Exhaust gas recirculation, function - GF14.20-P-3000MRA
Engine 274.9 in model 205 (except 205.047/147/247) with code 920 (Direct petrol injection with stratified charging)
Engine 274.9 in model 253 (except 253.354/954) with code 920 (Direct petrol injection with stratified charging)
Exhaust gas recirculation function requirements - general
- Circuit 87M (engine management ON)
- Engine in partial-load range
- Vehicle in motion
Exhaust gas recirculation, general
The exhaust gas recirculation lowers the combustion temperature through enrichment of the intake air with exhaust in stratified operation and in combined homogenous stratified operation, whereby the nitrogen oxide (NOx ) development is reduced-production is reduced. In this way the NOx storage catalytic converter is loaded more slowly with NOx and stratified 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 by the ME-SFI [ME] control unit (N3/10):
- Exhaust gas recirculation pressure sensor 1 (B5/5), exhaust pressure in the exhaust recycling housing upstream of the exhaust gas recirculation valve
- Exhaust gas recirculation pressure sensor 2 (B5/6), exhaust pressure in the exhaust recycling housing downstream of the exhaust gas recirculation valve
- Pressure sensor downstream of throttle valve (B28/7), engine load
- Oxygen sensor sensor element downstream of catalytic converter (G3/1b1), residual oxygen content
- Oxygen sensor sensor element upstream of catalytic converter (G3/2b1), residual oxygen content
- NOx sensor (N37/4b1), nitrogen oxide and oxygen contents in exhaust via the NOx sensor control unit (N37/4) and drive train sensor CAN (CAN I)
- Exhaust gas recirculation valve Hall sensor (Y27/1b1), position of the exhaust gas recirculation valve rotary solenoid (Y27/1y1)
View of engine from the rear right
Function sequence for exhaust gas recirculation
The exhaust for the exhaust gas recirculation is taken downstream of the ATL and led via an exhaust removal pipe to the exhaust gas recirculation valve. The exhaust gas recirculation rate is controlled by the opening cross-section of the exhaust gas recirculation valve. To do this the exhaust gas recirculation valve rotary solenoid that actuates the exhaust gas recirculation valve is actuated by the ME-SFI [ME] control unit depending on a characteristics map by means of a pulse width modulated signal (PWM signal). In order to keep the exhaust gas recirculation valve securely closed, the exhaust gas recirculation valve rotary solenoid is actuated with a duty cycle of about 15 % and reverse polarity. In the deenergized state, the exhaust gas recirculation valve is held closed by a spring integrated in the rotary solenoid. The position of the exhaust gas recirculation valve rotary solenoid is recorded via the exhaust gas recirculation valve Hall sensor and transmitted to the ME-SFI [ME] control unit for control and diagnosis.
Downstream of the exhaust gas recirculation valve, the exhaust flows through an exhaust gas recirculation cooler that is connected to the cooling system of the engine and is then directed rearward in the intake air system. There the exhaust is mixed with the drawn-in fresh air. The exhaust gas recirculation valve, the exhaust gas recirculation valve rotary solenoid and the exhaust gas recirculation valve Hall sensor are combined in the exhaust gas recirculation housing. This is connected for cooling to the coolant circuit.
In homogeneous operation, the exhaust gas recirculation valve is closed.
Diagnosis of the EGR system
If the ME-SFI [ME] control unit recognizes that the exhaust gas recirculation valve does not close, the engine goes into limp-home mode. A function test for the exhaust gas recirculation valve takes place shortly before starting the engine and shortly after stopping the engine. To do this, it is opened completely and then closed again. This test serves to reduce the tolerance and to increase the positioning accuracy.
Body
| Electrical function schematic for exhaust gas recirculation | PE14.20-P-2052-97FBA | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MRA |