Displacement control valve for use in a variable displacement compressor

Abstract: In a displacement control valve for use in a variable displacement compressor in which a displacement is variable with opening and closing of a communication passage between a crank chamber and a suction chamber, an operating point control arrangement (21, 23, 24) transmits discharge pressure of a discharge chamber to a valve body (7) to control an operating point of the valve body. A pressure transmission control arrangement (25, 26, 27, 28) is interposed between the discharge chamber and the operating point control arrangement and controls transmission of the discharge pressure to the operating point control arrangement. A pressure sensing member (6) senses, as sensed pressure, one of suction pressure and crank pressure to have a size variable in response to the sensed pressure. The valve body operates in response to the size of the pressure sensing member to open and close the communication passage.

Description: Background of the Invention: The present invention relates to a variable displacement compressor which is suitable for being used in an air conditioner of a vehicle, particularly of an automotive vehicle. Such a variable displacement compressor is, for example, disclosed in USP No. 4,960,367 under a title of "swash plate type compressor with a variable displacement mechanism". The compressor includes pistons, a swash plate mounted on a main shaft and a mechanism for converting a rotation of the swash plate into reciprocation of the pistons. A fluid is compressed in accordance with reciprocation of the pistons. The swash plate is structured such that an angle of incline with respect to the main shaft can be varied. A stroke of the piston is changed in accordance with a variation of the angle of incline. Of course, when the stroke of the piston is changed, a compression displacement of the compressor is changed. The angle of incline of the swash plate is controlled by a displacement control valve for controlling a communication between a crank chamber and a suction chamber in the compressor. The displacement control valve is structured such as to be opened and closed by an expansion and contraction of the bellows, and to be opened larger as a pressure of the discharge chamber in the compressor is higher. As a result, the higher the pressure of the discharge chamber in the compressor is, the more the pressure of the crank chamber in the compressor is reduced. In accordance of a reduction of the pressure of the crank chamber, the angle of incline of the swash plate in the compressor is increased, so as to direct the compression displacement to an increasing direction. Now, when the compressor is started in the state that a liquid refrigerant is stored in the suction side of the compressor, a liquid compression state is achieved. At this time, there is a case that the pressure of the discharge chamber becomes an abnormally high pressure (for example, 100 kg/cm 2 G) in a moment. In the conventional displacement control valve, a protecting mechanism for treating the abnormally high pressure is not provided. Accordingly, when the liquid compression state mentioned above is repeated, an expansion and contraction characteristic of the bellows is changed and an operating point for the displacement control valve is changed, so that a normal operation is prevented. In the case that the variable displacement compressor is used in the air conditioner, there is a risk that a freezing is generated in an evaporator of the air conditioner. In addition, from EP 0 366 348 A1 a displacement control valve for use in a variable displacement compressor according to the preamble of claim 1 can be derived. In the variable displacement compressor the pressure transmission control means of the displacement control valve is arranged in the cylinder block of the variable displacement compressor. Therefore, according to this disclosure, not only the pressure of the discharge chamber is applied to the pressure transmission control means, but also the pressure of the suction chamber can be applied to the pressure transmission control means, thus resulting in a complicated structure. Summary of the invention It is therefore an object of the present invention to provide a displacement control valve which can treat an abnormally high pressure in a discharge chamber of a variable displacement compressor, wherein the arrangement can be kept simple. Such an object is solved by a displacement control valve for use in a variable displacement compressor according to the independent claim 1. Preferred developments of the invention are given in the dependent claims. The object is also solved by a variable displacement compressor according to claim 8. Brief Description of the Drawing: Fig. 1 is a vertical cross sectional view of a conventional displacement control valve; Fig. 2 is a vertical cross sectional view of a variable displacement compressor provided with a displacement control valve in accordance with a first embodiment of the present invention; Fig. 3 is a vertical cross sectional view of the displacement control valve; Fig. 4 is a graph which shows a control characteristic of a pressure of a suction chamber in a variable displacement compressor in Fig. 2; and Fig. 5 is a vertical cross sectional view of a displacement control valve in accordance with a second embodiment of the present invention. Description of the Preferred Embodiments: With reference to Fig. 1, description will be made as regards a conventional displacement control valve for a better understanding of the present invention. The displacement control valve shown in Fig. 1 corresponds to a structure described in USP No. 4,960,367 mentioned above, which includes a cup-shaped valve casing 2 having an end opened, and a pedestal 3 mounted in an opening of the casing 2. Two through holes 4 are formed in the other end of the casing 2 to communicate with a crank chamber of a compressor through a first passage known in the art. The pedestal 3 has communication holes 3a and 3b. The communication hole 3a is connected to a suction