SLANT PLATE TYPE COMPRESSOR WITH VARIABLE DISPLACEMENT MECHANISM

Abstract: A wobble plate compressor, with a variable displacement mechanism which involve two bypass passages (25,27) between a crank chamber (22) and a suction chamber (40). A bellows (171) is disposed in one of the bypass passages and operates to open and close the communication between the crank chamber and the suction chamber in accordance with the pressure in the crank chamber to maintain the pressure in the crank chamber at a predetermined pressure. A solenoid operated control valve (18) is disposed in the other bypass passage and operates to open and close the communication between the crank chamber and the suction chamber by receiving a signal from an external sensor.

Description: The present invention relates to a slant plate type refrigerant compressor, such as a wobble plate compressor, with a variable displacement mechanism suitable for use in an automotive air conditioning system. One way of adjusting the capacity of a slant plate type compressor, particularly a wobble plate compressor, is disclosed in US-A-3861829. This discloses a wobble plate compressor which has a cam rotor driving device to drive a plurality of pistons and variation of the angle of inclination of a slant surface changes the stroke length of the pistons. Since the stroke length of the pistons within the cylinders is directly responsive to the angle of the surface, the displacement of the compressor is easily adjusted by varying the angle of inclination. Furthermore, variations in the angle can be effected by the pressure difference between a suction chamber and a crank chamber in which the driving device is located. In such a prior art compressor, the angle of the slant surface is controlled by pressure in the crank chamber. Typically this control occurs in the following manner. The crank chamber communicates with the suction chamber through an aperture and the opening and closing of the aperture is controlled by a valve mechanism. The valve mechanism generally includes a bellows element and a needle valve, and is located in the suction chamber so that the bellows element operates in accordance with changes of pressure in the suction chamber. In such compressor, the pressure in the suction chamber is controlled to be a predetermined value by the valve mechanism. But, when the predetermined value is below a certain value, there is a possibility of frosting on an evaporator in an associated air conditioning system. Because of this, the predetermined value is usually set higher than the certain value so as to prevent frosting on the evaporator. However, since the above certain value is higher than the pressure value in the suction chamber at the time that the compressor is operated in the maximum capacity of refrigerating, the cooling ability of the compressor is worse than that of the same type of compressor without a variable displacement mechanism as shown in Figure 2 of the accompanying drawings. US-A-3861829 dicloses a capacity adjusting mechanism used in a wobble plate compressor. As is typical in this type of compressor, the wobble plate, which is disposed at a slant or angle of inclination relative to the drive axis, nutates but does not rotate, and drivingly couples the pistons to the drive source. This type of capacity adjusting mechanism, using selective fluid communication between the crank chamber and the sucton chamber, however, can be used in any type of compressor which uses a slant plate or surface in the drive mechanism. For example, US-A-4664604 discloses this type of capacity adjusting mechanism in a swash plate compressor. The swash plate, like the wobble plate, is disposed at a slant angle and drivingly couples the pistons to the drive source. However, while the wobble plate only nutates, the swash plate both nutates and rotates. The term slant type compressor will therefor be used herein to refer to any type of compressor, including wobble and swash plate types, which use a slanted plate or surface in the drive mechanism. According to the present invention, a slant plate type compressor for use in a refrigeraton circuit, the compressor including a compressor housing having a front end plate at one end of the housing and at the other end of the housing a rear end plate in the form of a cylinder head defining a suction chamber and a discharge chamber, the housing having a cylinder block provided with a plurality of cylinders and a crank chamber adjacent to the cylinder block; a plurality of pistons slidably fitted within respective ones of the cylinders; a drive mechanism coupled to the pistons to reciprocate the pistons within the cylinders, the drive mechanism including a drive shaft rotatably mounted in the housing, a rotor coupled to the drive shaft and rotatable therewith, and coupling means for coupling the rotor to the pistons such that the rotary motion of the rotor is converted into reciprocating motion of the pistons, the coupling means including a member having a surface disposed at an inclination relatively to the drive shaft, and the angle of inclination of the member being adjustable to vary the stroke length of the pistons and the capacity of the compressor; a first bypass passage connected between the crank chamber and the suction chamber; and first valve means for controlling the closing and opening of the first bypass passage in response to changes in refrigerant pressure in the compressor to vary the capacity of the compressor by adjusting the angle of inclination; is characterised by a second bypass passage connected between the crank chamber and the suction chamber; and second valve means for controlling the closing and opening of the second bypass passage in response to an external signal to vary the capacity of the compressor by adjusting the angle of inclination. The first valve means then controls the compressor capacity in the known way, but the second valve means, which may be responsive, e.g. to a control signal from a sensor sensing the