A methodology of active control has been developed in an effort to alter (preferably to reduce) the tendency of a four-wheel land vehicle to roll over during tight turns and similar maneuvers. At the time of reporting the information for this article, hardware and software to implement the methodology were undergoing development and testing for incorporation into a variable-dynamics testbed vehicle (VDTV) an experimental automobile that will be capable of exhibiting a broad range of dynamic characteristics for research on crash avoidance and driving-related human factors.
The VDTV will have four-wheel steering, front and rear active antiroll-bar systems, four adjustable dampers, and other active control devices that will be controlled by a computer running algorithms based on mathematical models of the dynamics of the vehicle. These devices will be used to alter several rollover-related characteristics of the dynamics of the vehicle, including notably its understeer coefficient, front/rear load-transfer distribution in lateral maneuvers that involve high accelerations, and the frequency and damping coefficient of the vehicle roll mode. Load-transfer distributions are particularly significant because to prevent rollover, one must ensure that the load on any tire never approaches zero during a severe maneuver.
A study has been performed to investigate how changes in the algorithms that control the active devices could effect significant changes in these characteristics. In particular, the study focused on how (1) an increase in the stiffness of the front antiroll bar, in conjunction with an increase in the front damper rate and with out-of-phase rear steering, could increase resistance to rollover in high-acceleration lateral maneuvers without changing the vehicle understeer coefficient (see figure); and (2) conversely, an increase in the stiffness of the rear antiroll bar, in conjunction with decrease in the rear damper rate and with in-phase rear steering, could decrease resistance to rollover. The results of the study indicate that the design of the VDTV provides for the right combination of active devices that will make the VDTV an effective testbed for research on rollover-related human factors.
This work was done by Allan Y. Lee of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Mechanics category. NPO-20545