The present invention relates to a bumper assembly for vehicles,
and more particularly to improvement in the connection between the bumper and the
front/rear longitudinal structural members of the vehicle frame.
Various bumper assemblies known from the prior art are provided with
reinforcing or energy absorbing members disposed between the bumper and pair of
front members. Customarily the bumper is not a part of the vehicle frame's main
structure, but a so-called "hang on part" connected to the frame structure by bolts
or via an energy absorbing component.
Generally more complicated and heavy bumper assemblies are thus provided
contrary to the demand for light weight simple assemblies of the vehicle structure.
In order to reduce the vehicle weight and maintain the stiffness
the bumper is nowadays a part of the main frame forming a front/rear cross member
and often welded onto the rain structure.
Consequently, the conventional hydraulic or mechanic energy absorbing
elements between bumper and front/rear members can not be used. Thus new requirements
to the structure performance have to be met in order to avoid a high initial peak
load during a vehicle crash. This peak load is presently tried to be reduced by
weakening the front/rear members by pre-deformation, perforation or reduction
of their size (cross-section) something which in turn adversely effects the strength
of the body structure.
DE 41 27 597 A1 shows a bumper assembly comprising a pre-deformed
hollow front/rear member, the frontal area thereof being extended towards the
US-A-4,088,357 shows a bumper assembly comprising a hollow plastic
front/rear member being open to the side of and attached to a longitudinally extending
member 19 by a construction embracing said bearer 19 by means of bars 18, cf.
Fig. 2. Said bumper beam and said attaching construction are meant to prevent bearer
19 from damages. Particularly, there is no intention of deformation of bearer 19
during the initial stage of a collision.
In view of the above, it is an object of the present invention to
provide a novel light weight bumper assembly avoiding the above disadvantages of
the prior art, reducing a peak load during the initial phase of collapse of the
front/rear members and thereby the effects of a collision or alike upon the rest
of the vehicle body and vehicle occupance.
The above object is achieved by a bumper assembly according to claim
1. Preferred embodiments are claimed in claims 2 to 4.
This novel inventive design of the connection between the bumper
and the front/rear members, where a main part of the load from the bumper during
an impact is directed into a limited frontal area of the member, provides unstable
conditions on the members at an early (initial) stage of the collision. This ensures
a controlled collapse of the members by a free, unobstructed deformation of their
frontal parts and thus limiting the initial peak load.
Other objects, specific features and advantages of the present invention
will be apparent from the following detailed description of preferred embodiments
with reference to the accompanying drawings, Figs. where
- Fig. 1a
- is a schematic top view of an assembly employable in the present invention,
- Fig. 1b
- is a schematic cross-sectional view of the assembly taken along line I-I in
Fig. 1a, and
- Fig. 1c
- illustrates schematically in a cross-sectional view the assembly corresponding
to Fig. 1b after exposure to a front impact load,
- Fig. 2
- is a schematic top view and cross-sectional view of another particular embodiment
of the assembly (Figs. 2a and 2b, respectively), and
- Fig. 3
- is a graphic illustration of the relation between the applied load and longitudinal
displacement of the bumper assembly constructed in accordance with the present
Referring to the drawings and particularly to Fig. 1 a bumper assembly
is schematically illustrated in a top view (1a) and in a cross-sectional view (1b)
taken along lines I-I in Fig. 1a. The bumper assembly comprises a bumper bean 2
having a box-shaped configuration defined by a front wall 21, representing a load
surface accomodating a conventional energy absorbing bar 3, and a rear wall 22
facing and transversely fastened to a longitudinally extending front or rear structural
member 1 of a vehicle body, representing a load transferring contact area between
the members and the bumper. The front and rear walls 21,22 are interconnected
by side walls 23.
The bumper beam 2 being typically extruded as a multichamber hollow
shape in light metal (aluminium or Al-alloy) has an outer configuration allowing
the connecting rear wall 22 to cover only a portion of the frontal area 11 of the
longitudinal member 1. Furthermore, a free space 24 is provided between the free
perimeter of the frontal area and the bumper beam 2 by means of diverging side
walls 23 connecting the rear wall 22 and the front wall 21 of the bumper beam.
It is essential for the present innovative principle that such connection resulting
in unstable front walls of the members 1 under exposure to an axial impact load
via bumper beam 2 allows for folding of the longitudinal member around the bumper
beam 2 thanks to the provision of the free space 24 extending towards the beam
as illustrated in Fig. 1c.
Referring to Fig. 2, the beam assembly according to another embodiment
of the present invention is illustrated in a top view (Fig. 2a) and a cross-sectional
view (Fig. 2b), respectively. A conventional substantially rectangular bumper 2
is connected to the front member 1 by means of a connector 5 having a cross-sectional
area less than the available frontal area of the front member 1, thus ensuring
the required free space 24 between the remaining free frontal area 11 of the front
member and the bumper beam 2.
Tests conducted on the bumper assembly provided in accordance with
the above described inventive principle and examplified by different employable
embodiments thereof, show a successive reduction of the registered peak load with
decreasing load transferring contact area between the bumper beam and the front/rear
members. Fig. 3 illustrating in the form of a diagram horizontal displacement of
the assembly in mm versus measured load in kN confirms that the actual peak load
during the initial stage of a simulated collision is reduced by nearly 50% as a
function of gradually reducing the contact area between the bumper beam and the
frontal part of longitudinal members from a complete 100% contact (curve a) to
a contact area reduced to 40% (curve d) of the available cross-sectional area.
Curves b and c represent reduction of the contact area to 80 and 60%, respectively.
As it appears from the diagram the artificial unstability created in the front
walls of the members resulting in free collapse/deformation of the unconnected
frontal parts of the members into the provided free space lowers efficiently the
initial peak load and thus avoiding excessive damages to the vehicle body structure,
and last but not least reducing the risk of personal injuries for the occupants
of the vehicle.
An optimal reduction of the actual load transferring contact area
will in practice be determined by taking into account also other factors like
geometry (configuration) of the applied extruded members, their positioning etc.
The present invention is not limited to the above described and illustrated
preferred features and embodiments thereof. It is to be understood that various
changes and modifications may be made to the specifically described and illustrated
arrangements without departing from the scope of the present invention.