Roll cneter on a track bar?

[BioMax]

I tried to do a search for anything on this with no luck...

How would you find the roll center on a suspension system using a track locator/track bar?

 

[GregLocock]

What do you mean by a track bar or track rod? If it is a panhard rod then it is usually at the height of the panhard rod at the axle.



Cheers

Greg Locock

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

 

[BioMax]

I see it most commonly used on 1/4 mile cars. It would run from the lower rear mount of one bar to the lower front mount of the opposite bar.

 

[NormPeterson]

I think what you're describing is a sort of Panhard bar that has a lot of plan view skew, perhaps 45° or so with respect to the lateral. Are there any upper links, and if so do they have any plan view skew and/or side view inclination?

A little curiosity on my part - I'm not aware that drag strip cars normally worried about lateral inertia forces and the roll produced by same, but I have seen a write-up on something similar used for circle-track. Lateral wind effects on directional stability, perhaps?


Norm

 

[BioMax]

Drag cars are obviously not concerned about roll-center, but I have seen this type of lateral limiting device used on daily driven vehicles and have used them myself.

Lets assume that all 4 4-link bars are parallel, from an overhead view, to remove any extra influence on roll center.

Just a thought... On a wishbone style 3 link, like those used on offroad trucks, the roll center is the single point of the wishbone. Now, being that the track bar is creating a "detached" wishbone out of one of the lower link bars, would it make sence to assume that the instant center of trackbar and the link that it mates with would be the roll center?

 

[NormPeterson]

"Lets assume that all 4 4-link bars are parallel, from an overhead view, to remove any extra influence on roll center."

That makes the intersection of the uppers a virtual one, located at X = ±infinity. The track bar at vehicle centerline is another point of interest in the geometric roll center construction.

A wishbone is a slightly different animal, since its pivot point center is mechanically fixed to the diff housing. But strictly speaking, you still have to run a geometric construction back through a YZ plane at axle centerline.


Norm

 

[BioMax]

"A wishbone is a slightly different animal, since its pivot point center is mechanically fixed to the diff housing."

Agreed, but for simplistic's sake and assuming that you don't need to calculate the roll center to within ±.010, if you were to split a wishbone into a triangulated 4 link where the triangulated bars were close enough to share a common bolt, the roll center would be only slightly different than that of the wishbone. Assuming that I am on the right track, a parallel 4 link with a track bar could theoretically loose the opposite bar from which the track bar creates a "detached" wishbone, making a traditional triangulated 4 link with an off center instant center.

I know that I am trying to simplify an otherwise complicated calculation, but does what I am thinking make sence?