GF07.10-P-1008MG RPM Control, Function
GF07.10-P-1008MG Rpm Control, Function
ENGINES 271.8 in MODEL 204.0 /2 /3, 207.3 /4, 212.0 /2
Function requirements for rpm control, general points
^ Circuit 87 M ON (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
- Throttle valve positioner (M16/6), throttle valve position
- Electronic stability program control unit (N30/4) (except code (233) DISTRONIC PLUS) or Electronic stability program control unit Premium (N30/7) (with code (233) DISTRONIC PLUS), wheel speed via chassis CAN (CAN E)
- The electronic transmission control control unit (N15/3) (for code (423) 5-speed automatic transmission (NAG)) or fully integrated transmission control controller unit (Y3/8) (for code (427) 7-speed automatic transmission), gear range via the drive train CAN (CAN C)
The Electronic Stability Program control unit (N30/4) will be introduced into service as of 1.3.2011 (model 204.0/2) or as of 1.6.2011 (model 204.3) in 2 variants:
- Electronic Stability Program control unit, Basis variant (except code (233) DISTRONIC PLUS)
- Electronic Stability Program control unit, Premium variant (except code (233) DISTRONIC PLUS)
Up to 28.2.2011 or 31.5.2011 only the Electronic Stability Program control unit Basis variant will be used.
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)
- 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
The rpm control is described at the following points:
^ Function sequence for torque converter protection (for automatic transmission)
^ Manual transmission function sequence (for manual transmission)
^ Function sequence for a defective throttle valve actuator
^ Function sequence for driving mode
^ Function sequence for maximum speed limit
^ Function sequence for missing variant coding
^ 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 on the current selector lever position from the electronic transmission control unit or the fully integrated transmission controller unit via the drive train CAN.
Function sequence for manual transmission (for manual transmission)
To prevent damage to the manual transmission, the maximum engine idle speed is limited to about 4000 rpm when the vehicle is stationary.
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 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 "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 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 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 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)
- 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 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 20° KW (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)
^ 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 converter 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 "P" or "N" engaged (for automatic transmission)
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 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. For this purpose the ME-SFI [ME] control unit evaluates the "engaged drive stage" CAN signal from the electronic transmission control unit or the fully integrated transmission control.
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.
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.
