Depending on the operating status, a certain quantity of exhaust gas is returned via the EGR valve into the exhaust tract in order to reduce pollutant emission.
The exhaust gas is fed through a bore hole in the cylinder head from the exhaust side to the intake side. The EGR valve connects this bore hole with the intake pipe.
The pressure converter connects the vacuum unit with the vacuum supply by means of hoses. Depending on the activation status and controlled by the DDE control module, it switches a variable vacuum to the vacuum unit. The pressure converter is activated by a square-wave signal with duty factors (= variable pulse width) between 5 and 95%.
The throttle valve serves to create increased vacuum in the intake pipe. The more tightly the throttle valve is closed, the more exhaust gas flows into the intake pipe.
Activation of the throttle valve - in the same way as activation of the EGR valve - is also by means of a pressure converter activated by the DDE control module.
The quantity of recirculated exhaust gas influences the mass of the fresh air drawn in: The more exhaust gas is recirculated, the less fresh air is drawn in by the engine.
As a measurement of the recirculated exhaust gas volume, the fresh air mass taken in is used.
For the purpose of exhaust gas recirculation control, a nominal value of air mass is defined in a characteristic map for all operating conditions.
The pulse duty factors for the EGR valve and the throttle valve are calculated by the DDE control module from the deviation from the nominal and actual value of the air mass. The further the EGR valve is opened, the more tightly the throttle valve is closed.
If the control module detects a diskrepancy between the specified and actual intake air mass that is outside the permissible limits, a fault is stored.
The following states lead to deactivation of the exhaust gas recirculation:
As reaction, the EGR valve is closed and the throttle valve opened.