Hydraulic control arrangement for a steplessly variable power transmission

摘要

A hydraulic control arrangement for a steplessly variable power transmission comprises a drive belt wheel and an output belt wheel, a belt connected to both belt wheels, a hydraulic chamber for controlling the effective diameter of the belt wheels in order thereby to steplessly control a speed ratio, a speed ratio control valve for controlling the hydraulic pressure to the hydraulic chambers as a function of a control pressure which is introduced into a control chamber, which is provided in the speed ratio control valve. The arrangement is characterised by a solenoid valve for controlling the control pressure for the speed ratio control valve, a mechanical pressure-generating device in order to mechanically generate a control pressure as a function of a vehicle driving condition, and an adjusting valve in order to selectively connect the control chamber either to the solenoid valve or to the mechanical pressure-generating device. The adjusting valve is actuated in order to connect the control chamber to the mechanical pressure-generating device when a difference between an actual control pressure and a desired set control pressure exceeds a predetermined value. In this way a stable speed ratio control can be achieved.