Abstract:
A crush tube assembly for absorbing impact energy is provided. A first tube substantially free from convolutions is disposed about a second tube substantially free from convolutions. A third tube having convolutions is also disposed within the first tube, and may be interposed between the first and second tubes. The convolutions support the axial integrity, and minimize lateral bucking of the first and second tubes during the absorption of impact energy. Additional alternating layers of smooth and convoluted tubes may be alternatively disposed within the assembly to provide further strength and control for absorbing energy. A method for absorbing impact energy is also provided. The method includes the steps of providing a first tube substantially free from convolutions, disposing within said first tube a second tube substantially free from convolutions, interposing between said first and second tubes a third tube having convolutions; and impacting said first, second, and third tubes.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to an impact energy absorption system, and in particular to a crushable tubular assembly for efficient and controllable energy absorption.  
           [0003]    2. Background of the Invention  
           [0004]    In current vehicle structures, and particularly in front-end structures, it has become increasingly difficult to obtain package space for components that absorb impact energy created during a vehicle crash. Conventional designs for absorbing high-energy impacts, such as that described in U.S. Pat. No. 3,831,997 to Myers, typically include tubular structures that are made from high strength materials like various high strength steels. These tubular structures may be designed as vehicle rails, or may be separately positioned in a fore/aft direction of the vehicle to absorb the energy of a fore/aft collision. However, such designs have a tendency to buckle laterally if the load is offset, that is, if the load is not concentric with the tube.  
           [0005]    Moreover, because of the limited package spaces available, with limited frame selection allowed, improving the axial strength of such structures tends to increase the degree of lateral instability of the tubes.  
           [0006]    Other conventional designs include tubular assemblies that have structures for initiating deformations in the assembly, such as described in U.S. Pat. No. 5,914,163 to Browne. These features include slits or other structures to initiate longitudinal splitting, tearing, or peeling of the tubular assembly. While providing such structures may assist in controlling the energy absorbed in an impact, the overall axial strength of such tubular structures may be compromised.  
           [0007]    Still other systems for absorbing frontal impact energy include entire redesigns of an automotive vehicle body structure, such as, for example, the vehicle body structure described in U.S. Pat. No. 6,312,038 to Kawamura, et al. Such designs may include extensions of the vehicle body/frame in the fore/aft direction in order to accommodate one or more energy absorbing members. Such redesigns, however, are expensive to develop and are not compatible with automobiles in present production.  
           [0008]    In particular, presently produced automobiles may not have the necessary package space available for housing an increased number of absorbing members, or tubes.  
           [0009]    There is thus a need for an impact energy absorption system that will minimize or eliminate one or more of the above-mentioned deficiencies.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides an improved impact energy absorption system, and a method for absorbing impact energy.  
           [0011]    An impact energy absorption system in accordance with the present invention comprises an assembly of crush tubes. The crush tube assembly includes a first tube disposed about a second tube. A third tube having convolutions is also disposed within the first tube, and may be interposed between the first and second tubes. The third tube may alternatively be disposed within the second tube. The convolutions of the third tube support the axial integrity, and minimize lateral bucking of the first and second tubes during the absorption of impact energy. Additional alternating layers of smooth and convoluted tubes may be alternatively disposed within the assembly to provide further strength and control for absorbing energy.  
           [0012]    A method for absorbing impact energy is also provided. The method includes the steps of providing a first tube substantially free from convolutions, disposing within said first tube a second tube substantially free from convolutions, interposing between said first and second tubes a third tube having convolutions; and impacting said first, second, and third tubes.  
           [0013]    An impact energy absorption system in accordance with the present invention has several advantages as compared to conventional systems. The inventive device provides the axial strength of a conventional smooth, or unconvoluted tube and the energy absorption control of a convoluted tube. The inventive device, therefore, can absorb high-energy impacts that may be offset, while reducing the tendency to buckle laterally. Additionally, the inventive device maximizes the use of available package space by disposing each crush tube about one another. Accordingly, the present invention is able to absorb broad ranges of crush energy and maintain its lateral stability during a crash.  
