ME-SFI knock control, function

P07.61-3369-06

A16 Knock sensor

B2/5 Hot film mass air flow sensor

B6/1 Camshaft Hall sensor

B11/4 Coolant temperature sensor

B37 Accelerator pedal sensor

L8 Crankshaft rpm sensor

N3/10 Motor electronics control unit

T1/1 Cylinder 1 ignition coil

T1/2 Cylinder 2 ignition coil

T1/3 Cylinder 3 ignition coil

T1/4 Cylinder 4 ignition coil

Y62/1 Cylinder 1 fuel injection valve

Y62/2 Cylinder 2 fuel injection valve

Y62/3 Cylinder 3 fuel injection valve

Y62/4 Cylinder 4 fuel injection valve

Task

The task of anti-knock control (AKC) is to ensure knock-free operation of the engine with different fuel qualities and in all operating conditions from idling speed up to maximum engine speed. For this purpose, if uncontrolled combustion (knocking) occurs, ignition timing at the relevant cylinders is retarded. The anti-knock control function is integrated in the motor electronics control unit.

Function

The knock control is active from engine start. If knocking was detected at a cylinder, then ignition timing of this cylinder is retarded from the next ignition. If knocking continues to occur, the ignition timing (depending on engine speed) continues to be retarded in stages until maximum retardation is achieved.

If knocking-free combustion exists, the retardation is reduced in stages after a few ignitions (depending on engine speed) until the normal performance map value is achieved or knocking once again occurs.

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 If the knock control specifies retardation of the ignition angle for a lengthy period, the engine control system reduces the engine power output to protect the engine.

Faults if knocking detected
If no signals are received from the knock sensor, ignition timing of all cylinders is retarded by as much as 15° crank angle for safety reasons (depending on engine speed and temperature). The knock control and the adaptation are deactivated and a fault is stored in the fault memory.

Adaptation of the knock control

Any corrections required to ignition timing 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). During output of the individual ignition angles, the stored adaptation values are taken into consideration, so that the optimal ignition angle can be determined immediately for each cylinder.

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During abrupt acceleration, no values are stored in order to avoid any incorrect adaptation values.

The correction of the research octane number (RON) can be preset using
STAR DIAGNOSIS.
The ignition angle corrections of the overheating/pinging protection and knock control are added based on the performance map.

Input signals

 Knock sensor

 Hot film mass air flow sensor

 Camshaft Hall sensor

 Coolant temperature sensor

 Accelerator pedal sensor

 Crankshaft rpm sensor

Output signals

 Ignition angle correction for specific cylinder (to the map value calculated by the motor electronics control unit)

 Ignition angle emergency mode if knock sensor fault is detected