Roll Center height for 4-link 2

[RegisAlstom]

Sorry for the begginer level question, but I am struggling to find the roll center height on a 4- link rear suspension.

Looking in the plan view, the upper links are paralel, and the lowers are triangulated from the chassis to the axle.

The lowers are pointing inwards in the chassis and outwards in the axle.

Now looking in the side view, both links are pointing upwards in the chassis, the anti-squat is being 100% or more depending where I put the links. Now I don't know how to find the roll center height.

Can somebody give me some clue?

Thanks in advance

 

[GregLocock]

Well, it would probably help a lot if you look at the front elevation, since that is the one we use to find roll centres!

The roll centre is the point at which the resulatant of the lateral forces at the contact patch are resolved in the plane of the wheel centres, so the answer in your case is pretty obvious.

Cheers

Greg Locock

 

[Joest]

What lateral control device are you using? Panhard bar? Watts Link? Knowing this will help in formulating a clear answer to your question.

-Joest

 

[GregLocock]

V type arms are used to obviate the need for a panhard rod aren't they?

Cheers

Greg Locock

 

[bhart]

Referencing Race Car Vehicle Dynamics, Section 17.7, Figure 17.36 (the figure is basically the suspension you have described). To find the roll center of your suspension, you need to:
1. Draw a line to extend each of the triangulated links in the plan view and find the intersection point, note the fore/aft location of this point and draw a vertical line at this fore/aft location in the side view.
2. Draw a line to extend the triangulated links from the side view (it shouldn't matter what link you choose if you have a symmetric suspension).
3. Mark the point where the vertical line from step 1 and the extended line from step 2 intersect.
4. Now draw a line, in the side view, that is parallel to your parallel (upper) links and passing through the point from step 3.
5. The line drawn in step 4 is your "suspension roll axis" and the point where the roll axis intersects the vertical wheel plane in the side view is the "roll center" of the suspension.
The book also describes the procedure for finding the roll center of a 4-link w/ two sets of triangulated links (yours is considered somewhat special b/c one of the pair of links is parallel).
If you are dealing w/ this type of matter on a regular basis, you should probably look into buying a copy of Racecar Vehicle Dynamics by Bill and Doug Milliken. It is catered toward an engineering audience.

 

[Joest]

Ops! I must of glazed over the fact that this is a non-parellel triangulated system. In this case, I agree with what bhart wrote. The Milliken & Milliken approach will work. Good luck.

-Joest

 

[RegisAlstom]

Thanks to all for the answers.


Greg, I was not understanding exactly what you wrote, but now I can see and understand. Thanks

Joest, the triangulated links are used as lateral control devices too. Thanks for the validation on the Milliken's approach

bhart THANKS a lot! It was exactly what I was looking for. I am buying the Milliken's book now!

This suspension is for a Rockcrawler.. so most of the concepts I had for competition had to be "reversed" ... the roll center needs to be high to reduce the probability of roll over in a of camber situation and etc...

Thanks again

Regis