Boost Control Solenoid How Does It Work

[Seatdriver]

Hi,

 

Does anyone know how the Boost Control Solenoid works on a MK2 1.9 TDi 115 PD engine.

 

Im interested in how the ECU contols the vaccum to this valve, the way this valve regulates the vaccum to the turbo and what all the pipes are for.

 

Obviously one pipe is the main Vaccum feed, one is a atmospheric feed, what are the others for?

 

Anyone know or has anyone got an internal drawing of this valve?

 

Thanks

[Willie Krashitt]

For engines with variable nozzle turbochargers like the 115PS and above, a generic answer to this is that the vacuum pump provides the vacuum, which if the boost control solenoid is fully closed (0% duty cycle) goes fully to the turbocharger and pulls the vanes in. At high engine speeds, and high load operating points, the solenoid may have a 100% duty cycle, meaning no vacuum goes to the turbo, only atmospheric air, and the vanes are fully open.

Virtually all the time you are driving, the solenoid is operating somewhere in between 0 and 100%, blending a mixture of vacuum and air together to give the desired movement of the vanes.

 

Except for when either fully open or closed, the solenoid is always moving, and is controlled via a pulsed 'duty cycle' of voltage / current that is dictated by the ECU. There is a feedback control system in place, whereby the duty cycle output would initially be as per a 'map' in the ECU, but this can be varied higher or lower depending on how the actual boost pressure (measured by the MAP sensor)compares to the pre programmed boost value for that particular operating speed/load point. If less boost is required for example, the solenoid is opened to allow some air into the system, and simultaneously limiting the amount of vacuum being supplied. and conversely, for more boost, the air is limited and more vacuum applied.

 

Fixed geometry turbo's as used on the 90PS engine use a similar system but instead of vacuum, mix boost pressure with outside air to modulate the boost pressure going to the wastegate actuator.

 

George.