Abstract:
A tube comprising an outer tube section with a stepped outer surface and an inner tube section, with the inner tube section being located within the outer tube section. The tube also comprises a spanning section connecting an end of the outer tube section to an end of the inner tube section. The outer tube section is longer than the inner tube section, whereby, upon undergoing a longitudinal impact, the outer tube section crushes predictably and sooner than the inner tube section upon the energy management tube receiving forces from the longitudinal impact, to thereby create a first energy absorption level during crushing of the outer tube section alone and a second energy absorption level during crushing of the outer tube section and the inner tube section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/607,677 entitled PLASTIC ENERGY MANAGEMENT BEAM, which was filed Sep. 7, 2004, the entire contents of which are hereby incorporated herein by reference. This application also claims the benefit of U.S. Provisional Application No. 60/751,522 entitled ENERGY MANAGEMENT SYSTEM, which was filed Dec. 19, 2005, and U.S. Provisional Application No. 60/793,069 entitled ENERGY MANAGEMENT SYSTEM, which was filed Apr. 19, 2006, the entire contents of both of which are hereby incorporated herein by reference.  
         [0002]     This application is a continuation-in-part of U.S. application Ser. No. 11/220,881, filed Sep. 7, 2005 and entitled PLASTIC ENERGY MANAGEMENT BEAM, which is a continuation-in-part of U.S. application Ser. No. 10/997,332, filed Nov. 24, 2004 and entitled TUBULAR ENERGY MANAGEMENT SYSTEM FOR ABSORBING IMPACT ENERGY, which is a continuation of U.S. application Ser. No. 10/648,757, filed Aug. 26, 2003 and entitled TUBULAR ENERGY MANAGEMENT SYSTEM FOR ABSORBING IMPACT ENERGY, the entire contents of all of which are incorporated herein by reference. U.S. application Ser. No. 11/220,881, filed Sep. 7, 2005 and entitled PLASTIC ENERGY MANAGEMENT BEAM is also a continuation-of-part of U.S. application Ser. No. 10/808,127, entitled ENERGY MANAGEMENT BEAM, which was filed on Aug. 26, 2003, the entire contents of which are hereby incorporated herein by reference. Finally, U.S. application Ser. No. 11/220,881, filed Sep. 7, 2005 and entitled PLASTIC ENERGY MANAGEMENT BEAM is also a continuation-of-part of PCT application No. PCT/US03/39803 entitled BUMPER SYSTEM INCORPORATING THERMOFORMED ENERGY ABSORBER, which was filed on Dec. 15, 2003, and which claimed priority to U.S. Application Ser. No. 60/484,712, the entire contents of both of which are incorporated herein by reference.  
     
    
     BACKGROUND  
       [0003]     The present invention relates to energy-management systems configured to absorb significant impact energy in a consistent and predictable manner during an impact stroke, including energy absorbers made of polymeric materials.  
         [0004]     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.  
         [0005]     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-versus-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.  
         [0006]     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.  
         [0007]     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-versus-deflection curves, energy absorption curves, and crush failure points.  
         [0008]     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.  
         [0009]     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.  
         [0010]     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, and also in vehicle frames (longitudinal and cross car), and other applications, as well as in non-vehicle applications. Notably, it is important to control energy absorption even in components made of polymeric materials. For example, injection molded and thermoformed energy absorbers are often used in vehicle bumper systems, such as by placing the polymeric energy absorber on a face of a tubular metal reinforcement beam. It is also important to control initial energy absorption, especially as bumpers are made to improve pedestrian safety during impact by a vehicle.  
         [0011]     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 INVENTION  
       [0012]     An aspect of the present invention is to provide an energy management tube adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally. The energy management tube comprises an outer first tube section and an inner second tube section, with the inner second tube section being at least partially located within the outer first tube section, and with the outer first tube section having a stepped outer surface. The energy management tube also comprises at least one spanning section connecting a first outer end of the outer first tube section to a first inner end of the inner second tube section. The outer first tube section is longer than the inner second tube section, whereby, upon undergoing a longitudinal impact, the outer first tube section crushes predictably and sooner than the inner second tube section upon the energy management tube receiving forces from the longitudinal impact, to thereby create a first energy absorption level during crushing of the outer first tube section alone and a second energy absorption level during crushing of the outer first tube section and the inner second tube section.  
