Camless engine

[Adrian Broughton]

> This subject caught my eye and I looked into the toyota and rover VVT
> (variable valve timing I think) systems.  There are basically two types 
of
> systems in production/semiproduction right now.  I've seens systems with
> multiple lift lobes with hydraulic "shifters" to select the lobe they
> want (this was a wierd setup and I didn't understand the theory but the
> principle seemed like a good one).  Toyota's system and the most common 
is
> a cam gear on a kind of spedometer gear (for lack of a better
> description).  There is a mechanism that adjust the location of one of 
the
> gears and thus advances or subtracts from the inital position.  Thus with
> a seperate intake/exhaust cam you can overlap the openings for
> optimization ... this is great except all you can do is adjust the timing
> ... I'll try and find the webpage I was on and send it to the list.

Here's a good web-page explaining Variable Valve Timing, and comparing the 
Honda and Toyota methods.
The Toyota VVT you describe above has been superceded by TVVTiL, which is 
the same system (the VVT bit) but has "intelligence" (the i bit) that means 
it now has infinately variable timing, rather than just "mode A or mode B", 
and also variable lift (the L bit) which means it adjusts lift as well as 
timing.  Anyway, read the page, it explains it all...
http://www.onthenet.com.au/~billzila/vvtvtec.htm

> >My two cents worth:
> >Aren't we missing something?  If we do away with the camshaft, why not
> >do away with the valves as we know them?  How about an Iris?  Or maybe
> >some sort of sliding/rotating window?  Would seem to do away with the
>
> There are old engines that did this. They had a rotating sleeve around
> the cyclinder opening ports in it's walls. At least, I believe this is 
how it
> works, I'm sure others can tell us the details.
>
> I believe they are no longer made because they are difficult to make.

I think you are right Tom.. I remember reading an article in a really old 
copy of "Wheels" magazine (it was a 1960's issue) where they did a review 
of a new "Rotary Valve" engine that GM Holden had been developing here in 
Australia.  I read the article a long time ago (5 years?), but kind of 
remember it.  I think all the valve gear had basically been replaced by two 
overhead shafts (similar to an DOHC setup, but the shafts were much 
thicker) and these shafts had "flat spots" carved out of them.. basically 
the reverse of a normal cam, instead of having lobes that stick out you 
have indents that go in.  The shaft rotates and as the flat-spots come 
round, they create a gap between the head and the shaft which allows the 
air/fuel or exhaust to go in or out.
I'm not quite sure why they didn't take off.  I think they could develop a 
fair bit of power (for the time), and you could use a file to make the flat 
spots bigger to give you the same thing as a bigger cam... but there was a 
reason they didn't take off... maybe lubrication, longevity, I dunno, can't 
remember.
Anyway, the whole thing was basically self-contained in the head, so you 
could just bolt one of these heads onto your holden (not sure if it was for 
red motor or grey motor) and away you go.... They made 100 of them, so if 
you have a Holden with one of these heads then I reckon it would be worth a 
mint!

Cheers,
Adrian
___________________________________
Adrian Broughton
1990 GT-Four Celica (@15psi), 1974 VW Kombi, 1967 Holden HR
Fremantle, Western Australia
gtfour at one.net.au     http://web.one.net.au/~gtfour/
___________________________________


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