Abstract: A control valve system for controlling the operation of a continuously variable belt-driven motor vehicle transmission includes a first hydraulic pump that supplies fluid to the displacement cylinders of the transmission through a main pressure regulating valve and a transmission ratio control valve as a function of the setting of the manual selector valve and as a function of the torque requirement and speed of the vehicle. The torque converter is supplied with hydraulic fluid by way of a relief valve which comes into operating in the event of failure of an electronic control unit and a decrease in the vehicle speed. A first emergency operation on/off valve transmits torque at converter discharge pressure, by way of a second emergency on/off valve, as emergency operation control pressure to a transmission ratio control valve.

Abstract: A control valve system for a continuously variable belt transmission for an internal combustion engine comprising a main control valve acted upon by a force related to the transmission ratio and the rotational speed of the primary shaft, a transmission ratio control valve acted upon by a force related to the desired calibrated rotational speed of the engine and of the primary shaft, and an auxiliary valve connected mechanically to the transmission ratio control valve, the auxiliary valve (15) being acted upon by means of an electromagnetic pressure regulator (21) as a function of a selected characteristic relationship of desired rotational speeds for different operating conditions in an electronic control unit.