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

Engine 274 in model 447, 448 

except code XM0 (Facelift) 

Function requirements for rpm control, general points 

• Circuit 87M ON (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 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), engine rpm over direct line
• Actual value potentiometer 1 (M16/50r1) and actual value potentiometer 2 (M16/50r2), throttle valve position over direct line
• Fully integrated transmission control electric controller unit (VGS) (N1511), (with automatic transmission) gear range via the drive train CAN (CAN C)
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN (CAN E)

The ME-SFI [ME] control unit (N3/34) limits the engine speed by the following measures:

• Changing the opening angle of the throttle valve
• Changing the ignition angles of the ignition coils (T1)
• Cut out of the fuel injectors (Y62) (for rpm limitation)
• Adaptation of the injection period

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 

Torque converter protection function sequence (for automatic transmission) 

To protect the torque converter in selector lever positions "P" or "N" (no power flow) from excessive static internal pressure, the maximum engine speed is limited to approx. 4600 rpm. The ME-SFI [ME] control unit (N3/34) receives information about the current selector lever position from the fully integrated transmission control electric controller unit (N15/11) via the drive train CAN (CAN C).

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

To prevent damage to the manual transmission, the maximum engine speed is limited to about 4000 rpm when the vehicle is stationary.

Function sequence for rpm limitation 

In order to protect the engine from inadmissible engine speeds during driving mode, the maximum engine speed is limited to about 6000 rpm.

Driving operation is recognized by the ME-SFI [ME] control unit (N334) based on the CAN signal "wheel speed" which is transmitted by the Electronic Stability Program (ESP) control unit (N30/4) via the chassis CAN (CAN E).

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 (N3) are reduced by the ME-SFI [ME] control unit (Y62/34). These measures maximum speed limit limitation occurs through reduction of the engine torque.

Function sequence for a throttle valve actuator (M16/50) which is defective 

In the case of a defective throttle valve actuator (M16/50) the maximum engine speed is limited in neutral to about 1400 rpm and when driving to about 1800 rpm.

Function sequence for missing variant coding 

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

Function sequence for idle speed control 

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

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

• 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 (N3/34) controls the idle speed over the throttle valve actuator (M16/50) and appropriately adapts the injection period of the fuel injectors (Y62) to the altered air mass. To assist the idle speed control, the MESFI [ME] control unit (N3/34) can shift the ignition angles of the ignition coils (T1) towards "retard" by up to a 36° crank angle (CKA, or towards "advance" by up to a 20° crank angle (CKA).

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 the

Xentry Diagnostics.

The ME-SFI [ME] control unit (N3/34) regulates the idle speed under the following operating 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) 
• Switch-in of the A/C compressor (HH4/3) (with codeA9THERMOTRONIC automatic air conditioning), or with CODE HH9 (TEMPMATIC semi-automatically controlled air conditioning) 
• On-board electrical system battery undervoltage (G1) 
• Purging 

Warming-up phase 

In the warm-up phase, the ME-SFI [ME] control unit (N3/34) 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 for this are:

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

The ME-SFI [ME] control unit (N3/34) raises the idle speed up 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 in line with the temperature for approx. 50 seconds by approx. 50 to 100 rpm.

Engagement of the gear range "D" or "R" (for 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 (N3/34) evaluates the CAN signal "engaged gear range" over the fully integrated transmission control electric controller unit (VGS) (N15/11) and via the drive train CAN (CAN C).

Actuation of the clutch pedal (for a manual transmission) 

When actuating the clutch pedal the idle speed is stabilized. Actuation of the clutch pedal is detected by the ME-SFI [ME] control unit (N3/34) by the clutch pedal switch (S40/3) and the clutch pedal switch (S40/6) over a direct line.

Switch-in of the A/C compressor (HH4/3) (with code A9THERMOTRONICautomatic air conditioning), or with CODE HH9 (TEMPMATIC semi-automatically controlled air conditioning) 

In this way the engine rpm does not drop upon switch-in of the A/C compressor (A9/3) in idle and the A/C control and operating unit (KLA-V & KLA-H) (S98) sends a status signal to the ME-SFI [ME] control unit (N3/34) before switch-in. The ME-SFI [ME] control unit (N3/34) appropriately adapts the idle speed.

On-board electrical system battery undervoltage (G1) 

If the ME-SFI [ME] control unit (N3/34) detects an undervoltage, the idle speed is raised by about 100 rpm when gear range "D" or "R" is selected, until the ignition is switched off.

	Electrical function schematic for rpm control	Engine 274 in model 448 except code XM0 (Facelift)	PE07.10-S-2708-97VDC
		Engine 274 in model 447 except code XM0 (Facelift)	PE07.10-S-2708-97TRC
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-S-9998TRC