temperature in a compartment of a car which is cooled by an air conditioning system incorporating the compressor, enables an overriding increase in compressor capacity and cooling effect to be obtained when necessary. In the accompanying drawings:- Figure 1 is a cross-sectional view of one example of a wobble plate compressor with a variable displacement mechanism in accordance with the invention; and, Figure 2 is a graph which shows the relationship between time and the temperature in a compartment of a car when a slant plate type compressor without any variable displacement mechanism or with a conventional variable displacement mechanism is used in an automotive air conditioning system. A wobble plate compressor 1 includes a closed housing assembly formed by a cylindrical compressor housing 2, a front end plate 3 and a rear end plate in the form of cylinder head 4. A cylinder block 21 and a crank chamber 22 are located in the compressor housing 2. The front end plate 3 is attached to one end surface of the compressor housing 2, and the cylinder head 4, which is disposed on the other end surface of the compressor housing 2, is fixed on one end surface of the cylinder block 21 with an interposed valve plate 5. An opening 31 is formed in a central porition of the front end plate 3 to receive a drive shaft 6. The drive shaft 6 is rotatably supported in the front end plate 3 through a bearing 7. A shaft seal 8 is disposed between the inner surface of the opening 31 and the outer surface of the drive shaft 6 at the outside of the bearing 7. An inner end portion of the drive shaft 6 also extends into a central bore 23 formed in the central portion of the cylinder block 21 and is rotatable supported therein by a bearing 9. A rotor 10, which is disposed in the interior of the crank chamber 22, is connected to the drive shaft 6 so as to be rotatable with the drive shaft and engages an inclined plate 11 through a hinge portion 101. The angle of inclination of the inclined plate 11 with respect to the drive shaft 6 can be adjusted by the hinge portion 101. A wobble plate 12 is disposed on the other surface of the inclined plate 11 and bears against it through a bearing 13. A plurality of cylinders 24, one of which is shown in Figure 1, are equiangularly formed in the cylinder block 21, and pistons 14 is reciprocatably disposed one within each cylinder 24. Each piston 14 is connected to the wobble plate 12 through a connecting rod 15, i.e., one end of each connecting rod 15 is connected to the wobble plate 12 by a ball joint and the other end of each connecting rod 15 is connected to one of pistons 14 by a ball joint. A guide bar 16 extends within the crank chamber 22. The lower end portion of the wobble plate 12 engages the guide bar 16 to enable the wobble plate 12 to reciprocate along the guide bar 16 while preventing rotating motion. The pistons 14 are reciprocated in the cylinders 24 by the drive mechanism formed by the drive shaft 6, rotor 10, inclined plate 11, wobble plate 12 and connecting rods 15. The drive shaft 6 and rotor 10 are rotated; and the inclined plate 11, wobble plate 12 and connecting rods 15 function as a coupling mechanism to convert the rotating motion of the rotor into reciprocating motion of the pistons. The interior space of the cylinder head 4 is divided by a parition wall 47 into at least a suction chamber 40 and a discharge chamber 41, both of which communicate with the cylinders 24 through suction holes 50 or discharge hole 51 formed through the valve plate 5, respectively. Also, the cylinder head 4 is provided with an inlet port 42 and an outlet port 43, which put the suction chamber 40 and discharge chamber 41 in fluid communication with a refrigerant circuit. A first bypass hole 25 is formed in the cylinder block 21 to interconnect the suction chamber 40 and crank chamber 22 through a hollow portion 26 formed in the cylinder block 21 and a first communication hole 52 formed through the valve plate 5. The communication between the chambers 40 and 22 is controlled by a bellows 17, which is located in the hollow portion 26 and comprises a bellows element 171 and a needle valve 172. One end surface of the bellows element 171 is attached to one inner end surface of the hollow portion 26. The needle valve 172 is fixed on the other end surface of the bellows element 171 and operates to open and close the first communication hole 52 in accordance with the motion of the bellows element 171. A second bypass hole 27 is also formed in the cylinder block 21 to interconnect the suction chamber 40 and the crank chamber 22 through a second communication hole 53 formed through the valve plate 5. A control chamber 44 is formed in the suction chamber 40 of the cylinder head 4 by a dividing wall 46 and connected with the suction chamber 40 through a third communication hole 45 formed through the wall 46. A control alve 18 is disposed in the control chamber 44 and comprises a needle valve 181 and a solenoid actuator 182 is fixed on one inner end surface of control chamber 44. The needle valve 181 is attached to the other end surface of the solenoid actuator 182 and opens or closes the second communication hole 53 in accordance with the operation of the solenoid actuator 182. When the solenoid actuator 182 is not energized, the needle valve 181 closes the second communication hole 53. Accordingly, the pressure in the crank chamber 22 is determined by the operation of the bellows 17. That is if the pressure in the crank chamber 22 is lower than the stiffness of the bellows element 171, the bellows element 171 pushes or biases the needle valve 172 to the right (in Fig. 1) so that the projecting needle valve 172 closes the first communication hole 52 of valve plate 5. Thus, communication between the suction chamber 40 and the crank chamber 22 through the bypass hole 25 is obstructed. Under this condition, the pressure in the crank chamber 22 gradually increases, because gas leaks into the crank chamber 22 through any gaps between