Control valve for a torque converter lock-up clutch or the like

Abstract

A control valve pressurizes an outlet conduit when a variable fluid pressure signal rises above a first predetermined level and depressurizes the outlet conduit when the variable signal subsequently drops below a second level that is lower than the first level, the valve further functioning to maintain the outlet conduit unpressurized without regard to the variable fluid pressure signal level in the absence of a second fluid pressure signal. The control valve automatically controls a fluid pressure operated lock-up clutch of a torque converter in a vehicle transmission system. The variable fluid pressure signal source may be a governor producing a pressure proportional to vehicle speed while the second fluid pressure signal source is one or more of the transmission drive conditioning devices. The control valve then functions to engage the lock-up clutch to eliminate fluid drive from the vehicle power path at higher vehicle speeds while at higher gear settings but maintains the fluid drive, regardless of vehicle speed, when the transmission is at one or more of the lower speed settings. These control functions are accomplished with a simplified and economical spool valve construction which exhibits a reliable and pronounced hysteresis or snap action to avoid undesirable oscillations in switching the torque converter in and out of the vehicle drive line.