Exhaust Gas Recirculation: Description and Operation

Without Vacuum Amplifier

The EGR system consists of a recirculation channel and an EGR valve, which operates on vacuum.

Exhaust gas recirculation occurs when the air shutter is partly open between the closed (idle) and full throttle position.

Fig. 8 EXHAUST GAS RECIRCULATION SYSTEM, WITH THROTTLE CLOSED:

When the air shutter is closed, Fig. 10, the opening for the EGR hose on the EGR valve is in front of the air shutter. The pressure in the EGR valve hose and also in the EGR valve vacuum chamber is equal to atmospheric pressure. Pressure in the EGR valve reference chamber is always equal to atmospheric pressure, the same pressure exists on both sides of the vacuum diaphragm which keeps the valve in a closed position under spring tension.

Fig. 9 EXHAUST GAS RECIRCULATION SYSTEM, WITH THROTTLE PARTIALLY OPEN:

When the air shutter is partly open, Fig. 11, the opening for the EGR hose moves behind the air shutter. Behind the air shutter there is partial vacuum which is transmitted to the vacuum chamber of the EGR valve. The atmospheric pressure in the EGR valve reference chamber forces the diaphragm backward so that the valve opens. Exhaust gas now recirculates to the intake manifold and back into the cylinders for combustion.

Fig.12 - Exhaust Gas Recirculation System, With Air Shutter Fully Open:

When the air shutter is fully open, Fig. 12, atmospheric pressure in the intake manifold is transmitted to the vacuum chamber of the EGR valve. The pressure on both sides of the diaphragm is now equal which permits the valve to close under spring tension. Exhaust gas recirculation has now stopped.

With Vacuum Amplifier

The purpose of the EGR system incorporating a vacuum amplifier is to control the amount of gas recirculation, depending on the driving condition to meet NOx emission standards.

The principal operation is based on utilization of venturi vacuum at the air cleaner. This venturi vacuum signal, controls the vacuum amplifier which regulates the EGR valve to allow a correct amount of exhaust gas recirculation in relation to the intake air flow.

The vacuum amplifier receives two input vacuum signals, a weak venturi vacuum signal to be amplified and a strong manifold signal for its power source.

The system incorporates a vacuum reservoir tank and a check valve to maintain correct vacuum regardless of variations in engine intake manifold vacuum. The amplifier also provides vacuum amplification at higher engine speeds and moderate acceleration, when manifold vacuum decreases.

Fig.13 - Exhaust Gas Recirculation System, With Vacuum Amplifier:

The EGR valve is closed during idle by a solenoid valve positioned in front of the EGR valve. This solenoid valve is controlled by a micro switch, Fig. 13, which is mounted on the throttle valve.