Abstract:
A vehicle frame includes first and second lower rails and first and second upper rails operatively interconnected. Cross members horizontally interconnect the lower rails and the upper rails, and stanchions vertically interconnect the upper rails and the lower rails. The frame provides improved stiffness and strength at a reduced mass compared to the prior art.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to vehicle chassis frames having two upper rails and two lower rails. 
       BACKGROUND OF THE INVENTION 
       [0002]    Vehicles are typically characterized by one of two types of construction, namely body-on-frame construction and unibody construction, which is also sometimes referred to as body-frame integral construction. As understood by those skilled in the art, the vehicle body and the vehicle frame are the same in unibody construction; that is, the body forms the frame. With body-on-frame construction, a body is mounted to a separate chassis frame. 
         [0003]    Prior art chassis frames are referred to as “ladder frames” because they comprise two longitudinally-oriented rails that extend substantially the length of the body to which the frame is attached, and two or more transversely-oriented cross members that rigidly interconnect the two rails. 
       SUMMARY OF THE INVENTION 
       [0004]    A vehicle frame is provided. The vehicle frame includes first and second lower rails being horizontally spaced from one another, and first and second upper rails being horizontally spaced from one another and vertically spaced from the first and second lower rails. At least one lower cross member interconnects the first and second lower rails, and at least one upper cross member interconnects the first and second upper rails. 
         [0005]    In an exemplary embodiment, a plurality of stanchions vertically interconnects the first lower rail and the first upper rail, and a plurality of stanchions vertically interconnects the second lower rail and the second upper rail. Shear webs interconnect the upper and lower rails to provide torsional rigidity and, in the event of an impact, absorb energy and stabilize the upper and lower rails. 
         [0006]    Since the global bending stiffness of a frame is related to the total rail section height, with the new upper and lower rail frame design of the present invention, especially with the lower rails being routed under the chassis axles, the rail section height is substantially increased, leading to a higher bending stiffness. External loads can be channeled through both upper rails and lower rails, thus providing energy absorption. The upper and lower rails also provide structural stability to the frame under external loading. The frame of the invention allows the use of low gauge, or thinner gauge, metal, such as equal to or less than  3 . 0  millimeters, for the components of the frame, resulting in a lower weight for the frame. The lower rails also provide flexibility in cross member placement, and thus provide the opportunity to align cross members with anticipated external load paths. 
         [0007]    The frame of the invention also provides enhanced global frequencies, including bending, torsion, and lateral bending; the frame also provides enhanced global stiffness, including global bending, global twist, and global matchboxing. 
         [0008]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic, perspective view of a vehicle chassis including a frame in accordance with the claimed invention; 
           [0010]      FIG. 2  is a schematic, cross-sectional view of an upper and lower rail of the frame of  FIG. 1 ; 
           [0011]      FIG. 3  is another schematic, cross-sectional view of the upper and lower rail of  FIG. 2 ; and 
           [0012]      FIG. 4  is yet another schematic, cross-sectional view of the upper and lower rail of  FIGS. 2 and 3 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    Referring to  FIG. 1 , a vehicle chassis  8  is schematically depicted. The vehicle chassis  8  includes a frame  10 . The frame  10  includes two lower rails  14 A,  14 B that are longitudinally-oriented with respect to the frame  10 , and two upper rails  18 A,  18 B that are longitudinally-oriented with respect to the frame  10 . The two lower rails  14 A,  14 B are horizontally spaced from one another, and the two upper rails  18 A,  18 B are horizontally spaced from one another. The upper rails  18 A,  18 B are vertically spaced from the lower rails  14 A,  14 B. Those skilled in the art will recognize a variety of methods that may be used to form the rails  14 A,  14 B,  18 A,  18 B within the scope of the claimed invention, such as stamping, tube hydro-forming, roll forming, etc. 
         [0014]    The frame  10  further includes a plurality of upper cross members  22 A-E that extend transversely between the upper rails  18 A,  18 B. More specifically, one end of each cross member  22 A-E is connected to upper rail  18 A, and one end of each cross member  22 A-E is connected to upper rail  18 B to substantially rigidly connect the two upper rails  18 A,  18 B. Those skilled in the art will recognize a variety of methods and devices that may be employed to connect frame members together, such as welding, mechanical fasteners such as bolts, adhesive bonding, etc. 
         [0015]    The frame  10  also includes a plurality of lower cross members  26 A-E that extend transversely between the lower rails  14 A,  14 B. More specifically, one end of each cross member  26 A-E is connected to lower rail  14 A, and one end of each cross member  26 A-E is connected to lower rail  14 B to substantially rigidly connect the two lower rails  14 A,  14 B. 
