I ran across some questions about the knock sensor & piezo sensor on the test questions, but I can’t find any information in the book for them. Do any of you guys know we’re Danner explains the operation of them at? Thanks
I ran across some questions about the knock sensor & piezo sensor on the test questions, but I can’t find any information in the book for them. Do any of you guys know we’re Danner explains the operation of them at? Thanks
Piezo sensor basically produce a voltage when they are subject too mechanical vibration. They generate a voltage each time the vibration peaks and reverses as you can imagine on an vehicle engine this is a very noisey signal output. When it occurs engine combustion knock produces a shockwave in a very narrow frequench range by using very clever digital signal processing this is cleaned to extract only the signature of the knock shockwave and this can be used by the engine computer to retard the ignition or reduce boost or reduce drive by wire throttle opening.
A few points to note.
The easiest definative test to do on a knock sensor is to connect an oscilloscope to the sensor a tap the cylder block close to the sensor with a tool such as a socket exension watch the output trace of the scope. I would suggest a 500ms screen .
A knock sensor needs to be bolted firmly in its original location on the engine.
The mechanical and electronic design of the sensor is tailored to a specific engine --- not just the engine family but engine size cylinder bore size has an effect on the frequency of the knocking sound.
On some modern sensors digital processing of the raw signal occurs within the sensor before it goes to the engine computer.
Topic Author
