U.S. patent number RE40,736 [Application Number 11/950,855] was granted by the patent office on 2009-06-16 for vehicle bumper beam.
This patent grant is currently assigned to Shape Corp.. Invention is credited to Scott C. Glasgow, David W. Heatherington, Bruce W. Lyons.
United States Patent |
RE40,736 |
Heatherington , et
al. |
June 16, 2009 |
Vehicle bumper beam
Abstract
A bumper beam includes an open front section made from a
high-strength material such as ultra-high-strength steel (UHSS)
material, and further includes a mating back section made of
lower-strength material attached to a rear side of the front
section along abutting flanges. The front and back sections combine
to define different tubular cross sections. The front section can
be roll-formed, and the back section can be stamped, thus taking
advantage of roll-forming processes' ability to form high-strength
materials, while allowing the back section to have a more
complicated shape and be stamped. The abutting flanges
telescopingly overlap in a fore-aft direction of the vehicle and
are welded together at locations that potentially experience shear
upon impact, but the flanges of the front section are captured
within the flanges of the backs section, thus providing impact
strength even if the attachment locations shear off.
Inventors: |
Heatherington; David W. (Spring
Lake, MI), Glasgow; Scott C. (Spring Lake, MI), Lyons;
Bruce W. (Grand Haven, MI) |
Assignee: |
Shape Corp. (Grand Haven,
MI)
|
Family
ID: |
35786660 |
Appl.
No.: |
11/950,855 |
Filed: |
December 5, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10877326 |
Jun 25, 2004 |
6986536 |
|
|
Reissue of: |
10955384 |
Sep 30, 2004 |
06971691 |
Dec 6, 2005 |
|
|
Current U.S.
Class: |
293/102; 293/132;
293/154 |
Current CPC
Class: |
B60R
19/18 (20130101); B60R 2019/1813 (20130101); B60R
2019/1826 (20130101); B60R 19/24 (20130101) |
Current International
Class: |
B60R
19/02 (20060101); B60R 19/04 (20060101) |
Field of
Search: |
;293/102,117,120,121,132,133,154,155
;296/187.01,187.03,187.09,187.1,146.6 ;188/377 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gutman; H
Attorney, Agent or Firm: Price, Heneveld, Cooper, DeWitt
& Litton LLP
Parent Case Text
This is a continuation-in-part of co-assigned application Ser. No.
10/877,326, filed Jun. 25, 2004 .Iadd.now U.S. Pat. No.
6,986,536.Iaddend., entitled VEHICLE BUMPER BEAM, the entire
contents of which are incorporated herein in their entirety.
Claims
We claim:
1. A bumper beam for a vehicle comprising: a front section of high
material strength, the front section including a front wall and
upper and lower walls defining a rearwardly-facing C-shaped cross
section and a rearwardly open cavity; and a back section of lesser
material strength than the .[.metal.]. front section.Iadd.,
.Iaddend.the back section including a rear wall and top and bottom
walls defining a forwardly-facing C-shaped cross section and a
forwardly open cavity; the upper and lower walls of the front
section being positioned within the forwardly open cavity of the
back section and telescopingly engaging the top and bottom walls,
respectively, of the back section and being secured thereto at top
and bottom attachment locations that are subject to shearing forces
upon impact; the front section and rear section combining to form a
tubular section of changing cross-sectional size that, when
impacted, provides significant impact strength, even if one or more
of the attachment locations shearingly break loose.
2. The bumper beam defined in claim 1, wherein the rear wall of the
back section includes end portions formed flat into coplanar
alignment with each other, the end portions forming an integral
mounting surface on the back section suitable for attachment to a
vehicle frame.
3. The bumper beam defined in claim 2, wherein an end of the rear
wall of the back section includes an attachment flange integrally
formed from the material of the rear wall and that is bent
forwardly into abutment with a rear surface of the front wall of
the front section.
4. The bumper beam defined in claim 3, wherein the attachment
flange includes a foot flange that abuts the rear surface of the
front wall at a location longitudinally inboard of a terminal end
of the front wall.
5. The bumper beam defined in claim 4, wherein the attachment
flange includes an attachment tab that extend through an aperture
in the front wall, the attachment tab being bent to lay against a
front surface of the front wall.
6. The bumper beam defined in claim 1, wherein the front section
defines a continuous open cross section suitable for being formed
by a roll-forming process.
7. The bumper beam defined in claim 6, wherein the back section is
made from a flat sheet of formable material suitable for being made
using a stamping manufacturing process.
8. The bumper beam defined in claim 1, wherein the front section is
made from ultra-high-strength steel (UHSS) material and the back
section is made from a material other than UHSS material.
9. The bumper beam defined in claim 8, wherein the other material
is chosen from a stampable material selected from a group
consisting of high-strength low-alloy (HSLA) steel material,
drawable steel, and aluminum.
10. The bumper beam defined in claim 1, wherein the back section is
chosen from a stampable material selected from a group consisting
of ultra-high-strength steel (UHSS) material, drawable steel, and
aluminum.
11. The bumper beam defined in claim 1, wherein the front section
and the back section include abutting flanges and are welded
together along top and bottom walls of the back section.
12. The bumper beam defined in claim 1, wherein the front section
defines a continuous cross-sectional shape that is formed by a
roll-formed process and the back section defines a discontinuous
cross-sectional shape that is formed by a stamping process.
