Exhaust Gas Recirculation, Function - GF14.20-P-3000MRD

Engine 274.9 in model 213 (except 213.050/053/153), 238 

up to model year 2021 

with code 920 (Direct petrol injection with stratified charging) 

Function requirements, general 

• Engine in partial-load range

Exhaust gas recirculation, general 

The exhaust gas recirculation lowers the combustion temperature in stratified charge operation and in combined homogeneous stratified operation by enriching the intake air with exhaust gas, whereby the nitrogen oxide (NO_x ) development is reduced. In this way the NO_x storage catalytic converter is loaded more slowly with NO x 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 pressure upstream of exhaust gas recirculation valve (Y27/1)

  Exhaust gas recirculation pressure sensor 1 (B5/5)

• Exhaust gas pressure downstream of exhaust gas recirculation valve

  Exhaust gas recirculation pressure sensor 2 (B5/6)

• Exhaust-gas temperature

  Temperature sensor upstream of NOx storage catalytic converter (B16)

• Charge air temperature

  Charge air temperature sensor upstream of throttle valve (B17/7)

  Charge air temperature sensor downstream of throttle valve (B17/9)

• Engine load

  Pressure sensor downstream of throttle valve (B28/7)

• Residual oxygen content

  Oxygen sensor, sensor element downstream of catalytic converter (G3/1b1)

  Oxygen sensor, sensor element upstream of catalytic converter (G3/2b1)

• Nitrogen oxide and oxygen content in exhaust gas

  The NOx sensor control unit (N37/4) directly reads in the NOx sensor (N37/4b1) and transmits the information via the drive train sensor CAN (CAN I) to the ME-SFI [ME] control unit

• Position of exhaust gas recirculation valve (Y27/1)

  The ME-SFI [ME] control unit directly reads in the position of the exhaust gas recirculation valve rotary solenoid (Y27/1y1) via the exhaust gas recirculation valve Hall sensor (Y27/1b1)

The exhaust gas recirculation is divided into the following subfunctions:

• Exhaust gas recirculation 
• EGR diagnosis 

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 left exhaust gas recirculation valve securely closed, the exhaust gas recirculation valve moving magnet is actuated with a duty cycle of approximately 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.

EGR diagnosis 

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.

Design of exhaust gas recirculation 

Courtesy of MERCEDES-BENZ USA

	Electrical function schematic for exhaust gas recirculation		PE14.20-P-2052-97DBD
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRD