SCROLL TYPE COMPRESSOR WITH VARIABLE DISPLACEMENT MECHANISM

Abstract: A scroll type compressor with a variable displacement mechanism is disclosed which includes a housing (10) having a inlet port and an outlet port. A fixed scroll (21) is fixedly disposed with the housing and has a circular end plate (211) from which a first spiral element (212) extends. The circular end plate of the fixed scroll divides the interior of the housing into a front chamber (27) and a rear chamber (28). The front chamber (27) communicates with a fluid inlet port. The rear chamber (28) is divided into a discharge chamber (281) which communicates with a fluid outlet port and a central fluid pocket formed by both scrolls, and an intermediate pressure chamber (282). At least one pair of holes is formed through the circular end plate of the fixed scroll to form a fluid channel between the fluid pockets and the intermediate pressure chamber (282). A communicating channel (29) formed through the circular end plate of the fixed scroll provides a fluid channel betwee the intermediate pressure chamber (282) and the front chamber (27). Control mechaism (30) disposed on a portion of the intermediate pressure chamber (282) controls opening and closing of the communicating channel (29). A valve element of the control device is controlled by the compressed fluid in the central fluid pocket.

Description: The present invention relates to a scroll type compressor, and more particularly, to a scroll type compressor with a variable displacement mechanism. A compressor for use in an automotive air conditioning system is generally driven by an automobile engine through an electromagnetic clutch. If the compressor does not have a variable displacement mechanism, when the engine rotates at high speed, i.e., the compressor is driven at high speed, the capacity of the compressor is too high, and thereby requiring turning on and off of the electromagnetic clutch frequently. The changes of the load of the engine become large, and the automotive speed and the acceleration performance may thus be lower. For the purpose oif resolving the above problems, a scroll type compressor which can vary the compression ratio is well known in the art. For example, US-A- 4,744,733 shows such a compressor. With reference to Figure 1, a scroll type compressor with a conventional variable displacement mechanism is disclosed. Control mechanism 1 which includes cylinder 2 , piston valve 3 , bellows 4 , and spring 5 , Is disposed in a compressor housing to open and close the communication between suction chamber 6 and intermediate pressure chamber 7. Bellows 4 is disposed within piston valve 3 to open and close the communication between suction chamber 6 and discharge chamber 8 in accordance wih the refrigerant pressure in suction chamber 6. Piston valve 3 is slidably fitted within cylinder z and is supported by spring 5 to open the communication between suction chamber 6 and intermediate pressure chamber 7 when the pressure in suction chamber 6 is balanced to the pressure in discharge chamber 8. Piston valve 3 moves downward against the force of spring 5 to close the communication between suction chamber 6 and intermediate pressure chamber 7 when the pressure in the discharge chamber 8 is higher that that in suction chamber 6, and bellows 4 closes the communication between discharge chamber 8 and suction chamber 6 . Contrarily, piston valve 3 is moved upward by the force of spring 5 to open the communication between suction chamber 6 and intermediate presure chamber 7 when bellows 4 opens the communication between suction chamber 6 and discharge chamber 8 even though the pressure in discharge chamber 8 is at first higher than that in suction chamber 6 . In the above compressor, since the high pressure refrigerant gas in discharge chamber 8 is introduced into the upper portion of cylinder z through orifice tube 9 , piston valve 3 closes the communication between suction chamber 6 and intermediate pressure chamber 7 until the pressure in suction chamer 6 is balanced to that in discharge chamber 8 after the compressor has stopped operating. Bellows 4 contracts by increase of the pressure in suction chamber 6 after termination of operation of the compressor, and thereby closing the communication between suction chamber 6 and discharge chamber 8 . Thus, the pressure in the upper portion of cylinder 2 increases until the same as the pressure in discharge chamber 8 and then piston valve 3 moves downward to completely prevent the communication between suction chamber 6 and intermediate pressure chamber 7 . If the compressor starts to operate again while piston valve 3 closes the communication between suction chamber 6 and intermediate pressure chamber 7 , the compressor starts to operate at the largest volume, and thereby producing large damage of a driving mechanism of the automobile. In addition, the life of the compressor may be reduced. It is a primary object of this invention to provide a scroll type compressor with a variable displacement mechanism which can release the shock for a driving mechanism of an automobile when the compressor restarts. It is another object of this invention to provide a scroll type compressor with a variable displacement mechanism which can restart operation thereof at the lowest volume. It is still another object of this invention to provide a scroll type compressor with a variable