Abstract:
A tubular structural member of an automobile wherein such member includes a double wall construction. Such product is initially formed from a double walled tube. The resulting member exhibits superior sound and/or vibration dampening without sacrificing stiffness or strength.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to structural members for use in vehicles having dampened noise and vibration characteristics. More specifically, the invention relates to methods for forming laminated tubular components for use as structural members in vehicles, and products of such methods.  
         [0003]     2. Description of the Prior Art  
         [0004]     For various applications, there is a high desire for structural members with high strength to weight ratios. This is particularly true in the automotive industry where designers constantly strive to lower the weight of automobiles. In the result, a number of attempts have been made to reduce the weight of various structural members without affecting the strength and integrity of such components. These structural members include pillars (e.g. windshield pillars and centre pillars), rockers, support beams, drive shafts, side impact beams, bumpers, and crossmembers. The desire to reduce the weight of vehicles stems from a drive to increase vehicle fuel efficiency. To achieve this goal, many of the above structural components have been formed as hollow members.  
         [0005]     Although providing reduced weight, the stiffness of these components is greatly reduced, thereby resulting in increased vibration and noise. One solution to this problem has been to use hollow components filled with expandable foam, such as high-density plastic foam. Although such foam increases the stiffness of the hollow structural member, it still results in an increase in the weight of the component. Moreover, the filling of the hollow component with foam has associated with it various disadvantages. One of these disadvantages is the requirement of having at least one end of the component to remain open or to provide filling holes along the length of the component. Since most tubular members are flattened at their ends, the latter route is normally taken. However, adding holes to the members increases the production time and, therefore cost, of the product as well as leading to a reduction in the structural integrity of the component.  
         [0006]     U.S. Pat. Nos. 4,506,188 and 4,744,539 teach methods for dampening vibration in automobiles using resilient components. The following U.S. patents teach laminated metal sheets that can be used in constructing automobiles etc. and which serve to dampen vibration and/or noise: U.S. Pat. Nos. 4,678,707; 4,851,271; and, 5,338,599. The contents of the above patents are incorporated herein by reference.  
         [0007]     U.S. publication No. 2002/0178584 discloses a composite laminate structure to provide structural components having increased stiffness and reduced weight. In this reference, an expandable foam layer is laminated to a surface of an insert forming the structural member. However, the process to produce such component is relatively complicated and time consuming.  
         [0008]     There exists a need for an improved means of fabricating structural components with high strength to weight ratios.  
       SUMMARY OF THE INVENTION  
       [0009]     In one embodiment, the present invention provides a hollow structural member for an automobile having a double wall formed from a laminate of two metal sheets.  
         [0010]     In another embodiment, the present invention provides a method for forming a hollow structural member for an automobile comprising: 
        a) providing a hollow tube having a double wall comprising a laminate of two metal sheets;     b) forming the tube into said structural member.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     These and other features of the preferred embodiments of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein:  
         [0014]      FIG. 1  is perspective view of a typical vehicle cross member.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     In one embodiment, the present invention provides a structural member or component for automobiles and the like. An example of one such member, an automobile frame crossmember is illustrated in  FIG. 1 . As can be seen, such member is generally hollow and is formed into a desired three-dimensional shape. Persons skilled in the art will understand that the final shape of the cross member will depend on its location on the vehicle frame and the type of cross member (i.e. a crossmember for supporting the vehicle&#39;s radiator, a front or rear suspension cross member etc.).  
         [0016]     In accordance with the invention, the crossmember of  FIG. 1  has the shape of crossmembers commonly known. However, the crossmember is formed from a tube having a double wall or laminate construction. The tube is formed from, for example, a laminate of two metal sheets that are joined together. The sheets may be affixed to one another directly or with a resin or polymer sheet provided there between. The above-mentioned prior art references teach laminate sheets that are designed for vibration dampening. One such product is commercially available under the name Quiet Steel™, which is sold by MSC Laminates and Composites Inc (Elk Grove Village, Ill., USA). This product comprises a three layer laminate having a non-metal sheet sandwiched between two metal sheets. Such commercially available laminates can be used in the present invention. Further, a laminate of two metal sheets without a centre, non-metal layer may also be used.  
         [0017]     In the initial step, a laminate sheet (as described above) is provided, the sheet having sound and/or vibration dampening characteristics. The sheet is formed into a tube, as is commonly known in the art. Once made as a tube, the component is then formed into the desired 3-D shape. Such forming can be accomplished by any known means such as bending, crimping, hydroforming or any combination thereof.  
         [0018]     It has been found that components formed in the above manner are characterized with greatly improved sound and/or vibration dampening.  
         [0019]     The above description has been focussed on vehicular crossmembers. However, it will be apparent to persons skilled in the art the above method can be used to form various other structural components, particularly those for vehicles, to achieve the same qualities.  
         [0020]     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.