Knock control

The engine is equipped with a cylinder-selective adaptive knock control.

4 knock sensors detect combustion knock (cylinders 1 and 2, cylinders 3 and 4, cylinders 5 and 6, cylinders 7 and 8). The sensor signals are evaluated in the DME control unit.

If the engine is operated with combustion knock for longer periods of time, this can cause serious damage.

Knock is encouraged by:

• Increased compression ratio
• High cylinder fill levels
• Inferior fuel grade (RM/MM)
• High intake-air and engine temperature

The value of the compression ratio can also become too high due to spread due to deposits or the manufacturing process. On engines without knock control, these unfavorable influences must be taken into account. The design of the ignition system must include a safety gap to the anti-knock limit. This makes reduced efficiency in the upper load range unavoidable.

The knock control prevents knock. The firing point of the relevant cylinder (cylinder-selective) is set as far as possible in the retarded direction only when a knocking risk is present.

This means that the ignition control grid can be designed around ideal consumption values (without having to take the antiknock limit into account). A safety margin is no longer necessary.

The knock control performs all the necessary corrections to the firing point due to knock and also makes trouble-free driving with regular grade gasoline (minimum RM 91) possible. The knock control provides:

• Protection from damage caused by knock (also in unfavorable conditions)
• Reduced consumption and increased torque throughout the entire upper load range (according to the quality of fuel used)
• High economic efficiency through optimum use of the available fuel quality and by taking the specific engine condition into account

The knock control self-diagnosis performs the following checks:

• Check for signal interference, e.g. breaks in wiring or defective connector
• Self-test for evaluating circuit
• Check of engine noise level recorded by the knock sensor

If a fault is identified during one of these checks, knock control is deactivated. An emergency program assumes control of the ignition angle. A fault is simultaneously registered in the fault memory. The emergency program guarantees damage-free operation from a minimum of RON 91. The emergency program depends on the load, engine speed and engine temperature.