GF07.10-P-1008MMI RPM Control, Function
GF07.10-P-1008MMI Rpm Control, Function
ENGINES 152.9 in MODEL 172.4
Function requirements for rpm control, general points
^ Circuit 87M (engine timing ON)
^ Engine running
Rpm control, general
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
- Actual value potentiometer 1 and 2 (M16/6r1, M16/6r2), throttle valve position
- Fully integrated transmission control unit (Y3/8n4), 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 limits the engine speed by the following measures:
- Adjustment of the opening angle of the throttle valve by the actuator motor (M16/6m1) for the throttle valve actuator (M16/6)
- Adjusting the ignition angles of the ignition coils (T1)
- Cut out of the fuel injectors (Y76) (for 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 torque converter protection
^ Function sequence for driving mode
^ Function sequence for maximum speed limit
^ Function sequence for a defective throttle valve actuator
^ Function sequence for idle speed control
Function sequence for torque converter protection
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. 5000 rpm. The ME-SFI [ME] control unit receives information about the current selector lever position from the fully integrated transmission control unit via the drive train 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 7000 rpm.
The ME-SFI [ME] control unit detects the driving mode on the "wheel 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 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 limitation 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 (G1), on-board electrical system voltage (undervoltage)
- 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 injectors 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 gear range "D" or "R"
^ 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 less than 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 less than 70°C for about 50 s by the ME-SFI [ME] control unit by about 50 to 100 rpm.
Engagement of gear range "D" or "R"
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. To do this, the ME-MFI [ME] control unit evaluates the "gear range engaged" CAN signal from the fully integrated transmission control unit.
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.
