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

Engine 176.9, 177.9 in model 463 

as of model year 2019 

Function requirements for knock control, general points 

• Circuit 87M (Engine management ON)
• Engine runs

The circuit relay87M (K40/8 kN) is switched on for circuit 15 ON.

Knock control, general points 

The knock control is integrated in the ME-SFI control unit (N3/10) and has the task is to ensure knock-free engine operation when different fuel grades are used and under all operating conditions. In the case of uncontrolled combustion (knocking), the ignition angle of the ignition coils for cylinder 1 + 2 to cylinder 7 + 8 (T4 to T4/3) for the related cylinder is adjusted in direction of "retard."

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

• Knock sensor 1 (A16/1)
• Knock sensor 2 (A16/2)
• Knock sensor 3 (A16/3)
• Knock sensor 4 (A16/4)
• Left intake camshaft Hall sensor (B6/4) and right intake camshaft Hall sensor (B6/5), intake camshaft positions (ignition circuit detection)
• Left exhaust camshaft Hall sensor (B6/6) and right exhaust camshaft Hall sensor (B6/7), exhaust camshaft positions (ignition circuit detection)
• Coolant temperature sensor (B11/4), coolant temperature
• Left charge air temperature sensor (B17/14) and right charge air temperature sensor (B17/15), charge air temperature
• Pressure sensor downstream of left throttle valve (B28/22) and pressure sensor downstream of right throttle valve (B28/23), engine load
• Accelerator pedal sensor (B37), load request by driver
• Crankshaft Hall sensor (B70), engine speed and crankshaft position (ignition circuit detection)
• RON default setting (Research Octane Number) over Xentry Diagnostics

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

Function sequence for knock control 

The knock control function includes the following subfunctions:

• Function sequence for ignition angle setting 
• Function sequence for RON correction 
• Function sequence for knock control adaptation 
• Function sequence for knock identification error 

Function sequence for ignition angle setting 

Knock control is enabled under the following operating conditions:

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

According to its input signals, the ME-SFI control unit computes the cylinder-specific ignition angle correction.

If knocking is detected on one of the cylinders by the knock sensors, its ignition angle (depending on engine rpm) is adjusted in direction of "retard" as from the next ignition by approximately 3° crank angle (CKA). If knocking still occurs, the ignition angle is retarded by about another approximately 3° crank angle and so on until the maximum shift value is reached (15° CKA).

If there is no knocking combustion, after a few ignitions the retarding the ignition timing 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 of 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 rpm). 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 its adaptation are deactivated and a fault is stored in the fault memory.

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