| This dissertation includes a detailed study of the effects on jackknife stability when using brakes that have higher than standard torque output on the prime mover. This research was initiated by the National Highway Traffic Safety Administration (NHTSA) to investigate the long-term effects of reducing the government mandated stopping distances for heavy commercial vehicles (i.e., FMVSS 121 standards). A significant reduction in stopping distance requirements would result in the need for higher torque brakes on the prime mover (tractor) steer and drive axles. The brake type might change from drum to disc, changing not only the torque output in magnitude but the dynamic transfer function characters as well.; To investigate this phenomenon, a sophisticated nonlinear model for a complete pneumatic braking system, typically found on Class 8 heavy trucks in North America, was developed. Modern brake torque measurements were used to develop brake torque output relationships. The modeled pneumatic and anti-lock braking (ABS) systems were verified over a wide variety of load/surface mu conditions using experimental data taken at NHTSA's Vehicle Research and Test Center. The nonlinear model was then run in parallel with a proven commercial vehicle simulation package, as a hybrid computer model.; The rigorous investigations showed no detrimental effects on jackknife stability, with the prime mover ABS "on" or "off," due to higher-torque brakes that were electronically controlled (deleting the time lag of the traditional pneumatic control system).; To signal a hypothetical vehicle stability system of impending jackknife instability, a 15-state model was rigorously developed using Lagrange's method, then integrated into an Extended Kalman Filter (EKF). The assumed measured states of longitudinal slip ratios, prime mover lateral acceleration and yaw rate are used, in conjunction with the EKF, to estimate the states of trailer hitch angle and its rate of change. The hitch angle parameters were used to construct state phase plots, whose output was shown to agree with sophisticated vehicle modeling programs over a range of low-load and low-mu conditions. |
