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

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

Function requirements for rpm control, general points
^ Circuit 87M ON (engine control ON)
^ Engine running

Rpm control, general points
Rpm control stabilizes the idle speed and limits the motor speed to protect the engine, the drive train and the vehicle. The ME-SFI [ME] control unit (B70) detects the engine speed via the crankshaft Hall sensor signal (N3/10). The ME-SFI [ME] control unit reads in the following sensors and signals for rpm limitation:
- Crankshaft Hall sensor, engine speed
- Throttle valve positioner (M16/6), throttle valve position
- Electronic Stability Program control unit (N30/4) or Electronic Stability Program Premium control unit (N30/7) (for DISTRONIC PLUS), vehicle speed via the chassis CAN (CAN E)
- Fully integrated transmission control controller unit (Y3/8), gear range via the drive train CAN (CAN C) (for an automatic transmission)

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 angles of the ignition coils (T1) to "retard"
- Cut out of injection valves (Y62) (for rpm limitation)
- Adaptation of the injection time of the injection valve ( for idle speed control)

Function sequence for rpm control
Regulation of the motor speed is described in the following points:
^ Torque converter protection function sequence (for automatic transmission)
^ Driving mode function sequence
^ Function sequence for maximum speed limit
^ Function sequence for a defective throttle valve actuator
^ Missing variant coding function sequence
^ Function sequence for idle speed control

Function sequence for torque converter protection (for automatic transmission)
In order 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. 4200 rpm. The ME-SFI [ME] control unit receives information about the current selector lever position from the fully integrated transmission controller unit over the drive CAN.

Function sequence for driving mode
In order to protect the engine from inadmissible engine speeds during driving mode, the maximum engine speed is limited to about 6000 rpm.
The ME-SFI [ME] control unit detects the driving mode on the "vehicle speed" CAN signal, which is sent from the Electronic Stability Program control unit via the chassis CAN.

Function sequence for maximum speed limit
Upon reaching 250 km/h the opening angle of the throttle valve and the injection time of the injection valves are reduced by the ME-SFI [ME] control unit. These measures ensure simple maximum speed limitation 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.

Missing variant coding function sequence
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 and engine loads if the accelerator pedal is not actuated.
The ME-SFI [ME] control unit also reads in the following sensors and signals for idle speed control:
- Hot film MAF sensor (B2/5), engine load
- Coolant temperature sensor (B11/4)
- On-board electrical system battery (G1), on-board electrical system voltage (undervoltage)
- Clutch pedal switch (S40/3) (for manual transmission)
- Automatic air conditioning control and operating unit (N22/7), air conditioning system status over 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 injection valves according to variations in the air mass. To assist the idle speed control, the ME-SFI [ME] control unit can adjust the ignition angles of the ignition coils () by up to 36° CKA ( CranK Angle) toward "retard" or 20° CKA toward "advance".

Adjusting the ignition angle enables a faster response than adjusting the throttle valve.

The ME-SFI [ME] control unit regulates the idle speed in the following operating and engine load conditions:
^ Warming-up phase
^ Engagement of the gear range "D" or "R" (for an automatic transmission)
^ Operate the clutch pedal (for manual transmission)
^ Switching on the A/C compressor (A9)
^ Undervoltage of the on-board electrical system battery
^ Purge control

Warm-up phase
In the warm-up phase, the ME-SFI [ME] control unit controls the idle speed according to 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 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 evaluates the "gear range engaged" CAN signal of the fully integrated transmission control controller unit.

Operate the clutch pedal (for manual transmission)
When actuating the clutch pedal the idle speed is stabilized. Clutch pedal actuation is detected by the ME-SFI [ME] control unit through the clutch pedal switch.

Switching on the A/C compressor
When the engine is at idle, so that engine speed will not fall when the refrigerant compressor is engaged, the automatic air conditioning control and operating unit sends a status signal to the ME-SFI [ME] control unit before the AAC is engaged.
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 through "circuit 30", the idle speed is raised by about 100 rpm when gear range "D" or "R" is selected, 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.