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

Engine 264.9 in Model 205, 253 

Function requirements, general 

• Engine runs

The ME-SFI [ME] control unit (N3/10) detects the Engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

Smooth running control, general points 

Smooth running control ensures that the Engine is also smooth in fuel saving lean-burn operation in partial-load range and turns evenly. In this way the tangible rough running should be avoided for the driver.

Also the CATs are protected from thermal overloading if there are combustion misfires.

The ME-SFI [ME] control unit reads in the following signals for smooth running control:

• Intake camshaft position

  Intake camshaft Hall sensor (B6/15)

• Exhaust camshaft position

  Exhaust camshaft Hall sensor (B6/16)

• Coolant temperature

  Coolant temperature sensor (B11/4)

• Engine load

  Pressure and temperature sensor downstream of throttle valve (B28/27)

• Engine speed

  Crankshaft Hall sensor

The ME-SFI [ME] control unit also takes the vehicle speed into account. The ME-SFI [ME] control unit calculates the vehicle speed from the wheel speeds. The Electronic Stability Program control unit (N30/4) transmits the wheel speeds via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit.

The ME-SFI [ME] control unit evaluates the input signals and actuates the following components:

• Fuel system
  • Cylinder 1 fuel injector (Y76/1)
  • Cylinder 2 fuel injector (Y76/2)
  • Cylinder 3 fuel injector (Y76/3)
  • Cylinder 4 fuel injector (Y76/4)
• Ignition system
  • Cylinder 1 ignition coil (T1/1)
  • Cylinder 2 ignition coil (T1/2)
  • Cylinder 3 ignition coil (T1/3)
  • Cylinder 4 ignition coil (T1/4)

The following factors affect smooth running control:

• Engine speed and Engine load 
• Coolant temperature 
• Vibration transmitted via the drivetrain 
• Synchronization of injection and firing order 
• Sensor adaptation 
• Combustion misfires 

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.

Vibration transmitted via the drivetrain 

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 is drawn on here for the detection of smooth wheel running.

Synchronization of injection and firing order 

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

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 mode (accelerator pedal not operated) when uniform smooth operation is present. These are required as a comparison parameter for misfire detection.

Combustion misfires 

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 generate a characteristic acceleration at the sensor rotor.

If there are combustion misfires, the sensor rotor turns up to the next ignition somewhat slower (torque fluctuation).

If the smooth running control in the ME-SFI [ME] control unit detects combustion failures, the injection of the relevant cylinder is deactivated after a certain number of misfires. However, max. two cylinders are deactivated simultaneously.

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

• "cylinder-specific" combustion misfires
• "emission limit" combustion misfires
• "catalytic converter damaging" combustion misfires

What is detected is combustion misfiring caused by:

• Ignition system
• Fuel injection system
• Mechanical Engine components (for example, valve seats, valve springs, unmetered air)
• Fuel deficiency

Smooth running signal 

Courtesy of MERCEDES-BENZ USA

	Electrical function schematic for smooth running control		PE07.10-P-2711-97FBI
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRS