ME knock control function - GF07.61-P-4031G
ENGINE 273 in MODEL 463.202/222/236/237 up to 31.5.12 as of model year 2009/YoM 08
Function requirements for knock control for the ME-SFI gasoline injection and ignition system (engine electronics) (ME), general points
- Circuit 87M ON (engine control ON)
- Engine running
ME-SFI knock control, general points
Knock control is integrated in the ME-SFI [ME] control unit 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 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, right
- Knock sensor 2, left
- Hot film MAF sensor, engine load
- Intake air temperature sensor,
- LH and RH intake camshaft Hall sensor, intake camshaft positions (ignition circuit detection)
- LH and RH exhaust camshaft Hall sensor, exhaust camshaft positions (ignition circuit detection)
- Coolant temperature sensor
- Pressure sensor, intake manifold air pressure
- Accelerator pedal sensor, load request made by driver
- Crankshaft Hall sensor, engine speed and crankshaft position (ignition circuit detection)
- Presetting (research octane number) using the Diagnosis Assistance System (DAS) (without code (ZU8) USA version)
The requirements of the engine torque-requirement function are also taken into account.
ME-SFI knock control, function sequence
The function sequence consists of the following subfunctions:
- Ignition angle adjustment function sequence
- Function sequence research octane number correction
- Knock control adaptation function sequence
- Knock identification error function sequence
Ignition angle adjustment function sequence
Knock control is enabled in the following operating conditions:
- Coolant temperature > 40°C
- Engine load > 40%
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 a 3° crank angle (KW). If knocking still occurs, the ignition angle is adjusted towards "retard" by about another 3°CKA, and so on until the maximum adjustment is reached (about 10 to 15°CKA).
If there is no knocking, after a few ignitions the retard adjustment is reversed in steps of about 0.75° crank angle, until the normal performance map value is reached, or until knocking occurs again.
Function sequence research octane number correction
The correction can be preset with the DAS using the correction programming (without code (ZU8) USA version).
Knock control is also fitted out with an automatic switch. This detects a persistent high knocking tendency 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 angle of all the cylinders and the number of control interventions in certain engine load and speed ranges.
Depending on the threshold which has been exceeded, the stage is adjusted by one or several stages. The regulated stage remains until stopping of the engine.
The higher the stage selected, the lower the maximum retardation of the ignition angle.
Knock control adaptation function sequence
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 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. During abrupt acceleration, no values are stored for about 2 seconds in order to avoid any incorrect adaptation values.
Knock identification error function sequence
For safety reasons, if one of the knocking sensor signals fails, the ignition angles of all cylinders is retarded by up to 11° 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.
| Component description for ME-SFI [ME] control unit | N3/10 | GF07.61-P-6000G |