Did you get that thrust bearing 3D Doug? I am sure you will have some
questions
about it.
Yes Paul
I got it.
It seems the bearing 'sandwich' purpose is to handle the thrust
(clamping
force of the CVT) right? In principle your idea will work though in
application and assembly the part count seems high. Ten bearings?
Excuse my attitude. I am always looking for ways to lower part counts
and
simplify design. Design process takes longer though. Making it work is
another matter though. Couldn't we find a way to lower the clamping
force
and get away with a high speed ball bearing? Some of the designs can
accommodate a thrusting action as well.
I will try to find my NTN bearing catalog.
snips..
Doug in Japan
I expected you would have reservations about this design.
Yes the part count is high but the part cost are low. If you explore the
life
characteristics of needle bearings you will find the life drops off
exponentially
with RPM. The smaller the diameter the less the less this effect.
Therefore
you choose the smallest diameter bearing that will have the required
dynamic
thrust load. The max RPM on this size is only 20,000 RPM and the life
would
be short if we ran it at its rated load and that RPM. to extend the life
you
must drastically lower the RPM. By using 10 bearings back to back
the 100,000 input RPM is reduced to 10,000 RPM per bearings. This is not a
new
idea. Here is a shot of a Ross PSRU with three needle thrust bearings back
to back
for the same reason. Tracy Crook's first design on a PSRU sun gear thrust
bearing failed for similar reasons. We also went through this exercise
with
Perry Micks direct drive ducted fan and the stock Mazda e-shaft needle
thrust bearing. I would not want to use a ball bearing anyway as the
pinion shaft needs to find it own center relative to the planet wheels.
If I knew of a better way of doing this I would use it needless to say.
As far as I can tell there are no ball thrust thrust bearings that will
take
this load at this RPM. If you use ball bearings back to back to take
thrust
you risk overloading just one as both outer races are stationary.
I am wide open to suggestions on this. If anybody has a better idea I
would like to
hear about it.
snips...
Paul,
At least one of these bearings will have one race turning at 100000 RPM and
it's other race turning at 90000RPM. So the rollers will be subjected to
high centrifugal forces. Can the cage retain the needles reliably at these
RPM?
Regards,
Mark
I hope so :) Did you calculate the centrifugal force? The needle weigh
on the order of .001 pound. Radius is about .75 inch.
CF = (m X V^2)/radius. I think V is ft/sec. I'll leave the final calculations
to the reader :)
I think I figured out another way of doing it.
I need to talk to the Torrington Engineering department.
They claim the dn rating on ceramic ball bearings is 3,000,000.
dn = bore (mm) X RPM
That means a 12 mm ceramic super precision ball bearing like the kind used
in turbo chargers can operate at up to 250,000 RPM!!
I was simplifying matters by using the same thrust I needed on the CVT for the
first stage friction planetary drive thrust. Probably around a 1000 pounds
for the CVT. That is way overkill for the first stage. Since the first stage
friction planetary drive only needs about 100 pounds of thrust I think I have
figured out how to isolate the two.
Input torque on the first stage friction planetary is only 24 inch pounds
for 30 HP at 100,000 RPM. For a .5 inch dia. pinion shaft that is a
tangential friction force of only 44 pounds. For hard steel on hard steel
the coefficient of friction is 0.78. The same as steel locomotive wheels on steel
rails. Therefore the minimum required first stage thrust force is about 57
pounds. We will design for 100 pounds as a margin of safety. If Torrington
has a thrust only, small ceramic ball bearing capable of 250,000 RPM
and 100 pounds of thrust we are home free.
This is ignoring the help we will get from the slightly tapered pinion shaft and
stationary reaction ring. If Torrington has a thrust only small ceramic
bearing we are home free.
Check my calculations I could have made a mistake somewhere.
Kind of tricky but I think it can be done with just three small Belleville spring
packs and an extra thrust bearing for the CVT. I'll do a 3D here shortly for Doug.
Paul Lamar
OK Doug I hope this makes you happier.
The clamping force for the CVT goes through the gray pins into the green plate and then
in to the housing through the large needle thrust bearing. You may have to use as
many as three back to back here. Other types of thrust bearings will work
as max RPM is only about 8000. Thrust load is about 1000 pounds.
The 100 pound modest clamping force for the first stage is provided by the three
Belleville spring packs. The one bearing running at 100,000 RPM is the thrust bearing on the
half inch input shaft so a ceramic bearing is called for here. The planet disk bearings
are only going about 20,000 RPM or less with a 33 pound thrust load. They are a slip
fit on the gray pins.
This arrangement reduces the thrust on the 12 mm high speed bearing from 1000 pounds
to 100 pounds.
Paul Lamar
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