Designing sliding spline to minimize torque lock up
Designing sliding spline to minimize torque lock up
(OP)
Developing a CV axle with fixed end joints and a sliding spline in the center. Testing the prototypes found that the cages are breaking in the fixed joints because the splines are not slipping under heavy trottle. Current design is involute splines coated with blue antivibe material (Supplier English version of print says teflon, maybe be nylon). Looking for advice to three questions:
1. First question is would steel to steel splines slip better than steel to coated splines? Assume coating is standard driveshaft blue material. In this application noise and vibe are not the big concerns.
2. Second question would parallel splines reduce the torque lock up significantly versus the current involute spline? Involute splines were origonally chosen to simply manufactoring the axle shafts.
3. Last question is would changing the length of the sliding spline and surface area of tooth to tooth contact change the coeficient of friction?
Thanks for any feedback in advance.
1. First question is would steel to steel splines slip better than steel to coated splines? Assume coating is standard driveshaft blue material. In this application noise and vibe are not the big concerns.
2. Second question would parallel splines reduce the torque lock up significantly versus the current involute spline? Involute splines were origonally chosen to simply manufactoring the axle shafts.
3. Last question is would changing the length of the sliding spline and surface area of tooth to tooth contact change the coeficient of friction?
Thanks for any feedback in advance.





RE: Designing sliding spline to minimize torque lock up
What's the prospect for stronger cages?
Does the coating manufacturer provide PV ratings, so that you might stand a slim chance of actually engineering the connection? In general, more engaged area should help, but numbers would tell you how big a change you need to make.
How do you feel about ball splines?
Mike Halloran
Pembroke Pines, FL, USA
RE: Designing sliding spline to minimize torque lock up
My advice would be to develop a spec for breakaway axial thrust vs torque and talk to suppliers.
Cheers
Greg Locock
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RE: Designing sliding spline to minimize torque lock up
A remedy to this issue would be to increase the spline engaged length, so that the "cocking" angle is reduced. Or you could switch to a major diameter fit type of spline, which would provide axial alignment.
With regards to static/sliding frictions, surface contact area is normally not a factor.
Hope that helps.
Terry
RE: Designing sliding spline to minimize torque lock up
The axial alignment may be the issue.
What are thoughts on spline coating versuses steel to steel and is there a standard specification for material and thickness of coating.
Thanks again for the help.
RE: Designing sliding spline to minimize torque lock up
Steel on steel can do very well, provided the grease is actually present and dirt is excluded. Off road, that requires boots, so far not specified.
Mike Halloran
Pembroke Pines, FL, USA
RE: Designing sliding spline to minimize torque lock up
RE: Designing sliding spline to minimize torque lock up
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RE: Designing sliding spline to minimize torque lock up
It smells like you intend to solve a production problem by blindly changing a purchasing specification, without leaving your desk, based on exactly zero analysis and exactly zero actual data aside from the existence of one or more failures in a part that you may or may not change.
What I mean by 'zero actual data' is that you haven't gone out to the production line with a torque wrench and a force gage and tried to assess, not a friction coefficient directly, but a transfer function between torque and thrust for the splines as used right now.
My smell detector says that if the friction were anywhere near bad enough to be the root cause of the reported failures(s), some binding would have to be noticeable in normal riding as the suspension articulates.
Speaking of that, the suspension probably has rubber bushings instead of, e.g. rod ends, so it's not totally rigid. Which means that the arms may not pivot around the nice centered pivot points in your drawings and CAD models.
It also appears, talking about wobbly suspension bits, that you have not eliminated as a root cause, the possibility that the shafts are just a bit too long, and running out of spline travel is what's killing the joint races.
Have you broken a joint yourself? Go and do so.
Mike Halloran
Pembroke Pines, FL, USA
RE: Designing sliding spline to minimize torque lock up
While the surface speed here will be low, the pressure is probably very high.
With a high pressure low speed case, nylon should be better than PTFE (Teflon) as it has less creep and tendency to stiction caused by deformation of the surface by prolonged high load.
Regards
Pat
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RE: Designing sliding spline to minimize torque lock up
RE: Designing sliding spline to minimize torque lock up
Those splines need to be cut using tight tolerances and good quality control. The smallest nick/bur could cause them not to slide under high torque. Have you done a close inspection on the spline on the failed parts ?
Better lube is the obvious answer, with the limit being what is practical.
RE: Designing sliding spline to minimize torque lock up
FROM SAE "Univ Jt and Driveeshaft design manual" Advances in engineering series #7.
The 1979 nylon may well be The 2010 "blue anti-vibe" material
I'm unclear as to why a CV joint with slippery plunge capabilities is not being used at one end.
RE: Designing sliding spline to minimize torque lock up
I have been looking for the correct standard to read and reference for the sliding splines sizing and tolerances. Based on feedback in this thread it sounds like a major diameter alignment is better than a side fit alignment. I am not clear which is appropriate the SAE B92.1-1996, ISO 14:1982 , DIN 5463/64, or something else. I plan on purchasing a copy of a standard, but not sure which one. Any feedback to direct me to a standard would be helpful. The current print simply reads 19T, M1.25, 45degrees.
Thank you again for any help.
RE: Designing sliding spline to minimize torque lock up
Mike Halloran
Pembroke Pines, FL, USA
RE: Designing sliding spline to minimize torque lock up