Knock control

The engine is equipped with a cylinder-specific, adaptive knock control system. The knock sensor detects knock during combustion. The sensor signal is processed and evaluated in the DME control unit. Operation of an engine with knocking combustion over a prolonged period can lead to serious damage. Knocking tendency is increased by:

• Increased compression ratio
• High cylinder filling
• Poor fuel grade (RON/MON)
• 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. For engines without knock control, these unfavorable effects must be taken into consideration when designing the ignition system by applying a safety margin to the anti-knock limit. However, this results in unavoidable losses in efficiency in the upper load range. The knock control prevents knock. It retards the ignition point of the affected cylinder(s) (cylinder-specific) only as far as necessary and only if there is an actual risk of knocking. In this way, the ignition timing map can be adapted to the optimum consumption values (without having to take the knock limit into consideration). A safety distance is no longer necessary. The knock control performs all the necessary corrections to the ignition point due to knock and also makes trouble-free driving with regular grade gasoline (minimum RM 91) possible. The knock control provides:

• Protection against damage resulting from engine knock (also under unfavorable conditions)
• Lower consumption and higher torque over the entire upper load range (corresponding to the fuel grade used).
• High levels of economy thanks to optimal exploitation of the available fuel grade (octane level) and the ability to compensate for variations in the engine's condition

Self-diagnosis of the knock control system includes the following checks:

• Check for signal failure or interference, for example, from an open wire or defective plug connection
• Self-test of evaluation circuit
• Check of the noise level picked up by the knock sensor for the engine

The knock control system is switched off if a fault is found during the course of one of these checks. The emergency program adopts the task of controlling the ignition angle. At the same time, the relevant fault is entered in the DME fault memory. The emergency program ensures damage-free operation as from minimum RON 91. It depends on the engine load, speed and engine temperature.