Knock Sensor: Description and Operation
GF15.12-P-4024AM Anti-knock Control Function
ENGINE 113.990 in MODEL 211, 219
ENGINE 113.991 in MODEL 215, 220
ENGINE 113.992 in MODEL 230 up to Model Year 2008
ENGINE 113.993 in MODEL 463 up to 31.5.12
ENGINE 113.995 in MODEL 230 up to Model Year 2008
A16/1 Knock sensor 1, right
A16/2 Left knock sensor 2
B6/1 Camshaft Hall sensor
B11/4 Coolant temperature sensor
B17/8 Charge air temperature sensor
B28 Pressure sensor (charge air)
B37 Accelerator pedal sensor
L5 Crankshaft position sensor
N3/10 ME control unit
T1/1-
T1/8 -Cylinder 1 to 8 ignition coils
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 under 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 is integrated in the ME control unit.
Input signals:
^ Knock identification -> knock sensors
^ Engine speed -> Crankshaft position sensor
^ Ignition circuit detection -> Crankshaft position sensor and camshaft Hall sensor
^ Engine temperature -> Coolant temperature sensor
^ Air mass -> pressure sensor and charge air temperature sensor
^ Engine load -> Accelerator pedal sensor
^ Presetting (programming) -> 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 knock sensor fault is detected
The anti-knock control is active from engine start. If knocking was detected at a cylinder, the ignition angle of this cylinder is retarded from the next ignition. If knocking continues to occur, the ignition angle (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.
If the anti-knock control specifies retardation of the ignition angle for a lengthy period then the engine control system reduces the engine power output to protect the engine.
Fault if knocking is detected
If no signals are received from the knock sensor, the ignition angle of all cylinders is retarded by as much as a 15° 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 in the fault memory.
Adaptation of anti-knock control
The adaptation of the anti-knock control is active as of a coolant temperature of approx. 50°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).
When determining the individual ignition angles, the stored adaptation values are taken into account, so that the optimal ignition angle can be calculated immediately for each cylinder.
During an abrupt acceleration, no values are stored for about 2 seconds in order to avoid any incorrect adaptation values.
A default setting for the RON correction can be preprogrammed using the STAR DIAGNOSIS.
The ignition angle corrections of the overheating/pinging protection and anti-knock control are added based on the performance map.
