Although there was a safety awareness from the earliest days of
the automobile, systematic approaches to designing for safety
became more widespread after 1950 when large numbers of vehicles
came into use in both the United States and Europe, and governments
in both continents undertook a widespread highway development.
Industry response to safety objectives and also to government
regulation has produced a large number of safety enhancing
engineering developments, including radial tires, disc brakes,
anti-lock brakes, improved vehicle lighting systems, better highway
sign support poles, padded instrument panels, better windshield
retention systems, collapsible hood structures, accident sensitive
fuel pump shut-off valves, and other items.
A significant development was the design of the energy absorbing
front structures. Recognizing that most vehicle collisions involve
frontal impacts, engineers set about to design front structures
that, while not adversely affected in performing other vehicle
functions, would sacrificially collapse during a frontal impact to
help protect the structural integrity of the passenger compartment
while limiting the deceleration the occupant would experience.
Before the advent of unitized body construction the principal
energy absorbing member was the chassis frame rail. With unitized
construction the principal energy absorbing element is the body
lower front side member or, as referred to herein, the rail.
While designing the vehicle to enhance the safety of occupants
under a wide variety of operational conditions and during a
reasonable set of unintended or "accidental' events, the
design engineer must also produce a vehicle capable of reasonable
fuel efficiency, good performance, and acceptable cost. Fuel
efficiency, performance, and cost are directly related to vehicle
weight.
The achievement of the safety objective is a challenging
engineering assignment. To do so at low weight even more so.
The purpose of this paper is to outline design criteria and
principles for configuring the primary structural elements to more
efficiently, i.e. at low weight, achieve the desired vehicle safety
objectives