Scroll-type compressor with variable displacement mechanism

Abstract: A scroll-type variable displacement compressor used in an air conditioning system of a vehicle having a fixed scroll (25) and an orbiting scroll (26), wherein the minimum operating capacity has been lowered, is disclosed. The improvement consists of cylinder (48a) which is hollowed out within an end plate (251) of the fixed scroll (25) and which accommodates a capacity control mechanism and a plurality of pairs of bypass holes (51a,51b,51a',51b') which penetrate the end plate of the fixed scroll and the cylinder perpendicularly. Via one party of a pair of bypass holes the cylinder can communicate with compression chamber (P1,P2) enclosed by the orbiting scroll and the fixed scroll, and, via the other pair of the party of bypass holes, the cylinder can communicate with a low pressure chamber (54a) provided within rear portions of a compressor housing. One part of the low pressure chamber is always open to the suction chamber (40). The communication between the cylinder and low pressure chamber is controlled by the position of a piston (43) slidably accommodated within the cylinder. When the thermal load for the air-conditioning system is low, the piston retreats to the most recessed position of the cylinder, opening all pairs of bypass holes. By providing the low pressure chamber, an extra branch path (L2) for returning refrigerant gas is given, in addition to the conventional returning path (L1). Thus, pressure loss from the compression chamber through the suction chamber is reduced effectively. As a result, the capacity control mechanism of the present invention increases the feed back of refrigerant gas from the compression chamber to the suction chamber. Thus, the capacity control mechanism of the present invention can lower the minimum operating capacity lower than that of a conventional device, without any undesired increase in the size or weight of the compressor.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scroll-type compressor with a variable displacement mechanism. More particularly, it relates to a scroll-type compressor with a variable displacement mechanism for which the minimum operating capacity is improved. 2. Description of the Related Art Generally, a method of returning a portion of refrigerant gas in the compression chamber to the suction chamber is well known in the field of scroll-type compressors. Fig. 1 is a longitudinal cross sectional view of a prior art conventional compressor 1' according to Japanese patent publication Hei 5-280476. In Fig. 1, the capacity control mechanism 600 is comprised of: cylinder 510 which is hollowed out within the end plate 501 of fixed scroll 500; a plurality of bypass holes 530 which allow compression chambers 520a, 520b to be in communication with the cylinder 510; a plunger 540 which can open or close the bypass holes 530 sequentially; and a mechanism which regulates the position of plunger 540 along the axis of the cylinder 510. The outermost one of the bypass holes 530 permits cylinder 510 to be in communication with suction chamber 550. The mechanism that regulates the position of plunger 540 is comprised of control valve assembly 560, control pressure chamber 570, spring 580, and stopper 590. The control valve assembly 560 regulates the pressure in the control pressure chamber 570 so as to increase said pressure when the thermal load for the air conditioning system is high, and decrease it when the thermal load is low. Accordingly, when the thermal load is high, the plunger 540 is pushed to the radially outward direction of the compressor by the pressure in the control pressure chamber 570, so that the bypass holes 530 are closed sequentially. As a result, the return of the refrigerant gas from compression chamber 520a, 520b to suction chamber 550 is blocked, and the compressor operates at its maximum capacity. When the thermal load is low, the force exerted by the spring 580 overcomes the counter force exerted by the pressure in control pressure chamber 570, and therefore, plunger 540 is pushed to the radially inward direction of the compressor, so that the bypass holes 530 open sequentially. As a result, the return of the refrigerant gas from compression chambers 520a, 520b to suction chamber 550 is allowed, and the capacity of the compressor is decreased automatically. When the thermal load is very small, plunger 540 is in the most recessed position within cylinder 510, opening all bypass holes 530. In this state, part of the refrigerant gas in compression chamber 520a, for example, returns to suction chamber 550 via the path L1' as indicated in Fig. 1 . It is expected that the compressor should operate at its minimum capacity, for example, at about 25 percent of the full capacity of the compressor. However, in a compressor according to the prior