Abstract:
A motor vehicle sub-frame is provided. That motor vehicle sub-frame includes a front cross member, a rear cross member and first and second side rails connected to the front and rear cross members at each side of the sub-frame. The side rails both include a first component having a first extrusion axis and a second component having a second extrusion axis. The first and second components are joined together so that the two components effectively form an at least partially closed or boxed construction providing enhanced bending and torsion resistances while minimizing component weight.

Description:
TECHNICAL FIELD 
       [0001]    This document relates generally to the motor vehicle equipment field and, more particularly, to an extruded multi-component motor vehicle sub-frame as well as to an extruded side rail and extruded cross-member for that sub-frame. 
       BACKGROUND 
       [0002]    The use of aluminum by the automotive industry could achieve over 30% weight savings in vehicle body, chassis and closure components when replacing steel parts. An aluminum intensive vehicle is an efficient way to reduce weight and thus improve fuel economy. 
         [0003]    The sub-frame or engine cradle is an assembly with high potential for weight saving due to its size and weight. Conventional sub-frames are made of stamped steel parts. Some high performance automobiles utilize aluminum sub-frames made of aluminum castings or combinations of aluminum castings and extrusions. An aluminum sub-frame made by only extrusions is more attractive to automotive manufacturers since extrusion dies are more affordable compared to casting dies. 
         [0004]    It is challenging to design a perimeter type sub-frame with only extrusions to achieve stiffness, performance and weight savings due to the architecture of the sub-frame and the manufacturing constraints of extrusions. More specifically, a perimeter type sub-frame is constructed with a front cross member, a rear cross member and two side rails. The most efficient stiffness design of the side rail should have a closed cross section or partially closed sections at critical locations that will benefit both bending and torsion resistances. Unfortunately, the package space of a sub-frame generally will not allow a straight side rail with a sufficient cross section size, thereby limiting the use of extruded tubes. Thus, in the past, package feasible side rail components have been made by either lateral direction or vertical direction extrusions which have two open surfaces. 
         [0005]    This document relates to a new and improved motor vehicle sub-frame, a side rail for that sub-frame and a cross member for that sub-frame. Design challenges are overcome by providing an all extruded aluminum perimeter sub-frame that meets or exceeds strength, bending resistance and torsion resistance requirements while providing substantial weight savings for increased fuel economy. Thus, the motor vehicle sub-frame disclosed herein represents a significant advance in the art. 
       SUMMARY 
       [0006]    In accordance with the purposes and benefits described herein, a motor vehicle sub-frame is provided. That motor vehicle sub-frame comprises a front cross member, a rear cross member, a first side rail connecting the front cross member with the rear cross member at a first side of the motor vehicle sub-frame and a second side rail connecting the front cross member with the rear cross member at a second side of the motor vehicle sub-frame. The first and second side rails both include a first component having a first extrusion axis and a second component having a second extrusion axis. The first component is joined to the second component with the first extrusion axis and the second extrusion axis forming an included angle of between 60° and 90°. 
         [0007]    In one possible embodiment, the first component includes a first part and a second part wherein a first end of the first part is joined to a second end of the second part. In one possible embodiment, the second component includes a first element and a second element. The first element is joined to the inner surface of the first part and the second element is joined to the inner surface of the second part. Thus, the first component may include a first wall, forming an upper wall of the side rail and a second wall, forming a lower wall of the side rail. Further, the second component includes a third wall, forming an inner side wall of the side rail and a fourth wall, forming an outer side wall of the side rail. Accordingly, the second component may be positioned in the first component and the third wall and the fourth wall may be joined to the inner surfaces of the first wall and the second wall. In this way it is possible to produce at least a partially closed side rail from two extruded components. 
         [0008]    In accordance with an additional aspect, a motor vehicle sub-frame is provided including a front cross member, a rear cross member and first and second side rails connecting the front and rear cross members at respective first and second sides of the motor vehicle sub-frame. The first side rail and the second side rail are joined to the rear cross member by one or more friction stir welds while the first side rail and the second side rail are joined to the front cross member by one or more MIG welds. 
         [0009]    The motor vehicle sub-frame further includes a first front body attachment and a second front body attachment. The first front body attachment is joined to the first side rail by a first MIG weld and the second front body attachment is joined to the second side rail by a second MIG weld. 
         [0010]    In accordance with still another aspect, a side rail is provided for a motor vehicle sub-frame. That side rail comprises a first component having a first extrusion axis and a second component having a second extrusion axis. The first component is joined to the second component with the first extrusion axis and second extrusion axis forming an included angle of between 60 and 90 degrees. 
