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

Engine 264.9 in Model 205, 253 

Function requirements, general 

IMPORTANT The ME-SFI [ME] control unit (N3/10) detects the Engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

RPM control, general 

The RPM control stabilizes the Engine speed in neutral and limits the Engine speed to protect the Engine, the drivetrain and the vehicle.

For RPM control, the ME-SFI [ME] control unit reads in the signals of the following components:

The ME-SFI [ME] control unit also evaluates the following signals:

The ME-SFI [ME] control unit regulates the Engine speed via the following measures:

IMPORTANT The Engine responds more quickly to the ignition angle setting than to the throttle valve setting.

The ME-SFI [ME] control unit actuates the following components for this purpose:

RPM limitation 

In selector lever position "N" or "P" (no power transmission), the maximum Engine speed is limited to approx 4200 RPM to protect the torque converter against excessively high static internal pressure.

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 defined via the wheel speeds.

IMPORTANT In the case of a defective throttle valve actuator motor of the throttle valve actuator, the maximum Engine speed in idle is limited to approx. 1400 RPM and during vehicle operation to approx. 1800 RPM.

Maximum vehicle speed limit 

When the maximum speed is reached, the ME control unit reduces the opening angle of the throttle valve and the injection period. The Engine torque is thus reduced and the speed is limited.

Idle speed control 

The idle speed is regulated depending on the operating conditions and Engine load.

For idle speed control, the ME-SFI [ME] control unit reads in the signals of the following sensors:

The ME-SFI [ME] control unit also evaluates the on-board electrical system utilization and the air conditioning system requests.

Operating rate of the 12 V on-board electrical system (except code B01 (48V Technology)) 

The front SAM control unit (N10/6) sends the idle speed increase request and the specified voltage of the alternator (G2) via the interior CAN (CAN B), electronic ignition lock control unit (N73), suspension FlexRay, powertrain control unit, and Engine CAN (CAN C) to the ME-SFI [ME] control unit.

Operating rate of the 48 V on-board electrical system (with code B01 (48V Technology)) 

On the basis of current consumers, the charge level of the 48 V onboard electrical system battery (G1/3), and further criteria, the powertrain control unit calculates the value to which the idle speed is to be increased. The DC/DC converter control unit (N83/1) transmits the status of the 48 V on-board electrical system battery and information on the on-board electrical system operating rate via the interior CAN, the electronic ignition lock control unit, and the suspension FlexRay to the powertrain control unit. The powertrain control unit transmits the idle speed increase request via the Engine CAN to the ME-SFI [ME] control unit.

Air conditioning 

The climate control control unit (N22/1) transmits idle speed increase requests via the interior CAN, the electronic ignition lock control unit, the suspension FlexRay, the powertrain control unit, and the drive CAN to the ME-SFI [ME] control unit.

The ME-SFI [ME] control unit regulates the idle speed under the following operating conditions and Engine loads:

Warm-up 

In the warm-up phase, the idle speed is regulated depending on the coolant temperature in order to bring the catalytic converter more quickly to operating temperature after Engine start.

Additional function requirements for starting the warm-up phase:

The ME-SFI [ME] control unit increases the idle speed for approx. 20 s to between 1100 and1300 RPM. The idle speed is subsequently increased for a coolant temperature below 70 °C for approx. 50 s by 50 to100 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 forward.

Undervoltage in the on-board electrical system 

An undervoltage is detected by the ME-SFI [ME] control unit via circuit 30. The idle speed is then, with engaged drive range "D" or "R", increased by approx. 100 RPM until the ignition is switched off.

Purging 

The idle speed control prevents any change in the Engine speed due to purging.

IMPORTANT The basic setting of the idle speed can be read out and modified via the diagnostic tester.

  Electrical function schematic for RPM control   PE07.10-P-2708-97FBI 
  Overview of system components for gasoline injection and ignition system with direct injection   GF07.70-P-9998MRS 
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