chamber through a second passage known in the art. A combination of the first and the second passages is referred to as a communication passage. The casing 2 forms a valve chest 5 in cooperation with the pedestal 3. A bellows 6 is arranged in the valve chest 5. An inner portion of the bellows 6 is substantially vacuum. The bellows 6 has a size variable in a predetermined direction in the manner known in the art. A valve body 7 is provided in an end of the bellows 6. The other end of the bellows 6 is connected to the casing 2 by an adjusting screw 8. The bellows 6 is referred to as a pressure sensing member. The pedestal 3 integrally has a valve cylinder 12 facing to a discharge chamber 251 of the compressor. The valve cylinder 12 is integrally fixed to a valve plate 125 by bolts 17 and 18 in addition to a suction valve 14, a discharge valve 15 and a retainer 16. A transmission rod 21 is slidably inserted to the valve cylinder 12. A gap between the valve cylinder 12 and the transmission rod 21 is sealed by a seal member 22 such as a rubber. The transmission rod 21 is urged upward in the drawing by a spring 23. A lower end of the spring 23 is brought into contact with the valve body 7. A stopper 24 is fixed to the transmission rod 21. A gas of the crank chamber in the compressor enters into the valve chest 5 from the communication passage 4, passes through the communication holes 3b and 3a via the valve body 7 and reaches the suction chamber in the compressor. The transmission rod 21 is pushed against the spring 23 due to the discharge pressure of the discharge chamber 251. The force for pushing the transmission rod 21 is applied to the valve body 7. Now, when the compressor is started in the state that a liquid refrigerant is stored in the suction side of the compressor, a liquid compression state is achieved. At this time, there is a case that the pressure of the discharge chamber becomes an abnormally high pressure (for example, 100 kg/cm 2 G) in a moment. At this time, in the displacement control valve, the transmission rod 21 overcomes the urging force of the spring 23 and moves in a moment. Accordingly, a front end of the transmission rod 21 strikes the valve body 7 so as to apply an excessive load to the bellows 6. In the displacement control valve shown in Fig. 1, a protecting mechanism for treating the abnormally high pressure is not provided. Accordingly, when the liquid compression state mentioned above is repeated, an expansion and contraction characteristic of the bellows 6 is changed and an operating point for the displacement control valve is changed, so that a normal operation is prevented. With reference to Fig. 2, the description will be made as regards a variable displacement compressor provided with a displacement control valve in accordance with a first embodiment of the present invention. The compressor is designated by a reference numeral 100 and is of a swash plate type compressor, specifically a wobble plate type refrigerant compressor. The compressor 100 includes a cylindrical housing assembly 120 including a cylinder block 121, a front end plate 123 at one end of the cylinder block 121, a crank chamber 122 formed between the cylinder block 121 and the front end plate 123, and a rear end plate 124 attached to the other end of the cylinder block 121. The front end plate 123 is mounted on the cylinder block 121 forward (to the left in Fig. 2) of the crank chamber 122 by a plurality of bolts. The rear end plate 124 is mounted on the cylinder block 121 at its opposite end by a plurality of bolts 102. A valve plate 125 is located between the rear end plate 124 and the cylinder block 121. An opening 231 is centrally formed in the front end plate 123 for supporting a drive shaft 126 by a bearing 130 disposed in the opening. The inner end portion of the drive shaft 126 is rotatably supported by a bearing 131 disposed within a central bore 210 of the cylinder block 121. The bore 210 extends to a rearward end surface of the cylinder block 121 to dispose a displacement control valve 119 which will later be described in detail. A cam rotor 140 is fixed on the drive shaft 126 by a pin member 261 and rotates with the shaft 126. A thrust needle bearing 132 is disposed between the inner end surface of the front end plate 123 and the adjacent axial end surface of the cam rotor 140. The cam rotor 140 includes an arm 141 having a pin member 142 extending therefrom. A swash plate 150 is adjacent to the cam rotor 140 and includes an opening 153 through which passes the drive shaft 126. The swash plate 150 includes an arm 151 having a slot 152. The cam rotor 140 and the swash plate 150 are connected by the pin member 142, which is inserted in the slot 152 to create a hinged joint. The pin member 142 is slidable within the slot 152 to allow adjustment of the angular position of the swash plate 150 with respect to the longitudinal axis of the drive shaft 126. A wobble plate 160 is rotatably mounted on the swash plate 150 through bearings 161 and 162. A fork shaped slider 163 is attached to the outer peripheral end of the wobble plate 160 and is slidably mounted on a sliding rail 164 held between the front end plate 123 and the cylinder block 121. The fork shaped slider 163 prevents rotation of the wobble plate 160 and the wobble plate 160 nutates along the rail 164 when the cam rotor 140 rotates. The cylinder block 121 includes a plurality of peripherally located cylinder chambers 170 in which pistons 171 reciprocate. Each piston 171 is connected to the wobble plate 160 by a corresponding connecting rod 172. The rear end plate 124 includes a peripherally located annular suction chamber 241 and a centrally located discharge chamber 251. The valve plate 125 is located between the cylinder block 121 and the rear end plate 124 and includes a plurality of valved suction ports 242 linking the suction chamber 241 with the respective cylinders 170. The valve plate 125 also includes a plurality of valved discharge ports 252 linking the discharge chamber 251 with the respective cylinders 170. The suction ports 242 and the discharge ports 252 are provided with