Variable camshaft timing control VANOS

The variable camshaft timing control improves the torque in the lower and middle engine speed range. A greater valve overlap results in lower amounts of residual gas at idle speed. The exhaust-gas recirculation in the partial load range reduces the volume of nitrogen oxide. The following is also achieved:

• faster heating of the catalytic converters
• lower pollutant emissions after a cold start
• reduction in the fuel consumption

A controlled VANOS unit is fitted at both intake and exhaust camshafts. A VANOS solenoid valve activates the VANOS unit. The required positions of the intake and exhaust camshafts are calculated from the engine speed and the load signal (depending on the intake air temperature and engine temperature). The DME control unit activates the VANOS solenoid valves accordingly. The control of the intake and exhaust camshaft is variable within their maximum adjustment range. Once the correct camshaft position has been reached, the VANOS solenoid valves ensure that the oil volume in the positioning cylinders in both chambers remains constant. This keeps the camshafts in this position.

To perform the adjustment, the variable camshaft timing control requires a feedback signal on the current position of the camshaft. Camshaft sensors on the intake and exhaust side record the position of the camshafts. On engine start, the intake camshaft is in the end position ("late"). When the engine is started, the exhaust camshaft is pretensioned by a spring and held in the "advanced" position.