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Control valve for variable displacement compressorRelated Patent Categories: Pumps, Condition Responsive Control Of Drive Transmission Or Pump Displacement, Adjustable Cam Or Linkage, Axial Cam, With Sump Pressure ActuationControl valve for variable displacement compressor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060083625, Control valve for variable displacement compressor. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY [0001] This application claims priority of Japanese Application No. 2004-298794 filed on Oct. 13, 2004 and entitled "CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR". BACKGROUND OF THE INVENTION [0002] (1) Field of the Invention [0003] The present invention relates to a control valve for a variable displacement compressor, and more particularly to a control valve for a variable displacement compressor which is suitable for controlling refrigerant displacement of a variable displacement compressor for an automotive air conditioner. [0004] (2) Description of the Related Art [0005] A compressor used in a refrigeration cycle of an automotive air conditioner is driven by an engine whose rotational speed varies depending on a traveling condition of the vehicle, and hence is incapable of performing rotational speed control. For this reason, in general, a variable displacement compressor capable of changing refrigerant displacement is employed so as to obtain an adequate refrigerating capacity without being constrained by the rotational speed of the engine. [0006] In the variable displacement compressor, in general, a wobble plate disposed within a crankcase formed gastight, such that the inclination angle thereof can be changed, is driven by the rotational motion of a rotating shaft, for performing wobbling motion, and pistons caused to perform reciprocating motion in a direction parallel to the rotating shaft by the wobbling motion of the wobble plate draw refrigerant from a suction chamber into associated cylinders, compress the refrigerant, and then discharge the same into a discharge chamber. In doing this, the inclination angle of the wobble plate can be varied by changing the pressure in the crankcase, whereby the stroke of the pistons is changed for changing the discharge amount of the refrigerant. The control valve for a variable displacement compressor controls the changing of the pressure in the crankcase. [0007] In general, the control valve for a variable displacement compressor, which variably controls the displacement of the compressor, operates to introduce part of refrigerant at discharge pressure Pd discharged from the discharge chamber into the crankcase formed gastight, such that pressure Pc in the crankcase is controlled through control of the amount of refrigerant thus introduced. The control of the amount of introduced refrigerant is carried out e.g. by a known method of controlling the amount of introduced refrigerant according to suction pressure Ps in the suction chamber. That is, the control valve for a variable displacement compressor senses the suction pressure Ps, and controls the flow rate of refrigerant at the discharge pressure Pd introduced from the discharge chamber into the crankcase, so as to hold the suction pressure Ps at a constant level. [0008] To this end, the control valve for a variable displacement compressor is equipped with a pressure-sensing section for sensing the suction pressure Ps, and a valve section for causing a passage leading from the suction chamber to the crankcase to open and close according to the suction pressure Ps sensed by the pressure-sensing section. Further, a type of the control valve for a variable displacement compressor which is capable of freely externally setting a value of suction pressure Ps to be assumed at the start of the variable displacement operation, is equipped with a solenoid that enables configuration of settings of the pressure-sensing section by external electric current. [0009] By the way, conventional control valves for a variable displacement compressor which can be externally controlled include a type for control of a so-called clutchless variable displacement compressor configured such that an engine is directly connected to a rotating shaft without providing an electromagnetic clutch between the engine and the rotating shaft on which a wobble plate is fitted, for execution and inhibition of transmission of a driving force to the engine (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2000-110731 (Paragraph numbers [0010] and [0044], and FIG. 1)). [0010] This control valve comprises a valve section causing a passage communicating between a discharge chamber and a crankcase to be opened and closed, a solenoid for generating an electromagnetic force causing the valve section to operate in the closing direction, and a pressure-sensing section for causing the valve section to operate in the opening direction as suction pressure Ps becomes lower than the atmospheric pressure, which are arranged in this order. Therefore, when the solenoid is not energized, the valve section is in a fully open state, whereby pressure Pc in the crankcase can be held at pressure close to discharge pressure Pd. This causes the wobble plate to become substantially at right angles to the rotating shaft, enabling the variable displacement compressor to operate at the minimum displacement. Thus, the refrigerant displacement can be substantially reduced to approximately zero even when the engine is directly connected to the rotating shaft, which makes it possible to eliminate the electromagnetic clutch. [0011] However, the conventional control valve for controlling a variable displacement compressor having no use for the electromagnetic clutch is configured such that the pressure-sensing section and the valve section are arranged with the solenoid interposed therebetween, and the suction pressure Ps is introduced to the pressure-sensing section which compares the suction pressure Ps and the atmospheric pressure, via the solenoid. This necessitates the solenoid in its entirety to be