suitable reed valves as described in U.S. Pat. No. 4,011,029 to Shimizu. The suction chamber 241 includes an inlet portion 241a which is connected to an evaporator of the external cooling circuit (not shown). The discharge chamber 251 is provided with an outlet portion 251a connected to a condenser of the cooling circuit (not shown). Gaskets 127 and 128 are located between the cylinder block 121 and the inner surface of the valve plate 125, and the outer surface of the valve plate 125 and the rear end plate 124 respectively, to seal the mating surfaces of the cylinder block 121, the valve plate 125 and the rear end plate 124. A displacement control valve 119 is coaxially arranged with the central drive shaft 126 of the cylinder block 121, and a valve cylinder 12 is integrally fixed to the valve plate 125 by bolts 17 and 18 in addition to a suction valve 14, a discharge valve 15 and a retainer 16. Further, also with reference to Fig. 3, the displacement control valve 119 will be described below. The same reference numerals are assigned to the same or like elements as those of the displacement control valve shown in Fig. 1, and an explanation thereof will be omitted. In the displacement control valve in Fig. 3, the bellows 6 is structured such that an inner portion is vacuumed and an expansion and contraction amount is adjusted by the adjusting screw 8 adhered to a lower end portion. The transmission rod 21 has a first or upper end and a second or lower end opposite to the first end in the predetermined direction. The stopper 24 is fixed to the lower end of the transmission rod 21. The spring 23 is interposed between the stopper 24 and the valve body 7. A combination of the transmission rod 21, the spring 23, and the stopper 24 is referred to as an operating point control arrangement. The displacement control valve further includes a rod cover 25 which is fixed as a chamber defining arrangement to the valve cylinder 12 and covers the upper end of the transmission rod 21. An orifice 27 is formed in a orifice defining arrangement or a cover body 26 of the rod cover 25. In accordance with the orifice 27, it is structured such that an upper end of the transmission rod 21 can receive a pressure of the discharge chamber 251. In this manner, the rod cover 25 forms a kind of a pressure chamber 28. Accordingly, a pressure change in the discharge chamber 251 is damped through the orifice 27 so as to act on the transmission rod 21. Therefore, the transmission rod 21 does not directly receive a sudden pressure change. In this case, a seal member 22 is compressed between the valve cylinder 12 and the rod cover 25. A combination of the rod cover 25, the cover body 26, the orifice 27, and the pressure chamber 28 is referred to as a pressure transmission control arrangement. Next, with respect to Fig. 4 in addition, the description will be directed to control characteristic of the pressure of the suction chamber in the variable displacement compressor in Fig. 2. In the control characteristic of the pressure of the suction chamber, the operating point is changed due to the pressure of the discharge chamber applied to the transmission rod 21. That is, when the pressure of the discharge chamber increases, the operating point is lowered, and on the contrary, when the pressure of the discharge chamber is reduced, the operating point is increased. In this case, when the pressure of the discharge chamber is lowered in comparison with a predetermined value, the stopper 24 is brought into contact with the valve cylinder 12, so that the operating point becomes constant without being affected by the pressure of the discharge chamber. When starting the variable displacement compressor in the state that a liquid refrigerant exists in the suction side of the compressor, a liquid compression state is achieved, and the discharge chamber 251 becomes an abnormally high pressure in a moment. However, since the pressure chamber 28 within the rod cover 25 is communicated with the discharge chamber 251 via the orifice 27, a pressure thereof is reduced by the orifice 27, so that no excessive pressure is applied to the transmission rod 21 in a moment. That is, due to the pressure reduction effect in the orifice 27, the transmission 21 hardly responds to the instantaneous change of the pressure of the discharge chamber, but operates so as to respond to a gentle change of the pressure of the discharge chamber. As mentioned above, since the structure is made such as not to respond to the instantaneous pressure change within the discharge chamber in a moment, no excessive load is applied to the bellows, so that a durability and a reliability of the displacement control valve are improved. Further, since the structure is made in a very simple manner, a protecting function can be achieved without involving a characteristic change due to a repeating of the bellows or the like even when the discharge pressure becomes an abnormally high pressure by the liquid compression state. A volume of the pressure chamber 28 and a diameter of the orifice 27 can be properly obtained with respect to the discharge pressure as a result of an experiment, so that those skilled in the art can select an effective one. For example, it is possible to prepare some rod covers having different volumes of the pressure chamber 28 and different diameters of the orifice for the rod cover 25 and replace as occasion demands. With reference to Fig. 5 in addition, the description will be made as regards a displacement control valve in accordance with a second embodiment of the present invention. The same reference numerals are assigned to the same or like elements as those of the displacement control valve in Fig. 3, and an explanation thereof will be omitted. In the displacement control valve in Fig. 5, a rod cover 25 is integrally formed with a valve cylinder 12. In order to compress a seal member 22, a stop member 29 is adhered within the rod cover 25. In this case, it is a matter of course that the present invention can be used for the other compressor which generates a sudden liquid compression state and a pressure change.

