CAPACITY CONTROL SCROLL COMPRESSOR

Abstract: A capacity-controlled scroll compressor having a simple, compact and high-reliability control mechanism, including two pairs of bypass holes (50a, 50b, 51a and 51b) each communicating with each of a pair of fluid pockets in the same compression process, a bypass hole (52a) communicating with one fluid pocket formed from the pair of fluid pockets aligned as the compression process further proceeds, and a shuttle valve (60) for sequentially opening and closing the bypass holes by reciprocating motion, and fitted into a cylinder (61) disposed inside a fixed end plate (1a). The shuttle valve (60) has a stepped cylindrical structure having different outer diameters so as to improve the strength and rigidity of the shuttle valve itself. The smooth operation of the shuttle valve (60) can be ensured even at high temperatures and high pressures.

Description: The present invention relates to a capacity control mechanism for a scroll compressor to be employed in automobile air-conditioning apparatus. As a capacity-controlled type scroll compressor having a valve mechanism for opening and closing a bypass hole, there has been a configuration as disclosed in Japanese Laid-Open Patent Application No. Hei 4-179886, for example, in which a bypass hole is defined on an end plate of a fixed scroll, and a capacity control block incorporating a bypass passage enabling the bypass hole to communicate with a suction chamber formed inside the housing and a valve mechanism for opening and closing the bypass passage is constituted as a unit separate from the fixed scroll. As another example, there is a system as disclosed in Japanese Laid-Open Patent Application No. Hei 5-280476, in which a cylinder is provided in a fixed scroll member, into which a plunger which is capable of sequentially closing a group of bypass holes communicating between the cylinder and the compression chamber is inserted. However, in the above described prior art structure, as a gap is formed between the plunger (shuttle valve) and the cylinder wall, a bypass gas from a bypass hole communicating with a fluid pocket on the upstream side flows back from the gap to a fluid pocket on the downstream side through a bypass hole on the downstream side, it suffered a problem of an increase in the driving force and a decrease in the refrigerating capacity. In addition, during a high-speed high-load operation, as the interior of the cylinder is in a state of high temperature and high pressure by the influence of the bypass gas, it also suffered a problem of deformation of the shuttle valve, which impedes smooth motion of opening and closing. A similar capacity controlled scroll type compressor is known from DE-A-195 19 791. In a fixed end plate of this compressor two shuttle valves may slide in a cylinder to open bypass passages between fluid compression pockets and the suction chamber. The cylinder has one predetermined bore and the shuttle valve has a circumference matching the cylinder bore. The shuttle valve further comprises a groove and through holes for allowing air to flow through the valve. The present invention addresses the above described prior art problems and aims at providing a high-reliability capacity-controlled scroll compressor in which the discharge capacity can be smoothly changed with a simple and compact structure. These objects are achieved by the features of claim 1 for a capacity-controlled scroll compressor. Further embodiments are the subject matter of the dependent claims. it is possible to configure a bypass gas passage from each of the bypass holes communicating with fluid pockets as respective independent communicating passages via different stepped cylindrical or columnar portions of the shuttle valve. Also, by employing a stepped configuration for the shuttle valve, strength and rigidity of the shuttle valve itself can be enhanced and thus deformation due to pressure or heat can be prevented. Furthermore, by making the passages independent, back flow from the upstream side to the downstream side can be prevented thus increasing the compression efficiency. In other words, the invention as described in Claim 1 is one in which the shuttle valve is of a stepped cylindrical or columnar configuration having different outer diameters so as to prevent the deformation of the shuttle valve itself by increasing the strength and rigidity. The invention as described in Claim 2 is one in which the strength and rigidity of the shuttle valve is further enhanced and the machinability improved by making the stepped portion of the shuttle valve tapered. By employing this structure, a smooth operation of the shuttle valve is possible even inside a high-temperature, high-pressure cylinder during a high-load operation, and a capacity-controlled operation with a good response can be assured over a range from a maximum capacity operation to a minimum capacity operation. The invention as described