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

Engine 274 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 

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 from the camshaft/camshafts)
• Coolant temperature sensor (coolant temperature)
• Pressure and temperature sensor downstream of exhaust gas turbocharger (pressure and temperature downstream of exhaust gas turbocharger)
• Accelerator pedal sensor (accelerator pedal position and accelerator pedal movement)
• Crankshaft Hall sensor (engine speed, position of the crankshaft)
• RON default setting (R  esearch O  ctane N  umber)

RON [ROZ] correction 

The task of the Research Octane Number correction (RON correction) is to control the maximum retard position of the ignition angle in advance, through which the knock control is 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
	Electrical function schematic for knock control	Engine 274 in model 907	PE07.10-D-2715TSA
	Additional basic functions
	Ignition angle setting, basic function		GF07.10-D-1046A
	Control units
	Combustion engine control unit, basic function		GF07.08-D-9890A
	Components
	Knock sensor, basic function		GF07.04-D-2001A