Tranverse Leaf as ARB

[woodenwheel]

Does anyone have any experience with a tranverse leaf spring being used as an ARB? The application is a asphalt midget racecar with a beam axle and coil-over suspension, and will be used as a front ARB. Are there any noticible cornering differences as compared to the a standard ARB? Thanks.

 

[hemipanter]

What counts for antirol is the wheelrate in the roll situation. The problem is that an tranverse leaf spring will have a wheel rate even in heave.
Goran

 

[woodenwheel]

The major difference I understand is that as the chassis rolls, the tranverse leaf will load the LF tire, instrad of unloading it like a conventional ARB. I am interested in any performance gains from this, or anyone who has experience with it.

 

[hemipanter]

You may look at the sway bar as a bar that is welded solid to the chassis in the middle, during roll. It is a torsion bar and if the right wheel is going in to compression by the same amount as the left go to extension , the bar sees zero movement in the middle.
Besides, the trick with swaybars is to tune the car by altering the load transfer between the front and rear axles. To do so there must be a load difference between the inner and outer wheel. Other wise we just need different rate regular springs.
Regards
Goran

 

[Tmoose]

"the tranverse leaf will load the LF tire, instead of unloading it like a conventional ARB."

It sounds like the spring pivots in the middle, and that makes it a "camber compensator" used to good effect reducing over-steer on the hind end of swing axle cars like VW bugs and early Corvairs. I think the action is an anti-anti-roll bar, forcing the opposite end to provide roll stiffness.

 

[murpia]

"You may look at the sway bar as a bar that is welded solid to the chassis in the middle, during roll. It is a torsion bar and if the right wheel is going in to compression by the same amount as the left go to extension , the bar sees zero movement in the middle."

Yes, but an ARB is still transmitting torque (force) from one wheel to the other, but not to the chassis, even if the centre displacement happens to be zero.

That's very different from your description of a torsion bar attached to a chassis in the centre, which DOES react torque to the chassis.

Regards, Ian

 

[GregLocock]

I think we need a sketch!

Cheers

Greg Locock

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

 

[hemipanter]

Ian,
how is it that torque is transmitted to the chassis if the the attaching point dosent move?
Regards
Goran

 

[patprimmer]

I have to admit that your description sounds like a camber compensator bar, which in effect reduced roll resistance for the same spring rate rather than increasing it, ie an anti anti roll bar.

I used these on swing axle VWs with two standard front anti roll bars with great success in reducing over steer.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[murpia]

"Ian,
how is it that torque is transmitted to the chassis if the the attaching point dosent move?
Regards
Goran"
Newtons 3rd Law...

Fixing a torsion bar torque reaction point to the chassis is the ONLY way to get a torque transmission to the chassis.

But I get the feeling we aren't quite talking about the same thing...

Regards, Ian

 

[GregLocock]

i repeat,and amplify, we need a diagram.



Cheers

Greg Locock

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

 

[NormPeterson]

The only way I can see a transverse leaf acting as a sta-bar if it is supported at two points against vertical translation but not against leaf bending rotation. Even in that case, you can't avoid the heave rate, so the coils would have to be softer.

In heave, you get symmetrical deflections and one set of reactions (loads on the chassis) but in roll the deflections are antisymmetrical and the loads on the chassis are quite different (and opposite in direction). A spreadsheet to work up the deflections of a simple beam that overhangs the two supports and is loaded variously at the ends based on beam formulas might prove to be interesting re: the proportions of ride and roll stiffness that are reasonable (or even possible).

IIRC, the C5/C6 Corvettes use such an arrangement, though I'm pretty sure that they retained the sta-bar.


Norm

 

[hemipanter]

Ian, I get the same feeling. Let me try to explain. If we think of a regular swaybar installation using two caps each end bolted to the chassis and in the middle of the bar we should weld a steel wheel. If we then roll the car for equal but oposit deflection each side, the middle wheel sould remain in rest. It shouldnt matter then if the wheel was to be locked to the chassis or not.
This is presumed that the swaybar sees exactley the same movement each wheel.

I believe that the "lifting" force thinking of the inside wheel created by the sway bar is a bit confusing, even if right. The bar create a spring wheelrate in roll. If the regular spring wheelrate is 100N/mm it will take 100N to lift the car 1mm one side, and 100N to press it down 1 mm the other side. If we add a swaybar giving 50N each wheel in roll, it will resist roll in the same manner as using 150N/mm springs each side.

The difference is that the spring is loaded in rest by the weight of the car while the swaybar is not.

Regards
Goran

 

[murpia]

Goran,
Let's compare a car with 150N/mm front side springs to a car with 100N/mm springs and an ARB giving 50N/mm wheel rate effect and assume that everything is perfectly linear, including the tyre spring rate. You also have to assume that all load transfer forces go through the springs (no geometric load transfer).

You could then perform a static (d'Alembert) analysis that indicated that the roll couple distribution of the two cars was the same, and with no jacking forces you could indeed expect to see the ARB position in the exact centre be equal to the no-roll condition.

However, as soon as any longitudinal load transfer, geometric load transfer, single wheel bump or axle bump inputs get involved, there is no way the two cars will behave the same.

I don't know how this compares to the original question, because I need to see a sketch like Greg... I think the 'transverse leaf as ARB' is actually acting as a Z-bar (axle heave spring).

Regards, Ian

 

[hemipanter]

Ian, it was just an idea of mine that trying to show some other way of looking at the bar might put light on the situation of using a sway bar.

I absoulutley agree with your above description. Myself I usually calculate with a bar fuction as such, and dont pay to much attention to f,ex one wheel only deflection or geometric load transfer effects regarding swaybars.

Sorry if I went wrong on the subject.
Goran