Variable Induction System: Description and Operation
Resonance intake manifoldThe length of the intake manifold is a critical factor for the torque and power output of a combustion engine.
Strong vacuum is created by the pistons on the intake stroke, which, with the intake valves open, moves the air quantity in the intake manifold. The intake air flow or the air/fuel mixture thereby develops considerable kinetic energy (momentum). Back pressure, created when the intake valves close, immediately begins to expand in the opposite direction. The level of pressure is dependent on the air flow velocity and the gas quantity mass present in the intake manifold.
If the mixture column is quickly accelerated or braked, oscillation occurs, the frequency of which is dependent on intake manifold length. If the engine timing and mixture column oscillations match, then a certain charge effect is attained by means of resonance oscillation. Since the mixture column oscillations are also engine speed dependent, the resonance oscillations at a set intake manifold length can only be attained in particular engine speed range.
In order to make the charge effect available over a broader engine rpm range, engines 104.942/992 are equipped with a "resonance intake manifold". This manifold features a "resonance flap" which effectively makes two different intake manifold lengths available.
Design and function
A pneumatically controlled resonance flap (22) is located on the intake manifold.
The resonance intake manifold switchover valve (Y22/6) is connected to the resonance flap (22) and is controlled by the engine control module as follows:
No load (vehicle parked) at 3900 rpm
Full load (WOT) at:
(104.942) 3450 rpm
(104.992) 3350 rpm
WOT = Wide Open Throttle
Resonance flap closed
The intake air flows into the resonance intake manifold (19a) through intake ports, which branch off after the throttle valve, into the air collection housing of the oscillation pipe (19b). The collected air volume is split in half by the resonance flap (22). This leads to a distinct increase in low-end torque.
Resonance flap open
With the resonance flap open, the collected air volume in the oscillation pipe (19b) is not split. The respective intake cylinder is served by both intake lines of the resonance intake manifold (19a).