Variable Camshaft Timing - Exhaust Camshaft Only

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

The timing of the exhaust camshaft can be adjusted independently by an oil pressure controlled torsional assist Variable Camshaft Timing (VCT) system. The VCT solenoid which is controlled electrically determines the position of the VCT actuator which has a direct interface with the exhaust camshaft.

The VCT actuator is located on the exhaust camshaft at the rear of the engine and is secured with a center bolt. The center bolt contains an oil control valve. A slot in the VCT actuator locates over a timing pin on the exhaust camshaft and is used to maintain the timing of the VCT actuator relative to the exhaust camshaft lobe position.

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

The VCT actuator is operated by a VCT solenoid which is controlled by the Powertrain Control Module (PCM). The PCM can operate the VCT solenoid to move the pintle pin to a predetermined position to control the flow of pressurized engine oil into the VCT actuator

The VCT solenoid is mounted on and sealed with an O-ring seal to the VCT cover. The VCT cover seals to the cylinder head and cam carrier with a single layer steel gasket with RTV sealant at T joint. VCT cover is located on dowels in the cam carrier.

When advance or retard of the exhaust camshaft timing is required, the VCT solenoid operates, extending the pintle pin and moving the spool valve to direct pressurized engine oil into one side or the other of the central rotor chambers in the VCT actuator. The solenoid pintle moves towards the spool valve located in the center bolt and makes contact.

Further movement of the solenoid pintle pin will push the spool valve into a known (controlled) position and oil will pass through channels within the center bolt into the VCT actuator chambers. The pressurized engine oil rotates the internal rotor in the VCT actuator which is secured to the exhaust camshaft. This in turn changes the engine timing. The total available camshaft advance adjustment is 50° crankshaft angle towards advance.

The exhaust camshaft VCT actuator has three hydraulic chambers. Residual camshaft torque is used to ensure the VCT actuator is returned to the 'base' position as quickly as possible. The pressurized engine oil is supplied from the engine variable flow oil pump with integral vacuum pump and must be mapped to deliver a controlled oil pressure to the VCT actuator to ensure VCT performance and response times are maintained.

There is no VCT system on the intake camshaft.