Variable Camshaft Timing Operation

When the engine is running, the compression and expansion of the valve springs causes momentary increases and decreases in the torque acting on the camshafts. These momentary changes of torque are sensed in the Variable Camshaft Timing (VCT) actuators and used to change the camshaft timing.

Camshaft Torsional Energy (For A Single Valve Event) 

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

Schematic View - Variable Camshaft Timing Actuator -1 Of 4 - Base Timing 

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

At engine start-up, once the engine oil pressure in the camshaft is sufficient to open the inlet check valve, engine oil flows across the spool valve. The oil then flows through the advance and retard check valves and into the advance and retard chambers. During the start cycle, the Powertrain Control Module (PCM) signals the Variable Camshaft Timing (VCT) solenoid to move the spool valve into the sleeve and connect the lock pin to inlet oil pressure. The inlet oil pressure causes the lock pin to retract from the inner plate and unlock the rotor assembly and camshaft from the sprocket housing.

There is a constant supply of engine oil to the VCT actuator to provide that the VCT actuator remains filled during operation.

Schematic View - Variable Camshaft Timing Actuator - 2 Of 4 - Advance 

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

To advance the camshaft timing, the PCM adjusts the signal to the Variable Camshaft Timing (VCT) solenoid to move the spool valve. This causes the advance chamber oil passage to close and the retard chamber oil passage is connected to inlet oil.

Each momentary increase of the torque acting on the camshaft generates a pressure pulse in the retard chamber. The engine oil flows from the retard chamber, through the spool valve and the advance check valve to the advance chamber. This equalize the pressures in the 2 chambers. The displacement of engine oil from the retard chamber causes the rotor assembly to advance in relation to the sprocket housing. Each momentary decrease of torque acting on the camshaft also generates a pressure pulse in the advance chamber. As the advance chamber oil passage is closed, the oil does not flow between the advance and retard chambers, thus the rotor assembly cannot move in the retard direction.

Schematic View - Variable Camshaft Timing Actuator - 3 Of 4 - Null 

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

Once the camshaft has reached the required timing position the PCM adjusts the signal to the Variable Camshaft Timing (VCT) solenoid to set the spool valve in the null position. In the null position, the advance and retard chamber oil passages are both closed by the spool valve. This results, that the rotor assembly is hydraulically locked to the sprocket housing.

Schematic View - Variable Camshaft Timing Actuator - 4 Of 4 - Retard 

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

To retard the camshaft timing, the PCM adjusts the signal to the Variable Camshaft Timing (VCT) solenoid to move the spool valve to close the retard chamber oil passage. At this stage the advance chamber oil passage is connected to the inlet oil.

Each momentary decrease of the torque acting on the camshaft causes oil to transfer from the advance chamber. The oil flows through the spool valve and the retard check valve to the retard chamber, and so retard the camshaft timing.