         [0013]     Another aspect of the present invention is to provide a method of making an energy management tube adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally. The method comprises forming an outer first tube section and an inner second tube section, with the inner second tube section being at least partially located within the outer first tube section, with the outer first tube section being longer than the inner second tube section, and with the outer first tube section having a stepped outer surface. The method also comprises connecting a first outer end of the outer first tube section to a first inner end of the inner second tube section with at least one spanning section, crushing the outer first tube section predictably and sooner than the inner second tube section upon the energy management tube receiving forces from a longitudinal impact, creating a first energy absorption level during crushing of the outer first tube section alone, and creating a second energy absorption level during crushing of the outer first tube section and the inner second tube section.  
         [0014]     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  
       [0015]      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;  
         [0016]      FIG. 2  is a view similar to  FIG. 1 , but with the crush tower collapsed a first (relatively short) distance; and  
         [0017]      FIG. 3  is a view similar to  FIG. 2 , but with the crush tower collapsed a second (longer) distance.  
         [0018]      FIG. 4  is a side view of an energy management tube embodying the present invention;  
         [0019]      FIG. 5  is a perspective view of additional cross-sectional shapes that the energy management tube can take on;  
         [0020]      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;  
         [0021]      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;  
         [0022]      FIG. 12  is an enlarged view of the circled area XII in  FIG. 10 ;  
         [0023]      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;  
         [0024]      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;  
         [0025]      FIG. 16  is an enlarged view of the circled area XVI in  FIG. 15 ;  
         [0026]      FIG. 17  is a graph showing a load-versus-deflection curve for a longitudinal impact of the tube shown in  FIG. 10 ;  
         [0027]      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;  
         [0028]      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;  
         [0029]      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;  
         [0030]      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&#39;s floor-pan, and the other being a cross car beam used above the vehicle&#39;s floor pan and used to support vehicle seats;  
         [0031]      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;  
         [0032]      FIG. 22  is a perspective view of a cross car beam used to support an instrument panel; and  
         [0033]      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 .  
         [0034]      FIG. 25A  is a front perspective view of a plastic energy management tube (EMT) of the present invention.  
         [0035]      FIG. 25B  is a cross-sectional view of the plastic EMT of the present invention in an initial position.  
         [0036]      FIG. 25C  is a cross-sectional view of the plastic EMT of the present invention after impact.  
         [0037]      FIG. 25D  is a graph showing a load v. displacement chart for the plastic EMT of the present invention.  
         [0038]      FIG. 26A  is a cross-sectional view of a second embodiment of the plastic EMT of the present invention.  
         [0039]      FIG. 26B  is a graph showing a load v. displacement chart for the second embodiment of the plastic EMT of the present invention.  
         [0040]      FIG. 27A  is a cross-sectional view of a third embodiment of a plastic EMT of the present invention in an initial position.  
         [0041]      FIG. 27B  is a cross-sectional view of the third embodiment of a plastic EMT of the present invention in a first crush position.  
         [0042]      FIG. 27C  is a cross-sectional view of the third embodiment of a plastic EMT of the present invention in second crush position.  
         [0043]      FIG. 27D  is a graph showing a load v. displacement chart for the third embodiment of the plastic EMT of the present invention.  
         [0044]      FIG. 27E  is a front view of a modification to the plastic EMT of the present invention.  
         [0045]      FIG. 27F  is a graph showing a load v. displacement chard for the modified plastic EMT of the present invention.  
         [0046]      FIG. 28A  illustrates a first use of the plastic EMT of the present invention.  
         [0047]      FIG. 28B  illustrates a second use of the plastic EMT of the present invention.  
         [0048]      FIG. 28C  illustrates a third use of the plastic EMT of the present invention.  
         [0049]      FIG. 28D  illustrates a fourth use of the plastic EMT of the present invention.  
         [0050]      FIG. 29  is a perspective view of a first embodiment of a bumper beam employing the plastic EMT of the present invention.  
         [0051]      FIG. 30A  is a perspective view of a second embodiment of a bumper beam employing the plastic EMT of the present invention.  
         [0052]      FIG. 30B  is a perspective cut-away view of the second embodiment of the bumper beam employing the plastic EMT of the present invention.  
         [0053]      FIG. 30C  is a cross-sectional view of the second embodiment of the bumper beam employing the plastic EMT of the present invention.  
         [0054]      FIG. 31A  is a perspective view of a headliner employing the plastic EMT of the present invention.  
