Axle Wrap point of rotation
Axle Wrap point of rotation
(OP)
When a vehicle with a conventional hotchkiss suspensionsexperiences axle wrap and resulting "S" shaping of the leaf springs, does this roation happen about the axis of the axle or the point where the leaf springs mount to the axle?
Any help would be appreciated.
Any help would be appreciated.





RE: Axle Wrap point of rotation
That car tended to rotate about the leaf spring mount below the 2 1/2" lowering blocks I used. For that car, and considering at the time I was only a first year engineering student, the cure seemed to be to bolt/clamp a length of 'T' bar to the front portion of the leaf spring. Seemed to cure the axle wrap up and the attendant wheel hop.
I don't think that I would do that today. Of course I would not use lowering block and I have nothing worthy of drag racing should insanity come visiting. Now a days a good set of leading/trailing rods with urethane or rod ends would do the job without the attendant 'rock crusher' ride.
Rod
RE: Axle Wrap point of rotation
But naturally, the point of wrap (maximum rotation of the leafs) should be the axle. (hance, the "S")
I would expect the axle to rotate about the mounting point only if the leaf spring had one mount.
Fe
RE: Axle Wrap point of rotation
This is a non linear FEA of a leafspring showing it at the design load on the left, and then with a torque on the right.
Cheers
Greg Locock
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RE: Axle Wrap point of rotation
I have never done any analysis on leafsprings. By non-linear, are you referring to the analysis in general or to the fact that the leafsprings may exhibit a non-linear stiffness?
Fe
RE: Axle Wrap point of rotation
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Axle Wrap point of rotation
Thanks,
Fe
RE: Axle Wrap point of rotation
Rod
RE: Axle Wrap point of rotation
RE: Axle Wrap point of rotation
It is caused mainly by braking. And braking on a 60 percent slope at that.
RE: Axle Wrap point of rotation
As you can see there isn't really an axis of rotation in any helpful sense.
Incidentally the angle of the shackle (not shown in my picture, it is present in the model) has an enormous influence on this sort of problem.
Cheers
Greg Locock
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RE: Axle Wrap point of rotation
The axle center can't be the answer except perhaps by coincidence, as it is at the end of a cantilever and cannot offer geometric constraint (other than mostly ensuring that the two springs wrap/unwrap in unison).
Norm
RE: Axle Wrap point of rotation
RE: Axle Wrap point of rotation
Fe
RE: Axle Wrap point of rotation
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Axle Wrap point of rotation
Fe
RE: Axle Wrap point of rotation
Fe
RE: Axle Wrap point of rotation
Furthermore, in this particular problem one can easily prove that there will exist a COUPLING moment in the leafsprings. This justifies my agreement with Bribyk as before...
Fe
RE: Axle Wrap point of rotation
Whatever other things you are talking about cannot confuse this fundamental point.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Axle Wrap point of rotation
Statics book chapter 1.
Fe
RE: Axle Wrap point of rotation
Norm
RE: Axle Wrap point of rotation
Fe
RE: Axle Wrap point of rotation
Norm
RE: Axle Wrap point of rotation
Thanks.
Fe
RE: Axle Wrap point of rotation
Fe
RE: Axle Wrap point of rotation
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Axle Wrap point of rotation
I think Norm is saying that there are a number of forces acting on the leaf spring that contribute to axle location movements and spring shape under the loads.
Obviously some forces are, torque from the drive train from the pinion against the ring gear and torque from the ring gear turning the axle wheel tyre and toque when the brakes are applied. There is also thrust at the tyre road interface and resistance to these various forces at the shackles and spring mounts and vertical components from weight transfer.
Regards
Pat
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RE: Axle Wrap point of rotation
So, we have already established that there is no particular point of rotation and that there are obviously a number of forces that contribute. Not sure exactly what the OP wanted.
Fe
RE: Axle Wrap point of rotation
Regards
Pat
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RE: Axle Wrap point of rotation
"Would it be accurate to consider this situation as being an instantaneous center of rotation? I'm thinking that such an axis would start out close to the centerline of the leaf, but migrate as the spring develops its "S" shape and moves the axle longitudinally.
The axle center can't be the answer except perhaps by coincidence, as it is at the end of a cantilever and cannot offer geometric constraint (other than mostly ensuring that the two springs wrap/unwrap in unison)." - NormPeterson.
I agree.