art, minimum operating capacity does not decrease to the 25 percent due to the prior art's design. The design impedes the compressor from going down to its expected lower limit of capacity, due to path resistance against the returning gas from compression chambers 520a, 520b to suction chamber 550. The path resistance is affected by various factors, such as the diameter of bypass holes 530, cross sectional area of cylinder 510, the length of the path, and the bendings of the path for the returning gas. This phenomenon of path resistance manifests itself as a large pressure loss which means that the pressure difference between the compression chamber, where the returning gas departs, and the suction chamber, where the returning gas arrives, is large. For a long time, it has been desired to reduce the pressure loss of returning gas in a capacity control mechanism in order to secure a sufficient quantity of returning gas and to realize the expected minimum capacity. There are physical restrictions, however, that limit the ability to improve path resistance. For example, the diameter of the bypass holes can be no larger than the thickness of the spiral element 502, or else there is undesired communication between neighboring compression chambers when the bypass holes are closed by plunger 540. Similarly, the cross sectional diameter of cylinder 510 can be no larger than the thickness of end plate 501 of fixed scroll 500. Moreover, if the thickness of the end plate 501 is increased for the purpose of providing a larger sectional diameter of cylinder 510, the size in the axial direction of the compressor and weight of the compressor will be undesirably increased. From US patent 5,451,146 a scroll-type variable-displacement compressor for use with refrigerant gas according to the preamble of claim 1 is known. A single communication between the compression chambers and the suction chamber is provided. SUMMARY OF THE INVENTION It is the object of the present invention to provide a scroll-type variable displacement compressor equipped with a capacity control mechanism, which can lower the minimum operating capacity effectively without increasing the axial dimensions of the compressor or increasing the weight of the compressor. Such an object is solved by a scroll-type variable displacement compressor according to the independent claim 1. Preferred developments of the invention are given in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of a scroll-type variable displacement compressor according to the prior art. Fig. 2 is a cross-sectional view of a scroll-type variable displacement compressor according to the first embodiment of the present invention. Fig. 3 is a back view of a partially assembled end plate of a fixed scroll of a scroll-type variable displacement compressor according to the first embodiment of the present invention. Fig. 4 is a transverse sectional view of a scroll-type variable displacement compressor according to the first embodiment of the present invention along the line IV-IV' in Fig. 2 . Fig. 5 is a cross-sectional view of a scroll-type variable displacement compressor according to the second embodiment of the present invention. Fig. 6 is a back view of a partially assembled end plate of a fixed scroll of a scroll-type variable displacement compressor according to the second embodiment of the present invention. Fig. 7 is a cross-sectional view of a scroll-type variable displacement compressor according to the third embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described referring to Figs. 2-4. As shown in Fig. 2, a scroll-type compressor 1 has a housing 10 and a front plate 11 connected thereto. In the housing 10, a fixed scroll 25 is fixedly disposed and an orbiting scroll 26 is provided. Fixed scroll 25 includes a disk-shaped fixed end plate 251, and a fixed spiral element 252 formed integrally with and extending from an end surface of fixed end plate 251. Likewise, orbiting scroll 26 includes a disk-shaped orbiting end plate 261, and an orbiting spiral element 262 formed integrally with and extending from an end surface of orbiting end plate 261. As both spiral elements 252 and 262 slide against each other, a plurality of compression chambers P1, P2 are formed between fixed scroll 25 and orbiting scroll 26. In the front plate 11, a drive shaft 13 is rotatably supported by radial bearings 16 and 19. An eccentric pin 14 axially projects from an axial end surface of a large diameter portion 15 of the drive shaft 13. A counter weight 331 is secured to the proximal end side of the eccentric pin 14. A bushing 33 is fitted on the free end of the eccentric pin 14. Orbiting scroll 26 is rotatably supported on the bushing 33 by bearing 34. A fixed ring 28 is secured to an axial end surface of front plate 11, facing the orbiting scroll 26 with an orbiting ring 29 secured