Knock Control, Basic Function - GF07.10-P-1044A

Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 
  • Knock sensor system 
  • RON [ROZ] correction 
  • Adaptation 

General 

Knocking is a sudden, uncontrolled combustion of fuel in spark-ignition engines.

Knocking combustion takes place considerably more quickly than normal combustion. This subjects engine component parts to greater stress.

Knock control ensures that the uncontrolled combustion of fuel is prevented under all operating conditions. This also applies for differing fuel grades.

Knocking combustion is detected by knock sensors that are attached to the crankcase.

Function requirements 

• Engine management ON (circuit 87M)
• Engine in operation
• Coolant temperature > 30°C
• Engine load > 34 %

Function 

Knock sensor system 

When the knock sensors detect knocking, the ignition angle of the affected cylinder is adjusted towards "retarded."

If a knock sensor signal fails, the ignition angles of all cylinders (depending on engine speed and coolant temperature) are retarded by a maximum of 12° CKA before top dead center (BTDC). The knock control and the adaptation of the knock control are deactivated. A fault is stored in the fault memory.

The knock control takes the requirements of torque coordination into account. The following sensors are used for knock control:

• Knock sensors (knock signals)
• Camshaft Hall sensors (rpm signals of camshaft(s))
• Coolant temperature sensor (coolant temperature)
• Pressure and temperature sensor downstream of exhaust gas turbocharger (pressure and temperature)
• Accelerator pedal sensor (accelerator pedal position and accelerator pedal movement)
• Crankshaft Hall sensor (engine speed, position of the crankshaft)
• RON default setting (Research O ctane Number)

RON [ROZ] correction 

The task of the RON correction is to control the maximum timing retard of the ignition angles in advance, the knock control is thus relieved.

The higher the RON correction level, the smaller the maximum retard position of the ignition angle.

The following RON correction options are available:

• Permanently through correction programming
• Temporary, until the engine is switched off, through the automatic RON correction

If the automatic RON correction detects that the engine tends to knock frequently, the RON correction saves the following information and subsequently determines the RON correction level:

• Values for the adaptation of knock control
• Ignition angles of all cylinders
• Number of control interventions in particular engine load ranges and engine speed ranges

Depending on the engine's tendency to knock, the RON correction adjusts the correction level by one or multiple levels. This automatic RON correction level is retained until the engine is switched off.

Adaptation 

Adaptation also has the following function requirements:

• Coolant temperature > 75°C

To optimize the knock control for specific cylinders, the following values are continually stored:

• Ignition angle correction
• Engine speed
• Engine load

These stored adaptation values are taken into account when determining the individual ignition angles.

	Function schematics
	Function schematic for knock control	Engine 282 in model 118, 177, 247	PE07.61-P-2501-97A
		Engine 260 in model 118, 177, 247 Engine 264 in model 167	PE07.61-P-2501-97B
		Engine 256 in model 167 Engine 256 in model 213, 238 as of model year 2021 Engine 264 in model 213, 238, 257 as of model year 2021	PE07.61-P-2501-97C
		Engine 176, 177 in model 167 Engine 177 in model 290 as of model year 2021	PE07.61-P-2501-97D
		Engine 139 in model 118, 177, 247	PE07.61-P-2501-97E
		Engine 254 in model 206, 254 Engine 256 in model 223	PE07.61-P-2501-97F
		Engine 176 in model 223	PE07.61-P-2501-97G
		Engine 279 in model 223	PE07.61-P-2501-97H
		Engine 139 in model 206, 232	PE07.61-P-2501-97I
		Engine 177 in model 223, 232	PE07.61-P-2501-97J
		Engine 274 in model 213 as of model year 2021	PE07.61-P-2501-97K
	Additional basic functions
	Ignition angle setting, basic function		GF07.10-P-1046A
	Combustion engine control unit, basic function		GF07.08-P-9890A
	Knock sensor, basic function		GF07.04-P-2001A