Knock Sensor, Basic Function - GF07.04-P-2001A

Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 

Engine 177, 256 

Example illustration of knock sensor 

Overview 

This document contains information on:

• General 
• Function 

General 

The knock sensors (1.1, 1.2) detect, in each case, the vibrations at the crankcase that arise during the combustion in the individual cylinders.

The knock sensors (1.1, 1.2) transmit the detected vibrations as voltage pulses to the combustion engine control unit.

Example of knock sensor signal 

Function 

The knock sensors (1.1, 1.2) basically consist of a moving seismic mass and a layer of solid piezo crystals.

The vibrations at the crankcase are transmitted via an inertia mass to an inner piezoelement and are converted into electrical voltage pulses.

If the extraordinary vibrations that arise due to the knocking combustion occur at the crankcase, these are adapted by the seismic mass in the knock sensors (1.1, 1.2). The striking of the seismic mass impact against the piezo crystals generates a voltage signal which can be detected by the combustion engine control unit.

As a result, the firing point is retarded until no knocking noises whatsoever are registered by the knock sensors (1.1, 1.2). Via the knock control with knock sensors (1.1, 1.2), the combustion engine is permanently kept close to the so-called knock limit and the engine output is optimized.