           [0014]    These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating the features of this invention by way of example. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    [0015]FIG. 1 is an exploded cross-sectional perspective view of a crush tube assembly in accordance with one embodiment of the present invention.  
         [0016]    [0016]FIG. 2 is a side view of the components of the crush tube assembly of FIG. 1.  
         [0017]    [0017]FIG. 3 is a cross-sectional view of the crush tube assembly of FIG. 1.  
         [0018]    [0018]FIG. 4 is a magnified view of section  4  of the crush tube assembly of FIG. 3.  
         [0019]    [0019]FIG. 5 is a side view of alternative convoluted tubes for the crush tube assembly of FIG. 1.  
         [0020]    [0020]FIG. 6 is an exploded cross-sectional perspective view of a crush tube assembly in accordance with another embodiment of the present invention.  
         [0021]    [0021]FIG. 7 is a perspective view of the components of the crush tube assembly of FIG. 6.  
         [0022]    [0022]FIG. 8 is a partial cross-sectional side view of the crush tube assembly shown in FIG. 1.  
         [0023]    [0023]FIG. 9 is a magnified view of section  9  of the crush tube assembly shown in FIG. 8.  
         [0024]    [0024]FIG. 10 is a deformation profile of a conventional smooth crush tube.  
         [0025]    [0025]FIG. 11 is a deformation profile of a crush tube assembly in accordance with one embodiment of the present invention.  
         [0026]    [0026]FIG. 12 is a partial cross-sectional perspective view of a deformed crush tube assembly in accordance with the embodiment of the present invention shown in FIG. 1.  
         [0027]    [0027]FIG. 13 is a perspective view of each tube, contained within the deformed crush tube assembly shown in FIG. 12. 
     
    
     DETAILED DESCRIPTION  
       [0028]    Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views, FIGS. 1, 2, and  3  illustrate a crush tube assembly  10  in accordance with one embodiment of the present invention. Assembly  10  is provided to absorb impact energy sustained during an automobile collision.  
         [0029]    Assembly  10  is configured for use in a front-end structure of a vehicle, such as vehicle frame rails. It should be understood, however, that assembly  10  might find use in a variety of locations of and components for a vehicle structure. Assembly  10  includes a plurality of alternating smooth and convoluted crush tubes of a general cylindrical shape. It will be appreciated by those skilled in the art that other shapes may also be suitable. As discussed in greater detail below, assembly  10  may include an outer tube  12 , an inner tube  14 , a core tube  16 , a first convoluted tube  18 , a second convoluted tube  20 , and a seal cap  22 .  
         [0030]    Tube  12  provides a rigid outer support structure for assembly  10 . Tube  12  may be generally “flat” or “smooth,” which, as used herein, means substantially free from convolutions. Tube  12  may be constructed from various grades of mild steel, high strength steel or ultrahigh strength steel, such as dual phases steels or TRIP steels. It may further be constructed from composite materials such as Sheet Molded Composites (SMC) or Glass Reinforced Polyester Composites. It should be understood, however, that material composition and method of manufacture of tube  12 , as well as any other tube of this invention, might be varied without departing from the spirit of the present invention. Tube  12  may be disposed about a longitudinal axis  24 . Tube  12  may further have a neck, or turtleneck,  26  at one end. Neck  26  may be provided to initially receive the impact energy from a force directed along, or substantially along, axis  24 . Upon impact, neck  26  collapses, or otherwise axially directs the impact energy through assembly  10 . The remaining portion of tube  12  provides axial strength to assembly  10  for absorbing impact energy and provides a structure in which other tubes may be disposed.  
