1. Field of the Invention
The present invention relates generally to systems and methods for absorbing energy that is generated during a collision. More particularly, the present invention involves bumper systems for vehicles wherein the structure that is used to mount the bumper to the vehicle is also designed to absorb impact energy during a crash.
2. Description of Related Art
Bumper systems are commonly used on a wide variety of structures to protect the structure and/or its occupants during a collision. Bumper systems have been an integral and important part of automobile design for many years. As a result, many different types of systems have been developed. A popular type of bumper system is one that includes a bumper or impact member that is mounted to the vehicle using some type of mounting system that is able to absorb some of the impact energy during a collision. Mounting systems using pneumatic shock absorbers provide good absorption of impact energy and are able to withstand multiple minor impacts. However, such systems are relatively expensive and may require periodic maintenance.
Bumper supports that utilize metallic tubes which undergo lengthwise crushing during impact have also been popular. The metallic tubes provide a strong connection between the bumper and the vehicle. However, the specific energy absorption (kj/kg) of metallic tubes during crushing is not particularly high. In addition, the initial force required to initiate longitudinal crushing of a metallic tube may be too high for many situations.
Tubes made from composite materials are known to have a higher specific energy absorption than their metallic counterparts. This higher level of energy absorption is due in part to the energy absorbed when the composite tube undergoes inter-laminar splitting during longitudinal crushing. The basic problem with using composite tubes as the energy absorbing element is that the destruction of the tube that results during crushing renders the tube unable to support the bumper after a crash. In contrast, metallic tubes retain sufficient strength after crushing to provide adequate post crash support of the bumper.
As is apparent from the above, there is a present need to provide a simple energy absorbing system that has both the energy absorbing capabilities of a composite tube and the post-crash support strength of a metallic mounting system.
In accordance with the present invention, an energy absorbing composite tube is provided that is an efficient impact energy absorber and which retains good post-impact strength for maintaining a secure bumper-vehicle connection. The energy absorbing composite tube is particularly well-suited for connecting bumpers to automobiles. However, the energy absorbing composite tube may be used in any situation where two or more impact members are connected together. Typically, the invention is useful where a structure (first impact member) is protected by a bumper (second impact member) that is connected to the structure via an energy absorbing mounting system.
Energy absorbing composite tubes in accordance with the present invention are designed to provide an energy absorbing mount between a first impact member and a second impact member. The energy absorbing composite tubes include a mounting portion that is integral with a main tubular body portion. The mounting portion has a first impact member mounting end that is insertable into a sleeve or receptacle located in the first impact member. The mounting portion is made up of fibers embedded in a resin matrix and has an outer perimeter that is sized and shaped to matingly fit with the receptacle. The energy absorbing composite tube further includes a main tubular body portion that is integral with the mounting portion. The main tubular body portion is also made from one or more layers of fibers which are embedded in a resin matrix. The fiber layers and resin matrix may be the same or different from the mounting portion. The main tubular body portion has a perimeter that is larger than the mounting portion to provide a shoulder that extends around the perimeter of the mounting end where it meets the main tubular body.
As a feature of the present invention, a delamination wedge is provided that is located adjacent to the shoulder on the energy absorbing composite tube. The delamination wedge is forced against the shoulder during an impact. The resulting delamination of the main tubular body absorbs energy from the impact. The use of a delamination wedge reduces or eliminates the initial peak load that is usually necessary to initiate the delamination process. In addition, the delamination wedge eliminates the debris wedge that may form during longitudinal crushing of a tube made from composite materials.
As a further feature of the present invention, the mounting portion of the composite tube is not crushed and remains intact during the delamination process. The sleeve or receptacle in the impact member merely slides over the mounting portion as the delamination wedge is forced into the shoulder. The mounting portion and main tubular body retain sufficient structural integrity and strength to provide adequate post-crash support between the first and second impact members.
The present invention is directed not only to the energy absorbing composite tube, but also to the bumper systems and vehicles to which the energy absorbing composite tube is attached. In addition, the invention covers methods for making the energy absorbers and absorbing energy during an impact wherein the energy absorbing composite tube is utilized.
The present invention provides an especially useful energy absorbing mounting system that can be fine-tuned to provide a wide variety of energy absorption profiles. The number and/or types of laminates in the mounting end and main tubular body may be varied to provide a wide variety of shoulder sizes and shapes that have a direct relation to the amount of energy absorbed during delamination. In addition, the laminate layers in the main tubular body can be staggered to provide a stepped shoulder where the delamination wedge contacts each layer sequentially during a crash. Such stepped shoulder arrangements allow one to fine-tune the energy absorption profile. In addition a second mounting portion can be included at the end of the main tubular body that is mounted to the second impact member. This produces a second shoulder adjacent to the second impact member that can be used in combination with a second delamination wedge to provide even further energy absorption capabilities.
The energy absorbing composite tube of the present invention is a suitable replacement for metallic tube-type bumper mounting systems since it provides post-crash mounting strength equivalent to metallic tubes while at the same time providing for particularly effective energy absorption when the bumper is impacted.
The above described and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.