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

Engine All (Light transporter) 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 

General 

The smooth running control reduces wheel vibrations in the rpm range of 750 to 2600 rpm. In addition, the smooth running control 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.

Identifying combustion misfires 

In order to detect combustion misfires, 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

Deactivating fuel injectors (spark-ignition engine) 

When the smooth running control detects combustion misfires, the affected fuel injector is deactivated after a certain number of combustion misfires. In four-cylinder engines, a maximum of two fuel injectors are deactivated at the same time. In six-cylinder engines, a maximum of three fuel injectors are deactivated at the same time. In eight-cylinder engines, a maximum of four fuel injectors are deactivated at the same time.

Spark-ignition engine: Counting and storing combustion misfires 

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 654 in model 447.8 with code MO6 (Emissions class Euro 6d M/N1 Gr. II) with code MT6 (Emissions class Euro 6d N1 Gr.III/N2) with code XM0 (Facelift)	PE07.10-S-2502TRA
		Engine 654 in model 447.6/7 with code MO6 (Emissions class Euro 6d M/N1 Gr. II) with code MT6 (Emissions class Euro 6d N1 Gr.III/N2) with code XM0 (Facelift)	PE07.10-S-2502TRB
		Engine 654 in model 447.6/7 with code XM0 (Facelift) except code MO6 (Emissions class Euro 6d M/N1 Gr. II) except code MT6 (Emissions class Euro 6d N1 Gr.III/N2)	PE07.10-S-2502TRK
		Engine 654 in model 447.8 with code XM0 (Facelift) except code MO6 (Emissions class Euro 6d M/N1 Gr. II) except code MT6 (Emissions class Euro 6d N1 Gr.III/N2)	PE07.10-S-2502TRL
		Engine 200 in model 420	PE07.10-S-2502VRA
		Engine 608 in model 420	PE07.10-S-2502VRB
	Control units
	Combustion engine control unit, basic function		GF07.08-S-9890A