         [0031]    Tube  14  is disposed within tube  12 . Tube  14  may be disposed about a longitudinal axis which is common to axis  24  of tube  12 . In the embodiment shown in FIGS. 1, 2, and  3  tube  14  is concentrically disposed within tube  12 . However, it will be recognized by those skilled in the art that the longitudinal axes of tube  12  and tube  14  need not be concentric. As shown, tube  14  is generally smooth. Tube  14  is provided to reinforce the axial strength of assembly  10  for absorbing impact energy.  
         [0032]    Tube  14  may be constructed from the same materials as tube  12 . Tube  14  may be shorter than tube  12 . As shown in FIG. 4, tube  14  may further have a collar  28  extending radially outward at one end. Collar  28  provided to abut seal cap  22  and transmit an axial load to seal cap  22 .  
         [0033]    Tube  16  is disposed within tube  14 . Tube  16  may be disposed about a longitudinal axis which is common to axis  24  of tube  12 . In the embodiment illustrated in FIGS. 1, 2, and  3  tube  16  is concentric with tube  12  and tube  14 . Tube  16  may be constructed from the same materials as tube  12  and tube  14 . Tube  16  may be approximately same length as tube  12 . Tube  16  may have a generally smooth body. Tube  16  may further have an end segment  30  that has convolutions  31 . End  30  may be the approximate difference between the lengths of tube  12  and tube  14 , and extends axially distal from collar  28 . The convolutions  31 of end  30  may project radially outward to the inner periphery of seal cap  22 . Convolutions  31  may be formed similar to the convolutions of tube  18  and tube  20 , discussed below. Convolutions  31  are provided to allow tube  16  to axially deform to reduce the tendency to buckle laterally.  
         [0034]    Tube  18  is interposed between tube  12  and tube  14 . Tube  18  may be constructed from the same materials as tube  12 . Tube  18  may be disposed about a longitudinal axis. In the embodiment shown in FIGS. 1, 2, and  3 , tube  18  is concentric with tubes  12 ,  14 , and  16 . Tube  18  may be shorter than tube  12 , and substantially the same length as tube  14 . Tube  18  may have convolutions  32 , a smooth extended end  34 , and a collar  36 .  
         [0035]    Convolutions  32  are substantially disposed about the periphery of tube  18 . In the embodiment illustrated in FIGS. 1, 2, and  3 , convolutions  32  are entirely disposed about the body of tube  18 . As illustrated in FIGS. 1 and 2, convolutions  32  generally project radially outward from tube  18 . However, it will be appreciated by those skilled in the art that convolutions  32  may also project radially inward, or project both radially outward and inward from tube  18 . Convolutions  32  are provided to control the energy absorption from an impact to assembly  10 . Upon impact to assembly  10 , convolutions  32  compress axially and provide lateral stability to assembly  10  by minimizing, or preventing, buckling. Convolutions  32  may be shaped in sinusoidal waveform or gear tooth wave, however it will be appreciated by those skilled in the art that other shapes will be suitable. Convolutions  32  may be formed by molding, cutting, hydro-forming, or any other conventional industrial manufacturing method.  
         [0036]    As discussed in greater detail below and as specifically shown in FIGS. 8 and 9, convolutions  32  project outward to the inner periphery of tube  12 . Inward convolutions would similarly project to the outer periphery of tube  14 .  
         [0037]    Smooth end  34  extends from the convoluted body of tube  18  and is disposed within neck  26  of tube  12 . Smooth end  34  provide additional rigid support within neck  26 . Collar  36  projects radially outward from the other end of tube  18 . As shown in FIG. 4, Collar  36  abuts collar  28  for transmitting an axial load toward seal cap  22 .  
         [0038]    Tube  20  may be interposed between tube  14  and tube  16 . Tube  20  may be constructed from the same materials as tube  12 . Tube  20  may be disposed about a longitudinal axis. In the embodiment shown in FIGS. 1, 2, and  3 , tube  20  is concentric with tubes  12 ,  14 ,  16 , and  18 . Tube  20  may be shorter than tube  12 , and substantially the same length as tubes  14  and  16 . Tube  20  may have convolutions  38 , a smooth extended end  40 , and a collar  42 .  