to an end surface of orbiting scroll 26. A plurality of circular revolution position regulating holes 30 and 31 are bored at equal intervals in fixed ring 28 and orbiting ring 29, respectively. The position regulating holes 30 and 31 are arranged in facing pairs, and a transmission shoe 27 is provided between each such facing pair of position regulating holes 30 and 31. Fixed ring 28, orbiting ring 29 and transmission shoes 27 constitute a rotation preventing device. The action of the rotation preventing device allows orbiting scroll 26 to orbit without rotating as eccentric pin 14 revolves. When this scroll-type compressor is used as a compressor for vehicular air conditioning, drive shaft 13 is coupled to the driving system of the engine of a vehicle through an electromagnetic clutch 13a. When drive shaft 13 rotates in accordance with the rotation of the engine, the rotation of drive shaft 13 is transmitted via pin 14, bushing 33 and the rotation preventing device connected to orbiting scroll 26. As a result, orbiting scroll 26 revolves around the axis of fixed scroll 25. As orbiting scroll 26 orbits, orbiting spiral element 262 gradually reduces the volume of the compression chambers P1, P2 to the final compression stage. Referring to Fig. 3 , the compressed refrigerant gas pushes open a discharge valve 53b that is provided outside a discharge port 53a. The compressed gases arc thereby discharged into the discharge chamber (not shown). Referring back to the Fig. 2, the capacity control mechanism according to the first embodiment of the present invention is comprised of: piston valve mechanism 400 which is provided within end plate 251; control valve mechanism 450; and low pressure chamber 54a which is provided within a portion of rear side of housing 10. Piston valve mechanism 400 is comprised of cylinder 48a which was hollowed out within end plate 251 in a direction perpendicular to the longitudinal axis of compressor, a piston 43 accommodated slidably therein, a coil spring 42b which urges piston 43 in the direction of operating chamber 47 (identified below), a stopper 42a which restricts the outward movement of piston 43, and a snap ring 42c. Snap ring 42c packs the other parts of the piston valve mechanism 400 within cylinder 48a. In the most recessed portion of cylinder 48a, there is provided a operating chamber 47 with a smaller diameter than cylinder 48a, to which a control pressure is introduced from intermediate pressure chamber 44 via passageway 46b. The pressure of operating chamber 47 exerts a directional force on piston 43 while coil spring 42b urges piston 43 in a direction opposite the pressure force of operating chamber 47. Thus, the position of piston 43 is controlled so as to settle on a position where the force exerted by coil spring 42b and the force exerted by the pressure in operating chamber 47 are balanced. On fixed end plate 251, there are provided a plurality of bypass holes 51a, 51a', 51b, 51b', so as to penetrate fixed end plate 251 perpendicularly. When piston 43 is completely recessed within cylinder 48a (i.e., in a position physically adjacent operating chamber 47), cylinder 48a becomes in communication via the bypass holes 51a, 51b with the compression chambers P1, P2 which are enclosed by the orbiting scroll 26 and fixed scroll 25. At the same time, cylinder 48a becomes in communication via the bypass holes 51a', 51b' with low pressure chamber 54a. Hence, cylinder 48a can be placed in communication with low pressure chamber 54a. The outlet portion of cylinder 48a is always in communication with the suction chamber 40. Low pressure chamber 54a is always in communication via passageway 54a' with suction chamber 40. With reference to Fig. 3, another cylinder 48b of the same structure as cylinder 48a may be provided within end plate 251. Cylinder 48b is disposed antiparallel to cylinder 48a (i.e., the operating chambers 47 are on opposite sides of each plate 251). On cylinder 48b, there are provided bypass holes 51c, 51d (not shown), 51c', 51d'. Fig. 4 presents a cross-sectional view of the low pressure chambers 54a and 54b as viewed from rear side of the compressor. As described above, low pressure chamber 54a is capable of being in communication with the cylinder 48a shown in Fig. 3. In a similar way, low pressure chamber 54b is capable of being in communication with the cylinder 48b via bypass holes 51c' and 51d'. With reference to Fig. 2 again, the operation of the control valve mechanism 450 will be explained. The control valve mechanism 450 comprises bellows 45, first adapter member 60, globe valve body 45b, conically coiled spring 61, second adapter member 62 and rod 45c. A bellows chamber 45e surrounds the bellows 45 and is in communication with suction chamber 40 via the passageway 46a. The intermediate pressure chamber 44 is in communication with the