in Claim 3 is one in which a ring groove is provided on the outer peripheral surface of the shuttle valve so that a sealing member can be fitted. By employing this structure, as a compression gas from a bypass hole communicating with a fluid pocket on the upstream side can be completely returned to a suction chamber without flowing back into a bypass hole communicating with a fluid pocket on the downstream side by flowing down the gap between the cylinder and the shuttle valve, pressure loss is minimized and capacity-controlled operation with a high control efficiency can be assured. The invention as described in Claim 4 is one in which the shuttle valve is of a hollow structure so as to be formed by forging enabling to attain enhanced strength and lower cost. Also, the invention as described in Claim 5 is one in which a spring guide is formed on an end of the shuttle valve so as to prevent buckling of the spring supporting the shuttle valve. Fig. 1 is a partially in phantom sectional view of a capacity-controlled scroll compressor in an exemplary embodiment of the present invention. Fig. 2 is a partially in phantom sectional view of a fixed end plate portion of the compressor. Fig. 3 is a partially in phantom transverse sectional view of a compression chamber of the compressor. Fig. 4 is a characteristics diagram showing the relationship between the orbiting angle and enclosed volume of the compressor. Fig. 5 is a characteristics diagram showing the relationship between the shuttle valve stroke and controlled capacity of the compressor. Fig. 6 is a pressure characteristics diagram of the pressure control valve of the compressor. Fig. 7 is a diagram showing structure of a tapered stepped shuttle valve in second exemplary embodiment of the compressor. Fig. 8 is a diagram showing structure of a shuttle valve having a seal ring in third exemplary example of of the compressor. Fig. 9 is a partially cut-away view of a shuttle valve having a spring guide in fifth example of an embodiment of the compressor. Referring now to drawings, a description of the basic construction of exemplary embodiments of the present invention will be given. First exemplary embodiment: In FIG. 1, a compressor housing 3 is divided into a front housing 31 and a rear plate 5, and includes therein a fixed scroll 1 having a fixed end plate 1a and a spiral lap 1b erecting on fixed end plate 1a, and an orbiting scroll 2 having an orbiting end plate 2a and a spiral lap 2b erecting on orbiting end plate 2a and engaged with fixed scroll 1 with both laps 1b and 2b facing inward. As an orbiting mechanism, a cylindrical boss 2c is formed on the rear side of orbiting end plate 2a opposite spiral lap 2b of orbiting scroll 2, and an orbiting bearing 7 is provided on boss 2c. A drive shaft 9 is rotatably supported via a main bearing 15 fitted in front housing 31, and a main shaft portion 9a projects outside of front housing 31 passing through a shaft sealing device 17 and a subsidiary bearing 16. A drive pin 9b disposed at the end of drive shaft 9 on the orbiting scroll 2 side is coupled with an orbiting bush 8 functioning as a drive transmission mechanism inserted in orbiting bearing 7, and gives an orbiting motion to orbiting scroll 2 by transmitting the driving force from drive shaft 9. Between orbiting end plate 2a and front housing 31, a flat plate thrust bearing 4 for axially supporting a thrust exerted to orbiting scroll 2 in parallel to orbiting end plate 2a, and a revolution restraining component 6 for restraining the motion of an Oldham ring 5 which has a function of a rotation restraining component for restraining the rotation of orbiting scroll 2 so as to cause it to make an orbiting motion only along the single direction at right angles to drive shaft 9 are disposed. An O-ring 18 is inserted in a sealing groove 1f on the outer peripheral portion 1e of fixed end plate 1a of fixed scroll 1 as a sealing member for partitioning the interior of compressor housing 3 into a high pressure chamber 11 and a low pressure chamber 12. Fixed scroll 1 forms high pressure chamber 11 by having a fastening hole 1d provided on the rear side of fixed end plate 1a and a rear plate 35 having a discharge port 14 fastened with a bolt 19. Revolution restraining component 6 is secured on a front end portion 32 inside front housing 31 having a suction port 13, and orbiting scroll 2 is pushed by a thrust to revolution restraining component 6 via thrust bearing 4. Front housing 31 is closed by rear plate 35 in the vicinity of the outer circumference of fixed end plate 1a of fixed scroll 1 with a thrust clearance adjusting shim 20 interposed. By the orbiting motion of orbiting scroll 2, a refrigerant is introduced from outside of compressor housing 3 into interior low pressure chamber 12 through suction port 13 and led to the vicinities of the outer peripheries of lap 1b and lap 2b of respective fixed scroll 1 and orbiting scroll 2. The refrigerant is