A 1988 report from the National Highway Traffic Safety Administration showed rollover occurred in 52 percent of the heavy vehicle accidents in which the driver was killed. Another earlier report, concluded that heavy vehicle rollover was responsible for 95 percent of the bulk spillage of hazardous materials.
Dr. Moustafa El-Gindy, director of the Vehicle Simulation Research Center at Penn State’s Transportation Institute (PTI) who led the study, says, "The computer-based controller we’ve developed will adjust the brake forces on the right and left sides of the cab independently to stabilize the vehicle by reducing the spin which causes rollover. We expect to have a prototype to test on a vehicle in about a year."
El-Gindy detailed the approach in a paper, "Nonlinear Active Rollover Prevention Control Strategies for a 5-axle Tractor/Semitrailer," on Monday morning, Nov. 12, at the 2001 ASME International Mechanical Engineering Congress and Exposition in New York City. A. Scott Lewis, research associate at Penn State’s Applied Research Laboratory, is first author of the paper.
"A computer simulation of a 75,000 pound 5-axle tractor/semitrailer was used to demonstrate the effectiveness of the proposed active control system," Lewis says.
However, he adds that the approach is applicable to any configuration of truck or tractor trailer.
El-Gindy says the biggest problem the team had to overcome was developing a computer program that could adjust to the continuous changes that take place in a tractor-trailer as it maneuvers around a corner. For example, among the changes that can occur during cornering are shifts in the load in the trailer, changes in tire characteristics due to wear or varying inflation pressures, or differences in the truck suspension.
However, the simulation tests have shown that the controller they developed can prevent rollover without significantly changing the direction of the vehicle.
Dr. El-Gindy says that in the application he envisions the controller would engage differential braking automatically only if the lateral acceleration of the vehicle or its spin at its center of gravity exceeded a danger threshold.
"It only takes a few seconds of differential braking to steady the vehicle. If the driver responds and gets the truck under control via other means, the controller will not deploy," he says.
A car manufacturer is currently trying to add a differential-braking concept to passenger cars, says the Penn State researcher. He thinks the new Penn State controller for heavy trucks is the first of its type to offer a workable solution to the rollover problem.