SLANT PLATE TYPE COMPRESSOR WITH VARIABLE DISPLACEMENT MECHANISM

Abstract: A slant plate type compressor (1), such as a wobble plate type compressor, with a variable displacement mechanism is disclosed. The compressor (1) has a valve mechanism (17, 18) to control the opening and closing of a passageway (25) connected between a crank chamber (22) and a suction chamber (40) in accordance with the pressure condition in the crank chamber (22) and the suction chamber (40). Therefore, the compressor (1) can improve the characteristics of cooling down and prevent the out flow of lubricating oil.

Description: The present invention relates to a slant plate type compressor according to claim 1 Such compressors are designed for use in a refrigerant compressor, and more particularly, in a slant plate type compressor, such as a wobble plate type compressor, with a variable displacement mechanism suitable for use in an automotive air conditioning system. A slant plate type compressor similar to the claimed type is known from GB-A-2 003 991. This compressor includes a compressor housing having a rear end plate at one end, said housing having a cylinder block provided with a plurality of cylinders and a crank chamber adjacent said cylinder block, a piston slidably fitted within each of the cylinders, a drive mechanism coupled to said pistons to reciprocate said pistons within said cylinders, said drive mechanism including a drive shaft rotatably supported in said housing, a rotor coupled to said drive shaft and rotatable therewith, and coupling means for drivingly coupling said rotor to said pistons such that the rotary motion of said rotor is converted into reciprocating motion of said pistons, said coupling means including a member having a surface disposed at an inclination angle relative to said drive shaft, the said rear end plate having a suction chamber and a discharge chamber. A passageway connects said crank chamber and said suction chamber and valve means are provided to directly close and open said passageway. In this device the valve means include a bellows element exposed to the pressure in the suction chamber for controlling the opening and closing of said passageway. Another slant plate type compressor is known from US-A - 4,037,993. In this compressor the valve means controls the communicaton between the suction chamber and the crank chamber according to the change of the suction pressure. The valve means operates under the pressure of the suction chamber. If the actual suction pressure is too low, the valve means closes the communication to increase the pressure in the crank chamber. Hereby the slant angle of the wobble plate is reduced to reduce the capacity of the compressor. If the suction pressure is too high, the valve means opens the communication. The pressure in the crank chamber is reduced. The slant angle of the wobble plate is increased to increase the capacity of the compressor. The drastic changes of the pressure in the crank chamber influence the durability of the crank case badly. A varying force is exerted onto the back side of the pistons. The pressure acts onto the rotor, onto the wobble plate and other parts. Therefore axial movements of the shaft and the rotor are caused. This increases the wearing of the drive shaft. Due to the mechanical instability the leak of oil contained in the crank chamber is high. The response time is inferior. One construction to adjust the capacity of a slant plate type compressor, particularly a wobble plate compressor, is disclosed in the US-A-3,861,829. US-A-3,861,829 discloses a wobble plate type compressor which has a driving device included with cam rotor to reciprocate a plurality of pistons and varies the slant angle of a slant surface of the cam rotor to change the stroke length of the pistons. Since the stroke length of the pistons within the cylinders is directly responsive to the slant angle of the slant surface, the displacement of the compressor is easily adjusted by varying the slant angle of cam rotor. Furthermore, variations in the slant 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 slant angle of the slant surface is determined by the pressure condition in the crank chamber. The pressure condition in the crank chamber is controlled in the following manner: the crank chamber communicates with the suction chamber through an aperture formed within a cylinder block, and the opening and closing of the aperture is controlled by a valve mechanism. The valve mechanism generally includes a bellows and a needle valve, and is located in the suction chamber so that the bellows operates in accordance with changes of pressure in the suction chamber. In the above compressor, the pressure in the suction chamber is controlled by the valve mechanism to maintain the change of pressure within small range SR1 as shown in Fig. 3. Therefore, if the predetermined pressure value in the suction chamber is determined to be lower than a pressure limit value Pa, there is possibility of generating frost on an evaporator. Thus, a predetermined pressure value P1 in suction chamber should be determined