Ball Joints / Rod Ends / Spherical Brgs

[ricdat]

Rod Ends and Spherical Bearings are readily available from many manufacturers in a range of sizes and configurations and have published dimensional and load capacity data.
I want to peruse such data for "ball with integral stud" types.
My problem is that they are 'all the same' in that their axial capacity is only ~20% of their radial capacity as their raceway doesn't extend 'over the top' of the ball. Presumably the ball joints fitted to production cars do have races going over the top of the ball in order to resist the suspension spring load. These are made to suit individual applications and generally have taper studs, but where are the general purpose threaded stud equivalents where I can look up data sheets and select the appropriate size like for other rod ends?

 

[PTwizz]

Rick,
I can only say that during my time designing race car suspensions, I have not come across the style of bearing you are looking for. The type used on road cars are designed expressly for that purpose, with a taper fitting to 'idiot proof' them to some degree. Sphericals for race car use would normally be loaded radially, suspension loads being taken through a pushrod directly from the upright to the rocker. It is worth noting that there is a significant difference in durability requirements between the two applications. Road car parts are expected to last hundreds of thousands of miles, while race parts are stressed closer to their capacity to minimise weight and package space.
I would not be entirely happy using an integral stud design with any kind of high load, as the mounting is in single shear, and there is no length over which to generate preload. Note also that axially loading a rod end puts a bending load into the thread of the housing.
A road/track car I recently worked on uses a rod end at the upper wishbone (mostly radial loads, plus a bit of axial from friction) and a wide race spherical set into a U shaped lower wishbone, through which vertical loads are taken.

Pete.

 

[ricdat]

Thanks Pete,
the only place I have seen the type of bearing I am after is on the McLaren F1 road car, but I suspect they made their own (unlimited budget).
As you say, on race cars it is easier - they only have limited steering angle so a radially loaded bearing at the end of a pushrod is OK (while road cars need to steer +/-40 degrees).
The integral stud design would be OK in bending - as all production cars have it. Ideally the stud would have a flange and a length of plain shank (instead of the taper) with the normal thread at the end.
Re the road/track car you worked on: could you explain the set-up of the lower wishbone. Was the 'wide race spherical' suporting the spring load axially?

 

[GregLocock]

I wondered if you meant a tie rod end. It seems you do.

They are fragile compared with the same size of spherical joint, and under impact loads tend to break where you'd expect them to, at the end of the thread, or else the housing pops off.

You could grind the taper down to a parallel section in a cylindrical grinder, but you are in danger of removing material where it is needed.

I would really encourage you to reconfigure your design to one that can allow a normal spherical joint to be enclosed in a clevis with a bolt through it if possible, since this is fail-safe , strong, stiff and efficient. (It is also a bear to arrange, often).

Having said that we do use a taper ended rod end for our lower and upper arm to spindle joints on the front suspension, in production. They are about 40-45 mm dia, with an M12 or M14 thread.







Cheers

Greg Locock

 

[ricdat]

Hi Greg,

for me, a tie-rod end is the thing joining a steering arm to the steering link (that, in turn, goes to a steering rack). It has a female threaded housing for the steering link and a tapered stud to plug into the steering arm.
This is not what I am after.
I agree that a spherical joint in a clevis is excellent, but only for radial loads.
If it has a vertical axis, then it allows steering to +/-40 degrees and takes cornering and braking loads. But what about spring loads?
As Pete suggests, the spring load can be taken directly to the upright with a pushrod, but if a rod-end is used, it will only allow limited steering.
If it has a horizontal axis, then it takes cornering and spring loads. But what of the braking loads? and it only allows limited steering.
I'm not planning on grinding down any standard production car ball joints (at least not yet!).

Rick

 

[PTwizz]

Rick,

The lower wishbone on the road/track car has at its outboard end a housing for the spherical (around Ø40mm ball). The bearing outer race is retained, by a circlip, against an internal shoulder which supports suspension loads. These loads are indeed taken axially through the bearing. None of the bearings limit steering, as they are all arranged to be co-axial with the steer axis (at ride height).

Greg, as you seem to spend a signifacant portion of your life on this forum, is there any means by which we can post sketches? A picture being worth a thousand words etc.

Pete.

 

[GregLocock]

PTWizz - Yes there is. Upload your picture file to a website that allows external linking (not geocities), then you can link to it by typing
[
i
m
g

webaddress
]
all on one line

If you hit preview rather than submit you'll get some formatting hints when posting, and the option to re-edit your post.

RickDat, sorry, I was shooting from the hip there, hadn't realised quite what your concern was. Our upper and lower balljoints resemble tie rod ends except they have axisymmetric caps, that are pressed into the arms. The only way you could use conventional spherical joints on a front suspension is to limit the steering arc to 20 degrees or so, or take the vertical loads axially, which implies that it will be overrated for the likely radial loads. Either sounds do-able.



Cheers

Greg Locock

 

[cadastrophe]

Spherical rod ends mounted with their axis horizontal can be run at up to 36 degrees of steering with special spacers. This is done regularly by the off road fraternity so they have large amounts of vertical wheel travel and maintain respectable steering too.