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Inclined/rotated roll axis; handling effects.


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#1 maxay1

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Posted 05 March 2012 - 18:33

I thought I might have come up with a clever topic, only to find that someone far brighter and more capable had beat me to it...here

I was thinking of the effects of and inclined and/or skewed roll axis on handling in terms of load transfer. The poster in the fsae forum does a much better job of articulating the idea than I could, but I was trying to picture how the vertical and lateral location of the roll axis might cause load transfer even under constant throttle while cornering.

I do recall Mssr Rouelle discussing how an inclined roll axis can cause roll and yaw coupling (if memory serves)....

Thanks in advance for any insight, much appreciated.

Wil



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#2 Paolo

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Posted 19 March 2012 - 12:33

A roll axis inclined in the horizontal plane will, of course, cause a roll and yaw coupling.

Suppose a car is in a very long constant radius corner.

Taking the situation to the extremes, if the roll axis is directed perpendicularly to the car path, the suspension will not move unless the car is accelerating or braking.

In this situation, front-rear roll stifness distribution would become immaterial to the car's handling. Provided the chassis to be stiff, load transfer would be divided between front and rear axles following their mass ratio.

Edited by Paolo, 19 March 2012 - 12:34.


#3 Greg Locock

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Posted 19 March 2012 - 20:58

The quick easy example is setting the RCH of one axle at ground level and the other at the cg height. The first will create a moment Fy1*CGZ on the sprung mass, where Fy1=latacc*(axle mass1-unsprung mass1). The other won't create any moment at all. The springs and sta bar at each end have a roll stiffness k1 and k2 Nm/deg. So the total moment is Fy1*CGZ+0, and the total stiffness reacting it is (k1+k2). So the roll is Fy1*CGz/(k1+k2), from which you can work out the load transfer split front to rear.

Note this is the steady state cornering case.



#4 maxay1

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Posted 19 March 2012 - 23:36

Paolo and Greg, thanks very much...that helps a great deal.

Wil