Boost pressure control, basic function

Overview

This document contains information on:

 General

 Function requirements

 Function

General

If too much exhaust gas flows to the turbine wheel, this is redirected to prevent the turbine from turning too quickly.

Function requirements

 Engine management ON (circuit 87M)

 Engine in operation

Function

Exhaust gas turbocharger with bypass valve

In wide open throttle operation, maximum boost pressure builds up. By opening the boost pressure control flap, the exhaust flow to the turbine wheel is redirected via a bypass and the boost pressure is reduced. Part of the exhaust flow is directed through the bypass past the turbine wheel, whereby the boost pressure is regulated and the turbine speed is limited. The boost pressure can be adapted to the current load demand on the engine.

Exhaust gas turbocharger with variable turbine geometry

The control linkage of the boost pressure regulator alters the position of the guide vanes in the exhaust gas turbocharger. The adjustable guide vanes modify the flow cross-section through which the exhaust gas flows to the turbine wheel. The vanes adjust the gas pressure present at the turbine wheel to the required boost pressure. The turbine speed defines the amount of pre-compressed air and thus the boost pressure.

The boost pressure is constantly monitored by the charge air pressure and temperature sensor and passed on to the combustion engine control unit.

To protect the exhaust gas turbocharger from overload, the combustion engine control unit monitors the exhaust gas temperature via the temperature sensor upstream of the exhaust gas turbocharger and the exhaust gas pressure via the exhaust gas pressure sensor. The boost pressure is reduced if there is any risk of thermal or mechanical overload.