New safety technology from Bendix is designed to prevent
rollovers caused by a variety of factors, including oversteer, which the
company says is the cause of more than half of truckers’ rollover incidents.
Bendix Commercial Vehicle Systems is staging hands-on
demonstrations across the country for its Electronic Stability Program and Roll
Stability Program and Land Line was invited to observe and participate
in one of the demonstrations in the vast parking lot of the Route 66 Drag
Strip, part of the motor-sports complex in Joliet, IL.
Basically the Bendix systems use computer analysis to apply
all brakes to slow the vehicle, or just one brake selectively to push or pull a
tractor into line.
For the equipment demonstrations in Joliet, two courses were
laid out on the raceway’s parking lot. One was for a double lane change. The
other was for a decreasing radius turn.
A tank trailer with outrigger wheels demonstrated rollover
potential when the Bendix programs were turned off. The outrigger wheels
prevented any actual rollovers during the demonstrations.
A switch allowed Bendix engineers to turn the Bendix systems
on and off for comparative demonstrations. With the systems turn off, trailer
and tractor tandems (in that order) lifted off the ground. Generally when this
happens the driver can’t feel the lift until control is completely gone and a
rollover is inevitable.
With the Bendix programs active and the truck driven at the
same initial speeds, the computer took over, slowing the truck and allowing it
to complete each maneuver in what appeared to be a most unspectacular manner.
Inside the cab, however, you experienced hard braking that kept the vehicle
The Bendix systems are designed to prevent rollover crashes
in a variety of situations by overcoming the forces that cause trucks to roll
over – whether it’s wet or dry, icy or snow-packed.
For example, on dry surfaces with a lot of friction,
truckers that exceed the maximum speed for a turn or encounter a turn that
unexpectedly tightens can find themselves in a rollover situation. Centrifugal
force combine with the high center of gravity of the trailer to pull it outward,
but the tires resist this. The result is a pivoting action that rolls the
trailer. Once the trailer wheels lift, control is lost and the rollover is
virtually inevitable. Lift occurs before the driver senses any problem.
Rollovers can also occur on low friction surfaces, such as
icy, snow covered and rain slick roads. A tractor “oversteers” or starts to
skid at the drive wheels, and the truck starts to jackknife. Oversteer is a
condition in which rear (drive) wheels lose traction and slide to the outside
of a turn. On combination rigs, that pulls the trailer into a jackknife. If the
sliding rigs falls into a ditch or encounters something that will trip the rig,
a rollover occurs.
The new Bendix systems help with understeer, too. To
understand understeer picture a farm tractor in soft, plowed earth. Often the
front wheels steering the tractor lose grip, and the tractor will not respond
to steering. There are two brake pedals on farm tractors, one for each drive
wheel. A farmer applying just one brake can turn an understeering tractor by
pulling the tractor to the direction it is steered.
Instead of a farmer’s foot, the Bendix systems use computer
analyses of vehicle speed and attitude in relation to steering inputs and brake
applications. In addition to brake pressure applied, the computer examines the
rate of change of brake application. By applying any or all brakes
independently and selectively, Bendix’ systems retard excessive speed and bring
the rig back into line with where the driver wants to go.
Other competitive systems also compensate for speed by
applying brakes, but the Bendix system also corrects for oversteer, the cause
of more than 50 percent of rollovers.
Government figures presented by Bendix indicate that
rollover crashes occur about once every three million miles. Many drivers will
go an entire career without one, but statistically, one in three drivers can
expect one every ten years. Rollover crashes are the leading cause of truck
driver deaths and total incident costs can amount to hundreds of thousands of
dollars including medical and cleanup costs.
-- by Paul Abelson, Senior Technical Editor
Paul can be reached at email@example.com.