Exhaust Gas Recirculation: Description and Operation

This is a vacuum operated and electronically controlled EGR system. It consists of an electronic diesel system (EDS) control unit, air flow sensor, vacuum control valve, switchover valves, microswitches, coolant temperature sensor, injection pump rack position sensor, vacuum control flap, and a TDC transmitter.
The EDS control unit supplies the signal to the vacuum control valve, which controls the vacuum supply to the EGR valve. Vacuum is supplied by a pump. The EDS control unit receives input signals from sensors measuring the various engine conditions. The input sensors consist of engine speed, coolant temp, intake air flow, fuel injection rack position, and barometric pressure.
The vacuum control valve controls the EGR valve by way of a vacuum amplifier. The amplifier regulates the modulated vacuum according to load conditions (injection pump rack position). The vacuum control flap is activated by the EDS control unit through a switchover valve.
The EGR valve and the vacuum control flap are opened and closed by switchover valves, depending on operating conditions of the engine.