13. A vehicle bumper beam adapted to withstand an impact force
directed along a predetermined fore-aft direction of impact against
a vehicle, comprising: a front section including a front wall and
top and bottom walls defining a constant U-shaped cross section
having a rearwardly open cavity, the front section being elongated
in a direction perpendicular to the predetermined fore-aft
direction of impact, the front section being made from a material
selected from a group consisting of high-strength low-alloy (HSLA)
steel and ultra-high-strength steel (UHSS) material; and a back
section fit against and attached to a rear side of the front
section, the back section having a length close to a length of the
front section and including a first longitudinal portion that
extends between the top and bottom walls to define with the front
section a first shape having a first depth dimension, and including
second longitudinal portions on opposing sides of the first
portions that extend between the top and bottom walls to define
with the front section a second shape having a second depth
dimension, at least one of the first and second shapes being
tubular, the back section being made from a material selected from
a group consisting of ultra-high-strength steel (UHSS) material,
high-strength low-alloy (HSLA) steel, aluminum, and polymeric
material; the front and back sections having attachment flanges
that telescopingly overlap in a direction parallel to the
predetermined fore-aft direction of impact, the attachment flanges
being secured together at attachment locations that undergo shear
stress upon the beam receiving the impact force along the fore-aft
direction, but the attachment flanges of the front section being
located inside the attachment flanges of the back section so that,
even if the attachment locations shear off, the attachment flanges
of the front section remain captured within the attachment flanges
of the back section.
14. The vehicle bumper beam defined in claim 13, wherein the front
section defines a continuous cross-sectional shape that is formed
by a roll-formed process and the back section defines a
discontinuous cross-sectional shape that is formed by a stamping
process.
Description
BACKGROUND
The present invention relates to vehicle bumper beams, and more
particularly relates to a bumper beam having a front section of
continuous shape and a back section attached to the front section
to make a tubular beam of changing cross-sectional size.
Two basic types of bumper beams often used on modern vehicles are
tubular sections (also called closed sections, such as "B" or "D"
shapes) and open sections (such as "C" sections or "hat" sections).
The tubular sections and also the open sections each have their own
advantages and disadvantages. For example, from an engineering
standpoint, bumper beams made from tubular sections are inherently
more rigid and capable of absorbing and/or transmitting more energy
(especially based on a strength-to-weight ratio) on impact due to
the way that impact stresses are distributed around and along the
tubular shapes. In contrast, open sections tend to prematurely
buckle during impact since the "legs" of the open sections will
spread apart, kink, and quickly lose shape upon impact. However,
open sections tend to allow more styling and product variation.
There is a concurrent strong desire to use high-strength materials
for bumpers because it reduces weight while providing higher impact
strengths (as compared to lower strength materials). However as
higher and higher-strength materials are used, it becomes more and
more difficult to form raw sheet stock into the desired beam shape,
because the higher-strength materials are harder and harder on
tooling and the presses that run them. This is especially true for
stamping presses and stamping dies, where the dies move
perpendicularly against a sheet to form the sheet. Roll-forming
processes have the ability to form higher-strength materials than
stamping processes, however roll-forming processes are limited to
producing a constant cross-sectional shape along a length of the
roll-formed parts.
Roll-forming is a particularly attractive manufacturing method
because dimensionally-accurate bumper beams can be mass-produced at
good production speeds, with minimal manual labor, and using
high-strength materials, yet the tooling can be made more durable
and long-lasting than stamping dies when used to shape
ultra-high-strength steels and high-strength low-alloy steels. For
example, Sturrus U.S. Pat. No. 5,092,512 and Sturrus U.S. Pat. No.
5,454,504 disclose roll-forming apparatus of interest. However, as
noted above, a drawback to roll-forming is that the roll-forming
process can only produce a constant cross section over the entire
length of the part. Further, the material thickness and material
strength of the raw coil stock cannot change around a given cross
section, since the material begins as a unitary coil of material.
Regarding the constant cross section produced by roll-forming, this
often does not satisfy current styling trends which require
variations in cross-sectional size along a length of the beam due
to packaging space over the vehicle frame rails (versus the
packaging space available at a centerline of the vehicle), or which
require a longitudinal sweep with an increased curvature at corners
of the vehicle (e.g. at the fenders). These styling conditions
require roll-formed tubular parts to be end-formed or taper cut at
their ends by secondary processes. But these secondary processes
are expensive because end-forming and/or taper cutting the parts is
not easy (particularly when they are made of high-strength
materials). Also, the process of end-forming and/or taper cutting
require more than one secondary process. For example, taper cutting
requires some sort of cap to cover the sharp edges that result from
the cutting process, which must be accurately fixtured and then
welded in place. Alternatively, the ends of the tubular sections
may be reformed to better fit functional and aesthetic styling
concerns (see Sturrus U.S. Pat. No. 5,306,058), but it is difficult
to accurately and consistently deform the ends, thus potentially
leading to unacceptable dimensional variations and high tooling
wearout.
Beams made from C-shaped open sections can be formed to a desired
three-dimensional shape, including non-uniform cross sections along
their length, but their open section is inherently not as strong as
a tubular shape during an impact. Specifically, the open sections
include rearwardly-extending legs that tend to prematurely spread
apart or otherwise collapse upon impact. This greatly reduces the
beam's overall sectional impact strength and reduces its ability to
consistently and predictably absorb energy. By stabilizing the legs
of the front section, the front sections can be made much stronger
and more energy-absorbing. This is sometimes done in prior art by
adding reinforcements such as bulk heads, flat plating, and/or
bridging between the legs to prevent the legs from prematurely
spreading during an impact. (See FIG. 1 in the present drawings.)