Claims: A displacement control valve (119) for use in a variable displacement compressor (100) comprising: a discharge chamber (251) with discharge pressure; a suction chamber (241) with suction pressure, a crank chamber (122) with crank pressure; a communication passage between said crank chamber (122) and said suction chamber (241), said variable displacement compressor (100) having a displacement variable with opening and closing of said communication passage, said displacement control valve (119) comprising a pressure sensing member (6) for sensing, as sensed pressure, one of said suction pressure and said crank pressure to have a size variable in a predetermined direction in response to said sensed pressure; a valve body (7) connected to said pressure sensing member (6) for operating in response to said size of the pressure sensing member (6) to open and close said communication passage, said valve body (7) having an operation point between opening and closing of said communication passage; operating point control means (21, 23, 24) coupled to one of said valve body (7) and said pressure sensing member (6) for transmitting said discharge pressure to said valve body (7) in said predetermined direction to control said operating point of the valve body (7); pressure transmission control means (25, 26, 27, 28) interposed between said discharge chamber (251) and said operating point control means (21, 23, 24) for controlling transmission of said discharge pressure to said operating point control means (21, 23, 24); characterized in that said pressure transmission control means (25, 26, 27, 28) is arranged inside the discharge chamber (251). A displacement control valve as claimed in claim 1, wherein said pressure transmission control means (25, 26, 27, 28) comprises chamber defining means (25) for defining a pressure chamber (28) adjacent to said operating point control means (21, 23, 24) and orifice defining means (26) for defining an orifice (27) between said discharge chamber (251) and said pressure chamber (28). A displacement control valve as claimed in claim 2, wherein said operating point control means (21, 23, 24) comprises a transmission rod (21) extending in said predetermined direction and having a first end placed in said pressure chamber (28). A displacement control valve as claimed in claim 3, wherein said transmission rod (21) is movable in said predetermined direction and has a second end opposite to said first end, said operating point control means (21, 23, 24) further comprises a spring (23) interposed between said valve body (7) and said second end of the transmission rod (21), said valve body (7) being interposed between said pressure sensing member (6) and said spring (23). A displacement control valve as claimed in one of claims 2 to 4, further comprising a valve cylinder (12) fixed to said variable displacement compressor (100), said chamber defining means (25) being coupled to said valve cylinder (12). A displacement control valve as claimed in claim 5, wherein said chamber defining means (25) is formed separately from said valve cylinder (12) and fixedly connected to said valve cylinder (12). A displacement control valve as claimed in claim 5, wherein said chamber defining means (25) is formed integral with said valve cylinder (12). A variable displacement compressor comprising a discharge chamber (251) with discharge pressure, a suction chamber (241) with suction pressure, a crank chamber (122) with crank pressure, a communication passage between said crank chamber (122) and said suction chamber (241), and a displacement control valve (119) claimed in anyone of claims 1 through 7.

Inventors: FUJITA MASAAKI, TAGUCHI YUKIHIKO, FUJITA, MASAAKI, TAGUCHI, YUKIHIKO, Fujita, Masaaki, c/o Sanden Corporation, TAGUCHI, YUKIHIKO, C/O SANDEN CORPORATION
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1999
Main classification: F04B27
IPC codes: F04B27, F04B49