         [0039]    Convolutions  38  are substantially disposed about the periphery of tube  20 . In the embodiment illustrated in FIGS. 1, 2, and  3 , convolutions  38  are entirely disposed about the body of tube  20 . As illustrated in FIG. 1 and  2 , convolutions  38  generally project radially inward from tube  20 . However, it will be appreciated by those skilled in the art that convolutions  38  may also project radially outward, or project both radially outward and inward from tube  20 . Convolutions  38  are provided to control the energy absorption from an impact to assembly  10 . Upon impact to assembly  10  convolutions  38  compress axially and provide lateral stability to assembly  10  by minimizing, or preventing, buckling. Convolutions  38  may be formed by the same methods as convolutions  32 . As discussed in greater detail below and specifically shown in FIGS. 8 and 9, convolutions  38  project inward to the outer periphery of tube  16 . Outward convolutions would similarly project to the inner periphery of tube  14 .  
         [0040]    Smooth end  40  extends from the convoluted body of tube  20  and is disposed within neck  26  of tube  12 . Smooth end  40  provides additional rigid support within neck  26 . Collar  42  projects radially inward from the other end of tube  20 . As shown in FIG. 4, Collar  42  abuts for transmitting an axial load toward seal cap  22 .  
         [0041]    Seal cap  22  is provided for additional axial support of tubes  14 ,  16 ,  18 , and  20 . Seal cap  22  is disposed within tube  12  and about convoluted end  30  of tube  16 . Seal cap  22  may have a collar  44  projecting radially outward. As-shown in FIG. 4, collar  44  is axially adjacent to and supports axial loads transmitted from collars  28 ,  36 , and  42 . Seal cap  22  may be made out of the same material as tube  12 .  
         [0042]    [0042]FIGS. 1 and 2 further illustrate the construction of crush tube assembly  10 . Smooth tube  12  is provided. Smooth tube  14  is disposed within smooth tube  12 , and smooth tube  16  is disposed within smooth tube  14 . Convoluted tube  18  is interposed between tube  12  and tube  14 . Convoluted tube  20  is interposed between tube  14  and tube  16 . Upon the disposition of tubes within tube  12 , seal cap  22  may be disposed within tube  12  and about end  30  of tube  16 . The assembly  10  may then be sealed at the neck end  20  and at the seal cap  22  end.  
         [0043]    While FIGS. 1, 2, and  3  depicts assembly  10  as including outer tube  12 , inner tube  14 , core tube  16 , first convoluted tube  18 , second convoluted tube  20 , and seal cap  22 , it will be appreciated by those skilled in the art that the inventive assembly may include greater or fewer convoluted tubes. For example, depending on the size of tube  12 , additional alternating layers of smooth and convoluted crush tubes may be alternatively disposed within assembly  10  to provide further strength and control for absorbing impact energy. Similarly, assembly  10  may include fewer tubes than depicted. For example, assembly  10  may include outer tube  12 -, inner tube  14  disposed within tube  12 , and core tube  16 , disposed within tube  14 , having convolutions  31  at end  30 . Alternatively, assembly  10  may include outer tube  12 , tube  14  disposed within tube  12 , and convoluted tube  18  interposed between tube  12  and tube  14 .  
         [0044]    [0044]FIG. 5 depicts alternative convoluted crush tubes  19 ,  21 , which can replace convoluted tubes  18 ,  20 , respectively, in assembly  10 . Convoluted crush tubes  19 ,  21  are substantially the same as convoluted tubes  18 ,  20 , respectively, except that the form of convolutions  32 ,  38  are replaced with screw formed convolutions  33 ,  39 , respectively. Convolutions  33  may be in clockwise screw form, while convolutions  39  may be in counter-clockwise screw form. It will be appreciated by those skilled in the art that the directions of such convolutions may be reversed. The interlacing screw form of convolutions  33  and convolutions  39  provides a strong support to each other and complement the torsional deformation in tube  19  and tube  21 , which in turn provides a substantial stability for the entire assembly  10 . Additionally, screw form convolutions  33 ,  39  may be more economic to manufacture than other shapes.  
