The anti-knock control function - GF15.12-P-4024V
ENGINE 272.942 in MODEL 171
ENGINE 272.963 in MODEL 171
Shown on engine 272.963 in model 171
The task of the anti-knock control AKC is to ensure knock-free operation of the engine with different fuels and in all operating conditions from idling speed up to maximum engine speed.
For this purpose, if uncontrolled combustion (knocking) occurs, the ignition angle at the knocking cylinders is retarded.
The anti-knock control (AKR) is integrated in the ME-SFI [ME] control unit.
Input signals:
- Motor speed (crankshaft Hall sensor)
- Camshaft position (camshaft Hall sensor)
- Recognition of knocking over 2 knocking sensors
- Engine temperature (coolant temperature sensor)
- Engine load (hot film mass air flow sensor)
- Accelerator pedal position (accelerator pedal sensor)
- Precontrol by means of automatic RON switch (internal)
- RON correction with STAR DIAGNOSIS.
Output signals:
- Ignition angle correction for specific cylinder to the map value calculated by the ME control unit
- Ignition angle emergency mode if fault identified.
The anti-knock control is active from a coolant temperature of 40°C. If cylinder knocking is recognized above an engine load of about 40%, its ignition angle is adjusted to retarded by about a 3.0° crank angle after the next ignition. If knocking continues to be detected, the ignition angle is continuously retarded in steps of a 3° crank angle until the maximum retardation is reached (approx. a 10 -15° crank angle, depending on the engine speed). The automatic RON switch also influences the maximum retarding of the ignition timing - the higher the selected RON stage, the less is the maximum retarding of the ignition timing.
If knocking-free combustion exists, the retardation is reduced in steps of approx. 0.75° crank angle after a few ignitions (depending on the engine speed) until the map value is achieved, or knocking occurs again.
Adaptation of anti-knock control
The adaptation of the anti-knock control is active from a coolant temperature of approx. 75°C. Any corrections required to the ignition angle because of knocking combustion are constantly detected for the specific cylinder and stored together with the relevant operating state of the engine (engine load/speed range).
The stored adaptation value is taken into account in the output of the individual cylinder angles so that each cylinder is immediately operated with the optimal ignition angle.
During abrupt acceleration, no values are stored for about 2 seconds in order to avoid any incorrect adaptation values.
Faults if knocking is detected
If no signals are received from the knock sensors, the ignition angle of all cylinders is retarded by as much as a 11° crank angle for safety reasons, depending on engine speed and temperature. The anti-knock control and the adaptation are deactivated and a fault is stored.
Automatic RON switch
In addition to the RON correction using STAR DIAGNOSIS, the antiknock control features an automatic RON switch. This detects a persistent high knocking tendency of the engine and assists the anti-knock control by means of an appropriate pre-control.
This is done by analyzing the stored adaptation values, the ignition angles of all the cylinders and the number of control interventions in certain engine load and speed ranges. Depending on the threshold which has been exceeded, the RON value is adjusted by one or several stages. The value is retained until the engine is switched off.
After engine start, only the RON correction which is carried out by means of STAR DIAGNOSIS is at first active.
| Component description for the ME-SFI [ME] control unit | GF07.61-P-6000V |
| Component description for a knock sensor | GF07.04-P-6030V |
| Component description for the crankshaft Hall sensor | GF07.04-P-6220V |
| Component description for the camshaft Hall sensor | GF07.04-P-6020V |
| Component description for the coolant temperature sensor | GF07.04-P-6040V |
| Component description for the hot film MAF sensor | GF07.07-P-6000V |
| Component description for the accelerator pedal sensor | GF30.20-P-2010V |
| ME-SFI synchronization of fuel injection and firing order function | GF07.61-P-4009V |