operating chamber 47 via the passageway 46b. High pressure chamber 45d is in communication via the passageway 45h with discharge chamber (not shown). When the compressor is operating, the refrigerant gas introduced into the high pressure chamber 45d exerts an upward force on the bottom face of rod 45c to push it up. Between the peripheral surface of the rod 45c and inner surface of the through hole of the second adapter member 62 for the rod 45c is provided a small gap. Through this gap, the refrigerant gas introduced into the high pressure chamber 45d can leak to the intermediate pressure chamber 44 at all times. The gas in the intermediate pressure chamber 44, then, is conducted to the operating chamber 47 where it exerts a downward force upon the top of the piston 43 to push down it. The upper part of bellows 45 is fixed to case 63. A projection 45f is provided on the bottom face of bellows 45 and is slidably accommodated within the small through hole 60h. Since the upper part of bellows 45 is fixed, projection 45f moves in and out the small through hole 60h, according to the contraction of bellows 45. Between the peripheral surface of projection 45f and the inner surface of small through hole 60h is provided a small gap. So, if the pressure within intermediate pressure chamber 44 is greater than the pressure within bellows chamber 45e, refrigerant gas can leak from the intermediate pressure chamber 44 to bellows chamber 45e through this gap. When the compressor is operating, a downward force exerted by projection 45f of bellows 45 and a upward force exerted by conically coiled spring 61 and rod 45c are acting on globe valve body 45b. When the upward force acting on the globe valve body 45b is greater than the downward force, the globe valve body 45b shifts within the intermediate pressure chamber 44 upwardly and closes perfectly the gap between the peripheral surface of the projection 45f and the inner surface of small through hole 60h, thereby blocking any leakage of refrigerant from intermediate pressure chamber 44 to bellows chamber 45e. If, however, the downward force acting on the globe valve body 45b is greater than the upward force, the globe valve body 45b shifts within the intermediate pressure chamber 44 downwardly and opens the gap between the peripheral surface of the projection 45f and the inner surface of small through hole 60h, thereby permitting refrigerant gas to leak from intermediate pressure chamber 44 to bellows chamber 45e. When the thermal load for the refrigeratory circuit is high, for example, when starting the compressor, the pressure in suction chamber 40 is relatively high. Then the pressure in bellows chamber 45e, which is in communication with the suction chamber 40, is accordingly high. Consequently, bellows 45 contracts. Due to the contraction of bellows 45, globe valve body 45b displaces upwardly and closes the gap of small through hole 60h in first adapter member 60. As a result, all of the refrigerant gas in the intermediate pressure chamber 44 which has leaked from the high pressure chamber 45d via the gap around the peripheral of the rod 45c is conducted to operating chamber 47. In the operating chamber, a pressure grows to a magnitude that overcomes the force of coil spring 42b, and then pushes down piston 43 until the movement of said piston is restricted by stopper 42a. When the thermal load for the refrigeratory circuit is low, for example, when the compressor has been powered on for an extended period of time and has cooled the ambient air, the pressure in suction chamber 40 and in bellows chamber 45e decreases. Then bellows 45 expands, and projection 45f pushes down globe valve body 45b. As a result, refrigerant gas leaks through the gap of small through hole 60h of first adapter member 60. Consequently, a portion of the refrigerant gas in the intermediate pressure chamber 44 which has leaked from the high pressure chamber 45d via the gap around the peripheral surface of rod 45c escapes via the gap of small hole 60h, into bellows chamber 45e, through passageway 46a and into suction chamber 40. Therefore, a smaller amount of the refrigerant gas, compared to the case of high thermal load, is conducted from intermediate pressure chamber 44 into operating chamber 47. As a result, sufficient pressure to overcome the force of coil spring 42b cannot be attained in operating chamber 47, thereby causing piston 43 to shift gradually in the direction of operating chamber 47. By the mechanism explained above, the position of piston 43 within the cylinder 48a is adjusted in response to the thermal load of the refrigeratory circuit. That is, when the thermal load is high, piston 43 shifts to the position restricted by stopper 42a, closing all of pairs of bypass holes 51a, 51a', 51b, 51b', thereby blocking the return of refrigerant gas from compression chambers