By stabilizing the legs of an open section, it can be made to come
closer to matching the performance of the tubular sections.
However, these additional reinforcements require expensive
secondary operations since they utilize considerable fixturing and
welding machinery, and they often require several additional parts
and considerable assembly time and in-process inventory. Also, the
process of welding multiple reinforcements to an open beam can be
difficult to control, since multiple parts must be carefully
separately fixtured and each and every one of the parts welded very
consistently in place. Also, the location of each stabilizing strap
can greatly affect impact strengths along the beam.
To summarize, packaging and performance requirements of bumper
beams on vehicles and related vehicle front end (or rear end)
components often increase the complexity of a bumper design since
they result in the addition of other structural components, which
might include bridges, bulkheads, radiator supports, fascia
supports, fascia, and the like. Or they may require end treatment
of the bumper beam to include end-forming or taper cutting, so as
to form an increased angle at an end of the bumper in front of the
fenders. This increase in complexity results in an increase in cost
due to substantial secondary processing. It also results in
difficult tradeoffs between function and styling criteria. It is
desirable to provide a design and process that overcomes the
drawbacks of constant cross section roll-formed sections, yet that
takes advantage of roll-forming processes as a way of forming
ultra-high-strength materials for use in bumper beams, as discussed
below. Also, it is desirable to provide design flexibility that
allows tuning of the bumper beam in the bumper development program,
which can be very important for timing and investment reasons. At
the same time, it is desirable that the ultra-high-strength steels
be an option for components so that the bumper beam can be designed
for optimally high strength-to-weight ratios. Still further, even
though ultra-high-strength steels are used, it is desired that the
arrangement allow for some use of less expensive materials and of
materials that allow the use of relatively simple forming and
bending tooling to minimize investment while still being able to
form the ultra-high-strength materials without expensive tooling
and without having tooling quickly wear out. In other words, it is
desirable to utilize stamped or molded reinforcing components where
possible and in combination with high-strength materials where it
makes practical sense to do so.
An additional problem is that ultra-high-strength materials are
difficult to form in stamping presses, or at least it is preferable
not to do so. Specifically, those skilled in the art prefer not to
stamp materials such as ultra-high-strength steels (UHSS) because
the UHSS material is so strong that it is hard to form without
cracking and that it damages or quickly wears out the stamping dies
and the stamping press.
Thus, a bumper beam having the aforementioned advantages and
solving the aforementioned problems is desired.
SUMMARY OF THE PRESENT INVENTION
In one aspect of the present invention, a bumper beam for a vehicle
includes a metal front section of higher material strength, the
front section including a front wall and upper and lower walls
defining a rearwardly-facing C-shaped cross section and a
rearwardly open cavity. The beam further includes a metal back
section of lesser material strength, the back section including a
rear wall and top and bottom walls defining a forwardly-facing
C-shaped cross section and a forwardly open cavity. The upper and
lower walls of the front section are positioned within the
forwardly open cavity of the back section and telescopingly
engaging the top and bottom walls, respectively, of the back
section and are secured thereto at top and bottom attachment
locations that are subject to shearing forces upon impact. The
front section and rear section combine to form a tubular section of
changing cross-sectional size that, when impacted, provides
significant impact strength, even if one or more of the attachment
locations shearingly break loose.
In another aspect of the present invention, a bumper beam is
provided that is adapted to withstand an impact force directed
along a predetermined fore-aft direction of impact against a
vehicle. The bumper beam includes a front section including a front
wall and top and bottom walls defining a constant U-shaped cross
section having a rearwardly open cavity, the front section being
elongated in a direction perpendicular to the predetermined
fore-aft direction of impact, the front section being made from a
material selected from a group consisting of high-strength
low-alloy (HSLA) steel and ultra-high-strength steel (UHSS)
material. The bumper beam further includes a back section fit
against and attached to a rear side of the front section, the back
section having a length close to a length of the front section and
including a first longitudinal portion that extends between the top
and bottom walls to define a first shape having a first depth
dimension, and including second longitudinal portions on opposing
sides of the first portions that extend between the top and bottom
walls to define a second shape having a second depth dimension, at
least one of the first and second shapes being tubular, the back
section being made from a material selected from a group consisting
of ultra-high-strength steel (UHSS) material, high-strength
low-alloy (HSLA) steel, aluminum, and polymeric material. The front
and back sections have attachment flanges that telescopingly
overlap in a direction parallel to the predetermined fore-aft
direction of impact. The attachment flanges are secured together at
attachment locations that undergo shear stress upon the beam
receiving the impact force along the fore-aft direction, but the
attachment flanges of the front section are located inside the
attachment flanges of the back section so that, even if the
attachment locations shear off, the attachment flanges of the front
section remain captured within the attachment flanges of the back
section.
