it can from what i have been told, as it still goes away from the MBT
-
-
So, today I raised the ignition a lot in order to see where the engine will start to knock and noticed the following: with the old ignition table I was getting at 1 bar and above a more metallic noise something like in the file Marc posted. Today it was at 0.3 a distinctive sound not metallic but more solid. Something like when someone grounds a cable connected to a hifi amp.
Hearing is with a cable as Marc suggested (unfortunately I can't record because my laptop has no line in- I hear it through the car stereo).
Any ideas?
Can someone maybe record his car during a full boost run? I want to hear how a healthy engine in full boost from 2000-7000 sounds.Go Holset or Go RS4Comment
-
Here some random clips from the net to demonstrate the difference.
The first sound i get when i raise the timing advance is a clicking sound like in this clip (go to 6:50).
When i drop the timing then i am hearing this sound (but much much less intensity - consider it between the 4000 RPM non knock and 4000 RPM knock area):
Go Holset or Go RS4Comment
-
I have made a better shielded cable and now the sound quality is very good. I am using the audio input of a motorcycle intercom and the sound quality and dB are very good.
I have also made a det can but I need a good position to mount it. The IM (as suggested in other engines) is way too far to hear minor det.
When I hear the knockbox reference files, found on the 3 post I think in the first page, you hear that at the regions where it should not have any knock there is a noise like engine harmonics that are not dangerous. The middle sections where the raise the ignition it is clear to hear knock just as rain falls on a metal sheet.
In Marc's file we hear at sec 21-24 a sound similar to the sound that you can get from flexing a piece of sheet metal.
The question is what of both is dangerous?
Can please someone experienced describe it please?Go Holset or Go RS4Comment
-
Since there is so much interested in the subject i thought that you would also be interested in this!!!
A kind member of the DIYAudio forum calculated this bandpass filter for me (thanks Frank)!!!
Graph
Schematic
Go Holset or Go RS4Comment
-
today i managed to put toghether this bandpass filter. I run Marc's knock file through it and here is the result. Main issue is that it takes many dB from the overall loundness.
Go Holset or Go RS4Comment
-
I have also made some measurements with a Speaker test programm and a plain mikrofon to see how the frequency output would be with and without the filter.
The peak between 3-4000hz come from the speaker i am using to play the sound as you can see it is apparent on both measurements.Go Holset or Go RS4Comment
-
I don't have time atm to listen through everything, but I can write a bit about how Motronic works...
AFAIK there is no frequency filtering in Motronic 2.3.2... the frequency filter is built into the knock sensors.
There are three gates - one for knock window, and one on each sensor to select which sensor to listen to.
Then there is a special resistor array that it controls, and using that resistor array it selects gain. It dynamically alters gain based on noise.
The most important thing to make a good knock detection system is knock window. Without knock window, you will never reach a very good result. Motronic uses hall sensor for that, to determine engine phasing and time the knock window and knock sensor select events.
As for the knock sound - yes, it is like you ground a hifi cable, a sharp high pitch chirp.
About detcans - try to make electronical detcans using an amp, you can use a cheap china hearing device or alternatively a motorcycle intercom. Then attach a condenser mic to a clip, embed it in glue(!) and use shielded(!!!) wire to run it into the cabin.
I attach the clip to the stock knock sensor bolt at the back of the engine, and I can hear everything perfectly.
Because the mic is in glue, it only picks up vibrations, so you don't hear useless things.Comment
-
can i foreward this to the VEMS Wiki? It may be helpful with the knock sensing development.Go Holset or Go RS4Comment
-
I don't see why not...
VEMS needs cylinder-selective knock recognition with proper knock window.
The way motronic works is, after every ignition event, after the knock window passes, it runs an algorithm (threshold mappable, some other things too) to determine whether knock has occured.
If knock has occured, next time an ignition event happens, timing is retarded for that cylinder.
Knock control is adaptive, this means that it retards the timing based on a constantly changing map. In that map it remembers how many times it had to step back from the base timing before to achieve knock free operation. Then it starts slowly advancing the timing back up.
You don't see any of that happening in VAG-COM, this is all handled by boost/knock chip.
If the knocking is persistant, then the boost/knock chip sends a request to the fuel chip to increase safety. Based on some parameters the fuel chip decides if it should step down a map (to lower octane timing map) or to enrich fuel. This is when you see a jump in timing or IPW in VAG-COM.
If knocking continues, or if the knocking was on many cyls in a row, it also starts cutting boost bit by bit...Comment
-
Btw, in newer Motronics this is handled by a separate chip, which also has bandpass filter.
It is Bosch CC195, http://common.leocom.jp/datasheets/174382_22751.pdf or newer chips.
In the old Motronics it is an analogue schematic on the board and a bandpass filter is built into the knock sensors themselves.
There is a less proprietary circuit, from Texas Instruments, which should handle knock detection quite well. VEMS needs something like that...
Here is the datasheet:
And here is an interesting paper about knock detection from TI:
I suggest reading it, worth it's value in gold
Comment
-
made a new knock sensor recording. What do you think?
Go Holset or Go RS4Comment
-
any comment? Does it sound healthy?Go Holset or Go RS4Comment
Comment