R.M. Bownes III writes :
> -> Here's how it would work. (I'm not Marcus so I won't even attempt a
> ->cool ASCII drawing.) On the tense side of the chain, (driver's side),
> ->install a very small idler sprocket in the middle of the chain's travel
> ->between the crank and cam sprockets. This sprocket would 'push' into the
> ->chain from the outside, effectively advancing the relationship of the cam
> ->sprocket to the crank sprocket. Adjustment would be provided by an Allen
> ->stud, threading into the side of the timing chain cover. The Allen stud
> ->would be held fast by an outside nut.
> -> The slack taken up by the adjuster would be compensated for by the tension
> ->spring on the 'loose' side of the chain, as currently exists.
> -> 'Zero' could be achieved at the center of the adjuster's travel by
> ->using an offset key, or Zero could be set wherever convenient for the
> ->particular engine.
>
>
> The problem is:
>
> Take a quick compute of the side load onto your sprocket. On a 6
> cylinder engine, the torque required to turn the cam, move all the
> lifter gear, compress springs, etc is non-trivial. I don't know much
> about 4 cyl cars, but I figure the order of magnitude would be the
> same. Such a sprocket would need to be rather heavy duty, have a real
> pivot point, and I think a small allen wouldn't really be up to it.
> Such a system is used in a few vehicles I can think of, some on a more
> active basis than you plan. Hooking a servo motor up to the equivalant
> of your allen screw and a computer gives variable cam timing dependant
> on other input factors...Ask the folks @ Toyota about it, or Honda,
> though they do it at the cam itself.
Hmmm, But the force needed to move the chain sideways (or the sideload)
would be much less - think how tight a tightrope has to be before the
circus artiste can walk across without it drooping. Or for those of
you who have never been circus performers, how tight a washing line
has to be to support any weight of wet clothes without sagging into the
dirt.
This force would be there 2T sin @, where T is the tension in the chain, and
@ the angle of deflection at the sprocket. (This assumes that the chain is
not elastic, so does not stretch.
I think the most important thing would be to have a sprocket the other side
of the timing chain (on the 'slack' side) to mov in at the same time, to
maintain the tension in the chain.
Anyway, my simulation has come back so I'm off to see weather my
megadoudelacious system has worked !
TTFN,
--
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_/ Ben Hodson, _/ Email : hodsonb@prl.philips.co.uk _/
_/ Philips Research Labs, _/ Tel : 0293 815000 ext 5750 _/
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