hall sensor simple questions

[nacelp]

> >As I understand it, a hall sensor can detect a metal mass approaching the
> >sensor i.e. a distributor cam rotating and a hall sensor sensing the
lobes.
>
> The Hall sensor picks up a chnage in the magnetic field. It can be
> used to sense the position of a camshaft drive gear tooth.

?. What signifigance is a camshaft drive tooth.
Camshaft posistion sensor, yes, the two thou are entirely different, the
posistion sensor is to find a relative TDC, or sync for a specific cylinder.
The only thing constant about camshaft gear teeth is that there is an even
number.

> "Reluctance" sensore are also used commonly. A reference signal to
> identify a particular tooth on the gear wheel is used so that the
> absolute position of the camshaft can be determined. If you're using
> an encoder wheel, the most accurate (but also more costly) method,
> then a "missing tooth" is quite a common method of identifying one
> particular position.

Actually a missing notch is best.  Take a steel wheel, and cut several
notches into it.  Those are easiest to find.  Specially at cranking speeds.

> >Crank shaft sensors can determine the position of the piston and
therefore
> >give the ECU a timing reference inorder to inject fuel at the right time.
> The sensors are used to sense the position of the crankshaft,
> not the piston. The crankshaft detrmines the relative locations of
> the pistons.
> >How many sensors do you need around the crank inorder to get a resolution
> >that is useful? Is this multiplied by each cylinder as well? or can the
ECU
> >calculate where one piston is compared to another's location?
> You *need* none at all. Basic engine timing can be determined from
> the camshaft position, with a TDC and BDC signal required as a
> minimum. The ECU can interpolate intermediate positions given the
> elapsed time between TDC and BCD.

If your implying just two distributor reference pulses good luck.  I'd
imagine real hard starting in cold weather when the cranking speed is
erratic.
   I'd use at least one notch for every two cylinders if crank, and 1 per
cylinder distributor, as mins.

> >Crank shaft sensors seem hard to implement on an old engine with no stock
> >electronics what so ever. I was thinking about using the distributor's
cam
> >with a hall sensor in order to get spark timing and as well as Fuel
> >Injection timing and thereby doing away with crank sensors completely. Is
> >this possible? are the hall sensors accurate enough to not only detect a
> >lobe peak but the lobe's approach and exit?
>
> The common method is to use a magnet with an "interruptor" wheel.
> Edges of the openings are treated (nominally) as the TCD position
> for each cylinder - the Hall sensor is accurate if the distributor
> does not have any advance mechanism.

???, the sensor in it's operation don't care if there is an advance
mechanism.  If there is a timing problem in the advance mechanisms, then
timing will be erratic.  Just the same as if there were points, IR detector
or anything else triggering off of the distributor shaft.

> Such a method has in the past been employed successfully by VW's
> Digifant, which integrates fuel injection and ignition.  More
> accuracy is possible with camshaft and/or crankshaft sensing to
> detect transitions in engine speed more easily and reliably; as well
> as allowing sequential injection and other goodies.

??. Accuracy (at least in the mechanical sense), is a function of the number
of references, not number of sensors.  You can do equally well with crank or
cam, the only time you need both is in SEFI (meaning timing or fuel).  If
you want to measure crankshaft accleration rates accurately then you need a
crank sensor, since there is always "gearing" for the distributor, and that
alllows for slow, and erratic signaling for that level of resolution,
needed.  You can get by with dissy, but the resolution of input, and
filtering gets more complex, and hence more room for error.
>
> --
> Real Name: Bernd Felsche
>     Email: nospam.bernie at perth.DIALix.com.au
>      http://www.perth.dialix.com.au/~bernie - Private HP
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