Lateral Load Transfer and Camber

[GEspo]

Hello eng-tips experts. I'm using 3D rigid body dynamics software to model a few car designs. I wanted to check a fairly simple concept in transient state,

How camber affects overturning and slide out(loss of traction):

- M*a_y acts on CM to start lateral load transfer to outside tires

- Moment produced at the suspension joint involving the wheel and load on it(not going into detail here, roll centers etc)

- Depending on wheel camber angle a camber force in y-dir can be generated that can a) act against M*a_y and will resist load transfer or b) act with M*a_y and assist load transfer


Resisting load transfer can 1) resist overturning and 2) keep tires from reaching max traction levels(slide out)

Am I close here? Thanks for the help!

 

[BrianPetersen]

The slip-angle vs lateral force vs camber angle relationship is a multi-dimensional "map" that is specific to the tire and to the tire's inflation pressure ... and the inflation pressure is a function of the end user.

High-sidewall-profile tires can be surprisingly grippy under positive-camber conditions.

Very wide low-profile tires might not be too happy about it.

 

[GEspo]

Assuming the same tire, various suspension geometry(causing camber change) will affect lateral load transfer?

 

[GregLocock]

Typically yes , because you are changing the roll centre height when you change the camber curve.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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

 

[GEspo]

I'll have to investigate roll center vs camber change with the DW suspension. Currently modeling with only lateral spring compression and manual camber change(a near rigid chassis) to split up the effects of a rolling sprung mass. Thanks again.

 

[GEspo]

Hopefully there's still an audience here for one more question, somewhat on this topic:

I'm feeling confident in my models and understanding of dynamics so am considering what type of vehicle to design and test. A large portion of my learning over the past year etc has been building models in my RBD software, ranging from very detailed/complex to fully rigid/simplified, and extracting data from them. I also use the models to confirm equations from my dynamics texts, Gillespie etc. so all in all they've been fun and very helpful. Now to my question:

What are the problems with using an RBD model for the foundation of a vehicle design? ie what can go wrong when using a model to design an actual vehicle? Is there anything specific that doesn't translate well? I assume the tire will be the most problematic due to RBD not being anywhere close to a real tire.. Anything else that will not translate well or that I should keep my eye on?

Thanks again very much for the attention and answers.

 

[GregLocock]

Tires are about 70% of the job. In my case I'm also interested in steering feel (in a general sense) so the steering system is about 10% of the job. The remaining 20% is kinematics and compliances, and shock absorbers and springs and so on. The list of gotchas is so long that we have an internal wiki to document work arounds.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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

 

[cibachrome]

Don't forget that vehicles with 4 tires on 2 axles work in pairs. Your load transfer affects both the inside and outside tire forces and moments which are summed to get you a net axle force (and residual moments. As usual, academic studies seem to forget about the 8 moments that go along with those 4 tires. They has a substantial effect on the load transferred, the transient response, and can induce positive feedback in the roll control mechanism.
If you ignore them, as well as the kinematic and elastic compliances, you're work will have little chance of correlation, even with a go-kart without a steering system (if that can be imagined), especially if you want to put a driver model in there, too.