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

PURPOSE:To prevent occurrence of a shock and an engine stop during running of a vehicle at its low speed, by applying an opposed oil pressure, relating to a car speed with a large pressure drop speed in case of the increase of the car speed, to the spool of a lockup control valve oppositely to an input signal oil pressure. CONSTITUTION:A lockup clutch controller 80 switches the flow direction of working fluid in a fluid coupling 100 by the spool 82 of a lockup control valve 81 so as to control a directly coupled clutch 108. This spool 82 receives the secondary line pressure via an oil passage 2B as an input signal, and also receives as the opposite oil pressure a working oil pressure on the output pulley side of a V-belt type stepless speed changer, having a pressure drop speed which increases in response to increase of a car speed, from an oil passage 10. In this way, the directly coupled clutch 108 is fixed to the release side with the car speed below the preset value, thus occurrence of a shock during low speed running and an engine stop, when an engine generates a low output at stopping or the like of a vehicle, can be surely prevented.