higher than the pressure limit value Pa so as to prevent frosting on the evaporator. As a result, a capacity adjusting mechanism starts its operation to control the capacity of the compressor at a higher pressure level than the pressure value Pa, the characteristic for the cooling down of the above compressor is thus inferior to that of the same type compressor without a variable displacement mechanism. Further, since the range of the pressure change CR1 in the crank chamber becomes large, the lubricating oil contained in the crank chamber may flow out to a refrigeration circuit through the suction chamber and cylinders. This lubricating oil existing in the refrigeration circuit causes the reduction of the heat-exchanging ratio of the evaporator. One solution to resolve the above disadvantages is disclosed in US-A-4846049. This document discloses a capacity adjusting mechanism for a slant plate type compressor which controls the capacity of the compressor while uniformly maintaining the pressure in a crank chamber, as shown in Fig. 1. In these compressors, the capacity adjusting mechanism operates to control the capacity of the compressor under the condition that a pressure P2 in the suction chamber is lower than a pressure limit value Pa. Therefore, the characteristic for cooling down is improved. However, during the control of the capacity of the compressor the range of the pressure change SR2 in the suction chamber becomes large. Therefore, the changes of the temperature of the air which flows out from the evaporator and into a compartment of automobile also becomes large. US-A-3,861,829 discloses the capacity adjusting mechanism used in a wobble plate type compressor. As is typical in this type of compressor, the wobble plate is disposed at a slant or inclination or inclination angle relative to the drive axis, and 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 suction chamber, however, can be used in any type of compressor which uses a slanted plate or surface in the drive mechanism. For example, US-A-4,664,604, issued to Terauchi, discloses this type of capacity adjusting mechanism in a swash plate type 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 therefore 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. It is another object of this invention to provide a slant plate type compressor which has an improved characteristic for cooling down. It is the other object of this invention to provide a slant plate type compressor which can prevent the outflow of lubricating oil. The invention attains the above objects by the means indicated in claim 1. Further objects, features and other aspects of this invention will be understood from the following detailed description of preferred embodiments of this invention, while referring to the annexed drawings. Fig. 1 is a cross-sectional view of a slant plate type compressor in accordance with one embodiment of this invention. Fig. 2 is an enlarged cross-sectional view of a part of a slant plate type compressor illustrating a variable displacement mechanism shown in Fig. 1. Fig. 3 is a graph illustrating the relationship between time and the pressures in a crank chamber and a suction chamber of a slant plate type compressor with a conventional variable displacement mechanism which operates to uniformly maintain the pressure in the suction chamber. Fig. 4 is a graph illustrating the relationship between time and the pressures in a crank chamber and a suction chamber of a slant plate type compressor with another conventional variable displacement mechanism which operates to uniformly maintain the pressure in the crank chamber. Fig. 5 is a graph illustrating the relationship between time and the pressures in a crank chamber and a suction chamber of a slant plate type compressor with a variable displacement mechanism in accordance with one embodiment of this invention. Fig. 6 is an enlarged cross-sectional view of a variable displacement mechanism in accordance with another embodiment of this invention. Referring to Fig. 1, there is shown the construction of a slant plate type compressor with a variable displacement mechanism in accordance with one embodiment of this invention. A compressor 1 includes a closed housing assembly formed by a cylindrical housing 2, a front end plate 3 and a rear end plate in the form of a cylinder head 4. A cylinder block 21 and a crank chamber 22 are formed 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 is fixed on one end surface of the cylinder block 21 through a valve plate 5. An opening 32 is formed in the central portion of the front end plate 3 to be penetrated by a drive shaft 6. The drive shaft 6 is rotatably supported within the front end plate 3 through a bearing 7. A shaft seal (not shown) 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 rotatably supported therein through a bearing 8. A rotor 9, which is disposed in the interior of the crank chamber 22, is connected to the drive shaft 6 and engages with an inclined plate 10 through a hinge portion 90. The inclination angle of the inclined plate 10 with respect to the drive shaft 6 can be