# Patent

## Title
Tubular energy management system for absorbing impact energy

## Abstract

An energy-absorbing system includes a tube made of a continuous material, such as heat-treatable steel. The tube has first and second ring sections connected by an intermediate section. In one aspect, the intermediate section is flared and/or pinched to cause one tube section to predictably telescopingly roll upon impact. In another aspect, one section is annealed to optimize elongation and yield properties to facilitate rolling upon impact. By this arrangement, upon the bumper system receiving a longitudinal impact, the first and second ring sections telescopingly collapse with a predictable and consistent rolling collapse. Methods related to the above are also described.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No. 09/964,914, filed Sep, 27, 2001, now U.S. Pat. No. 6,648,384, entitled “CRUSH TOWER WITH RINGS OF VARIED STRENGTH” the entire contents of which are incorporated herein by reference.


BACKGROUND
The present invention relates to energy-management systems configured to absorb significant impact energy in a consistent and predictable manner during an impact stroke.
The federal government, insurance companies, and agencies, associations, and companies concerned with vehicle safety have established standardized impact tests that vehicle bumper systems must pass. Bumper mounts and crush towers are commonly used to support bumper bars on vehicle frames and often are used to absorb energy during a vehicle impact. Several characteristics are beneficial for “successful” bumper mounts and crush towers. It is desirable to manufacture bumper mounts and crush towers that provide consistent and predictable impact strength within a known narrow range, so that it is certain that the bumper systems on individual vehicles will all pass testing. This lets manufacturers make a safer vehicle and also lets them more precisely optimize their bumper systems to reduce excess weight and to utilize lower cost materials. More specifically, it is desirable to manufacture bumper mounts and crush towers that provide a consistent force-vs-deflection curve, and to provide a consistent energy absorption-vs-time curve, and to provide a consistent and predictable pattern of collapse. This lets vehicle manufacturers know with certainty how much deflection is created with any given impacting force, and how much energy is absorbed at any point during an impact or vehicle collision. In turn, this allows vehicle manufacturers to design enough room around the bumper system to permit non-damaging impact without wasting space to compensate for product variation and to provide enough support to the bumper system on the vehicle frame. The force-vs-deflection curve has several important ranges at which the crush tower changes from elastic deformation to permanent deformation to total collapse and bottoming out. It is important that these various points of collapse be predictable to assure that substantial amounts of energy are absorbed before and during collapse, and also to assure that collapse occurs before excessive loads are transferred through the bumper system into the vehicle and its passengers.
In addition to the above, bumper development programs require long lead times, and it is important that any crush tower be flexible, adaptable, and “tunable” so that it can be modified and tuned with predictability to optimize it on a given vehicle model late in a bumper development program. Also, it is desirable to provide a crush tower design that can be used on different bumper beams and with different bumper systems and vehicle models, despite widely varied vehicle requirements, so that each new bumper system, although new, is not a totally untested and “unknown” system.
Some tubular crush towers are known for supporting bumper beams in a bumper system. In one type, two stamped half shells are welded together. However, this process generates raw material scrap. Also, the welding process is a secondary operation that adds to manufacturing overhead costs. Further, the welded crush towers are subject to significant product variation and significant variation in product impact strength, force-vs-deflection curves, energy absorption curves, and crush failure points.
Some crush towers use stronger materials than other crush towers. However, as the STRENGTH of a crush tower is increased, there is a tendency to transmit higher and higher loads from the bumper beam directly into the vehicle frame. This is often not desirable. Instead, it is desirable that the tower itself predictably crush and collapse and absorb a maximum of energy over a distributed time period. In particular, crush towers that are very high in strength will tend to transmit undesirably high load spikes from the bumper beam to the vehicle frame. This is often followed by a catastrophic collapse of the crush tower where very little energy is absorbed and where the energy absorption is not consistent or predictable from vehicle to vehicle. Also, it results in premature damage to a vehicle frame. It is particularly important that a crush tower be designed to flex and bend material continuously and predictably over the entire collapsing stroke seen by the crush tower during a vehicle crash. At the same time, a design is desired permitting the use of ultra-high-strength materials, such as high-strength low alloy (HSLA) steels or ultra-high-strength steels which have a very high strength-to-weight ratio. As persons skilled in the art of bumper manufacturing know, the idea of simply making a crush tower out of a stronger material is often a poor idea, and in fact, often it leads to failure of a bumper system due to transmission of high impact loads and load spikes to the vehicle frame, and also to problems associated with insufficient energy absorption.
Vehicle frames, like bumper mounts and crush towers, are preferably designed to manage impact energy, both in terms of energy absorption and energy dissipation. This is necessary to minimize damage to vehicle components, and also is necessary to minimize injury to vehicle passengers. Like bumper mounts and crush towers, vehicle frames have long development times, and further, they often require tuning and adjustment late in their development. Vehicle frames (and frame-mounted components) have many of the same concerns as bumper mounts and crush towers, since it is, of course, the vehicle frame that the mounts and crush towers (and other vehicle components) are attached to.