displacement mechanism with a high durability. A scroll type compressor according to the present invention includes a housing having a inlet port and an outlet port. A fixed scroll is fixedly disposed with the housing and has a circular end plate from which a first spiral element extends into the interior of the housing. An orbiting scroll has a circular end plate from which a second spiral element extends. The two spiral elements interfit at an angular and radial offset to make a plurality of line contacts and to define at least one pair of fluid pockets within the interior of the housing. A driving mechanism is operatively connected to the orbiting scroll to effect orbital motion of the orbiting scroll. A rational preventing mechanism prevents rotation of the orbiting scroll during the orbital motion. The circular end plate of the fixed scroll divides the interior of the housing into a front chamber and a rear chamber. The front chamber communicates with a fluid inlet port. The rear chamber is divided into a discharge chamber which communicates with the outlet port and a central fluid pocket formed by both scrolls, and an intermediate pressure chamber. At least one pair of holes is formed through the circular end plate of the fixed scroll to form a fluid channel between the fluid pockets and the intermediate pressure chamber. A communicating channel formed through the circular end plate of the fixed scroll forms a fluid channel between the intermediate pressure chamber and the front chamber. Control means disposed on a portion of the intermediate pressure chamber controls fluid communication between the intermediate pressure chamber and the front chamber, the control means comprising a valve element operated by the compressed fluid in a space in which exhaust pressure prevails, a cylinder, a piston slidably disposed within the cylinder and a control valve element, a top portion of the cylinder being connected to the space, and the control valve element controlling the communication between the space and the front chamber. The compressor is characterised in that the space is the central fluid pocket. In the accompanying drawings : Figure 1 is a cross-sectional view of a scroll type compressor with a conventional variable displacement mechanism; Figure 2 is a cross-sectional view of a scroll type compressor with a variable displacement mechanisme in accordance with one embodiment of this invention; Figure 3 is a partial cross-sectional view of a scroll type compressor with a variable displacement mechanisme in accordance with an alternate embodiment of this invention; and, Figure 4 is a cross-sectional view of a scroll type compressor with a variable displacement mechanisme in accordance with another embodiment of this invention. Referring to Figure 2, a scroll type compressor according to one embodiment of this invention is shown. The scroll type compressor includes a compressor housing 10 having front end plate 11 and cup-shaped casing 12 which is attached to an end surface of end plate 11. Opening 111 is formed in the center of front end plate 11 and drive shaft 13 is disposed in opening 111. Annular projection 112 is formed in a rear surface of front end plate 11. Annular projection 112 faces cup-shaped casing 12 and is concentric with opening 111. An outer peripheral surface of projection 112 extends into an inner wall of the opening of cup-shaped casing 12. Opening 121 of cup-shaped casing 12 is covered by front end plate 11. O-ring 14 is placed between the outer peripheral surface of annular projection 112 and the inner wall of the opening of cup-shaped casing 12 to seal the mating surface of front end plate 11 and cup-shaped casing 12. Annular sleeve 16 projects from the front end surface of front end plate 11, surrounds drive shaft 13, and defines a shaft seal cavity. In the embodiment shown in Figure 2, sleeve 16 is integrally formed with front end plate 11. Alternatively, sleeve 16 may be fixed to the front end surface of front end plate 11 by screws. Drive shaft 13 is rotatably supported by sleeve 16 through bearing 17 located within the front end of sleeve 16. Drive shaft 17 has disk-shaped rotor 131 at its inner end which is rotatably supported by front end plate 11 through bearing 15 located within opening 111 of front end plate 11. Shaft seal assembly 18 is coupled to drive shaft 13 within the shaft seal cavity of sleeve 16. Pulley 201 is rotatably supported by ball bearing 19 which is carried on the outer surface of sleeve 16, electromagnetic coil 202 is fixed about the outer surface of sleeve 16 by a support plate. Armature plate 203 is elastically supported on the outer end of drive shaft 13. Pulley 201, electromagnetic coil 202, and armature plate 203 form electromagnetic clutch 20. In operation, drive shaft 13 is driven by an external power source, for example, the engine of an automobile, through a rotation transmitting device such as electromagnetic clutch 20. Fixed scroll 21, orbiting scroll 22, a driving mechanism for orbiting scroll 22, and rotation preventing/thrust bearing mechanism 24 for orbiting scroll 22 are disposed in the interior of housing 10. Fixed scroll 21 includes circular end plate 211 and spiral element 212 affixed to or extending from one end surface of circular end plate 211. Fixed scroll 21 is fixed within the inner chamber of cup-shaped casing 12 by screws (not shown) screwed into end plate 211 