P1, P2 to suction chamber 40. So the compressor operates at its full capacity. On the contrary, as the thermal load decreases and becomes low, the piston 43 shifts toward operating chamber 47, thereby opening the pairs of bypass holes 51a, 51a', 51b, 51b' sequentially. In this condition, refrigerant gas from compression chambers P1, P2, enclosed by orbiting scroll 26 and fixed scroll 25, is allowed to return to suction chamber 40, permitting the compressor to operate at its minimum capacity in this state. The principal object of the present invention is to improve the minimum capacity of the scroll-type variable displacement compressor, without increasing the size or weight of the compressor. Another object of the present invention is to provide a low pressure chamber 54a that functions as a branch path for returning gas, said low pressure chamber 54a being located within the housing of the scroll-type variable displacement compressor in order to increase the effective cross sectional area for the passage of the returning gas. By increasing the effective cross sectional area for the returning gas, the pressure loss from the compression chamber to the suction chamber can be reduced and the net quantity of the returning gas can be increased. Ultimately, the operative minimum capacity of the compressor can be reduced below that of comparable prior art compressors. In Fig. 2 , two representative paths of returning gas in the present invention are indicated as L1 and L2. Path L1 starts from at compression chamber P1, passes through bypass hole 51 b, through cylinder 48a, and arrives at suction chamber 40. Path L2 starts at compression chamber P1, passes through bypass hole 51b, cylinder 48a, bypass hole 51b', and low pressure chamber 54a, and arrives at suction chamber 40. Compared with the structure of a conventional scroll-type variable displacement compressor as shown in Fig. 1, wherein only path L1' is provided for the returning gas, a compressor according to the present invention as shown in Fig. 2 is provided with path L2 in addition to path L1 which corresponds to path L1' shown in Fig. 1 . The additional path L2 reduces the pressure loss of returning gas greatly, because the effective cross sectional area for the passage of returning gas is significantly increased by bypass hole 51b' and by the low pressure chamber 54a. In fact, the ratio of the quantities of the returning gas via path L1 and path L2 can be estimated to be approximately 40 percent and 60 percent respectively, based on the relative of cross sectional areas of paths L1 and L2. So, the pressure loss of returning gas is greatly reduced, and the minimum capacity of the compressor according to the present invention can be effectively reduced to the expected value. In Fig. 5 and Fig. 6, a second embodiment of the present invention is shown. Considering the second embodiment of the present invention with the first embodiment, an additional bypass hole 55a is provided between bypass holes 51b' and 51a'. As a result, a returning path L3 is provided in addition to returning paths L1 and L2, further reducing the pressure loss of the returning gas. Thus, the minimum operative capacity of the compressor can be reduced even less than that for a compressor with paths L1 and L2. With reference to Fig. 6, cylinder 48a is provided with an additional bypass hole 55a between the bypass holes 51a' and 51b', and cylinder 48b is provided with an additional bypass hole 55b between the bypass holes 51c' and 51d'. In Fig. 7 , a third embodiment of the present invention is shown. The third embodiment illustrates a case in which the inner most bypass hole 51b' is permanently closed by a block 10a in the housing 10. Although bypass hole 51b' is closed, there is still provided a branch path L4 as shown in Fig. 7 , which starts from compression chamber P1, passes through the bypass hole 51b, cylinder 48a, bypass hole 51a', and low pressure chamber 54a, and arrives at the suction chamber 40. As explained thus far, the scroll-type variable displacement compressor according to the present invention can reduce the pressure loss of the returning gas and also reduces the minimum capacity of the compressor by providing a branch path via the low pressure chamber utilizing a portion of the housing in addition to the conventional returning path via only the cylinder. Moreover, the present invention can attain these purposes without any accompanying increase of size in the axial direction of the compressor or increase in weight of the compressor. Although the present invention has been described in detail in connection with preferred embodiments, the invention is not limited thereto. It will be understood by those of ordinary skill in the art that variations and modifications may be made within the scope of this invention, as defined by the following claims.

