SLANT PLATE TYPE COMPRESSOR WITH VARIABLE DISPLACEMENT MECHANISM

Abstract: A slant plate type compressor 10 has a plurality of cylinders 70 formed around the periphery of a cylinder block 21 and a piston 71 slidably fitted within each cylinder. A coupling mechanism drivingly couples a rotor 40 to the pistons 71 such that rotary motion of the rotor is converted into reciprocating motion of the pistons. The coupling mechanism includes a plate 50 having a surface disposed at a slant angle relative to the drive shaft and the slant angle changes in response to a change in pressure in a crank chamber 22 to change the capacity of the compressor. The compressor housing includes a rear end plate 24 defining suction 241 and discharge 251 chambers. A communication path 210,195-198 connects the crank chamber and the suction chamber. A valve control mechanism 19,80 controls the opening and closing of the communication path to cause changes of pressure in the crank chamber, the valve control mechanism including first 19 and second 80 valve control devices disposed within the communication path in series. The first valve control 19 device operates in response to pressure in the suction chamber 241 and the second valve control device 80 operates in response to an external signal. When pressure in the suction chamber falls below a predetermined value, the first valve control device 19 closes the communication path so that unusual decreasing pressure in the suction chamber, which might cause seizure of frictional members of the compressor, is prevented.

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 compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system is disclosed in US-A-3,861,829. As disclosed therein, the compression ratio of the compressor may be controlled by changing the the slant angle of the sloping surface of the wobble plate. The slant angle of the wobble plate is adjusted by changing crank chamber pressure which is generated by controlling communication between the suction chamber and the crank chamber. In JP-A-60-135,680 corresponding US-A-4,586,874, the communication between the suction chamber and the crank chamber is controlled by an electromagnetic valve which is operated by receiving an external signal, such as, an electrical ON/OFF signal having a variable ON/OFF ratio. In the ON/OFF signal, an ON signal and an OFF signal cause the communication between the suction chamber and the crank chamber to be accomplished and to be blocked respectively. Therefore, when the communication between the suction chamber and the crank chamber is controlled by a high ON ratio signal, the crank chamber is substantially maintained at suction chamber pressure whereby the compressor is maintained at maximum displacement. Accordingly, when the electromagnetic valve receives the high ON ratio signal in an operation of the compressor with extremely high revolution, unusual decreasing of suction chamber pressure occurs so that frictional members of the compressor may be damaged, for example, seizure of frictional members due to reducing of the lubricating oil in the compressor. Accordingly, it is an object of this invention to provide a variable capacity slant plate type compressor in which an externally controlled valve control mechanism can control a communication between a suction chamber and a crank chamber without unusual decreasing of suction chamber pressure. DE-A-2 704 729 discloses a method of operating a slant plate type compressor for use in a refrigeration circuit, the compressor including a compressor housing having a cylinder block provided with a plurality of cylinders; a front end plate disposed on one end of the housing and enclosing a crank chamber within the housing; a piston slidably located within each of the cylinders; a drive mechanism coupled to the pistons to reciprocate the pistons within the cylinders, the drive mechanism including a drive shaft rotatably supported in the housing, a rotor coupled to the drive shaft and rotatable therewith, and coupling means for drivingly coupling the pistons, such that the rotary motion of the rotor is converted into reciprocating motion of the pistons, the coupling means including a plate having a surface disposed at a slant angle relative to the drive shaft, the slant angle changing in response to a change in pressure in the crank chamber to change the capacity of the compressor; a rear end plate disposed on the opposite end of the housing from the front end plate and defining a suction chamber and a discharge chamber therein; a communication path linking the crank chamber with the suction chamber; a valve control means for controlling the opening and closing of the communication path to cause a change in pressure in the crank chamber, the valve control means including a first valve control means comprising a bellows valve, operating in response to pressure in the suction chamber and a second valve control means comprising an electromagnetic valve, operating in response to an external signal, the first and second valve control means being disposed along the communication path in series, and, according to the invention, such a method is characterised in that the electromagnetic valve controls the communication path between the suction chamber and the bellows valve; in that under normal operation an external electrical ON/OFF signal having a variable ON/OFF ratio is continuously sent to the electromagnetic valve to set the instantaneous opening of the communication path and set the instantaneous capacity of the compressor; and in that the bellows valve acts as a low pressure safety valve such that when the suction chamber pressure falls to a dangerously low level, the bellows valve expands to close the communication path between the suction chamber and crank chamber, thereby causing pressure to build up in the crank chamber, forcing the slant plate into a less inclined position and thus reducing the capacity of the compressor. The single figure of the accompanying drawings is a sectional view of a wobble plate type refrigerant compressor in accordance with this invention. Although the present invention is described below in terms of a wobble plate type compressor, is not limited in this respect. The present invention is broadly applicable to slant plate type compressors. A wobble plate type refrigerant compressor in accordance with one embodiment of the present invention is shown in drawing. 