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CV joints

CV joints

CV joints

I am seeking opinions on a suitable bearing support method for the half shafts on a kitcar on the rear axle (please see diagram).

The usual arrangement for independent rear suspension vehicles would be to connect the diff and each wheel hub with a single shaft which has a CV joint at each end, one or both of which would have plunge.

However, there is a vertical chassis member in the way which makes this not possible and so the idea is to use two shorter shafts on each side with a third CV joint with a support bearing so the layout would be = diff - CV1 – shaft1 – support bearing – CV2 – shaft 2 - CV3 – wheel.

Each of the shorter shafts will be around 40cm. CV1 will run at a permanent angle of around 10 degrees, and CV2 will be similar but vary with suspension travel and I wonder what sort of loads the bearing will see?

A standard prop shaft rubber supported bearing assembly would be the simplest and cheapest solution and allow for some small initial misalignment of the bearing or imperfect positioning of the diff in the chassis (diff is solid mounted) and also accommodate dynamic misalignment as a result of chassis flex but I wonder if the 10-degree angles will result in a radial or axial load on the shaft rendering a rubber mounted bearing assembly unsuitable or are there no loads other than the usual torsion?

Is there an equation to calculate the radial and axial loads on shaft1?

RE: CV joints

Yes there is. Torques behave like forces, you use triangles to resolve them. So in order to get the torque T to transmit from shaft 1 to shaft 2 you'd have to apply a torque of T*sin (or tan, I can't remember, and am too lazy to draw it, machs nicht) 10 degrees to the bearing near CV2, out of the page. This is created by vertical forces at each CV, so you need to draw a free body diagram of each shaft to figure out those forces. I'd point out you could replace CV1 and CV2 with hookes joints if you haven't got much wheel travel.

Incidentally you should give the designer of the kit car a smack around the head, that is a stupid piece of design. It won't work with a live axle and as you've found out, it doesn't work with an IRS.

Very similar hardware is used on some front wheel drives, where they use a layshaft or intermediate shaft across the back of the gearbox so that they can have equal length halfshafts.



Greg Locock

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RE: CV joints

thanks Greg,
do you think that the typical rubber propshaft support bearing would suffice or are the loads likely to be higher such that e.g. a self aligning roller bearing would be required?

RE: CV joints

I'd use a standard centre bearing from a 4WD with two piece prop. Your problem is that your torques are high, because of the axle ratio, but a 4WD probably has a low first gear ratio that is equivalent.

But this baffles me. If you've got 50mm clearance to fit one of those, why not drop or raise the diff and solve the problem directly?


Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: CV joints

the car wasn't designed for the engine/diff installation I'm attempting & the chassis member is diagonal so cant raise the diff. Also can't lower the diff (which would clear the chassis member) but would have it hanging out under the car. the easiest solution looks like two piece half shafts as described but I'm trying to ascertain what sort of axial / radial load such an arrangement would introduce

RE: CV joints

It sounds to me like the easiest solution, by far, is to move that chassis member out of the way.

What you're describing sounds like a mess that will be difficult to make robust. Moving structural members around isn't the easiest thing in the world, but when you're done welding them they don't move. Half shafts not so.

RE: CV joints

Study the passenger side CV axle setup on a Left hand steering, Nissan Murano and I suppose other such Nissan models too. Especially on the AWD models they use a stub drive axle that passed through the transfer case to engage with the differential. There is an outboard bearing on that shaft that is supported in a special bearing bracket that is bolted to the engine crankcase to locate and hold that outside bearing.

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