Knock Sensor

Regarding their principle of functionality, knock sensors are basically vibration sensors and are suitable for detecting structure-borne acoustic oscillations. These occur as “knock” for instance in a vehicle's engine when uncontrolled ignition takes place, and are converted into electrical signals by the sensor and inputted to the ECU. As a rule 4 cylinder in-line engines are equipped with one knock sensor; 5 and 6 cylinder engines, with two; and 8 and 12 cylinder engines have two or more. They are switched in accordance with the ignition sequence. Thanks to their robust design, these vibration sensors can withstand even the most severe operating conditions.

The main areas of application for these sensors include:

• Knock control for internal combustion engines.
• Machine tool protection.
• Cavitation detection.
• Monitoring of pivot bearings.
• Anti theft systems.

Operation

On account of its inertia, a mass exerts compressive forces on the piezoceramic element in the same rhythm as the vibrations causing them. As a result of these forces, charge transfer occurs within the ceramic element and a voltage is generated between the upper and lower sides of the ceramic element. This voltage is tapped via contact washers, often filtered and integrated, and is available for use as a measurement signal.

Installation

The sensors must rest directly on their metal surfaces. Use must not be made of packing plates, spring or toothed lock washers for support. The contact surface of the mounting hole must be of high quality to ensure low resonance coupling of the sensors to the measurement location. The sensor cable is to laid so that no resonance vibration can occur. The sensor must not be allowed to have contact with liquids for any lengthy periods.

Bosch Knock Sensors are competitively priced and sold through leading automotive part stockists. Please see our ‘Dealer Locator’ at the top of the page to locate you local store.