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Displacement control valve of clutchless variable displacement inclined plate-type compressorRelated Patent Categories: Pumps, Condition Responsive Control Of Drive Transmission Or Pump Displacement, Adjustable Cam Or Linkage, Axial Cam, With Sump Pressure ActuationDisplacement control valve of clutchless variable displacement inclined plate-type compressor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070183904, Displacement control valve of clutchless variable displacement inclined plate-type compressor. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD OF THE INVENTION [0001] The present invention relates to a displacement control valve of a clutchless variable displacement inclined plate-type compressor which is connected directly to a drive source without using a clutch. BACKGROUND ART OF THE INVENTION [0002] Patent Document 1 discloses a displacement control valve of a clutchless variable displacement inclined plate-type compressor for controlling a discharge displacement of the compressor by opening and closing a valve hole formed in a communication path between a discharge chamber and a crank chamber of the compressor, the displacement control valve including the valve hole always communicating with the crank chamber, an inside control valve for opening and closing the valve hole by a valve body operated in response to expansion and contraction of a pressure sensing member for sensing a suction pressure, and an electromagnetic solenoid connected to the inside control valve for switching the inside control valve between an operating condition where the valve body opens and closes the valve hole in response to the expansion and contraction of the pressure sensing member and a non-operating condition where the valve body opens the valve hole independently of the expansion and contraction of the pressure sensing member, and the displacement control valve controls the discharge displacement so that a suction pressure and a discharge pressure have a predetermined correlation. This Patent Document 1 describes that the displacement control property is expressed by the following equation in a region of Pd>Pd.sub.0.Ps=P.sub.0-(Pd-Pc)S.sub.1/S.sub.2 Where, [0003] Pd: discharge pressure [0004] Pc: crank chamber pressure [0005] Ps: suction chamber [0006] P.sub.0: equivalent internal pressure of bellows [0007] S.sup.1: cross-sectional area of valve hole [0008] S.sub.2: effective cross-sectional area of bellows [0009] Patent Document 1: JP-A-7-127566 DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention [0010] However, there are the following problems in the displacement control valve disclosed in the above-described Patent Document 1. [0011] Because the discharge pressure Pd urges the valve body in a direction of valve closing, in order to forcibly open the valve body by degaussing of the electromagnetic solenoid, it is necessary to set the force of a releasing spring of the electromagnetic solenoid at a value of (Pd-31 Ps)S.sub.1 or more. In order to forcibly open the valve body in a region with a high discharge pressure Pd, it is necessary to use a releasing spring with a great spring force, and it is necessary to generate a great electromagnetic force for exciting the electromagnetic solenoid and attracting a movable core against the spring force of the releasing spring, and whereby, the electromagnetic solenoid becomes large. [0012] Accordingly, paying attention to the above-described problems, an object of the present invention is to provide a displacement control valve of a clutchless variable displacement inclined plate-type compressor, which can be made smaller than the displacement control valve disclosed in Patent Document 1. Means for Solving the Problems [0013] To achieve the above-described object, a displacement control valve of a clutchless variable displacement inclined plate-type compressor according to the present invention is provided as a displacement control valve for controlling a discharge displacement of the compressor by opening and closing a communication path between a discharge chamber and a crank chamber of the compressor. The displacement control valve comprises a valve hole formed in the communication path and always communicating with the discharge chamber, an inside control valve for opening and closing the valve hole by a valve body operated in response to expansion and contraction of a pressure sensing member for sensing a suction pressure, and an operation switching device connected to the inside control valve for switching the inside control valve between an operating condition where the valve body opens and closes the valve hole in response to the expansion and contraction of the pressure sensing member and a non-operating condition where the valve body opens the valve hole independently of the expansion and contraction of the pressure sensing member. [0014] In the present invention, because the valve hole is always communicated with the discharge chamber, the force for urging the valve body in a valve opening direction by a discharge pressure Pd can be decreased as compared with that in the displacement control valve disclosed in the aforementioned Patent Document 1, and the switching device for forcibly opening the valve body may be made smaller. [0015] In such a displacement control valve according to the present invention, a structure is preferably employed wherein the above-described operation switching device has an electromagnetic solenoid, when the electromagnetic solenoid is excited, the inside control valve becomes the operating condition, and when the electromagnetic solenoid is degaussed, the