T-BAR VS. U-BAR ARBs

[autogyro46]

First, thanks to all who responded to this newbies very first thread last week.
Having set aside geometry for awhile, here's my next query.
I'm intrigued by the use of T-bar ARB's on some cars (there a beautiful pic of one on the Radical SR9). Nobody seems to talk much about this, but it's function with respect to the opposite wheel seems to be fundamentally different to the conventional U-bar.
Is the simplest terms, roll induced compression on the outside wheel is tranlated as a downward force on the inside wheel, rather than an upward force in the U-bar version.
Rotation torque is still referred to the chassis by the torsional compliance of the bar, although the bar is now 90 deg. from the the U-bar version.

The load transfer to the inside wheel would seem to be highly advantageous. Why isn't this used more..or at least talked about more?
As an aside, it seems to function much the same the oh-so-trendy "monoshock" configuration of a few years back, but without the potential binding and friction problems in that design.
Is there an Achilles heel that I'm missing here?

 

[GregLocock]

I'm guessing you are talking about 3 spring suspensions driven by rockers and pushrods?

You wouldn't use it on a road car, it's only really practical if you are going to do lots of maintenance, and adjustability just isn't a requirement for road cars.

The vast mass of suspension theory and practice is aimed at roadcars, racers deal with much smaller wheel velocities and have a simpler task. They also have fewer resources of course.

Here's a MBS simulation of a Lola 3 spring setup

http://greglocock.webs.com/

So far as tuning them goes you can do things like adding inerters and also jounce and rebound stops in roll, which is cute.

FSAE kids like them, personally if I am ever a design judge for FSAE again then I will be marking them down unless they can give a good reason why they are being used.

"The load transfer to the inside wheel would seem to be highly advantageous."

Don't agree.


Cheers

Greg Locock

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

 

[autogyro46]

Thanks. I take your point that in practical terms, the complexity and maintainance problems may outweigh any theoretical advantage. I was just wondering what, if any, theoretical advantage there was.
The Matthews Lola dwg, by the way, does a beautiful job of showing how this setup separates differential and common mode movements into two orthogonal movements: differential being the transverse Belleville arrangement, and common mode bump via the longitudinal bump stop.

 

[GregLocock]

The main reason they are used is that they allow easy tuning, and can be used to give LOWER antiroll rates than a conventional setup with the same bounce rates would give, even without an a/r bar (although I suppose you could use a Z bar instead). Also of course inboard springs are better aerodynamically, not, I think a big deal.

Yes, Tony's drawing is rather good, he's a clever bloke.







Cheers

Greg Locock

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

 

[autogyro46]

Aha! I thought aerodynamic downforce might have something to do with this.

 

[GregLocock]

It does. Aero cars need to be very stiff in pitch (especially), so they need stiff bounce rates, but also need to be able to hop over kerbs, so need low single wheel bump rates. The latter is the average of the bounce rate and the roll rate. So you need super soft or negative roll rates on an aero car.

If it is ground effect aero then this is a bigger concern as the ride heights also need to be controlled as well.





Cheers

Greg Locock

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

 

[Cholio]

Autogyro46, you are misunderstanding how the pictured setup works.

http://www.f1technical.net/forum/viewtopic.php?t=4785

It does not work any differently than the conventional U-shaped ARB. It pushes (or pulls) the other wheel in the same direction.

The T-bar is a torsion bar. See the square end? It is twisted when the car rolls. It is free to move fore-aft with the vertical motion of the suspension. There is another tee on the other end of it that is hidden in the monocoque that is has ball bearings on the ends. The "T" (or the horizontal "H" to be exact) can rock freely, but it takes an effort to twist it. It is the same Anti-roll bar, not a pro-roll bar.

 

[autogyro46]

Actually, if you look, I attached (and mentioned) that very link in my first post.

There seems to be some contention here: In one of the submissions above, it is suggested that a T-bar functions exactly the same as a Z-bar (commonly used as an anti-jacking devive in VWs and swing-axle Corvairs).

Its application in a high downforce racecar makes perfect sense, given the very stiff anti pitch springing required, which would otherwise suppress individual wheel motion in bump.

 

[Cholio]

Yes, I copied and pasted your own link from you first post. I am just explaining what it is showing.

 

[GregLocock]

autogyro - You are misquoting me.

Cheers

Greg Locock

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

 

[autogyro46]

My face is red..Sorry, I got carried away.