Control device of variable displacement compressor

Abstract

An apparatus controls a variable displacement compressor used in a refrigerant circuit. The compressor includes a drive shaft, which is rotated by an engine. When the drive shaft rotates, the compressor compresses refrigerant sent from the external refrigerant circuit and discharges the compressed refrigerant to an external refrigerant circuit. When the displacement of the compressor is minimized, the circulation of refrigerant in the refrigerant circuit is stopped. The apparatus has a control mechanism for varying the pressure in the crank chamber. A detector detects a physical quantity that reflects the heating status of the compressor. When the compressor displacement is minimized and the quantity detected by the detector indicates that the heating status of the compressor is deteriorating, a controller commands the control mechanism such that the displacement of the compressor is greater than the minimum displacement.

1 . An apparatus for controlling a variable displacement compressor used in a refrigerant circuit, wherein the refrigerant circuit includes the compressor and an external refrigerant circuit, which is connected to the compressor, wherein the compressor includes a drive shaft, which is rotated by an external drive source, wherein, when the drive shaft rotates, the compressor compresses refrigerant sent from the external refrigerant circuit and discharges the compressed refrigerant to the external refrigerant circuit, wherein the compressor varies the displacement of the compressor in accordance with the pressure of a crank chamber, and wherein, when the displacement of the compressor is minimized, the circulation of refrigerant in the refrigerant circuit is stopped, the apparatus comprising: 
 a control mechanism for varying the pressure in the crank chamber;    a detector for detecting a physical quantity that reflects the heating status of the compressor; and    a controller, wherein, when the compressor displacement is minimized and the quantity detected by the detector indicates that the heating status of the compressor is deteriorating, the controller commands the control mechanism to change the crank chamber pressure such that the displacement of the compressor is greater than the minimum displacement.    
     
     
         2 . The apparatus according to  claim 1 , wherein the control mechanism has a control passage, which connects the crank chamber to a pressure zone in which the pressure is different from the pressure of the crank chamber, and wherein the control mechanism has a control valve, wherein the control valve controls the opening degree of the control passage, the control valve comprising: 
 a valve body;    a pressure sensing mechanism for detecting the pressure difference between two pressure monitoring points which are located in the refrigerant circuit, wherein the pressure sensing mechanism has a pressure sensing member, which moves in accordance with the pressure difference between two pressure monitoring points, wherein the pressure sensing member moves the valve body in accordance with the pressure difference such that the displacement of the compressor is varied to counter changes of the pressure difference; and    an actuator for applying force to the pressure sensing member in accordance with external commands, wherein the force applied by the actuator corresponds to a target value of the pressure difference, and wherein the pressure sensing member moves the valve body such that the pressure difference seeks the target value.    
     
     
         3 . The apparatus according to  claim 2 , wherein the refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor, and wherein the control passage is a supply passage for connecting the crank chamber to the high pressure zone.  
     
     
         4 . The apparatus according to  claim 1 , wherein the physical quantity reflects the speed of the external drive source and the detector has a rotation speed sensor for detecting the quantity, and wherein, when the quantity detected by the rotation speed sensor is greater than a predetermined referential value, the controller determines that the heating status of the compressor is deteriorating.  
     
     
         5 . The apparatus according to  claim 4 , wherein, when the quantity detected by the rotation speed sensor has been greater than the predetermined referential value for more than a predetermined time period, the controller determines that the heating status of the compressor is deteriorating.  
     
     
         6 . The apparatus according to  claim 1 , wherein the physical quantity reflects the refrigerant temperature in the compressor and the detector has a refrigerant temperature sensor for detecting the quantity, and wherein, when the quantity detected by the refrigerant temperature sensor is greater than a referential refrigerant value, the controller determines that the heating status of the compressor is deteriorating.  
     
     
         7 . The apparatus according to  claim 1 , wherein the compressor is used for an air conditioner for a vehicle, and wherein the external drive source is an engine of the vehicle.  
     
     
         8 . The apparatus according to  claim 7 , wherein the drive shaft is directly connected to the engine.  
     
     
         9 . The apparatus according to  claim 1 , wherein the refrigerant is carbon dioxide.  
     
