Bumper assembly including and energy absorber

A bumper system for an automobile vehicle includes a beam configured to attached to vehicle rails and an energy absorber coupled to the beam. The energy absorber is tunable for meeting predetermined criteria for both low speed and pedestrian impacts, and includes a flanged frame for attachment to the beam, a body that includes a plurality of lobes extending from the flanged frame and spaced apart from each other. Each lobe includes first and second side walls, having a concave shape.

BACKGROUND OF THE INVENTION

This invention relates generally to bumpers and, more particularly, to energy absorbing vehicle bumper systems.

A known standard which bumper systems often are designed to meet is the United States Federal Motor Vehicle Safety Standard (FMVSS). For example, some energy absorbing bumper systems attempt to reduce vehicle damage as a result of a low speed impact by managing impact energy and intrusion while not exceeding a rail load limit of the vehicle. In addition, some bumper systems attempt to reduce pedestrian injury as a result of an impact.

A bumper system typically includes a beam that extends widthwise across the front or rear of a vehicle and is mounted to rails that extend in a lengthwise direction. The beam typically is steel, and the steel beam is very stiff and provides structural strength and rigidity. To improve the energy absorbing efficiency of a bumper system, some bumper systems also include shock absorbers.

The efficiency of an energy absorbing bumper system, or assembly, is defined as the amount of energy absorbed over distance, or the amount of energy absorbed over load. A high efficiency bumper system absorbs more energy over a shorter distance than a low energy absorber. High efficiency is achieved by building load quickly to just under the rail load limit and maintaining that load constant until the impact energy has been dissipated.

To improve the energy absorbing efficiency, shock absorbers sometimes are positioned, for example, between the steel bumper beam and the vehicle rails. The shock absorbers are intended to absorb at least some of the energy resulting from an impact. Adding shock absorbers to a bumper assembly results in an added cost and complexity as compared to a steel beam. The shocks also add weight to the bumper assembly, which is also undesirable since such added weight may reduce the overall fuel efficiency of the vehicle.

Other known energy absorbing bumper systems include a foam energy absorber. Foam based energy absorbers typically have slow loading upon impact, which results in a high displacement. Further, foams are effective to a sixty or seventy percent compression, and beyond that point, foams become incompressible so that the impact energy is not fully absorbed. The remaining impact energy is absorbed through deformation of the beam and/or vehicle structure.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a bumper system for an automobile vehicle is provided. The vehicle includes vehicle rails. The bumper system includes a beam configured to attached to vehicle rails and an energy absorber coupled to the beam. The energy absorber is tunable for meeting predetermined criteria for both low speed and pedestrian impacts, and includes a flanged frame for attachment to the beam, a body that includes a plurality of lobes extending from the flanged frame and spaced apart from each other. Each lobe includes first and second side walls, having a concave shape.

In another aspect, a bumper assembly for an automobile vehicle having vehicle rails is provided. The bumper assembly includes a beam configured to attached to vehicle rails, an energy absorber coupled to the beam, and a fascia attachable to the energy absorber to substantially envelop the beam and the energy absorber. The energy absorber is tunable for meeting predetermined criteria for both low speed and pedestrian impacts, and includes a flanged frame for attachment to the beam, a body that includes a plurality of lobes extending from the flanged frame and spaced apart from each other. Each lobe includes first and second side walls, having a concave shape.

In another aspect, an energy absorber for a vehicle bumper system is provided. The energy absorber is tunable for meeting predetermined criteria for both low speed and pedestrian impacts, and includes a flanged frame and, a body that includes a plurality of lobes extending from the flanged frame and spaced apart from each other. Each lobe includes first and second side walls, having a concave shape.

DETAILED DESCRIPTION OF THE INVENTION

A bumper system that includes a tunable energy absorber is described below in detail. In an example embodiment, an energy absorber of the non-foam type is attached to a beam. The beam is fabricated, for example, from steel, aluminum, or glass mat thermoplastic (GMT). The energy absorber, in the example embodiment, is fabricated from Xenoy® material and is tunable so as to meet desired impact criteria, e.g., pedestrian and low speed impacts. More particularly, a front portion of the energy absorber is tuned, and tunable, to absorb pedestrian leg form impact, and a rear portion of the energy absorber is tuned, and tunable, for low speed barrier and pendulum impact. Impact forces during the specified types of impacts are maintained just below a predetermined level by deforming the energy absorber and beam until the kinetic energy of the impact event has been absorbed. When the impact is over, the energy absorber returns substantially to its original shape and retains sufficient integrity to withstand subsequent impacts.

Although the bumper system is described below with reference to specific materials (e.g. Xenoy® material (commercially available from General Electric Company, Pittsfield, Mass.) for the energy absorber), the system is not limited to practice with such materials and other materials can be used. For example, the beam need not necessarily be a steel, aluminum, or GMT compression molded beam, and other materials and fabrication techniques can be utilized. Generally, the energy absorber is selecting from materials that result in efficient energy absorption, and the beam materials and fabrication technique are selected to result in a stiff beam.

FIG. 1is an exploded perspective view of one embodiment of a bumper system20. System20includes an energy absorber22and a beam24. Energy absorber22is positioned between beam24and a fascia26which, when assembled, form a vehicle bumper. As should be understood by those skilled in the art, beam24is attached to lengthwise extending frame rails (not shown).

Fascia26typically is generally formed from a thermoplastic material amenable to finishing utilizing conventional vehicle painting and/or coating techniques. Generally, fascia26envelops both energy absorber22and reinforcing beam24such that neither component is visible once attached to the vehicle.

