Re: V-5 cylinder engine balance

[ti@amb.org (Ti Kan)]

Mike Arman writes:
> I've seen 5 cylinder in-line engines and 5 cylinder radial (and rotary)
> engines, and even a "Megola" motorcycle circa 1922, which used the
> cylinders as spokes in the front wheel and the whole dang engine rotated
> (Yes, you stopped the engine to stop. No, it couldn't idle), but I have a
> question about V-5 engines, being, I presume, a bank of two cylinders plus
> a second bank of three, joined at the hip, as it were.
> 
> Obviously, it is mechanically possible to build such and engine (Honda?
> Volvo? V-5 VW), but how the heck can you BALANCE it?

The VW "V-5" is actually a misnomer.  It's actually a VR5, or basically
the current VR6 engine with one less cylinder.  If you haven't seen the
VR6, it's sort of in between an inline 6 and a V6.  It has a very narrow
V angle (15 degrees), such that the two rows of three cylinders are
sort of staggered next to each other, with a single cylinder head over
both banks of the V.  The "V-5" is the same as the VR6 except it's
got one bank of three cylinders and another bank of two.  The two banks
are again topped by a single cylinder head.  Neither the VR6 nor the VR5
are perfectly balanced.  The 15 degree V design makes a very compact
engine for its displacement.  For a V6 to be balanced it needs to have a
60 degree Vee, so at 15 degrees the VR6 is nowhere near that.  However,
by careful design of the crank counterweights and other things like
engine mounts, etc., vibrations can be dealt with and the engine can be
made relatively smooth.  The VR6 is subjectively a very smooth engine.
If Audi can make the inline 5 run smoothly then it's possible also to
make the V5 run smooth too.

ASCII art top view of the various layouts.  (non-proportional font needed
to display properly):

I5
     +-----------+
     | O O O O O |
     +-----------+

V6
     +-------+
     | O O O |
     +-------+
      +-------+
      | O O O |
      +-------+

VR6
     +--------+
     | O O O  |
     |  O O O |
     +--------+

VR5
     +-------+
     | O O O |
     |  O O  |
     +-------+

WR-12 (VW concept car)
     +--------+
     | O O O  |
     |  O O O |
     +--------+
      +--------+
      | O O O  |
      |  O O O |
      +--------+

W-12 (Audi Avus)
     +---------+
     | O O O O |
     +---------+
       +---------+
       | O O O O |
       +---------+
      +---------+
      | O O O O |
      +---------+

-Ti
96 A4 2.8 quattro
84 5000S 2.1 turbo
80 4000 2.0
-- 
    ///  Ti Kan                Vorsprung durch Technik
   ///   AMB Research Laboratories, Sunnyvale, CA. USA
  ///    ti@amb.org
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