         [0055]      FIG. 31B  is a cross-sectional view of the headliner employing the plastic EMT of the present invention taken along the line A-A of  FIG. 31A .  
         [0056]      FIG. 32  is a representation of an elevator shaft employing the plastic EMT of the present invention.  
         [0057]      FIG. 33  is a perspective view of a further energy management tube of the present invention.  
         [0058]      FIG. 34A  is cross-sectional view of the further energy management tube of the present invention.  
         [0059]      FIG. 34B  is cross-sectional view of the further energy management tube of the present invention at a first stage of crushing.  
         [0060]      FIG. 34C  is cross-sectional view of the further energy management tube of the present invention at a second stage of crushing.  
         [0061]      FIG. 34D  is cross-sectional view of the further energy management tube of the present invention at a third stage of crushing.  
         [0062]      FIG. 35  is a graph showing a load v. time (or displacement) chart for the further energy management tube of the present invention for the stages of crushing illustrated in  FIGS. 34B-34D .  
         [0063]      FIG. 36  is a perspective view of a second embodiment of the further energy management tube of the present invention.  
         [0064]      FIG. 37  illustrates a first use of the further energy management tube of the present invention.  
         [0065]      FIG. 38  illustrates a second use of the further energy management tube of the present invention.  
         [0066]      FIG. 39  illustrates a third use of the further energy management tube of the present invention.  
         [0067]      FIG. 40  illustrates a fourth use of the further energy management tube of the present invention.  
         [0068]      FIG. 41  is a perspective view of a first embodiment of a bumper beam employing the further energy management tube of the present invention.  
         [0069]      FIG. 42  is a perspective view of a second embodiment of a bumper beam employing the further energy management tube of the present invention.  
         [0070]      FIG. 43  is a perspective cut-away view of the second embodiment of the bumper beam employing the further energy management tube of the present invention.  
         [0071]      FIG. 44  is a cross-sectional view of the second embodiment of the bumper beam employing the further energy management tube of the present invention.  
         [0072]      FIG. 45  is a perspective view of a headliner employing the further energy management tube of the present invention.  
         [0073]      FIG. 46  is a cross-sectional view of the headliner employing the further energy management tube of the present invention taken along the line B-B of  FIG. 45 .  
         [0074]      FIG. 47  is a representation of an elevator shaft employing the further energy management tube of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0075]     For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as orientated in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.  
         [0076]     It is noted that the present invention can include utilizing the energy management technology (EMT) in thermoplastic and thermoset polymeric materials, with and without filler and reinforcement materials such as talc, glass fibers, and the like.  
         [0077]     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 .  
         [0078]     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.  
         [0079]     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.  
         [0080]     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.  
         [0081]     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.  
         [0082]     The internal cavity  25  within the crush tower  13  is open and stays open during impact.  
         [0083]     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.  
         [0084]     In operation, the crush towers  13  are manufactured by making a tube, such as by rollforming, then rollforming 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.  
         [0085]     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.  
         [0086]     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  
       [0087]     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”, etc. This is done to reduce redundant discussion.  
         [0088]     A modified energy management tube  13 A ( FIG. 4 ) is provided that is adapted to reliably and predictably absorb substantial impact energy when impacted longitudinally. The energy management tube  13 A includes a first tube section  14 A, a second tube section  15 A that is aligned with the first tube section  14 A, and an intermediate tube section  16 A with first and second end portions  30  and  31 , respectively. The end portions  30  and  31  integrally connect the first and second tube sections  14 A and  15 A, respectively. The first tube section  14 A is dimensionally larger in size than the second tube section  15 A, and has a similar cylindrical cross-sectional shape. However, it is noted that the first and second tube sections  14 A and  15 A can be different shapes including rectangular, square, oval, round, or other geometric shapes. (See  FIG. 5 .) Further, it is contemplated that the tube sections  14 A and  15 A may have different cross-sectional shapes along their lengths, especially at locations spaced away from the intermediate tube section  16 A where the tube sections  14 A and  15 A must be adapted to connect to different structures, such as vehicle frame components and the like. (See  FIGS. 19-22 .) The intermediate tube section  16 A has a shape transitioning from the first tube section  14 A to the second tube section  15 A, and further the first and second end portions  30  and  31  are dissimilar in shape as noted below ( FIGS. 9-12 ).  
