The VANOS control unit serves the purpose of increasing torque in the lower and medium engine speed ranges. Reduced valve overlap results in lower residual-gas quantities while idling. Nitrous oxide components are reduced by internal exhaust-gas recirculation in the partial load range. This achieves faster heating of the catalytic converters, lower untreated emissions after cold starting and reduced fuel consumption.
A regulated VANOS control unit for intake and exhaust is fitted in this engine. It is activated by means of an electromagnetically operated 4/3-way valve.
The required position of the intake and exhaust camshafts is calculated from the engine speed and load signal depending on the intake air and engine temperature and the VANOS VANOS adjustment unit is controlled accordingly by the engine control unit. The inlet and exhaust camshafts can be variably controlled within their maximum adjustment range, i.e. any arbitrary positions are possible corresponding to the specified values of the engine control unit. When the relevant optimum camshaft position is reached, the solenoid valves maintain a constant oil volume in the adjustment cylinder on both sides of the chamber so that the camshafts remain in the corresponding positions.
When the engine starts up, the intake camshaft is in its end position, i.e. it is initially in the retard position. During engine start, the exhaust camshaft is held in the advance position by means of a spring.