Principle of operation of two-position variable valve timing system

A signal from the control module (DME) establishes the position of the solenoid valve that releases oil into the hydraulic starting system. The force created by the oil pressure shifts the piston in which a pinion is mounted on two thrust bearings.

The pinion has both external and internal helical splines. The internal spline works in tandem with the hub of the timing gear sprocket, while the external spline works with the suction camshaft. The spline’s helical teeth cause the camshaft to rotate relative to the sprocket when the piston pinion is sliding in and out. This alters the camshaft timing (in this case, the inlet valve timing).


At low engine speeds, the camshaft is in a position for later opening of the inlet valves. At medium engine speeds (circa 3,000 rpm) the control element rotates the camshaft for earlier opening of the inlet valves. Once a certain engine speed is exceeded, the control element resets the camshaft to the position for later opening of the inlet valves.