         [0089]     The present energy management tube  13 A ( FIG. 4 ) is disclosed as being made from a sheet of annealable steel material with each of the tube sections  14 A,  15 A, and  16 A 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  15 A and  16 A annealed, and then formed to a shape  61  ( FIG. 7 ) where the second tube section  15 A is compressed to a reduced diameter, with the intermediate section  16 A temporarily taking on a temporary frustoconical shape. It has been determined that it is beneficial to fixture and longitudinally deform the energy management tube  13 A to a pre-set condition ( FIG. 8 ), so that the intermediate section  16 A 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).  
         [0090]     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&#39;s attention is directed to ASTM A1008/A and A1008M-Ola, and also to ASTM A1011A and A1011M-01 a 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  13 A and  13 B). 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.  
         [0091]     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&#39;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.  
         [0092]     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  16 A 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 .)  
         [0093]     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.  
         [0094]     As illustrated in  FIGS. 9-12 , the first tube section  14 A is larger in size than the second tube section  15 A. The first tube section  14 A includes an outer surface defining a tubular boundary  32 . The tubular boundary  32  matches a cross-sectional shape of the first tube section  14 A 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  14 A 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  14 A.  
         [0095]     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  15 A and is less supportive of the columnar strength of the second tube section  15 A. In fact, second end portion  31  is configured to initiate a telescoping rolling of the second tube section  15 A during impact as the first tube section  14 A maintains its columnar strength. The fact that the tube sections  15 A and  16 A are annealed, and the first tube section  14 A 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  14 A and  15 A 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  16 A 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 .)  
         [0096]     A second energy management tube  13 B ( FIGS. 14-16 ) includes a first tube section  14 B, a second tube section  15 B, and an intermediate tube section  16 B interconnecting the tube sections  14 B and  15 B. However, tube  13 B differs from tube  13 A. In tube  13 B, the end portion  30 B of the larger-diameter first tube section  14 B includes deformed material  34 B defining a larger radius. Further, the deformed material  34 B is not flared outwardly, but instead remains generally within a boundary defined by an outer surface of the first tube section  14 B. Concurrently, the end portion  31 B of the second tube section  15 B includes deformed material  35 B defining a smaller radius. The deformed material  35 B is flared inwardly inside of a tubular boundary  32 B, such as at a minimum angle of about 12°.  
         [0097]      FIG. 13  shows a partial stroke impact where a section of material  36  from the first tube section  14 B of tube  13 B has rolled. (In tube  13 A, the second smaller tube section  15 A is the one that rolls during an impact as it rolls in a similar manner.)  
         [0098]      FIG. 17  illustrates a typical load-versus-deflection curve for tubes  13 A and  14 A. 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 (D 1 ) times the full impact stroke (D 2 ). 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.  
         [0099]      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.  
         [0100]      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.  
         [0101]     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 ( 16 C) (see  FIG. 11 ) configured to initiate rolling material of one of the tubes ( 14 C or  15 C) during telescoping impact. The energy management tube  40  is located in a similar forward location on the vehicle frame. Tube  40  is circular in cross section, and includes a single intermediate tube section ( 16 D) for initiating rolling of material during telescoping impact. The tube  40  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  40  could be used, for example, to support a vehicle bumper.  
         [0102]     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.  
         [0103]      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  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  13 A (or  13 B) can be annealed to facilitate reforming to better match the geometry of the frame rails.  
         [0104]     The other energy management system of  FIG. 20  includes a pair of tube sections  55  placed as cross car beams but used above the vehicle&#39;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 .  
         [0105]      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  40  and does not need to be discussed in detail.  
         [0106]      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 a 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 .  
         [0107]      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.  
         [0108]     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. 22 and 23  is 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 an alternative way to tune performance without the addition of significant cost and without the added penalty of weight.  
       FURTHER MODIFICATION  
       [0109]     The reference numeral  113  ( FIG. 25A ) generally designates another embodiment of the present invention, having a plastic energy management tube. The plastic energy management tube  113  is similar to the previously described energy management tube  13 A. The plastic energy management tube  113  includes a first tube section  114 , a second tube section  115  that is aligned with the first tube section  114 , and an intermediate tube section  116  connected to the first tube section  114  and the second tube section  115 . The first tube section  114  is dimensionally larger in size than the second tube section  115 , and preferably has a similar cross-sectional shape. However, it is noted that the first and second tube sections  114  and  115  can be different shapes including hexagonal, octagonal, elliptical, race-track shaped, cylindrical, rectangular, square, oval, round, or other geometric shapes. Furthermore, it is contemplated that the tube sections  114  and  115  may have different cross-sectional shapes along their lengths, especially at locations spaced away from the intermediate tube section  116  where the tube sections  114  and  115  must be adapted to connect to different structures, such as vehicle frame components and the like. The intermediate tube section  116  has a shape transitioning from the first tube section  114  to the second tube section  115 .  
