Sensor Question (and the usefulness of cam sensors)

[James Montebello]

Every Audi turbo, and every other car equipped with Bosch Motronic, which 
covers nearly every German car sold since the mid to late 80s, and a good 
number of other European cars, as well.  It's a very common system, used 
on literally millions of cars to date.

While we're on the subject, I've heard that argument (cam signals are no
good for timing because of the cam drive) several times.  It seems to me
that having ignition timing be more accurate than cam timing is a
relatively useless feature.  Therefore, using a cam sensor is perfectly
adequate.  Indeed, one could make the case that synchronizing ignition
with valve events is "more accurate" than synchronizing it with crank
(i.e., piston) position.  If you're going to do full sequential, you'll
need some indication of cam position, anyway.

The advantage I see of using many teeth for the crank position isn't
relative positioning, but rather high-resolution and redundancy when
measuring speed.  You can miss the signals from many teeth and still not
lose track of the current engine speed.  Watching many teeth also gives
you the ability to watch the rate of change of the crank speed more
closely, and potentially divine things like misfires (which should show up
as two anomolously large changes in crank speed during one or two
revolutions) for very sophisticated control strategies.  Finally, as
discussed not long ago on this list was the big advantage of timing
everything with continuous external, engine-driven interrupts, rather than
relying on long-running calculations seeded by one or two samples early in
the process.

james montebello

On Tue, 11 Dec 2001, Orin wrote:

> > Bernd Felsche wrote:
> > > 
> > > You mean the starter drive teeth on the flywheel for timing?
> > > 
> > > Even the manufacturers don't stoop that low.
> 
> Every Audi turbo since the early 80s thru mid 90s
> used the flywheel teeth for timing.  Why?  Because signals
> derived from the cam suffer from backlash in the cam drive
> and similarly for the distributor.
> 
> Orin.
> 
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