OPERATION - Shift Control Valve operation / Engine Brake Valve (D range OVERDRIVE)

The shift control valve controls continuous speed changes from low to overdrive in "D" and "Ds" modes. This valve controls the pulley ratio by controlling the flow of line pressure into the primary pulley according to input signals from the accelerator position and engine speed. In low, the shift control valve is positioned to the left. As engine speed increases, pitot pressure moves the control valve to the right, and line pressure is directed to the primary pulley via circuit. As the pulley ratio changes from low to overdrive, a "rise characteristic" increases engine speed to the required rev/min. This is achieved by the modulator linkage connecting the pulley ratio sensor to the shift control valve and compensation plunger. The pin and spring 4 prevent sudden draining of hydraulic pressure from the primary pulley by slowing down the movement of the shift control valve when the accelerator pedal is pressed suddenly. A shift lock valve also prevents oil draining from the primary pulley circuit.

The engine brake valve enables the engine to maintain a comparatively high speed during deceleration when the selector lever is in the "Ds" position. In "D" position, the engine brake plunger blocks the oil passage, pressure is directed to the engine brake valve, valve spring force is overcome and the valve spool moves to the right.