         [0016]    The frame  10  includes substantially vertical stanchions  30 A-G,  34 A,  34 C-G to connect the upper rails and the lower rails, and to provide torsional rigidity to the frame  10 . Each of stanchions  30 A-G is rigidly connected at one end to lower rail  14 B and is rigidly connected at the other end to upper rail  18 B to interconnect lower rail  14 B and upper rail  18 B. Stanchions  34 A,  34 C-G similarly interconnect lower rail  14 A and upper rail  18 A. Exemplary stanchions include hollow tubular members. It should be noted that the frame  10  is symmetrical about a vertical plane extending longitudinally at the centerline of the frame  10 . 
         [0017]    Shear webs  38 A-C interconnect lower rail  14 A and upper rail  18 A. Similarly, shear webs  38 D-F interconnect lower rail  14 B and upper rail  18 B.  FIG. 2 , wherein like reference numbers refer to like components from  FIG. 1 , is a schematic cross-sectional view of lower rail  14 B, upper rail  18 B, and shear web  38 F taken about a vertical plane rearward of stanchion  30 F. Referring to  FIG. 2 , lower rail  14 B defines three walls  42 A,  42 B,  42 C that cooperate to define a cavity  46  that is upwardly open. That is, lower rail  14 A defines an opening  50  to cavity  46 . The lower rail  14 B also defines a weld flange  54  that extends at a right angle from wall  42 C adjacent the opening  50  to cavity  46 . 
         [0018]    Upper rail  18 B defines three walls  58 A,  58 B,  58 C that cooperate to define a cavity  62  that is downwardly open. That is, upper rail  18 B defines an opening  66  to cavity  62 . The upper rail  18 B also defines a weld flange  70  that extends at a right angle from wall  58 C adjacent the opening  66  to cavity  62 . 
         [0019]    Shear web  38 F, like the other shear webs, is a single piece of sheet metal that has been stamped or otherwise formed into the shape shown. More particularly, shear web  38 F includes a first segment  74 , a second segment  78  that is at a generally right angle from the first segment  74 , and a third segment  82  that is generally at a right angle from the second segment  78 . The first segment  74  is connected to the upper rail  18 B at the weld flange  70  and at wall  58 A, such as by spot welding, seam welding, or adhesive bonding, to extend across, and thereby close, opening  66 . Thus, segment  74  of shear web  38 F cooperates with the upper rail  18 B to form a closed section. 
         [0020]    Similarly, the third segment  82  is connected to the lower rail at the weld flange  54  and at wall  42 A, such as by spot welding, seam welding, or adhesive bonding, to extend across, and thereby close, opening  50 . Thus, segment  82  of shear web  38 F cooperates with the lower rail  14 B to form a closed section. The second segment  78  of the shear web interconnects the upper rail  18 B and the lower rail  14 B. In the embodiment depicted, segment  78  includes strengthening formations  86 . 
         [0021]      FIG. 3 , wherein like reference numbers refer to like components from  FIGS. 1 and 2 , is a schematic cross-sectional view of lower rail  14 B and upper rail  18 B taken about a vertical plane proximate to stanchion  30 E. Referring to  FIG. 3 , shear web  38 E includes a first segment  90 , a second segment  94 , and a third segment  98 . The first segment  90  is connected to the upper rail  18 B at the weld flange  70  and at wall  58 A, such as by spot welding, seam welding, or adhesive bonding, to extend across, and thereby close, opening  66 . Thus, segment  90  of shear web  38 E cooperates with the upper rail  18 B to form a closed section. 
         [0022]    Similarly, the third segment  98  is connected to the lower rail at the weld flange  54  and at wall  42 A, such as by spot welding, seam welding, or adhesive bonding, to extend across, and thereby close, opening  50 . Thus, segment  98  of shear web  38 F cooperates with the lower rail  14 B to form a closed section. The second segment  94  of the shear web interconnects the upper rail  18 B and the lower rail  14 B. 
         [0023]    Sections of the frame may include two shear webs. In  FIG. 3 , shear web  102  includes a flange  106  that is connected to segment  90  of shear web  38 E, such as by welding. Flange  110  is connected to segment  98  of shear web  38 E and weld flange  54 . 