         [0011]    More specifically, the first component includes a first wall, forming an upper wall of the side rail, and a second wall, forming a lower wall of the side rail. The second component includes a third wall, forming an inner side wall of the side rail, and a fourth wall, forming an outer side wall of the side rail. 
         [0012]    In one possible embodiment, the second component is positioned in the first component and the third wall and fourth wall are joined to the inner surfaces of the first wall and the second wall. 
         [0013]    In another possible embodiment, the first component includes a first part and a second part wherein a first end of the first part is joined to a second end of the second part. In such an embodiment, the second component may include a first element and a second element. The first element is joined to an inner surface of the first part while the second element is joined to an inner surface of the second part. Thus, the second component at least partially closes the first component to provide and at least partially close the side rails. The first and second components may be joined by a weld. 
         [0014]    In accordance with still another aspect, a cross member is provided for a motor vehicle sub-frame. That cross member comprises a hollow body having an extrusion axis and a wall having a first edge and a second edge. The wall is positioned inside and extends across the hollow body with the first edge and the second edge joined to the hollow body. 
         [0015]    In one possible embodiment the wall has a longitudinal axis that extends parallel to the extrusion axis of the hollow body. Further the wall may be planar. 
         [0016]    The hollow body may include an attachment hole and the wall is aligned with that attachment hole. Still further, a cylindrical reinforcement may be provided in the hollow body around the attachment hole. In such an embodiment, the wall may extend radially outwardly from the cylindrical reinforcement but the wall does not cross the attachment hole defined within the cylindrical reinforcement. Thus, the wall extending across the hollow body is discontinuous. 
         [0017]    In the following description, there are shown and described several preferred embodiments of the motor vehicle sub-frame, the side rail for a motor vehicle sub-frame and the cross member for the motor vehicle sub-frame. As it should be realized, the motor vehicle sub-frame, side rail and cross member are all capable of other, different embodiments and their several details are capable of modification in various, obvious aspects all without departing from the sub-frame, side rail and cross member as set forth and described in the following claims. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0018]    The accompanying drawing figures incorporated herein and forming a part of the specification, illustrate several aspects of the motor vehicle sub-frame, the side rail for a motor vehicle sub-frame and the cross member for a motor vehicle sub-frame and together with the description serve to explain certain principles thereof. In the drawing figures: 
           [0019]      FIG. 1  is a perspective view of a first possible embodiment of the motor vehicle sub-frame. 
           [0020]      FIG. 2A  is a perspective view of a first component of a side rail including first and second parts that are joined end to end. 
           [0021]      FIGS. 2B and 2C  are perspective views illustrating first and second elements of a second component for a side rail of a motor vehicle sub-frame. 
           [0022]      FIG. 2D  is a perspective view illustrating the assembled side rail utilizing the components illustrated in  FIGS. 2A-2C . 
           [0023]      FIG. 3  is a perspective view of the rear cross member of the motor vehicle sub-frame. 
           [0024]      FIG. 4  is a detailed perspective view of that rear cross member illustrating the structural details of the cross member including the hollow body including various attachment holes, the cylindrical reinforcements for those attachment holes and the reinforcing walls, aligned with the cylindrical reinforcements and attachment holes, extending across the hollow body. 
       
    
    
       [0025]    Reference will now be made in detail to the present preferred embodiments of the motor vehicle sub-frame, the sub-frame side rail and the sub-frame cross member, examples of which are illustrated in the accompanying drawing figures. 
       DETAILED DESCRIPTION 
       [0026]    Reference is now made to  FIG. 1  illustrating a motor vehicle perimeter sub-frame or engine cradle  10 . As illustrated, the sub-frame  10  includes a front cross member  12 , a rear cross member  14 , a first side rail  16  and a second side rail  18 . The first side rail  16  connects the front cross member  12  with the rear cross member  14  at a first side of the motor vehicle sub-frame  10  while the second side rail  18  connects the front cross member with the rear cross member at a second side of the motor vehicle sub-frame. 
         [0027]    The front cross member  12 , has a shape of an irregular box with no side walls. The rear cross member  14  is also an irregular box with no side wall. As should be appreciated, the front cross member  12 , the rear cross member  14  and the first and second side rails  16 ,  18  may all be made via extrusions of aluminum or aluminum alloy. 
