Control system for steplessly variable power transmission

Abstract

A control system for a steplessly variable transmission comprising a drive pulley and driven pulley formed with V-shaped grooves respectively, an endless belt engaged with the both grooves of the pulleys and tensioned between the pulleys to transmit engine torque therethrough, cylinders provided on the pulleys for being subjected to a hydraulic pressure to vary an effective diameter of the pulleys so that a speed ratio of the transmission is continuously changed, a hydraulic pressure supply device for introducing the hydraulic pressure into the cylinder means, a line pressure control device for controlling a line pressure of a hydraulic circuit which controls operation of the cylinders, a line pressure detecting device for detecting the line pressure, a torque detecting device for detecting the engine torque transmitted to the drive pulley, a torque allowance computing device for computing a maximum allowable belt transmitting torque which is effectively transmitted from the drive pulley to the driven pulley through the belt under the line pressure detected by the line pressure detecting device, and the torque control device for controlling a torque transmitted from the drive pulley to the driven pulley to a value smaller than the maximum torque when the engine torque detected by the torque detecting device is greater than the maximum torque. When a line pressure of a hydraulic control circuit therefor is unduly lowered, the slip between the drive and driven pulleys can be effectively suppressed.