More broadly, an energy absorption system is desired that is flexible, and able to be used in a wide variety of circumstances and applications. It is preferable that such an energy absorption system be useful both in a bumper system, but also in vehicle frames (longitudinal and cross car), and other applications, as well as in non-vehicle applications.
Accordingly, an energy management system is desired solving the aforementioned problems and having the aforementioned advantages. In particular, an energy management system is desired that provides consistent impact strength, consistent force-vs-deflection curves, consistent energy absorption (for elastic and permanent deformation), and consistent collapse points and patterns, with all of this being provided within tight/narrow ranges of product and property variation. Also, a cost-competitive energy management system is desired that can be made with a reduced need for secondary operations and reduced need for manual labor, yet that is flexible and tunable.
SUMMARY OF THE PRESENT INVENTION
In one aspect of the present invention, an energy management tube adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally includes a first tube section, a second tube section aligned with the first tube section, and an intermediate tube section. The intermediate tube section includes first and second end portions integrally connecting the first and second tube sections, respectively. The first and second tube sections are dimensionally different in size, and the intermediate tube section has a shape transitioning from the first tube section to the second tube section. The first tube section is larger in size than the second tube section and includes an outer surface defining a tubular boundary. The first end portion includes a continuous band of deformed material flared outward radially beyond the outer surface, which acts to support and maintain a columnar strength of the first tube section upon longitudinal impact. The second end portion contrastingly is configured to initiate a telescoping rolling of the second tube section during impact as the first tube section maintains its columnar strength.
In another aspect of the present invention, an energy management tube includes first and second aligned tube sections, and an intermediate tube section with first and second end portions integrally connecting the first and second tube sections, respectively. The first and second tube sections are dimensionally different in size and the intermediate tube section has a shape transitioning from the first tube section to the second tube section. The second tube section is smaller in size than the first tube section, and includes an inner surface defining a tubular boundary. The second end portion includes a continuous band of deformed material flared inward radially inside of the boundary, which acts to support and maintain a columnar strength of the second tube section upon longitudinal impact. The first end section is configured to initiate a telescoping rolling of the first tube section during impact as the second tube section maintains its columnar strength.
In another aspect of the present invention, an energy management tube includes first and second aligned tube sections, and an intermediate tube section with first and second end portions integrally connecting the first and second tube sections, respectively. The first tube section is dimensionally larger in size than the second tube section and the intermediate tube section has a shape transitioning from the first tube section to the second tube section. The intermediate section forms a continuous ring and, when cross sectioned longitudinally, forms a non-linear wall segment where the first end portion defines a first radius on the wall segment and the second end portion defines a second radius on the wall segment, with one of the first and second radii being smaller than the other radii. The end portion with the one smaller radius provides a relatively greater support for columnar strength than the end portion with the other larger radius. The end portion with the other larger radius is configured to initiate a telescoping rolling of the tube section with the larger radius. By this arrangement, upon undergoing a longitudinal impact, the intermediate tube section and the second tube section roll predictably and sooner than the first end portion and sooner than the first tube section upon the intermediate section receiving forces from the longitudinal impact.
In yet another aspect of the present invention, an energy management tube is provided that is adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally. The energy management tube includes first and second aligned tube sections, and an intermediate tube section with first and second end portions integrally connecting the first and second tube sections, respectively. The first tube section is dimensionally larger in size than the second tube section, and the intermediate tube section has a shape transitioning from the first tube section to the second tube section. A crushable support member is positioned inside of the first tube section and is configured to crush and simultaneously to assist in controlling rolling of material upon a longitudinal impact. A crushable support member is positioned inside of the first end portion and supports the second end portion to apply additional resistance to initiate and maintain telescoping rolling. Support member functionality is independent of which end portion telescopingly rolls.
In still another aspect of the present invention, an energy management tube includes first and second aligned tube sections and an intermediate tube section with first and second end portions integrally connecting the first and second tube sections, respectively. The first tube section is larger in size than the second tube section, and the intermediate tube section has a shape transitioning from the first tube section to the second tube section. The intermediate tube section and one of the first and second tube sections are annealed to have different material properties than the other of the first and second tube sections. The different material properties including a change in yield and elongation properties are adapted to facilitate deformation and shaping of the intermediate tube section upon the intermediate tube section receiving stress sufficient to deform the intermediate tube section.
