cavity 840 from first annular groove 711b. Second O-ring seal element 841b sealingly insulates first annular groove 711b from second annular groove 711c. Third O-ring seal element 841c sealingly insulates from second annular groove 711c from the atmosphere of outside compressor 10''. Fourth O-ring seal element 843a is disposed at an outer peripheral surface of cylindrical member 770 to seal the mating surfaces between the outer peripheral surface of cylindrical member 770 and the inner peripheral surface of small diameter portion 843 of cylindrical cavity 840. Fourth O-ring seal element 843a sealingly insulates an upper hollow space of small diameter portion 843 of cavity 840 from an upper hollow space of intermediate diameter portion 842 of cavity 840. A plurality of holes 770c are bored through cylindrical member 770 so as to link the upper hollow space of intermediate diameter portion 842 to the lower end portion of cylindrical cavity 771. Hole 156 is formed in rear end plate 24 so as to link the upper hollow space of small diameter portion 843 of cavity 840 to discharge chamber 251. A throttling device, such as, orifice tube 156a is fixedly disposed in hole 156. Conduit 157 is axially bored through cylinder block 21, valve plate assembly 200 and rear end plate 24 so as to link the upper hollow space of intermediate portion 842 of cavity 840 to crank chamber 22. In the third embodiment of the present invention, valve control device 700 includes first and second valve control mechanisms 700a and 700b. First valve control mechanism 700a is substantially formed by diaphragm 742, cylindrical valve member 760, first valve seat 731a, cylindrical member 753, rod 760c, cylindrical member 752 and electromagnetic coil 750. First communication path 700c communicating suction chamber 241 to crank chamber 22 is formed by conduit 155, second annular groove 711c, holes 711e, large and small diameter portions 731 and 732 of cylindrical cavity 730, holes 711d, first annular groove 711b, conduit 154, hole 153 and conduit 152. Every portion of first communication path 700c is designed so as to cause a negligible pressure reduction thereat. First valve control mechanism 700a is disposed within first communication path 700c. Second valve control mechanism 700b is substantially formed by ball valve member 776, second valve seat 772c, rod 755, first circular plate 773 and electromagnetic coil 750. Furthermore, Second communication path 700d communicating discharge chamber 251 to crank chamber 22 is formed by hole 156, the upper hollow space of small diameter portion 843 of cylindrical cavity 840, hole 777a, the upper hollow space of second cylindrical depression 772b, holes 775c, the lower hollow space of second cylindrical depression 772b, hole 772d, first cylindrical depression 772a, cylindrical cavity 771, holes 770c, the upper hollow space of intermediate diameter portion 842 of cylindrical cavity 840 and conduit 157. Every portion of second communication path 700d is designed so as to cause a negligible pressure reduction thereat except for hole 156 in which orifice tube 156a is fixedly disposed. Second valve control mechanism 700c is disposed within second communication path 700d at the downstream side of hole 156. In the third embodiment of the present invention, an operational manner of compressor 10'' is also substantially similar to the operational manner described in the first embodiment of the present invention without an operational manner of valve control device 700. Therefore, the operational manner of valve control device 700 is described in detail below. In operation of first valve control mechanism 700a, the refrigerant gas conducted from suction chamber 241 to second annular groove 711c via conduit 155 flows into large diameter portion 731 of cylindrical cavity 730 via boles 711e. Therefore, an upper surface of diaphragm 742 receives pressure in suction chamber 241. On the other hand, a lower surface of diaphragm 742 receives pressure in the atmosphere which flows from the outside compressor to circular depression 740a via the gap created between the outer peripheral surface of adjusting screw 744 and the inner peripheral surface of circular hole 741. Hence, the lower surface of diaphragm 742 always receives the constant value of pressure. A first force downwardly acting on diaphragm 742 is the sum of the restoring force of coil spring 774 and the force generated by the suction pressure which is received on the upper surface of diaphragm 742. A second force upwardly acting on diaphragm 742 is the sum of the restoring force of coil spring 745 and the force generated by the atmospheric pressure which is received on the lower surface of diaphragm 742. Since the value of the restoring force of each of coil springs 774 and 745 are constant when coil spring 774 has once selected and when the restoring force of coil spring 745 has once adjusted, diaphragm 742 is bent upwardly and downwardly in response to the changes in the pressure in suction chamber 241. Accordingly, first truncated cone shaped portion 760a of cylindrical valve member 760 moves upwardly and downwardly so as to be received on and left from first valve seat 731a in response to the changes in the pressure in suction chamber 241. That is, first communication path 700c is blocked and communicated by cylindrical valve member 760 in response to the changes in the pressure in suction chamber 241 so that the pressure in suction chamber 241 is adjusted at a predetermined constant value. A first electric current received by electromagnetic coil 750 as a first signal represents the subtracted value. A second electric current also received by electromagnetic coil 750 as a second signal represents the step amount of the accelerator of the vehicle. The subtracted value is correspondingly transformed to the magnitude of amperage of the first electric current in a process in a micro computer (not shown). The magnitude of amperage of the first electric current is inversely proportional to the subtracted value. When electromagnetic coil 750 receives the first electric current from the micro computer through a wire (not shown), magnetic attraction force upwardly attracting cylindrical member 752 against the restoring force of coil spring 774, thereby upwardly moving cylindrical valve member 760 through rod 760c and cylindrical member 753 is generated. The magnitude of the magnetic attraction force in varied in response to the changes in the magnitude of amperage of the first electric current. Therefore, a radial position of cylindrical member 752 is varied in response to the changes in the magnitude of amperage of the first electric current. The adjusted constant value of the pressure in suction chamber 241 is shifted in response to the changes in the radial position of cylindrical member 752. Therefore, the adjusted constant value of the pressure in suction