Off Panhard Bar

H. J. Zivnak bztruck at email.msn.com
Fri Mar 19 04:44:56 GMT 1999


Hello Gary,

It's posted to Incoming at ftp://efi332.eng.ohio-state.edu

Regards,

Joe

-----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: Thursday, March 18, 1999 8:20 PM
Subject: Re: Off Panhard Bar


>Hi Joe
>
>The Alfa setup has no bind because the angled arms intersect at the joint.
>When two arms are angled to form a virtual apex, they intersect only when
>the body is level.  As soon as the body rolls, these two angled arms become
>skew and no longer have a virtual intersection.  Now that I am thinking
>about it more, if from a side view, the upper and lower arms are parallel,
>binding will not occur, but now there is no anti-squat.  Not from torque,
>anyway.  Any other orientation will cause bind when the body rolls.
>
>Reversing the arms so the virtual intersection is in front of the axle does
>not change the roll center location.  The roll center is always in the
>vertical plane that contains the axle shafts.  A line has to be drawn
>rearward from the virtual intersection, parallel to the lower control arms
>until it intersects that plane.  If both upper and lower control arms form
a
>virtual intersection, a line is drawn through both intersections.  Where
>that line intersects the vertical plane is the roll center.
>
>Where did you post that drawing?
>
>Gary Derian <gderian at oh.verio.com>>
>>
>>>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
>>
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