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

Engine 276.8 in model 213, 238 

up to model year 2021 

Function requirements for RPM control, general points 

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

The "Engine running" function requirements include all function sequences of the fuel low pressure and fuel high-pressure circuit, as described in the "Fuel supply" function.

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 the following signals:

• Crankshaft Hall sensor, engine speed
• Actual value potentiometer 1 and 2 (M16/6r1, M16/6r2), throttle valve position
• Electronic Stability Program control unit (N30/4), wheel speed via suspension FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1)
• Fully integrated transmission control unit (Y3/8n4), gear range via drive train CAN

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

• Adjustment of throttle valve opening angle by actuation of actuator motor for throttle valve (M16/6m1)
• Ignition angle setting of cylinder 1 to 6 ignition coils (T1/1 to T1/6)
• Cut out of the fuel injectors (Y76) (for RPM limitation)
• Adaptation of the injection period of the fuel injectors (for idle speed control)

Function sequence for RPM control 

Regulation of the engine speed is described in the following partial functions:

• Function sequence for RPM limitation 
• Function sequence for maximum speed limit 
• Function sequence for a defective throttle valve actuator (M16/6) 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 train CAN.

Function sequence for maximum speed limit 

Upon reaching maximum speed, the opening angle of the throttle valve and the injection period of the fuel injectors are reduced by the ME-SFI [ME] control unit. These measures ensure simple maximum speed limit through the 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 when 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 throttle valve (B28/7), engine load
• On-board electrical system battery (G1), on-board electrical system voltage (undervoltage)
• Climate 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 train CAN

The ME-SFI [ME] control unit controls the idle speed via the throttle valve actuator 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 36° CKA (Crank Angle) toward "retarded" or 20° CKA toward "advanced".

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

Warming-up phase 

In the warm-up phase, the ME-SFI [ME] control unit controls the idle speed according to the coolant temperature in order to bring the catalytic converters (three-way catalytic converters) up to operating temperature more quickly 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.

Purging 

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

Diagnosis

The basic setting of the idle speed can be read out and influenced using the Xentry Diagnostics.

	Electrical function schematic for RPM control		PE07.10-P-2708-97DBF
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MND