Due to the stopping distance disparity between heavy trucks and passenger cars, a proposed amendment to FMVSS 121 (Federal Motor Vehicle Safety Standards) will require heavy truck manufacturers to reduce truck-tractor stopping distances.
A typical FMVSS 121 stopping distance test takes two to three weeks to complete. It is not practical or cost effective to test all brake, tire, wheel base, and suspension combinations. The ABS (anti-lock brake system) controller also contributes greatly to the complexities of the brake system. A new method has been developed by Navistar, Inc. utilizing extensive computer simulation to study the parameters that affect stopping distance.
The simulation model utilizes both real-time HIL (hardware-in-the-loop) and SIL (software-in-the-loop) simulation technologies. The ABS ECU (Electronic Control Unit) was coupled in the simulation through HIL. Commercial vehicle dynamics software is integrated with simulation through SIL to calculate the stopping distance and predict the vehicle directional behavior. Detailed brake pneumatic system and brake torque sub-models were developed in house. The results generated by the model show very good correlation with the physical tests.
This paper assumes the reader has a computer simulation background and has some familiarity with HIL and SIL simulation environment.