Variable Cam Timing....

Andrew Dalgleish andrewd at axonet.com.au
Tue May 14 04:38:16 GMT 1996


You're spot on.

About 6 years ago I built a proof of concept, and it works just fine.

Picture a "normal" differential.

Drive it on the left wheel, hold the tail shaft still, and allow the   
right wheel to turn.
(It turns backwards, but imagine you've inserted a gear to reverse that.)

Now rotate the tail shaft by some small fixed amount. Just once, not   
continuously.

The right wheel has now had a fixed amount of rotation added (or   
subtracted) to it.

If you keep turning the left wheel, the right wheel still turns, but now   
its *phase* has changed.

So the power to drive the cam still comes from the crank, and only the   
adjustment has to be provided by a stepper motor.

With a four cam desmo, the phase of each cam is individually adjustable.
(As others have pointed out, you don't really need to adjust all four.)

It's perfectly reliable. If the electronics fails the cam still drives,   
it just isn't adjustable.

But it's not cheap to build. Internal tooth ring gears are expensive.

Regards,
Andrew Dalgleish


 ----------
From:   
 owner-diy_efi-outgoing[SMTP:owner-diy_efi-outgoing at coulomb.eng.ohio-state  
.edu]
Sent:  Monday, 13 May 1996 11:47
To:  diy_efi
Cc:  ducharme
Subject:  Re:  Variable Cam Timing....

Paul Beam wrote:

> You would have to have one on both the cam and the crank.  Slipping the
> crank would counteract slipping the cam.


Maybe I've been lurking too long, but *HOW* can you advance the cam if   
you
use two clutches?  The crank is the driving member, and de-coupling   
anywhere
in the drive train would still retard the cam timing further.

How about a "differential",  i.e. a gear mixer driven by a stepper motor?

You could use a planetary gear set.  The crankshaft driving input would   
come
through the sun gear, the camshaft would be attached to the planet   
carrier,
and the stepper motor would index the ring gear to advance/retard timing.

Not bad for a EE...


Cliff Ducharme



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