Brakes – Plastic deformation or breakage of retarder element – Crushable element
Patent
1992-08-31
1996-02-20
Oberleitner, Robert J.
Brakes
Plastic deformation or breakage of retarder element
Crushable element
188374, F16F 712
Patent
active
054922070
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to energy absorbing structures used in assemblies exposed to impact loads to control the amount of resulting damage to the assemblies and to protect the occupants or contents thereof. More particularly the invention relates to energy absorbing structures incorporated into motor vehicle frames to absorb impact energy and to a method of providing such structures.
The ever increasing number of road accidents has resulted in development of the present basic car body concept comprising a rigid cabin for occupants and deformable body parts having a high energy absorption capacity forwardly and rearwardly of the cabin. Aluminum and alloys thereof, due to excellent corrosion behavior, good extrudability, high ductility and low specific weight, consequently are natural material choices for motor vehicle body parts. However, the specific mass energy absorption of an aluminum extrusion construction having the same stiffness as steel sheet constructions, which have so far been used as energy absorbing structures in vehicles, can be twice as high as that of such steel sheet constructions. Such substantially higher specific energy absorption applied in the front part of vehicle would result in higher forces acting on vehicle occupants during a frontal collision. This means that in order to achieve a complete control of the energy absorption and the progressive collapse of the deformable body parts, ensuring a sufficient deceleration path so that the physical capacity of human bodies to survive a sudden stop is not exceeded, a simple switch over to application of, e.g., extruded Al-shapes in the energy absorbing structure is not possible.
Several approaches are known from the prior art to resolve this problem by e.g. provision of several individual sections having different material characteristics and being connected together by mechanical means or provision of reinforcing means attached outside or inside of the extruded shape at predetermined locations along an underdimensioned cross-section of the shape.
Apart from offering a rather complicated solution comprising several parts and the necessity of a laborious assembling operation, the provision of a reduced cross-section of the shape in the latter case also means reduced strength or stiffness of the structure overall, which is not desirable for the normal handling and performance of the vehicle frame.
SUMMARY OF THE INVENTION
Consequently, it is an object of the present invention to provide a new energy absorbing structure avoiding the above drawbacks and enabling a simple assembly of the structure.
This and other objects according to the present invention are achieved by provision of a longitudinal bearing member differentially heat treated to have varying strength longitudinally.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more details by the way of examples and preferred embodiments and with reference to the accompanying drawings, wherein:
FIG. 1 is a schematical cross-sectional view of an energy absorbing structure assembly;
FIGS. 2a-2c are schematic views a heat treated longitudinal bearing member exposed to increasing impact loads; and
FIG. 2d is a graph illustrating the energy/path characteristics of the member and loads of FIGS. 2a-2c.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows schematically a cross-section of a motor vehicles front brace or part comprising a longitudinal front bearing member 1 extending from a side sill 4 towards a bumper 2. A hydraulic impact absorber 3 extending between the bumper and the front brace is an optional additional equipment. Such hydraulic absorbers are installed in order to ensure that under a low speed collision, up to approximately 5 km/h, all the impact energy is absorbed without any permanent deformation of the front bearing member.
Impacts already at rather moderate speeds of from 15 to 20 km/h will result in a permanent deformation of the structure, especially the front bearing members, requiring repair or exchange of
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Patent Abstracts of Japan, vol. 17, No. 211, M243, abstract of JP 58-105881, publ. Jun. 23, 1983.
Norsk Hydro a.s.
Oberleitner Robert J.
Young Lee W.
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