         [0024]      FIG. 4 , wherein like reference numbers refer to like components from  FIGS. 1-3 , is a schematic cross-sectional view of lower rail  14 B, upper rail  18 B, and shear web  38 D. Referring to  FIG. 4 , shear web  38 D includes a first segment  114 , a second segment  118 , and a third segment  122 . The first segment  114  is connected to the upper rail  18 B at the weld flange  70  and at wall  58 A, such as by spot welding, seam welding, or adhesive bonding, to extend across, and thereby close, opening  66 . Thus, segment  114  of shear web  38 D cooperates with the upper rail  18 B to form a closed section. 
         [0025]    Similarly, the third segment  122  is connected to the lower rail at the weld flange  54  and at wall  42 A, such as by spot welding, seam welding, or adhesive bonding, to extend across, and thereby close, opening  50 . Thus, segment  122  of shear web  38 D cooperates with the lower rail  14 B to form a closed section. The second segment  118  of the shear web interconnects the upper rail  18 B and the lower rail  14 B. 
         [0026]    The shear webs are configured to absorb energy and stabilize the upper and lower rails during an impact event, and are configured to provide torsional rigidity to the frame  10 . 
         [0027]    It should be noted that, although the rails in the embodiment depicted have an open cross section that is closed by a shear web, rails may be characterized by any cross-sectional shape within the scope of the claimed invention. 
         [0028]    Referring to  FIGS. 2-4 , it should be noted that the upper rails  18 B and lower rails  14 B vary in cross-sectional geometry and size along the length of the frame. Furthermore, the vertical distance between the upper and lower rails varies along the length of the frame. Thus, for example, the cross-sectional area of the rails (or the cavities  46 ,  62 ) at the rearward and forward portions of the frame (as shown in  FIGS. 2 and 4 , respectively) is smaller than at the center portion of the frame, as shown in  FIG. 3 . The vertical distance between the upper rails  18 B and the lower rails  14 B is greater at the rearward portion of the frame ( FIG. 2 ) than at the center portion of the frame ( FIG. 3 ). The relative horizontal distance between the upper rail  18 B and the lower rail  14 B also varies along the length of the frame. For example, the upper rail  18 B is further outboard relative to the lower rail in  FIGS. 3 and 4  than in  FIG. 2 . 
         [0029]    Referring again to  FIG. 1 , upper rail  18 A and the lower rail  14 A define an open space  126  therebetween through which a rear axle  130  extends. Similarly, upper rail  18 B and lower rail  14 B define an open space  126  therebetween through which axle  130  extends. Lower rail  14 A and upper rail  18 A also define an open space  134  through which a front axle  138  extends. Lower rail  14 B and upper rail  18 B also define an open space through which a front axle extends. The routing of the lower rails  14 A,  14 B under front and rear axles  130 ,  138  may provide front and rear impact benefits and improve global bending stiffness. 
         [0030]    The portion of the lower rails  14 A,  14 B near the rear axle and cross member  26 E may be made as a subassembly and bolted onto the rest of the frame  10  after installation of the axle and exhaust system (not shown). The subassembly may also be selectively removable to facilitate servicing of the axle and exhaust system. 
         [0031]    Cross member  26 D is configured to provide impact resistance for the passenger compartment of a body (not shown) attached to the chassis  8 . Cross members  26 D,  26 E provide additional torsional and bending stiffness for the frame  10 . 
         [0032]    Body mounts  142  are brackets each with a respective hole  146 . The body mounts  142  are mounted to the upper rails  18 A,  18 B for marrying a body (not shown) to the chassis  8  as understood by those skilled in the art. The frame  10  in accordance with the invention may enable the reduction of the quantity of body mounts employed. For example, the frame  10  of the embodiment depicted employs ten body mounts instead of the typical twelve body mounts. 
         [0033]    A front bumper beam  150  is mounted to the upper rails  18 A,  18 B at the forward end of the frame  10 . A rear bumper beam  154  is mounted to the upper rails  18 A,  18 B at the rearward end of the frame  10 . Front and rear suspension brackets  158 ,  162  are mounted to the upper rails  18 A,  18 B. 
         [0034]    It may be desirable for members of the frame  10 , such as the rails, stanchions, cross members, etc., to comprise high-strength steel. Holes may be formed in the shear webs, rails, and cross members for weight reduction, weld access, and paint and coating drainage. Beads and indentations may also be formed in members of the frame  10  for local stiffening or for initiating deformation in an impact event. Exemplary joints for joining members of the frame  10  are described in U.S. Pat. No. 6,402,414, issued Jun. 11, 2002 to Kanodia, et al., which is hereby incorporated by reference in its entirety. 
         [0035]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.