Beam24, in the example embodiment, is fabricated from extruded aluminum. In other embodiments, beam24is fabricated from roll formed steel or a compression molded glass mat thermoplastic (GMT). Beam24can have one of multiple geometries, including being configured as a B-section, a D-section, an I-beam, or having a C or W cross-sectional shape. The geometry of beam24is selected to provide a desired section modulus depending on the particular application in which the beam is to be used. Beam24includes rail attachment openings28so that bolts (not shown) can pass therethrough to secure bumper system20to the frame rails.

Energy absorber22includes a frame50having first and second longitudinally extending flanges52and54, respectively, which overlap beam24. Absorber22further includes a body58that extends outward from frame50. The specific configuration of body58is illustrated and described below in connection withFIGS. 2,3, and4.

Referring now toFIGS. 2,3, and4, energy absorber body58, sometimes referred to herein as a front portion, includes a plurality of lobes60extending from frame50between flanges52and54. Each lobe60is spaced apart from each other and includes a first transverse wall62and a second transverse wall64. Transverse walls62and64are rippled and include alternating raised areas66and depressed areas68which provide the transverse walls with an added degree of stiffness to resist deflection upon impact. Transverse walls62and64further include a plurality of teardrop shaped windows or openings70. The width and depth dimensions of the ripples, as well as the dimensions of openings70, can be modified to achieve different stiffness characteristics as desired. Each lobe60also includes a first side wall72and a second side wall74. An outer wall76extends between the distal ends of traverse walls62and64, and side walls72and74to form a tunable hollow crush box77having a cavity78defined by traverse walls62,64, side walls72,74, and outer wall76. Also, a strap member80is located between each lobe60. Strap members extend between flanges52and54of frame50and prevent energy absorber22from “opening” during an impact event.

In the example embodiment, side walls72and traverse walls62and64vary linearly in thickness from a first front-most portion82to a rearmost portion86. In one embodiment, the wall thickness varies from about 1 millimeter (mm) to about 7 mm, in another embodiment, from about 1.5 mm to about 5 mm, and still another embodiment, from about 2.5 mm to about 3.5 mm. In further embodiments, the thickness of the walls is constant from front-most portion82to rearmost portion86and is between about 1 mm to about 7 mm. In still further embodiments, the thickness of the walls are stepped. Particularly, the thickness of the walls of front-most portion82is constant and the thickness of the walls of rearmost portion86is constant with the walls of rearmost portion86thicker than the walls of front-most portion82.

Energy absorber22is tunable in that by selecting a thickness of each portion82and86, the response of energy absorber22can be altered depending on the application in which absorber22is used. For example, front portion82of energy absorber22is tuned, and tunable, to absorb pedestrian leg form impact, and rear portion86is tuned, and tunable, for low speed and pendulum impact.

Each lobe60can, of course, have any one of a number of different geometries depending on the impact energy requirements for the vehicle. Each lobe60has an axial crush mode in both barrier and pendulum impacts according to Federal Motor Vehicle Safety Standard (FMVSS) and also has a stiffness tunability in order to meet the desired impact load deflection criteria.

For example, the walls may have a thickness that broadly ranges from about 1.0 mm to about 7.0 mm. More specifically, for certain low speed or pedestrian impact applications the nominal wall thickness may generally range from about 1.0 mm to about 5.0 mm and for other applications, particularly those for a 5 mph FMVSS system, the nominal wall thickness for the side and rear walls would more likely be in the range of about 2.5 mm to 7.0 mm.

Another aspect in appropriately tuning energy absorber22is the selection of the thermoplastic resin to be employed. The resin employed may be a low modulus, medium modulus or high modulus material as needed. By carefully considering each of these variables, energy absorbers meeting the desired energy impact objectives can be manufactured.

The characteristics of the material utilized to form energy absorber22include high toughness/ductility, thermally stable, high energy absorption capacity, a good modulus-to-elongation ratio and recyclability. While the energy absorber may be molded in segments, the absorber also can be of unitary construction made from a tough plastic material. An example material for the absorber is Xenoy material, as referenced above. Of course, other engineered thermoplastic resins can be used. Typical engineering thermoplastic resins include, but are not limited to, acrylonitrile-butadiene-styrene (ABS), polycarbonate, polycarbonate/ABS blend, a copolycarbonate-polyester, acrylic-styrene-acrylonitrile (ASA), acrylonitrile-(ethylene-polypropylene diamine modified)-styrene (AES), phenylene ether resins, blends of polyphenylene ether/polyamide (NORYL GTX® from General Electric Company), blends of polycarbonate/PET/PBT, polybutylene terephthalate and impact modifier (XENOY® resin from General Electric Company), polyamides, phenylene sulfide resins, polyvinyl chloride PVC, high impact polystyrene (HIPS), low/high density polyethylene (1/hdpe), polypropylene (pp) and thermoplastic olefins (tpo).

As shown more clearly inFIG. 4, side walls72and74have a concave shape or profile between a front-most portion90add a rearmost portion92. The concave shape encourages the deflection of side walls72and74into cavity78during an impact in the area of strap80. This deflection of side walls72and74into cavity78during impact prevents a stack-up of material which could adversely affect the ability of energy absorber22to absorb energy.FIG. 5shows energy absorber22during an impact in the area of strap80and the deflection of side walls72and74into cavity78.

As shown more clearly inFIG. 6, traverse walls62and64have a convex shape or profile between front-most portion82add rearmost portion86. The convex shape encourages the deflection of traverse walls62and64away from cavity78during an impact. This deflection of traverse walls62and64away from cavity78during impact prevents a stack-up of material which could adversely affect the ability of energy absorber22to absorb energy.FIG. 7shows energy absorber22during an impact and the deflection of traverse walls62and64away from cavity78.