         [0110]     The illustrated plastic energy management tube  113  is preferably made of a thermoplastics often used in parts for absorbing energy such as PC, PBT, PC/PBT, PC/ABS, and other combinations plastic with each of the tube sections  114 ,  115 , and  116  being integrally formed or molded together as a unit. The plastic energy management tube  113  is preferably made in an injection mold, although it is contemplated that the plastic energy management tube  113  can be made in other manners. The wall thickness can be varied as needed to satisfy functional design requirements. The plastic energy management tube  113  can also include a metal parts insert molded therein to build reinforcing strength of the plastic energy management tube  113  and/or to assist in assembling the plastic energy management tube  113  to other components.  
         [0111]     As illustrated in  FIGS. 25A-25C , the first tube section  114  is larger in size than the second tube section  115 . The intermediate tube section  116  includes a first end portion  130  connected to a top of the first tube section  114  and a second end portion  131  connected to a bottom of the second tube section  115 . The illustrated first end portion  130  has an inverted “L” shaped section and the second end portion  131  has a “U” or “J” shaped section and is connected to the first end portion  130 . As illustrated in  FIGS. 25B and 25C , the first end portion  130  preferably includes additional material  133  extending between the two legs of the “L” shaped section. During crushing of the plastic energy management tube  113 , the second tube section  115  begins telescoping rolling at the second end portion  131  of the intermediate tube section  116  to crush the plastic energy management tube  113  as illustrated in  FIG. 25C . The first tube section  114  and the first end portion  130  preferably remain stationary during crushing of the second tube section  115 . The additional material  133  helps to reinforce the first end portion  130 . Therefore, the second end portion  131  is configured to initiate a telescoping rolling of the second tube section  115  during impact as the first tube section  114  maintains its columnar strength. Clearances are provided for the flow of material as necessary as it rolls. Potentially, the tube sections  114  and  115  can be sized to provide support to each other during the rolling of material during an impact. The second end portion  131  (or the pre-set condition of the intermediate tube section  116 ) 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. The plastic energy management tube  113  uses the rolling of material to create a load versus deflection response that is void of peaks and valleys but instead can be designed to produce a flat response as illustrated in  FIG. 25D . A square wave response represents the most efficient absorption of energy. Upon loading, load increases until the column strength of the structure is reached and then rolling will initiate. Uniform rolling will happen at a level load until all energy is absorbed.  
         [0112]     The reference numeral  113   a  ( FIG. 26A ) generally designates another embodiment of the present invention, having a second embodiment for the plastic energy management tube. Since plastic energy management tube  113   a  is similar to the previously described plastic energy management tube  113 , similar parts appearing in  FIGS. 25A-25C  and  FIG. 26A , respectively, are represented by the same, corresponding reference number, except for the suffix “a” in the numerals of the latter. The second embodiment of the plastic energy management tube  113   a  includes a second tube section  115   a  having an inner wall  134  tapering from the second end portion  131   a  of the intermediate tube section  116   a . The tapering of the inner wall  134  provides a rising load as illustrated in the load versus deflection graph of  FIG. 26B .  
         [0113]     The reference numeral  113   b  ( FIG. 27A-27D ) generally designates another embodiment of the present invention, having a third embodiment for the plastic energy management tube.  
         [0114]     Since plastic energy management tube  113   b  is similar to the previously described plastic energy management tube  113 , similar parts appearing in  FIGS. 25A-25C  and  FIG. 27A-27D , respectively, are represented by the same, corresponding reference number, except for the suffix “b” in the numerals of the latter. The third embodiment of the plastic energy management tube  113   b  includes an inner energy management tube section  140 . The inner energy management tube  140  is substantially an inverted version of the first embodiment of the plastic energy management tube  113 , which is connected by a spanning portion  141  to an end of the second tube section  115   b  distal the second end portion  131   b  of the intermediate tube section  116   b . Therefore, the inner energy management tube  140  includes a first tube section  114   b ′, a second tube section  115   b ′ and an intermediate tube section  116 ′.  
