Method and apparatus for clutch pressure control

Abstract

A method, apparatus and system for controlling transmission clutch and/or variator system pressures is provided. A transmission control unit and a pressure control device including an electro-hydraulic valve and a pressure switch cooperate to provide self-calibrating clutch and/or variator pressure control systems.

1 . A method for calibrating a clutch trim pressure, the method comprising:
 determining an electrical input value for a clutch trim system, the clutch trim system configured to control application of at least one clutch of a transmission, the electrical input value corresponding to a reference output pressure value associated with the clutch trim system; and   calibrating a clutch trim pressure of the clutch trim system based on the electrical input value.   
     
     
         2 . The method of  claim 1 , comprising determining the electrical input value and calibrating the clutch trim pressure during operation of the transmission. 
     
     
         3 . The method of  claim 2 , comprising determining the electrical input value without applying the at least one clutch. 
     
     
         4 . The method of  claim 2 , comprising determining the electrical input value prior to applying the at least one clutch. 
     
     
         5 . The method of  claim 1 , wherein the transmission comprises a variator. 
     
     
         6 . The method of  claim 1 , comprising determining at least one offset based on the electrical input value and using the offset to calibrate the clutch trim pressure. 
     
     
         7 . The method of  claim 6 , comprising selecting a method of calculating the at least one offset from a plurality of methods of calculating an offset. 
     
     
         8 . A transmission control system comprising at least one routine configured to execute the method of  claim 1  during normal or factory-test operation of the transmission. 
     
     
         9 . A computer program product embodied in at least one machine-readable storage medium, comprising at least one routine configured to execute the method of  claim 1  during normal or factory-test operation of the clutch trim system. 
     
     
         10 . A variator trim system comprising:
 an electrohydraulic actuator;   a valve fluidly coupled to the electrohydraulic actuator, the valve being axially movable to a plurality of positions in response to fluid pressure output by the electrohydraulic actuator; and   a plurality of fluid passages in communication with the valve and configured to supply a first fluid pressure to the valve to counteract fluid pressure output by the electrohydraulic actuator during a first phase of operation of the variator and supply a second fluid pressure to the valve to counteract fluid pressure output by the electrohydraulic actuator during a second phase of operation of the variator.