Axle Wrap point of rotation

[heavytrucker]

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.

 

[NormPeterson]

The moment is only part of the story here. What is happening to the longitudinal force that is presumably helping to decelerate the vehicle? If My > 0 and we ignore tire/wheel/brake MOI, then Fx <> 0.


Norm

 

[FeX32]

This effect helps to decelerate the vehicle?

Fe

 

[NormPeterson]

A moment does not directly cause linear acceleration to happen. It may be easier here to think of the moment as being part of the reaction to that which does.


Norm

 

[FeX32]

Yes, of course. I completely understand linear dynamics. I thought you meant that the "S" effect helps the vehicle to decelerate. If it does, plz let me know your reasoning.
Thanks.



Fe

 

[FeX32]

I would presume the "S" effect is not a likable effect in any manner as it imposes large deflections that the vehicle is probably not designed for.

Fe

 

[GregLocock]

OK, one more time. If we split a torque up into two equal opposite parallel forces, we can apply one of those two forces ANYWHERE on the rigid body. The point of application of the other force is then constrained to anywhere along a line.





Cheers

Greg Locock

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

 

[patprimmer]

Umm

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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[FeX32]

Ok, I am in agreement.
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

 

[patprimmer]

I think this may have moved well beyond the intended scope of the OP, who incidentally has not logged on since 09/04/09

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[heavytrucker]

Thank you all for your input. I have been away from the world for a while and just checked the board.

"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.