Rpm control, function - GF07.10-P-1008MMC

ENGINES 157.9 in MODEL 216.3, 221.0/1

ENGINES 278.9 in MODEL 216.3, 221.0/1

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. On the signal from the crankshaft Hall sensor (B70), the ME-SFI [ME] control unit (N3/10) detects engine speed. The ME-SFI [ME] control unit reads in the following sensors and signals for rpm limitation:

Crankshaft Hall sensor, engine speed
Throttle valve actuator (M16/6), throttle valve position
Electric controller unit (VGS) (Y3/8), gear range via the drive train CAN (CAN C)
ESP control unit (N47-5), vehicle speed over the chassis CAN (CAN E)

The ME-SFI [ME] control unit limits the engine speed by the following measures:

Adjusting the opening angle of the throttle valve
Ignition angle adjustment 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 partial functions:

Function sequence for torque converter protection (for engine 278) or start-up clutch (for engine 157)
Function sequence for rpm limitation
Function sequence for maximum speed limit
Function sequence for throttle valve actuator fault
Function sequence for idle speed control

Function sequence for torque converter protection (for engine 278) or start-up clutch (for engine 157)

In order to protect the torque converter or the start-up clutch in selector lever positions P and N (no power transmission) from excessive static internal pressure, the maximum engine speed is limited to about 5000 rpm. The ME-SFI [ME] control unit receives the information about the current selector lever position from the electric controller unit (VGS) via the drivetrain CAN.

Function sequence for rpm limitation

In order to protect the engine from the consequences of impermissibly high engine revs, the engine speed is limited to approx. 6000 rpm.

The ME-SFI [ME] control unit detects the driving mode on the "vehicle speed" CAN signal, which is sent by the ESP 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 the reduction of the engine torque.

Function sequence for throttle valve actuator fault

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 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:

Coolant temperature sensor (B11/4)
Pressure sensor downstream of throttle valve actuator (B28/7), engine load
On-board electrical system battery (G1), on-board electrical system voltage (undervoltage)
AAC control unit (N22/1), air conditioning status via the 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 (C ranK A ngle) toward "retard" or 20° CKA toward "advance".

Altering the ignition angle provides more rapid control than altering the position of 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 refrigerant 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 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 forward. To do this, the ME-SFI [ME] control unit evaluates the "gear range engaged" CAN signal from the electric controller unit (VGS).

Switching on refrigerant compressor

In order that the engine idle speed does not drop when the refrigerant compressor engages, the AAC [KLA] control unit first sends a status signal to the ME-SFI [ME] control unit.

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 adjusted with the Diagnosis Assistance System (DAS.

Electrical function schematic for rpm control	Model 216	PE07.10-P-2708-97CAH
Electrical function schematic for rpm control	Model 221	PE07.10-P-2708-97SAH
Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MMB