         [0115]     As illustrated in  FIG. 27B , the third embodiment of the plastic energy management tube  113   b  crushes in the same manner as the first embodiment of the plastic energy management tube  113 . Therefore, the second tube section  115   b  begins telescoping rolling at the second end portion  131   b  of the intermediate tube section  116   b  to crush an outer portion of the plastic energy management tube  113   b  as illustrated in  FIG. 27B . The first tube section  114   b  and the first end portion  130   b  preferably remain stationary during crushing of the second tube section  115   b . The additional material  133   b  once again helps to reinforce the first end portion  130   b . Therefore, the second end portion  131   b  is configured to initiate a telescoping rolling of the second tube section  115   b  during impact as the first tube section  114   b  maintains its columnar strength. Clearances are provided for the flow of material as necessary as it rolls. Potentially, the tube sections  114   b  and  115   b  can be sized to provide support to each other during the rolling of material during an impact. The second end portion  131   b  (or the pre-set condition of the intermediate tube section  116   b ) 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.  
         [0116]     After the outer portion of the third embodiment of the plastic energy management tube  113   b  has been crushed as illustrated in  FIG. 27B , the inner energy management tube section  140  will crush along with a continuation of a crush of the outer portion of the third embodiment of the plastic energy management tube  113   b . Therefore, the first tube section  114   b ′ begins telescoping rolling at a first end portion  131   b ′ of the intermediate tube section  116   b ′ to crush the inner energy management tube section  140  as illustrated in  FIG. 27C . The second tube section  115   b ′ and a second end portion  130   b ′ preferably remain stationary during crushing of the second tube section  115   b . The additional material  133   b ′ once again helps to reinforce the second end portion  130   b ′. Therefore, the first end portion  131   b ′ is configured to initiate a telescoping rolling of the first tube section  115   b ′ during impact as the second tube section  115   b ′maintains its columnar strength. Clearances are provided for the flow of material as necessary as it rolls. Potentially, the tube sections  114   b ′ and  115   b ′ can be sized to provide support to each other during the rolling of material during an impact. The first end portion  131   b ′ (or the pre-set condition of the intermediate tube section  116   b ′) 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.  
         [0117]     The plastic energy management tube  113   b  uses the rolling of material to create a load versus deflection response that is void of peaks and valleys but instead can be designed to produce a flat response during the crush of the outer portion of the third embodiment of the energy management tube  113   b  as illustrated between points  145  and  150  in  FIG. 27D  and another higher flat response during the crush of both outer portion of the third embodiment of the energy management tube  113   b  and the inner energy management tube section  140  as illustrated between points  150  and  160  in  FIG. 27D .  
         [0118]     In the plastic energy management tubes  113 ,  113   a  and  113   b  described above, either the first tube section  114  or the second tube section  115  can be connected to a support structure such that the plastic energy management tubes  113 ,  113   a  and  113   b  can be reversible. Furthermore, the inner energy management tube section  140  of the third embodiment of the plastic energy management tube  113   b  can be positioned in a reverse orientation such that the second tube section  115   b ′ is connected to the spanning portion  141 . Furthermore, the plastic energy management tube  113 ,  113   a  or  113   b  could comprise several sections that get progressively smaller (see  FIG. 28C ). Moreover, any of the tube sections can include tapering walls as described above in the second embodiment of the plastic energy management tube  113   a . Furthermore, any of the plastic energy management tubes  113 ,  113   a  and  113   b  could include crush initiating grooves  177  as illustrated in  FIG. 27E , which will provide a sinus wave energy curve as illustrated in  FIG. 27F . Although the grooves  177  are shown as being on the second tube section  115 , the grooves  177  can be on any of the tube sections.  