In another aspect of the present invention, a method comprises
steps of roll-forming a front section including a front wall and
top and bottom walls defining constant cross section and a
rearwardly open cavity, and stamping an elongated back section from
a sheet of material, the back section having a length approximating
the front section. The method further includes fitting the back
section against a rear side of the front section, the back section
including a first longitudinal portion that defines with the front
section a first cross-sectional shape having a first depth
dimension, and including second longitudinal portions on opposing
sides of the first portions that fit against the front section to
define a second cross-sectional shape having a second depth
dimension; the front and back sections having attachment flanges
that telescopingly overlappingly engage in a direction generally
perpendicular to the front wall. The method still further includes
attaching the attachment flanges together to secure the back
section to the front section together to form a reinforced beam
section, the attachment flanges of the front section being
positioned inside of and captured by the attachment flanges of the
back section even if some of the attachment locations shear off and
come loose.
An object of the present invention is to provide a design that
accommodates complexity without a concurrent increase in cost due
to the need for substantial secondary processing.
Another object of the present invention is to provide a design and
process that overcomes the drawbacks of roll-formed sections having
a constant cross section, yet that allows their use to make beam
sections with ultra-high-strength materials.
Another object of the present invention is to provide design
flexibility that allows tuning of the bumper beam (early or late)
in the bumper development program, which can be very important for
timing and investment reasons.
Another object of the present invention is to provide a design that
allows use of materials such as ultra high-strength steels for
components so that the bumper beam can be designed for optimally
high strength-to-weight ratios, while yet keeping the ability to
provide optimal beam strengths in particular regions of the
beam.
Another object of the present invention is to provide an
arrangement allowing for relatively simple forming and bending
tooling to minimize investment while still being able to form the
ultra-high-strength materials without prohibitively expensive
tooling and without having tooling and/or stamping presses quickly
wear out.
Another object of the present invention is to provide a bumper beam
design where a size of the beam's tubular cross section can easily
and substantially be varied across an entire length of the bumper
beam, even where very high-strength materials are used. Yet this
can be accomplished without substantial secondary processing and/or
heat treating and/or annealing.
Another object is to provide a bumper beam that optimally utilizes
roll-forming processes and stamping processes to make component
sections of the beam.
The present invention overcomes the drawbacks of roll-formed
sections having a constant cross section, by providing for an
optimized utilization of geometry and material to produce a bumper
beam that possesses the strength and rigidity characteristics of a
tubular bumper section. The present invention combines
manufacturing processes and material to produce a tubular section
that has varying cross-sectional geometries along a length of the
part and different material properties around the cross section of
the part. The present invention differs from prior art that
includes the addition of material to specific areas to provide
localized stiffening.
These and other aspects, objects, and features of the present
invention will be understood and appreciated by those skilled in
the art upon studying the following specification, claims, and
appended drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic view illustrating prior art beam
constructions;
FIG. 2 is a top view of a bumper beam embodying the present
invention, including an open front section (also called a "hat
section") and a back section attached to its rear face;
FIGS. 3-4 are cross sections along lines III--III and IV--IV in
FIG. 2;
FIG. 4A is a modified version of FIG. 1, and FIG. 4B is a cross
section along line IVB--IVB;
FIG. 5 is a top view of a bumper beam embodying the present
invention, including an open front section and a back section
attached to its rear face;
FIGS. 6-7 are cross sections along lines VI--VI and VII--VII in
FIG. 5;
FIGS. 8-10 are alternative attachment structures for securing the
front section and the back section together; and
FIG. 11 is a flow chart showing a method of manufacture for beams
in FIGS. 2 and 5.
FIG. 12 is a perspective view of half of a modified bumper system
incorporating aspects of the present invention;
FIG. 13 is an exploded perspective view of FIG. 12;
FIGS. 14-15 are additional perspective views of FIG. 12, FIG. 15
being enlarged to better show an end of the back section; and
FIGS. 14A-14C are cross sections taken through FIG. 14 at lines XIV
A, XIV B, and XIV C, respectively.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention focuses on a bumper beam 20 (FIG. 2) (and
beam 20A, FIG. 5; and beam 20B, FIG. 4A) utilizing a roll-formed
front section (22, 22A) (also called a "front channel" or "rolled
section") and a stamped or molded back section (27, 27A, 27B) (also
called a rear channel" or "reinforcement section") mated together
to form a beam of varied tubular cross-sectional shape. More
specifically, the present invention represents a two-piece solution
that when combined produces a tubular bumper beam with varying
cross section across the length of the bumper and material
properties that change around the cross section. The ability to
change cross section across bumper length allows for optimization
of impact beam performance, weight, and cost along any selected
region of the beam. For example, the use of ultra-high-strength
steels (UHSS steels) provides desirable characteristics for impact
beam construction. The high mechanical properties inherent to UHSS
steels support impact beam designs with high levels of energy
absorption for structural components that deform with impact
loading. The UHSS material also provides desirable spring back
characteristics that help in returning beam sweep and
cross-sectional geometry after impact loading is relieved, and also
provides for excellent strength-to-weight ratios in each region.
The present invention takes advantage of the material properties of
UHSS material, even though the UHSS material presents difficult
manufacturing issues when considered for stamping. For example,
UHSS material, since they are ultra-strong, are difficult to form.
They also tend to rapidly wear out tooling. In fact, the mechanical
properties inherent to UHSS materials make them a poor choice for
stampings. The roll-forming process is capable of forming
complicated parts from UHSS due to the more stepped approach
associated with forming a simple uncomplicated geometry. The
limitations associated with forming UHSS materials are not as
restrictive when roll-forming as compared to stamping. The present
invention takes advantage of the ability to roll form the UHSS
material and uses the high mechanical properties associated with
the UHSS material to produce impact systems that are conscious of
performance, weight, and cost.