An object of the present energy absorption technology is to provide a flexible energy management system that is able to be used in a variety of circumstances and applications, such as bumper systems, vehicle frames (longitudinal and cross car), systems that anchor major vehicle components to vehicle frames, vehicle roof structures, as well as non-frame applications, such as steering column systems, instrument panel supporting systems, and the like.
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 horizontal cross-sectional view of a bumper system including a mounting plate attached to a vehicle frame, a bumper beam, and a crush tower including opposite ends attached to the mounting plate and the bumper beam;
FIG. 2 is a view similar to FIG. 1, but with the crush tower collapsed a first (relatively short) distance; and
FIG. 3 is a view similar to FIG. 2, but with the crush tower collapsed a second (longer) distance.
FIG. 4 is a side view of an energy management tube embodying the present invention;
FIG. 5 is a perspective view of additional cross-sectional shapes that the energy management tube can take on;
FIGS. 6-8 are side views of a tubular blank with a first diameter (FIG. 6), the tubular blank being compressed to a reduced diameter at one end (FIG. 7) and then deformed longitudinally at an intermediate tube section to take on an S-shaped pre-set (FIG. 8), FIG. 8 showing an energy management tube of the present invention;
FIGS. 9-11 are side, end, and longitudinal-cross-sectional views of the tube of FIG. 8, the tube having an outwardly flared end portion of its intermediate tube section adjacent its large diameter tube section;
FIG. 12 is an enlarged view of the circled area XII in FIG. 10;
FIG. 13 is a perspective view of the tube shown in FIG. 14, the tube being partially telescopingly collapsed and including rolled material on the larger diameter tube section;
FIGS. 14-15 are side and longitudinal-cross-sectional views of a modified energy management tube, the tube having an inwardly flared end portion of its intermediate tube section adjacent its small diameter tube section;
FIG. 16 is an enlarged view of the circled area XVI in FIG. 15;
FIG. 17 is a graph showing a load vs deflection curve for a longitudinal impact of the tube shown in FIG. 10;
FIG. 18 is a chart showing the effect of annealing on hardness and tensile strength versus a distance from a bottom of the tube of FIG. 10 with the tube stood on end and with the intermediate section (ranging from about 75 mm to about 95 mm) and the second tube section being annealed;
FIG. 18A is a graph showing the affect of annealing on material used in the tube of FIG. 18, the sequence of annealing temperature lines A-J showing a gradual reduction of yield strength, a reduction in tensile strength, and an overall increase in strain and formability based on increasing annealing temperatures;
FIG. 19 is a perspective view of a vehicle frame incorporating the present energy management tube of FIG. 10, including enlargement of four particular areas where the energy management system of the present invention is used;
FIG. 20 is a perspective view of two cross car beams, one being a cross car beam used in a vehicle frame located under the vehicle's floor-pan, and the other being a cross car beam used above the vehicle's floor pan and used to support vehicle seats;
FIG. 21 is a perspective view of a bumper system incorporating a bumper reinforcement beam and a crush tower supporting the bumper beam on a vehicle frame;
FIG. 22 is a perspective view of a cross car beam used to support an instrument panel; and
FIGS. 23-24 are perspective views showing a crushable support member exploded from an energy management tube in FIG. 23 and positioned within the tube in FIG. 24.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A vehicle bumper system 10 (FIG. 1) includes a vehicle front bumper beam 11 with a mounting bracket, a vehicle frame including a rail mounting plate 12, and a crush tower 13 mounted between the bracket and the plate 12. The crush tower 13 comprises a tube made of a continuous contiguous material, such as high-strength heat-treatable steel. The tube has first and second ring sections 14 and 15 connected by an interconnecting section 16. The interconnecting section 16 has a frustoconically-shaped portion 17 forming a funnel-shaped ramp. In one mode, the first ring section 14 is heat-treated to a high material strength, such as about 140 KSI tensile strength, which is substantially higher than the second ring section 15, which is kept at about 60 KSI tensile strength. It is contemplated that the tensile strength of the first ring section 14 should be above the tensile strength of the second ring section 15 by a significant amount, such as about 10%, but preferably should be about double the tensile strength or about 60 KSI above it. This arrangement provides the stiffness necessary for the ring section 14 to telescope onto the ring section 15 and to provide bunching at the frustoconically-shaped portion 17 of the interconnecting section 16.
By this arrangement, upon the bumper system 10 receiving an end impact parallel a length of the crush tower 13, the first and second ring sections 14 and 15 telescopingly collapse into each other with a predictable and consistent multi-phase deformation sequence where a third ring or small radius pinched section 18 (FIG. 2) begins to form and then does form (FIG. 3) between the first and second ring sections 14 and 15. Once the third ring 18 is fully formed, as limited by a length of the interconnecting section 16, material begins to buckle and bunch up at location 20 under the “hook” formed by the section 22. It is contemplated that additional ring sections and interconnecting sections could be provided if a vehicle model has enough room, and additional energy absorption is desired before final bottoming out of the crush tower.
The illustrated bumper beam 11 is a tubular beam and is known in the art. For example, see Sturrus U.S. Pat. Nos. 5,092,512 and 5,813,594. However, it is contemplated that the beam could be an open non-tubular beam as well. Also, the bumper beams can be linear or curved. Depending on their shapes, mounting brackets or plates can be used to provide a relatively flat mounting surface on the bumper adapted for attachment to a crush tower. (See FIG. 14 of U.S. Pat. No. 5,092,512 and FIG. 4 of U.S. Pat. No. 5,813,594.) Similarly, at the vehicle-connected end of a crush tower, a variety of different means can be used to provide a point of attachment for securing the crush towers to a vehicle frame.
