Variable Valve Timing

Variable Valve Timing (VVT)





The variable valve timing system improves both low speed and high speed engine performance, engine idle quality and exhaust emissions. It is a two position system operating on the intake camshafts only. There is the equivalent of 30° of crankshaft movement between the retarded and advanced positions. Engine oil pressure operates the system under the control of the ECM.

For each intake camshaft there is a valve timing unit, a bush carrier assembly and a VVT solenoid.

Valve Timing Unit





The valve timing unit turns the intake camshaft in relation to the primary chain to advance and retard the timing.

The unit consists of a body and sprocket assembly separated from an inner sleeve by a ring piston and two ring gears; the inner sleeve is bolted to the camshaft.

The ring gears engage in opposing helical splines on both the body and sprocket assembly and the inner sleeve, to transmit drive from the assembly to the inner sleeve.

Engine oil pressure moves the ring gears and piston to turn the inner sleeve in the advanced timing direction and a return spring reverses the direction for retard.

Additional springs absorb rotational and axial backlash to reduce noise and wear.

Bush Carrier





This contains the oil passages that link the engine oil supply to the valve timing (VVT) unit. A lug on the bush carrier locates in the central bore of the VVT unit.

Two hollow dowels at the bush carrier and cylinder block ensure that the lug is accurately located. A scarf jointed fiber ring seals the joint between the lug and the valve timing unit. An integral shuttle valve, biased by a coil spring, controls the oil flow to the VVT unit.

VVT Operation

With the valve timing solenoids de-energized, the coil springs in the bush carriers position the shuttle valves to connect the valve timing units to drain.

Within the VVT units, the return springs hold the pistons and gears in the retarded position.

When the timing solenoids are energized, the solenoid plungers position the shuttle valves to direct engine oil to the VVT units. In the units, the oil pressure overcomes the force of the return springs and moves the gears and ring pistons to the advanced position.

Maximum system response time: 1.0 second for advancing and 0.7 second for retarding.

With valve timing in the retarded mode, the ECM produces a periodic lubrication pulse once every 5 minutes. This momentarily energizes the valve timing solenoids to allow a spurt of oil into the VVT units.

Variable Valve Timing (VVT) Solenoid





The valve timing solenoid controls the position of the shuttle valve in the bush carrier. A plunger on the solenoid extends when the solenoid is energized and retracts when the solenoid is de-energized.

With the vehicle stationary and the engine compartment open, operation of the valve timing solenoids may be audible when the lubrication pulse occurs at engine idle speed.