CAPACITY CONTROL SCROLL COMPRESSOR

Abstract: A capacity-controlled scroll compressor for reducing a start shock and improving machinability of a fixed end plate, wherein a high pressure Ph to be guided to a control valve (70) for controlling a control pressure Pm for operating a shuttle valve (60) is introduced from a high pressure passage (72) opening at a discharge port (1c) to reduce a start shock. A bypass hole (52a) and the high pressure passage (72) are constituted by a straight through-hole extending through a cylinder (61) from the outer peripheral portion of a fixed end plate (1a) and consequently, machinability of the fixed end plate (1a) can be improved.

Description: The present invention relates to a capacity control mechanism of a scroll compressor for use in automotive 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 so that a high pressure introduced from a discharge cavity can be supplied to a control valve for regulating the control pressure of the valve mechanism for opening and closing the bypass hole. Such a separate capacity control block on the fixed end plate of a scroll compressor is also described in EP-A-0 486 121. This capacity control mechanism comprises a control valve which obtains a high pressure signal from a discharge chamber which is located downstream of a discharge valve provided on the fixed end plate. DE-A-195 19 791 shows another scroll compressor with a capacity control mechanism wherein a passage from a discharge port is connected to two shuttle valves. 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, and in which a high pressure to be supplied to a control valve for controlling the control pressure for reciprocating the plunger is introduced from nearby the front end of the innermost periphery of a vane formed on the fixed scroll. US-A-5 577 897 describes a scroll compressor having a capacity control mechanism comprising two shuttle valves. A first valve opens or closes bypass holes of fluid compression pockets for varying the capacity between 20% and 100%. The second valve opens a bypass passage between the discharge port and the low pressure chamber in order to vary the capacity between 0% and 20 %. A control valve controls the operation of the shuttle valves. A high pressure signal for the control valve is obtained from a passage through the fixed end plate and through the spiral vane of the fixed scroll to the inside of the compressor. However, in the above-described prior art configuration, as the high pressure to be supplied to the control valve is introduced from a discharge cavity, when the compressor is restarted under a state of a high discharge pressure, the high discharge pressure is applied to the control valve and the valve mechanism causing the bypass holes closed. Consequently, the compressor is started at a maximum capacity thus suffering from a large shock. On the other hand, in the latter example, although the high pressure to be supplied to the control valve is introduced from nearby the front end of the innermost periphery of the vane formed on the fixed scroll member, the configuration and machining of the lead-in passage are extremely difficult. In view of the above described shortcomings of the prior art, it is an object of the present invention to provide a capacity-controlled scroll compressor in which the start shock is reduced and the machinability of the fixed end plate is improved. This object is achieved by the features of claim 1. Further embodiments are subject-matter of the dependent claims. By forming one of the bypass holes communicating with a fluid pocket on the side wall of the discharge hole such that the bypass hole communicates with a cylinder with a straight through-hole from the outer peripheral end of the fixed end plate, or making the cylinder, the bypass hole, and the high pressure passage communicate with a straight through-hole from the outer peripheral end of the fixed end plate, it is possible to reduce the start shock of the compressor as well as to improve the machinability of the fixed end plate. In other words, the invention is one in which a high pressure is introduced through a passage opening at a discharge hole to a control valve for controlling the control pressure for opening and closing bypass holes with a shuttle valve. By employing this structure, as a high pressure is instantaneously reduced to a low pressure immediately after a compressor operation has stopped, the control pressure acting on a shuttle valve is also reduced to a low pressure and the shuttle valve comes to a state of opening the bypass holes. As a result, when the compressor is restarted, the start shock can be reduced as the compressor is always started at a minimum capacity. Also, the structure of the high pressure passage can be made simpler as the control-pressure chamber and the discharge hole can be made closer to each other. Further preferred embodiments are ones in which one of the bypass holes is formed on the side wall of the discharge hole and the bypass hole and the cylinder are made to communicate with a straight through-hole from the outer peripheral end of the fixed end plate, or the cylinder, the bypass hole formed on the side wall of the discharge hole and a high pressure passage opening at the discharge hole and introducing a high pressure to the control-pressure chamber are made to communicate with a straight through-hole from the outer peripheral end of the fixed end plate. According to this structure, it is possible to reduce the start shock as well as to make the machining of the individual communicating holes and the passage of the fixed end plate at a time thereby improving machinability. 