In beam 20 (FIG. 2), the impact face (herein called the "front
section 22") of the bumper beam is a roll-formed section made from
an UHSS material. The rear face (herein called the "rear section
27") of the impact beam is a stamped part with relatively flat
sections and is made from a high-strength low-alloy (HSLA) steel.
The two halves of the impact beam are joined together at the
flanges, such as by welding (FIGS. 2 and 11), crimping (FIGS. 9 and
11), or mechanical fastening (FIGS. 10 and 11). The combination of
the two manufacturing processes and different materials produces an
impact beam that can have an infinite number of carefully designed
geometries along a length of the impact beam, such as
differently-sized tubular sections, and different materials from
front to back of the impact beam. This flexibility allows for the
design of an impact beam that can be optimized for performance,
weight, and cost.
It is clear from beam 20 (FIG. 2) that beam strength can be greatly
varied along different portions of a length of the part. However,
this advantage is even more dramatically shown by studying the beam
20A (FIG. 5), where a "deep" tubular cross section is formed at the
center of the beam 20A and a "shallow" tubular (or laminar)
dimension is formed at the ends of the beam 20A. For example, the
design in FIG. 5 will allow for more centerline deformation while
providing considerable section stiffness and reduced section
deformation over the frame rails at ends of the beam 20A.
Persons skilled in the art of vehicle bumper beams will recognize
that an increase in impact beam depth will increase stiffness of
the section and make it more stable during impact, and further will
realize the tremendous advantages of doing this at strategic
locations along the beam. The beam 20A (FIG. 5) uses the stamped
section to increase section depth at a vehicle's center region
while providing a shallower section over the frame rails at ends of
the beam. The shallow depth over the frame rails reduces the
packaging space required to package the design at the rails, and
will allow for more curved styling at the ends of the impact beam.
The ability to easily deform the shallower depth over the vehicle
frame rails is overcome by having the stamped section increase
stiffness over the frame rails via geometry (i.e. the laminated
"zero depth" section double-wall sections 29A and 30A at the rails)
and not section depth.
The roll-formed front impact face (front section 22 or 22A) of the
impact beam is a constant cross section across its center region
and can either be swept at a constant sweep radius or could
potentially be swept at a compound sweep radius by tooling in-line
with the roll-forming process. The constrained sweep radius will
cause more localized loading and potentially more system stroke
(intrusion into the vehicle) as measured from the front face inward
to the vehicle. Typical compound swept beams would provide for a
flatter surface across the center of the impact beam and greater
curvature on the ends of the impact beam. The compound sweep may be
more accommodating for current styling trends in vehicles. A
compound swept beam would allow for distributed loading across the
front face of the impact and in turn less system stroke of the
impact beam. The ability of a compound swept beam to distribute
load across a greater surface area can also be replicated with a
constant swept beam and an engineered energy absorber. The energy
absorber would be engineered to easily crush across a greater
length from impact beam center and in turn load the impact beam
over a greater distance extending from impact beam center.
The front and rear sections of the impact beams can be attached
using different attachment methods. These methods would include
crimping or hemming (FIG. 8), welding (FIGS. 2-4, 4A-4B and 5-7),
mechanical fastening processes (FIGS. 9-10), or other attachment
means known in the art for securing two structural components
together. Each of the illustrated methods are potentially suitable
for joining and each method would potentially produce an impact
beam suitable for crashworthiness. The attachment method of choice
for each system constructed according to the present invention
would be identified and supported with a cost analysis of each of
the methods.
The present invention illustrated in the beams 20 and 20A (FIGS. 2
and 5) is an impact beam system constructed from a roll-formed UHSS
front section and a stamped HSLA rear section. It is to be
understood by those skilled in the art that various other materials
can be used to design a system that may or may not trade off on the
design criteria of performance, weight, and/or cost. For example,
the front section (22 or 22A or 22B) can be made from UHSS
material, HSLA material, drawable-grade steel, boron steel which is
heated and quenched after forming, high-strength aluminum, extruded
aluminum, polymeric material, or other engineering structural
materials. The rear section (27 or 27A or 27B) can also be made
from HSLA material, drawable-grade steel, boron steel which is
heated and quenched after forming, high-strength aluminum, extruded
aluminum, polymeric material, and other engineering structural
materials. In each of these materials, their thickness and hardness
can be varied within parameters of commercially available raw
material. It is contemplated that the back section could be made
from UHSS material, but that a shape of the back section wold need
to be potentially modified or simplified (such as by modifying back
section 27 to include a shallower draw at center section 28, or to
eliminate the flanges and side walls at sections 28, 31-32) if one
desires to produce a significant number of bumpers, since the UHSS
material is very tough on tooling and hard to form due to low
elongation. One alternative contemplated by the present inventors
is to provide a sheet of material for producing the back section
(27 or 27A or 27B) from a plurality of strips welded together. For
example, for beam 20 (FIG. 2), strips of UHSS material would be
welded to opposite edges of a center strip of drawable grade steel.
The strips of UHSS material would each have a width sufficient to
form the sections 29 and 30, while the center strip of drawable
grade steel would have a width sufficient to form sections 28, 31,
and 32.
The ultra-high-strength steel (UHSS) material is a well known and
well defined category of material in the art. UHSS material
commonly has a tensile strength of about 120 to 200 KSI (or
higher). The high-strength low-alloy (HSLA) steel material is also
a well known and well defined category of material in the art.