from the outside of cup-shaped -casing 12. Circular end plate 211 of fixed scroll 21 partitions the inner chamber of cup-shaped casing 12 into two chambers, front chamber 27 and rear chamber 28. Spiral element 212 is located within front chamber 27. Partition wall 122 projects axially from the inner end surface of cup-shaped casing 12. The end surface of portion wall 122 contacts the end surface of circular end plate 211. Thus, partition wall 122 divides rear chamber 28 into discharge chamber 281 formed at the center portion of rear chamber 21 and intermediate pressure chamber 282. A gasket(not shown) may be disposed betweent the end surface of partition wall 122 and end plate 211 to secure the sealing. Orbiting scroll 22, which is located in front chamber 27, includes circular end plate 221 and spiral element 222 extending from one end surface of circular end plate 221. Spiral element 222 of orbiting scroll 22 and spiral element 212 of fixed scroll 21 interfitting at an angular offset of 180° and a predetermined radial offset, form sealed spaces between spiral elements 212 and 222. Orbiting scroll 22 is rotatably supported by bushing 23, which is eccentrically connected to the inner end of disc-shaped rotor 131 through radial needle bearing 231. While orbiting scroll 22 orbits, rotation is prevented by rotation preventing/thrust bearing mechanism 21 which is placed between the inner end surface of front end plate 11 and circular end plate 221 of orbiting scroll 22. Rotation preventing/thrust bearing mechansim 24 includes fixed ring 241, fixed race 242, orbiting ring 243, orbitlng race 244, and balls 245. Fixed ring 241 is attached to the inner end surface of front end plate 11 thorough fixed race 212 and has a plurality of circulate holes 241a. Orbiting ring 243 is attached to the rear end of orbiting scroll 22 through orbiting race 211 and has a plurality of circular holes 243a, Each ball 215 is placed between hole 243a of fixed ring 211 and circular hole 243a of orbiting ring 243, and moves along the edges of both circular holes 241a and 243a. Also, the axial thrust load from orbiting scroll 22 is supported on front end plate 11 through balls 245. Compressor housing 10 is provided with an inlet port and an outlet port (not shown) for connecting the compressor to an external refrigeration circuit. Refrigeration fluid from the external circuit is introduced into suction chamber 271 through the inlet port and flows into sealed spaces formed between spiral elements 212 and 222 through open spaces between the spiral elements. The spaces between the spiral elements sequentially open and close during the orbital motion of orbiting scroll 22. When the spaces are open, fluid to be compressed flows into these spaces but no compression occurs. When the spaces are closed, no additional fluid flows into the spaces and compression begins. Since the location of the outer terminal ends of spiral elements 212 and 222 is at a final involute angle, location of the spaces is directly related to the final involute angle. Furthermore, refrigeration fluid in the sealed space is moved radially inwardly and iscompressed by the orbital motion of orbiting scroll 22. Compressed refrigeration fluid at the center sealed space is discharged to discharge chamber 281 through discharge port 213, which is formed at the center of circular end plate 211. A pair of holes, one of which is 214 and the other one is not shown, are formed in end plate 211 of fixed scroll 21 and are symetrically placed so that an axial end surface of spiral element 222 of orbiting scroll 22 simultaneously crosses over both holes. Both holes communicate between the sealed space and intermediate pressure chamber 282. Hole 214 is placed at a position defined by involute angle 1(not shown) and opens along the inner side wall of spiral element 212. The other hole is placed at a position defined by involute angle (1-π)(not shown) and opens along the outer side wall of spiral element 212. A control device, such as valve member having valve plates is attached by fasteners to the end surface of end plate 211 opposite the above holes, respectively, Each valve plate is made of a spring type material so that the bias of each valve plate pushes it against the opening of holes to close each hole. End plate 211 of fixed scroll 21 also has communicating channel 29 at an outer side portion of the terminal end of spiral element 212. Communicating channel 29 connects suction chamber 271 of front chamber 27 and intermediate pressure chamber 282 through control mechanism 30 and opening 122a which is formed through partition wall 122. Control mechanism 30 controls fluid communication between suction chamber 271 and intermediate pressure chamber 282 and includes cylinder 301, piston valve 302, bellows 303, and spring 304. Piston valve 302 is slidably disposed within cylinder 301 and has openings 302a and 302b, Piston 302 is pushed upwardly (to the night in Figure 2) by spring 304 disposed between the bottom portion of cylinder 301 and the lower end surface of piston 302. Bellows 303 is disposed in the interior of piston valve 302, and includes needle-ball portion 303a and bellows portion 303b. Needle-ball portion 303a is disposed within opening 302a and connected to the upper end of bellows portion 303b through a connecting rod. Opening 302a is formed on the upper portion of piston valve 302. Cylinder 301 is connected to