adjusted by the hinge portion 90. A wobble plate 11 is disposed on the other side surface of the inclined plate 10 and bears against it through a bearing 12. A plurality of cylinders 24, one of which is shown in Fig. 1, are equiangularly formed in the cylinder block 21, and a piston 13 is reciprocatably disposed within each cylinder 24. Each piston 13 is connected to the wobble plate 11 through a connecting rod 14, i.e., one end of each connecting rod 14 is connected to the wobble plate 11 with a ball joint and the other end of each connecting rod 14 is connected to one of the pistons 13 with a ball joint. A guide bar 15 extends within the crank chamber 22 of the compressor housing 2. The lower end portion of the wobble plate 11 engages the guide bar 15 to enable the wobble plate 11 to reciprocate along the guide bar 15 while preventing rotating motion. The pistons 13 are thus reciprocated within the cylinders 24 by a drive mechanism formed of the drive shaft 6, the rotor 9, the inclined plate 10, the wobble plate 11 and the connecting rods 14. If the drive shaft 6 and the rotor 9 are rotated, the inclined plate 11, the wobble plate 12 and the connecting rods 14 function as a coupling mechanism to convert the rotating motion of the rotor 9 into a reciprocating motion of the pistons 13. The cylinder head 4 is divided in its interior space into at least two chambers, such as a suction chamber 40 and a discharge chamber 41 by a partition wall 44, both of which communicate with the cylinders 24 through suction holes 50 or discharge holes 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 place the suction chamber 40 and th e discharge chamber 41 to be in fluid communication with a refrigeration circuit. A passageway 25 is formed within the cylinder block 21 to communicate between the crank chamber 22 and the suction chamber 40 through a hollow portion 26, which is also formed within the cylinder block 21. With reference to Fig. 2, a valve control mechanism 17 is located in the hollow portion 26. The mechanism 17 comprises a cup-shaped casing 171, a bellows 172 which serves as a first pressure sensing portion and is disposed within the casing 171 and a valve element 173 which serves as a second pressure sensing portion. The casing 171 is fixedly disposed within the hollow portion 26 and an 0-ring 174 is disposed on the outer peripheral surface of the casing 171 to accomplish the sealing between the casing 171 and the hollow portion 26 to thereby obstruct the communication between the passageway 25 and the suction chamber 40 through a gap between the inner surface of the hollow portion 26 and the outer peripheral surface of the casing 171. The casing 171 is provided with an opening 171a at the outer peripheral surface to connect the passageway 25 with the interior of the casing 171 and a hole 171b at the bottom portion thereof. A screw thread portion is formed in the hole 171b to receive an adjusting screw 172a of the bellows 172. The bellows 172 includes the adjusting screw 172a to adjust the operating point thereof and a bellows element 172b within which a coil spring 172c is disposed for determining the operating point thereof. The adjusting screw 172a is attached to one end portion of the bellows element 172b. The valve element 173 comprises an operating valve 173a which is attached to the other end portion of the bellows element 172b and a valve seat 173b which is fixed on the opening portion of the casing 171. A guide pin 173c is attached to the end surface of the operating valve 173a to guide the axial movement of the bellows 172. A depressed portion 173d is formed on the valve seat 173b at the opposite side of the suction chamber 40 to define a suction pressure acting area. A hole 173e is formed through the valve seat 173b to communicate between the suction chamber 40 and the depressed portion 173d, and a hole 173f is also formed through valve seat 173b to be penetrated by the guide pin 173c of the operating valve 173a. The reaction force F of the bellows 172 which is composed by the reaction force of the bellows element 172b and the recoil strength of the coil spring 172c is determined by the following equation: F = (A1 - A2) · Pc + A2 · Ps (1) wherein A1 is an effective sectional area of the bellows element 172b, A2 is an effective sectional area of the depressed portion 173d, Pc is the pressure in the crank chamber, and Ps is the pressure in the suction chamber. The above equation can be changed into the following equation: Pc = A2/(A2 - A1) · Ps + F/(A1 - A2) (2) The above equation shows that the pressure Pc in the crank chamber is changed in accordance with the change of the pressure Ps in the suction chamber. With reference to Fig. 5, if the compressor starts its operation, the pressure Ps in the suction chamber 40 and the pressure Pc in the crank chamber 22 are greater than the amount of the recoil strength of the coil spring 172c and the stiffness of the bellows element 172b, i.e., the pressures Ps, Pc in the suction and crank chambers 40, 22 are greater than the operating point of the bellows 172. Therefore, the operating valve 173a