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"True" VR6 Engine

An Improvement on Volkswagen's Straight-Vee Design
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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 shape.

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.

discontinuuity, Jun 02 2005

Volkswagen's VR6 http://en.wikipedia.org/wiki/VR6
Tech descriptions about the VR6 engine [discontinuuity, Jun 02 2005]

Scuderi Group's split-cycle engine http://www.scuderigroup.com/index.html
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]

[link]






       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.
discontinuuity, Jun 02 2005
  

       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.
RayfordSteele, Jun 02 2005
  

       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.
5th Earth, Jun 03 2005
  

       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.
angel, Jun 04 2005
  

       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.
david_scothern, Jun 04 2005
  

       //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.
angel, Jun 04 2005
  

       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.
5th Earth, Jun 04 2005
  

       Hey, I've got a 1997 VW Jetta VR6. Its black :D
ghillie, Jun 04 2005
  

       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.
david_scothern, Jun 04 2005
  

       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 would work.
discontinuuity, Mar 09 2006
  
      
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