Control valve for variable displacement compressor

Abstract

The object of the present invention is to provide a control valve for a variable displacement compressor, which is used for controlling differential pressure between discharge pressure and suction pressure such that the differential pressure becomes equal to differential pressure set by duty ratio control, and improved in characteristics thereof when it is in the vicinity of the valve-closing position. A valve section for controlling the flow rate of refrigerant at discharge pressure Pd to thereby supply refrigerant at pressure Pc to a crankcase is implemented by a spool valve structures. A spool valve element and a shaft arranged coaxially with each other are configured such that the spool valve element and the shaft oppositely receive the discharge pressure Pd and the suction pressure Ps, respectively. The differential pressure between, the discharge pressure Pd and suction pressure Ps, which is to be controlled, is set by a pulse current supplied to a solenoid section which is duty ratio controlled. As a result, the spool valve element performing micro vibration due to duty ratio control is prevented from colliding against a valve seat when it is in the vicinity of the: valve-closing position, so that it is possible to enhance the lift characteristics of the valve, and improve durability of component parts of the same.

What is claimed is:  
     
         1 . A control valve for a variable displacement compressor, for controlling a difference between discharge pressure and suction pressure in the variable displacement compressor such that the difference becomes equal to constant differential pressure set by an electromagnetic solenoid which is duty ratio controlled, 
 characterized in that a valve section that carries out opening and closing control of a passage between a first port into which refrigerant is introduced and a second port from which the refrigerant is guided out is formed by a spool valve.    
     
     
         2 . The control valve according to  claim 1 , wherein the valve section includes a valve seat formed in a passage between the first port and the second port, a spool valve element disposed such that it can be moved into and away from a valve hole in an upstream side space or a downstream side space adjacent to the valve seat, a spring for urging the spool valve element in a valve-opening direction, and a pressure-sensing shaft for transmitting pressure introduced thereto from a third port, to the spool valve element.  
     
     
         3 . The control valve according to  claim 2 , wherein the spool valve element is disposed on the downstream side of the valve seat, the discharge pressure in the variable displacement compressor being introduced into the first port, pressure in a crankcase of the variable displacement compressor being guided out from the second port, and the suction pressure in the variable displacement compressor being introduced,into the third port.  
     
     
         4 . The control valve according to  claim 2 , wherein the spool valve element is disposed on the upstream side of the valve seat, pressure in a crankcase of the variable displacement compressor being introduced into the first port, the suction pressure in the variable displacement compressor being guided out from the second port, and the discharge pressure in the variable displacement compressor being introduced into the third port.  
     
     
         5 . The control valve according to  claim 2 , wherein the spool valve element and the pressure-sensing shaft are integrally formed with each other.  
     
     
         6 . The control valve according to  claim 2 , wherein the spool valve element, the pressure-sensing shaft, and a drive shaft via which the electromagnetic solenoid actuates the spool valve element are integrally formed with each other.  
     
     
         7 . The control valve according to  claim 2 , wherein a predetermined clearance is provided between an end of the spool valve element moved into the valve hole, and an inner wall surface of the valve hole, so as to cause the clearance to function as an orifice.  
     
     
         8 . A control valve for a variable displacement compressor, for controlling a difference between discharge pressure and suction pressure in the variable displacement compressor such that the difference becomes equal to constant differential pressure set by an electromagnetic solenoid which is: duty ratio controlled, characterized by comprising: 
 a first valve section that carries out opening and closing control of a passage between a first port into which refrigerant from a discharge chamber is introduced and a second port from which the refrigerant having a flow rate thereof controlled is guided out to a crankcase; and    a second valve section that carries out opening and closing control of a passage between a third port into which the refrigerant is introduced from the crankcase and a fourth port from which the refrigerant having a flow rate thereof controlled is guided out to a suction chamber, in a manner interlocked with operation of the first valve section, and    wherein at least one of the first valve section and the second valve section is formed by a spool valve whose valve element can be moved into and away from a valve hole of a valve seat associated therewith.    
     
     
         9 . The control valve according to  claim 8 , wherein a valve element of the first valve section and a valve element of the second valve section are integrally formed with each other.  
     
     
         10 . The control valve according to  claim 8 , wherein the valve element of the first valve section, the valve element of the second valve section, and a drive shaft via which the electromagnetic solenoid actuates the valve elements are integrally formed with each other.  
     
     
         11 . The control valve according to  claim 8 , wherein a predetermined clearance is provided between an end of the valve element of the spool valve moved into the valve hole, and an inner wall surface of the valve hole, so as to cause the clearance to function as an orifice.