suspension bellcrank bearings

[rpmag]

In a pushrod suspension, compressing the spring and damper via a bellcrank, much attention is placed on the bearings used in the bellcrank. In formula cars these bellcranks are in single shear and attach to the tub via a stiff post embedded into the tub.
With a different application, i.e. using a bellcrank in a spaceframe chassis the bellcrank can be mounted in double shear. What bearings could be used for this when weight is of slightly lesser importance.
I was wondering if two sherical bearings running on the same shaft, spaced 10mm apart would do the job...or two cone and cup needle roller bearings would also be suitable?

 

[Fabrico]

Anything can be used. However, things such as load, longevity, stiction, etc., all have thier own requirements. In addition, leverage and total movement are just as important as the weight of the car.

If things are well aligned and rotate upon a common plane, a single-row ball bearing will do fine. If there are angles or side loads, a double row or spaced pair of bearings would be best. Swivel rod ends will work but life span will be limited and in some situations, stiction can be high. High stiction, will cause higher than calculated loads to be present in other places.

 

[Tmoose]

I have no idea what is commonly done, or what the economical tradeoffs might be, but if the angular rotation is small some kind of flexural pivot would be zero wear and zero stiction.

 

[BillyShope]

Good thinking, Tmoose!! I like it. Would probably never be used on a "one-off," but the concept might be useful in a torsion bar car with a secondary "trimming" spring.

 

[patprimmer]

Billy

I think you just described the so called rubber torsion bar type of suspension commonly used on light duty trailers.

Regards

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[BillyShope]

Yes, Pat, but do they ever offer a secondary spring? What I find unique in Tmoose's suggestion is that a "springs in series" situation might, in some cases, be beneficial.

 

[BillyShope]

Forget it! I'm posting before I'm fully awake again. The "secondary" spring has nothing to do with the torsion bar or with Tmoose's idea. I got caught up with the bellcrank bit and lost perspective.

 

[patprimmer]

Been there done that.

I am not a suspension guy, so I did not respond, presuming I was in over my head.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[WolfHR]

I'm by no means an expert, but I seem to recall reading somewhere about that sort of bearings. The argument was that because of, relatively small, oscillating movement bearings with (relatively) larger rotating elements (like balls and cylinders) would/could suffer excessive, and irregular, wear because they'd never turn a whole rotation... ISTR something like needle bearings were deemed a better choice, since with even small range of movement rotating elements would do a whole turn (or few)- resulting in more even and smaller wear.