LOCKUP CLUTCH CONTROL MECHANISM OF FLUID COUPLING IN AUTOMATIC STEPLESS SPEED CHANGER FOR VEHICLE

PURPOSE:To decrease a frequency of engagement and disengagement of a directly coupled clutch, by disconnecting an input signal to a lockup control valve by a lockup signal valve when a difference between an input signal oil pressure and an opposite oil pressure exceeds a prescribed value. CONSTITUTION:A lockup control valve 81, to which the oil pressure from a hydraulic pressure source is input in accordance with the running condition of a vehicle by applying the secondary line pressure, regulated by a secondary regulator valve 35, as an input signal oil pressure while the output pulley working oil pressure of a V-belt type stepless speed changer as an opposite oil pressure, engages the directly coupled clutch of a torque converter 100 only when a difference between those pressures of oil is below the prescribed value. While said both oil pressures are input to also a lockup signal valve 85, and if the difference exceeds the prescribed value, the input signal oil pressure to the lockup control valve 81 is disconnected, and a directly coupled clutch 108 is released and prevented from its engagement. Accordingly, decreasing a frequency of engagement and disengagement of the directly coupled clutch, its durability can be improved.