Functional description

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
  Fig 1: VANOS Solenoid Valve (Exhaust) - Circuit Diagram

  Courtesy of BMW OF NORTH AMERICA, INC.

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 coolant temperature). The DME control unit activates the VANOS unit accordingly. The intake camshaft can be variably regulated within its maximum adjustment range. When the correct camshaft position has been reached, the VANOS solenoid valve keeps the oil volume in the positioning cylinder in both vane cell chambers constant. This holds the intake camshaft in this position. To perform the adjustment, the variable camshaft timing control requires a feedback signal on the current position of the camshaft. A camshaft sensor on the intake side picks up the position of the camshaft. On engine start, the intake camshaft is in the end position ("late").