Variable Valve-Lift (mechanical)

Assignment

In the petrol engine the throttle valve obstructs the free throughflow in the inlet port. It's throttle effect slightly reduces the full performance development and especially the optimum efficiency. By doing away with the throttle flap, fuel savings in the partial load area of up to 10% are possible. It is still used for certain operating conditions, otherwise it is fully open. Of course now, exactly the same as in the Diesel engine, a vacuum pump must be installed for the power braking.

Function

In the cylinder head, above the intake camshaft, there is a second shaft. This carries eccentric cams, which can move the top center rotation point of the rocker arm to the right (in the picture on the right) or to the left (in the picture on the left). Through a servo-motor with a worm drive the eccenteric shaft can be moved a half a rotation. During full strain (e.g. full acceleration) it is in the position shown in the right picture. This enables the camshaft, to open the intake valve to a maximum (of nearly 10 mm).
In the left picture the idling position can be seen. The eccentric cams are positioned far to the left. The intake-camshaft can only transfer a small amount of valve-lift (approx. 0,2 mm) through the rocker arm to the roller-cam-follower.The rocker arm is returned by a spring, which permanently presses the rocker arm against the inlet cam.