There are HSLA steel materials that are 120 KSI, but the higher
grade HSLA materials are not usually considered stampable.
Nonetheless, it should be understood that the ability to stamp is
also related to material thickness, size and shape of the part
being stamped, and the degree of material flow and "draw" required.
HSLA steel material that can be stamped has a tensile strength
commonly around 80 KSI. Boron steels and heat-treatable hardenable
steels can also be used. For example, boron steels can be formed
while at lower KSI strengths, and then hardened either during a
stage of the forming process or in secondary processing.
Higher-strength aluminum materials are also well known in the art.
For example, it is contemplated that aluminum series 6000 materials
will work in the present invention. The aluminum series 6000
material commonly has a tensile strength of up to about 40 KSI.
Some extrudable grades of aluminum may also work in forming front
section 22, such as extrudable aluminum series 6000 or 7000
materials. Back sections 22 may also be made from glass-reinforced
nylon, glass-reinforced polyester, or other (reinforced or
unreinforced) structural polymers.
As noted above, the illustrated bumper beam 20 (FIG. 2) includes a
front section 22 and a rear section 27. The front section 22
include a front wall 23 and top and bottom walls 24 and 25 defining
a constant open cross section (also often called a hat-shaped
section) that defines a rearwardly open cavity 26. The illustrated
front section 22 is longitudinally swept (i.e. curved), such as by
a process disclosed in Sturrus U.S. Pat. Nos. 5,306,058 and
5,395,036, the entire contents of which are incorporated herein by
reference for the purpose of teaching formation of the front
section 22. The bumper beam 20 further includes an elongated back
section 27 fit against and attached to a rear side of the front
section 22. The back section 27 includes a longitudinal center
portion 28 that is curved longitudinally to match the associated
center region of the beam 22, and that is deep-drawn to generally
match a cross-sectional shape of the front section 22. The back
section 27 further includes end portions 29 and 30 that are also
curved longitudinally to match the associated end regions of the
beam 22, and still further includes angled intermediate portions 31
and 32 that interconnect the end portions 29 and 30 to the center
portion 28. The center portion 28 is hat-shaped and includes a
middle portion that lies relatively close or in contact with the
front wall 23 in the center region in a laminar arrangement, thus
minimizing a total depth and strength of the "tubular part" of the
cross section in the center area. At the same time, the top and
bottom portions of the hat section stiffen and help stabilize the
corresponding walls in the center of the front section 22. It is
noted that the center region of the bumper beam 20 must be strong
enough to pass impact testing against a center of the bumper beam
20 without unacceptable damage, yet the center region must be
flexible enough to absorb energy or transmit energy for functional
impact testing so that the vehicle itself does not become
prematurely damaged during a front impact.
In the illustrated center region, the center portion 28 lies
relatively tight against or in contact with the front wall 23 of
the front section 22, but it is contemplated that any desired
spacing can be created, such that the illustrated arrangement is
intended to illustrate both a "flat tube" in the center region as
well as a "non-flat" or "thin" tube in the center region. In the
end regions, the end portions 29 and 30 of the back section 27 are
fit against the rear edges of the top and bottom walls 24 and 25 to
form a tubular cross-sectional shape having a "deep" depth
dimension D1. It is contemplated that the end portions 29 and 30 of
the back section 27 can be relatively flat (as illustrated by the
solid lines in FIG. 4), or that the end portions 29 and 30 can have
a reverse hat shape that extends in a direction opposite the hat
shape of the center portion 28 of the back section 27 (as
illustrated by the dashed lines in FIG. 4).
The angled intermediate portions 31 and 32 provide a changing
cross-sectional tubular shape that transitions between the center
and end portions of the beam 20. It is contemplated that the
intermediate portions 31 and 32 can be deep-drawn to form mounting
surfaces adapted for attachment to vehicle frame rails, such as the
illustrated beam 20B having a back section 27B with deep-drawn
mounting surfaces 29B and 30B (FIG. 4A) which are coplanar and
spaced apart as desired.
It is contemplated that the back section 27 will be made by an
optimal process. The illustrated back section 27 can be stamped
using stamping technology. The simplicity of the back section 27
(FIG. 2) potentially allows it to be made from high-strength
low-alloy (HSLA) material since it incorporates relatively simple
bends. However, it is contemplated that drawable grade steel will
be used whenever the back section 27 has "deep" areas that require
material flow. Alternatively, it is contemplated that the back
section 27 could be molded of polymeric material.
It is contemplated that top and bottom edges of the back section 27
can be secured to the front section 22 by several different means.
For example, where steels are used for the front section 22 and the
back section 27, MIG puddle welding or "standard" MIG welding can
be used. It is also contemplated that various welding such as
spot-welding can be used to secure edge flanges of the back section
27 and front section 22 together. Also, rivets and other mechanical
attachment means known in the art can be used. Again, the optimal
process will depend upon the strength and properties of the back
section 27 and the front section 22, and also will depend on the
functional requirements of the beam 20. Where a formable material
is used, such as drawable steel, it is conceived that alternative
attachment methods can be used such as a hemmed flange 35 (FIG. 9)
where the edges of the back section 27 near the ends are doubled
back on themselves to capture the edges 36 of the front section 22.
Where the materials of the front and back sections differ,
mechanical attachment may be preferred, such as rivets, hemming, or
toggle-lock methods.