The present inventive crush tower 13 is made from a single tubular shape. It is contemplated that the tubular shape initially will be rollformed and welded into a permanent tube to have a constant and circular cross section, with uniform walls having a constant thickness. Nonetheless, it is contemplated that non-circular tubes could also be used in the present invention.
After the tube is formed and cut to a desired length, the interconnecting section 16 is rolled or stamped to form an inwardly-deformed frustoconically-shaped portion 17 (shaped like a funnel) having a low angle to a centerline 21 of the tube, and an inwardly-deformed radiused “quick-out” portion 22 having a greater angle to the centerline 21. The illustrated frustoconically-shaped portion 17 has a relatively linear funnel-shaped segment so that it forms a stiff ramp for guiding the ring section 15 into the ring section 14 during impact. Also, the quick-out portion 22 is radiused and angled so that it undergoes a bending force causing it to roll into an inwardly deformed hook shape (see FIG. 2). The inwardly deformed material forms a uniform columnar support for the section 15 that maintains a columnar strength of the tube section 15. This helps the telescoping action of sections 14 and 15 during impact, as discussed below.
The internal cavity 25 within the crush tower 13 is open and stays open during impact. As a result, a component can be positioned within the cavity 25 without adversely affecting a performance of the crush tower 13. For example, a tow hook bushing can be located within the cavity 25, if desired.
In operation, the crush towers 13 are manufactured by making a tube, such as by rollforming, then roll forming or deforming into the tube the reduced-diameter interconnecting section and then by heat-treating the ring section 14 (and/or sections 15, 17, and 22). A pair of the crush towers 13 are then assembled into a bumper system 10 by attachment to the bumper beam 11, with the crush towers 13 being horizontally and laterally spaced from each other. The bumper system 10 is then attached to a vehicle frame.
During impact, the interconnecting section 16 begins to buckle due to a linear strength of the ring sections 14 and 15 along their centerline 21. In particular, the frustoconically-shaped portion 17 is driven under the quick-out portion 22 as the quick-out portion 22 doubles back upon itself, forming an inwardly-deformed hook-like ring that grips the portion 17. The radius of portion 22 as compared to the rest of the material of portion 17 helps cause this result. This provides a first stage of collapse at a first (lower) level of energy absorption. As the crush tower 13 undergoes further telescoping during a long stroke from a vehicle crash, an end of the interconnecting section 16 is bent over and drawn under the remaining material of ring section 14. The third ring section 18 is formed between the ring sections 14 and 15 as the end of ring section 15 bends and rolls onto an outside surface of tube section 15. This sequential collapse and deforming of the various sections 14-16 and in particular, the rolling of the material of tube section 14 absorbs substantial energy in a very predictable manner and within a relatively narrow range of variation.
It is contemplated that the present crush tower can be made on a rollforming machine from a roll of high-strength low alloy (HSLA) steel. Further, it is contemplated that the roll of steel can be high-strength steel (such as 70 KSI tensile strength), or an ultra-high-strength steel (such as 80 KSI tensile strength or above). If needed, these materials can be annealed in selected areas to improve their elongation properties or to lower their yield strength (such as 60 KSI tensile strength or lower) and/or can be heat-treated in selected areas for increased strength. For example, crush towers having an area at one end with a 60 KSI tensile strength and an area at an opposite end with a 120 KSI strength can be made by either method. The intermediate ring section is preferably about 60 KSI and similar in strength to the lower strength ring section to better assure a good collapse sequence. It is noted that, in the present disclosure, the term “heat treat” is considered to be broader than the term “anneal”, and that the term heat treat includes increasing or decreasing material properties through use of heat and thermal means. It is also contemplated that the heat-treating and/or the annealing can be done in-line with the rollforming apparatus and simultaneous with the rollforming as a continuous process. When the step of annealing is done in-line with and simultaneous with the apparatus and rollforming process, it is beneficial to have the rollformed tubular shape be made so that adjacent crush towers face in opposite directions. For example, where the ring 15 (i.e. the end to be attached to the bumper beam) is annealed from a higher strength to a lower strength, it is beneficial to have two ring sections 15 of adjacent crush towers (i.e. before separation into separated tube sections) be next to each other so that a single annealing heat can be applied over a wider area. This adds efficiency, control, and line speed to the rollforming process and to the annealing process.
Modification
In the following description, similar components, features, and aspects are identified with the same identification numbers, but with the addition of a letter “A”, “B”, and etc. This is done to reduce redundant discussion.
A modified energy management tube 13A (FIG. 4) is provided that is adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally. The energy management tube 13A includes a first tube section 14A, a second tube section 15A that is aligned with the first tube section 14A, and an intermediate tube section 16A with first and second end portions 30 and 31, respectively. The end portions 30 and 31 integrally connect the first and second tube sections 14A and 15A, respectively. The first tube section 14A is dimensionally larger in size than the second tube section 15A, and has a similar cylindrical cross-sectional shape. However, it is noted that the first and second tube sections 14A and 15A can be different shapes including rectangular, square, oval, round, or other geometric shapes. (See FIG. 5) Further, it is contemplated that the tube sections 14A and 15A may have different cross-sectional shapes along their lengths, especially at locations spaced away from the intermediate tube section 15A where the tube sections 14A and 15A must be adapted to connect to different structures, such as vehicle frame components and the like. (See FIGS. 19-22) The intermediate tube section 16A has a shape transitioning from the first tube section 14A to the second tube section 15A, and further the first and second end portions 30 and 31 are dissimilar in shape as noted below (FIGS. 9-12).