Claims: A scroll-type variable displacement compressor for use with refrigerant gas comprising: a housing (10); a front plate (11); a drive shaft (13); an orbiting scroll (26); a converting mechanism (14, 33, 34) to convert rotational motion of said drive shaft (13) into orbiting motion for said orbiting scroll (26); a mechanism (27, 28, 29) to prevent rotational motion of said orbiting scroll; a fixed scroll (25); a piston valve mechanism (400) which provides a return path L1 for a portion of refrigerant gas from a plurality of compression chambers (P1, P2) enclosed by said orbiting scroll (26) and said fixed scroll (25) to a suction chamber (40) of the compressor, said piston valve mechanism (400) being provided for capacity control; a control valve mechanism (450) which supplies a control pressure to said piston valve mechanism (400); said piston valve mechanism (400) comprising a cylinder (48a) which is hollowed out within an end plate (251) of said fixed scroll (25) so that an axis of said cylinder lies in a plane perpendicular to a longitudinal axis of compressor, said cylinder (48a) being communicated with said suction chamber (40) and having an interior surface with a plurality of first bypass holes (51a, 51b) which penetrate said end plate (251) of said fixed scroll (25) between said cylinder (48a) and one or more of said compression chambers (P1, P2) to communicate said compression chambers (P1, P2) with said cylinder (48a); a piston (43) which is slidably accommodated within said cylinder (48a) to open or close said first bypass holes (51a, 51b), a coil spring (42b) which urges said piston (43) in a direction opposite to a force of said control pressure, and a stopper (42a) which restricts displacement of said piston (43), characterized by a snap ring (42c) which secures the piston (43) and the coil spring (42b) within said cylinder (48a); a low pressure chamber (54a) being disposed within a portion of said housing (10) and being in communication with said suction chamber (40) at all times; and a plurality of second bypass holes (51a', 51b') which penetrate said end plate (251) of said fixed scroll (25) between said cylinder (48a) and said low pressure chamber (54a) to communicate said cylinder (48a) with said low pressure chamber (54a) for forming a second return path L2 for a portion of said refrigerant gas from the plurality of compression chamber (P1, P2) to said suction chamber (40), wherein said piston (43) opens or closes said second bypass holes (51a', 51b') and said first and second bypass holes (51a, 51b, 51a', 51b') are formed as pairs of bypass holes (51a, 51a', 51b, 51b'). The scroll-type variable displacement compressor of claim 1, wherein an additional bypass hole (55a) is provided between said bypass holes (51a', 51b') by which said cylinder (48a) communicates with said low pressure chamber (54a). The scroll-type variable displacement compressor of claim 1, wherein at least one of said bypass holes (51a', 51b') by which said cylinder (48a) communicates with said low pressure chamber (54a) is blocked.

Inventors: HIGASHIYAMA AKIYOSHI, HIGASHIYAMA, AKIYOSHI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1997
Main classification: F04C29
IPC codes: F04B49, F04C18, F04C28