It is also conceived that a combination of attachment methods can
be used, such as by using welding at critical high-stress areas,
and rivets or other means on less-stressed attachment areas.
Drawable steel and aluminum, depending on their grade, can be
toggle-locked together, which is a mechanical connection using the
material of the sheets themselves to form the rivet-like
connection. An exemplary toggle lock connection 40 is shown in FIG.
9. It is noted that toggle lock technology is commercially
available. In the toggle lock connection 40, the edge flanges 41
and 42 abut along end regions of the back section 27 and the front
section 22. A tooling pin (not shown) is forced through the edge
flanges 41 and 42 to stretch the flange material to form a
double-thickness protrusion. The tooling pin is removed (or
temporarily left in place during the peening step), and then the
section is peened or struck in a manner causing the head 44 to
mushroom while the neck 45 remains relatively thin. As a result the
material of the back section's flange 41 in the head 44 is trapped
by the material of the front section's neck 45 after the step of
peening. The effect is much like a rivet 46, as shown in a lower
portion of the FIG. 10. It is of course contemplated that rivets 46
could also be used for securement. Where the material of the
reinforcement and/or the front section 22 are substantially
different materials (such as one is steel and the other is aluminum
or plastic), mechanical attachment such as by the use of rivets 46
or a hemmed edge are potentially a realistic and desirable option.
Hemming the flanges 41-42 (i.e. folding one flange 41 back on
itself to capture the mating flange 42) is an attractive
alternative attachment method since it uses the material of the
sections 22 and 27 themselves without the need for additional parts
or components. The illustrated flange 41 is continuous, though a
slit 48 could be used.
One contemplated alternative is to weld multiple strips of material
together to form a long roll, from which the back section 27 would
be made. The multiple strips of material would be chosen to have
optimal strengths and material properties in each of their ultimate
positions in the back section 27. For example, end portions 29 and
30 could be made from one material (such as UHSS), while the
intermediate portions 31 and 32 and the center portion 28 could be
from a more ductile or lower strength material such as HSLA steel.
Also, the portions 28-32 could each have different material
thicknesses and properties. A variety of different options are
possible, as will be quickly understood by a person skilled in the
art of vehicle bumper manufacture and in the art of roll-forming
and stamping.
A bumper beam 20A (FIGS. 5-7) is similar to bumper beam 20 in many
aspects. To reduce redundant discussion, the same members are used
to identify the same or similar parts, features and
characteristics, but with the addition of the letter "A". This is
done to reduce redundant discussion, and not for another
purpose.
The bumper beam 20A (FIGS. 5-7) is similar to bumper beam 20 in
that it includes a front section 22A and a back section 27A. But in
a center region of the bumper beam 20A, the back section 27A forms
a tubular section with the front section 22A. At the same time, the
illustrated end portions 29A and 30A of the back section 27A lie
relatively close to and flat against the ends of the front section
22A. Thus, the bumper beam 20A has a tubular section across its
center region, while its ends are stiffer. Potentially, the ends of
the back section 27A have a B-shaped cross section as opposed to a
laminar double-thick arrangement. The front section 22A and back
section 27A of bumper beam 20A could be secured together by any of
the illustrated attachment means shown in FIGS. 8-10 and/or the
other attachment methods discussed herein.
The method of the present invention is shown in FIG. 11. The method
includes selecting a strip of material in a step 49 (such as UHSS
material, or UHLA steel material), and then roll-forming the strip
of material in a step 50 to form an open front section 22 (which
can be C-shaped, W-shaped, or hat-shaped), including (optionally)
sweeping the front section in a step 51 to form a longitudinally
curved part. The material for the back section 27 is selected in a
step 52, prepared as required in a step 53, and stamped in a step
54. The step 53 of preparing the strip may include welding multiple
strips (tailor welded blanks) together and/or heat-treating (e.g.
annealing) various sections of a single strip so that particular
strength characteristics end up at predetermined locations on the
finish back section 27. It is contemplated that where heat-treating
is used, this preparation can be done before, during, or after the
step of stamping. Alternatively, instead of steps 52-54, the back
section 27 can be made by molding in step 54' (or alternatively can
be made using other forming and bending techniques). The back
section 27 is then mated together with the front section 22 in a
step 55, and then attached in a step 56. As noted above, the step
55 of mating the back section 27 to the beam 22 can form a variety
of different shapes, including different tubular cross-sectional
sizes and depths along a length of the beam 20. It is contemplated
that the mating step 55 can be done in-line with the roll-forming
machine, or done off-line in a secondary operation at an end of the
roll-forming process such that it forms part of a continuous
manufacturing process, or done off-line in a separate operation.
Another option is to take the roll-formed front section and feed it
into a transfer press where it is fastened to the back section
after the back section has been stamped. For example, the transfer
press could include tooling for stamping the back section 27. In a
last stage (or near-to-last stage) of the stamping operation, the
roll-formed front section 22 would be fed into the transfer press,
and attached to the front section 22 such as by a hemming
operation, welding, riveting, or a toggle-lock process.
Alternatively, one could use mechanical fasteners or spot-welding
in the press. It is contemplated that the attachment step 56 can
include a variety of different attachment means, including welding
(MIG puddle welding, standard MIG welding, spot-welding, mechanical
fastening such as hemming attachment, toggle lock attachment (see
earlier discussion on toggle lock and UHSS materials), rivet
attachment, and other attachment means).
