Opels Torsion beam watts link

Thought it was interesting, the main reason I believe is to allow a softer compound to be used in the two rear beam bushings, the watts link then keeping check on increased movement as a result.

BG.

 

[BrianGar]

And a video of it in motion,

 

[GregLocock]

2 expensive bushes and 5 cheap ones. Two 'scissors' right across the body to design around. One complete new x member

Just because Opel call it clever doesn't mean we have to agree!

The obvious advantage is that the lateral toe compliance is more likely to be understeer than in a conventional twistbeam.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[Pcar928]

Looks like a typical beam axle found on a modern minivan with a watts link.... and if independence is a key benefit then the watts link would give unequal lateral motions side to side in one wheel jounce it seems. Am I seeing this wrong??

 

[BrianGar]

Greg, agree on all that indeed. Instantly thought of the B class Merc when I saw it. Opel seem to think they have invented the idea, but the Merc rear is 'similar'

@Pcar, your seeing it correct. As for Jounce, theres a lot going on when you see a torsion beam simulated and some effects are pros, others cons. Im thinking the main reason also as Greg touched on is toe.
Look at some torsion beam(twist beam) simulations to see how the watts could steady up the trailing end of things.

And Greg, heres the Merc layout, Im sure you've seen it,

 

[LionelHutz]

Are they saying the torsion beam also doubles as the "sway bar"? That makes the aftermarket suspension "tuners" job more difficult.

I had though a watts link was really only advantageous for a solid axle too. Wouldn't just 2 long links from opposite sides to the ends of the arms be about as good?

Am I not correct in thinking that the Merc design is not really a torsion beam since it appears it should be considered as a solid rear axle?

As a general question - why do the manufacturers go through the work to produce a suspension such as these when a single a-arm and a strut could do the job?

 

[BrianGar]

LionelHulz

Yes, a torsion beam by design doubles as a sway bar. Nothing new here its been around for years. All the older Vws and some Audis use them. They also featured in the Mk1-Mk4 Vw Gtis so they do work.

In the Gti's another hollow bar is run through the cross torsion channel to further increase its torsion resistance.

Aftermarket anti roll bars could be added to this torsion beam and came in a U shape, the base of the 'U' fixed to cross torsion tube, and the legs of the 'U' locating onto the ends of the arms where the shocks/hubs mount to.

Two solid links would not have the same effect, as the watts link pivot connects to body.

Im not 100% sure how the Merc setup operates, but it appears to also be a torsion style setup too. I can see no further components.

As for why they just dont use a chapman strut as you mentioned,

Cost.
Extra wear items.
Space, a chapman strut or double wishbone setup would eat into floor pan, and possible boot space.

Theres loads of other reasons of course but theres just a few.

The torsion beam is very simple, works ok, handles ok, is cheap to manufacture, etc.


Brian,

 

[GregLocock]

"That makes the aftermarket suspension "tuners" job more difficult."

As it happens, not really, but frankly that is not a consideration for /most/ car designs, particularly in the A/B segments where cost of ownership is so important. The twistbeam suspension does a lot of things well enough, and provides probably the best performance/price ratio. A chapman strut will normally need an isolated subframe, or some very expensive bushes, to meet the same refinement.







Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[LionelHutz]

I was basing my observation on the Merc design looking at the single big bushing in the middle of the beam. It just looked like the beam was meant to be solid and not flex. It also has a seperate sway bar but that could just be because the beam itself didn't give the right rate.


Brian - I meant just 2 links from the body structure to each end of the beam arms, not going between the ends of the beam arms.

Greg - Yes, I know the manufacturer doesn't care.