Periodic pressure fluctuations are produced in the intake pipe by the induction strokes of the cylinders. These pressure waves run through the intake tube and are reflected at the closed inlet valves. The intake tube length precisely adapted to the valve timing ensures that a pressure peak of the reflected air wave reaches the inlet valve just before the end of its opening range. A post-charging effect is achieved in this way. This post-charging effect conveys a larger volume of fresh mixture into the cylinder.
The variable intake manifold uses the advantages of short and long intake pipes.
Short intake pipes or intake pipes with a large diameter have the effect of producing higher output values in the upper engine speed range together with lower torque values in the medium engine speed range. Long intake pipes or intake pipes with a small diameter develop high torque in the medium engine speed range.
A rotating rotor is located the variable intake manifold. Turning alters the effective intake pipe length. This means that any intake pipe length can be set between the two end stops.
Drive for the rotor is a 12 V DC motor with worm gear mechanism. The electric motor is activated directly via a powerful output stage in the DME control unit.
A potentiometer provides the position feedback; the voltage supply for this comes from a 5 V output of the DME.
If the drive unit fails, the system remains its position. This can become noticeable during driving in that there is a lack of power or reduced flexibility.