GF07.10-P-1008OGG RPM Control, Function
GF07.10-P-1008OGG Rpm Control, Function
- as of model year 09
Function requirements for rpm control, general points
^ Circuit. 87 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 and the drive train. On the signal from the crankshaft Hall sensor (B70), the CDI control unit (N3/9) detects the engine speed.
For rpm limitation the CDI control unit reads in the following sensors and signals:
- Crankshaft Hall sensor, engine speed
- Rail pressure sensor (B4/6)
- Electric controller unit (VGS) (Y3/8), gear range over the engine compartment CAN (CAN C)
- ESP control unit (N47-5), vehicle speed over the engine compartment CAN
The motor speed is regulated by the CDI control unit by the following measures:
- Actuation of the pressure regulating valve (Y74) (rail pressure regulation)
- No actuation of the fuel injectors (Y76) (for rpm limitation)
- Adaptation of the injection time of the fuel injectors (for idle speed control)
- Actuation of the quantity control valve (Y94) (rail pressure regulation)
Function sequence for rpm control
Regulation of the motor speed is described in the following points:
^ Torque converter protection function sequence
^ Function sequence for maximum engine speed limitation
^ Function sequence for maximum speed limit
^ Function sequence for idle speed control
Torque converter protection function sequence
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 CDI control unit receives the information about the current selector lever position from the electric controller unit (VGS) over the engine compartment CAN.
Function sequence for maximum engine speed limitation
When driving, in order to protect the engine from the effects of inadmissibly high engine speeds, the maximum engine speed is limited to 4500 rpm for a speed >0.
The CDI control unit detects the driving mode on the "vehicle speed" CAN signal, which is sent by the ESP control unit via the engine compartment CAN.
Function sequence for maximum speed limit
Upon reaching 250 km/h the injection times of the fuel injectors are reduced by the CDI control unit and the fuel pressure in the rails is reduced via the quantity control valve and the pressure regulating valve. These measures ensure simple maximum speed limitation the reduction of the engine torque.
The fuel pressure in the rails and the injection time of the fuel injectors determine the injection quantity.
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.
For idle speed control the CDI control unit also reads in the following sensors and signals:
- Boost pressure sensor (B5/1), engine load
- Coolant temperature sensor (B11/4)
- Charge air temperature sensor (B17/8)
- AAC [KLA] control and operating unit (N22) (except code (581) Comfort automatic air conditioning) or comfort AAC control and operating unit (N22/7) (with code (581) Comfort automatic air conditioning), outside temperature and status of the air conditioning via the interior CAN (CAN B), central gateway control unit (N93) and engine compartment CAN
The idle speed can raised for a limited time to about 1600 rpm depending on the atmospheric pressure and ambient temperature.
The CDI control unit regulates the idle speed in the following operating and engine load conditions:
^ Engagement of gear range "D" or "R"
^ Switching on the refrigerant compressor (A9)
^ Battery (G1) undervoltage
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 forward. To do this, the CDI control unit evaluates the "gear range engaged" CAN signal from the electric controller unit (VGS).
Switching on refrigerant compressor
In order to ensure that the motor speed in idle does not drop upon switching on of the refrigerant compressor, the AAC [KLA] control and operating unit (except code (581) Comfort automatic air conditioning) or the comfort AAC control and operating unit (with code (581) Comfort automatic air conditioning) sends a status signal to the CDI control unit before switching on.
The CDI control unit adapts the idle speed appropriately.
For the following conditions the CDI control unit interrupts switching on of the refrigerant compressor:
- Engine speed < 2000 rpm
- Value of the accelerator pedal sensor (B37) >95%
Battery (G1) undervoltage
The CDI control unit recognizes an undervoltage of the battery over "circuit 30" and increases the idle speed for an engaged gear range "D" or "R" up to switch off of the engine at about 100 rpm.
Diagnosis
The basic setting of the idle speed can be read out and adjusted with the Diagnosis Assistance System (DAS).
