Off Panhard Bar

[H. J. Zivnak]

----Original Message-----
From: Gary Derian <gderian at oh.verio.com>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Monday, March 15, 1999 10:33 AM
Subject: Re: Off Panhard bar


>There was a general discussion of rear suspension design.  My point was
that
>a 4 link, where two of the links are angled to provide lateral location
will
>bind up when the car leans in a corner.  One angled link will pull forward,
>the other will push rearward.  The amount is small but it is there.  With
>rubber bushings, it works OK.  This type of 4 link is popular on many US
>cars, notably GM intermediate and full size and Ford Fox chassis Mustangs
>and their siblings.
>

Wouldn't the upper bars pull/push the same amount if spaced exactly
>>>the same distance apart from the center?  I need to draw something to
>>>understand this better.


>No.  The binding is not from the change in angle between the rod and the
>pivot axis.  Its because one link tries to rotate the axle pinion up and
the
>other tries to rotate the axle pinion down.  This occurs only when the body
>rolls.

>
Hello Gary,

I was going to send this off list, but in view of the other interest I
thought I'd share.

Earlier in this thread Greg wrote:
"Or go scrounging in a boneyard that has some old Alfas. They used an upper
triangle, with two pivot points on the chassis, and a BALL joint attached
just to the left side of the pumpkin, plus two lower trailing arms.
Particularly if you replaced the chassis pivots of the triangle (rubber
stock) with bronze on steel, also if you replaced the lower rod ends with
real rod ends, they were as NICE a live rear axle setup as you could want."

I believe that this worked, and worked well. The ball joint located the roll
center. As the body rolled in a turn, the worst action I can see is that the
axle rotated slightly. Most certainly there was not binding, even with rod
ends and bronze bushes, in spite of the off center location. Some might even
suggest that the roll center would be better placed to the right, since this
is the side which unloads under acceleration. I think this demonstrates how
much a design can deviate from a theoretical ideal, or how much you
sacrifice an ideal in one area chasing the overall performance of a system.

When I suggested two angled arms, I saw a virtual triangle with the roll
center located where lines projected from the arms intersected the
centerline of the axle. In this case we have two rod ends in shear rather
than a single ball joint with bending stress. As long as I picture this
virtual triangle, I can so no reason for bind. The virtual triangle acts the
same as the real one.

Also, I don't see any reason not to turn this virtual triangle around so the
base is connected to the axle. The virtual apex still determines the roll
center, the body will roll about this point, and the axle will still rotate
slightly, but still no bind. Now the roll center has a more constant
relationship to the center of gravity, and since this relationship
determines the amount of body roll, perhaps the car will behave more
consistently.

As I have said before, ASCII is not an easy medium. It's hard to describe a
concept in a concise manner and show a rapier like wit at the same time. :-)

Maybe we are not seeing the same picture. I know now that I wasn't when I
visualized
your description of the torque arm setup from the Vega. To that end I have
posted an AutoCad Whip file which contains a drawing of a Satchell Link
suspension to incomming, Satchell Link.dwf. If you need a viewer it is
available free at
http://www.autodesk.com/products/whip/index/htm . If you prefer I can
convert it to .dxf .wmf .eps or .bmp.
This suspension has no
relationship to any car, it is just a "reasonable facsimile" of an
illustration from Chassis Engineering.

Someone said that the harder you defend a position the more likely you are
to be wrong. Prolly a corollary to Murphy's Law. So, like Bruce's ECM, I'm
going to "bench" this thing and build a half-scale model and see what
happens as soon as I have the chance. Maybe both Andy and I will learn
something. Maybe that lesson will be to suggest  Shannen switch to Decaf
:-).

I'll let you know how it works.

Regards,

Joe