This invention concerns so called “knee bolsters”, which are structures installed in automotive vehicles forward of the driver's seat positioned to be engaged by the driver's knees if the person submarines below the steering wheel mounted air bag during a collision.
Knee bolsters sometimes employ crushable or deformable impact absorbing structures which restrain the driver by contact by his or her knees, the crushing of the structure absorbing the energy of the person's momentum over a range of deformation to lower the stress on the person's knees and the load transmitted to the thigh bone.
Deformable structure knee bolsters are designed to be crushed by the person as the person is decelerated by the collision in order to reduce or prevent injury to the person.
Another requirement is the prevention of damage to or interference with the steering column mechanism during crushing of the knee bolster impact absorbing structure so as to allow the steering column to steer axially and absorb the upper body impact and to allow steering control to be maintained after a collision, if possible.
Costs are always a problem in automotive design, and the knee bolsters have sometimes been assembled from a number of components, representing an assembly cost.
Large aluminum sections have been proposed to be extruded to eliminate assembly costs, with portions cut out from the large extrusions. Large extrusions are themselves costly such that these structures are still somewhat expensive to manufacture.
Other knee bolsters have involved crush cells which have curved webs which are deformed, but such webs have a geometry which results in a buckling collapse of the web, greatly reducing the structure's ability to absorb energy. This can result in a great reduction in the restraining resistance of the structure. Such collapse can also produce gross bulging which can interfere with proper operation of the steering mechanism. Also, such a collapse mode can cause the surface impacted by the knees to directly hit the steering column and hinder the proper functioning of the steering column.
It is the object of the present invention to provide a deformable structure type knee bolster which is low in cost yet reliably providing adequate resistance to deformation over a range of crushing movement and prevents the development of any interference with the steering column mechanism.