The present energy management tube 13A (FIG. 4) is disclosed as being made from a sheet of annealable steel material with each of the tube sections 14A, 15A, and 16A being integrally formed together as a unit. The wall thickness can be varied as needed to satisfy functional design requirements. For example, for bumper crush towers and/or vehicle frames, the thickness can be about 1.5 mm to 4 mm, depending on material strengths and the specific application requirements of use. It is contemplated that the sheet will initially be made into a continuous long tube by a rollforming machine, and thereafter cut into tubular blanks 60 (FIG. 6) of predetermined lengths. Then, the tubular blanks will have the areas of tube sections 15A and 16A annealed, and then formed to a shape 61 (FIG. 7) where the second tube section 15A is compressed to a reduced diameter, with the intermediate section 16A temporarily taking on a temporary frustoconical shape. It has been determined that it is beneficial to fixture and longitudinally deform the energy management tube 13A to a pre-set condition (FIG. 8), so that the intermediate section 16A takes on a particular shape that avoids high load spikes during initial impact, as noted below. For automotive bumper systems and frame components, it is preferable that the sheet of material be a good, reliable grade of steel, such as structural steel. Steels having greater than about 35 KSI yield strength work very well. Steels that can be heat-treated or annealed to achieve optimal yield and elongation properties in selected areas are also excellent candidates, such as structural steels, or high-strength low-alloy steel (HSLAS) or ultra-high-strength steel (UHSS).
A specific comment about materials is appropriate. As selected materials get stronger and harder, with higher yield strengths, higher tensile strengths and lower elongation values, they often become more sensitive to tight radius and will tend to resist rolling. Instead, they will tend to break, kink, shear, crack, and/or fracture at tight radii. This breaking problem gets worse as the radii approach a thickness dimension of the material. The present invention utilizes outward and inward flaring, clearances, and radii specifically chosen to help deal with this problem. Various grades of steel are known in the art and understood by skilled artisans. The reader's attention is directed to ASTM A1008/A and A1008M-01a, and also to ASTM A1011A and A1011M-01a for standardized industry definitions. Structural steels such as steels having about 25 KSI and above, have strength properties where the quality problems noted above begin to occur. Structural steels are typically a slightly better grade than cold rolled commercial quality steel or hot-rolled commercial quality steel. Nonetheless, especially as they approach 25 to 35 KSI tensile strength, they tend to have problems. It is specifically contemplated that the present invention will work well using structural steels, such as steels having a tensile strength of about 25 KSI or greater, in the above-illustrated energy management tube 13 (and tubes 13A and 13B). The present invention also is well adapted for and works well for stronger materials of 80 KSI and above, and ultra-high-strength steels (UHSS). Where workability and enhanced rolling of material is desired, these steels can be heat treated or annealed to achieve optimal properties at strategic regions along the energy management tubes.
It is noted that the various steels discussed herein are intended to be and are believed to be well understood by persons skilled in the art of steel materials and in the art of rollforming. For the reader's benefit, it is noted that additional information can be obtained from the American Society for Testing and Materials (ASTM). The terms for steels as used herein are intended to be consistent with ASTM standards and definitions. Nonetheless, it is emphasized that the present technology is very flexible and adaptable to work with a wide variety of materials. Accordingly, the various terms are intended to be broadly construed, though reasonably construed.
The present concepts are believed to be particularly useful for HSLA steels, and ultra-high-strength steels (UHSS), such as dual phase steel, tri phase (TRIP) steel, or martensitic materials. The present concepts are also useful for other engineering grade materials, such as aluminum and even softer materials. The present concepts are particularly useful where high strength materials permit weight reduction through reduced wall thicknesses (i.e. gauge reduction). By being heat treatable, the material is inherently more workable and flowable, and/or can be made more workable and flowable in selected areas. For example, this allows a pre-set to be formed in the intermediate tube section 16A with small radii, yet with less risk of developing microcracks and/or macrocracks and/or splitting, less risk of shearing problems and material separation such as shelving, and less risk of other quality defects causing reduced material strength in the area of small-radius bends. The property of being annealed also allows the material to roll without shearing, ripping, or tearing, which is important to achieving maximum energy absorption during impact and longitudinal crush. (See FIG. 13.)
Notably, a performance of the present energy management tube can be adjusted and tuned to meet specific criteria by numerous methods, including by adjustment of the following variables: material thickness, material type, material hardness and yieldability, annealing temperatures and conditions, tube diameter and shapes, the particular rolling radius design and the degree of pre-set, use of crushable inserts positioned within (or outside) the tube sections, and other factors affecting rolling of material, columnar strength, energy absorption, and distribution of stress during a longitudinal crushing impact.