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 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. Referring to FIG. 1, basic construction of an exemplary embodiment of the present invention will be described in the following. 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 wrap 1b erecting on fixed end plate 1a, and an orbiting scroll 2 having an orbiting end plate 2a and a spiral wrap 2b erecting on orbiting end plate 2a and engaged with fixed scroll 1 with both wraps 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 wrap 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 wrap 1b and wrap 2b of respective fixed scroll 1 and orbiting scroll 2. The refrigerant is then sucked into a fluid pocket 10 enclosed between both wraps 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 wraps 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 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 on the side wall of the discharge hole. A shuttle valve 60 which sequentially closes these bypass holes 50a, 50b, 51a, 51b and 52a is slidably inserted in a cylinder 61 provided inside fixed end plate 1a. One end of cylinder 61 is open at a cut-away portion 1g formed on the outer peripheral portion 1e 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 by a holder 63 and a stop ring 64. Two recessed portions 60a and 60b are provided on shuttle valve 60. Recessed portion 60a is provided at a position at which it communicates with bypass holes 51a and 51b at the time shuttle valve 60 is in the state of being pushed in the leading end direction. Similarly, recessed portion 60b is provided at a position at which it communicates with bypass hole 52a. Furthermore, a communicating hole 66 is drilled on recessed portion 60a allowing communication with low pressure chamber 12 through the interior of shuttle valve 60. The other recessed portion 60b communicates with low pressure chamber 12 through a passage 67 passing through fixed end plate 1a and cut-away portion 1h formed on outer peripheral portion 1e. 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 high pressure passage 72 for taking in a high pressure Ph 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. Also, high pressure passage 72 communicates with discharge hole 1c. 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 high pressure Ph 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 open and the operation will be at a minimum capacity. Conversely, when shuttle valve 60 is at its lowermost position (on the holder side), all the bypass holes are fully closed and the operation will be at a maximum 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 0% 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 lowermost 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 and when shuttle valve 60 reaches the uppermost position [Ls = 13 (mm)], the operation will be at about 0% of the capacity. As has been described earlier, bypass hole 52a has an independent bypass passage thus preventing back flow of a bypass gas into bypass holes 50a, 51a, 50b, and 51b 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 pressum 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 lowermost position (Ls = 0) is calculated to be: Fs0 = k × (X0 + X1). The spring force Fs1 acting on shuttle valve 60 when shuttle valve 60 is at the uppermost position (Ls = X1) is calculated to be: Fs1 = k × X0. Consequently, at the time of operation at the maximum capacity, Fp ≥ Fs0 holds and shuttle valve 60 is at the lowermost position, whereas at the time of operation at the minimum capacity, Fp ≤ Fs1 holds and shuttle valve 60 is at the uppermost 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 high pressure Ph is 15 kgf/cm 2 , for example. Also, the load characteristics of spring 62 are designed as below: Fs0/Sv = 3.0 kgf/cm 2 , Fs1/Sv = 0.5 kgf/cm 2 . When the cooling load is high, the suction pressure Ps rises accompanying a rise in the control pressure Pm. In FIG. 6, when a state of Ps ≥ 1.8 kgf/cm 2 is reached, a state of Pm - Ps ≥ 3 kgf/cm 2 (= Fs0/Sv) is caused meaning that Fp ≥ Fs0, and thus shuttle valve 60 is pushed down to the lowermost position effecting an operation at the maximum capacity and the cooling capacity is increased. Conversely, when the cooling load is low, the suction pressure Ps drops accompanying a drop in the control pressure Pm. When a state of Ps ≤ 1.3 kgf/cm 2 is reached, a state of Fp ≤ Fs1 is caused, and shuttle valve 60 is pushed up to the uppermost position effecting an operation at the minimum capacity, and the cooling capacity is decreased. The Ps range of 1.8 kgf/cm 2 < Ps < 1.3 kgf/cm 2 is the range of controlled operation in which the control mechanism works so as to stabilize the suction pressure Ps at an optimum value for the cooling load. Also, when the compressor stops the high pressure Ph drops accompanying a drop in the control pressure Pm resulting in Pm being nearly equal to Ps, and Fp becomes nearly equal to zero kgf/cm 2 causing shuttle valve 60 to be pushed upward thereby making all the bypass holes open. Accordingly, when the operation is subsequently started, it starts from the minimum capacity thus relieving the start shock and assuring a smooth start-up. As is clear from the above-described exemplary embodiment, with the capacity-controlled scroll compressor in accordance with the present invention, it is possible to reduce the start shock as the high pressure which