Exhaust gas recirculation, function - GF14.20-P-3000MM

ENGINE 276.9 in MODEL 204, 207, 212 (except 212.095), 218 with CODE 920 (Direct petrol injection with stratified charging) 

Exhaust gas recirculation function requirements - general 

• Circuit 87M (engine timing 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 by 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 right NOx storage catalytic converter (B16), exhaust temperature
• Temperature sensor upstream of left NOx storage catalytic converter (B16/1), exhaust temperature
• Left and right oxygen sensors upstream of catalytic converter (G3/3, G3/4), residual oxygen content
• Left and right oxygen sensors 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 reicirculation 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 recirculated exhaust mixes with the fresh air intake 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 valves 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 exhaust gas recirculation system 

Fig 1: Exhaust Gas Recirculation System Components

Courtesy of MERCEDES-BENZ USA