Exhaust Gas RECIRCULATION, Function - GF14.20-D-3000TSC
Engine 642.8 in model 907
Block diagram
Function requirements for exhaust gas recirculation (EGR), general points
- Circuit 87M (Engine management ON)
- Engine running.
- Engine in load range from idle to the upper partial-load range
Exhaust gas recirculation, general
The EGR lowers the nitrogen oxide (NOx) portion in the exhaust. This takes place via the following 3 processes:
- Reduction of oxygen (O 2) 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
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
The EGR is active from neutral through to the upper partial-load range.
Determination of the exhaust gas recirculation 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 temperature
- Diesel particulate filter status
- Exhaust pressure
- Time limitation (in idle)
- Boost pressure
- Coolant temperature
To do so, the CDI control unit (N3/28) reads signals from the following component parts:
- Engine oil sensor (B40/8)
- Hot film mass air flow sensor (B2/14)
- Boost pressure sensor (B5/8)
- Coolant temperature sensor (B11/19)
- Charge air temperature sensor (B17/15)
- Temperature sensor upstream of catalytic converter (B19/18)
- Temperature sensor upstream of diesel particulate filter (B19/19)
- Exhaust gas recirculation cooler temperature sensor (B19/21)
- Temperature sensor upstream of ATL (B16/11)
- DPF differential pressure sensor (B28/16)
- Accelerator pedal module (A68)
- Exhaust back pressure sensor (B60/4)
- From crankshaft position sensor (B70/1)
After evaluating the input signals, the CDI control unit uses the stored characteristics map to actuate the exhaust gas recirculation positioner (Y27/17) using a pulse width modulated signal. The exhaust gas recirculation positioner (Y27/17) increases or decreases, depending on its actuation, the quantity of recirculated exhaust gas, which is directed into the charge air distributor via a mixing tube downstream of the throttle valve actuator (M16/48).
To increase the effect of EGR, the exhaust gas is led to 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 electronic vacuum regulator bypass flap (Y85/4) 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.
The exhaust gas temperature determined by the exhaust gas recirculation cooler temperature sensor is used by the CDI control unit to monitor the cooling function of the exhaust gas recirculation cooler.
| Electrical function schematic for exhaust gas recirculation | PE14.20-D-2052-97TSC |
| Overview of system components for common rail diesel injection (CDI) | GF07.16-D-9997TSC |