Driveshaft Critical Speed calculation

[brgriffi]

Hi all,

I'm looking for a way to roughly estimate the critical speed for an automotive driveshaft. It's a typical RWD driveshaft -- a hollow tube supported at each end by a U-Joint. 3" O.D., .083" thickness, 4130 steel. We have lengths from 10" through 60" in increments of 5".

 

[GregLocock]

Not in general, not accurately enough. For a specific application, where you know the engine mount rates, inertias and the same for the axle, then you can start to estimate it fairly accurately.

The reason that you have to know so much is that the ends of the shaft are not pin jointed to massive foundations, but instead are connected to systems which have their own set of natural frequencies.

You'll also find that the presence of cardboard liners and internal harmonic absorbers have a big effect.

There is also the additional complication that the measured natural frequency in the lab, may not correlate to a problem on the road, for a particualr car, and the speed may be out by several kph. The peak is fairly broad as well.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kitabel]

Read some comments here:

http://www.markwilliams.com/Catalog/pg70.pdf

 

[GregLocock]

It would be interesting to see a graph of actual whirlspeed versus those predictions.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.