Mark, and others -
To relieve your suspicions that the phasing is wrong unless both axis of
both yokes at ends of the drive shaft are in line or parallel, I'll try to
explain why they are oriented the way they are. This is for one joint, but
you'll see why it applies to both. This is much easier to understand if
you can see what's going on though. When both rotating SHAFT axis are
concentric, parallel, and the input shaft is rotated, the rotational speed
of the output shaft is equal to the input. However, when you change the
ANGLE of one shaft relative to the other, the rotational speed of the
output shaft changes or fluctuates in relation to the speed of the input
shaft. depending upon the angle, the output shaft actually does fluctuate
in it's output speed. The greater the angle, the greater the fluctuation.
(remember, we aren't talking about constant velocity u-joints here). For
arguments sake, let's say the input shaft in our example (the one connected
to the engine) is rotating at a given RPM with a material linear speed of
10 inches per second (in other words, if drew a line on the shaft, and
projected it in a straight line instead of rotating it, it would be
traveling at a CONSTANT speed of 10 inches pre second. With the output
shaft at an angle of say, 10 deg relative to the input shaft, it's rotation
WILL fluctuate (within one full 360 deg rotation). If a line was drawn on
this shaft and projected the same way, it's LINEAR speed would fluctuate
with one complete rotation. It would start out at 10 inches pre second for
the first quarter of the distance (rotation), then speed up to, say, 11
inches per second through the next quarter of the distance, then slow back
down to 10 inches for the third quarter, and finally slow down to 9 inches
for the last quarter. As you can see the ROTATIONAL speed would be
fluctuating at the output end. This is because the radius traveled changes
in relation to the angle of the joint itself, and we all know that the
larger the radius (for a given rotational speed) the faster that linear
speed would be to cover the same number of degrees in the SAME TIME. I'm
not sure if that makes things clearer or muddies the water further, but if
you under stand what I am trying to explain then you can see why its
important to phase the joints correctly. With two joints, and BOTH the
input and output shaft axis are parallel, the fluctuations cancel each
other out, and you have the exact SAME smooth rotational speed at both the
input and output ends.
I hope that helps explain the importance of correct phasing, and hopefully,
when I re-read this explanation, it will make sense ( I'm kinda rushing
this out, gotta go to a meeting in a few)-
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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