The Exhaust Gas Recirculation (EGR) System recirculates some of the exhaust gases to the intake air system. The flame propagation becomes slow during the combustion when the exhaust gases are mixed with the air-fuel mixture because most of them are the inert (incombustible) gases. Also the combustion temperature drops to reduce the NOx generation because the inert (incombustible) gas absorbs the heat generated by burning.
When the vacuum is applied to the EGR valve, the valve opens and the exhaust gas recirculates.
The vacuum, which operates on the EGR valve, is controlled in accordance with the engine coolant temperature or throttle valve opening to control the ratio of the EGR.
Engine cold The BVSV opens toward the atmosphere side while the engine is cold. Therefore the exhaust gas does not recirculate because a vacuum is not applied to EGR valve.
Idling A vacuum is not applied to the EGR port. Therefore the exhaust gas does not recirculate.
Throttle valve between EGR&EGR R port The vacuum of the EGR port is applied to the EGR valve to open the valve. The vacuum is controlled by the modulator and recirculates a constant ratio of the exhaust gas. EGR port Throttle valve EGR valve Exhaust gas EGR vacuum modulator BVSV EGR Rport EGR port Throttle valve EGR valve Exhaust gas EGR vacuum modulator BVSV Air EGR Rport
Throttle valve opening above EGR R port The vacuum of the EGR port is applied to the EGR valve to open the valve. As the vacuum of R port is applied to the modulator, the vacuum applied to the EGR valve becomes larger so that the EGR opening becomes greater. Throttle valve fully open The exhaust gas is not recirculated because the vacuum applied to the EGR valve with full load is less than the vacuum required to operate the valve.
3. Internal EGR effect of VVT-i (Variable Valve Timing-
Part of the exhaust gas is drawn in during the intake stroke by overlapping of the intake valve and exhaust valve. The VVT-i system controls the valve timing to control the internal EGR actively. The VVT-i system opens the intake valve quickly and lets some of the exhaust gas flow backwards to the intake side when the end of the exhaust stroke overlaps. The EGR effect is attained by drawing the back-flowing gas and the air-fuel mixture into the cylinder at the same time during the intake stroke. The VVT-i system changes the timing of the valve opening by the engine ECU. Refer to the engine control system for more details.