Control system for controlling the line pressure in a continuously

Abstract

A pressure transducer, which senses clutch pressure and effects closed loop clutch control in a continuously variable transmission, is used after the clutch is fully engaged to provide closed loop line pressure control to a desired setpoint, which line pressure regulates the tension on the belt in the transmission. Only a single transducer is needed since there is a known relationship between the clutch and line pressures when the clutch is locked up. Prior to lockup, the line pressure is governed by an open loop controller which establishes the line pressure at a level higher than that called for by the setpoint. This ensures that the line pressure will be high enough to provide the required tension on the belt so that it will not slip. After the clutch is engaged, the closed loop line pressure controller (which includes both the open loop line pressure controller and the closed loop clutch controller) establishes the line pressure at the setpoint. For stable operation, the closed loop controller responds only to relatively slow changes of the setpoint. In response to fast changes, the closed loop controller is made ineffective so that the line pressure will be determined only by the open loop controller and will be greater than the level called for by the setpoint.