Dual CrIP

[Holmz]

How accurate is the CrIP in the Mx00 series?
I am assuming repeatable within some fraction of a degree, and I am not concerned with absolute accuracy, only repeatability.

So is it possible to have two measurements of the CrIP, and display one relative to the other?
I want to log the data as some function of RPM or time, and sampled pretty fast.

[MarkMc]

Hello Holmz,
There will be no problem with repeatability for the crip but obviously the accuracy of the ECU really depends on the information you are feeding it.....the old computer saying of "garbage in is garbage out".

What type of engine, crank trigger, crank sensor, mounting, etc?

I am not really sure what you are trying to achive or investigate.

[Holmz]

Hello Holmz,
There will be no problem with repeatability for the crip but obviously the accuracy of the ECU really depends on the information you are feeding it.....the old computer saying of "garbage in is garbage out".

What type of engine, crank trigger, crank sensor, mounting, etc?

I am not really sure what you are trying to achive or investigate.

Mark,

Wanting to measure crank twist and torsional resonance, on a Rover K-series.
The engines have few options for a harmonic balancer. One is the OEM HB, which comes apart pretty quickly at high RPM (debonds the outer ring from the inner ring). The other option is no HB, which results in eventual breakage of crank, or at least tearing it down and checking for cracking often.
So the sensible (?) thing I think I should do is to make a harmonic balancer.
But I need to be able to verify what it is doing before and after.

The front of the engine already has a crank trigger, but I will have to look up the teeth etc; and the more the better.
I will have to see what I can do for the rear of the engine; maybe some inserts into the engine side of the flywheel?
I'll need to keep the inserts in and not shoot them out, so I suspect that threaded inserts are not the go. And welding onto the flywheel also gives me a bit of heartburn; but perhaps some small dowels can be tig welded in without doing harm to the flywheel.???

I think that I figured I could probably get the data using a 192kHz sound card and record the crank signals off the front, and also use the flywheel to measure them off the back. And I already have a multichannel sound card.
Should be able to figure out the relative phase of the front versus rear of the engine.

I guess I will test out the sound card option using the front pickup and then decide what to do.
Thanks ~Holmz

[stevesingo]

What about measuring ring gear teeth?

[Holmz]

What about measuring ring gear teeth?

Thanks Steve... That could work.
192kHz at 8000 is 1440 samples per revolution, so I see no show stopper to it (assuming that the number of teeth is only a few hundred.

The easiest would be if the front and rear were the same signal, so I could do a relative phase of the signals.
Otherwise I might have to do something based upon the rising edge of the pulses.

[SportsCarRacer]

Ring gear teeth not much good...you need a HIGH precision pickup, and something with a high dat rate input.

Most (read all!) ring gears don't have enough tooth form precision (tooth tot tooth postion & form accuracy) to detect torsion vibrations....remeber you are looking in the order of 0.15-1.5 deg max for a sensible, late model, stiff crank engine (old crap that you would never fit EFI to is much worse, but that is why the broke cranks when revved & powered up).

I have done this test MANY times during OEM engine developemnt and durability, to analyse such crank breakages, and even with a high precison 1800 or 3600 pulse per rev OMRON Shaft Encoders (0.5 or 0.1 deg resolution!!!!!!!!!!!!!!!), TV (torsion vibration) surveys are difficult to conduct accurtately & repeatably...ususally is is done on the average of many individual cycles, and processed via a digital signal processor to detemine the amplitudes...the frequencies are usually readily apparent when passed thru a sprectrum analyser, and are dominant at certain engine orders (ie: 6cyl is 1.5, 3rd & 4.5 order harmonics)...believe me, destructive torsional vibes have got to be seen to be believed!!...broken oil pump rotors are a giveaway, usually caused by no damper on a 4 cyl with a not so stiff crank, and being revved into a resonant harmonic region that is probably only 10-12% above the production rpm band...(see 4age toyo engines with 7a stroker cranks in them!).....

I've tried to do the same thing you're attempting (i think!) and even using precison machined flywheel / crank pcilup wheel it is VERY difficult...but there is a way....but this is of signifiacance in many modern OBD2/EOBD cars for the purpose of misfire detection...emission requirements......they use algorithms to detect precise engine acceleration...but this is tricky, as it relies on your ref "missing tooth" and sync edges to be in area of the engine operation that are in regions of low angular acceleration.....eg:60-80 deg BTDC for a 6cyl....but if the flywheel mass is reduced, it makes detection even harder, as angular accels are much increased....aftermarket flywheels on OBD2 cars causing false misfire codes.

