Knock Detector System – Features To Look For4 min read
If you are in the market for an engine knock detector system, here is a list of features we think are nice to have. From identifying knock to increasing detection accuracy to allowing fine tuning, these features all add something.
Cylinder detection – RPM detection – Detection window (frequency) – Detection window (degrees of crank rotation) – 5v & 12 volt outputs – Variable output signal – MAP/Engine load detection – Adjustable threshold volume – Adjustable frequency detection range – Knock frequency detection
Engine Knock Detector – Features To Look For
Here are some great features for an engine knock detector to have (in no particular order).
Adjustable detection frequency
Be able to adjust which frequency counts as knock. This allows us to customise the detection primarily based on cylinder bore but also allows us to compensate for wiring and knock sensor mounting location.
Detect knock frequency
There are knock frequency calculators, they calculate the knock frequency solely based on cylinder bore diameter. However they can’t help us identify potential inaccuracies of the knock sensor we are using, effects due to where the knock sensor is mounted or issues related to the wiring.
A knock sensor system which offers us the ability to visually identify the knock frequency of our specific engine is highly beneficial. Being able to identify the knock frequency also lets us tune our audio knock detection tools.
Adjustable threshold volume
Every knock detection system we have seen will have a volume threshold, above which will be identified as knock. Having an adjustable threshold allows us to customise that threshold volume according to different inputs such as RPM and/or engine load. Having this ability allows us to more precisely optimise the engine for different engine conditions.
5v and 12v output
Having a visual and/or audio knock indication built into the knock detector unit is better than nothing. However it is nice to have some output so the user can hook up whatever indicators or indication methods he or she wishes to use.
5v is nice/essential for connecting the knock system to an ECU and the 12v output can be used to trigger buzzers or lights. The knock detector unit will usually have a bundle of wires coming out of it. Its not ideal to have to mount this unit in a place where you have to see it to get the visual or audio indication. A 12v output allows to use something discreet like LED.
Variable output 5v
A digital 5 volt output is nice, a variable 0-5v output is even better. A variable output lets us tell whatever device its connected to the intensity of the knock.
Detection window (frequency)
This is a continuation of the knock frequency adjustment. The difference here is being able to select a minimum and maximum frequency that will count as knock rather than picking one frequency or having a non adjustable window around that frequency. An adjustable frequency lets the user choose a narrow or wide frequency window.
Detection window (degree of crank rotation)
Listening for knock according to degrees of crank rotation. Engine knock occurs in a window (approximately) between TDC and 40 degrees ATDC. If we can listen to the knock sensor only in this window, we can help the detection system eliminate any noises that we know cannot be knock. This has the potential to improve knock detection accuracy.
The noise coming from the engine will differ in volume and frequency makeup according to RPM. If the knock detection system has an RPM input, it opens up the possibility of being able to program the system with different knock intensity thresholds according to the engine RPM, again, increasing knock detection accuracy. Also it may or may not be helpful to adjust the knock frequency according to RPM
If we can adjust our knock volume threshold according to engine load, we can increase our knock detection accuracy. If we can detect knock not only at wide open throttle (when it should be loudest) but also at part throttle, our knock detector can help us optimise our engine tune in more conditions. Sure wide open throttle is where maximum power is but finding optimum ignition timing at part throttle will also improve engine efficiency.
Being able to identify which cylinder is knocking. The benefits of being able to do this are obvious. It allows us to adjust ignition timing for individual cylinders, it can also help us identify potential issues in the motor for example a fuelling problem on a specific cylinder. This has the potential to increase engine efficiency, engine safety, engine reliability and engine power.