GF15.12-P-4024M Anti-Knock Control Function

GF15.12-P-4024M Anti-Knock Control Function
ENGINE 275.950 in MODEL 215, 220
ENGINE 275.951 in MODEL 230 up to Model Year 8
ENGINE 275.953 in MODEL 216, 221 up to Model Year 8
ENGINE 275.954 in MODEL 230 up to Model Year 8
ENGINE 275.980 in MODEL 215, 220
ENGINE 275.981 in MODEL 230 up to Model Year 8
ENGINE 275.982 in MODEL 216, 221 up to Model Year 8
ENGINE 285.950 in MODEL 240
ENGINE 285.980 in MODEL 240





A29/1 Front knock sensor (left side of engine)
A29/2 Rear knock sensor (left side of engine)
A30/1 Front knock sensor (right side of engine)
A30/2 Rear knock sensor (right side of engine)
B6/2 Camshaft Hall sensor, left cylinder bank (with ME-SFI 2.7.1)
B6/3 Camshaft Hall sensor, right cylinder bank
B11/4 Coolant temperature sensor
B17/8 Charge air temperature sensor
B28/7 Pressure sensor downstream of throttle valve actuator
B37 Accelerator pedal sensor
L5 Crankshaft position sensor
M16/6 Throttle valve actuator
N3/10 alternator control unit
N92/1 ECI ignition module, right cylinder bank
N92/2 ECI ignition module, left cylinder bank
X11/4 Data link connector

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 relevant cylinder or cylinders is retarded. The anti-knock control (AKC) function is integrated in the ME-SFI [ME] control unit (N3/10).

Input signals:
^ Engine speed (crankshaft position sensor)
^ Camshaft position (camshaft Hall sensor)
^ Recognition of knocking over 4 knocking sensors
^ Engine temperature (coolant temperature sensor)
^ Engine load (pressure sensor downstream of throttle valve actuator)
^ 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 alternator control unit
^ Ignition angle emergency mode if fault identified.

Anti-knock control is active from a coolant temperature of 70 °C. If cylinder knocking is recognized above an engine load of about 40%, its ignition angle is retarded by approx. 3.0° crank angle after the next ignition. If knocking continues to be detected, the ignition angle is continuously retarded in 3° crank angle increments 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 retardation of ignition timing - the higher the selected RON stage, the less the maximum retardation of ignition timing.
If knocking-free combustion exists, retardation is reduced in approx. 0.75° crank angle increments after a few ignitions (depending on the engine speed) until the performance map value is achieved, or knocking occurs again.

Adaptation of anti-knock control
Adaptation of anti-knock control is active from a coolant temperature of approx. 75 °C. Any corrections required to the ignition angle due to 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 to avoid any incorrect adaptation values.

Faults in knocking detection
If no signals are received from the knock sensors or from ionic current measurement, the ignition angle of all cylinders is retarded for safety reasons by as much as approx. 11° crank angle 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 anti-knock 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 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 performed via STAR DIAGNOSIS is active at first.

The engines are designed to run with RON 98 fuel. If only fuel with RON 91 is available, the RON correction must be carried out immediately using STAR DIAGNOSIS, otherwise engine damage is possible.