ackerman angle

[choubak]

hello, we are french student. And for a school project we must measure the ackerman angle of a race car. We have a problem because the rod aren't in the same reference area.

[Wojtek]

Hi,
There are a number of ways to work our Ackerman angle, either by drawing or measurement. I'm not sure what you mean by the rod not being in the same reference area. Could you elaborate on this please? If you can give an outline of the suspension on this race car, that would be helpful as well.

Regards,
Wojtek.

[choubak]

we study a double wishbone suspension with rod push and a single longitudinal shock.

the antiroll system is made with belleville stacks

we have already calculated the effect of the compression on the differents angle of the suspension.

And now we have to study the effect of the steering on camber, toe and caster. That's why we want to calculate the ackerman angle but the pivot axis isn't vertical.

We have search way to calculate the ackerman angle. The classic method consist to consider the car seen from the top. In our case it can't be used because we haven't fixation point in the same reference area.

We have chosen to use school method : we have considered that the point of fixation between the wheel carrier and the steering is turning around the axis built by the points of fixation between the wheel carrier and the 2 wishbones. Then we calculate the vector associated to the wheel and we deduce the ackerman with a geometric relation (Al Kashi); But we couldn't check if our results are right or wrong, because we use Catia to draw the suspension system; And we have problem to know if the measures are in the good reference area.

[Wojtek]

Hi,
I think I understand your predicament with your Ackerman calculations. That is, how does the steering arm pivot relate to the steering axis.
I think?.that the a line must be drawn perpendicular to the steering axis and which intersects the steering arm pivot point. The angle of this line will depend on the angle of the steering axis. This will plot an intersection point on the steering axis. Then in top view, project the line through the steering axis intersection point and steering arm pivot point back to the rear axle.
This is only my understanding. This would also mean that the Ackerman effect can change dynamically throughout the vertical suspension travel if the steering axis changes.
Let me know what you think.
Regards,
Wojtek.