Exhaust Gas Recirculation: Description and Operation

Fig. 54 EGR system (California):

Exhaust gas recirculation, Fig. 54 is used to reduce oxides of nitrogen emissions in the vehicle exhaust. EGR uses partial recirculation of the exhaust gases from a port in the cylinder head to a port in the intake manifold.

Fig. 41 EGR control valve:

A vacuum regulated EGR valve, Fig. 41 is used to control the amount of exhaust gas admitted to the intake manifold. The amount of exhaust gas flowing through the valve is proportional to the valve opening which in turn is a function of the amount of vacuum applied to the EGR valve. The valve is open at closed throttle and closed at wide open throttle.

Fig. 42 Vacuum regulator valve:

At intermediate throttle positions, EGR valve position is proportional to throttle position. Throttle position or movement is transferred to a vacuum regulator valve, Fig. 42 mounted on the throttle shaft on the injection pump. The vacuum regulator valve then generates a vacuum signal proportional to control lever travel.

The EGR system consists of an EGR control valve, EGR control solenoid valve, EGR vacuum reducer solenoid valve, vacuum regulator valve, EGR control unit, coolant temperature sensor, accelerator switch, and engine speed sensor.

The EGR control unit monitors coolant temperature and engine speed to determine if the EGR control unit should generate an output signal to open the EGR valve under the current engine operating conditions.

The EGR control unit de-energizes the EGR control solenoid during warm-up when less NOx is generated. When the solenoid valve closes the vacuum signal to the EGR valve is removed allowing the valve to close. Less EGR during warm-up helps maintain acceptable driveability. The EGR control unit also de-energizes the EGR solenoid valve during high and low engine speed operation to maintain acceptable driveability.

An accelerator switch energizes the EGR vacuum reducer solenoid valve when the throttle is open wider than a pre-set amount to improve driveablity or when operating at high altitude to reduce smoking.