works as the control pressure of a shuttle valve for opening and closing bypass holes is introduced from a high pressure passage opening at a discharge hole. Also, by employing a configuration in which one of the bypass holes is formed on the side wall of the discharge hole and in which simultaneous machining of a hole that communicates with the bypass hole and the cylinder can be performed from the outer peripheral end of a fixed end plate, it is possible to improve the machinability of the fixed end plate. Furthermore, by employing a configuration in which the hole communicating with the high pressure passage, bypass holes, and cylinder can be simultaneously machined from the outer peripheral end of the fixed end plate, it is possible to reduce the start shock as well as to provide a compressor having a fixed end plate with superior machinability. 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 peripheral portion of fixed end plate 1f. Sealing groove 1g, 1h, 1i. Cut-away portion of outer periphery of fixed end plate 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 60a, 60b. Recessed portions 61. Cylinder 62. Spring 63, 78. Holders 64, 79. Stop rings 66, 74. Communicating holes 67, 76. Passages 68. Lead-in hole 70. Pressure control valve 71. Control-pressure chamber 72. High pressure passage 73. Flow-out hole

Claims: A capacity-controlled scroll compressor comprising a compressor housing (3); a fixed scroll (1) having a fixed end plate (1 a) and a spiral wrap (1 b) extending from said fixed end plate (1 a); an orbiting scroll (2) having an orbiting end plate (2a) and a spiral wrap (2b) extending from said orbiting end plate (2a) and disposed in engagement with said fixed scroll (1) with respective wraps (1b, 2b) facing each other; said wraps (1b, 2b) of said fixed scroll (1) and said orbiting scroll (2) intermeshed to define a plurality of fluid compression pockets (50, 51, 52) and positioned to receive fluid to be compressed from a suction chamber (12) in said housing (3), said fixed scroll (1) and said orbiting scroll (2) being disposed inside of said compressor housing (3); an orbiting mechanism formed on the rear side of said orbiting end plate (2a) opposite the spiral wrap (2b) of said orbiting scroll (2); 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 trough a shaft sealing device and a subsidiary bearing through a main bearing; 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) 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); a discharge port (1 c) formed in said fixed end plate (1a) communicating with the fluid compression pocket (52) near the end of its formation; and a discharge valve (21) at the end of said discharge port (1c); further comprising an improved capacity control mechanism characterized by : at least a pair of bypass holes (50a, 50b, 51 a, 51 b) in said fixed end plate communicating with a pair of fluid compression pockets (50, 51, 52) formed in between both wraps (1b, 2b); a cylinder (61) formed inside said fixed end plate (1a) in a manner communicating with said pairs of fluid pockets (50, 51, 52) through said bypass holes (50a, 50b, 51a, 51b); a shuttle valve (60) inside said cylinder (61) mounted for reciprocal motion therein to vary the opening of said bypass holes (50a, 50b, 51a, 51b) to change the capacity of said compressor; a spring (62) in said cylinder (61) opposing reciprocation of said shuttle valve (60); said fixed end plate (1) further including a control-pressure chamber (71) housing a pressure control valve (70) for generating a control pressure for causing the reciprocation of said shuttle valve (60) against said spring (62) responsive to said control pressure; and a high pressure passage (72) in said fixed end plate (1a) between said control-pressure chamber (71) and said dischange port (1c) of said fixed end plate (1a) located upstream of said discharge valve (21) for introducing said compressed fluid at relatively high pressure to said pressure control valve (70) wherein said pressure control valve (70) generates a control pressure from said relatively high pressure fluid responsive to pressure in said compressor housing (3). The capacity-controlled scroll compressor of claim 1, further including a bypass hole formed on the side wall of the discharge port (1c) and a passage between said bypass hole and said cylinder (61), whereby said compressed fluid at relatively high pressure is directed to said shuttle valve (60) through said passage and the reciprocation of said shuttle valve (60) responsive to said control pressure selectively varies the output of said compressor. The capacity-controlled scroll compressor of claim 2, wherein said fixed end plate (1a) further includes a low pressure passage (67) communicating with said cylinder (61) and providing a passageway from said cylinder (61) to the outer peripheral surface of said fixed end plate (1a). The capacity-controlled scroll compressor of claim 3, wherein said low pressure passage (67), said bypass hole and said passage between said bypass hole and said cylinder (61) are formed of a straight though-hole from said outer peripheral surface of said fixed end plate (1a). The capacity-controlled scroll compressor of any of claims 2 to 4, wherein said at least a pair of bypass holes (50a, 50b, 51 a, 51 b) and said bypass hole formed on the sidewall of the discharge port (1c) selectively communicate with the low pressure area (12) of said compressor through separate passages responsive to said control pressure.

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