Knock control, function - GF07.10-P-1015MI

ENGINE 272.9 (except 272.982) in MODEL 204.0/2 as of model year 2009 

ENGINE 272.9 (except 272.983) in MODEL 212 

ENGINE 272.9 (except 272.984) in MODEL 207 

ENGINE 272.9 in MODEL 204.9 

ENGINE 273.9 in MODEL 207, 212 

Function requirements for knock control, general points 

• Circuit 87M ON (engine timing ON)
• Engine running

Knock control, general points 

The knock control is integrated in the ME-SFI [ME] control unit (N3/10) and its purpose 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 ignition coil (T1) for the related cylinder is adjusted towards "retard". The ME-SFI [ME] control unit manages the knock control according to the following sensors and signals:

• right knock sensor (A16/1)
• left knock sensor (A16/2)
• hot film MAF sensor (B2/5), engine load
• intake air temperature sensor (B2/5b1)
• left and right intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions (ignition circuit detection)
• left and right exhaust camshaft Hall sensor (B6/6, B6/7), exhaust camshaft positions (ignition circuit detection)
• coolant temperature sensor (B11/4)
• pressure sensor (B28), intake manifold air pressure
• accelerator pedal sensor (B37), engine load request from the driver
• crankshaft Hall sensor (B70), engine speed and crankshaft position (ignition circuit detection)
• RON default setting (Research Octane Number) with the Diagnosis Assistance System (DAS) (except code (494) USA version)

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 adjustment 
• Function sequence for RON correction 
• Function sequence for knock control adaptation 
• Function sequence for knock identification error 

Function sequence for ignition angle adjustment 

Knock control is enabled under the following operating conditions:

• coolant temperature >40°C
• engine load > 40%

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 sensors, the ignition angle for this cylinder is retarded by about a 3° crank angle (dependent on engine speed) at the next ignition. If knocking still occurs, the ignition angle is adjusted towards "retard" by about another 3° CKA, and so on until the maximum adjustment is reached (about 10 to 15° CKA).

If there is no knocking combustion, after a few ignitions the retarding the ignition timing is reversed in operation steps of about 0.75° crank angle, until the normal performance map value is reached, or until knocking occurs again.

Function sequence for RON correction 

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.

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 retardation of the ignition angle.

Function sequence for knock control adaptation 

Adaptation by the knock control becomes active starting from a coolant temperature of about 75°C.

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 speed).

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.

Function sequence for knock identification error 

For safety reasons, if one of the knocking sensor signals fails, the ignition angles of all cylinders is retarded by up to a 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.

	Electrical function schematic for knock control	MODEL 204	PE07.10-P-2715-97FAB
		MODEL 207	PE07.10-P-2715-97EAB
		MODEL 212	PE07.10-P-2715-97DAB
	Overview of system components motor electronics (ME-SFI) fuel injection and ignition system		GF07.61-P-9997MI