Hybrid Car – More Fun with Less Gas

What's Wrong with my Diodes? - Page 12

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Posted by daestrom on June 10, 2009, 12:12 am


The problem isn't in the starting, it's the firing of one cylinder every
other revolution.  Without a large flywheel to absorb the energy and spread
it out, it creates a lot of torsional vibration.  Worse, if you have a large
inertial mass on the other side of the coupling, then the coupling is
constantly being 'compressed' and 'relaxed' with each firing.

But it isn't insurmountable.  That's basically what a harmonic balancer on
automotive engines does.  Designs vary somewhat, but it smooths out the
torsional vibrations caused by the 'pulsations' of each cylinder firing,
into a smoother rotation for the drive pulley.  Probably the right material
will be all you need.


Posted by wmbjkREMOVE on June 10, 2009, 6:36 pm

Many small engines have internal crank-driven balancer shafts. The one
I use for my backup generator has 2. There's still some visible
flapping on the slack side of the belt though. I'd expect a
rubber-cushioned coupling to be able to handle those pulses with such
engines, but belt-drive gives the option of running the engine and the
alternator at different speeds, which is mandatory in a lot of these


Posted by Tim Jackson on June 10, 2009, 9:04 pm
 wmbjkREMOVE@citlink.net wrote:

Harmonic balancers aren't there to smooth out the fundamental power
cycle, but to damp out resonant ringing in the crankshaft as a result of
the higher frequency components of the power pulse.  They won't do much
to reduce the torque peak seen at the drive belt.

Countershafts don't do this either, they are there to cancel (some of)
the vibrations transmitted to the engine mountings from the piston motion.

The only ways to reduce the crest factor of the output torque at the
crankshaft is to fit a bigger flywheel or to reduce the compression
ratio. You can reduce it at the alternator either by fitting a flexible
coupling or by using softer engine mounts.  Either method absorbs power
and wears out after a while.  It's generally better to use a
transmission strong enough to cope with pulses and misalignment, like a
broad toothed belt.

Tim Jackson

Posted by wmbjkREMOVE on June 6, 2009, 6:42 pm
 On Sat, 6 Jun 2009 08:11:41 -0700, "Ulysses"

As Ken said, get on their free catalog mailing list. Lots of good buys
on surplus goodies that you can design projects around, and easier to
page through than a web site. Good staff as well in my experience,
people you reach on the phone actually know what they're talking
about. I think they have a service charge on orders now, which was a
bit of a disappointment but not a deal breaker. Not everything they
sell is a bargain, so always check prices against other suppliers.


Posted by Ulysses on June 7, 2009, 2:30 pm


Meanwhile, after trying the tensioner and longer belt I have concluded that
the belt is slipping off the alternator pulley and not the engine pulley.
According to the surplus pulley web site I have a 3/8" pulley on my Delco
alternator and that seems to be the only one they have available.  I'm now
thinking that if I could find an A (1/2") pulley that would fit it would be
a considerable improvement.  I'm looking on eBay now but sometimes it's hard
to tell what I'm looking at from the lack of information on some of the
listings.  Part of the limitation seems to be the odd size of the Delco
shaft--just a little over 5/8".  I'm not sure if it's metric or what.

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