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 formed between cylinder block 21 and 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 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 formed centrally in front end plate 23 for supporting drive shaft 26 through bearing 30 disposed therein. The inner end portion of drive shaft 26 is rotatable supported by bearing 31 disposed within central bore 210 of cylinder block 21. Bore 210 extends to a rearward (to the right in drawing) end surface of cylinder block 21 and houses first valve control device 19 described in detail below. 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 inserted in slot 52 to form a hinged joint. Pin member 42 slides within slot 52 to allow adjustment of the angular position of slant plate 50 with respect to the longitudinal axis of drive shaft 26. Wobble plate 60 is rotatably mounted on slant plate 50 through bearing 61 and 62. Fork shaped slider 63 is attached to the outer peripheral end of wobble plate 60 by pin member 64 and is suitably mounted on sliding rail 65 disposed between front end plate 23 and cylinder block 21. Fork shaped slider 63 prevents rotation of wobble plate 60. Wobble plate 60 reciprocates along rail 65 when cam rotor 40 rotates. Cylinder block 21 includes a plurality of peripheral located cylinder chamber 70 in which pistons 71 reciprocate. Each piston 71 is coupled to wobble plate 60 by a corresponding connecting rod 72. A pair of seamless piston rings 73 made of polytetrafluoroethylene is disposed at an outer peripheral surface of piston 71. Piston rings 73 prevent the wear of both aluminum alloy piston 71 and aluminum alloy cylinder block 21 due to friction therebetween and prevent any direct contact between piston 71 and the inner surface of cylinder 70. Rear end plate 24 includes peripheral 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 cylinder 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 provides with suitable reed valves as described in US-A-4,011,029. Suction chamber 241 includes inlet portion 241a which is connected to an evaporator of an external cooling circuit (not shown). Discharge chamber 251 is provided with outlet portion 251a 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 mating surface of cylinder block 21, valve plate 25 and rear end plate 24. Snap ring 33 is attached to drive shaft 26 to be adjacent to an open end of bore 210 (to the left in drawing). Bias spring 34 is mounted on drive shaft 26 to have a its location between an rear end surface of slant plate 50 (to the right in drawing) and snap ring 33 so as to continuously urge slant plate 50 toward the maximum slant angle thereof with respect to a perpendicular to an axis of drive shaft 26, that is, the maximum compressor displacement. First valve control device 19 including cup-shaped casing member 191 is disposed within central bore 210. Cup-shaped casing member 191 defines valve chamber 192 therein. O-Ring 19a is disposed at an outer surface of casing member 191 to seal the mating surface of casing member 191 and cylinder block 21. Circular plate 194 having hole 194a is fixed to an open end (to the right in drawing) of cup-shaped casing member 191 to leave an axial gap 194b between valve plate 25 and itself. Screw member 18 for adjusting an axial location of drive shaft 26 is disposed between the inner end of drive shaft 26 and a closed end (to the left in drawing) of cup-shaped casing 191. Screw member 18 includes hole 18a formed at a center thereof. Hole 19b is formed at a center of a closed end of casing member 191 to face hole 18a. First valve control device 19 further includes valve member 193 having bellows 193a, valve element 193b attached to a top end (to the left in drawing) of bellows 193a and male screw element 193c attached to a bottom end (to the right in drawing) of bellows 193a. Bellows 193a is charged with gas to maintain predetermined range of pressure, for example, 1.0-1.2 KG/cm².G which is permitted as a range of normal lowest pressure in suction chamber 241. Male screw element 193c is screwed into circular plate 194 to firmly secure the bottom end of bellows 193a to circular plate 194. First conduit 195 radially extending from gap 194b is formed at a rear end (to the right in drawing) of cylinder block 21 and is terminated at hole 196 formed at valve plate 25. Second conduit 197 axially extending from hole 196 is formed at rear end plate 24 and is terminated at electromagnetic valve 80 as a second valve control device. Third conduit 198 axially extending from electromagnetic valve 80 is also formed at reat end plate 24 and is terminated at suction chamber 241. Therefore, a communication path between crank chamber 22 and suction chamber 241 is obtained by via a gap between bearing 31 and the outer peripheral surface of drive shaft 26 and the inner wall of bore 210, hole 18a, hole 19b, valve chamber 192, hole 194a, gap 194b, first conduit 195, hole 196, second conduit 197 and third conduit 198. Accordingly, bellows 193a contracts and expands longitudinally to open and close hole 19b in response to pressure in suction chamber 241. Electromagnetic valve 80 controls a communication between second conduit 197 and third conduit 198 in response to an external signal, such as, an electrical ON/OFF signal having variable ON/OFF ratio. During operation of compressor 10, drive shaft 26 is rotated by the enging of the vehicle (not shown) through electromagnetic clutch 300. Cam rotor 40 is rotated with drive shaft 26 causing slant plate 50 to rotate. 