accommodated within a pressure chamber, and hence components of the solenoid need to be designed with considerations given to resistance to pressure. [0012] To eliminate this inconvenience, the present applicant has proposed a control valve for a variable displacement compressor configured such that the plunger of a solenoid is divided into a first plunger and a second plunger, and a pressure-sensing member, such as a diaphragm or a bellows, is interposed therebetween for sensing suction pressure Ps, whereby the suction pressure Ps is isolated from the atmospheric pressure in which the solenoid is disposed (Japanese Patent Application No. 2003-289581). [0013] Further, the present applicant has proposed a control valve for a variable displacement compressor that accommodates one of the divided plungers in a vacuum container, and sealing an opening of the vacuum container with a diaphragm, whereby the diaphragm isolates suction pressure Ps from the atmospheric pressure in which the coil of a solenoid is disposed (Japanese Patent Application No. 2004-125532). Hereafter, a description will be given of details of the construction of the control valve. [0014] FIG. 2 is a cross-sectional view showing the construction of the conventional control valve for a variable displacement compressor. [0015] The control valve includes a valve section, as shown in an upper part of FIG. 2, which receives discharge pressure Pd from a discharge chamber of the compressor to supply controlled pressure Pc to the crankcase. The valve section comprises a valve seat 101, a valve element 102 disposed on a downstream side in opposed relation thereto, and a spring 103 urging the valve element 102 in a valve closing direction. The valve element 102 is formed integrally with a shaft 104 that is formed to have an outer diameter equal to the inner diameter of a valve hole, and is held in a body in a manner axially movable back and forth. [0016] A solenoid is disposed, as shown in a lower part of FIG. 2. The solenoid comprises a core 106 and a first plunger 107 that are disposed within a bottomed sleeve 105, and a second plunger 108 and a coil 109 that are disposed outside the bottomed sleeve 105, with a diaphragm 110 provided between the first plunger 107 and the second plunger 108, such that the diaphragm 110 seals the open end of the bottomed sleeve 105. Within the bottomed sleeve 105, the first plunger 107 is fixed to a shaft 111 that is disposed to extend through the center of the core 106, and the shaft 111 is urged by a spring 112 in a direction of causing the first plunger 107 to be moved away from the core 106, whereby the first plunger 107 is brought into contact with an inner surface of the diaphragm 110. [0017] Suction pressure Ps in the suction chamber of the variable displacement compressor is introduced into a space within which the second plunger 108 is disposed, and the diaphragm 110 senses the suction pressure Ps. The second plunger 108 is fixed to an end of the shaft 104 opposite to an end thereof where the valve element 102 is provided, and further is urged by a spring 113 larger in load than the spring 103 of the valve section, in a direction of moving away from the diaphragm 110. This urges the shaft 104 upward as viewed in FIG. 2, and when the control valve is not in operation, the valve section is held in a fully-open state as shown in FIG. 2. Therefore, in this state, even if the rotating shaft of the compressor is driven by the engine for rotation, the compressor is operated at the minimum displacement. [0018] Now, if control current is supplied to the coil 109 of the solenoid, the first plunger 107 and the second plunger 108 are magnetically coupled to each other with the diaphragm interposed therebetween so as to behave as one plunger. At this time, the axial positions of the first plunger 107 and the second plunger 108 determine a valve lift of the valve section, and the valve lift is set according to the control current supplied to the coil 109. On the other hand, the diaphragm 110 receives the suction pressure PS, and hence is axially displaced according to the suction pressure Ps. The displacement of the diaphragm is transmitted to the valve element 102 via the second plunger 108 and the shaft 104. [0019] Therefore, the control valve for a variable displacement compressor introduces refrigerant at pressure Pc into the crankcase by controlling the flow of refrigerant at discharge pressure Pd to a flow rate dependent on the control current supplied to the coil 109. This causes the compressor to operate at displacement dependent on the control current. In this state, if the suction pressure Ps rises, the diaphragm 110 is displaced downward as viewed in FIG. 2, while if the suction pressure Ps drops, the diaphragm 110 is displaced upward as viewed in FIG. 2. According to the displacement of the diaphragm 110, the valve lift of the valve section is varied to thereby adjust the pressure Pc in the crankcase, and hence after all, the compressor has its displacement controlled such that suction pressure Ps becomes equal to a value set by the solenoid. [0020] However, in the control valve described above, the shaft formed integrally with the valve element also has the function of guiding the second plunger. Therefore, when the second plunger is axially moved by an attractive force produced on the second plunger by the solenoid, the second plunger is tilted depending on the state of the spring axially urging the second plunger, so that a couple of forces act on the shaft held in the body, to markedly spoil the axial slidability of the shaft, so that the valve element becomes incapable of moving smoothly. SUMMARY OF THE INVENTION [0021] The present invention has been made in view of this problem, and an object thereof is to provide a control valve for a variable displacement compressor which is improved in slidability of a shaft that transmits a change in suction pressure to a valve element and is enhanced in controllability. Continue reading about Control valve for variable displacement compressor... 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