Variable Cam Stuff

[Ludis Langens]

Frederic Breitwieser <frederic.breitwieser at xephic.dynip.com> wrote:
> But, basically is nothing more than adding a few links to the timing chain, 
> pinching it with two gears that are at a fixed distance, and sliding the gears 
> left and right across the front of the engine.  By doing so, the relationship 
> between the crank and the cam adjust "on the fly".  We used simple hydralics 
> to move the two gears, and it worked pretty good.

This same subject came up on the list a long time ago.  At the time, I
had needed to loosen quite a few CV axle nuts, and had to deal with
motion through a differential.  Putting 2 and 2 together led to an idea
of how to do variable cam timing:

Attach a small differential to the end of a cam.  The cam is connected
as one (half)axle.  The "drive shaft" input connects to the timing chain
/ belt / self-destructing-fiber-gear.  Now connect a small electric
stepper motor or solenoid as the other (half)axle.  This motor/solenoid
only needs to turn a few degrees.

A computer can now control the motor/solenoid to adjust the cam timing. 
A one degree movement in it will cause the cam timing to adjust by one
degree in the opposite direction.  The chain/belt/gear still provides
all the normal cam motion.  Thus, if the computer fails, the engine will
still run.  (As opposed to a cam driven just by an electric
motor/stepper.)

On a DOHC engine, attach one of these gizmos to each cam.  If the intake
and exhaust valves are controlled by opposite cams, the intake to
exhaust timing relationship can now also be controlled.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/