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 cylinder 70. As pistons 71 are reciprocated, refrigerant gas is introduced into suction chamber 241 through inlet portion 241a 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 outlet portion 251a. When electromagnetic valve 80 receives a low ON ratio signal, the communication between second conduit 197 and third conduit 198 is substantially blocked. Therefore, the communication between crank chamber 22 and suction chamber 241 is substantially blocked even though first valve control device 19 operates in response to any pressure in suction chamber 241. Accordingly, pressure in crank chamber 22 is gradually increased by inter-compressed refrigerant gas blown through a gap between piston 71 and cylinder 70 thereby the slant angle of wobble plate 60 tends to be minimized against a urging force of bias spring 34 to minimize the compressor displacement. On the other hand, when electromagnetic valve 80 receives a high ON ratio signal, the communication between second conduit 197 and third conduit 198 is substantially accomplished. Therefore, when pressure in suction chamber 241 exceeds pressure in bellows 193 a thereby bellows 193a contracts to open hole 19b, the communication between crank chamber 22 and suction chamber 241 is substantially accomplished. Accordingly, pressure in crank chamber 22 is decreased to the pressure in suction chamber 241 thereby the slant angle of wobble plate 60 is maximized to maximize the compressor displacement. Operation of compressor 10 with maximum displacement makes pressure in suction chamber 241 decrease. However, when pressure in suction chamber 241 falls below pressure in bellows 193a thereby bellows 193a expands to close hole 19b, the communication between crank chamber 22 and suction chamber 241 is substantially blocked even though the communication between second conduit 197 and third conduit 198 is substantially accomplished. Accordingly, pressure in crank chamber 22 is gradually increased by inter-compressed refrigerating gas blown through the gap between piston 71 and cylinder 70 thereby the slant angle of wobble plate 60 tends to be minimized against the urging force of bias spring 34 to minimize the compressor displacement. As described above, even though the electromagnetic valve receives the high ON ration in the operation of the compressor with extremely high revolution, unusual decreasing of suction chamber pressure is prevented thereby the compressor can be prevented from damage, such as, seizure of frictional members of the compressor.

Claims: A method of operating a slant plate type compressor (10) for use in a refrigeration circuit, the compressor including a compressor housing (20) having a cylinder block (21) provided with a plurality of cylinders (70); a front end plate (23) disposed on one end of the housing and enclosing a crank chamber (22) within the housing; a piston (71) slidably located within each of the cylinders; a drive mechanism (26,40,50,60,72) coupled to the pistons to reciprocate the pistons within the cylinders, the drive mechanism including a drive shaft (26) rotatably supported in the housing, a rotor (40) coupled to the drive shaft and rotatable therewith, and coupling means (50,60,72) for drivingly coupling the pistons, such that the rotary motion of the rotor is converted into reciprocating motion of the pistons, the coupling means including a plate (50) having a surface disposed at a slant angle relative to the drive shaft, the slant angle changing in response to a change in pressure in the crank chamber to change the capacity of the compressor; a rear end plate (24) disposed on the opposite end of the housing fromm the front end plate and defining a suction chamber (241) and a discharge chamber (251) therein; a communication path (210,195,196,197,198) linking the crank chamber with the suction chamber; a valve control means (19,80) for controlling the opening and closing of the communication path to cause a change in pressure in the crank chamber, the valve control means including la first valve control means (19) comprising a bellows valve (193a,193b), operating in response to pressure in the suction chamber and a second valve control means (80) comprising an electromagnetic valve (80), operating in response to an external signal, the first and second valve control means being disposed along the communication path in series, characterised in that the electromagnetic valve (80) controls the communication path between the suction chamber and the bellows valve (193a,193b); in that under normal operation an external electrical ON/OFF signal having a variable ON/OFF ratio is continuously sent to the electromagnetic valve to set the instantaneous opening of the communication path and set the instantaneous capacity of the compressor; and in that the bellows valve acts as a low pressure safety valve such that when the suction chamber pressure falls to a dangerously low level, the bellows valve expands to close the communication path between the suction chamber and crank chamber, thereby causing pressure to build up in the crank chamber, forcing the slant plate into a less inclined position and thus reducing the capacity of the compressor.

Inventors: TERAUCHI, KIYOSHI
Applicants: SANDEN CORPORATION
Application year: 1989
Main classification: F04B1
IPC codes: F04B49, F04B27