cv axle inner (sliding) joint question

[stewdesignjts]

Hello,
I have a friend who sells atv parts and we are currently investigating different brand cv axles for the polaris ranger/sportsman. After studying some broken axles, the inner joint of the polaris originals are made differently from a popular "premium" aftermarket axle brand.
The inner joint of the original polaris axle attains movement by allowing the cage to side inside the inner end of the cv axle. The aftermarket axle attains motion with longer splines on the axle shaft, and allowing motion between the axle shaft and the cage. (sorry if i'm using the wrong termonology)

My question is which design is stronger, and/or which design better accounts for the suspension geometry changes throughout the travel range? Maybe the aftermarket design is just more simple and is a cheaper way to make it?

Thanks in advance for your help,

Jason

 

[Warpspeed]

Probably not a lot of difference strength wise.

But sliding splines tend to lock up under high torque transmission, whereas the sliding cage design allows the balls in the CV to simply roll along the outer grooves with very low friction in plunge.

All that can be fairly significant for predictable suspension freedom of movement in a very high powered race car. But for an ATV, I am not so sure it matters quite so much.

I guess wear may be higher in a sliding spline than in locked splines, where the CV balls absorb all the plunge movement by rolling.

 

[GregLocock]

The best CV joints for this are the rubber donuts

Second best are the tripod design, with three ball races.

Third are the plunging Rzeppa 6 ball units

All the above are capable of plunging under load, to some extent.

The spline type will generally only slide if there is a torque reversal.

Cheers

Greg Locock

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

 

[Fabrico]

Nearly all ball type CV's that plunge are cross-groove joints as found on many German cars and rear wheel drive. A true Rzeppa joint is stronger for a given size and can articulate more degress than a cross-groove unit, but it does not plunge. That's why they are almost universally used for the outer end of front drive axles to accomodate steering.

Rubber and tripod (also called tripot) joints are strong and plunge but have less articulation. If angles exceed that which can be accomodated by them, you either need to go to a larger cross-groove joint or use a Rzeppa joint and provide plunge elsewhere.

A fairly common alternative is to include a larger slip joint upon the axle itself. It also may help, if possible, to reduce plunge.

 

[Fabrico]

Actually the rubber joints barely plunge but they do cushion the load.

There are also some tricks that off-road racers do to make cross-groove joints more reliable.

 

[Warpspeed]

Rubber donuts have a lot going for them for off road use. No grease, no sliding or rolling parts, no problems with dirt, grit or water.

Not sure of the application here, but Polaris make some cold weather tracked machinery. Highly stressed rubber parts may not be a good choice for sub zero temperature conditions.

 

[GregLocock]

Yeah that was confusing, I meant plunging 6 ball, which are not Rzeppas.

Cheers

Greg Locock

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

 

[Fabrico]

Every joint known has been developed to the point of having and equal pitfall.

 

[Warpspeed]

Yes indeed !

The art of engineering design, is to tip toe across the minefield without blowing up.

 

[stewdesignjts]

Thanks guys for your help - it will help us when talking to our supplier.

As a side note, it is amazing to me how many atv cv joints people are breaking (on all brands, not just polaris) for a variety of reasons. Especially considering the horsepower of the bikes and that the size of the axle looks similar to an automotive axle. Sometimes people put lift kits on the bikes that will put the joints at ridiculous angles, but usually they break them on stock height bikes. I'm sure it is from shock loading (one wheel is off the ground, then suddenly it is loaded), but we still are only talking about 50hp max.

thanks, jason

 

[Warpspeed]

It is surprising what shock loads can do, especially with lots of gear ratio and traction. Metal fatigue may be a factor, where breakage does not occur immediately, but over many stress reversals may start those dreaded growing cracks.

Some sort of torque absorption in the drive train may help to reduce peak loads. Torsionally flexible drive shafts may allow some windup, and be more suitable than large diameter very stiff thin wall tubular shafts. Just adding more strength may not be the solution. Lowering the peak loads may work better.

 

[Fabrico]

There are also torque limiting devices. Some use a clamping means that can slip, others have one or more links designed to shear.

 

[eddyesi]

a lot of ATV's now have LSD's too, which drive up shock loads and torque cycling too, especially wheel off ground applications. I bet shaft sizes we done for none LSD setups and lower power/eweights and have been upgraded past htere limitations

If you want some help Formula SAE/Student cars use a lot of ATV joints and diffs in there cars, there are some SAE papers about and a lot of technical knowledge on joint strengths etc, maybe a great place to start. These guys are uni students so will have trawled the market for the best most efficient designs. Start with honda's there big ATV's have very good drivelines, mainly all tripode LSD setups with high strength splines

It would help if we knew where they were breaking too