MODIFICATION
A modified bumper beam 20C (FIGS. 12-15) includes components,
features, and characteristics similar or identical to the beams
20-20B. In beam 20C, identical and similar features are identified
using the same identification numbers to reduce redundant
discussion. Nonetheless, it should be understood that the
discussion of beams 20-20B also apply to beam 20C.
Beam 20C (FIG. 12) includes a front section 22C and a back section
27C mated together to form a tubular beam of varying
cross-sectional size along its length. The front section 22C is
made of relatively higher-strength material, preferably a material
such as ultra-high-strength steel (UHSS) or an advanced
ultra-high-strength steel such as a material having a tensile
strength of 220 KSI. The front section 22C preferably has a more
uniform cross-sectional shape permitting it to be roll-formed. The
back section 27C is made of a material, permitting it to be formed
by a stamping operation. The vertical cross sections defined by the
beam 20C have depth dimensions that are different depending upon
where the cross section is taken along the beam's length, with each
cross section being optimally suited for the particular location on
the beam 20C for optimal impact strength and energy absorbing
capability. The illustrated front section 22C and back section 27C
include top and bottom edge flanges 41C and 42C that telescopingly
overlap when the sections 22C and 27C are brought together. The
abutting surfaces on the edge flanges 41C of the front section 22C
and the edge flanges 42C of the back section 27C define horizontal
planes that extend in a fore-aft direction. The edge flanges 41C
and 42C are secured together, such as by spot-welding, or by a
stitch or continuous weld such as a MIG weld, or by any of the
various welding and mechanical attachment techniques previously
disclosed in this application. It is noted that the edge flanges of
the front section 22C are positioned inside the edge flanges of the
back section 27C. This is so that, if the beam 20C is impacted
sufficiently to shear the attachment weld (i.e. shear the weld bead
or other attachment means), the front section 22C will slide
rearwardly within the top and bottom walls of the back section 27C
until the flanges 41C of the front section 22C engage the rear wall
of the back section 27C. By this mechanism, the front section 22C
is contained within the back section 27C, and the beam 20C retains
a majority of its strength, even if some or all of the attachment
arrangement shears prematurely. This is a secondary safety feature
that can be desirable in some circumstances and for some
vehicles.
The front section 22C (FIG. 13) (preferably made from an advanced
UHSS having tensile strength of 220 KSI) is longitudinally curved
and has a front wall 23C with a channel 52C formed longitudinally
therein, and also has top and bottom walls 24C and 25C that extend
from front wall 23C. The walls 23C-25C define a rearwardly-facing
C-shaped cross section. An aperture 53C is formed in the channel
52C at each end.
The back section 27C (preferably made from a stamped material such
as high-strength, low alloy or UHSS steel) is longitudinally curved
and has the edge flanges 42C shaped to match the front section 22C,
and includes a center portion 28C and end portions 29C shaped to
mate as desired with the walls 24C and 25C of the front section
27C. A rear wall 55C extends a length of the back section 27C. In
the center portion 28C, the rear wall is relatively planar in
shape. At an inboard part 56C of the end portions 29C, the rear
wall is depressed forwardly toward the front wall 23C of the front
section 22C. At an outboard part 57C of the end portions 29C, the
rear wall is formed rearwardly to form a flat area that aligns with
the similar outboard part on the other end portion. The
intermediate part 58C of the end portions 29C transitions between
the two parts 56C and 57C. The illustrated outboard part 57C is
flat and is adapted to abut and be attached directly to the end cap
59C which forms the end of the frame side rail on the vehicle
frame. This arrangement eliminates extra parts, since a bracket
does not need to be attached to the beam 20C in order to attach the
vehicle frame to the bumper 20C. The illustrated end cap 59C is
channel shaped, and has a flat center plate 60C that attaches to
the rear wall 55C in the outboard part 57C, and further has a pair
of parallel flanges 61C and 62C that extend rearwardly for engaging
an end of the vehicle frame side rails. Stiffening embossments or
channels 63C are formed in the top wall 64C (and bottom wall) of
the back section 27C, and also embossments or channels 65C are
formed in the rear wall 55C of the back section 27C as desired for
strength. The illustrated rear wall 55C terminates short of the end
of the front section 22C (FIG. 15). An attachment flange 66C is
formed integrally from an end of the rear wall 55C, and tabs 67C
are extended from the top and bottom ends of the flange 66C. The
tabs 67C are welded to otherwise be secured to the top and bottom
walls of the back section 27C. A stanchion flange 68C extends from
the attachment flange 66C, and a foot flange 69C extends from the
stanchion flange 68C. The foot flange 69C abuts the surface of the
front wall 23C of the front section 22C. Foot flange 69C can be
welded to the front section 22C by applying MIG weld through the
aperture 53C. In the absence of the aperture 53C, the foot flange
69C can be attached to the front section using either a spot weld
or a mechanical fastener. Another attachment method might be the
use of a finger tab 70C that extends from the foot flange 69C
through the aperture 53C and is bent onto the channel 52C where it
is out of the way. The arrangement including flanges 66C-70C
support the ends of the front section 22C and provide the bumper
20C with good corner impact strength.
It is to be understood that variations and modifications can be
made on the aforementioned structure without departing from the
concepts of the present invention, and further it is to be
understood that such concepts are intended to be covered by the
following claims unless these claims by their language expressly
state otherwise.
* * * * *