DISA Changeover Valve

Individual Control Intake System (DISA)

Function
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.

DISA utilizes 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.

Operating principle
A headpipe is arranged ahead of the oscillating tubes of the two cylinder banks.

When the connecting flap valve is closed, the headpipe and oscillating tube together act as a long intake pipe. The pulsating gas column produces a distinct increase in torque in the medium engine speed range.

The connecting flap between the two cylinder banks is opened in order to increase the output in the upper engine speed range. As a result, the dynamics of the headpipes is reduced to a large extent. The short oscillating tubes which are now effective enable higher output values in the upper engine speed range.

The vacuum tank is evacuated by the vacuum applied in the intake pipe in the partial load range. The connecting flap is closed with the aid of the vacuum unit and the pneumatic actuator.

If the switching speed is exceeded, the DME control unit deactivates the solenoid valve, i.e. it is switched off. As a result, the vacuum unit is aerated and the flap opened.

As soon as the solenoid valve switches (on dropping below the switching speed) the vacuum reservoir and vacuum unit are reconnected and the connecting flap closed.

The switching speeds for activation and deactivation are shifted with respect to each other (hysteresis) in order to avoid opening and closing in rapid succession.

This control configuration ensures that the connecting flap always remains open in the event of a fault in the electropneumatic flap operation. This ensures the complete engine output is available in the upper engine speed range (e.g. for overtaking). The basic setting of the flap is therefore "open".

The flap is returned or opened by means of two springs:
- A torsion spring on the flap shaft
- A coil spring in the diaphragm cell

The solenoid valve is activated directly via a powerful output stage in the DME control unit.