Structural beam

A beam for reinforcement of a vehicle body is extruded as a hollow shape having substantially planar parallel longitudinally extending deformation walls each of which is of variable wall thickness along its length. Two laterally extending grooves define a deformation zone having a maximal wall thickness allowing for a controlled folding of the shape.

BACKGROUND OF THE INVENTION 
The present invention relates to a beam employed as a reinforcement of a 
vehicle body, in an impact structure or the like, and more particularly to 
a structural beam comprising a hollow shape having parallel or 
substantially parallel deformation walls oriented perpendicularly to a 
direction of anticipated load impact exposure. 
Such beams are employed, e.g., in car doors as protection for vehicle 
occupants against a side collision. Apart from the need to absorb applied 
impact energy, the beam should also be as light as possible in order to 
avoid an unnecessary increase in body weight of the vehicle. German DE 
3,606,024 discloses a beam of this type that is dimensioned over its 
entire length to absorb the actual maximal anticipated impact load. 
Consequently, such beam does not comply with the need regarding an optimal 
strength/weight relationship. 
From German DE 380 724 it is known to resolve the above problem by 
provision of a constructed beam where one or more additional complementary 
shapes are connected to a hollow shape along the actual area to be exposed 
to an impact load. German DE 3,826,958 discloses a constructed beam 
consisting of two spot welded shapes locally reinforced by means of 
outwardly or inwardly positioned and fastened additional shapes. Rather 
complicated solutions are presented in both the above cases, and the 
application therein of additional shapes results in extra assembly 
operations and increased manufacturing costs. 
SUMMARY OF THE INVENTION 
The object of the present invention therefore is to provide a weight 
optimized beam exhibiting a variable deformation resistance along its 
length without the requirement for supplemental reinforcing elements or 
the need for extensive assembly machining of the beam. 
This object is achieved according to the invention by provision of a beam 
comprising an integral one-piece, unitary extruded hollow shape having 
parallel deformation walls having a variable wall thickness along their 
longitudinal dimension. According to a preferred embodiment, the hollow 
shape is extruded to have a rectangular cross-sectional configuration with 
two parallel longitudinally extending walls arranged perpendicularly to a 
direction of impact load exposure, with a wall thickness of each wall 
gradually increasing from opposite longitudinal ends thereof towards a 
central deformation zone having a maximal wall thickness. The central zone 
of the deformation wall on the predicted impact load side of the shape may 
be delimited against end portions thereof by laterally extending grooves 
to ensure a controlled folding of the shape. 
BRIEF DESCRIPTION OF THE DRAWINGS

DETAILED DESCRIPTION OF THE INVENTION 
A hollow shape 1 shown in FIGS. 1 and 2 has a substantially rectangular 
cross section and is extruded to have two opposite generally parallel and 
planar longitudinally extending deformation walls 2, 3 connected by two 
opposite substantially parallel and planar longitudinally extending 
connecting walls 9, 10. Each deformation wall 2, 3 has a gradually 
increasing wall thickness from each of opposite longitudinal ends 4 or 5 
thereof toward a respective central deformation zone 6 or 7 thereof. The 
maximal wall thickness at zones 6 or 7 is dimensioned according to the 
expected impact load. As will be apparent particularly from FIG. 2, each 
connecting wall 9, 10 has a uniform wall thickness throughout the length 
or longitudinal extension thereof, and the wall thickness of connecting 
walls 9, 10 is less than the maximum wall thickness of deformation walls 
2, 3, i.e. at zones 6, 7. As further shown in FIG. 2, deformation walls 2, 
3 extend laterally outwardly beyond both of the connecting walls 9, 10. 
The hollow shape having the desired longitudinal contour and wall thickness 
is provided ready to use in one simple extrusion operation without any 
need for subsequent machining, removal of excess material or similar 
operations. This can be done, e.g., by means of a radially movable tool 
attached to the orifice of a conventional extrusion die, the tool being 
periodically lowered at predetermined intervals and amplitudes to restrict 
the material flow and thus vary the wall thickness of the shape being 
extruded. As will be apparent from the drawing, the hollow shape or 
extrusion 1 is formed to be unitary and one-piece and is entirely free of 
seams or joints. 
The deformation surface of a wall facing the direction of an expected 
impact load, indicated at F in FIG. 1, is furthermore provided with two 
laterally and parallelly extending grooves or rills 8 which limit the 
deformation zone against opposite end zones of the wall surface. This 
weakening of the wall thickness by means of grooves 8 ensures that a 
controlled folding of the hollow shape will be achieved in a defined area 
of the deformation wall during energy absorption, e.g. upon collision with 
a vehicle. 
The hollow shape is preferentially provided as an extruded aluminum member 
of a high strength Al-alloy. 
The illustrated rectangular configuration of the beam shape is only one 
possible embodiment. A hollow shape having, e.g., a flat oval or polygonal 
cross-section extruded in accordance with the invention to have a variable 
wall thickness increasing from opposite shape ends toward a central 
deformation zone of opposite deformation walls also can be employed as 
actual shape configurations. 
The obvious advantages of the beam according to the invention are the 
possibility to achieve an optimal strength/weight ratio within a given 
space, minimal assembly machining and controlled development of shape 
folding with predicted localization of deformation zones. The beam of the 
invention also provides a smooth, gently curved surface, a feature that is 
advantageous for adaptation to other parts of a vehicle body.