Continuous Variable Valve Timing (CVVT)

Continuous Variable Valve Timing (CVVT)

The Engine Control Module (ECM) infinitely variable controls the CVVT valve which in turn controls the CVVT unit with engine oil pressure.

The CVVT unit is mounted either on the exhaust camshaft or the intake camshaft or both, depending on which engine it is. The CVVT unit is used on all 5 and 6 cylinder engines.

The variable camshaft is hydraulically controlled by the engine oil. (The camshaft rotation takes place by the engine oil, using the CVVT valve it is transferred to either the CVVT unit front or rear chambers.) The chambers are divided by a piston.

When oil presses the piston back or forward it results in a rotating motion in the piston because it is installed in the CVVT unit cover with splines. The tooth wheel for the timing belt is located on the CVVT unit outer cover.

The control is fast and exact, it only takes approximately 500 ms to transfer between the outer positions.

The variable camshaft main task is to minimize exhaust emissions, mainly at cold start, but also gives an improved idling quality.

Before the engine starts an internal check occurs as follows:
1. When the ignition is switched on an electrical check is carried out on the signal cable, the power supply cable and the solenoid. The check is carried out for a short-circuit to supply voltage/ground and open-circuit.
2. The camshaft checks if it is in the correct position compared to the flywheel, when the camshaft is in its 0-position (mechanical resting position). This can be done by comparing the signals from The Camshaft Position (CMP) sensor and the engine speed (RPM)/ position sensor. This is being done while the engine is running and is saved until the next start.

If the deviations are too large between these the CVVT valve does not activate and the diagnostic trouble code (DTC) is stored.

3. In case of larger controlled deviations at the variable camshaft the time taken to regulate to the control value is measured. This time is used partially to determine how long it takes to alter the camshaft angle and partially to switch off the variable camshaft if the time exceeds a certain maximum time. The camshaft uses the engine oil and oil pressure to turn. The rotation time depends on engine speed (RPM), oil pressure, viscosity etc. which in turn depends on oil temperature and quality etc.
4. To check that the Camshaft Position (CMP) sensor is correct it is compared to the signal from the engine speed (RPM)/position sensor when the engine turns. If the check gives faulty values a DTC is stored and CVVT control ceases.