GF07.10-P-1015MMI Knock Control, Function

GF07.10-P-1015MMI Knock Control, Function
ENGINES 152.9 in MODEL 172.4

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 in all operating conditions and when different fuel grades are used. In 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:

- Knock sensor 1 (A16/1)
- Knock sensor 2 (A16/2)
- Knock sensor 3 (A16/3)
- Knock sensor 4 (A16/4)
- LH and RH intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions (ignition circuit detection)
- LH and RH intake camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions (ignition circuit detection)
- Coolant temperature sensor (B11/4)
- Intake air temperature sensor (B17)
- 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 (Research-Octane Number) with Xentry Diagnostics

The requirements of the engine torque requirement function must also be taken into account.

Function sequence for knock control
The function sequence is described in the following Operation 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 in the following operating conditions:

- Coolant temperature greater than 30°C
- Engine load greater than 34%

According to its input signals, the ME-SFI [ME] control unit calculates 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" (depending on engine speed) by about 3° CKA (Crank Angle) at the next ignition.
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.