         [0028]    Reference is now made to  FIGS. 2A-2D  illustrating the construction of the two side rails  16 ,  18 . More specifically, each side rail  16 ,  18  includes a first component  20 . More specifically, the first component  20  illustrated in  FIG. 2A  includes a first part  24  and a second part  26 . A first end  28  of the first part  24  is joined to a second end  30  of the second part  26  so that the two parts are welded end to end and the two parts have an extrusion axis extending parallel to the extrusion axis line  22 . 
         [0029]    As illustrated in  FIGS. 2B and 2C  each side rail  16 ,  18  also includes a second component  32  having a second extrusion axis  34 . The first element  36  of the second component  32  is illustrated in  FIG. 2B  while the second element  38  of the second component is illustrated in  FIG. 2C . 
         [0030]    Each side rail  16 ,  18  is constructed from the first and second component  20 ,  32 . More specifically, the first component  20  includes a first wall  40  forming an upper wall of the side rail  16 ,  18  and a second wall  42  forming a lower wall of the side rail. The second component  32  includes a third wall  44  that forms an inner side wall of the side rail  16 ,  18  and a fourth wall  46  that forms an outer sidewall of the side rail. 
         [0031]    As best illustrated in  FIG. 2D , the first element  36  is positioned inside the first part  24  while the second element  38  is positioned inside the second part  26 . The third and fourth walls  44 ,  46  are then joined to the inner surfaces of the first and second walls  40 ,  42  by means of welding thereby providing at least partially closed side rails  16 ,  18  as best illustrated in detail in  FIG. 2D . In one particularly useful embodiment of the motor vehicle sub-frame  10 , the walls  40 ,  46  of the components  20 ,  32  are welded together by one or more friction stir welds. As best illustrated in  FIG. 1 , the first extrusion axis  22  of the first component  20  runs laterally while the second extrusion axis  34  of the second component  32  runs vertically in the assembled sub-frame  10 . The two extrusion axes  22 ,  34  may form an included angle of between 60° and 90° or of between 70° and 90° or of between 80° and 90°. In the illustrated embodiment, the two extrusion axes  22 ,  34  are substantially perpendicular to one another. 
         [0032]    Reference is now made to  FIGS. 3 and 4  illustrating in detail the rear cross member  14  of the sub-frame  10 . As illustrated, the rear cross member  14  includes an extruded hollow body  48  having an extrusion axis  50  that extends laterally across the sub-frame  10 . A series of walls  52  are positioned inside the hollow body  48  and extend across the hollow body. Each wall  52  includes a first edge  54  and a second, opposite edge  56  that are joined to the inner surface of the hollow body  48  by appropriate welds. In the illustrated embodiment, each wall  52  has a longitudinal axis that extends parallel to the extrusion axis  50  of the hollow body  48 . Further each wall  52  is planar. 
         [0033]    As further illustrated in  FIGS. 3 and 4 , the hollow body  48  includes various attachment holes  58  for, for example, rear body attachments, stabilizer bar attachments, lower control arm attachments and steering attachments. A cylindrical reinforcement  60  may be provided in the hollow body  48  to reinforce the hollow body around each attachment hole  58 . As illustrated, a wall  52  may extend radially outwardly from each cylindrical reinforcement  60 . Here it should be appreciated that the walls  52  are not continuous but extend up to and are welded to the cylindrical reinforcements  60 , they do not cross the attachment hole  58  defined within the cylindrical reinforcements. 
         [0034]    In summary, the sub-frame  10  provides a number of benefits and advantages. The sub-frame  10  provides a desired strength relying upon friction stir welds to assemble the components  20 ,  32  of the side rails  16 ,  18  together, the rear cross member components  48 ,  52 ,  60  together and to join the side rails,  16 ,  18  to the rear cross member components. In contrast, one or more MIG welds are utilized to join the front cross member  12  with the side rails  16 ,  18  through a first front body attachment  62  and second front body attachment  64  (see  FIG. 1 ). 
         [0035]    Further, the sub-frame  10  provides the desired bending and torsion resistances through the provision of side rails  16 ,  18  incorporating a first component  20  having a first extrusion axis  22  and a second component  32  having a second extrusion axis  34  joined together so that the two extrusion axes form an included angle of between 60 and 90 degrees. In one particularly useful embodiment, the two extrusion axes  22 ,  34  are substantially perpendicular to one another and provide an at least partially closed side rail. 
         [0036]    The foregoing has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Obvious modifications and variations are possible in light of the above teachings. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.