The anti-knock control function - GF15.12-P-4024V

ENGINE 272.920 in MODEL 203 up to Model Year 8

ENGINE 272.922 in MODEL 211

ENGINE 272.940 in MODEL 203 up to Model Year 8

ENGINE 272.941 in MODEL 203 up to Model Year 8

ENGINE 272.942 in MODEL 171 up to Model Year 8

ENGINE 272.943 in MODEL 211, 219

ENGINE 272.944 in MODEL 211

ENGINE 272.945 in MODEL 251 up to Model Year 8

ENGINE 272.946 in MODEL 221 up to Model Year 8

ENGINE 272.960 in MODEL 203 up to Model Year 8

ENGINE 272.963 in MODEL 171 up to Model Year 8

ENGINE 272.964 in MODEL 211, 219

ENGINE 272.965 in MODEL 221 up to Model Year 8

ENGINE 272.966 in MODEL 230 up to Model Year 8

ENGINE 272.967 in MODEL 164, 251 up to Model Year 8

ENGINE 272.970 in MODEL 203 up to Model Year 8

ENGINE 272.972 in MODEL 211

ENGINE 272.975 in MODEL 221 up to Model Year 8

ENGINE 273.922 in MODEL 221 up to Model Year 8

ENGINE 273.923 in MODEL 164 up to Model Year 8

ENGINE 273.924 in MODEL 221 up to Model Year 8

ENGINE 273.960 in MODEL 211, 219

ENGINE 273.961 in MODEL 216, 221 up to Model Year 8

ENGINE 273.962 in MODEL 211

ENGINE 273.963 in MODEL 164, 251 up to Model Year 8

ENGINE 273.965 in MODEL 230 up to Model Year 8

ENGINE 273.967 in MODEL 209

ENGINE 273.968 in MODEL 221 up to Model Year 8

ENGINE 272.940 in MODEL 209

ENGINE 272.960 in MODEL 209

Fig 1: Anti-Knock Control Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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 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 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