         [0119]     Applications of plastic energy management tubes  113 ,  113   a  and  113   b  include stand alone crushable structures and/or crushable features molded into larger plastic molded parts without the need for tolling action and moving parts in the tooling for providing uncuts and blind surfaces in the molded parts. The size of the parts can be molded to any size desired and the combination of multiple plastic EMTs can be molded to work in either parallel, series or configured to encompass a large surface area. A single plastic EMT  113 ,  113   a  or  113   b  can be used as a knee bolster  200  in vehicles in front of the driver&#39;s knee  202  as illustrated in  FIG. 28A , as a crushable member in front of another structure such as a plastic EMT  113 ,  113   a  and  113   b  in front of a bumper system  210  and behind facia  212  as shown in  FIG. 27B , as a bumper bracket between a support frame  220  of a vehicle and facia  222  as shown in  FIG. 28C , as an inside component to A and B pillars of a vehicle (not shown), as a highway embankment to protect supports  240  for a bridge  242  as shown in  FIG. 27D  or in other manners. Furthermore, a grouping of plastic EMTs can be used across a face of a bumper  300  as an energy absorber as shown in  FIG. 29  or within a beam  400  (e.g., the beam disclosed in U.S. Pat. application Ser. No. 10/808,127 entitled ENERGY MANAGEMENT BEAM, the entire contents of which are herein incorporated herein by reference) as shown in  FIGS. 30A-30C , or used within a headliner of a vehicle for head protection as shown in  FIGS. 31A and 31B . Furthermore, the plastic energy management tube  113 ,  113   a  or  113   b  can be used in a bottom of an elevator shaft  500  to absorb energy of a dropping elevator  502  as shown in  FIG. 32 . Basically, anywhere that energy absorption is needed either as a stand alone structure or for larger areas where an area is required to provide energy absorption, the plastic EMT technology can be used.  
         [0120]     The advantages of using plastic to fabricate the part include flexibility to mold complicated shapes and mold in complex features that can be used to tune the performance of the invention. The plastic EMT does not need a larger tube having an outwardly flared larger diameter section that promotes telescoping of the smaller diameter section into the larger diameter section due to the ability to change thickness in the molding process. The plastic molding process is extremely flexible. Simple single or multiple EMT structure parts are easily molded in simple in/out dies. More complex structures that include internal stiffening ribs and vanes may require a die that incorporates action. The flexibility of molding plastic allows for the specification of material thickness where it is needed. Changes in thickness can be used to provide column strength and desired rolling loads. The ability to change thickness of the plastic and the flexibility provided by the molding process illustrate the advantage associated with the use of plastic. EMTs can also be molded within and nested within other EMTs to create additional load tuning capability (see  FIG. 28B ).  
       ADDITIONAL EMBODIMENTS  
       [0121]     The reference numeral  1010  ( FIGS. 33 and 34 A) generally designates an embodiment of the present invention, having an energy management tube. The energy management tube  1010  includes an outside tube  1012  and an inside tube  1014 . The outside tube  1012  has a generally hexagonal cross section and includes a bottom first tube section  1016 , a middle second tube section  1018  and a top third tube section  1020 . The first tube section  1016  is dimensionally larger in size than the second tube section  1018 , and preferably has a similar cross-sectional shape. Likewise, the second tube section  1018  is dimensionally larger in size than the third tube section  1020 , and preferably has a similar cross-sectional shape. However, while the outside tube  1012  is illustrated as having a hexagonal cross-sectional shape, it is noted that the first tube section  1016 , the second tube section  1018  and the third tube section  1020  can be different shapes including octagonal, elliptical, race-track shaped, cylindrical, rectangular, square, oval, round, or other geometric shapes. Furthermore, it is contemplated that the tube sections may have different cross-sectional shapes along their lengths, especially at locations where the tube sections must be adapted to connect to different structures, such as vehicle frame components and the like. Moreover, the wall thickness can be varied as needed to satisfy functional design requirements. The energy management tube  1010  can be formed of any material (e.g., metal or plastic) and can be made by any method (e.g., vacuum forming). The energy management tube  1010  can also include a metal parts insert molded therein to build reinforcing strength of the energy management tube  1010  and/or to assist in assembling the energy management tube  1010  to other components. In the illustrated embodiment, the energy management tube is connected to a plate  1022  at the first tube section  1016 . The plate  1022  can be welded to portions of a vehicle and/or can be connected to portions of the vehicle by inserting screws into openings  1024  in the plate  1022 .  