         [0045]    [0045]FIGS. 6 and 7 illustrate an alternative crush tube assembly  48  according to the present invention. Crush tube assembly  48  is similar to assembly  10 , but is generally rectangular in cross-sectional shape. Assembly  48  includes a plurality of alternating smooth and convoluted crush tubes. Assembly  48  may include an outer tube  50 , an inner tube  52 , a core tube  54 , a first convoluted tube  56 , a second tube convoluted tube  58 , and a seal cap  60 . Tube  50  and tube  52  may be similar to tube  12  and tube  14 , respectively, as tube  50  and tube  52  may generally be smooth. Further, like tube  12 , tube  50  includes neck  62  at one of its ends. Tube  52  may have a collar  64  projecting outward from the end distal to neck  62 . Tube  54  may be similar to tube  16  as it may have an end  66  with convolutions  68 . Convoluted tube  56  may be interposed between tube  50  and tube  52 , and convoluted tube  58  may be interposed between tube  52  and tube  54 . Like tube  18 , tube  56  may have outward projecting convolutions  57 , and like tube  20 , tube  58  may have inward projecting convolutions  59 . Those skilled in the art, however, will similarly recognize that convolutions  57  and convolutions  59  may be outwardly projecting, inwardly projecting, or both outwardly and inwardly projecting from their respective tubes. Tube  56  may have a smooth extended end  70  disposed within neck  62  and an outwardly projecting collar  72  disposed about its other end. Similarly, tube  58  may have a smooth extended end  74  disposed within neck  62  and an inwardly projecting collar  76  disposed about its other end. The smooth ends  70 ,  74  and collars  72 ,  76  serve similar functions as smooth ends  34 ,  40  and collars  36 ,  42 , respectively. Depending on the size of tube SO, additional layers of alternating smooth and convoluted crush tubes may be alternatively disposed within assembly  48  to provide further strength and control for absorbing impact energy. Seal cap  60  is similar to seal cap  22  and has a collar  78  projecting from its end proximate to collars  64 ,  72 , and  76 . Seal cap  60  axially supports loads transmitted from tube  52 , tube  54 , tube  56 , and tube  58 .  
         [0046]    [0046]FIG. 8 illustrates a partial side sectional view of assembly  10  and depicts, from outer most to inner most, outer smooth tube  12 , convoluted tube  18 , smooth tube  14 , convoluted tube  20 , and smooth tube  16 . FIG. 9 depicts a magnified view of portion  9  in FIG. 8. FIG. 9 further shows the development of membrane forces during axial loading. During an impact, axial force  80  is loaded on assembly  10 . Axial force  80  causes a variety of compressive forces throughout assembly  10 . In particular, axial force  80  results in longitudinal compressive forces  82 ,  84 , and  86  on smooth tubes  12 ,  14 , and  16 , respectively and compressive forces  88  and  90  on convolutions  32 ,  38  respectively. Compression force  88  transfers to convolutions  32  of tube  18 , and results in compressive forces  92  along convolutions  32  and normal contact forces  96  on the smooth tubes  12  and  14 . Similarly, compression force  90  transfers to convolutions  38  of tube  20 , and results in compressive forces  94  along convolutions  38  and normal contact forces  96  on the smooth tubes  14  and  16 . Compressive forces  92  and  94  act to compress, or collapse, the convolutions of tubes  18  and  20 , respectively. As convolutions  32  and  38  are being compressed, the convolutions provide lateral forces  96  to support the smooth tubes of assembly  10 . For example, convolutions  32  support the inner periphery of tube  12  and the outer periphery of tube  14 , and convolutions  38  support the inner periphery of tube  14  and the outer periphery of tube  16 . Lateral forces  96  stabilize and reduce the buckling tendency of smooth tubes  12 ,  14 , and  16  during axial loading. Such stabilization improves the ability of assembly  10  to absorb axial loaded impact energy. The angle of convolutions  32  and convolutions  38  may be adjusted to vary the energy absorption and stabilization capacity of tubes  12 ,  14 , and  16 . The energy absorption and stabilization capacity are inversely related to each other. For example, as the angle of convolution is increased, that is, as the convoluted tube approaches a smooth tube, the energy absorbing capacity of the convoluted tube increases, but the amount of lateral forces  96  the convolution provides decreases. Those skilled in the art will recognize that the angle of convolution may be optimized based on the application of the invention.  
