Bendix Debuts Stability Control

Steve Sturgess
Senior Editor

      Long-awaited stability control for North America's heavy trucks is on the horizon with the announcement of an anti-lock braking-based system from Bendix.
      Offering a level of sophistication greater than just rollover protection, the Electronic Stability Program doesn't require the electronically controlled braking that is the platform for the stability control systems already available as options on European heavy trucks. Bendix says its ESP and less fully featured rollover protection systems will be available towards the end of 2004 as they become engineered into heavy truck chassis offered by North American truckmakers.
      However, the company is demonstrating the systems — for which there is, as yet, no available pricing — to fleets and government agencies to alert them to the technology that is production-ready today.
      The Bendix systems offer very nearly all the benefits of the ECBS stability programs but without the need to abandon the conventional ABS air brakes found on North American heavy-duty vehicles today. By adding an Automatic Traction Control feature and a few additional sensors and valves, the Bendix ABS/ATC is the basis for a stability system that will intervene in run-off-the-road and rollover accident situations. These accidents account for 58% of fatal accidents, according a preliminary report by the Washington-based National Center for Statistics and Analysis.

The System

     Bendix is not unique in applying rollover warning and intervention for heavy truck braking systems. Indeed, MeritorWabco debuted tractor and trailer systems in 2002, also based on the ABS platform. Like those products, the Bendix technology is based on the ABS sensors and controllers, but with the addition of lateral accelerometers and the addition of mass and stability calculation algorithms to the controller.
      The system measures the lateral acceleration on the vehicle, knows the wheel speed and can calculate the mass from the torque-demand and the vehicle acceleration. It then can predict the height of the center of gravity, compare it with thresholds built in and, should there be a likelihood of a rollover, the system will intervene, using the ABS brake modulators to reduce the speed of the truck and, within the limits of physics, reduce speed and prevent a rollover.
      But according to Bendix engineers, this is only half the solution that is possible using the vehicle ABS platform. Adding a yaw sensor to the electronics package, together with input from steering angle allows the system to look at the direction that the tractor is heading and compare it with the driver input. If it shows a discrepancy, then selective braking of the front wheels and braking on the trailer axles will correct the potential accident situation. Again, this will occur only up to a certain level, and the vehicle system's ability to correct for a driver will still be limited by the physical limits on the truck. However, intervention by the system gives a major warning to the driver to correct his driving behavior. Moreover, if a driver gets into a situation where the system has to intervene, the vehicle slows to a speed less than the optimum, thereby penalizing the driver and providing an incentive to modify behavior.
      Bendix says it has chosen to base its ESP on the North American ABS platform because it delivers virtually all of the safety benefits of the ECBS-based systems in Europe.

Bendix continued...