ROLLOVERS continue to pose a higher risk for tank trailers and other vehicles with high centers of gravity. The latest initiative to reduce the rollover threat comes from ArvinMeritor and its MeritorWABCO unit.
Rollovers account for about 6% of tractor-trailer rig accidents, and there are casualties in about 50% of the incidents, according to Rick Romer, director of electronic products at MeritorWABCO Vehicle Control Systems. With each rollover accident costing an average of $120,000, the trucking industry loses at least $1.3 billion annually.
In an effort to lower the risk, MeritorWABCO Vehicle Control Systems formally introduced its new Roll Stability Control (RSC) and Roll Stability Support (RSS) systems at a December 2002 press conference in East Liberty, Ohio. The new brake enhancements are designed for tractor-trailer combinations and provide intervention to reduce the likelihood of a rollover situation. The RSC tractor system is now available through original equipment manufacturers (OEMs). The trailer system, RSS, will be available through trailer OEMs in mid-2003.
Romer stressed that RSC is production technology that is ready for the market. Praxair is among the fleet operators that have tested the system, which will cost less than $1,000 per vehicle. “It's very affordable for what it achieves,” he said.
Rollover dynamics
The RSC system focuses on a vehicle's center of gravity and the lateral acceleration limit or rollover threshold. MeritorWABCO engineers studied the dynamics of a rollover and developed algorithms calculating the critical lateral acceleration limit.
When critical lateral acceleration thresholds are exceeded, RSC intervenes to regulate the vehicle's deceleration functions. Track and field testing demonstrated the system's ability to slow the vehicle, giving the driver better control and maneuverability.
Intervention by the system occurs in three forms — engine, retarder, and brake control. An accelerometer mounted directly to the antilock braking system (ABS) electronic control unit (ECU) monitors the vehicle's lateral acceleration. RSC constantly monitors driving conditions and intervenes if critical lateral acceleration is detected. The system provides control of engine and retarder torque as well as automatically activating the drive axle and trailer brakes. The brakes release automatically once the danger of rollover dissipates.
“Our technology team has analyzed several stability enhancement designs, and we believe the RSC provides an effective combination of vehicle control functions to help reduce the likelihood of a rollover,” said Dennis Sandberg, president of MeritorWABCO Vehicle Control Systems.
He added that while RSC is an aid, drivers are still the most important element and must ensure the physical limits of the vehicle are not exceeded.
RSS is an independent system for trailers and offers electronic assistance to reduce the likelihood of rollover. Five trailer tests currently are underway, and MeritorWABCO soon will be expanding to wider scale field tests.
The RSS technology is integrated into the trailer brake electronics requiring no additional hardware. Similar to the tractor's RSC system, the RSS focuses on lateral acceleration and wheel speed, monitoring the critical acceleration limit. If this limit is exceeded, the trailer brakes are automatically applied helping to reduce the vehicle's speed.
“The introduction of trailer RSS is one more building block in providing comprehensive vehicle stability control systems. As the industry continues to move toward more advanced foundation braking, our systems will be in place, ready to meet this challenge,” said Sandberg.
Disc brakes
Along with other MeritorWABCO executives at the December press conference, Sandberg stressed that air disc brakes and electronic braking systems (EBS) will get more attention in the future. These are considered to be the best technologies for meeting the heavy vehicle braking requirements in coming years.
One reason is that the National Highway Traffic Safety Administration (NHTSA) wants a 30% reduction in braking distance for heavy-duty vehicles. This means that the current braking distance of 355 feet would be reduced to 250 feet. NHTSA has indicated that it believes air disc brakes will provide the best means of meeting that objective.
EBS also will contribute to shorter braking distances and is seen as the successor to the current antilock braking systems. EBS already has made significant inroads in Europe, but has not been embraced by North American truck fleets, which are unwilling to pay a premium.
Bob Sibley, MeritorWABCO director of trailer products, said he anticipates no significant increase in EBS interest until the Department of Transportation makes changes in FMVSS-121. In addition, fleets may be more willing to put EBS on trailers first.