Abstract:
A hollow reinforced structural member has a bulkhead having a layer of thermally expanded resin disposed between opposed side walls. A sleeve is retained within the resin layer and is oriented perpendicular to the longitudinal axis of the reinforce structural member. The sleeve is an alignment with bolt holes in opposite sides of the reinforced structure such that a bolt can be inserted there through. A component can then be bolted to the reinforced structural member at the site of the reinforcement. The invention not only increases the strength of the part, but also reduces vibration and noise transmission.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on provisional application Ser. No. 60/053,118, filed Jul. 18, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     Particularly in automotive applications, box sections such as main frame rails are subjected to considerable stress forces where cross members are bolted to the rails. For example, when engine cradles are bolted to main frame rails they produce joints that are susceptible to durability cracking over time. In addition, the bolts which hold such components in place may loosen due to vibration at the joint. Moreover, conventional structures create a “noise path” which extends from the vehicle wheels and engine through the frame and into the passenger compartment. 
     As will be appreciated by those skilled in the art, in order to bolt a heavy component to the side of a rail section it is necessary to create a reinforced region or support structure at the site of attachment of the bolt. One approach which is used in the art is to provide a stamped bulkhead which supports a metal bushing. The bulkhead generally has three flange portions which are spot welded to the rail C-section. More specifically, the stamped bulkhead has a wall portion that extends from one wall of the rail section to the opposite wall or cap. Thus, the bulkhead forms a partition in the channel or cavity defined by the rail. In order to secure this wall portion in place, the bulkhead has three surfaces or flanges that are perpendicular to the bulkhead wall portion; that is, the bulkhead is in essence a shallow rectangular box that is open on one side. These three surfaces mate with the inner surfaces of the rail and are spot welded in place. 
     In order to utilize the bulkhead as a support for the cross structure which is attached thereto, it is designed to position a metal bushing that is spot welded to the bulkhead stamping. A bolt then passes through the bushing and secures the cross structure to the rail at the bulkhead-reinforced region. This conventional approach will be more fully illustrated hereinafter. 
     While the conventional bulkhead design does serve to reinforce the rail section at the attachment site of the cross member, it generally requires large gauge bushings and stampings and can actually increase unwanted vibration and noise. Moreover, the through-bolt, bushing, metal stamping and rail section essentially perform as discrete elements more than a unitary, integral reinforcement structure. This results not only in the above-mentioned increase in vibration and noise, but also fails to provide full reinforcement of the rail, resulting in metal fatigue at the joint and, in particular, at weld locations. 
     The present inventor has developed a number of approaches to the reinforcement of hollow metal parts such as: a reinforcing beam for a vehicle door which comprises an open channel-shaped metal member having a longitudinal cavity which is filled with a thermoset or thermoplastic resin-based material; a hollow torsion bar cut to length and charged with a resin-based material; a precast reinforcement insert for structural members which is formed of a plurality of pellets containing a thermoset resin with a blowing agent, the precast member being expanded and cured in place in the structural member; a composite door beam which has a resin-based core that occupies not more than one-third of the bore of a metal tube; a hollow laminate beam characterized by high stiffness-to-mass ratio and having an outer portion which is separated from an inner tube by a thin layer of structural foam; an I-beam reinforcement member which comprises a preformed structural insert having an external foam which is then inserted into a hollow structural member; and a metal w-shaped bracket which serves as a carrier for an expandable resin which is foamed in place in a hollow section. 
     None of these prior approaches, however, deal specifically with solving the problems associated with conventional reinforcing bulkheads in rail sections at cross member attachment sites. The present invention solves many of the problems inherent in the prior art. 
     It is an object of the present invention to provide a reinforced hollow metal structure which incorporates a bushing and a stamping in a bulkhead structure in a manner in which the components of the bulkhead work together as an integral unit with the reinforced structure. 
     It is a further object of the invention to provide a reinforced metal box section which provides greater strength to the section without significantly increasing vibration and noise transmission levels. 
     It is a further object of the present invention to provide a reinforced frame rail section at the attachment of a cross member such as an engine cradle in a manner in which stress forces are distributed over a region of the reinforced rail rather than at the discrete welds and in which noise and vibration are dampened. 
     These and other objects and advantages of the invention will be more fully appreciated in accordance with the detailed description of the preferred embodiments of the invention and the drawings. 
     SUMMARY OF THE INVENTION 