As illustrated in FIGS. 9-12, the first tube section 14A is larger in size than the second tube section 15A. The first tube section 14A includes an outer surface defining a tubular boundary 32. The tubular boundary 32 matches a cross-sectional shape of the first tube section 14A at an area near the first end portion 30. The first end portion 30 includes a circumferentially-continuous band of tightly deformed material 34 that is flared outward radially beyond the boundary 32, such as at a minimum angle of about 25°. This tightly deformed material 34 defines a small radius that effectively forms a “pinched” area that resists rolling of the material. Also, there is some work hardening of the material at the small radius. The small radius (on its concave surface) is preferably not less than about 0.5 times a thickness of the material of the first end portion 30. Thus, it adequately resists a tendency to shear or crack. The reasons for the deformed material 34 resisting rolling are numerous and subtle. It is believed that the tight “small” radius along with the flared shape forms a uniform ringed support for the first tube section 14A that acts to support and maintain a columnar strength of the first tube section upon longitudinal impact. When longitudinally stressed, the tightly deformed material 34 resists rolling of the material of first end portion 30 and of the first tube section 14A.
Contrastingly, the second end portion 31 (FIG. 12) has a deformed material 35 defining a relatively larger radius (on its concave surface), such as at least about 1.0 times a thickness of the material of the second end portion 31. The deformed portion 35 of the second end portion 31, due to its larger radius, is less resistant to rolling of the material of the second tube section 15A and is less supportive of the columnar strength of the second tube section 15A. In fact, second end portion 31 is configured to initiate a telescoping rolling of the second tube section 15A during impact as the first tube section 14A maintains its columnar strength. The fact that the tube sections 15A and 16A are annealed, and the first tube section 14A is not annealed, further facilitates and causes this result (although annealing is not required to have a tendency of a material to roll). Clearances are provided for the flow of material as necessary as it rolls. Potentially, the tube sections 14A and 15A can be sized to provide support to each other during the rolling of material during an impact. The pre-set condition of the intermediate tube section 16A also is important since it helps avoid an initial sharp high load peak, such that the load quickly levels off as it reaches a predetermined initial level, and then remains at that level during the impact stroke. (See FIG. 17).
A second energy management tube 13B (FIGS. 14-16) includes a first tube section 14B, a second tube section 15B, and an intermediate tube section 16B interconnecting the tube sections 14B and 15B. However, tube 13B differs from tube 13A. In tube 13B, the end portion 30B of the larger-diameter first tube section 14B includes deformed material 34B defining a larger radius. Further, the deformed material 34B is not flared outwardly, but instead remains generally within a boundary defined by an outer surface of the first tube section 14B. Concurrently, the end portion 31B of the second tube section 15B includes deformed material 35B defining a smaller radius. The deformed material 35B is flared inwardly inside of a tubular boundary 32B, such as at a minimum angle of about 12°.
FIG. 13 shows a partial stroke impact where a section of material 36 from the first tube section 14B of tube 13B has rolled. (In tube 13A, the second smaller tube section 15A is the one that rolls during an impact as it rolls in a similar manner.)
FIG. 17 illustrates a typical load-versus-deflection curve for tubes 13A and 14A. While there is some variation in loading during the impact stroke, it will be apparent to a person skilled in the art of designing energy management systems, such as for bumpers and frames, that the load quickly comes up to a predetermined level, and stays relatively consistently at the selected level throughout the impact stroke. The area under the load deflection curve represents actual energy absorption (“AEA”) during an impact stroke. A perfect energy absorption (“PEA”) would be calculated by multiplying the maximum load achieved during an impact (D1) times the full impact stroke (D2). The present energy management system provides an exceptionally high efficiency rating (i.e. “AEA” divided by “PEA”). Specifically, the present energy management tube technology ends up with much higher and more consistent energy-absorption efficiency rating than known bumper crush towers, due to a relatively fast initial loading, and a relatively well-maintained and consistent level of loading continued through the entire impact stroke. Specifically, the present inventive concepts provide surprising and unexpected consistency and reliability of the load-versus-deflection curves, and also provide for consistent and reliable energy absorption and crush strokes.
FIG. 18 is a chart showing a typical annealed tube such as may be used to get the result of FIG. 17, and FIG. 18A is a graph showing the affect of annealing on material used in the tube of FIG. 18. The sequence of annealing temperature lines A-J shows a gradual reduction of yield strength, a reduction in tensile strength, and an overall increase in strain and formability based on increasing annealing temperatures. It also shows a general relationship between tensile strength and yield strength, as well as a relationship between those properties and strain.
FIG. 19 is a perspective view of a tubular vehicle frame incorporating concepts of the present energy management tube of FIGS. 11 and 15 into its tubular side members. Four particular areas are shown in enlargements next to the four areas, each illustrating a place where the energy management system technology of the present invention could be used. However, it is noted that the present technology could be used in additional areas. Further, in a “real” frame, the locations of use would most likely be in more symmetrical locations on the frame.
The illustrated tube 40 (FIG. 19) is located near a front end of the vehicle frame 39, in a longitudinal portion of the front frame side frame member, just in front of a front cross car beam. The tube 40 is rectangular in cross section, and includes a single intermediate tube section (16C) (see FIG. 11) configured to initiate rolling material of one of the tubes (14C or 15C) during telescoping impact. The energy management tube 41 is located in a similar forward location on the vehicle frame. Tube 41 is circular in cross section, and includes a single intermediate tube section (16D) for initiating rolling of material during telescoping impact. The tube 41 also includes a transition zone 42 on one end where the circular cross section transitions to a square section for engaging a front (or rear) end of a vehicle frame member. Tube 41 could be used, for example, to support a vehicle bumper.
