On 2/7/2013 7:09 PM, Cor van de Water wrote:
Great way to make an electric LSD (Limited Slip Diff)
Practically, I fail to see any significant issues.
The only issue is when turning a corner on normal dry pavement. The
outside wheel has to rotate faster than the inner wheel. The inner wheel
has to produce all the "motoring" torque, and the outer wheel becomes a
brake, trying to hold the vehicle back.
The sharper you turn, and the faster you go, the worse this effect
becomes. As for how "bad" the extra loss is, that will depend on how
efficient the motors are. This is a case where the worse the motor's
efficiency is, the less of a problem this will be.
If a car's wheels are 5 feet apart, and it has a 30-foot turning circle,
then the inner wheel has a 27.5-foot circle and the outer wheel a
32.5-foot circle. That's a 18% difference in wheel speeds. This is
probably tolerable with 80% efficient motors, whose speed difference
could be 20% between full load and no load. But it could make 90%
efficient motors really fight!
If this turned out to be a problem, you could simply force the motors to
be in series during sharp turns. Save parallel operation for high speeds
where you should never be turning sharp anyway.
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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