     
         10 . An apparatus for controlling a variable displacement compressor used in a refrigerant circuit, wherein the refrigerant circuit includes the compressor and an external refrigerant circuit, which is connected to the compressor, wherein the compressor includes a drive shaft, which is rotated by an external drive source, wherein, when the drive shaft rotates, the compressor compresses refrigerant sent from the external refrigerant circuit and discharges the compressed refrigerant to the external refrigerant circuit, wherein the refrigerant is carbon dioxide, wherein the compressor varies the displacement of the compressor in accordance with the pressure of a crank chamber, and wherein, when the displacement of the compressor is minimized, the circulation of refrigerant in the refrigerant circuit is stopped, wherein the compressor has a control passage, which connects the crank chamber to a pressure zone in which the pressure is different from the pressure of the crank chamber, the apparatus comprising: 
 a control mechanism for varying the pressure in the crank chamber, and wherein the control mechanism has a control valve, wherein the control valve controls the opening of the control passage, the control valve comprising: 
 a valve body;  
 a pressure sensing mechanism for detecting the pressure difference between two pressure monitoring points which are located in the refrigerant circuit, wherein the pressure sensing mechanism has a pressure sensing member, which moves in accordance with the pressure difference between two pressure monitoring points, wherein the pressure sensing member moves the valve body in accordance with the pressure difference such that the displacement of the compressor is varied to counter changes of the pressure difference; and  
 an actuator for applying force to the pressure sensing member in accordance with external commands;  
   a detector for detecting a physical quantity that reflects the heating status of the compressor; and    a controller, wherein the controller, when the compressor displacement is minimized and the quantity detected by the detector shows that the heating status of the compressor is deteriorating, changes electric current supplied to the actuator to change the crank chamber pressure such that the displacement of the compressor is greater than the minimum displacement.    
     
     
         11 . The apparatus according to  claim 10 , wherein the refrigerant circuit has a high pressure zone, which is exposed to the pressure of refrigerant that is compressed by the compressor, and wherein the control passage is a supply passage for connecting the crank chamber to the high pressure zone.  
     
     
         12 . The apparatus according to  claim 10 , wherein the physical quantity reflects the speed of the external drive source and the detector has a rotation speed sensor for detecting the quantity, and wherein, when the quantity detected by the rotation speed sensor is greater than a predetermined referential value, the controller determines that the heating status of the compressor is deteriorating.  
     
     
         13 . The apparatus according to  claim 12 , wherein, when the quantity detected by the rotation speed sensor is greater than the predetermined referential value continues more than a predetermined time period, the controller determines that the heating status of the compressor is deteriorating.  
     
     
         14 . The apparatus according to  claim 10 , wherein the physical quantity reflects the refrigerant temperature in the compressor and the detector has a refrigerant temperature sensor for detecting the quantity, and wherein, when the quantity detected by the refrigerant temperature sensor is greater than a referential refrigerant value, the controller determines that the heating status of the compressor is deteriorating.  
     
     
         15 . The apparatus according to  claim 10 , wherein the compressor is used for an air conditioner for a vehicle, and wherein the external drive source is an engine of the vehicle.  
     
     
         16 . The apparatus according to  claim 15 , wherein the drive shaft is directly connected to the engine.  
     
     
         17 . A method for controlling a variable displacement compressor used in a refrigerant circuit, wherein the refrigerant circuit includes the compressor and an external refrigerant circuit, which is connected to the compressor, wherein the compressor includes a drive shaft, which is rotated by an external drive source, wherein, when the drive shaft rotates, the compressor compresses refrigerant sent from the external refrigerant circuit and discharges the compressed refrigerant to the external refrigerant circuit, wherein the compressor varies the displacement of the compressor in accordance with the pressure of a crank chamber, and wherein, when the displacement of the compressor is minimized, the circulation of refrigerant in the refrigerant circuit is stopped, the method including: 
 detecting a physical quantity that reflects the heating status of the compressor; and    setting the displacement of the compressor to be greater than the minimum displacement of the compressor when the quantity detected by the detector shows that the heating status of the compressor is deteriorating.