> snip> When the shaft is at an angle, the slower spinning
>yoke half on one end compensates for the faster spinning one on the opposite
>side of the other end of the shaft. Did I get that right?
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Well, basically, yes, the two yokes cancel out the fluctuations if phased
correctly. And yes I am a mechanical engineer (23 years now). But, the
yokes at each end of the typical driveshaft don't really rotate at
different rpm's. Two of the opposing "cup's" linear speed, in feet per
minute on each yolk, (the ones that change their angle in relation to the
centerline of the input shaft) do vary in a sine wave manner as it rotates
for one full revolution, so that you don't have a smooth rotating
intermediate shaft, but rather a pulsing one. It's still the same "rpm",
but the velocity (in feet per minute) of each revelation is not constant.
Constant velocity joints take care of this problem hence the name. I
usually try to explain complex operations in simpler, easier to understand
terms and sometimes I get it right, other times I miss the boat. If you
ever see it in action it's really easy to understand, but it's VERY hard to
explain (for me anyway)! Maybe this would be easier to visualize - If your
familiar with the old phonograph record or the more modern CD's, when
spinning at a constant rotational speed (RPM), the distance traveled at the
edge (larger radius) is far greater than the distance nearer the center
(much smaller radius) for a single revolution. If you try to match the
distance traveled using your finger, you'll find that you have to move your
finger at a much faster RATE (higher velocity) the farther away you get
from the center. The arc drawn through the angled u-joint (cup) is much
the same. That is to say, the arc traveled at the outer angled cup is
greater than the arc travelled at the inner cup in relation to the input
shaft centerline so in effect you actually have a sine wave fluctuation in
velocity of the two shafts. The RPM or "revolutions per minute" is the
same, but the RATE at which the two shafts revolve is not. The VELOCITY
of the input shaft is constant, the VELOCITY of intermediate shaft
fluctuates (speeds up slows down for each revolution). Stick another
joint, on the other end of the intermediate shaft at the exact opposite
angle and it fluctuates in exactly the opposite direction, and viola, the
output rotational speed matches the input with no fluctuations! Granted
these fluctuations are rather small in a typical driveshaft, but can and do
induce vibration in a driveshaft that can spin upwards of 6000 rpm. An
axle shaft with a max rotational speed of maybe 1500 rpm isn't affected as
much-
Barry Schwartz (San Diego) bschwart@pacbell.net
72 PI, V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (long term project)
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