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

ENGINE 157.9 in MODEL 212, 218 

ENGINE 278.9 in MODEL 207, 212, 218 

Function requirements for knock control, general points 

• Circuit 87M (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:

• Left cylinder bank front knock sensor (A29/1)
• Left cylinder bank rear knock sensor (A29/2)
• Right cylinder bank front knock sensor (A30/1)
• Right cylinder bank rear knock sensor (A30/2)
• Left and right intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions (ignition circuit recognition)
• Left and right exhaust camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions (ignition circuit recognition)
• Coolant temperature sensor (B11/4) (model 207, 212), coolant temperature sensor (B11/4) (model 218)
• Charge air temperature sensor (B17/8)
• Pressure sensor downstream of throttle valve (B28/7), engine load
• Accelerator pedal module (B37), load request by driver
• Crankshaft Hall sensor (B70), engine speed and crankshaft position (ignition circuit detection)
• RON presetting (R  esearch-O  ctane N  umber) with Xentry Diagnostics

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 >30°C
• Engine load > 34%

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 adjusted towards "retard" (dependent on engine speed) by about 3° CKA (Crankshaft Angle). 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 a 15° crank angle).

If there is no knocking, after a few ignitions the retard adjustment 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 using Xentry Diagnostics by means of correction programming.

The regulated RON stage remains until stopping of the engine.

Function sequence for knock control adaptation 

Adaptation by the knock control becomes active starting from a coolant temperature of about 70°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.

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 12° 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 207	PE07.10-P-2715-97EAI
		MODEL 212	PE07.10-P-2715-97DAK
		Model 218	PE07.10-P-2715-97XAC
	Overview of system components for gasoline injection and ignition system with direct injection	ENGINE 157.9 in MODEL 212, 218 ENGINE 278.9 in MODEL 207, 212, 218	GF07.70-P-9998MM