chamber 241 is shifted in response to the changes in the magnitude of amperage of the first electric currant, i.e., the changes in the subtracted value. For example, when the subtracted value is zero which is represented by a first magnitude of amperage of the first electric current, cylindrical member 752 is located at a first position so that the pressure in suction chamber 241 is adjusted at a first constant value. If the subtracted value is changed from zero to a positive large value, the magnitude of amperage of the first electric current is changed from the first magnitude to a second magnitude which is smaller than the first magnitude by a great amount. Therefore, the magnitude of attraction force upwardly attracting cylindrical member 752 against the restoring force of coil spring 774 is decreased with a great amount. Therefore, a radial location of cylindrical member 752 is changed from the first position to a second position which is downwardly away from the first position with a long distance. Accordingly, an adjusted constant value of the pressure in suction chamber 241 is shifted from the first constant value to a second constant value which is smaller than the first constant value by a great amount. On the other hand, if the subtracted value is changed from zero to a negative large value, the magnitude of amperage of the first electric current is changed from the first magnitude to a third magnitude which is greater than the first magnitude by a great amount. Therefore, the magnitude of attraction force rearwardly attracting cylindrical member 752 against the restoring force of coil spring 774 is increased with a great amount. Therefore, the radial location of cylindrical member 752 is changed from the first position to a third position which is upwardly away from the first position with a long distance. Accordingly, an adjusted constant value of the pressure in suction chamber 241 is shifted from the first constant value to a third constant value which is greater than the first constant value by a great amount. In operation of second valve control mechanism 700b, when the step amount of the accelerator pedal is below a predetermined value, that is, when the engine of the vehicle is not demanded to be derived a large amount of energy therefrom, the first signal overrides the second signal in the process of the micro computer. Therefore, electromagnetic coil 750 receives only the first electric current. Accordingly, the capacity of compressor 10'' is controlled by operation of first valve control mechanism 700a. On the other hand, when the step amount of the accelerator pedal is equal to or exceeds the predetermined value, that is, when the engine of the vehicle is demanded to be derived a large amount of energy therefrom, such as a stage of accelerating the vehicle or a stage of driving the vehicle in an ascent, the second signal overrides the first signal in the process of the micro computer. Therefore, electromagnetic coil 750 receives the second electric current of which amperage is a predetermined magnitude which can generate the magnetic attraction force sufficiently attracting cylindrical member 752 upwardly against the restoring force of coil springs 774 and 778. In detail, cylindrical member 752 is moved upwardly against the restoring force of only coil spring 774 until an upper end of small diameter portion 773b of rod 773a becomes in contact with a lower spherical surface of ball valve member 776. Then, cylindrical member 752 is further moved upwardly with pushing ball valve member 776 upwardly through rods 755 and 773a against the restoring force of coil spring 778 in addition to the restoring force of coil spring 774 so that ball valve member 776 is left from second valve seat 772c. Therefore, second communication path 700d communicating discharge chamber 251 to crank chamber 22 is communicated by operation of second valve control mechanism 700b. That is, the capacity of compressor 10'' is quickly minimized by operation of second valve control mechanism 700b. Furthermore, the maximum magnitude of amperage of the first current is appropriately determined so that ball valve member 776 is maintained to be received on second valve seat 772c, thereby maintaining to block second communication path 700d in the operation of first valve control mechanism 700a. At the time immediately after changing from the blocking stage to the communicating stage of second communication path 700d, the refrigerant gas in the upper hollow space of small diameter portion 843 of cavity 840 maintained at the discharge chamber pressure quickly flows into crank chamber 22 via hole 777a, the upper hollow space of second cylindrical depression 772b, holes 775c, the lower hollow space of second cylindrical depression 772b, hole 772d, first cylindrical depression 772a, cylindrical cavity 771, holes 770c, the upper hollow space of intermediate diameter portion 842 of cylindrical cavity 840 and conduit 157. However, once second communication path 700d has been communicated, the refrigerant gas in discharge chamber 251 flows into the upper hollow space of small diameter portion 843 of cavity. 840 with pressure reduction thereof by virtue of the throttling effect of orifice tube 156a, and then flows into crank chamber 22 via hole 777a, the upper hollow space of second cylindrical depression 772b, holes 775c, the lower hollow space of second cylindrical depression 772b, hole 772d, first cylindrical depression 772a, cylindrical cavity 771, holes 770c, the upper hollow space of intermediate diameter portion 842 of cylindrical cavity 840 and conduit 157. Accordingly, pressure in crank chamber 22 is quickly increased, but is maintained at a certain value which can make slant plate 50 be positioned in the minimum slant angle, that is, the capacity of the compressor be quickly minimized, without causing damage of the internal component parts of the compressor. In the event, when the engine of the vehicle is demanded to be derived a large amount of energy therefrom to drive the vehicle, second communication path 700d is communicated by virtue of operation of second valve control mechanism 700b in order to compulsorily quickly minimize the capacity of the compressor. Therefore, the energy which is derived from the engine to be consumed in operation of the compressor is compulsorily minimized without causing damage of the internal component parts of the compressor. Accordingly, the energy derived from the engine of the vehicle is effectively used for accelerating the vehicle or driving the vehicle in the ascend. This invention has been described in connection with the preferred embodiments. These embodiments, however, are merely for example only and the invention is not restricted thereto. For example, the terms right and left are used merely for convenience of description, and the invention is not restricted in this manner.

