System and method for controlling a variable displacement compressor

Abstract

A system and method for controlling the displacement of a variable displacement compressor by feeding back crankcase pressure as part of a control scheme is disclosed.

1 . A system for controlling a variable displacement compressor comprising:
 a control valve for controlling pressure in a crankcase of a variable displacement compressor; and   a control unit that controls said control valve based on a comparison between a target pressure and said pressure in said crankcase.   
   
   
       2 . The system of  claim 1  wherein the system further comprises:
 a pressure sensor disposed in said crankcase, said pressure sensor being in communication with said control unit to send said control unit a pressure sensor signal, said control unit being responsive to said pressure sensor signal to cause a change in said control valve position.   
   
   
       3 . The system of  claim 2  wherein said pressure sensor is one of an electronic pressure sensor and a mechanical feedback pressure sensor. 
   
   
       4 . The system of  claim 2  wherein the said pressure sensor is disposed in a passage or subchamber of said crankcase. 
   
   
       5 . The system of  claim 1  wherein the control valve is a pilot operated macro-sized valve, the position of which is controlled by a microvalve operated by said control unit. 
   
   
       6 . The system of  claim 1 , wherein the control valve opens to raise pressure in said crankcase, and further comprising a second control valve which opens to lower pressure in said crankcase, said control unit controlling both the control valve and the second control valve based at least in part on pressure in said crankcase. 
   
   
       7 . The system of  claim 5 , wherein the control valve and the second control valve are pilot valves controlling the position of a third control valve, said third control valve being selectively positionable thereby to a position in which the third control valve ports high pressure fluid from a discharge path of the compressor to said crankcase to raise pressure in said crankcase, a position in which the third control valve vents said crankcase to a suction flow path of the compressor to lower pressure in said crankcase, and a position in which said crankcase is isolated from said discharge flow path and isolated from said suction flow path to hold pressure in said crankcase constant. 
   
   
       8 . The system of  claim 1  further comprising a plurality of pilot valves which control the position of the control valve and the second control valve based at least in part on pressure in said crankcase. 
   
   
       9 . The system of  claim 1 , wherein said control unit is one of a bellows and a diaphragm, exposed on one side to a reference pressure and on another side to actual crankcase pressure, and wherein said control valve position is determined by movement of said one of a bellows and a diaphragm in response to a differential in the pressures acting across said one of a bellows and a diaphragm. 
   
   
       10 . The system of  claim 1  wherein said control unit is one of an electrical control unit, a pneumatic control unit, an electro-pneumatic control unit, and a hydraulic control unit. 
   
   
       11 . The system of  claim 1  wherein the system further comprises:
 a thermostatic system connected to said control unit, said thermostatic system operable to generate a target crankcase pressure, wherein said control unit is responsive to control said control valve based at least in part upon said target crankcase pressure.   
   
   
       12 . The method of  claim 19  wherein the controlling the position of the control valve includes the steps of:
 d1) determining a desired change of position of a control valve for controlling the amount of the displacement of the compressor based on the difference determined between the target crankcase pressure and the actual crankcase pressure; and   d2) changing the position of the control valve to the desired position.   
   
   
       13 . The method of  claim 12  wherein the desired change of position determined in step d1) is determined by utilizing a simulated annealing algorithm dependant upon predetermined optimization parameters. 
   
   
       14 . The method of  claim 12  wherein the desired change of position determined in step d1) is based at least in part on the magnitude of the difference determined in step c). 
   
   
       15 . The method of  claim 12  wherein the determination performed in step d1) minimizes the difference between the target crankcase pressure and actual crankcase pressure by utilizing one of a derivative optimization algorithm, a simulated annealing algorithm, and a genetic optimization algorithm. 
   
   
       16 . The method according to  claim 20 , comprising the steps of:
 a) setting a reference pressure;   b) measuring an actual crankcase pressure;   c) comparing the reference pressure and the actual crankcase pressure to determine a difference between the reference pressure and the actual crankcase pressure; and   d) changing the position of a control valve controlling crankcase pressure, with the change in position of the control valve being based on the comparison of the actual crankcase pressure and the reference pressure.   
   
   
       17 . The method according to  claim 20 , wherein the reference pressure is a target crankcase pressure. 
   
   
       18 . The method according to  claim 20 , wherein the reference pressure is related to a target crankcase pressure as an inverse function. 
   
   
       19 . A method for controlling a variable displacement compressor having a control valve for controlling the amount of the displacement of the compressor utilizing crankcase pressure, comprising the steps of:
 a) setting a target crankcase pressure;   b) measuring crankcase pressure of a variable displacement compressor;   c) comparing the target crankcase pressure and the measured crankcase pressure to determine a difference between the target crankcase pressure and the measured crankcase pressure; and   d) controlling the position of a control valve for controlling the amount of the displacement of the compressor based on the difference determined between the target crankcase pressure and the measured crankcase pressure.   
   
   
       20 . A method for controlling a variable displacement compressor of the type in which the amount of the displacement of the compressor is controlled by varying crankcase pressure, comprising the step of varying a signal to control compressor displacement as a function of a comparison between a target crankcase pressure and a measured crankcase pressure. 
   
   
       21 . (canceled)