Exhaust Gas Recirculation: Description and Operation
GF14.20-P-3000MM Exhaust Gas Recirculation, Function
ENGINE 276.9 in
MODEL 204.0 /2 /3 /9, 207.3 /4, 212.0 /2, 218
with engine with stratified operation
Exhaust gas recirculation function requirements - general
^ Circuit 87M ON (engine control ON)
^ Engine running
^ Engine in partial-load range
^ Vehicle in motion
Exhaust gas recirculation, general
The exhaust gas recirculation lowers the combustion temperature during enrichment of the intake air with exhaust (lean-burn operation, stratified and homogenous stratified operation), whereby the NOX development is reduced.
In this way the NOx storage catalytic converters are loaded more slowly with NOx and the lean-burn operation is enabled for longer periods.
The exhaust gas recirculation quantity can be up to 30% of the intake air and is calculated on the basis of the following sensors and signals from the ME-SFI [ME] control unit (N3/10):
- Hot film MAF sensor (B2/5), engine load
- Pressure sensor downstream of throttle valve actuator (B28/7), intake manifold air pressure
- RH and LH Hall sensors (M16/45b1, M16/45b2), positions of the exhaust gas recirculation actuator motors (M16/45)
- Intake manifold intake air temperature sensor (B17/1), intake manifold temperature
- Temperature sensor upstream of NOx storage catalytic converter on the right (B16), exhaust temperature
- Temperature sensor upstream of NOx storage catalytic converter on the left (B16/1), exhaust temperature
- Left and right oxygen sensor upstream of catalytic converter (G3/3, G3/4), residual oxygen content
- Left and right oxygen sensor downstream of catalytic converter (G3/5, G3/6), residual oxygen content
The exhaust gas recirculation valves are closed in homogeneous mode.
Function sequence for exhaust gas recirculation
The exhaust for AGR is removed downstream of both catalytic converters for the left and right bank. The exhaust flows over the AGR lines to both exhaust gas recirculation valves.
The required exhaust quantity is adjusted by the exhaust gas recirculation valve. The exhaust gas recirculation valves for both cylinder heads are brought together in one component. After the exhaust gas recirculation valves the exhaust flows together through a connecting pipe into the intake manifold. The recycled exhaust mixes with the suctioned in fresh air in the intake manifold.
Regulation of the amount of recycled exhaust is over the exhaust gas recirculation valves. To do this the right and left AGR actuator motors (M16/45m1, M16/45m2) which actuate the exhaust gas recirculation valves are actuated by the ME-SFI [ME] control unit by means of a pulse width modulated signal (PWM signal) according to the engine load. The position of the respective exhaust gas recirculation valve is detected and transmitted to the ME-SFI [ME] control unit over the Hall sensors on the right and left.
The exhaust gas recirculation valve are connected to the engine cooling circuit for cooling.
Diagnosis of the AGR system
In deceleration mode the ME-SFI [ME] control unit recognizes from the intake manifold pressure whether the exhaust gas recirculation valves are open or the EGR lines to the exhaust system are clogged.
In order to keep the exhaust gas recirculation valves securely closed the actuator motors are actuated with a duty cycle of about 15% and reverse polarity.
If the ME-SFI [ME] control unit recognizes a not closed exhaust gas recirculation valve, the engine goes into limp-home mode (vehicle maximum speed about 40 km/h).
A function test on both exhaust gas recirculation valves takes place shortly after stopping the engine. Both exhaust gas recirculation valves are opened completely and closed again to do this.
Design of the AGR
1 Exhaust removal pipe
2 Exhaust gas recirculation valve
3 Connecting pipe to intake manifold
4 Coolant connection
155 Exhaust manifold
158 Catalytic converter
M16/45m1 AGR actuator motor on the right (with Hall sensor on the right (M16/45b1)
M16/45m2 AGR actuator motor on the left (with Hall sensor on the left (M16/45b2)