Claims: A slant plate type compressor (10) including a compressor housing (20) enclosing a crank chamber (22), a suction chamber (241) and a discharge chamber (251) therein, the compressor housing comprising a cylinder block (21) having a plurality of cylinders (70), a piston (71) slidably fitted within each of the cylinders (70), a drive means coupled to the pistons (71) for reciprocating the pistons (71) within the cylinders (70), the drive means including a drive shaft (26) rotatably supported in the housing (20), coupling means for drivingly coupling the pistons (71) with the drive shaft (26) and for converting rotary motion of the drive shaft (26) into reciprocating motion of the pistons (71), the coupling means including a slant plate (50) having a surface disposed at a slant angle relative to a plane perpendicular to the drive shaft (26), the slant angle changing in response to a change in pressure in the crank chamber (22) relative to the suction pressure to change the capacity of the compressor (10), a first communication path (400a) linking the crank chamber (22) with the suction chamber (241), a first valve control mechanism (400) disposed within the first communication path (400a), the first valve control mechanism (400) controlling the opening and closing of the first communication path (400a) in response to changes in pressure in the suction chamber (241), a second communication path (500a) linking the crank chamber (22) with the discharge chamber (251) a second valve control mechanism (500) disposed within the second communication path (500a) the second valve control mechanism (500) responding to an external signal and opening the second communication path (500a) to increase the pressure in the crank chamber (22), to thereby minimize the capacity of the compressor (10), characterised by a throttling means (249a) disposed within the second communication path (500a) between the discharge chamber (251) and the second valve control mechanism (500) so as to regulate the quantity of fluid which flows from the discharge chamber (251) to the crank chamber (22) when the second valve control mechanism (500) opens the second communication path (500a) and wherein the first (400) and the second valve control mechanisms (500) operate independently. A compressor (10) according to claim 1, wherein the first valve control mechanism (400) includes pressure sensing means for sensing pressure in the suction chamber (241). A compressor (10) according to claim 2, wherein the pressure sensing means is a diaphragm (428). A compressor (10) according to claim 2, wherein the pressure sensing means is a bellows (636a). A compressor (10) according to claim 1, the first valve control mechanism (400) including a first valve member (407), the first communication path (400a) including a first valve seat (408) formed at one portion thereof, the second valve control mechanism (500) including a second valve member (530), the second communication path (500a) including a second valve seat (513b) formed at one portion thereof, the first communication path (400a) being opened and closed when the first valve member (407) is moved away from and received on the first valve seat (408), the second communication path (500a) being opened and closed when the second valve member (530) is moved away from and received on the second valve seat (513b), the second valve member (530) moved away from the second valve seat (513b) and the first valve member (407) received on the first valve seat (408) when the second valve control mechanism (500) opens the second communication path (500a). A compressor (10) according claim 1, further comprising a cavity (247a) disposed in the second communication path (500a) between the throttling means (249a) and the second valve control mechanism (500). A compressor (10) according to claim 6, wherein the cavity (247a) is cylindrical. A compressor (10) according to claim 1, further comprising means for storing discharge pressure fluid, disposed in the second communication path (500a) between the throttling means (249a) and the second valve control mechanism (500). A compressor (10) according to claim 1, further comprising means for reducing the capacity of the compressor (10) disposed in the second communication path (500a) between the throttling means (249a) and the second valve control mechanism (500). A compressor (10) according to claim 1, wherein the second valve control mechanism (500) comprises a valve cavity (247a) and a valve seat (513b), the valve cavity (247a) disposed in the second communication path (500a) upstream of the valve seat (513b), and wherein the throttling means (249a) is in fluid communication with the valve cavity (247a).

Inventors: INOUE ATSUO C O SANDEN CORPORA, INOUE, ATSUO, C/O SANDEN CORPORATION
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1992
Main classification: F04B1
IPC codes: F04B27