Exhaust Gas Recirculation: Description and Operation

EGR System (Ca. Models):

This system controls the formation of NOx emission by recirculating the exhaust gas into the combustion chamber through the intake manifold.

The EGR valve is controlled by EGR modulator and VSV controlled by ECM according to signals from various sensors.

The diaphragm mounted in the EGR modulator is operated by back pressure of the exhaust gas to open and close the valve. By this opening and closing action of the valve, the EGR modulator controls the vacuum transmitted to the EGR valve.

Under a low load condition such as low speed driving, the exhaust pressure is low. In this state, the diaphragm in the EGR modulator is pushed down by the spring force and the modulator valve opens to allow the air into the vacuum passage from the outside.

As a result, the vacuum transmitted to the EGR valve becomes smaller and so does the opening of the EGR valve. Thus, less amount of exhaust gas is recirculated to the intake manifold.

Under a high load condition such as high speed driving, on the other hand, the exhaust pressure is high. By the high exhaust pressure, the diaphragm in the modulator is pushed up and closes its valve. As the air does not enter the vacuum passage in this state, the vacuum transmitted to the EGR valve grows larger and so does the opening of the EGR valve.

Thus, larger amount of exhaust gas is recirculated to the intake manifold.

Under any one of the following conditions, ECM closes the vacuum passage of VSV. In this state, as the vacuum is not transmitted to the EGR valve, it remains closed.

- When engine cooling water temp. is lower than 50cc (122°F) or higher than 1OO~C (212°F)
- When engine speed is lower than 1000 r/min.
- When throttle valve is at idle position
- At engine start and when fuel injection is increased after engine start
- When engine is running under high load

Other than the above, EGR valve opens and closes in accordance with the EGR modulator operation.

The operation of EGR valves in monitored by ECM through the signal from the REGTS (Recirculated Exhaust Gas Temperature Sensor) which measures the temperature in the exhaust passage. Should anything abnormal occur, "CHECK ENGINE" light turns ON to warn it.