central pocket 272 defined spiral elements 212, 222 through bypass hole 31, which includes first conduit 311 which is formed through circular end plate 211, interior space 312 which is formed in partition wall 122, and second conduit 313 which is formed in the inner end surface of cup-shaped casing 12. First conduit 311 directly connects central pocket 272 with interior space 312 and interior space 312 is coupled with second conduit 313 through orifice tube. One end of orifice tube 314 is covered with filter 315 which is disposed within interior space 312. When the pressure in cylinder 301 is less than the pressure within bellows portion 303b, i.e., the air conditioning load is small, bellows portion 303b expands, control valve 30 is pushed rightwardly, and opening 302a of piston valve 302 is opened. Therefore, central pocket 272 is placed in fluid communication with the interior of piston valve 302 through bypass hole 31, and the compression ratio is reduced. When the pressure in cylinder 301 is greater than the pressure within bellows portion 303b, i.e., the air conditioning load is large, bellows portion 303b contracts and control mechanism 30 is pushed leftwardly and obstructs opening 302a of piston valve 302. Thus, central pocket 272 is not in fluid communication with the interior of piston valve 302, and the compressed fluid from central pocket 272 acts on the upper end surface of piston valve 302 to push leftwardly piston valve 302 against the recoil strength of spring 304. This obstructs communication between suction chamber 271 and intermediate pressure chamber 282 and increases tje compression ratio. As mentioned above, the compressor is automatically controlled to be a predetermined suction pressure and thereby controlling the compression ratio. Even though the compressor is stopped when control mechanism 30 obstructs communication between suction chamber 271 and intermediate pressure chamber 282, the high pressure gas in central pocket 272 leaks into the pockets , which are located outwardly of central pocket 272 since orbiting scroll 22 reacts on the direction opposite to the rotational direction of drive shaft 13 by the expanding force of the compressed pressure gas in the spaces defined by both the spiral elements 222,212. Therefore, upon restarting operation, the compressor can start at the lowest volume. The force of bellows portion 303b is controlled by adjusting screw mechanism 303c. With reference to Figure 3, a part of a scroll type compressor with a variable displacement mechanism in accordance with another embodiment of this invention is shown. Bottom plate 40 is disposed on the inner end surface of annular end plate 211 of fixed scroll 21 and extends to the opening of bypass hole 31. Therefore, the volume of gas flow which passes through bypass hole 31 is throttled, and thereby being able to omit an orifice and a capillary. A control mechanism in accordance with the invention applied to US-A-4,744,733 is sown in Figure 4.

Claims: 1. A scroll type compressor including a housing having an inlet port and an outlet port, a fixed scroll (21) fixedly disposed within the housing and having a circular end plate (211) from which a first spiral element (212) extends into the interior of the housing, an orbiting scroll (22) having a circular end plate (221) from which a second spiral element (222) extends, the spiral elements interfitting at an angular and radial offset to make a plurality of line contact and define at least one pair of fluid pockets within the interior of the housing, a driving mechanism operatively connected to the orbiting scroll to effect the orbital motion of the orbiting scroll, a rotation preventing mechanism (24) for preventing the rotation of the orbiting scroll during the orbital motion, the circular end plate of the fixed scroll dividing the interior of the housing into a front chamber and a rear chamber, the front chamber communicating with the inlet port, and the rear chamber being divided into a discharge chamber (281) which communicates between the outlet port and a central fluid pocket (272) foirmed by both the scrolls and an intermediate pressure chamber (282), at least one pair of holes (214) formed through the circular end plate of the fixed scoll forming a fluid channel between the fluid pockets and the intermediate pressure chamber, a communication channel (29) formed through the circular end plate of the fixed scroll to form a fluid channel between the intermediate pressure chamber and the front chamber, and control means (30) disposed on a portion of the intermediate pressure chamber for controlling fluid communication between the intermediate pressure chamber and the front chamber, the control means comprising a valve element operated by the compressed fluid in a space in which exhaust pressure prevails, a cylinder (301), a piston (302) slidably disposed within the cylinder, and a control valve element (303), a top portion of the cylinder being connected to the space, and the control valve element controlling the communication between the space and the front chamber. characterised in that the space is the central fluid pocket (272) 2. A scoll type compressor according to claim 1, wherein the valve element is disposed in the piston.

Inventors: MABE, ATSUSHI, YAMAMOTO, TAMAKI
Applicants: SANDEN CORPORATION
Application year: 1988
Main classification: F04C29
IPC codes: F04C28, F04B49, F04C18