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

ENGINE 642.8 in MODEL 166 as of model year 2016 

ENGINE 642.8 in MODEL 292 

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

• Circuit 87M (engine management ON)
• Engine runs
• 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 temperature
  • 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 mass air flow sensor (B2/6)
  • Left intake air temperature sensor (B2/6b1)
  • Right 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)
  • Exhaust gas recirculation temperature sensor (B16/14) (with CODE U77 (BLUETEC (SCR) diesel exhaust treatment) and CODE 494 (USA version))
  • 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 ATL (B19/11)
  • Pressure sensor downstream of air filter (B28/11)
  • DPF differential pressure sensor (B28/8)
  • Accelerator pedal sensor (B37)
  • Throttle valve actuator (M16/6)
  • Exhaust pressure sensor (B60)
  • Crankshaft Hall sensor (B70)
  • Exhaust gas recirculation cooling bypass flap Hall sensor (B90) (with CODE U77 (BLUETEC (SCR) diesel exhaust treatment) and CODE 494 (USA version))

After evaluating the input signals, the CDI control unit uses the stored characteristics map to actuate the exhaust gas recirculation actuator (Y27/9) with a pulse width modulated signal. The exhaust gas recirculation actuator increases or decreases, depending on its actuation, the quantity of recirculated exhaust which is directed 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. The exhaust temperature determined by the exhaust gas recirculation temperature sensor is used by the CDI control unit to monitor the cooling function of the exhaust gas recirculation cooler.

For vehicles with code 494 (USA version) the position of the bypass flap (open, closed) is determined via the exhaust gas recirculation cooling bypass flap Hall sensor.

Exhaust emissions standard

Engine 642.8 complies with the EU-5 exhaust emissions standard.

Vehicles with CODE U77 (BLUETEC (SCR) diesel exhaust treatment) fulfill the EU-6 exhaust emissions standard or the BIN5 LEVII exhaust emissions standard for USA.

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