RPM Control, Function - GF07.10-P-1008KJ

ENGINE 281.910 in MODEL 453.0/3/4 

Function requirements for rpm control, general points 

• Circuit 87 (Engine management ON)
• Engine runs

Rpm control, general 

Rpm control stabilizes the idle speed and limits the motor speed to protect the engine, the drivetrain and the overall vehicle. The ME-SFI [ME] control unit (N3/10) detects the engine speed via the crankshaft position sensor (L5) signal.

For rpm limitation, the ME-SFI [ME] control unit reads in the following signals:

• Crankshaft position sensor, engine speed
• Actual value potentiometer 1 (M16/6r1) and actual value potentiometer 2 (M16/6r2), throttle valve position
• DKG control unit (N15/13) (for code 429 (twinamic)), gear range via drive train CAN (CAN C)
• Electronic Stability Program control unit (N30/4) wheel speed via the interior CAN (CAN B)

The ME-SFI [ME] control unit limits the engine speed by the following measures:

• Adjusting the opening angle of the throttle valve
• Adjusting the ignition angle of cylinder 1 ignition coil (T1/1) to cylinder 3 ignition coil (T1/3)
• Switching off of the cylinder 1 injection valve (Y62/1) to cylinder 3 injection valve (Y62/3) (for rpm limitation)
• Adaptation of the injection period of cylinder 1 injection valve to cylinder 3 injection valve (for idle speed control)

Function sequence for rpm control 

Regulation of the engine speed is described in the following points:

• Function sequence for rpm limitation 
• Function sequence for maximum speed limit 
• Function sequence for idle speed control 
• Function sequence for throttle valve actuator defective 

Function sequence for rpm limitation 

In order to protect the engine from the consequences of impermissibly high engine revs, the maximum engine speed is limited.

The ME-SFI [ME] control unit detects the driving mode based on the "wheel speed" CAN signal, which is sent from the Electronic Stability Program control unit via the interior CAN.

Function sequence for maximum speed limit 

To achieve the model-dependent maximum speed, the opening angle of the throttle valve and the injection period of the cylinder 1 injection valve to cylinder 3 injection valve is lowered by the ME-SFI [ME] control unit.

These measures ensure simple maximum speed limit through the reduction of the engine torque.

Function sequence for idle speed control 

The idle speed control regulates and stabilizes the idle speed depending on operating conditions and engine loads when the accelerator pedal is not actuated.

For idle speed control, the ME-SFI [ME] control unit also reads in signals from the following sensors:

• Coolant temperature sensor (B11/4)
• Pressure sensor downstream of throttle valve (B28/7), engine load
• On-board electrical system battery (G1), on-board electrical system voltage (undervoltage)
• Clutch pedal switch (S40/3) (for code 410 (5-speed manual transmission)) via middle SAM control unit (N10/10) and interior CAN
• Climate control control unit (N22/1) (for code I01 (AAC Plus), status of A/C via interior CAN, middle SAM control unit, interior CAN to ME-SFI [ME] control unit

The idle speed control is primarily influenced by the following parameters:

• Achieving the operating condition of the catalytic converter
• Electrical consumer (e.g. PTC heater (R22/3) and fan motor (M4/7))
• Climate control control unit load request (for code I01 (AAC))

The ME-SFI [ME] control unit regulates the idle speed over the throttle valve actuator (M16/6) and appropriately adapts the altered air mass to the injection period of cylinder 1 injection valve to cylinder 3 injection valve. To assist the idle speed control, the ME-SFI [ME] control unit can shift the ignition angles of the ignition coils towards "retard" by up to 36° CKA (crankshaft angle), or towards "advance" by 20° crank angle.

The ignition angle initiates a faster response through the ignition angle setting than the throttle valve adjustment.

The ME-SFI [ME] control unit regulates the idle speed in the following operating conditions and engine load conditions:

• Warming-up phase 
• Engagement of gear range "D" or "R" (for code 429 (twinamic)) 
• Actuation of the clutch pedal (for code 410 (5-speed manual transmission)) 
• Switching in the A/C compressor (A9) 
• Undervoltage of the on-board electrical system battery 
• Purging 

Warming-up phase 

In the warm-up phase, the ME-SFI [ME] control unit controls the idle speed according to coolant temperature, in order to bring the catalytic converter more quickly up to operating temperature after engine start.

Additional function requirements in the warm-up phase are:

• Coolant temperature < 40°C
• Gear range "N" or "P" engaged (for code 429 (twinamic))

The ME-SFI [ME] control unit raises the idle speed for a short time.

Engagement of gear range "D" or "R" (for code 429 (twinamic)) 

When gear range "D" or "R" is selected, the idle speed is set to a lower value to reduce the tendency of the vehicle to creep forward. To do this, the ME-SFI control unit evaluates the "gear range engaged" CAN signal from the DKG control unit.

Actuation of the clutch pedal (for code 410 (5-speed manual transmission)) 

When actuating the clutch pedal the idle speed is stabilized. Clutch pedal actuation is detected by the ME-SFI [ME] control unit through the clutch pedal switch.

Switching in the A/C compressor 

To ensure that, when in neutral, the engine rpm does not drop off when the A/C compressor is switched on, the A/C control unit (for code I01 (AAC)) sends a status signal to the ME-SFI [ME] control unit before switch on. The ME-SFI [ME] control unit adapts the idle speed appropriately.

Undervoltage of the on-board electrical system battery 

If the ME-SFI [ME] control unit recognizes an undervoltage at "circuit 30", the idle speed is increased slightly up to switching off of the ignition.

Purging 

The idle speed control prevents any change in the engine speed due to purging.

Function sequence for throttle valve actuator defective 

For a defective throttle valve actuator the maximum engine speed is limited in neutral and in driving mode.

	Electrical function schematic for rpm control		PE07.10-P-2708-97BBA
	Overview of system components motor electronics (ME-SFI) fuel injection and ignition system		GF07.61-P-9997KJ