Knock Control, Function - GF07.10-S-1015TRC

Engine 274 in model 447, 448 

except code XM0 (Facelift) 

Function requirements for knock control, general points 

• Circuit 87M ON
• Engine runs
• Coolant temperature > 30°C
• Engine load > 34%

Knock control, general points 

The knock control is integrated in the ME-SFI [ME] control unit (N3/34) and has the task to ensure knock-free engine operation under all operating conditions and when different fuel grades are used.

The ME-SFI [ME] control unit (N3/34) controls the knock control according to the following sensors and signals:

• Knock sensor 1 (A16/8) over a direct line
• Knock sensor 2 (A16/9) over a direct line
• Intake camshaft Hall sensor (B6/29) over direct line
• Exhaust camshaft Hall sensor (B6/30) over direct line
• Coolant temperature sensor (B11/21) over direct line
• Charge air temperature sensor upstream of throttle valve (B17) over direct line
• Charge air temperature sensor downstream of throttle valve (B1716) over direct line
• Intake manifold pressure sensor (B28/24) over direct line
• Accelerator pedal module (B37/4) over direct line
• Crankshaft Hall sensor (B70/2) over direct line
• RON default setting (Research Octane Number) 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 correction of the ignition timing 
• Function sequence for RON correction 
• Function sequence for knock control adaptation 
• Function sequence for knock identification error 

Function sequence for correction of the ignition timing 

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

If knocking is detected in a cylinder by the knock sensors, the cylinder's ignition timing is adjusted towards "retard" at the next ignition (dependent on engine speed). If knocking continues to occur, the ignition timing is adjusted further towards "retard", and so on until maximum adjustment is reached.

If knocking-free combustion exists, retarding of 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 

The research octane number correction can be set with XD.

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 timing of all the cylinders and the number of control interventions in certain engine load and speed ranges.

The RON stage is adjusted in one or several stages depending on the threshold which has been exceeded. 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 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 rpm).

When determining the individual ignition timings, the stored adaptation values are taken into account so that the optimal ignition timing can be determined immediately for each cylinder.

Function sequence for knock identification error 

For safety reasons, if the knock sensor signal fails, the ignition timings of all cylinders are "retarded" (dependent on engine rpm and coolant temperature) by up to 12°CKA (Crankshaft Angle). 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 characteristics map.

	Electrical function schematic for knock control	Engine 274 in model 448 except code XM0 (Facelift)	PE07.10-S-2715-97VDC
		Engine 274 in model 447 except code XM0 (Facelift)	PE07.10-S-2715-97TRC
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-S-9998TRC