The two-ended tube 43 is located at a mid-section of a side of the illustrated vehicle frame. The tube 43 is circular in cross section, and includes two intermediate tube sections 44 and 45 facing in opposite directions on opposing ends of a smaller diameter centrally located tube section 46. The tube 43 further includes two larger diameter tube sections 47 and 48 on each outer end of the intermediate tube sections 44 and 45. Further, the larger diameter tube sections transition to a square cross section at their outer ends. Another energy management tube 49 is similar to tube 40, and is located at an end of one side member of the vehicle frame. However, instead of being in front of the nearest cross beam, the cross beam 50 is attached directly to the larger diameter tube section of the energy management tube 49, such as by welding.
FIG. 20 is a perspective view of two cross car beams, one being a cross car beam 52 used in the same plane as a vehicle frame. The beam or energy-management tube 52 is similar to two-ended tube 43, discussed above. It includes a smaller diameter tube section 53 is placed in a middle position, and two larger diameter tube sections 54 and 55 are attached to the side members of the vehicle frame. Notably, the ends of the tube 13A (or 13B) can be annealed to facilitate reforming to better match the geometry of the frame rails.
The other energy management system of FIG. 20 includes a pair of tubes 55 placed as cross car beams but used above the vehicle's floor pan . . . or at least positioned at a location relative to the floor pan where the seats can be anchored on them. Each tube 55 is similar to tube 52, in that opposing ends of it are anchored to sides of the vehicle. Each tube 55 includes a smaller middle tube section 56 and two outer larger tube sections 57 and 58. The vehicle includes seats 59 and 60 with front and rear outer legs 61 attached to the larger tube sections 57 and 58, and with front and rear inner legs 62 attached to the smaller tube section 56.
FIG. 21 is a perspective view of a bumper system incorporating a bumper reinforcement beam 64 and an energy management tube 65 supporting the bumper beam 64 on a vehicle frame. The crush tower 65 is an energy management tube similar to the tube 41, does not need to be discussed in detail.
FIG. 22 is a perspective view of a cross car beam 67 used to support an instrument panel 68. The beam 67 includes a single long smaller diameter tube section 69, and two larger diameter tube sections 70 at each end. The larger diameter tube sections 70 are attached to vehicle structure, such as at the vehicle “A” pillars just in front of the front passenger doors. Several collars 71 are positioned on the smaller diameter tube section 69, for supporting brackets 72 and opened attachment flanges 73. Brackets 72 are used to anchor various items, such as the instrument panel 68, and various components and accessories in and around the instrument panel 68.
FIG. 23 is a perspective view showing a crushable insert 75 positioned at an outer end of an energy management tube 76, and ready to be axially installed therein. The tube 76 includes a small diameter tube section 77, a large diameter tube section 78, and an intermediate tube section 79 interconnecting them and designed to provide a predetermined rolling of material of the small diameter tube section 77 as the small diameter tube section 77 moves rollingly into the large diameter tube section 78 upon longitudinal impact. The crushable insert 75 includes structural rings 80 having circumferential strength and that are adapted to radially support the large diameter tube section 78. The structural rings 80 are interconnected by thin rings 81 that space the structural rings 80 longitudinally apart. However, the thin rings 81 have a predetermined longitudinal strength, such that they collapse with a predetermined force upon receiving forces in a longitudinal direction. Thus, the crushable insert 75, when positioned within the energy management tube 76 (FIG. 24), initially fits snugly into the large diameter tube section 78 in a manner that prevents rattling. However, during longitudinal impact, as the small diameter tube section 77 is moved into and toward large diameter tube section 78, the material of the small diameter tube section 77 begins to roll and move into engagement with an end of the crushable insert 75. As the small diameter tube section 77 rolls, the thin rings 81 of the crushable insert 75 collapse, making additional room for more rolled material. The sequence continues, until the crushable insert 75 is fully crushed. During the impact stroke, the crushable insert 75 engages and helps control the material that is rolling. For example, in one test, the crushable insert 75 increased the longitudinal load by 10,000 pounds force. Also, testing has potentially shown that the load can be made more consistent, thus increasing the efficiency rating (i.e. “AGA” divided by “PEA”, as described above) of the energy management system.
Thus, the crushable inserts provide additional resistance to rolling of tube section 77 and can be used to tune the performance of the energy management tube. The illustrated crushable insert 75 in FIGS. 23 and 24 are made of an elastomer material that, upon longitudinal loading, will crush when imparted by the rolling radius of the intermediate tube section 79. Convex circular rings 81 are positioned between thicker boundary rings 80. When the crushable inserts are loaded, the rings 80 transfer load to the convex region which initiate crush on loading. Outward crushing of the convex region 81 is impeded by the inner surface of tube section 78. Similar performance can be achieved when tube section 78 rolls and tube section 77 maintains column strength. The crushable inserts can be made from various materials and different geometry can be used to tune the performance of the energy management tube. Crushable inserts can be used to tune the tube performance instead of increasing tube diameter or material thickness. Some standard ways to tune the performance of the tube can be accomplished by increasing the material thickness or increasing the tube diameter. The use of crushable inserts provides and alternative way to tune performance without the addition of significant cost and without the added penalty of weight.
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.

