EGR System - Diesel: Operation

The EGR flow rate is controlled in 3 stages in accordance with the engine speed, load and altitude. The first stage, high EGR, is obtained in the combination of closed throttle valve and open EGR valve. The second stage, low EGR, is obtained by opening the throttle valve. The third stage is zero-EGR condition and is obtained by closing the EGR valve.

The EGR flow is determined by position of throttle and EGR valves. Engine load information is signaled to EGR control unit by potentiometer installed on injection pump lever. Engine speed is signaled to control unit by a magnetic sensor on the injection pump. A water temperature sensor is located at water inlet.

The control unit signals the solenoid valves to open or close, determining vacuum levels at EGR control valve and throttle diaphragm. To make sure of good driveability, EGR is deactivated when engine temperatures are low or extremely high.

Fig 1: EGR System (Diesel)