Exhaust gas recirculation, function

GF14.20-P-3000OGS

Exhaust gas recirculation, function

10.4.13

ENGINE

642.8 in MODEL 222

Function requirements for exhaust gas recirculation (EGR), general points

 Circuit 87M (engine timing ON)

 Engine running

 Engine in load range from neutral to the upper partial-load range

Exhaust gas recirculation, general

The EGR lowers the nitrogen oxide (NOx) portion in the exhaust. This occurs by means of the following 3 processes:

– reduction of oxygen (O2) concentration in combustion chamber

– reduction of the combustion temperature through reduction of the combustion speed

– reduction of the combustion temperature through a higher heat capacity of the recirculated exhaust compared to the intake air

 Heat capacity

The heat capacity is a material property and indicates how much heat a substance can store per temperature change.

Function sequence for exhaust gas recirculation

EGR is active from idle through to the upper partial-load range. Determination of the EGR rate takes place depending on the following variables:

– engine temperature, engine load and engine rpm

– ambient conditions such as the air intake or the charge air temperature

- exhaust temperatures

– diesel particulate filter status

– exhaust pressure

– Time limitation (in idle)

- boost pressure

- coolant temperature

For this purpose, the CDI control unit (N3/9) reads signals from the following components:

– engine oil temperature sensor (B1)

– left hot film MAF sensor (B2/6)

– Left intake air temperature sensor (B2/6b1)

- hot film mass air flow sensor (B2/7)

– Right intake air temperature sensor (B2/7b1)

– boost pressure sensor (B5/1)

– coolant temperature sensor (B11/4)

– charge air temperature sensor (B17/8)

- temperature sensor upstream of catalytic converter (B19/7)

- temperature sensor upstream of diesel particulate filter (B19/9)

– temperature sensor upstream of turbocharger (B19/11)

– pressure sensor downstream of air filter (B28/5)

- DPF differential pressure sensor (B28/8)

– accelerator pedal sensor (B37)

- throttle valve actual value potentiometer 1 (M16/6r1)

– exhaust pressure sensor (B60)

– crankshaft Hall sensor (B70)

After evaluating the input signals, the CDI control unit uses a stored characteristics map to actuate the exhaust gas recirculation actuator (Y27/9) by means of a pulse width modulated (PWM) signal. Depending on its actuation, the exhaust gas recirculation actuator increases or decreases the quantity of recirculated exhaust, which is led into the charge air manifold via a mixing tube downstream of the throttle valve actuator (M16/6).

To increase the effect of EGR, the exhaust gas is passed through the exhaust gas recirculation cooler where it is cooled.

If the temperature of the recirculated exhaust gas is too low, the recirculated exhaust gas can be guided past the exhaust gas recirculation cooler via a bypass duct.

If the exhaust gas recirculation cooler bypass switchover valve (Y85) is actuated by the CDI control unit by means of a ground signal based on a characteristics map, then the vacuum stored in the vacuum reservoir acts on the exhaust gas recirculation cooler bypass vacuum unit and opens the bypass in the exhaust gas recirculation cooler via a linkage.

 Exhaust emissions standard

Engine 642.8 complies with the EU-6 exhaust emissions standard.

	Electrical function schematic for exhaust gas recirculation		PE14.20-P-2052-97SEB
	Overview of system components for common rail diesel injection (CDI)		GF07.16-P-9997OGS