Practical solution to variable compression

[jb24 at chrysler.com]

Variable compression will see you huge gains in part-throttle
fuel-economy.  It's that thermodynamics thing that expresses work being
done is the area between max pressure and min pressure on a
pressure/volume diagram.  If you up expansion ratio (by way of upping
compression ratio) you get more work for a given amount of pressure.
When my variable compression ratio two-stroke patent gets approved, I
will share it with the list (and no, it is totally different than the
below mechanism, you hope :).
---------------------- Forwarded by John R Bucknell/JTE/Chrysler on
03/13/98 09:50 AM ---------------------------

        owner-diy_efi @ efi332.eng.ohio-state.edu
        03/12/98 12:24 PM
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Subject: Re: Practical solution to variable compression

>
> I was thinking about this while designing a model of a 200cc
> two stroke engine (single bore only) that uses opposing pistons...
>
> What if one tied the cranks together with a gear drive mechanism
> having a gear on each crank and a pair of idler gears coupled
> together with a clutch that could only slip say, 15 degrees.  By
> effectively putting the two cranks out of exact synchronization,
> wouldn't you change the engine's compression?
>
> Think about it a minute.  If at exact alignment, the two pistons
> reach TDC at the same time, then you have MAX compression.
> If the alignment is offset by allowing the clutch to slip just a
little
> and then lock back up say ten degrees off sync, then you would
> never have the two pistons reaching TDC at the same time.  Thus,
> your compression ratio would drop.
>
> Now, my next question is...  Would you gain significant performance
> by allowing high compression at low throttle settings and then use
> a lower compression at WOT?
>
> Having variable compression seems like a cool idea, and I
> believe an engine and management system could be built to
> do it.  Looking this whole thing over, I'm pretty sure that
> MAX performance would still be limited the way any other
> engine is, but couldn't the whole power curve starting from
> way down low near idle be boosted considerably?
>
> Does this idea warrant any merit?
>
> Can anyone shoot BIG holes in it?
>

The only real problem I can see is that one of the pistons would
be potentially moving into the flame front, which could be a
problem.  I think it would be more useful with a gas engine,
where too much compression detonates things, and less useful in a
diesel engine where this is mostly normal operation.   Still
it may be a problem with the piston trying to compress an expanding
gas, knowing what knock does to an engine

   Roger
> Matt
> ______
>
>
>