Half Shaft design

[Das Autos]

Hi,

Firstly, I apologize if this topic is rather elementary, or if it has been discussed before.

I was just wondering how other teams go about designing the rear axle half shafts.

We started by considering the torsional moment, taking the whole rear axle to be a single shaft. It's a rather crude method, but I'm only in my second year. We've used this procedure before, and it seemed to work well, but we needed to take collosal tolerances and really high strength steels.

Thing is, we couldnt consider the housing and its mountings as seperate enities. I would really appreciate if anyone can show me the light, since it is all a confusing mess at the moment.


Once again, my apologies for the long post, and for the confusing language, and for posting an elementary question.....

Viren
Transmission Team
Formula Manipal

[Tilman]

Heyho,

what exactely is your problem?

You are talking about the half shafts between your CV-Joints, right?

Get the maximum torque output of your engine, multiply it by all your gearing ratios and then you got your maximum torque at your half shafts.

Note: You have to design your drivetrain for your engine's maximum torque, not the torque at which your tires will start spinning up, because there is a phenomenon called inertia.

[The AFX Master]

Also you'll need to multiply that maximum nominal torque for a safaty factor.. impact loads under stand still acceleration or when you drop the clutch are huge... an DO break shafts.

The big deal designing shafts is more than basic stress calculations, in fact you need to avoid stress raisers, do the correct heat treatement and shoot peen the thing if you do have contact with someone willing to do it well done. Also fatigue design is very important if you get the car early and do lots of testing.

About steels for shafts, 4340 or 4340M are the way to go, don't even think on 4130.

[Das Autos]

Thanks AFX and Tilman, advice understood and taken. But the whole problem stems from the fact that we probably will get very little time for proper testing.

Heat treatment is definitely something on the list. However, I will have to look into the availability of people capable of performing shot peening.

Cheers

[Wesley]

I agree with AFX - I've seen three or so designs fail because of impact loadings, when every calculated number says it should be fine. Don't underestimate the shock a dumped clutch can make on the drivetrain, or especially a hard downshift.