Mark - thx - agreed - almost!
Energy is absorbed when you bend (or deflect) the gear metal but only some of it
is available to be returned to the system (the rest becoming heat) BUT, unless
gears have improved much more than I think they have in the couple of decades,
very little of that can actually be returned to the system in a positive way -
think gear speeds, tooth frequencies, vibration etc - again it becomes waste
heat (and noise).
When you say "friction" what do you mean? Friction implies sliding and I hope
gears don't actually touch metal to metal or racing could get VERY expensive. If
you mean oil shearing I agree.
Heh Doug - thanks for asking!
Derek
Mark Palmer wrote:
> Derek,
>
> Just sent another reply, but wanted to comment on one or two things here.
> Loss in gear mesh is due to friction, not "metal bending". Let's hope the
> teeth aren't bending much or we're in real trouble! Actually, there is
> always some deflection but bending does not dissipate energy -- bending is
> what springs do, which are energy STORAGE devices not energy ABSORBING
> devices. The energy put in to bending the gear tooth is returned to the
> system as the tooth unloads & returns to its "normal" position. Think of a
> sling shot, if that helps.
>
> Otherwise you're on the right track. Oil "churning" (usually called
> windage) losses are proportional to speed, oil shearing proportional to
> speed & load.
>
> Perhaps surprisingly, very little of the loss actually occurs at the gear
> mesh itself -- typically 1.5% of transmitted power per mesh. Most of the
> losses are due to the bearings, and windage. This is because, in involute
> profile gear teeth, the relative motion is actually a rolling motion, NOT a
> sliding motion (true for spur or "straight cut", & helical). The losses
> are typically 5% or so, if you include the radial & thrust bearings that
> support that gear mesh (1.5% mesh loss + 3.5% bearing loss). Bevel gears
> have a combination of rolling & sliding motion, hence are less efficient
> (typically 2.5 - 3% loss per mesh; 6 - 8% when you add in the supporting
> bearings) and worm gears are the worst, all sliding, that's why we don't see
> them much on cars.
>
> Regards,
> Mark
>
> >From: Derek Harling <derek.lola@home.com>
> >Reply-To: Derek Harling <derek.lola@home.com>
> >To: vintage-race@autox.team.net
> >CC: S800Racer@aol.com, brian@uunet.ca, ralph@cloverleaf-auto.com
> >Subject: Re: horsepower
> >Date: Mon, 13 Nov 2000 14:09:39 -0500
> >
> >I would suspect that the truth is somewhere between your respective answers
> >- in
> >other words the total loss is partially depended on hp/torque transmitted
> >and
> >partially independent. No doubt it is also dependent on speed.
> >
> >The losses occur because of metal bending, mainly in the gear teeth, which
> >I
> >suspect is very dependent on torque transmitted, on oil shearing (dependent
> >on
> >torque and speed?), oil churning (speed?) - and other things.
> >
> >Lets hear it from a gearing/transmisison expert.
> >
> >Derek
> >
> >S800Racer@aol.com wrote:
> >
> > > In a message dated 11/13/00 9:16:09 AM, brian@uunet.ca writes:
> > >
> > > << How about 15% loss for a Hewland( rear wheel drive, all straight cut
> > > gears), up to 20% loss for typical rear wheel drive helical trans, >>
> > >
> > > I've often heard the 15 - 20 % "rule of thumb". Is this true
> >regardless
> > > of HP? If a 100hp vehicle lost 25hp, would a 500hp vehicle lose 125hp?
> > > Wouldn't it take roughly the same # of HP to drive similar Trans & rear
> >end
> > > gears regardless of the HP of the engine?
> > >
> > > Doug Meis
> > >
> > > P.S. Would a hand count necessarily yield a better result? ;-)
> >
> > I dunno - you'll have to ask the countess!
> >
> >
>
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