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Knock control

Knock control


A high compression ratio is favourable for engine efficiency and thereby fuel consumption. The tendency of the engine to knock increases with the compression ratio, however, so a compression ratio is selected that is as high as possible with regard to the knock resistance of the engine's recommended fuel. Knock control in modern engines is not a safety function but a normal one. Therefore, there is nothing wrong with knock control being active during normal operation.

Trionic T7 does not have a conventional knock sensor. Instead, the ignition discharge module analyses the ionization current across the spark plug gap on all cylinders and sends a knock signal from each cylinder to control module pin 38.

From the combustion signals, the control module will be aware of which cylinder has fired and if a knock signal above a certain level is registered at the same time by the control module, it will gradually retard the ignition for the cylinder in questio n until the knocking ceases. Timing correction then returns slowly to zero.

If the mean value of the ignition retardation on all cylinder exceeds a certain level, fuel enrichment will take place. If the mean value of the ignition retardation on all cylinders increases further despite fuel enrichment, the maximum permissible air mass/combustion will be limited.

The control module expects the knock signal to be at a certain level as the spark is produced, so it will therefore start the actual knock detection in the respective cylinder only after the spark has been produced.

Diagnostics


• If there is an open circuit or a short circuit on the knock lead between the ignition discharge module and the control module, diagnostic trouble code P0327 will be generated.