variable cam profile/timing (was: Twin injector system?)

[Chris Conlon]

Adrian Teo wrote:

> > frederic.breitwieser wrote:
> > 
> > > The "ultimate" solution, one that I and a friend applied for a patent
on
> > > (expensive process, but worth it), is to vary the timing relationship
of
> the
> > > Cam/Crank across the RPM band.  By adjusting the cam for low-RPM the
> engine
> 
> I hate to burst your bubble but these schemes have already been
> implemented in a ton of everyday applications.
> 
> Add to the list below:
> -Nissan VVT-i
> -Porsche's VarioCam
> -...and of course Honda's VTEC.
> 
> Some of these shcemes (Nissan's VVT and Honda's VTEC) switch to a
> (sometime two or more) completely different cam profiles.

I didn't know Nissan had a scheme called VVT or VVT-i. Toyota has
two that have exactly the same names. They don't switch cam profiles
though. VVT switches between one of 2 predetermined advance/retard
settings, but the cam of course stays the same. VVT-i (incremental)
allows a finer selection of advance/retard, again within preset
limits. All the Toyota motors that I know of that use VVT or VVT-i
are twincam models, and I think that some of those vary only one of
the two cams, to save money I guess.

I always thought it would be way cool to have the valves activated
hydraulically, controlled by solenoids or something. But I have no
real idea how to do this. I would think that a completely flexible
"cam" profile would be a real big advantage, and since I haven't
seen it anywhere I assume it must be a very difficult thing to do.

   Chris C.