         [0047]    Computer simulated deformation profiles for a single smooth crush tube  98  and crush tube assembly  10 ″ are shown in FIGS. 10 and 11, respectively. FIG. 10 illustrates a section view of a conventional smooth tube  98  after a simulated axially loading of a high-speed impact at end  100 . After a high-speed impact at end  100 , energy is only absorbed by the relatively small area of deformation  102 . If the same space, material and weight of material are available, smooth tube  98  will result in less dissipated energy because, after impact, less material resulted in plastic (non-linear) deformation state as compared with the inventive assembly  10 ″. The structure of tube  98  may produce higher impact force and intrusion to the backup structure where occupants of the vehicle may be seated. Conversely, a reduction of the gauge of smooth tube  98 , so as to reduce the impact and intrusion to the backup structure, results in an increased tendency for tube  98  to buckle laterally.  
         [0048]    In contrast, FIG. 11 depicts crush tube assembly  10 ″ following a similar impact to crush tube assembly  10 . Assembly  10 ″ includes the same structure of assembly  10  and its features are identified by the same reference number with a prime″″ “to indicate that such features have sustained an impact. Neck area  26 ″ receives the axial load. The convolutions of tubes  18 ″ and  20 ″ compress and provide lateral support to the peripheries of smooth tubes  12 ″,  14 ″ and  16 ″. Accordingly, smooth tubes  12 ″,  14 ″, and  16 ″ did not buckle and instead absorbed the axial impact energy while supported laterally by the convolutions so as to minimize the tendency to buckle.  
         [0049]    [0049]FIGS. 12 and 13 illustrate perspective views of assembly  10 ″, and of each deformed tube. Neck area  26 ″ has absorbed significant impact energy, as it is shown to be significantly deformed in the axial direction. That is, neck area  26 ″ axially collapses, or telescopes, toward the seal cap end of assembly  10 ″. Convolutions of tubes  18 ″ and  20 ″ have compressed in the axial direction and provide lateral support to tubes  12 ″,  14 ″, and  16 ″. Additionally, convolutions  31 of end  30  of tube  16 ″ have also compressed axially to further prevent tube  16  from buckling. Smooth tubes  12 ″,  14 ″, and  16 ″ did not buckle and instead absorbed the axial load as indicated by deformation areas  104 ,  106 , and  108 , respectively.  
         [0050]    [0050]FIGS. 1, 11,  12 , and  13  further depict a method of absorbing crash energy. Smooth tube  12  is provided. Smooth tube  14  is disposed within tube  12 . Smooth tube  16  is disposed within tube  14 , and may include an end  30  with convolutions  31 . Convoluted tube  18  is interposed between tube  12  and tube  14 , and convoluted tube  20  is interposed between tube  14  and tube  16 . The assembly of tubes is then axially impacted. During impact, the convolutions of tube  18  and tube  20  laterally support smooth tubes  12 ,  14  and  16 .  
         [0051]    Through various combinations of smooth and convoluted tubes, and through various arrangements of convolutions, the present invention accommodates broad ranges of crush energy absorption. The present invention further maintains lateral stability and constant axial compression force during upon impact. Additionally, the invention efficiently employs package space through the use of nested, or telescoping tubes. While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be appreciated by those skilled in the art that various changes and modifications can be made in the invention without departing from the spirit and scope of the invention.