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Page 40
3LINK SETUP
(also: Triangulated 4link and Torque Arm suspensions)
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This is something which is probably of more interest to the dragracer,
but, since Jaguar used this on their early C-Types, I would urge those who are running a
RWD beam axle car on road courses to consider this information.
This is an asymmetric trailing 3 link arrangement which, during
forward acceleration, completely cancels driveshaft torque, thereby providing equal rear
tire loading for maximum acceleration. There are 2 symmetrically situated links (in plan
view) and a third "odd" link which is offset from the car's centerline (to the right). All
links, in plan view, are assumed to be parallel to the long axis of the car (i.e.,
parallel to the SAE X-axis).
TRIANGULATED 4LINK:
(An exception to the above paragraph is the triangulated 4link, where the
triangulated pair can be treated as an "odd" link which is centrally located (zero
offset). In other words, by "combining" the triangulated pair into a single link, the
triangulated 4link can be treated as a 3link in this spreadsheet.
TORQUE ARM SUSPENSION:
Another exception is the torque arm suspension. This can be accommodated
by inserting the distance forward from the axle centerline to the torque arm contact point
as the "distance forward to IC" and, also, the "distance forward from rear axle centerline" in
the "ODD LINK REAR MOUNTING POINT" section. A value of zero should be inserted for the
odd link length. The offset is determined by the lateral location of the torque arm
contact point. The "vertical distance from track surface" for the rear mounting point of the odd link is not used in the torque
arm calculation.)
In the dragracing application, it is generally desirable to have the
antisquat at or near 100%. In a road racing application, however, this high value of
antisquat commonly causes wheel hop during braking. The spreadsheet allows the user to
specify the percent antisquat. The default value is 100%.
Jaguar placed the odd link above the axle, but it can be either above
or below. When placed below, the situation becomes more favorable with a "tubbed" car.
The drawback is that the single lower link is carrying a very large compressive load.
Care should be taken to use tubing with sufficient wall thickness and diameter for safety.
This spreadsheet...as opposed to the earlier spreadsheet...takes advantage
of odd link offset AND an asymmetrical adjustment of the other two links. In other words,
the side view will show the other two links having different angles. In addition, the user
has the freedom to use different rear pivot locations for the links.
The spreadsheet assumes the rear pivots to be in essentially the same side
view location. If, however, the locations of the front pivots are to be controlled, it is
only necessary that the appropriate values be input as "rear" values and a negative sign
be placed before the link length value.
Another difference (from the earlier spreadsheet) is that the user is
allowed to locate the forward position of the instant center.
It is assumed that the symmetrical links, in plan view, are arranged symmetrically about
the car's centerline and that the center of gravity is on or near that same centerline.
It should be noted, however, that the spreadsheet equations assume the odd link offset to
be measured from the midpoint of the transverse spacing of the symmetrical links. In
other words, it is not required that the "symmetrical" links be truly symmetrical. The
two links, themselves, could be offset from the car's centerline. If the link pair were
offset, say, 2 inches to the left of the car's centerline and the odd link 4 inches to
the right of the car's centerline, the true odd link offset would be 6 inches and it is
this number that should be inserted in the spreadsheet. This might be considered if a
packaging problem exists.
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