GF07.61-P-4031MAR ME Knock Control, Function
GF07.61-P-4031MAR ME Knock Control, Function
- refinement package
- as of model year 09
Function requirements for knock control, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
Knock control, general points
The knock control is integrated in the ME-SFI control unit (N3/10) and its purpose is to ensure knock-free engine operation in all operating conditions and when different fuel grades are used. If there is uncontrolled combustion (knocking), the ignition angle of the ignition coil (T1) of the related cylinder is adjusted to "retard".
The ME-SFI control unit (N3/10) manages the knock control according to the following sensors and signals:
- Knock sensor 1, on the right (A16/1)
- Knock sensor 2, on the left (A16/2)
- LH and RH hot film MAF sensor (B2/6, B2/7), engine load
- LH and RH intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions (ignition circuit detection)
- LH and RH exhaust camshaft Hall sensor (B6/6, B6/7), exhaust camshaft positions (ignition circuit detection)
- Coolant temperature sensor (B11/4)
- Intake air temperature sensor (B17)
- Pressure sensor (B28), intake manifold air pressure
- Sensor accelerator pedal (B37), driver engine load request
- Crankshaft Hall sensor (B70), engine speed and crankshaft position (ignition circuit detection)
- RON setting (Research - Octane Number) with the DAS (except Code (494) USA version)
The requirements of the engine torque-requirement function are also taken into account.
Knock control function sequence
The function sequence is described in the following steps:
^ Ignition angle adjustment function sequence
^ RON correction function sequence
^ Knock control adaptation function sequence
^ Knock identification error function sequence
Ignition angle adjustment function sequence
Knock control is enabled in the following operating conditions:
- Coolant temperature > 40°C
- Engine load > 40 %
According to its input signals, the ME-SFI control unit calculates the cylinder-specific ignition angle correction.
If knocking is detected in a cylinder by the knock sensors, the ignition angle of the cylinder is adjusted by about 3° crank angle towards "retard" (depending on engine speed), starting from the next ignition. If knocking still occurs, the ignition angle is retarded by about another 3° crank angle, and so on until the maximum shift value is reached (about 10 to 15°).
If there is no knocking, after a few ignitions the retard adjustment is reversed in steps of about 0.75° crank angle, until the normal performance map value is reached, or until knocking occurs again.
RON correction function sequence
The RON correction can be preset with the DAS using correction programming (except code (494) USA version).
Knock control is also fitted out with an automatic RON switch. This detects a persistent high knocking tendency of the engine and assists the knock control by means of an appropriate pre-control. This is done by evaluating the stored adaptation values, the ignition angle 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 stage is adjusted by one or several stages. The regulated RON stage remains until stopping of the engine.
The higher the RON stage selected, the lower the maximum retardation of the ignition angle.
Knock control adaptation function sequence
The adaptation of the knock control is active from a coolant temperature of approx. 75°C.
The ignition angle corrections required due to knocking combustion are stored continuously, with the associated cylinder and related engine operating state (engine load and rpm).
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 abrupt acceleration, no values are stored for about 2 seconds in order to avoid any incorrect adaptation values.
Knock identification error function sequence
For safety reasons, if one of the knocking sensor signals fails, the ignition angles of all cylinders is retarded by up to 11° crank angle (according to engine speed and coolant temperature). Knock control and the adaptation are deactivated and a fault is stored in the fault memory.
