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DodgeMudder
01-18-2011, 05:47 PM
Ok, I'm going to start by saying that I have too much free time at work when we are slow, so I got to thinking about suspension designs and the various downfalls to different designs. I also got to thinking about what the good points are about other designs, and came up with a really off the wall idea.

Can a solid axle link style suspension use torsion bars for springs?

I'm thinking that if used with a cantilever style link they would work.

What are your thoughts?

joe_and_jeep
01-18-2011, 06:13 PM
Ok, I'm going to start by saying that I have too much free time at work when we are slow, so I got to thinking about suspension designs and the various downfalls to different designs. I also got to thinking about what the good points are about other designs, and came up with a really off the wall idea.

Can a solid axle link style suspension use torsion bars for springs?

I'm thinking that if used with a cantilever style link they would work.

What are your thoughts?


Yes, but why? Thats a lot of twist on the torsion bar so I would assume breakage.

joe_and_jeep
01-18-2011, 06:19 PM
Thinking more... To get twist you need length, and these bars would most like have to run parralel to the axle. Unless you run them staggered they would have to be half the vehicle width (30-40")

I'm thinking here... They could be run legth wise and a cantilever sorta similar to a lower control arm on a GM with Torsion bar then a link from the cantilever to the axle. But with a short arm I dont see a lot of flex.

tjblair
01-18-2011, 06:22 PM
If the arm of the cantilever had a hex in it for the torsion bar then yah I would think that it would work. but as stated above I would expect breakage. I have never messed with cantilever suspension much though. LOL

john00TJ
01-18-2011, 06:23 PM
We use to break torsion bars on the old VW style suspensions a good bit on my VW tube buggy..they never seemed to last when the where cranked down and you beat on it

SirFuego
01-18-2011, 08:29 PM
http://en.wikipedia.org/wiki/Torsion_bar_suspension

I'm not a materials guy or mech eng, but here are my thoughts.

1) Spring rate is determined by torsion bar material, torsion bar length, torsion bar diameter, and arm length. It looks like the material is fixed in this calculator: http://www.proshocks.com/calcs/torsionrate.htm
2) Total travel is determined by the arm length and how far you want to allow the torsion bar to twist while cycling the suspension. This should be determined by some simple trig.
3) I may be wrong on this, but I would assume that the less "twist" you design into the wheel travel, the more reliable the setup will be.
4) The longer the arms are, the less twist you can get away with while still getting the desired wheel travel.
5) You'll need to play with all of these variables to get a desired spring rate and wheel travel while minimizing twist and maintaing realistic values of the torsion bar, arm length, and "link" length (or whatever it's called -- attaches to the arm and the axle)
5) You will still want to limit the suspension in both directions through bumpstops and limit straps to prevent twisting beyond your designed twist angle.

I'm probably over simplifying the problem, but those are my initial thoughts.

DodgeMudder
01-19-2011, 10:18 AM
Thinking more... To get twist you need length, and these bars would most like have to run parralel to the axle. Unless you run them staggered they would have to be half the vehicle width (30-40")

I'm thinking here... They could be run legth wise and a cantilever sorta similar to a lower control arm on a GM with Torsion bar then a link from the cantilever to the axle. But with a short arm I dont see a lot of flex.

This is along the lines of what I was thinking.


http://en.wikipedia.org/wiki/Torsion_bar_suspension

I'm not a materials guy or mech eng, but here are my thoughts.

1) Spring rate is determined by torsion bar material, torsion bar length, torsion bar diameter, and arm length. It looks like the material is fixed in this calculator: http://www.proshocks.com/calcs/torsionrate.htm
2) Total travel is determined by the arm length and how far you want to allow the torsion bar to twist while cycling the suspension. This should be determined by some simple trig.
3) I may be wrong on this, but I would assume that the less "twist" you design into the wheel travel, the more reliable the setup will be.
4) The longer the arms are, the less twist you can get away with while still getting the desired wheel travel.
5) You'll need to play with all of these variables to get a desired spring rate and wheel travel while minimizing twist and maintaing realistic values of the torsion bar, arm length, and "link" length (or whatever it's called -- attaches to the arm and the axle)
5) You will still want to limit the suspension in both directions through bumpstops and limit straps to prevent twisting beyond your designed twist angle.

I'm probably over simplifying the problem, but those are my initial thoughts.

I never said it would be easy to build this system, just more of design idea to see if a different way about doing things could turn out better in the end.

I'm thinking that since a tortion bar works along the lines of a leafspring when it comes to how it controls movement in both compression and extention, that they could be made to work w/ a radius arm suspension to avoid the unloading you get with coils. I'm also thinking if you play with how the connecting link between the axle and the arm sits (ie straight up and down, at different angle) will change the amount of twist the bar recieves for a given amount of axle flex.

oros35
01-19-2011, 10:33 AM
Something to think about.

If you fix the center of a sway bar, you have essentialy created a torsion bar spring set up. If you make some major design changes to the sway bar, that might work.

You could also use a link mechanism to limit the range of motion the torsion bar would travel. Something like how you can mount coilovers horizontally.

SirFuego
01-19-2011, 11:52 AM
they could be made to work w/ a radius arm suspension to avoid the unloading you get with coils.
Someone correct me if I'm wrong, but radius arms unload because of the geometry, not because of the coil springs.


I'm also thinking if you play with how the connecting link between the axle and the arm sits (ie straight up and down, at different angle) will change the amount of twist the bar recieves for a given amount of axle flex.
IIRC, the link is typically designed to be on the same plane as the arm in a cantilever suspension to minimize any binding. For a torsion bar setup, I would think that you would want that same concept to be true or else you would be binding/overstressing/pushing off the arm. That said, the arm must be perpendicular to the torsion bar in this case, so if you want to angle your link you may need to run the torsion bars parallel to the frame or angle upwards and out like \ /. I don't know how well this would work with packaging.

DodgeMudder
01-19-2011, 12:39 PM
Someone correct me if I'm wrong, but radius arms unload because of the geometry, not because of the coil springs.



It's my understanding that a radius arm design unloads as a combination of the spring and geometry, it's kind of which came first the chicken or the egg, when the suspension unloads whats really going on is an abrupt extention of an axle to it's full droop point at an unwanted time, in a coil spring suspension since the coil has no extention control over the axle it allows this to happen, this can happen w/ any link style suspension now with a torsion bar in use instead of the coil, as the axle extends it will twist the tortion bar and this will limit the effect of the axle unloading.

I have been thinking of this as it corresponds to how leafsprings behave, if you look at a rig running leaf springs and revolver shackles going down a steep decent, the rear will unload to the extension point of the revolvers pretty easily, which has caused a few front rolls, and why people don't seem to like the revolvers, now if you take the same vehicle w/o the revolvers, the leafs control that downward travel and keep the suspension from unloading, giving it a more controlled movement and keeping it rubber side down.