P07.04-A021-79
Example illustration |
1.1 | Knock sensor 1 | 1.2 | Knock sensor 2 |
Overview
This document contains information on:
General
Function
General
The knock sensors each record the vibrations at the crankcase which occur in the individual cylinders during combustion.
The knock sensors send the detected vibrations as voltage pulses to the combustion engine control unit.
Knock sensor signal |
U | Electrical voltage |
a | Signal curve in the case of controlled combustion |
b | Signal curve in the case of uncontrolled combustion (knocking) |
c | Oscilloscope |
t | Time |
P07.04-2247-12
Function
The knock sensors essentially 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 caused by the knocking combustion occur at the crankcase, these are adapted by the seismic mass in the knock sensors. 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 the knock sensors no longer detect any knocking noises. Knock control with knock sensors permanently keeps the combustion engine close to the so-called knock limit, thereby optimizing the engine output.