RPM Control, Function - GF07.10-S-1008TRJ

Engine 274 in model 447.6/7 

with code XM0 (Facelift) 

Function requirements for rpm control, general points 

• Circuit 87M ON (Engine management ON)
• Engine running.

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 (N3/34) detects the engine speed via the crankshaft Hall sensor (B702) signal.

The ME-SFI [ME] control unit (N3/34) reads in signals for rpm limitation from the following assembly parts:

• Crankshaft Hall sensor (B70/2)
• Actual value potentiometer 1 (M16/50r1) and actual value potentiometer 2 (M16/50r2)
• Fully integrated transmission control (VGS) electric controller unit (N15/11) (Automatic transmission with code G42 (7G-TRONIC PLUS))
• Fully integrated transmission control (VGS) electric controller unit (N15/15) (Automatic transmission with code G43 (9G-TRONIC))
• Electronic Stability Program (ESP) control unit (N30/4) for wheel speed

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

• Changing of the opening angle of the throttle valve.
• Changing the ignition angles of the ignition coils (T1).
• Switching off the fuel injectors (Y62) (in case of rpm limitation).
• Adaptation of injection duration.

Function sequence for rpm control 

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

• Function sequence for torque converter protection (with automatic transmission)
• Function sequence for manual transmission protection (with a manual transmission)
• Function sequence for rpm limitation
• Function sequence for maximum speed limit
• Function sequence for throttle valve actuator defective
• Function sequence for missing variant coding
• Function sequence for idle speed control

Function sequence for torque converter protection (with automatic transmission) 

To protect the torque converter in selector lever position "P" and "N" (no power transmission) against increased static internal pressure, the maximum engine speed is limited to approx. 4600 rpm. The ME-SFI [ME] control unit (N3/34) receives the information on the current selector lever position from the fully integrated transmission control (VGS) electric controller unit.

Function sequence for manual transmission protection (with a manual transmission) 

To prevent damage to the manual transmission, the maximum engine speed is limited during vehicle stillstand to approx. 4000 rpm.

Function sequence for rpm limitation 

To protect the engine during vehicle operation against the consequences of an impermissibly high engine speed, the maximum engine speed is limited to approx. 6000 rpm.

The operating status is detected by the ME-SFI [ME] control unit via the CAN signal "wheel speed" that is transmitted from the Electronic Stability Program control unit (ESP) (N30/4).

Function sequence for maximum speed limit 

Once the maximum permissible speed is reached, the ME-SFI [ME] control unit reduces the opening angle of the throttle valve and the injection duration of the fuel injectors (Y62). These measures maximum speed limit limitation occurs through reduction of the engine torque.

Function sequence for throttle valve actuator defective 

In the case of a defective throttle valve actuator (M16/50), the maximum engine speed is limited in idle to approx. 1400 rpm and during vehicle operation to approx. 1800 rpm.

Function sequence for missing variant coding 

If no variant coding exists, the maximum engine speed is limited to approx. 2400 rpm.

Function sequence for idle speed control 

The idle speed control regulates and stabilizes the idle speed depending on operating conditions.

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

• Coolant temperature sensor (B11/21)
• Intake manifold pressure sensor (B28/24)
• Clutch pedal switch (S40/3) and clutch pedal switch (S40/6) (with manual transmission)
• Automatic air conditioning control and operating unit (KLA-V & KLA-H) (S98) (with code HH4 (THERMOTRONIC automatic air conditioning)) and (with code HH9 (Semi-automatic regulated A/C, TEMPMATIC))

The ME-SFI [ME] control unit regulates the idle speed via the throttle valve actuator (M16/50) and adapts the injection duration of the fuel injectors (Y62) according to the changed air mass. To support the idle speed control, the ME-SFI [ME] control unit can change the ignition angles of the ignition coils (T1) by an up to 36° CKA (crank angle) towards "retarded" or 20° CKA towards "advance".

An ignition angle setting intervention reacts faster than any adjustment of the opening angle of the throttle valve.

Diagnosis

The basic setting of the idle speed can be read out and influenced using XENTRY Diagnosis.

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

• Warming-up phase
• Engagement of the gear range "D" or "R" (with an automatic transmission)
• Actuation of the clutch pedal (with a manual transmission)
• Switching in the A/C compressor
• Undervoltage of the on-board electrical system battery
• Purge control

Warming-up phase 

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

Additional function requirements for this are:

• Coolant temperature < 40°C
• Drive range "N" or "P" engaged (with automatic transmission)

The ME-SFI [ME] control unit increases the idle speed for approx. 20 s to approx. 1100 up to 1300 rpm. After this time has expired, the idle speed will be increased for a coolant temperature < 70°C for approx. 50 s by approx. 50 up to 100 rpm.

Engagement of the gear range "D" or "R" (with an automatic transmission) 

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 [ME] control unit evaluates the "gear range engaged" CAN signal via the fully integrated transmission control electric controller unit.

Actuation of the clutch pedal (with a manual transmission) 

When actuating the clutch pedal the idle speed is stabilized. The actuation of the clutch pedal is detected by the ME-SFI [ME] control unit by the clutch pedal switch (S40/3) and clutch pedal switch (S40/6) via a direct line.

Switching in the A/C compressor 

Vehicles with code HH4 (THERMOTRONIC automatic climate control) or with code HH9 (Semi-automatically controlled air conditioning, TEMPMATIC)

So that the engine speed does not decrease in idle when the refrigerant compressor with magnetic clutch (A9/10) switches in, the air conditioning system control and operating unit (AAC-V & AAC-H) (S98) outputs a status signal to the ME-SFI [ME] control unit before switch-in. 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 detects an undervoltage of the on-board electrical system battery (G1) via circuit 30, the idle speed will be increased up to the deactivation of the ignition by approx. 100 rpm for an engaged drive range "D" or "R".

Purge control 

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

	Function schematic for rpm control		PE07.10-S-2500-97TRN
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-S-9998TRJ