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

PURPOSE:To increase the life of a clutch, by applying a working oil pressure of the output pulley hydraulic servo of a V-belt type stepless speed changer to the spool of a lockup control valve oppositely to the secondary line pressure of an input signal oil pressure. CONSTITUTION:A lockup clutch controller 80 switches the flow direction of working fluid in a fluid coupling 100 in accordance with an input signal oil pressure so as to control a directly coupled clutch 108 by means of a lockup control valve 81 provided in an oil passage connecting the fluid coupling 100 to a hydraulic pressure source. The spool 82 of the lockup control valve 81 receives the secondary line pressure as the input signal oil pressure, and also receives a working oil pressure of the output pulley hydraulic servo in a V-belt type stepless speed changer, in which a pressure drop speed is arranged to increase in response to the increase of a car speed, oppositely to the secondary line pressure, causing the directly coupled clutch 108 to be released only when an oil pressure in the input pulley hydraulic servo decreases below the prescribed value, thus the working frequency is decreased, resulting in the longer period of a life and the improvement of drive feeling.