Energy absorbing steering column assembly having a passive restraint

Abstract

A passive restraint load limiting steering column support assembly for a motor vehicle which, in effect, provides a fuse in the primary collapsible steering column assembly for allowing the system to accept impact loads greater than the design impact load and those which impact the system in a direction other than that for which it was designed. The system includes a collapsible energy absorbing steering column assembly having upper and lower column tubes telescopically engaged within one another, the steering shaft rotatably suspended within the upper and lower column tubes and the steering wheel secured to the rearward end of the steering shaft. A primary energy absorbing system is affixed to the steering column assembly and secures it to a steering column support member, with the primary energy absorbing system allowing the upper column tube to collapse upon the lower column tube over a predetermined distance in a controlled manner to absorb an impact load of a first predetermined magnitude. The steering column support member further includes a plurality of symmetrically disposed stress risers providing a controlled complete break or fracture across the support member, preferably in a direction generally transverse of the axis of the upper column tube, upon receiving an impact load of a second predetermined magnitude substantially greater than that necessary to implement the primary energy absorbing system, thus freeing the steering column assembly and bringing into effect a normally passive secondary energy absorbing system.