Knock Control, Function - GF07.10-P-1015KJ

ENGINE 281.910 in MODEL 453.0/3/4 

Function requirements for knock control, general points 

• Circuit 87 (Engine management ON)
• Engine runs

Knock control, general points 

The knock control is integrated in the ME-SFI [ME] control unit (N3/10) and has the task is to ensure knock-free engine operation under all operating conditions and when different fuel grades are used. In the case of uncontrolled combustion (knocking), the ignition angle of the effected cylinder is adjusted to "retarded".

The ME-SFI [ME] control unit manages the knock control according to the following signals:

• Knock sensor (A16)
• Intake camshaft Hall sensor (B6/15), intake camshaft position (ignition circuit detection)
• Coolant temperature sensor (B11/4)
• Intake air temperature sensor (B17)
• Charge air temperature sensor (B17/8)
• Pressure sensor downstream of throttle valve (B28/7), engine load
• Accelerator pedal sensor (B37), load request by driver
• Crankshaft position sensor (L5), engine speed and crankshaft position (ignition circuit detection)

The requirements of the torque coordination function are also taken into account.

Function sequence for knock control 

The function sequence is described in the following steps:

• Function sequence for ignition angle setting 
• Function sequence for RON correction (Research Octane Number control) 
• Function sequence for knock control adaptation 
• Function sequence for knock identification error 

Function sequence for ignition angle setting 

Knock control is enabled under the following operating conditions:

• Low coolant temperature
• Part load

According to its input signals, the ME-SFI [ME] control unit computes the cylinder-specific ignition angle correction.

If knocking is detected in a cylinder by the knock sensor, the ignition angle for this cylinder is adjusted towards "retard" at the next ignition (depending on engine speed). If knocking continues to occur, the ignition angle is adjusted further towards "retard", and so on until maximum adjustment is reached.

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

Function sequence for RON correction (Research Octane Number control) 

Knock control is also fitted out with an automatic RON switch. This detects a persistent high tendency to knock 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.

The RON stage is adjusted by one or several stages depending on the threshold which has been exceeded. The regulated RON stage remains until stopping of the engine.

The higher the RON stage selected, the lower the maximum retarding the ignition timing of the ignition angle.

Function sequence for knock control adaptation 

Adaptation by the knock control becomes active starting from a high coolant temperature.

The ignition angle corrections required due to combustion knocking are stored continuously for the specific cylinder, along with the related operating condition of the engine (engine load and engine 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.

Function sequence for knock identification error 

For safety reasons, if the knocking sensor signal fails, the ignition angles of all cylinders are "retarded" (according to engine speed and coolant temperature). Knock control and the adaptation are deactivated and a fault is stored in the fault memory.

The ignition angle corrections of the thermal management and the knock control are added based on the performance map.

	Electrical function schematic for knock control		PE07.10-P-2715-97BBA
	Overview of system components motor electronics (ME-SFI) fuel injection and ignition system		GF07.61-P-9997KJ