     In one aspect the present invention provides a reinforced structure. The reinforced structure includes a hollow structural member and a reinforcing member disposed therein. The reinforcing member has a pair of opposed walls. A layer of thermally expanded polymer is disposed between and is bonded to the opposed walls. This layer of polymer is also bonded directly to the structural member. A sleeve extends through the polymer parallel with and between the opposed walls. The polymer is bonded to the sleeve and the sleeve defines a passage through the polymer. The reinforced structure has holes that are in alignment with the ends of the sleeve. A bolt is then used to secure a component to the structural member. Thus, the hollow structural member is reinforced locally in the present invention at that position by virtue of the reinforcing member. The polymer is expanded in place by heating the entire structure after assembly, where it expands to fill gaps between the reinforcing structure and the structural member and bonds the reinforcing structure to the structural member. 
     In another aspect the reinforced structure of the present invention is a motor vehicle rail such as a front rail where local reinforcement for the attachment of components such as an engine cradle is required. In this aspect, the invention reduces vibration and noise transmission as well as increases the strength of the part at the site of the reinforcement. 
     In still another aspect the sleeve is a thin wall metal bushing, the opposed walls are metal stampings with flanges which are welded to the structural member and the polymer is a thermally expanded epoxy resin which contains hollow microspheres for density reduction. 
     In still another aspect the present invention provides method of reinforcing a structural member having a longitudinal channel. In this aspect a laminated structure having two opposed walls separated by a layer of thermally expandable polymer is placed in the channel of a rail section or the like. The laminated structure has a sleeve disposed in the layer of thermally expandable polymer. The sleeve defines a passage perpendicular to the opposed walls. The laminated structure also has a pair of end flanges. The laminated structure is placed in the longitudinal channel such that said sleeve passage is perpendicular to the longitudinal channel. The laminated structure is then welded to the structural member at the flanges. The entire structure is then heated to a temperature effective to activate the blowing agent of the polymer and thereby thermally expand the polymer such that it bonds the laminated structure to the structural member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic exploded perspective view of a conventional prior art bulkhead reinforcement structure; 
     FIG. 2 is a diagrammatic front elevational view of the structure of FIG. 1 with the cap plate removed; 
     FIG. 3 is a diagrammatic exploded perspective view of the reinforced rail section of the present invention illustrating the construction of the reinforcing laminate bulkhead; 
     FIG. 4 is a diagrammatic front elevational view of the structure shown in FIG. 3 with the cap plate removed; and 
     FIG. 5 is a diagrammatic back view of the bulkhead portion of FIGS.  3  and  4 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIGS. 1 and 2 of the drawings, prior art front rail section  20  is shown having C-section  22  that defines channel  23  and which receives cap plate  24 . Bulkhead stamping  26  is seen having vertical wall  28  and flanges  30 . Bushing  32  is welded to wall  28  at an arcuate bend  33  in wall  28 . Flanges  30  are welded to section  22  to hold bulkhead  26  in place. Bolt  36  extends through cap  24 , bushing  32  and vertical wall  37  of section  22  and then through a component  38  which is to attached to rail  20 . Nut  40  is then attached to bolt  36  to secure component  38  in place. This is representative of the prior art and suffers from the drawbacks described above, i.e. inadequate reinforcement, inadequate sound dampening and vibration problems. 
     Turning now to FIG. 3 of the drawings, reinforced structure  50  is shown in one embodiment as a reinforced front rail of an automotive frame and includes frame rail C-section  52  which is closed by cap plate  54  such that channel or cavity  56  is defined in reinforced structure  50 . In other words the frame rail is hollow. C-section  52  includes vertical wall portion  58  and opposed wall portions  60  and  62 . Each opposed wall portion  60 , 62  has a flange portion  64  of the attachment of cap plate  54  by welding or the like at the flange areas. Reinforcing member or bulkhead  68  is seen disposed in channel  56  of C-section  52  and has a first wall or side  70  and a second wall or side  72 . Walls  70  and  72  are parallel to one another and are separated by polymer layer  74 ; that is, polymer layer  74  is disposed between walls  70  and  72 . 
     As best seen in FIGS. 4 and 5 of the drawings, each wall  70 , 72  has an associated arcuate portion ( 76  for wall  72  and  78  for wall  70 ) which is designed to accommodate sleeve  81  in a manner to be more fully described hereinafter. Each arcuate portion  76 , 78  is approximately midway along the length of each wall  70 , 72  and can be viewed as a curved inner surface. Sleeve  81  is a metal bushing or the like and, as best seen in FIG. 4 of the drawings is spot welded to walls  70  and  72  at weld points  83  and  85 . Polymer layer  74  essentially envelopes sleeve  81  as shown in FIG.  4 . 
     Bulkhead  68  is secured in place in channel  56  by virtue of attachment flanges  80  and  82  which extend from walls  70  and  72  at 90 degree angles. That is, each wall  70 ,  72  has at each end a bent portion that mates with a similar portion on the opposed wall to form an attachment flange  80 , 82  that is welded on side wall  60 , 62 , respectively. 
     The width of walls  70  and  72  (distance between vertical wall  58  and cap plate  54 ) is such that bulkhead  68  is in contact with vertical wall  58  and cap plate  54 . Accordingly, bolt  84  extends through cap plate  54  at hole  66 , through sleeve  81  and through a corresponding hole in vertical wall  58  (not shown). Bolt  84  then extends through a hole in a cross member such as engine cradle  86  which is shown in phantom as fragment  86 . Nut  88  is then secured on bolt  84  to secure engine cradle  86  onto reinforced structure  50 . 