You really need to determine the CHANGE IN RELATIVE POSTION of the front of the crank to the rear...so the best way i have found on engines, in a car, is to have a high precsion pickup, say minimum 36 teeth to say around 60 teeth (with the gap, mirroring the crank sensor) machined for the flywheel....exact postion isn't important, we'll fix that later....

You need a 36 tooth min. wheel on the nose of the crank....say ford 36-1 or bosch 60-2...best to use the flywheel one (for this test) as your ref (it is ususally the node of the TV your are trying to measure!), and connect the other one into a dig-input and set it to measure angle (eg: cam angle from TDC#1...just like you would for cam control)....now, set the offset precisely (to 0.1deg) with the engine running as STEADY AS YOU CAN at 2000 rpm, NO LOAD (this is important)...bring it down to idle, and you may see some deviation hunting around the mean postion..

Now, at VERY LIGHT LOAD, ie: almost no cyl pressure, run the engine up through the rev range slowly ...say 10-20 rpm second up to max revs whilst logging the two channels plus rpm at 200hz minimum.

Now return to 2000 rpm, check offset to see it hasn't moved, and try again, but a FULL LOAD WOT (max cyl pressure and therefore max TV excitation)....compare the traces...if it's a 4 cyl, you should see bands of higher diplacement between the signals at the 2nd/4th/6th order's of rpm of resonance....but mainly, just look at the amplitude of the error angle between your DIG IN and your ref.....if it is noticeably bigger in amplitude than at no load, it is DEFINITELY RELATED TO TV issues....i have used this method several times and has always worked effectively....but getting high enough data rates is hard at high rpm....

AS a special "quick & dirty trick"...do the above test (loaded/unloaded ) with jsut the ref sesnor as it is now....if the rpm jump around a lot at WOT at say 600-1200rpm heavily loaded (engine labouring, but running smooth, at MAX MAP reading), but improves when you bring the load off it and run much lighter cyl pressure (ie: low MAP)reading), it's a good idea to investigate the TV side further....if it's not worse, or the rpm jumps around loaded & unloaded, your pickup trigger is shite and needs to be fixed!....the little cell ponter arrows on your fuel/ign tables should almost be rock steady, and their jitter shouldn't change between unloaded/loaded condition as described above...

if your were in Melbourne or nearby by, i could probably lend you some kit that would do a very good job...essentially a phase comparator between two precsion encoders....accurate to 0.1 deg...used to find cam/crank torsional vibrations affecting the drivetrain, and for validating VCT measurement & control...

But beart in mind, as littel as 0.4deg of TV (ie: 2/5 ofd bugger all) can kill a crank at high rpm, over enough cycles...most OEM stuff wouldn't be much more than 0.15...the worse i have seen on an engine is 1.4deg and it kept breaking oil pump gears.....


Good luck!

[Holmz]

Does anyone know of where torsiograph measurement is done in Australia?

[Holmz]

What is the spec for getting a good CRIP sensed?

I have a GT-101 hall effect sensor, and want to put some dowel pins coming out of the harmonic damper.

The question is will 1/8" dowel pins that stick up ~5-mm be enough to get a good trigger off of?
Or do they need to be higher and/or thicker to provide enough flux to get it to work?
Diameter is ~130-mm and the pins will be 10 degrees apart (in a 36-2 configuration of some sort)

[Holmz]

I can use this http://www.motec.com/filedownload.php/?docid=1308, but I do not have enough room for the height or the width for the tabs.

But if I use these rare earth magnetics http://www.rare-earth-magnets.com/p-14-nsn0577.aspx then I can have them flush, or just proud of the surface.

How much magnetic flux is acceptable?
And will that work?

[Scott@FP]

Holmz-

If you can find good info on the old mid-90's Chrysler setup, specifically the JTEC (Jeep Truck Engineering) ECU's it might help. They used a 36-x hall effect setup to detect misfires and knock. Any time you replaced the ECU, flywheel/flexplate or crank sensor you had to do an 'adaptive numerator' re-learn, which was a deceleration in low gear from high RPM so the ECU could learn the individual mass produced stamped or rough cut flywheel/flexplate trigger gaps. The system was quite sensitive, even an overly tight or loose serp belt would trigger misfires.