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

Engine 264.9 in Model 205, 253 

Function requirements, general 

• Engine runs

The ME-SFI [ME] control unit (N3/10) detects the Engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

Knock control, general points 

The function of the knock control is to ensure operation without uncontrolled Engine combustions (knocking) for different fuel grades and all operating conditions. If the sensor system detects knocking combustion, the ME-SFI [ME] control unit adjusts the ignition of the affected cylinder in the "retarded" direction.

The ME-SFI [ME] control unit regulates the knock control dependent on the following signals:

• Knock signals

  Knock sensor 1 (A16/1)

  Knock sensor 2 (A16/2)

• Intake camshaft position (ignition circuit detection)

  Intake camshaft Hall sensor (B6/15)

• Exhaust camshaft position (ignition circuit detection)

  Exhaust camshaft Hall sensor (B6/16)

• Coolant temperature

  Coolant temperature sensor (B11/4)

• Engine load

  Pressure and temperature sensor downstream of throttle valve (B28/27)

• Accelerator pedal position

  The powertrain control unit (N127) reads in the accelerator pedal sensor (B37) signals directly, and transmits the accelerator pedal position via the drive CAN (CAN C1) to the ME-SFI [ME] control unit.

• Engine speed and crankshaft position (ignition circuit detection) Crankshaft Hall sensor

The requirements of the torque coordination function are also taken into account.

If a knock sensor fails, the ignition angles of all cylinders are adjusted by up to 12° in the "retarded" direction for safety reasons. The knock control is blocked and a fault is stored in the fault memory.

The research octane number (RON) can be changed using the diagnostic tester. The ME-SFI [ME] control unit adapts the knock control accordingly.

The knock control detects a persistently high knocking tendency and accordingly counteracts this. To do this, the knock control evaluates the number of control interventions in certain Engine load and RPM ranges. From a defined threshold, the presetting (RON stage) is changed.

Ignition angle setting 

Knock control is enabled under the following operating conditions:

• Coolant temperature above 30 °C
• Engine load above 34 %

The ME-SFI [ME] control unit evaluates all incoming information and calculates the cylinder-specific ignition angle corrections.

If knocking combustion is detected at a cylinder, the ME-SFI [ME] control unit adjusts the ignition angle at this cylinder by approx. 3° in the "retarded" direction as of the next ignition. If further knocking combustion is then detected, the ME-SFI [ME] control unit adjusts the ignition angle by an additional 3° in the "retarded" direction. The ignition angle can be adjusted by a maximum of 15° in the "retarded" direction. When the combustion is then free of knocking, the ME-SFI [ME] control unit gradually reduces the retarding (steps of approx. 0.75°) until the normal performance map value has been reached or knocking starts again.

The ME-SFI [ME] control unit actuates the following components for the ignition angle setting:

• Cylinder 1 ignition coil (T1/1)
• Cylinder 2 ignition coil (T1/2)
• Cylinder 3 ignition coil (T1/3)
• Cylinder 4 ignition coil (T1/4)

Adaptation of knock control 

The adaptation of the knock control is active from a coolant temperature of 75 °C The ignition angle corrections required due to combustion knocking are stored continuously in a cylinder-specific way, together with the respective operating state of the Engine (Engine load and Engine RPM). If knocking combustion starts again, the stored adaptation values are taken into account so that the optimal ignition angle can be set immediately for each cylinder.

	Electrical function schematic for knock control		PE07.10-P-2715-97FBI
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRS