Friction control in automotive seat belt systems by piezoelectrically generated ultrasonic vibrations

Active control of friction between sliding surfaces is of significant interest in automotive applications. It has been shown that the friction force between sliding surfaces can be reduced by superimposing ultrasonic vibrations on the sliding velocity. This principle can be applied to systems in which solid state lubrication is advantageous. This paper investigates ultrasonic lubrication for creating adaptive seat belts with controllable force at the interface between the D-ring and webbing. By precisely controlling the seat belt force during a crash event, superior restraint can be achieved relative to existing systems which are designed as a compromise for various occupants and loading conditions. Proof-of-concept experiments are conducted in order to experimentally determine the performance limits and mechanics of a seat belt webbing subjected to macroscopic sliding motion and superimposed out-of-plane ultrasonic vibrations. The experimental setup consists of a high-capacity ultrasonic plastic welder and an apparatus for creating controlled relative motion between the welder tip and seat belt webbing. Analytical modeling using LuGre friction is presented which characterizes the parametric dependence of friction reduction on system settings in the presence of ultrasonic vibrations.