Symbol for a knock-sensorTypical knock sensor.This is a piezo-crystal sensor bolted into the crankcase of a petrol engine. Its purpose is to detect rapid pressure rises in the combustion cylinders. This normally happens when something other than the spark plug initiates the combustion process.

Such events can very quickly damage the pistons and cylinders of an engine. It is vital that the ECU knows when they are begining, so that it can take corrective action (retard ignition timing, and possibly inject extra fuel in order to cool the cylinders).

Piezo crystal will emit a small voltage whenever it is stressed. If we put this crystal into a suitable housing and bolt it to the side of the engine, it will detect all combustion events, and emit a small electrical signal which reflects these events. Should knock occur, the frequency and amplitude of the signal will change, and this change can be detected by the ECU, which will then take corrective action.

» Course Glossary


Please note, if you want to contact the main Training Centre in Baldoyle, you need to ring 01-8167400.

If you want to contact the CP Fitters' Section, you can Contact Us by email, admin@cpfitters.info, or by telephone: 00 353 1 8167543 This number gets you through to the CP Fitters' Section, Baldoyle Satellite Unit.

Our Address is : Construction Plant Fitters' Section, Unit 116, Grange Way, Baldoyle Industrial Estate, Baldoyle, Dublin D13 CA48.
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