         [0122]     As illustrated in  FIGS. 33 and 34 A, the energy management tube  1010  comprises the first tube section  1016  including a first end portion  1026  connected to a top of the plate  1022  and a second end portion  1028  connected to the second tube section  1018  by a slanted first step  1030 . The first tube section  1016  tapers slightly inwardly from the first end portion  1026  to the second end portion  1028 . The second tube section  1018  includes a first end portion  1032  connected to the slanted first step  1030  and a second end portion  1034  connected to the third tube section  1020  by a slanted second step  1036 . The second tube section  1018  tapers slightly inwardly from the first end portion  1032  to the second end portion  1034 . The third tube section  1020  includes a first end portion  1038  connected to the slanted second step  1036  and a second end portion  1040  connected to an end hexagonal plate  1042 . The third tube section  1020  tapers slightly inwardly from the first end portion  1038  to the second end portion  1040 . The end hexagonal plate  1042  includes a centrally located opening  1044 , with the inside tube  1014  connected to the hexagonal plate  1042  at the opening  1044 . In the illustrated example, the inside tube  1014  includes a first tapered portion  1050 , a second tapered portion  1052  and a third tapered portion  1054 .  
         [0123]     During crushing of the energy management tube  1010 , the third tube section  1020  begins to crush in a corrugated manner as illustrated in  FIG. 34B . Thereafter, the third tube section  1020  will continue to crush and the second tube section  1018  will crush in a corrugated manner. Finally, the inside tube  1014  will abut against a face of the member that the plate  1022  is connected to and will begin to crush along with the first tube section  1016 .  FIG. 35  shows a load v. time (or displacement) chart for the energy management tube of the present invention for the stages of crushing illustrated in  FIGS. 34B-34D .  
         [0124]     Applications of energy management tubes include stand alone crushable structures and/or crushable features incorporated into larger parts. The size of the parts can be formed to any size desired and the combination of multiple energy management tubes can be formed to work in either parallel, series or configured to encompass a large surface area. A single energy management tube  1010  can be used as a knee bolster  1200  in vehicles in front of the driver&#39;s knee  1202  ( FIG. 37 ), as a crushable member in front of another structure such as an energy management tube  1010  in front of a beam  1209  of a bumper system  1210  and behind facia  1212  ( FIG. 38 ), as a bumper bracket between a support frame  1220  of a vehicle and a beam  1209  of a bumper system  1210 , as an inside component to A and B pillars of a vehicle, and as a highway embankment to protect supports  1240  for a bridge  1242  ( FIG. 40 ) or in other manners. Furthermore, a grouping of energy management tubes can be used across a face of a bumper  1300  (see  FIG. 41 ) as an energy absorber or within a beam  1400  (see  FIGS. 42-44 ) (e.g., the beam disclosed in U.S. Pat. application Ser. No. 10/808,127 entitled ENERGY MANAGEMENT BEAM, the entire contents of which are herein incorporated herein by reference), or used within a headliner of a vehicle for head protection as shown in  FIGS. 45 and 46 . Furthermore, the energy management tube can be used in a bottom of an elevator shaft  1500  to absorb energy of a dropping elevator  1502  as illustrated in  FIG. 47 . Basically, anywhere that energy absorption is needed either as a stand alone structure or for larger areas where an area is required to provide energy absorption, the energy management tube technology can be used. Furthermore, more complex structures that include internal stiffening ribs and vanes may require a die that incorporates action. Changes in thickness can be used to provide column strength and desired rolling loads. Energy management tubes can also be molded or formed within and nested within other energy management tubes to create additional load tuning capability.  
         [0125]     The reference numeral  1010   a  ( FIG. 36 ) generally designates another embodiment of the present invention, having a second embodiment for the energy management tube. Since energy management tube  1010   a  is similar to the previously described energy management tube  1010 , similar parts appearing in  FIGS. 33-34D  and  FIG. 36 , respectively, are represented by the same, corresponding reference number, except for the suffix “a” in the numerals of the latter. The energy management tube  1010   a  is identical to the previously described energy management tube  1010 , except that the second embodiment of the energy management tube includes a plurality of fins  1100  on each side of the polygon of the first tube section  1016   a . The fins  1100  assist in ensuring that the first tube section  1016   a  of the energy management tube  1010   a  crush after the second tube section  1018   a  and the third tube section  1020   a . Furthermore, the fins  1100  add extra crush resistance. While three fins  1100  are illustrated as being located on each side of the polygon of the first tube section  1016   a , it is contemplated that any number of fins  1100  (including only one) could be used on the first tube section  1016   a  or each side of the polygon of the first tube section  1016   a . Furthermore, it is contemplated that the second tube section  1018   a  and/or the third tube section  1020   a  could include fins  1100 , either along with the fins on the first tube section  1016   a  or as an alternative thereto.  
         [0126]     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.