Sensor Question

[Andrew Theurer]

Carter,

Thanks for sticking to the original thread :)

The ring gear was brought up in efi332 a while back, and was discarded for a
number of reasons including the concerns you wrote about below.  One other
valid concern: It's quite possible that a tooth will break off, making a
difficult situtation much worse :(

-Andrew



> One problem with using a distributor to generate
> timing is the jitter due to mechanical backlash in the
> drive. Many use some sort of helical gear arrangement
> off of the camshaft, often in common with the oil pump
> drive. Any wear in the system will result in timing
> innacuracies. To compensate, you would have to run a
> more conservative advance map.
>
> Using the starter ring gearteeth has some issues. The
> environment is not friendly; clutch dust, road dirt,
> water, bits of metal from the gearteeth, oil leaks
> (engine and transmission), heat, vibration, etc. The
> frequency of a 150 tooth gear at 9,000 RPM is 2250 Hz.
> So pulsewidth is around 440 microseconds. Since the
> ECU is already pretty busy, it may not appreciate
> handling an interrupt so often. That means some kind
> of frequency divider circuitry (and intermediary
> signal conditioning if you use a mag pickup). Well
> within the state of the art, just more bother.
> As for pickups, you have 3 main choices, opto,
> inductive, or hall.
> Both opto detectors and hall sensors must be able to
> handle the frequency (not all can). The opto emitter
> and detector, and the hall sensor are semiconductors,
> so you must specify parts capable withstanding the
> environment. An inductive sensor can handle the
> frequency, but the air gap may be critcal and require
> fine adjustment. The sensing edge of the ring gear may
> also require machining to insure that the runout is
> small enough to yield reliable operation.
>
> With an opto sensor, whether you choose a reflective
> or transmissive scheme, the obvious issue is
> obscurement of the beam by debris.
>
> An inductive or hall pickup can be affected by a
> buildup of ferrous dust or particles, since the sensor
> must be biased with a magnet to detect the teeth.
>
> Detection of TDC (or equivalent) can be accomplished
> by altering one tooth somehow, to give a detectably
> different waveform.
>
> If I was forced to make a choice, I'd probably go with
> inductive. The detector itself is more robust. To
> combat crud buidup, I would probably fashion a 'wiper'
> that would sweep the pickup each revolution. A small
> piece of teflon or whatnot on the tip of one geartooth
> (maybe 0.02-0.05" thick). Maybe spring load it so the
> root of the starter pinion gear could compress it
> during starts.
>
> Lucky for me, I'm not faced with such a choice.
>
> Carter Shore
>
> __________________________________________________
> Do You Yahoo!?
> Send your FREE holiday greetings online!
> http://greetings.yahoo.com
> --------------------------------------------------------------------------
--
> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the
quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org
>
>

----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org