then sucked into a fluid pocket 10 enclosed between both laps 1b and 2b by an orbiting motion of orbiting scroll 2, compressed into a smaller volume as it goes from the outer peripheries of both laps 1b and 2b toward the center, and is discharged into high pressure chamber 11 through a gas discharge hole 1c of fixed end plate 1a. A reed valve 21 is fitted on gas discharge hole 1c from the side of high pressure chamber 11 to prevent a back flow of the discharged gas. Referring now to FIGS. 2 and 3, construction of the capacity control mechanism will be described. In fixed end plate 1a, two pairs of bypass holes 50a, 50b, and 51a, 51b, each pair respectively communicating with each of a pair of fluid pockets 50 and 51 which are in the same compression process, are defined, and a bypass hole 52a which communicates with the region in which the pair of fluid pockets merge into one fluid pocket 52 as the compression process further proceeds is defined. A stepped cylindrical shuttle valve 60 having three different circular cross sections and which sequentially opens bypass holes 50a, 50b, 51a, 51b and 52a is inserted inside a cylinder 61 provided inside a fixed end plate 1a in such a way that it can make a reciprocating motion. One end of cylinder 61 opens at a cut-away portion 1g formed on the outer periphery of fixed end plate 1a and communicates with low-pressure chamber 12. Shuttle valve 60 is pushed by a spring 62 in the leading end direction, and one end of spring 62 is held inside fixed end plate 1a with a holder 63 and a stop ring 64. A communicating passage 67a which guides a bypass gas from bypass holes 50a, 50b to cut-away portion 1g by opening and closing shuttle valve 60 is provided on cylinder 61. Similarly, a communicating passage 67b communicating with bypass holes 51a and 51b and a communicating passage 67c communicating with bypass hole 52a are provided. A lead-in hole 68 is drilled at the leading end of cylinder 61 to allow introduction of a control pressure Pm which makes shuttle valve 60 operable by overcoming the pushing force of spring 62. On the other hand, a pressure control valve 70 for controlling the control pressure Pm is incorporated in a control-pressure chamber 71 inside fixed end plate 1a and is held by a holder 78 and a stop ring 79. In control-pressure chamber 71, a flow-in hole 72 for taking in an intermediate pressure Pc for generating the control pressure Pm and a flow-out hole 73 are drilled and flow-out hole 73 communicates with low pressure chamber 12 via a cut-away portion 1i formed on the outer peripheral portion 1e of fixed end plate 1a. The flow-out hole 73 also serves as a passage for taking in a suction pressure Ps as a low pressure signal. Also, a communicating hole 74 for taking in atmospheric pressure Pa to be used as a base signal is drilled on the rear side of fixed end plate 1a and is open to the air through a hole 36 drilled on an O-ring 75 and rear plate 35. Pressure control valve 70 generates an adequate control pressure Pm in response to changes in the intermediate pressure Pc and the suction pressure Ps. The control pressure Pm is transmitted to cylinder 61 through passage 76 formed on the rear side of fixed end plate 1a and the earlier-mentioned lead-in hole 68. Passage 76 is sealed with rear plate 35 and an O-ring 77. Operation of the capacity control mechanism will now be described with reference to FIGS. 4 and 5, . When shuttle valve 60 is at its uppermost position (in the leading end direction of the cylinder), all the bypass holes are fully closed and the operation will be at a maximum capacity. Conversely, when shuttle valve 60 is at its lowermost position (on the holder side), all the bypass holes are fully open and the operation will be at a minimum capacity. As can be seen in FIG. 4. bypass holes 51a and 51b communicate with the fluid pockets up to 100% to about 60% of the region of the maximum compressed volume Vmax. Likewise, bypass holes 50a and 50b communicate with 100% to about 50%, and bypass hole 52a communicates with about 60% to about 7% of the region. By adjusting the openings of these bypass holes with the shuttle valve, the controlled capacity (Vc) vs. shuttle valve stroke (Ls) relationship as shown in FIG. 5 can be obtained. In FIG. 5, the controlled capacity Vc on the ordinate axis represents percentage ratio of the enclosed volume under control to the maximum enclosed volume of the compressor, and the position of Ls = 0 (mm) on the abscissa axis represents a state in which the shuttle valve is at the uppermost position. In the range from Ls = 0 (mm) to Ls = 7 (mm), bypass holes 50a, 51a, 50b, and 51b are opened sequentially and a capacity control range up to about 50% is covered. Beyond Ls = 7 (mm), bypass hole 52a opens sequentially and when shuttle valve 60 reaches the lowermost position [Ls = 13 (mm)], the operation will be at about 7% of the capacity. As has been described earlier, each of the bypass holes has