     Bulkhead  68  is a relatively light weight structure for the amount of strength added to the frame rail. Walls  70  and  72  can be formed of thin steel stampings, for example from 0.02 to about 0.08 inch in thickness. Mild to medium strength steel is particularly preferred. Also, sleeve  81  which is preferably a metal bushing may b a thin wall tube having a wall thickness of from about 0.08 to about 0.2 inch and is preferably mild steel. Of course, these dimensions are merely illustrative and are not intended to limit the full scope of the invention as defined in the claims. Each attachment flange  80 , 82  is generally from about 15 percent to about 30 percent of the length of walls  70 , 72 . The outer diameter of sleeve  81  will typically be from about ½ to about 1 inch. The width of polymer layer  74  will be a function of the distance between walls or plates  70  and  72  and will generally be between about 0.1 and about 0.4 inch. It is to be understood that the entire depth of bulkhead  68  is filled with polymer layer  74 ; that is, as shown in FIG. 5 of the drawings polymer layer  74  extends from the front of bulkhead  68  to the back. 
     The polymer used to form polymer layer  74  is a resin based material which is thermally expandable. A number of resin-based compositions can be utilized to form thermally expanded layer  74  in the present invention. The preferred compositions impart excellent strength and stiffness characteristics while adding only marginally to the weight. With specific reference now to the composition of layer  74 , the density of the material should preferably be from about 20 pounds per cubic feet to about 50 pounds per cubic feet to minimize weight. The melting point, heat distortion temperature and the temperature at which chemical breakdown occurs must also be sufficiently high such that layer  74  maintains its structure at high temperatures typically encountered in paint ovens and the like. Therefore, layer  74  should be able to withstand temperatures in excess of 320 degrees F. and preferably 350 degrees F. for short times. Also, layer  74  should be able to withstand heats of about 90 degrees F. to 200 degrees F. for extended periods without exhibiting substantial heat-induced distortion or degradation. 
     The foam  74  may be initially applied to one or both walls  70 , 72  and then expand into intimate contact with both walls and with sleeve  81 . Advantageously heat from the paint oven may be used to expand foam  74  when it is heat expandable. 
     In more detail, in one particularly preferred embodiment thermally expanded structural foam for layer  74  includes a synthetic resin, a cell-forming agent, and a filler. A synthetic resin comprises from about 40 percent to about 80 percent by weight, preferably from about 45 percent to about 75 percent by weight, and most preferably from about 50 percent to about 70 percent by weight of layer  74 . Most preferably, a portion of the resin includes a flexible epoxy. As used herein, the term “cell-forming agent” refers generally to agents which produce bubbles, pores, or cavities in layer  74 . That is, layer  74  has a cellular structure, having numerous cells disposed throughout its mass. This cellular structure provides a low-density, high-strength material, which provides a strong, yet lightweight structure. Cell-forming agents which are compatible with the present invention include reinforcing “hollow” microspheres or microbubbles which may be formed of either glass or plastic. Also, the cell-forming agent may comprise a blowing agent which may be either a chemical blowing agent or a physical blowing agent. Glass microspheres are particularly preferred. Where the cell-forming agent comprises microspheres or macrospheres, it constitutes from about 10 percent to about 50 percent by weight, preferably from about 15 percent to about 45 percent by weight, and most preferably from 20 percent to about 40 percent by weight of the material which forms layer  74 . Where the cell-forming agent comprises a blowing agent, it constitutes from about 0.5 percent to about 5.0 percent by weight, preferably from about 1 percent to about 4.0 percent by weight, and most preferably from about 1 percent to about 2 percent by weight of thermally expanded structural foam layer  74 . Suitable fillers include glass or plastic microspheres, fumed silica, calcium carbonate, milled glass fiber, and chopped glass strand. A thixotropic filler is particularly preferred. Other materials may be suitable. A filler comprises from about 1 percent to about 15 percent by weight, preferably from about 2 percent to about 10 percent by weight and most preferably from about 3 percent to about 8 percent by weight of layer  74 . 
     Preferred synthetic resins for use in the present invention include thermosets such as epoxy resins, vinyl ester resins, thermoset polyester resins, and urethane resins. It is not intended that the scope of the present invention be limited by molecular weight of the resin and suitable weights will be understood by those skilled in the art based on the present disclosure. Where the resin component of the liquid filler material is a thermoset resin, various accelerators, such as imidazoles and curing agent, preferably dicyandiamide may also be included to enhance the cure rate. A functional amount of accelerator is typically from about 0.5 percent to about 2.0 percent of the resin weight with corresponding reduction in one of the three components, resin, cell-forming agent or filler. Similarly, the amount of curing agent used is typically from about 1 percent to about 8 percent of the resin weight with a corresponding reduction in one of the three components, resin, cell-forming agent or filler. Effective amounts of processing aids, stabilizers, colorants, UV absorbers and the like may also be included in layer. Thermoplastics may also be suitable. 
     In the following table, a preferred formulation for layer  74  is set forth. It has been found that this formulation provides a material which full expands and cures at about 320 degrees F. and provides excellent structural properties. All percentages in the present disclosure are percent by weight unless otherwise specifically designated. 
     
