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

Engine 176.9, 177.9 in model 463 

as of model year 2019 

Function requirements for rpm control, general points 

• Circuit 87M (Engine management ON)
• Engine runs

The circuit relay 87M (K40/8kN) is switched on for circuit 15 ON.

Rpm control, general 

Rpm control stabilizes the idle speed and limits the motor speed to protect the engine, the Drivetrain and the vehicle. The ME-SFI [ME] control unit (N3/10) detects the engine speed via the crankshaft Hall sensor (B70) signal.

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

• Crankshaft Hall sensor, engine speed
• Left and right actual value potentiometer 1 and 2 (M16/60r1, M16/60r2, M16/61r1, M16/61r2), throttle valve position
• Electronic Stability Program control unit (N30/4), vehicle speed via suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1)
• Fully integrated transmission control unit (Y3/8n4), gear range via drive CAN

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

• Adjustment of throttle valve opening angle by actuation of left and right throttle valve actuator motor (M16/60m1, M16/61m1)
• Ignition angle setting of ignition coils for cylinders 1 + 2 to cylinders 7 + 8 (T4 to T4/3)
• Cutout of fuel injectors for cylinder 1 to 8 (Y76/1 to Y76/8) (for speed control)
• Adaptation of injection period for the cylinder 1 to 8 fuel injectors (for idle speed control)

Function sequence for rpm control 

The rpm control function includes the following subfunctions:

• Function sequence for rpm limitation 
• Function sequence for maximum speed limit 
• Function sequence for throttle valve actuator defective 
• Function sequence for idle speed control 
• 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 to approx. 6800 rpm.

The ME-SFI [ME] control unit detects the driving mode using the CAN "wheel speed" signal, which is sent by the Electronic Stability Program control unit over the chassis FlexRay, powertrain control unit and drive CAN.

Function sequence for maximum speed limit 

Upon reaching maximum speed dependent on the model, the opening angle of the throttle valve and the injection period of the cylinder 1 to 8 fuel injectors are reduced by the ME-SFI [ME] control unit. Based on these measures, the maximum design speed is limited by reduction of the engine torque.

Function sequence for throttle valve actuator defective 

In the event of a defective throttle valve actuator, the maximum engine speed is limited in idle to approx. 1400 rpm and in driving mode to approx. 1800 rpm.

Function sequence for idle speed control 

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

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

• Coolant temperature sensor (B11/4), coolant temperature
• Pressure sensor downstream of left throttle valve (B28/22) and pressure sensor downstream of right throttle valve (B28/23), engine load
• On-board electrical system battery (G1), on-board electrical system voltage over "circuit 30" (undervoltage)
• Status of air conditioning

  Climate control, control unit (N22/1), air conditioning system status via interior CAN (CAN B), electronic ignition lock control unit (N73), chassis FlexRay, powertrain control unit and drive CAN

The ME-SFI [ME] control unit controls the idle speed via the throttle valve actuators and adapts the injection period of the fuel injectors in accordance with the modified air mass. To assist with idle speed control, the ME-SFI [ME] control unit can adjust the ignition angle of the ignition coils as far as a 36°CKA (Crank Angle) toward "retard" or a 20° CKA toward "advance".

Intervention by means of the ignition angle setting reacts more quickly than intervention by means of adjustment of the throttle valves.

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

• Warming-up phase
• Undervoltage of the on-board electrical system battery
• Purge control

Warming-up phase:

In the warm-up phase, the ME-SFI [ME] control unit controls the idle speed dependent on the coolant temperature, in order to bring the catalytic converters 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

The ME-SFI [ME] control unit raises the idle speed for about 20 s to about 1100 to 1300 rpm. After this time has elapsed, the idle speed is increased at a coolant temperature of < 70 °C for about 50 s by the ME-SFI [ME] control unit by about 50 to 100 rpm.

Undervoltage of the on-board electrical system battery:

If the ME-SFI [ME] control unit detects an undervoltage through circuit 30, the idle speed is raised by about 100 rpm when gear range "D" or "R" is engaged, until the ignition is switched off.

Purge control:

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

The basic setting of the idle speed can be read out over the diagnostic device and influenced.

	Electrical function schematic for rpm control		PE07.10-P-2708-97ZGF
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