is urged toward left to open the communication between the suction chamber 40 and the interior of the casing 171 through the depressed portion 173d and the hole 173e, to thereby accomplish the communication between the crank chamber 22 and the suction chamber 40. In that condition, the pressure Pc in the crank chamber 22 is maintained at the pressure Ps in the suction chamber 40. If the amount of the pressure Pc in the crank chamber 22 and the pressure Ps in the suction chamber 40 is below the operating point of the bellows 172, the bellows element 172b extends toward right (in Fig. 2) together with the operating valve 173a. Therefore, the end opening of the depressed portion 173d is closed by the operating valve 173a, and the communication between the crank chamber 22 and the suction chamber 40 is obstructed. At that time, the inclination angle of the inclined plate is maintained to be the same angle as previously. Therefore, the pressure Ps in the suction chamber 40 decreases in inverse proportion to the increase of the pressure Pc in the crank chamber until the suction pressure Ps reaches a predetermined pressure P3, which is between pressures P1 and P2, as shown in Fig. 5. After the opening 173e was closed by the operating valve 173a, the opening and closing operation of the operating valve 173a is controlled by the valve control mechanism 17 to satisfy the equation (1). That is, when the operating valve 173 accomplishes the communication between suction chamber 40 and the interior of the casing 171 through the depressed portion 173d and the hole 173e, the pressure Pc in the crank chamber 22 becomes higher as the pressure Ps in the suction chamber 40 becomes lower as mentioned above. In other words, the pressure Pc in the crank chamber 22 is changed in accordance with the pressure Ps in the suction chamber 40 and the change ratio Pc/Ps is determined by A2/(A2 - A1) . The opening and closing operation of the bellows 173 is efficiently repeated in accordance with the pressures Pc, Ps in crank and suction chambers 22, 40, respectively. With reference to Fig. 6, the construction of a valve control mechanism 18 in accordance with another embodiment of this invention is shown. An operating valve 181a of a valve mechanism 181 is in the form of a sphere and the inner surface of an opening 181b of a valve seat 181c is formed conically to fit with the outer surface of the operating valve 181a. The sealing between the operating valve 181a and the opening 181b is improved.

Claims: A slant plate type compressor (1) for use in a refrigeration circuit, including a compressor housing (2) having a central portion, a front end plate (3) at one end and a rear end plate (4) at its other end, said housing (2) having a cylinder block (21) provided with a plurality of cylinders (24) and a crank chamber (22) adjacent said cylinder block (21), a piston (13) slidably fitted within each of the cylinders (24), a drive mechanism coupled to said pistons (13) to reciprocate said pistons within said cylinders (24), said drive mechanism including a drive shaft (6) rotatably supported in said housing (2), a rotor (9) coupled to said drive shaft (6) and rotatable therewith, and coupling means for drivingly coupling said rotor (9) to said pistons (13) such that the rotary motion of said rotor (9) is converted into reciprocating motion of said pistons (13), said coupling means including a member having a surface disposed at an inclination angle relative to said drive shaft (6), said inclination angle of said member being adjustable to vary the stroke length of said pistons (13) and the capacity of the compressor (1), said rear end plate (4) having a suction chamber (40) and a discharge member (41) a passageway (25) connected between said crank chamber (22) and said suction chamber (40), and valve means (17, 18) for controlling the closing and opening of said passageway (25) to vary the capacity of the compressor (1) by adjusting the inclination angle, said valve means (17, 18) includes a valve (173a) to directly close and open said passageway (25), first valve control means (172b) to control the movement of said valve (173a) in accordance with pressure condition in said crank chamber (22), and second value control means (173d) to control the movement of said valve (173a) in accordance with the pressure condition in said suction chamber (40), said first valve control means (172b) comprising a bellows element (172) exposed to the crank chamber pressure. The slant plate type compressor (1) of claim 1 wherein said passageway (25) is formed within said cylinder block (21). The slant plate type compressor (1) of claim 1 wherein said valve means (17,18) are integrally formed. The slant plate type compressor (1) of one of claims 1 to 3 wherein the valve means comprises a bellows (172) and a coil spring (172c) for generating a reacting force (F) to the pressure (Pc) in the crank chamber (22) and the pressure (Ps) in the suction chamber (40). The slant plate type compressor (1) of claim 4 wherein the interior of said bellows is vacuum.

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