       
         
               
               
             
               
               
             
           
               
                   
               
               
                   
                 PERCENTAGE 
               
               
                 INGREDIENT 
                 BY WEIGHT 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 EPON 828 (epoxy resin) 
                 37.0 
               
               
                 DER 331 (flexible epoxy resin) 
                 18.0 
               
               
                 DI—CY (dicyandiamide curing agent) 
                 4.0 
               
               
                 Imidazole (accelerator) 
                 0.8 
               
               
                 FUMED SILICA (thixotropic filler) 
                 1.1 
               
               
                 Celogen AZ199 (asodicarbonamide blowing agent) 
                 1.2 
               
               
                 83 MICROS (glass microspheres) 
                 37.0 
               
               
                 WINNOFIL CALCIUM CARBONATE (CaCO 3  filler) 
                 0.9 
               
               
                   
               
             
          
         
       
     
     While the invention has been described primarily in connection with vehicle parts, it is to be understood that the invention may be practiced as part of other products, such as aircrafts, ships, bicycles or virtually anything that requires energy for movement. Similarly, the invention may be used with stationary or static structures, such as buildings, to provide a rigid support when subjected to vibration such as from an earthquake or simply to provide a lightweight support for structures subjected to loads. Additionally, while the invention has been described primarily with respect to heat expandable foams and with respect to metal parts such as the inner tubes  16 ,  58  and  76 , other materials can be used. For example, the foam could be any suitable known expandable foam which is chemically activated into expansion and forms a rigid structural foam. The bulkhead walls  70 , 70  and sleeve  81  could be made of materials other than metal such as various plastics or polymeric materials or various wood type fibrous materials having sufficient rigidity to function as a back drop or support for the foam. Where a heat expandable foam is used the bulkhead walls and sleeve should be able to withstand the heat encountered during the heat curing. Where other types of foam materials are used, however, it is not necessary that the bulkhead walls and sleeve be able to withstand high temperatures. Instead, the basic requirement for the bulkhead walls and sleeve is that it have sufficient rigidity to function in its intended manner. It is also possible, for example, to use as the bulkhead walls and sleeve materials which in themselves become rigid upon curing or further treatment. The invention may also be practiced where the bulkhead walls and sleeve are made of materials other than metal. It is preferred, however, that materials be selected so that the thin unexpanded foam upon expansion forms a strong bond with the bulkhead walls and sleeve so that a structural composition will result. 
     While particular embodiments of this invention are shown and described herein, it will be understood, of course, that the invention is not to be limited thereto since many modifications may be made, particularly by those skilled in this art, in light of this disclosure. It is contemplated, therefore, by the appended claims, to cover any such modifications as fall within the true spirit and scope of this invention.