Steve Cron

Experimental Investigation of Tire Torsional Dynamics on the Performance of an Anti-Lock Braking System

The designs of commercial Anti-Lock Braking Systems often rely on assumptions of torsionally rigid tire-wheel assemblies. However, some recent tire/wheel technologies often involve lower torsional stiffnesses that cannot be captured well using these rigid wheel assumptions. This paper presents both simulation and experimental analysis of the interaction between a typical ABS controller and tire torsional dynamics. The simulation work includes a comprehensive model that incorporated sidewall flexibility, transient and hysteretic tread-ground friction effects, and the dominant dynamics of a hydraulic braking system. The experimental tests were conducted on a quarter-vehicle ABS test fixture built around a chassis dynamometer. Sensitivity studies are completed through changes in the tire/wheel properties such as wheel inertia, torsional stiffness and ABS controller properties such as the controller’s filter cutoff frequency applied to the wheel speed signals. The results showed strong interactions between the tire’s torsional natural frequency and the filter cutoff frequency of the controller.Copyright

On the Stability of Tire Torsional Oscillations Under Locked-Wheel Braking

This paper deals with the stability of self-excited tire torsional oscillations during locked-wheel braking events. Using a combination of torsionally flexible tire-wheel model and a dynamic tire-ground friction model, it is highlighted that the primary cause of unstable oscillations is the ‘Stribeck’ effect in tire-ground friction. It is also shown analytically that when suspension torsional compliances are negligible, the bifurcation parameters for the local torsional instability include forward speed, normal load and tire radius. In the presence of significant suspension torsional compliance, it is shown that the stability is also affected by suspension torsional stiffness and damping. Furthermore, the tire torsional stiffness becomes an important bifurcation parameter only in the presence of significant suspension compliance. This analysis gives useful insights for the selection of tire sidewall stiffness ranges and their proper matching with targeted vehicle suspensions at the design stage.Copyright