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PostPosted: Sat Apr 28, 2012 3:14 pm 
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What I can't figure is how to find the effective pivot point of the ball joints.

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PostPosted: Sat Apr 28, 2012 4:00 pm 
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So there are 3 ball joints on the top alone?

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PostPosted: Sat Apr 28, 2012 4:18 pm 
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The third ball joint is on the steering tie rod end.

The upper ball joints appear to share the same rotation line which is parallel to the road surface. The different length upper control arms will cause a variation in caster in the jounce-rebound cycling range unless the lower arms are proportionally unequal in length as are the uppers. Thanks for the complexity and doubling of parts, Audi.

I think car makers realize more profit in replacement parts than car sales.


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PostPosted: Sat Apr 28, 2012 5:53 pm 
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draw lines through the upper control links. their intersection is the virtual pivot. This allows minimal scrub, without huge wheel offset/backspace. It puts the pivot closer to the rotor than it would otherwise be possible to do. I have seen this on LCAs (my wifes chrysler 300) but not on uppers. Might create a negative KPI(?) This might be desirable on powered front wheels to minimize torque steer.
Sean


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PostPosted: Sat Apr 28, 2012 8:58 pm 
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Though the rest of the car is junk, the front suspension does track well on road crown and bumps.

The Hyundai Genesis (RWD) also uses this type of suspension.

Thanks for the info though. With a custom upright, standard spherical joints and turnbuckles could be used. Especially flexible if push-rod suspension, with the rod acting on the upright, were used.

What if you used an over sized steering rack, and then the actual tie rods as either the front (- scrub) or back (+ scrub) upper control arm.

I may have changed the direction of my own thread, it may now be in more suited to the "In Theory It Could Work..." forum.


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PostPosted: Sun Apr 29, 2012 6:52 am 
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you need 5 "links" or points of restraint to locate the wheel. An "A-arm" counts as 2 points. If you use the steering tie rod to replace one of the upper links in the VW design, the top of the upright will flop around..probably not one of your design goals.


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PostPosted: Mon May 07, 2012 1:49 am 
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Only the Genesis Sedan (not coupe) uses the Audi style arms.

And yes, dealerships make 80-105% of their profit in the parts and service department (105 would be when the sales departments- new and used- rotuinely run at losses.)

But that's not why the designs are like that- it's about 50/50 - functional advantage & engineers justifying their salaries and stroking their own egos getting "their" designs into production.


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PostPosted: Mon May 07, 2012 2:27 am 
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Sean in CT wrote:
draw lines through the upper control links. their intersection is the virtual pivot. This allows minimal scrub, without huge wheel offset/backspace. It puts the pivot closer to the rotor than it would otherwise be possible to do. I have seen this on LCAs (my wifes chrysler 300) but not on uppers. Might create a negative KPI(?) This might be desirable on powered front wheels to minimize torque steer.
Sean


Huh, interesting. I knew it gave more flexibility with suspension design, but I didn't think much about how it improved design flexibility. I think the Wishbone program would need to be a bit more involved to fully simulate that effectively!


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PostPosted: Mon May 07, 2012 3:32 pm 
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"you need 5 "links" or points of restraint to locate the wheel"

true if you're actually talking about the wheel and meant to leave one DOF (degree of freedom) for wheel rotation.

If you really meant the spindle, it's 6, the usual 3 in translation and 3 in rotation

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PostPosted: Wed May 09, 2012 1:06 am 
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Just remember these multiple link suspensions are coming about because of the weight increases we see in modern cars and the effects that weight has on the bushing compliance/comfort.

Generally not required for lightweight specials with bushes and absolutely not required for double Aarms that use all spherical joints (that have no compliance).


Last edited by cheapracer on Wed May 09, 2012 7:23 am, edited 2 times in total.

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PostPosted: Wed May 09, 2012 1:43 am 
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NoahKatz wrote:
If you really meant the spindle, it's 6, the usual 3 in translation and 3 in rotation
Not if you want your suspension to be able to travel up and down...That requires one DoF from a compressible member in place of the sixth rigid link.

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PostPosted: Wed May 09, 2012 2:13 am 
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Driven5 wrote:
NoahKatz wrote:
If you really meant the spindle, it's 6, the usual 3 in translation and 3 in rotation
Not if you want your suspension to be able to travel up and down...That requires one DoF from a compressible member in place of the sixth rigid link.


Hmm...ok, I guess a spring-restrained DOF is closer to a DOF than to a restraint

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