## Claims

1. An energy management tube adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally, comprising:
a first tube section; 
a second tube section aligned with the first tube section; and 
an intermediate tube section with first and second end portions integrally connecting the first and second tube sections, respectively; the first and second tube sections being dimensionally different in size and the intermediate tube section having a shape transitioning from the first tube section to the second tube section; 
the first tube section being larger in size than the second tube section and including an outer surface defining a tubular boundary, the first end portion including a continuous band of deformed material flared outward radially beyond the outer surface and which acts to support and maintain a columnar strength of the first tube section upon longitudinal impact, the second end portion contrastingly being configured to initiate a telescoping rolling of the second tube section during impact as the first tube section maintains its columnar strength; 
wherein the first tube section has a yield strength of at least about 10% greater than the second tube section.

2. An energy management tube adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally, comprising:
a first tube section; 
a second tube section aligned with the first tube section; and 
an intermediate tube section with first and second end portions integrally connecting the first and second tube sections, respectively; the first and second tube sections being dimensionally different in size and the intermediate tube section having a shape transitioning from the first tube section to the second tube section; 
the first tube section being larger in size than the second tube section and including an outer surface defining a tubular boundary, the first end portion including a continuous band of deformed material flared outward radially beyond the outer surface and which acts to support and maintain a columnar strength of the first tube section upon longitudinal impact, the second end portion contrastingly being configured to initiate a telescoping rolling of the second tube section during impact as the first tube section maintains its columnar strength; 
wherein the first end portion has a radius of not less than about 0.5 times a wall thickness of the first tube section.

3. The energy management tube defined in claim 2, wherein the second end portion has a second radius of more than about 1.0 times a wall thickness of the second tube section.

4. An energy management tube adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally, comprising:
a first tube section; 
a second tube section aligned with the first tube section; and 
an intermediate tube section with first and second end portions integrally connecting the first and second tube sections, respectively; the first tube section being larger in size than the second tube section, and the intermediate tube section having a shape transitioning from the first tube section to the second tube section; and 
the intermediate tube section and one of the first and second tube sections being annealed to have different material properties than the other of the first and second tube sections, the different material properties including a change in yield and elongation properties and being adapted to facilitate deformation and shaping of the intermediate tube section upon the intermediate tube section receiving stress sufficient to deform the intermediate tube section.

5. The energy management tube defined in claim 4, wherein the different material properties include increased elongation and lower yield properties adapted to support predictable and desired telescoping roll of the annealed one tube section during a longitudinal impact.

6. The energy management tube defined in claim 5, wherein the different material properties include increased elongation and lower yield properties adapted to support mechanically forming the one tube section, including changing a cross section of the one tube section to be different in size.

7. The energy management tube defined in claim 5, wherein the different material properties include increased elongation and lower yield properties adapted to support up-setting the intermediate tube section to a shape promoting rolling of material during a longitudinal impact.

8. An energy management tube adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally comprising:
a first tube section having a first resistance to deformation; 
a second tube section having a second resistance to deformation, the second resistance to deformation being greater than the first resistance to deformation; and 
an intermediate tube section connecting the first tube section to the second tube section; 
whereby, upon undergoing a longitudinal impact, the intermediate tube section and the first tube section roll predictably and sooner than the second tube section upon the intermediate tube section receiving forces from the longitudinal impact; 
wherein the second tube section is heat-treated, thereby making the second resistance to deformation greater than the first resistance to deformation.

9. The energy management tube defined in claim 8, wherein the intermediate tube section is heat treated.

10. The energy management tube defined in claim 9, wherein the second tube section and the intermediate tube section are annealed.