Tucson, AZ--During serious off-road driving, it's not unusual for
one of a vehicle's wheels to get hung up in the air. When that happens, the
vehicle suddenly loses stability as it teeters precariously on three wheels.
To solve that problem, one engineer has developed a three-link suspension
that makes it almost impossible for any wheel to lose contact with the terrain.
The new suspension accomplishes that by allowing for an extraordinary 21/2 ft of
vertical wheel travel--about five times as much as a conventional sport utility
vehicle. "We knew there had to be some way to make these vehicles more stable,"
notes David Burke, the designer of the three-link suspension. "The best way was
to keep the wheels in contact with the terrain, so that you're never spinning
your wheels."
Developed as part of a design project at the University of Arizona, the
three-link suspension departs radically from conventional designs. Unlike
virtually every system on the market today, the three-link allows the vehicle's
axle to separate completely from the suspension. That's critical, because it not
only lets one wheel droop more when climbing over rough terrain, but it also
keeps the center of gravity low, thus providing a measure of resistance against
accidental rollover.
Burke's system consists of four main parts: the three-link suspension;
quarter-elliptical springs; variable dampening shocks; and nylon limiting
straps.
The key to the system is the three-link suspension. It includes two
truss-like lower links, which connect the axle to the vehicle's frame on the
left and right side, and an A-shaped upper link, which runs from the top of the
differential to points on both sides of the frame. Together, the three links
absorb the same forces as any conventional suspension. The lower links prevent
fore-and-aft movement and yawing of the vehicle, while the upper link absorbs
lateral forces and prevents rolling.
That's critical, because the system's quarter-elliptical springs arenot rigidly attached to the axle. Instead, they sit loosely on rollers
atop the axle, and are kept in place only by the weight of the vehicle.
In that sense, the design departs from conventional leaf or coil spring
configurations, in which the spring is constrained in the vertical and
horizontal directions by an attachment to the axle. That constraint, Burke says,
is responsible for the lack of wheel travel in conventional suspensions. Because
those axles are mechanically attached to the springs, their wheels can droop no
more than about 6 inches.
The three-link, in contrast, allows huge wheel droop, while still maintaining
stability against yaw, roll, lateral, and fore-and-aft forces. "The three-link
always lets the axle stay connected to the ground," Burke says. "That's a big
help in rock climbing, because if you have a high center of gravity and you get
the vehicle up on top of a rock, you're going to tip over." Burke says that the
additional stability has allowed his vehicle to roll as much as 35º without
tipping. Most conventional vehicles dare not roll more than about 25º, he says.
 Un der
normal driving conditions, quarter-elliptical springs maintain contact
with the vehicle’s axle. |
Under extreme conditions, the axle separates from the
spring, allowing the wheel to droop. The three-link suspension keeps the
axle stable with respect to the
frame. |
Burke's system does place some constraint on wheel travel through its use of
variable dampening shocks and nylon limiting straps. Without the shocks, he
says, wheel travel would be as much as 3 ft. The shocks, he says, are mainly for
the higher speeds of on-road driving. Nylon straps, which extend from a truss
atop the axle to the vehicle frame, have been added mainly as a means to prevent
the shocks from overextending and pulling apart.
Burke's design has won awards at the University of Arizona and in a contest
sponsored by B.F. Goodrich. The suspension has not yet been offered to the
public, however.
Burke believes that the three-link suspension offers safety advantages for
serious off-roaders, however, because of its ability to keep all four wheels on
the ground. "It's virtually impossible for one of my wheels to lose contact with
the terrain," he says. "The mass of the tires, wheels, and axle give me enough
down force on the terrain to provide good traction, so I never spin my wheels."
Additional details…Contact David Burke, 5652 E.
Whittier St., Tucson, AZ 85711, (520) 747-8702.
Other Application
• Any solid axlefour-wheel drive
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