Ring gear as toothed wheel?

[robs]

Ok, so how crazy an idea is this?

Both my cars are currently using the OEM distributor reluctor for tach input. So the 4-cylinder is in effect running a 2 toothed crank wheel. I'm pretty sure that a decent crank wheel, say 36-1, would noticeably improve the way they both run. Mounting up a wheel and sensor doesn't look a simple matter on either vehicle and it struck me that it would be pretty easy to just drill a couple of holes in the bell housing and mount a sensor reading the ring gear.

Obviously too many teeth, but it would not be terribly hard to put one of my pet microcontrollers to work turning (say) 185 teeth (or whatever) into a simulated 36 teeth. Can read the distributor reluctor to simulate the missing tooth. I see the Honeywell 1GT101 claims bandwidth of 25kHz which a back-of-the-envelope calculation suggests something like 8000rpm maximum speed and 40µs minimum processing time available per tooth. More than enough for my engines, and plenty of time for a processor with nothing better to do.

I can certainly try the experiment, RS-232 logging tooth counts per reluctor pulse while driving around with the current set up, but since the whole motivation is my laziness, if anybody sees a reason this is a really dumb idea, it might save me the bother and I can go back to scratching my head about fitting a pulley or dizzy mounted wheel.

Have fun,

Rob.

[ol boy]

I see what your trying to do. My SBFord has a 164 tooth ring gear. 41 teeth per 90 degrees. Not sure how to deal with the very odd math with only 4 dividing into 164 evenly. 4.55 degrees per tooth. With a cam sync mixed in there i could run dual wheel. Id need to upgrade to ms3 first to take advantage of sequential fuel and spark.

[slow_hemi6]

Honeywell is a geartooth sensor. They are usually fairly picky about minimum tooth sizes and gaps. Honeywell should have a datasheet with that info on it though.

[jsmcortina]

Timing belt or chain stretch is likely to move the cam pulse more than one ring gear tooth.

Add a 36-1 instead and have a reliable well-known configuration.

James

[robs]

Thanks for the replies guys. I already had plans on the division concern that ol boy raised, and not sure that cam drift would have sunk me either. I even had plans for a limp mode working with the distributor signal alone if the ring gear one failed. But taking slow_hemi6's advice, I looked more closely at the Honeywell datasheet and while tooth height (5mm), tooth width (2.5mm) and target thickness (6.4mm) would all be within spec., slot width (10mm) -- the gap between teeth -- is obviously much wider spacing than a ring gear.

Ok, a pulley mounted wheel it is then. One more question, is the Honeywell a decent sensor to use? The bandwidth sounds plenty, but then their datasheet only promises 5rpm - 3600rpm for their reference wheel. Even I'd find 3600rpm a bit limiting. Better choices?

Have fun,

Rob.

[slow_hemi6]

I haven't tried the honeywell as the diy sensor was better value and tested to a lot more rpm than I could use. I am almost certain that I read the cams V8 super car specs from maybe 10 years ago and the regulation crank sensor was a honeywell. They must work outside the recommended parameters but I was not keen on doing the experiment as they were over $100au at the time.

[robs]

Thanks Luke. I've just gone for wheel and sensor from DIY. FWIW, Honeywells were available a bit cheaper than DIY's (dearer in other places too).

Have fun,

Rob.

[mickeymarrows]

My Audi 2.8 V6 used the ring gear from the factory as part of a triple sensor setup and I continued to use it when I converted to Megasquirt, in my case I used a devider board from JBPerf.

Worked fine. 100% reliable.

[slow_hemi6]

Was your sensor a VR type? They tend to be better for pointy teeth.

[mickeymarrows]

Was your sensor a VR type? They tend to be better for pointy teeth.

Yes it was. The V6 uses a hole in a crank counterweight for TDC, but I believe the Audi I5 uses a dowel in the flywheel and a second VR sensor for TDC

[ol boy]

Id think a Ford ABS wheel speed sensor would work. I used one to limp the wagon home after the magnet fell out of a standard VR pickup. Had it mounted too close and the teeth wacked it too many times. Only issue i can think.of is the rpm/tooth count. Wheel speed is only in the 1400 rpm area amd thats at 130 mph. Most wheel hubs only have 30 to 50 teeth.

I was running a 20-1 wheel at 3k rpm with out issues. Tested a 36-1 on a drill press at 3k rpm.

[robs]

My Audi 2.8 V6 used the ring gear from the factory as part of a triple sensor setup and I continued to use it when I converted to Megasquirt, in my case I used a devider board from JBPerf.

Worked fine. 100% reliable.

Good to know I wasn't completely off the planet anyway. Who knows, maybe I'll end up revisiting it if I make a mess of mounting the sensor up front.

The JBPerf divider board sounds like an interesting thing, but I don't see anything at the website that'd do the job. Old product I guess.

Have fun,

Rob.