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Smooth Running Control, Function - GF07.10-P-1011MRH

Engine 274.9 in model 205.047/053/054/147/247/253 

Engine 274.9 in model 253.353/953 

Engine 274.9 in model 253.354/954 

Function requirements for smooth running control, general points 

Smooth running control, general points 

Engine running is constantly monitored in order to protect the catalytic converter from thermal overload if combustion misfiring occurs.

For smooth running control, the ME-SFI [ME] control unit (N3/10) reads in the following signals:

Function sequence for smooth running control 

The function sequence is described in the following steps:

Function sequence for combustion misfire detection 

For the smooth running control, the signal from the crankshaft Hall sensor is evaluated using a comprehensive mathematical procedure, to check for precise uniformity of timing between individual combustions. Each individual combustion must produce a characteristic acceleration at the multiple wheel which is located on the crankshaft. If there are combustion misfires, the multiple wheel turns slightly more slowly until the next ignition (due to torque fluctuation).

If the smooth running control in the ME-SFI [ME] control unit detects combustion misfiring, the corresponding fuel injector (Y76/1 to Y76/4) is no longer actuated after a certain number of combustion misfires.

However at least two fuel injectors are deactivated simultaneously.

Function sequence for misfire counter 

The total number of combustion misfires detected is stored in the fault memory and subdivided into:

Smooth running signal 

G12816687Courtesy of MERCEDES-BENZ USA

What is detected is combustion misfiring caused by:

Function sequence for factors for smooth running control 

The following factors affect smooth running control:

Engine speed and Engine load 

Using the Engine speed and Engine load, the ME-SFI [ME] control unit computes a reference value for the time between two combustions.

Coolant temperature 

For a cold Engine more combustion misfires are permissible than for an Engine at operating temperature.

Recognition of road bumps 

Vibrations transmitted through the drivetrain may have a negative effect on evaluation of the Engine running at certain Engine speeds and load conditions. Therefore, the tolerance range for smooth running control is increased on poor road surfaces. The wheel speed signal (for uniform wheel arch detection) is received by the ME-SFI [ME] control unit over the drive train CAN, powertrain control unit and chassis FlexRay from the Electronic Stability Program control unit.

Synchronization of injection and firing order 

Cylinder identification is required for fault storage and evaluation using the signals from the crankshaft Hall sensor and intake camshaft Hall sensor or exhaust camshaft Hall sensor.

Sensor adaptation 

The tolerance range for smooth running control is reduced after successful adaptation of the crankshaft Hall sensor. In this way, the smooth running control can be adapted to the specific smooth running characteristics of the Engine. The ME-SFI [ME] control unit saves the smooth operation characteristics of the Engine during a deceleration phase (accelerator pedal not operated) when uniform smooth operation is present. These are required as a comparison parameter for misfire detection.

  Electrical function schematic for smooth running control   PE07.10-P-2711-97FBH
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