Smooth Running Control, Basic Function - GF07.10-P-1048A

Engine All (4xWD) 

Engine All (CAR) 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 
  • Smooth running control 
  • Detecting combustion misfiring 
  • Switching off injection valves (spark-ignition engine) 
  • Counting and storing combustion misfires (spark-ignition engine) 
  • Adjusting the fuel injection quantity (diesel engines  )
  • Engine speed and engine load 
  • Coolant temperature 
  • Road bumps 
  • Synchronization of injection and firing order 
  • Engine smooth running characteristics 

General 

The smooth running control reduces any rough running in the rpm range from 750 to 2600 rpm. It also protects the catalytic converter from overheating.

Function requirements 

• Engine management ON (circuit 87M)
• Engine in operation

Function 

Smooth running control 

In the event of combustion misfiring, unburnt fuel can find its way into the catalytic converter. When this fuel ignites in the catalytic converter, the catalytic converter may be damaged by thermal overload. In order to prevent unburnt fuel from getting into the catalytic converter, the smooth running control detects combustion misfiring and intervenes in the engine running.

Detecting combustion misfiring 

In order to detect combustion misfiring, the combustion engine control unit evaluates the engine speed signal from the crankshaft Hall sensor.

Each combustion produces an acceleration at the multipole wheel on the crankshaft. If a combustion misfires, the multipole wheel turns measurably more slowly until the next combustion. The engine torque fluctuates.

Signal path for smooth running 

Courtesy of MERCEDES-BENZ USA

The following causes of combustion misfiring are detected:

• Faulty ignition system
• Faulty fuel injection system
• Mechanical engine components (for example, valve seats, valve springs, unmetered air)
• Fuel deficiency

Switching off injection valves (spark-ignition engine) 

If the smooth running control detects combustion misfires, the affected injection valve is switched off after a certain number of combustion misfires. In four-cylinder engines, a maximum of two injection valves are switched off simultaneously. In six-cylinder engines, a maximum of three injection valves are switched off simultaneously. In eight-cylinder engines, a maximum of four injection valves are switched off simultaneously.

Counting and storing combustion misfires (spar k-ignition engine) 

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

Adjusting the fuel injection quantity (diesel engines) 

When the smooth running control detects combustion misfires, the combustion engine control unit adjusts the fuel injection quantity. To this end, the combustion engine control unit adjusts the following parameters:

• The fuel pressure in the fuel distributor is regulated via the pressure regulating valve and the quantity control valve.
• The injection duration is regulated via the actuation duration of the fuel injectors.

Influencing factors for smooth running control 

The following factors affect smooth running control:

• Engine speed and engine load
• Coolant temperature
• Road bumps
• Synchronization of injection and firing order
• Engine smooth running characteristics

Engine speed and engine load 

Using the engine speed and engine load, the combustion engine control unit calculates a reference value for the time between two power strokes.

Coolant temperature 

The smooth running control permits more combustion misfires for a cold engine than for an engine at operating temperature.

Road bumps 

Vibration influences on the drivetrain may have a negative effect on the evaluation of the engine running at certain engine speeds and load conditions. Therefore, the tolerance range for the smooth running control is increased on poor road surfaces.

In order to detect road bumps, the combustion engine control unit evaluates the wheel speed signal.

Synchronization of injection and firing order 

The cylinder recognition is required for the storage and assessment of faults. The cylinder recognition evaluates the signals from the Hall sensors of the crankshaft and the intake and exhaust camshafts. Using these signals, the cylinder recognition can determine the stroke sequence of the individual cylinders.

Engine smooth running characteristics 

When the vehicle is in overrun mode and the engine is operating in a uniform, smooth manner, the combustion engine control unit stores the smooth running characteristics of the engine as reference values. The combustion engine control unit uses these reference values to detect combustion misfiring.

Once the reference value has been successfully stored, the tolerance range of the smooth running control is downsized. In this way, the smooth running control is adapted to the specific smooth running characteristics of the engine.

	Function schematics
	Function schematic for smooth running control	Engine 608 in model 118, 177, 247 Engine 654 in model 213, 238, 257 as of model year 2021 Engine 654, 656 in model 167	PE07.10-P-2502-97A
		Engine 282 in model 118, 177, 247	PE07.10-P-2502-97B
		Engine 256 in model 213, 238 as of model year 2021 Engine 260 in model 118, 177, 247 Engine 264 in model 167 Engine 264 in model 213, 238, 257 as of model year 2021	PE07.10-P-2502-97C
		Engine 139 in model 192, 206, 232	PE07.10-P-2502-97D
		Engine 176, 177 in model 167 Engine 177 in model 290 as of model year 2021	PE07.10-P-2502-97E
		Engine 139 in model 118, 177, 247	PE07.10-P-2502-97F
		Engine 254 in model 206, 214, 254 Engine 256 in model 223	PE07.10-P-2502-97G
		Engine 176 in model 223	PE07.10-P-2502-97H
		Engine 279 in model 223	PE07.10-P-2502-97I
		Engine 274 in model 213 as of model year 2021	PE07.10-P-2502-97J
		Engine 654 in model 206, 214, 254 Engine 656 in model 223	PE07.10-P-2502-97K
		Engine 177 in model 223, 232	PE07.10-P-2502-97L
		Engine 656 in model 464	PE07.10-P-2502-97M
	Additional basic functions
	Combustion engine control unit, basic function		GF07.08-P-9890A