an independent bypass passage thus preventing back flow of a bypass gas into bypass holes on the downstream side thereby enabling capacity control without reducing the control efficiency. Next, a description of the operation of shuttle valve 60 will be given by using the following symbols: spring constant of spring 62: k; initial flection of spring 62: X0: maximum stroke of shuttle valve 60: X1 (= 13 mm); and cross-sectional area of cylinder 61: Sv. The forces acting on shuttle valve 60 can be obtained by the following equations. The force Fp with which control pressure Pm moves shuttle valve 60 downward is: Fp = (Pm - Ps) × Sv. The force Fs with which spring 62 moves shuttle valve 60 upward is: Fs = k × (X0 + X1 - Ls). From the above equations, the spring force Fs0 acting on shuttle valve 60 when shuttle valve 60 is at the uppermost position (Ls = 0) is calculated to be: Fs0 = k × X0. The spring force Fs1 acting on shuttle valve 60 when shuttle valve 60 is at the lowermost position (Ls = X1) is calculated to be: Fs1 = k × (X0 + X1). Consequently, at the time of operation at the maximum capacity, Fp Fs0 holds and shuttle valve 60 is at the uppermost position, whereas at the time of operation at the minimum capacity. Fp Fs1 holds and shuttle valve 60 is at the lowermost position. Also, at the time of controlled capacity operation. Fp = Fs holds, and shuttle valve 60 is balanced at an intermediate position. The pressure characteristics (Pm vs. Ps characteristics) of pressure control valve 70 of the compressor of an exemplary embodiment of the present invention are designed as illustrated in FIG. 6. When the cooling load is high the suction pressure Ps rises accompanying a drop in the control pressure Pm. In other words, Fp Fs0 holds and shuttle valve 60 is pushed up to the uppermost position causing a maximum capacity operation thus increasing the cooling capacity. Conversely, when the cooling load is low, the suction pressure Ps drops accompanying a rise in the control pressure Pm. In other words, Fp Fs1 holds and shuttle valve 60 is pushed down to the lowermost position causing a minimum capacity operation thus decreasing the cooling capacity. The range of Fs1 > Ps > Fs0 (kgf/cm 2 ) is a range of controlled operation where the control mechanism works so as to stabilize the suction pressure Ps at an optimum value in accordance with the cooling load. In the above structure, as the shuttle valve 60 is of a stepped cylindrical configuration with different outer diameters, the rigidity against axial bending is higher compared to prior art single cylindrical configuration. As a result, when shuttle valve 60 reciprocates inside cylinder 61 depending on the cooling load, the clearance is maintained constant allowing a controlled operation with a superior response. Second exemplary embodiment: FIG. 7 illustrates a shuttle valve 60 with a step portion 60c connecting steps tapered. With this, not only the strength and rigidity of shuttle valve 60 are further enhanced but the wear of the cylinder wall surface owing to the edges of step portion 60c is also prevented, thus improving the operability. Here, tapering of step portion 60c may be of a degree made by chamfering. Third exemplary embodiment: FIG. 8 is an illustration of a shuttle valve 60 provided with ring grooves on the outer peripheral surface and fitted with seal rings made of PTFE. In this embodiment, it is possible to prevent back flow of a bypass gas from bypass hole 52a to bypass holes 50a, 50b, and 51a, 51b, thereby improving control efficiency by completely bypassing a compression gas to the low pressure side. Fourth exemplary embodiment: By machining only the external surface, the surface being sliding surface, after forging shuttle valve 60 into a hollow structure, the processing time can be shortened and the machining cost reduced, and a higher strength than that of an article in which the entire surface is machined can be obtained. Fifth exemplary embodiment: As has been described in the description of the first exemplary embodiment, as the compressor in accordance with the present invention has a sufficiently long axial dimension of shuttle valve 60 relative to the radial dimension owing to its simple structure, buckling of spring 62 supporting shuttle valve 60 is easy to take place. In this embodiment, the above-mentioned shortcomings can be prevented by providing a spring guide portion on the end of shuttle valve 60 as illustrated in FIG. 9. As is clear from the above exemplary embodiments, in the capacity-controlled scroll compressor in accordance with the present invention, it is possible to enhance strength and rigidity of the shuttle valve by employing a stepped cylindrical or columnar configuration having different outer diameters. Specially, strength and operability of the shuttle valve can be further improved by tapering the step portion. Also, as ring grooves are provided on the outer peripheral surface of the shuttle valve