Rpm Control, Function - GF07.10-P-1008MNL
Engine 176.9, 177.9 in model 217
Engine 176.9, 177.9 in model 222
Engine 177.9 in model 290
up to model year 2021
Function requirements for rpm control, general points
- Circuit 87M (Engine management ON)
- Engine runs
Rpm control, general
Rpm control stabilizes the idle speed and limits the motor speed to protect the engine, the drivetrain and the vehicle. The ME-SFI [ME] control unit (N3/10) detects the engine speed via the crankshaft Hall sensor (B70) signal.
For rpm limitation, the ME-SFI [ME] control unit reads in signals from the following sensors and control units:
- Crankshaft Hall sensor, engine speed
- Left and right actual value potentiometer 1 and 2 (M16/60r1, M16/60r2, M16/61r1, M16/61r2), throttle valve position
- Electronic Stability Program control unit (N30/4), vehicle speed via suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1)
- Fully integrated transmission control unit (Y3/8n4) (model 217, 222), drive range via drive CAN
- Fully integrated transmission control electric controller unit control unit (Y3/8n4) (model 290), drive range via the drive CAN
The ME-SFI [ME] control unit limits the engine speed by the following measures:
- Adjustment of throttle valve opening angle by actuation of left and right throttle valve actuator motor (M16/60m1, M16/61m1)
- Ignition angle setting of ignition coils of cylinder 1+2 to cylinder 7+8 (T4 to T4/3)
- Cutout of fuel injectors for cylinder 1 to 8 (Y76/1 to Y76/8) (for speed control)
- Adaptation of injection period for the cylinder 1 to 8 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 rpm limitation
- Function sequence for maximum speed limit
- Function sequence for throttle valve actuator defective
- Function sequence for idle speed control
Function sequence for rpm limitation
In order to protect the engine from the consequences of impermissibly high engine revs, the maximum engine speed is limited to approx. 6800 rpm.
The ME-SFI [ME] control unit detects the driving mode using the CAN "wheel speed" signal, which is sent by the Electronic Stability Program control unit over the chassis FlexRay, powertrain control unit and drive CAN.
Function sequence for maximum speed limit
Upon reaching maximum speed dependent on the design, the opening angle of the throttle valve and the injection duration for the fuel injectors for cylinder 1 to 8 are reduced by the ME-SFI [ME] control unit. These measures ensure simple maximum speed limit through the reduction of the engine torque.
Function sequence for throttle valve actuator defective
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.
For idle speed control the ME-SFI [ME] control unit also reads in the following signals:
- Coolant temperature sensor (B11/4), coolant temperature
- Pressure sensor downstream of left and right throttle valve (B28/22, B28/23), engine load
- On-board electrical system battery (G1), on-board electrical system voltage (undervoltage)
- Climate control control unit (N22/1), air conditioning system status via interior CAN (CAN B), electronic ignition lock control unit (N73), chassis FlexRay, powertrain control unit and drive train CAN
The ME-SFI [ME] control unit controls the idle speed via the throttle valve actuators and adapts the injection duration for the fuel injectors for cylinder 1 to 8 in accordance with the modified air mass. To assist with idle speed control, the ME-SFI [ME] control unit can adjust the ignition angle of the ignition coils for cylinder 1+2 to cylinder 7+8 up to 36° CKA (C rank A ngle) toward "retarded" or 20° CKA toward "advanced".
Intervention by means of the ignition angle setting reacts more quickly than intervention by means of adjustment of the throttle valve.
The ME-SFI [ME] control unit regulates the idle speed in the following operating conditions and engine load conditions:
- Warming-up phase
- Undervoltage of the on-board electrical system battery
- Purge control
Warming-up phase
In the warm-up phase, the ME-SFI [ME] control unit controls the idle speed dependent on the 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 for about 20 s to about 1100 to 1300 rpm. After this time has elapsed, the idle speed is increased at a coolant temperature of < 70°C for about 50 s by about 50 to 100 rpm by the ME-SFI [ME] control unit.
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 engaged, until the ignition is switched off.
Purge control
The idle speed control prevents any change in the engine speed due to purging.
The basic setting of the idle speed can be read out and influenced using the Xentry Diagnostics.
| Electrical function schematic for rpm control | Engine 177.9 in model 290 up to model year 2021 | PE07.10-P-2708-97XBA | |
| Engine 176.9, 177.9 in model 217Engine 176.9, 177.9 in model 222 | PE07.10-P-2708-97SEL | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNL |