Knock Sensors

Thread Starter

Tree1

Joined Nov 30, 2010
46
Or can anyone please explain the relationship between acceleration and frequency for knock sensors ? How does one affect the other?
 

Thread Starter

Tree1

Joined Nov 30, 2010
46
And yes, I've googled knock sensors. I do have a lot of info. but I'm still confused as to the relationship between these two parameters and voltage.The sensor is senstive to acceleration. If the acceleration is constant and the frequency is increased what happens to the output ?? Is there a direct relationship between the two? I just really want to what happens to acceleration as frequency is increased or vice versa.
 

KMoffett

Joined Dec 19, 2007
2,918
Is the knock sensor sensitive to acceleration?... or is it just that the engine computer inputs a knock signal from the knock sensor, and interprets acceleration from a speed sensor?

Ken
 

Thread Starter

Tree1

Joined Nov 30, 2010
46
Hmm, well technical info. that I have indicates that the sensitivity is measured in mV/g. Sensitivity at 5kHz 26 (+/_ 8) mV/g. It seems to be sensitive acceleration.
 

KMoffett

Joined Dec 19, 2007
2,918
The acceleration (i.e. at 5KHZ) is probably indicating the sensor response to motion due the detonation in the cylinder, not motion of the vehicle. Do you have a link to the datasheet?

Ken
 

Thread Starter

Tree1

Joined Nov 30, 2010
46
Yes, http://www.bosch-motorsport.de/pdf/sensors/knock/KS-P.pdf. Yes I agree with your last statement but whether its acceleration of the sensor or vehicle. I just wanted to know the relationship between frequency and acceleration for these type of sensors. If the frequency of the vibrations increases does that mean the acceleration will increase. Is there direct relationship between the frequency of the knock and the acceration of that vibration creating that knock ?
 

KMoffett

Joined Dec 19, 2007
2,918
Within limits, the frequency and the acceleration will be independent of each other. The output voltage amplitude will be proportional to the acceleration. Frequency will determine whether it's knock, as opposed to other vibrations of the engine. Acceleration will determine how severe the knock is.

Ken
 

debe

Joined Sep 21, 2010
1,389
A Knock sensor on an engine is listening for pre ignition knocks, these signals are sent to the ECU & filtered. The resulting signal is used to alter IGN timing. In Fords which i trained on, the ECU ramps up the timing untill there is pre inition which the Knock sensor detects, then the timing is retarded, the process is then repeated. All this happens very quickly. The knock sensor is only a piezo transducer being used as a microphone so to speak. It is not an acelleration sensor on an engine.
 

Thread Starter

Tree1

Joined Nov 30, 2010
46
Thank you!!!!!!!!!!!!!!!!!!!!! Soo much guys!. Thanks for this clarification! A special thanks to Kmoffett.
 
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