the inner wall surfaces of the cylinder 24 and the outer wall surfaces of the piston 14. Gas pressure in the crank chamber 22, which acts on the rear surface of the pistons 14, and changes the balance of moment on the inclined plate 11 relative to the drive shaft 6, is thereby decreased; and the stroke of the pistons 14 is thus also decreased. As a result, the colume of refrigerant gas taken into the cylinders 24 is decreased and the capacity of the compressor is thus decreased. On the other hand, if the pressure in the crank chamber 22 exceeds the stiffness of the bellows element 7, the bellows element 171 pushes the needle valve 172 towards the left against the inherent stiffness of the bellows element 171, and the needle valve 172 moves out of the first communication hole 52 of the valve plate 5. Accordingly, the crank chamber 22 is placed in fluid communication with the suction chamber 40 through the bypass hole 25. The refrigerant gas in the crank chamber 22 flows into the suction chamber 40 through the bypass hole 25, the hollow portion 26 and the first communication hole 52. Gas pressure which acts on the rear surface of the piston 24 thus decreases in accordance with the decreasing in the gas pressure in the crank chamber 22. The balance of moments acting on the inclined plate 11 thus increases so that the angle of the inclined plate 11 relative to drive shaft 6 also changes. The stroke of piston 14 is thus increased, and the volume of refrigerant gas being compressed is increased. When the solenoid actuator 182 is energized, it attracts the needle valve 181 to the right (in Fig.1), and the needle valve 181 moves out of the second communication hole 53 of the valve plate 5. Accordingly, the crank chamber 22 is placed in fluid communication with the control chamber 44 through the bypass hole 26 and the second communication hole 53, and the crank chamber 22 is thus interconnected with the suction chamber 40, because the control chamber 44 is always in fluid communication with the suction chamber 40 through the third communication hole 45. Therefore, the crank chamber 22 is in fluid communication with the suction chamber 40 independently of opening and closing of the bellows element 171, i.e., the crank chamber 22 is interconnected with the suction chamber 40 even though the needle valve 172 closes the first communication hole 52. The balance of moments acting on the inclined plate 11 is thus increased, and the stroke of the pistons 14 is thus also increased. As a result, the volume of refrigerant gas taken into the cylinders 24 is increased. When an air conditioning system which includes the above compressor is turned on, a signal for operating the needle valve 181 to open the second communication hole 53 is supplied to the solenoid valve 182 until the temperature in a compartment of a car is below the desired temperature. Accordingly, the needle valve 181 moves out of the second communication hole 52, and the crank chamber 22 is placed in fluid communication with the suction chamber 40. As a result, the compressor operates at the greatest volume until the temperature in the compartment of the car decreases to the desired temperature. When the temperature in the compartment of the car is below the desired temperature, a signal for operating the solenoid valve 182 to open the second communication hole 53 ceases. Thus needle valve 181 moves to close the second communication hole 53. Thereafter, communication between the crank chamber 22 and the suction chamber 40 is controlled by operation of the bellows 17. In the above compressor, the pressure in the suction chamber 40 is controlled by the bellows 17 so that the evaporator in the refrigeration circuit is prevented from frosting.

Claims: 1. A slant plate type compressor for use in a refrigeraton circuit, the compressor including a compressor housing (2) having a front end plate (3) at one end of the housing and at the other end of the housing a rear end plate (4) in the form of a cylinder head defining a suction chamber (40) and a discharge chamber (41), the housing having a cylinder block (21) provided with a plurality of cylinders (24) and a crank chamber (22) adjacent to the cylinder block; a plurality of pistons (14) slidably fitted within respective ones of the cylinders; a drive mechanism coupled to the pistons to reciprocate the pistons within the cylinders, the drive mechanism including a drive shaft (6) rotatably mounted in the housing, a rotor (10) coupled to the drive shaft and rotatable therewith, and coupling means (11,12,15) for coupling the rotor to the pistons such that the rotary motion of the rotor is converted into reciprocating motion of the pistons, the coupling means including a member (11) having a surface disposed at an inclination relatively to the drive shaft, and the angle of inclination of the member being adjustable to vary the stroke length of the pistons and the capacity of the compressor; a first bypass passage (25,26,52) connected between the crank chamber (22) and the suction chamber (40); and first valve means (171,172) for controlling the closing and opening of the first bypass passage in response to changes in refrigerant pressure in the compressor to vary the capacity of the compressor by adjusting the angle of inclination; characterised by a second bypass passage (27,53) connected between the crank chamber and the suction chamber; and second valve means (18) for controlling the closing and opening of the second bypass passage in response to an external signal to vary the capacity of the compressor by adjusting the angle of inclination. 2. A compressor according to claim 1, wherein the first valve means comprises a bellows including a bellows element (171) and a needle valve (172) and the second valve means comprises a solenoid actuator (182) and a needle valve (181).

Inventors: HIGUCHI, TERUO, KIKUCHI, SEI, TAKAI, KAZUHIKO, TERAUCHI, KIYOSHI
Applicants: SANDEN CORPORATION
Application year: 1987
Main classification: F04B1
IPC codes: F04B27