Rpm control, function - GF07.10-P-1008MMO

ENGINE 276.9 in MODEL 212.095 up to model year 2014 

Function requirements for RPM control, general points 

• Circuit 87M ON (engine timing ON)
• Internal combustion engine running

The function requirements "internal combustion engine running" includes all function sequences of the fuel low pressure and high-pressure circuit, as described in the function "fuel supply".

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 (B70) detects the engine speed from the signal from the crankshaft Hall sensor signal (N310).

The ME-SFI [ME] control unit reads in the following sensors and signals for RPM limitation:

• Crankshaft Hall sensor, engine speed
• Throttle valve actuator (M16/6), throttle valve position
• Fully integrated transmission control unit (Y3/8n4), gear range over drive train CAN (CAN C)
• RBS control unit (N30/6), vehicle speed via the chassis CAN (CAN E)

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 the ignition coils (T1)
• Shutoff of the fuel injectors (Y76) (with RPM limitation)
• Adaptation of the injection time of the fuel injectors (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 a defective throttle valve actuator 
• 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 on the CAN signal "wheel speed" which is transmitted by the RBS control unit via the chassis CAN.

Function sequence for maximum speed limit 

Upon reaching v = 250 km/h the opening angle of the throttle valve and the injection time 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 a defective throttle valve actuator 

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.

The ME-SFI [ME] control unit also reads in the following sensors and signals for idle speed control:

• Coolant temperature sensor (B11/4)
• Pressure sensor downstream of throttle valve (B28/7), engine load
• On-board electrical system battery at the rear (G1/11), on-board electrical system voltage (undervoltage)
• Automatic air conditioning control and operating unit (N22/7), air conditioning system status via the interior CAN (CAN B) and chassis CAN

The ME-SFI [ME] control unit regulates the idle speed through the throttle valve actuator and adapts the injection time of the fuel injectors according to variations in the 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 (C  rank A  ngle) toward "retarded" or 20° CKA toward "advanced".

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

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

• Warming-up phase 
• Undervoltage of the on-board electrical system battery at the rear 
• Purging 

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 to about 1100 to 1300 RPM for about 20 s. 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 at the rear 

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-2708-97DAI
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MMO