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Idea vs. Ego
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Volkswagen makes an engine it calls the
VR6 (see link), which is really just a V6
with 15 degrees between the "banks" so
that it can have a single block and head,
as well as a compact size, because the
cylinders can nest together. It is still
essentially a V6, though.
To make a "true"
VR6, you would need to
have two crankshafts with gears that
mesh together. It would essentially be
two straight-three engines put together.
This would still allow a single block and
head, but with an even more compact
design. One "bank" would be offset a
few inches to allow the cylinders to fit
closely together. This would be similar
to the square-four engines on some
motorcycles, but more of a diamond
The head would be similar to a V6, but
the two heads would be joined together
into one piece with a flat bottom (minus
the combustion chambers). Since the
two crankshafts would rotate in opposite
directions, it would aid in spreading oil
around the crankcase. The two
crankshafts would mesh together into a
common output shaft.
Tech descriptions about the VR6 engine [discontinuuity, Jun 02 2005]
Scuderi Group's split-cycle engine
This six-cylinder engine has a similar design and shape as my idea, but with only one crankshaft shared between the two "banks." I think this design only works with a split-cycle engine, but I'm sure you could try to make a regular 4-cycle engine this way. [discontinuuity, Mar 09 2006]
||I mean that it doesn't have two banks jutting out from the block, it's just one big chunk that looks like a parallelogram from the top and a rectangle from the side.
||The torsional balancing and NVH characteristics would be horrendous to try and figure out. I'd think you'd need to have both cranks driving the flywheel somehow; the accessories and cams don't eat that much power I don't think. Another difficulty comes when you try and mesh two power-providing gears together. The engines would fight eachother constantly, either one would drive, or the other, due to gear lash. Finally, engines don't rotate smoothly at all; if these are timed opposite eachother, the gears would swap drive vs. driven for each pulse. One of these would need some sort of hyper-stiff torsional spring system to eat up the vibrations, similar to the torsional springs built into modern clutches.
||The VR6 is closer to an I6 than a V6. I think the idea is feasible given that square-4 engines already exist, but I think that the VR6 is simpler and more stable than a "square 6" configuration would be anyway.
||As you say, this is very like the square four used on bikes, notably the Ariel, but is also similar in concept to the H16 engine used in BRM racing cars in the 60s. I'm not seeing anything really new here.
||Rayford makes good points. Swapping a well-balanced single-crankshaft engine for a horrendously complex gear-driven twin-three-cylinder system is in no way a good idea.
||Angel's H-16 produced frightening power output from just 1.5 litres, but was known for unreliability.
||//frightening power output from just 1.5 litres//
I think you'll find that the H16 was 3 litre (plus a 4.2 litre for Indianapolis). It first appeared for the 1966 season when the 3 litre formula was introduced, and Jim Clark used it in the Lotus 43. He won at Watkins Glen, but yes, it was generally unreliable.
||Some research has told me that the "square" configureation is also sometimes called the "U" configuration--so what you've got is basically a U6.
||Hey, I've got a 1997 VW Jetta VR6. Its black :D
||You're right [angel], I was confusing it with the BRM V16. That one was also known for unreliability, as it was only 1.5l but made (I think) 450bhp via a massive supercharger.
||I've added a link that shows a more viable
solution with a single crankshaft. This
would make it work much more like a
conventional V6, but the odd angles
involved might take away some of the
mechanical advantage inherent in the
piston and crank of a conventional engine,
and I'm not sure how well the timing