Crank+Cam based input pattern support requests thread

[ababkin]

I should also add that because of the other things I mentioned, the tooth count in them is usually small, and thus the gaps between the teeth get larger, and consequently the ability for the engine to accelerate and change rpm between the EMS's only way of knowing about it is much greater.

If you put fine teeth in so that that accuracy is there, then the jitter and play etc cause even more pronounced effects.

I think you are confusing accuracy that i was referring to with the update rate. I was referring to the accuracy of the measured cam phase in relation to the crank phase. As long as you need this data accurately only once per crank revolution, 1 tooth is enough.
Essentially my algorithm of measuring this phase difference would be:
- have hardware interrupt on both triggers (duh)
- timestamp every crank tooth
- in the event of encountering an f/r or r/f edge on cam wheel, timestamp it and compare to the timestamps of the previously triggered crank teeth (within a certain history window) to determine the phase shift in terms of time difference.
- using an averaged RPM (or RPM history for past teeth for more accuracy) determine the phase difference in terms of angle. Add some fudge-factor for the valvetrain slack (as a function of the crank or cam position) and we get what we need.

(my point is that IMO number of crank teeth doesn't matter unless you want accurate phase shift determination more than once every crank revolution, which i believe is excessive and not needed)

[Fred]

I'm certainly not confusing them, however I may not have been articulating myself very well.

I was simply trying to convey that there were two issues with trying to use a camshaft only for full engine control. Since you understood that, I guess what I said was clear enough. I did not mean to imply that both things mattered to you, and I apologise if that is how it seemed. Rather I was ensuring that any readers of this (not vvt specific) thread are clear as to what a cam trigger can and cannot do well.

Admin.

[ababkin]

No problems, thats why we clarify things

So for the case of no vanos/vvt, i am guessing the only use of the cam wheel would be for the cylinder id. From how i see it (and please correct me if i'm wrong), one tooth is quite enough (and also accurate enough). Besides, the cyl id could be done in the first few revs after which cam tach is quite useless, no?

now i am a bit confused as to why you needed cam tach to be accurate at all? (again, for non vvt/vanos engines, the only use i see is cyl id).

[Fred]

So for the case of no vanos/vvt, i am guessing the only use of the cam wheel would be for the cylinder id.

now i am a bit confused as to why you needed cam tach to be accurate at all? (again, for non vvt/vanos engines, the only use i see is cyl id).

Because some engines in stock form at least only have a cam sensor with dual triggers, one that simulates being on the crank, the other that is unique per engine cycle. Such engines can (and potentially should be able to) be run with that trigger setup alone.

From how i see it (and please correct me if i'm wrong), one tooth is quite enough (and also accurate enough).

When using it only for cylinder ID, yes, one tooth is enough and desirable even, and accuracy (within a certain margin) isn't important. Obviously you don't want to have the tooth show up in the other half of the cycle do you.

Besides, the cyl id could be done in the first few revs after which cam tach is quite useless, no?

It's a very good idea to continue to verify your engine position as you roll. The chances of lost sync with the whole wheel are minimal, but still....

Admin.

[AbeFM]

Agreed - certainly for the (not insignificant) number of motors running only cam timing, you need to know it. And as well for VVT of any sort, knowledge of the cam position (though once a cycle may be enough) is important. But the more information you can reasonably record, the more noise rejection you can have - and that helps keep people from blowing holes in their downpipes.

[ababkin]

... keep people from blowing holes in their downpipes.

it's ok if it's just downpipes. It's bit more inconvenient when a hole is in the block

[Fred]

....or piston(s)...

[SleepyKeys]

My motor has a dual channel cam sensor. Agreed, motors with timing chains tend to have slop and that slop gets worse as the chain stretches. But a 360 tooth cam wheel with a second channel each cylinder with varying lengths provides for very fast syncs. With 1/4 turn of the crank on a V8 engine the computer can know where the crank is. I think this option should be supported and I will further investigate when my 12x board comes in. It may not be very popular but I know there are 1/2 a dozen cars like this from the factory.

[Fred]

Wow, that's a new one on me, is it a VH41 or VH44? ;-) (or something else??? could I be wrong?)

Skyline and Silvia and a LOT of Nissans use such triggers too. The bad news is that Nissan do it in hardware Not software AFAIK. I should put a thread up about it. I've always been keen to try to build that hardware and try it, but to date haven't had a chance to.

In essence though, there is a counter and some other components that multiplex the ignition output to the different ignitors. Is it wasted spark, or COP?

If you look in the firmware feature wishlist under "advanced implementation" you will see that listed as a goal :-) However, even with XGATE doing the job, the interrupt load might be too high to cope with.

I look forward to your experimentation!

I'll start a thread with the photos and descriptions in it shortly and you can take ownership of it from there on and baffle us with your brilliance :-)

If you have an OEM ECU to diagnose and copy the circuits from that would be ever so useful too! First hand information is always much more useful than second or third or more hand information.

Admin.

[Fred]

Thread started :-)

http://www.diyefi.org/forum/viewtopic.php?f=8&t=71

Admin.