for fitting a sealing member, capacity-controlled operation at a high control efficiency can be effected. By forming the shuttle valve by forging into a hollow structure, it is also possible to attain a high strength and low cost. Furthermore, by forming a spring guide portion in the shuttle valve, it is possible to prevent deformation due to buckling of the spring. As set forth above, the present invention provides a capacity-controlled scroll compressor having a simple construction and high reliability. List of Reference Numerals: 1. Fixed scroll 1a. Fixed end plate 1b. Spiral lap of fixed scroll 1c. Discharge hole 1d. Fastening hole 1e. Outer periphery of fixed end plate 1f. Sealing groove 1g, 1i. Cut-away portion of fixed end plate outer periphery 2. Orbiting scroll 2a. Orbiting end plate 2b. Spiral lap of orbiting scroll 2c. Boss 3. Compressor housing 4. Thrust bearing 5. Oldham ring 6. Revolution restraining component 7. Orbiting bearing 8. Orbiting bush 9. Drive shaft 9a. Main shaft portion 9b. Drive pin 10, 50, 51, 52. Fluid pockets 11. High pressure chamber 12. Low pressure chamber 13. Suction port 14. Discharge port 15. Main bearing 16. Subsidiary bearing 17. Shaft sealing device 18, 75, 77. O-rings 19. Bolt 20. Adjusting shim 21. Reed valve 31. Front housing 32. Front end portion 35. Rear plate 36. Hole 50a, 50b, 51a, 51b, 52a. Bypass Holes 60. Shuttle valve 60c. Step portion 61. Cylinder 62. Spring 63, 78. Holders 64, 79. Stop rings 67a, 67b, 67c. Communicating passages 68. Lead-in hole 70. Pressure control valve 71. Control-pressure chamber 72. Flow-in hole 73. Flow-out hole 74. Communicating hole 75, 77. O-rings 76 Passage

Claims: A capacity-controlled scroll compressor including in a compressor housing (3) thereof: a fixed scroll (1) having a fixed end plate (1a) and a spiral lap (1b) erecting from the fixed end plate (1a); an orbiting scroll (2) having an orbiting end plate (2a) and a spiral lap (2b) erecting from said orbiting end plate (2a) and disposed in engagement with said fixed scroll (1) with respective laps (1b, 2b) facing each other; an orbiting mechanism formed on the rear side of said orbiting end plate (2c) opposite the spiral lap (2b) of said orbiting scroll (2); a flat plate thrust bearing for axially supporting a thrust exerted to said orbiting scroll (2); and a drive shaft (9) rotatably supported in said compressor housing (3) with the main shaft portion thereof projecting to outside of said compressor housing (3) passing through a shaft sealing device and a subsidiary bearing through a main bearing; and comprising: a drive transmission mechanism for transmitting the driving force from said drive shaft to said orbiting mechanism; a rotation restraining component for restraining rotation of said orbiting scroll (2) so as to make it orbit; a revolution restraining component adjacent to said rotation-restraining component for restraining the direction of motion of said rotation restraining component to the direction at right angles to said drive shaft (9); at least a pair of bypass holes (50a, 50b, 51a, 51b) communicating with a fluid pocket (50, 51) formed in between both laps (1b, 2b) by the orbiting motion of said orbiting scroll (2) and provided at positions symmetrical with respect to said fluid pocket (50, 51); a cylinder (61) formed inside said fixed end plate (1a) in a manner communicating with said fluid pockets (50,51) through said bypass holes (50a, 50b, 51a, 51b); and a shuttle valve (60) which can reciprocate inside said cylinder (61); and performing compression from the outer periphery of said both laps (1b, 2b) toward the center and the discharge capacity is made to continuously change by sequentially opening and closing said bypass holes (50a, 50b, 51a, 51b) by said shuttle valve (60), wherein said shuttle valve (60) has a stepped or columnar structure having at least two different circular cross sections characterized in that the cylinder (61) is adapted to receive the parts of the shuttle valve (60) with the at least two different cross sections in sliding surfaces of corresponding different cross sections. The capacity-controlled scroll compressor of Claim 1, wherein the portion (60c) connecting steps of the stepped portion of said shuttle valve (60) is tapered. The capacity-controlled scroll compressor of Claim 1 or Claim 2, wherein said shuttle valve (60) is provided with at least one ring groove for fitting a ring-shaped sealing member. The capacity-controlled scroll compressor of Claim 1 or Claim 2, wherein said shuttle valve (60) is formed by forging into a hollow structure. The capacity-controlled scroll compressor of Claim 1 or Claim 2, wherein a spring guide portion (63) is provided on an end portion of said shuttle valve (60).

Inventors: MAKINO MASAHIKO, SHIMIZU AKIHIKO, MAKINO, MASAHIKO, SHIMIZU, AKIHIKO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1998
Main classification: F04C18
IPC codes: F04C18, F04B49, F04C29, F04C28