need definition: "articulation" & "cross articulation&qu

[JRPE]

Hello all! I am new to eng-tips. It looks like there is a great knowledge base here. I am hoping someone can help me out, as I am a mechanical engineer and do not work in the automotive field.

I am working on a project and we are putting together a white paper. In this paper, I need to reference and define "cross articulation" as it relate to the suspension of a heavy truck.

We have commonly talked about articulation and cross articulation. I have also seen the terms used in other forums such as 4wd forums etc. We have come to two different definitions and can't diverge to just one.

In an effort to be as accurate and correct as possible I decided to look for an "industry standard" definition. After contacting SAE, ASTM, and a couple of automakers, I have been unsuccessful in finding anything documented.

Imagine a truck with a 10" block under the right front wheel and the rear left wheel. My understanding is that articulation is essentially the difference in the ride heights between two wheels. Using my definition, one axle is articulated +10" and the other is articulated -10". I then consider cross articulation as the difference in articulation between two axles. In this case, cross articulation would be 20".

Is this correct? Is there a standard? Should I be using a different term altogether?

Thanks for your help!

Jeremy

 

[GregLocock]

That's warp.

Across the vehicle is roll (LF+LR-RF-RR)/4

Along the vehicle is pitch (LF-LR+RF-RR)/4

warp (LF-LR-RF+RR)/4

bounce (or heave) (LF+LR+RF+RR)/4

I think that's right. Note that your example is 5 inches of bounce plus 5 inches of warp.



Cheers

Greg Locock

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

 

[JRPE]

Thanks Greg ... I think we are on the right track now. Is there a standard in which these definitions are documented?

Can frame twist be included in these #'s also or is this just for suspension movement? If not, is there a term that would include suspension movement and frame twist as one measurement?

Bottom line I would like to say something similar to "In order for the truck to navigate from point A to point B, it may experience x inches of __________." (originally we wanted to fill in the blank with cross-articulation)

 

[Fabrico]

The industry term for measurement of longitudinal chassis twist in race cars to rock crawlers is called "torsionl stiffness". Try a web search on "race car torsional stiffness".

 

[Fabrico]

Actually, the term is quite universal. You can also try "truck chassis torsional stiffness".

They should not be combined, suspension is articulation, chassis is twist.

 

[GregLocock]

Except of course in the case of old British lorries, which used the chassis as the suspension.

As fabrico says, use a total warp figure but split it up into chassis + suspension.



Cheers

Greg Locock

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

 

[JRPE]

Thanks guys for your help!

Is there a specific SAE standard (or similar) that I can reference?

Jeremy