inside control valve becomes the non-operating condition. In such a structure, because the variable displacement inclined plate-type compressor can be switched to between a displacement control condition and a minimum displacement condition by exciting/degaussing the electromagnetic solenoid, the control unit for the variable displacement inclined plate-type compressor may be simplified. [0016] Further, in the displacement control valve according to the present invention, it is preferred that the electromagnetic solenoid includes a movable core connected to the inside control valve and a positioning member for positioning the inside control valve at an operating position when the electromagnetic solenoid is excited. By providing such a positioning member, it becomes possible to position the inside control valve at an operating position by exciting the electromagnetic solenoid, and the switching of the variable displacement inclined plate-type compressor to its operating condition becomes possible by the excitation of the electromagnetic solenoid. [0017] Further, in the displacement control valve according to the present invention, it is preferred that the positioning member is formed by one end of the pressure sensing member and an end surface of a case of the electromagnetic solenoid. By forming the positioning member with one end of the pressure sensing member and the case of the electromagnetic solenoid, it is not necessary to dispose a particular positioning member separately, and the structure of the displacement control valve may be simplified. [0018] Further, in the displacement control valve according to the present invention, it is preferred that the electromagnetic solenoid includes a releasing spring for urging a movable core in a direction apart from a fixed core, and when the electromagnetic solenoid is degaussed, the inside control valve becomes the non-operating condition by the releasing spring. Because the releasing spring of the electromagnetic solenoid can turn the inside control valve into the non-operating condition, it is not necessary to provide a spring separately for turning the inside control valve into the non-operating condition, and the structure of the displacement control valve may be simplified. [0019] Further, in a preferred embodiment of the present invention, the inside control valve includes a pressure sensing rod which is slidably inserted into a hole formed in a valve housing and communicating with the valve hole and which is connected to the valve body, and a cross-sectional area of the pressure sensing rod is set greater than a cross-sectional area of the valve hole. In such a structure, because a control property is realized wherein the suction pressure decreases when the discharge pressure increases, the discharge displacement increases in a high thermal-load region with a high discharge pressure. Therefore, a cooler comprising a variable displacement inclined plate-type compressor with this displacement control valve does not deteriorate in cooling performance even in a high thermal-load region with a high discharge pressure. [0020] Alternatively, in another preferred embodiment of the present invention, the inside control valve includes a pressure sensing rod which is slidably inserted into a hole formed in a valve housing and communicating with the valve hole and which is connected to the valve body, and a cross-sectional area of the pressure sensing rod is set smaller than a cross-sectional area of the valve hole. In such a structure, because a control property is realized wherein the suction pressure increases when the discharge pressure increases, the discharge displacement decreases in a region of a high discharge pressure. As a result, occurrence of a condition, in which the compressor operates at an excessive load, may be prevented. Effect According to the Invention [0021] In the displacement control valve of a clutchless variable displacement inclined plate-type compressor according to the present invention, because the valve hole is always communicated with the discharge chamber, the force for urging the valve body in a valve opening direction by a discharge pressure can be decreased as compared with that in the displacement control valve disclosed in the aforementioned Patent Document 1, and the switching device for forcibly opening the valve body may be made smaller than that in the displacement control valve of Patent Document 1. Therefore, the displacement control valve of a clutchless variable displacement inclined plate-type compressor according to the present invention can be made smaller than the displacement control valve of Patent Document 1. Brief Explanation of the Drawings [0022] FIG. 1 is a vertical sectional view of a clutchless variable displacement inclined plate-type compressor having a displacement control valve according to an embodiment of the present invention. [0023] FIGS. 2A and 2B are sectional views of the displacement control valve according to the embodiment of the present invention, showing operations of an inside control valve when an electromagnetic solenoid is excited, FIG. 2C is a sectional view of the displacement control valve, showing an operation of the inside control valve when the electromagnetic solenoid is degaussed, and FIG. 2D is an enlarged, partial sectional view of the inside control valve. [0024] FIGS. 3A and 3B are graphs showing the control property of the displacement control valve according to the embodiment of the present invention, FIG. 3A shows a control property in a case of Sr>Sv, and FIG. 3B shows a control property in a case of Sr<Sv. 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