Involute Spline Question 1

[Heckler]

A large Aerospace company (name withheld to protect me) designed this system drive system using one of our pumps. It is coupled together using a external splined shaft. Our pump has an internal spline shaft and the drive motor (electrical) has also an internal spline. Their is a cold plate that the pump and motor are mounted too. The spline is a 12 tooth 20/40 pitch, 30 deg PA with a .6000 PD.

We are having problems with our pump siezing. Partly do to a misunderstanding of requirements which we are willing to fix. But as the system is mounted due to poor tolerance stack analysis the problem is amplified.

In my nine years of mechancial engineering I have never come across this direct coupling configuration. I've always seen a couple between to splines to take up any misalignment, or even a crowned middle shaft design. I believe this is a bad design resulting from lack of analysis.

What I'm asking for is any reference material for spline design. I read the Machinists hardbook already and need more. Also, any ideas on how to solve this problem. I can send X-sec pictures from my Pro/E model. Thanks

 

[arto]

try
"Design Guide for Involute Splines" by R.W.Cedoz & M.R. Chaplin SAE 1994 M-177:

http://www.sae.org/servlets/productDetail?PROD_TYP=BOOK&PROD_CD=M-117

also
"When Splines need stress Control" by Darle W. Dudley
Product Engineering 12/23/57

& "How to design Involute Splines by Darle W. Dudley
Product Engineering 10/28/87

Maybe try crowned teeth to handle the misalignment?

 

[arto]

whoops 10/28/57 for the 2nd article

oldies but goodies!

 

[enirwin]

arto,

Do you know where I can get copies of the Dudley articles? I've tried to find old Product Engineering articles before with no success. Any help would be appreciated.

Thanks,

enirwin

 

[MikeHalloran]

You _might_ be able to find an externally splined shaft with two slightly crowned splines to act as a wobble drive between motor and pump.

If you put a notch in the middle of a straight splined shaft, you might be able to support it there, while pressing on the ends, one at a time, with a hydraulic jack, while heating the spline with a torch, enough to make it yield plastically and bulge a little.

[ Powroll used to do something like this to motorcycle connecting rods, bulging them in the middle and shortening the eye to eye distance so they would work with stroker cranks. ]

Expect accelerated wear of the spline parts.

Better solution: Mount the lighter component, motor or pump, by some means that is torsionally rigid but somewhat compliant to radial and moment loads. E.g. rubber bushings or hourglass springs around the affected mounting screws, and a couple of leaf springs for torque links. The compliant parts have to be stiff enough to support the component's weight, but flexible enough to allow the entire component to precess around a rigid but not perfectly straight coupling, without overloading either motor or pump shaft bearings.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[arto]

Try the MIT Library - they have all kinds of stuff:

http://libraries.mit.edu/docs/