Abstract:
A vehicle body structure is disclosed that comprises a pair of rear rails, a bumper beam and a spare tire compartment including a spare tire. The rear rails have a rear segment aligned with the bumper beam, a middle segment disposed above the rear segment and a front segment that extends downwardly from the middle segment. After a 50 mph 70% Movable Deformable Barrier rear impact test, the spare tire compartment including the spare tire hinges downwardly to create added crush space and the middle section is raised upwardly to reduce the extent of intrusions into the passenger compartment.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to the structure of a rear rail of a vehicle that predisposes a spare tire to rotate to provide additional crush space in a rear-end collision. 
       BACKGROUND 
       [0002]    Under current motor vehicle safety standards automotive vehicles are tested in a 50 MPH 70% offset Moving Deformable Barrier (MDB) rear impact test. The test is intended to test fuel system integrity in a rear-end collision. In the test procedure, 70% of the rear of the vehicle is impacted by a 1,368 kg deformable barrier at 80 km/h. 
         [0003]    An important factor in passing the MDB test is providing sufficient crush space in the vehicle to absorb the force of the impact. One possible solution is to reduce the volume of the fuel tank but this is undesirable because it reduces the range of the vehicle between refueling. In many vehicle designs a spare tire is attached to the vehicle below the rear trunk floor. The spare tire reduces the available crush space and results in additional deformation, higher plastic strain and increased pressure applied to the fuel tank. The spare tire is usually laterally squeezed in the crush zone in the MDB test and reduces the available crush space. 
         [0004]    Referring to  FIG. 1 , a rear rail “R” of a vehicle is illustrated in a side elevation view. The rear rail is aligned at the same height as the crush cans “C” and rear bumper “RB” and is approximately  137  mm above the frame “F” at the passenger compartment. This arrangement causes the spare tire to be laterally squeezed in the MDB test. 
         [0005]    This disclosure is directed to solving the above problems and other problems as summarized below. 
       SUMMARY 
       [0006]    According to one aspect of this disclosure, a vehicle body structure is disclosed that comprises a rear bumper beam, a spare tire, and a pair of rear rails. The rear rails each have a rear segment vertically aligned with the bumper, and a middle segment vertically offset above the rear segment. The diameter of the spare tire is vertically aligned with the bumper beam. In a rear-end collision, the spare tire rotates with the rear segment to move a rear portion of the spare tire downwardly below the rear bumper beam. 
         [0007]    According to another aspect of this disclosure, a vehicle body structure is disclosed for absorbing a load in a rear-end collision. The vehicle body structure comprises a bumper beam that receives the load and two rear rails that each includes a rear segment and a middle segment disposed above the rear segment. A spare tire is disposed between the rear rails. The load from the rear-end collision bends the rear rail at a juncture of the middle segment and rear segment to move a rear portion of the spare tire downwardly below the middle segment. 
         [0008]    According to yet another aspect of this disclosure, a vehicle body structure is disclosed for absorbing a load in a rear-end collision. The vehicle body structure includes a bumper beam that initially receives the load and a pair of rear rails that are attached to the bumper beam. The rear rails each include a middle segment disposed above the front segment. The load from the rear-end collision raises the rear rail at a juncture of the middle segment and the front segment to reduce the extent of intrusion into a passenger compartment area. 
         [0009]    According to other alternative aspects of this disclosure, the rear rail may include a front segment that extends from the middle segment to the rocker panel that is disposed below the vertical level of the bumper. A bend may be formed in the rear rail where the front segment and middle segment meet, wherein in a rear collision the middle segment is configured to be driven upwardly at the bend. The vertical center of gravity of the spare tire is disposed below the middle segment. 
         [0010]    The cross-sections of the front segment, the middle segment and the rear segment of the rear rail may be the same. A bend may be provided at the juncture of the front rail segment and the middle segment that creates a stress riser that predisposes the middle segment to be raised in a rear-end collision. A second bend may be provided at the juncture of the rear rail segment and the middle segment that creates a stress riser that predisposes the rear rail to bend in a downward hinging motion relative to the middle segment in a collision. 
         [0011]    The spare tire may be disposed in a horizontal plane that rotates in a rear-end collision to a position with a rear-end of the spare tire being moved below a front end of the tire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a fragmentary side elevation view of a vehicle showing a prior art rear rail, wheel housing and bumper assembly. 
           [0013]      FIG. 2  is a fragmentary side elevation view of a vehicle showing a rear rail made according to this disclosure, wheel housing and bumper assembly. 
           [0014]      FIG. 3  is a fragmentary bottom perspective view of the vehicle showing a rear rail made according to this disclosure, wheel housing and bumper assembly. 
           [0015]      FIGS. 4A-4D  are a series of side elevation views of the vehicle showing a rear rail made according to this disclosure, wheel housing and bumper assembly at four different time intervals during a rear-end collision. 
           [0016]      FIG. 5A  is a bottom plan view of the prior art design shown in  FIG. 1  after a rear-end collision. 
           [0017]      FIG. 5B  is a bottom plan view showing a rear rail made according the embodiment of  FIG. 2  of after a rear-end collision. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The illustrated embodiments are disclosed with reference to the drawings. However, it is to be understood that the disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed are not to be interpreted as limiting, but as a representative basis for teaching one skilled in the art how to practice the disclosed concepts. 
         [0019]    Referring to  FIG. 2 , a vehicle body generally indicated by reference numeral  10  is partially shown including the rear bumper beam  12 , or bumper, a spare tire compartment  16 , a rear rail  18  and a wheel housing  20 . Modifications in the disclosed design compared to the prior art structure shown in  FIG. 1  relate to the structure of the rear rail  18 . The rear rail  18  includes a front/rear rail  22 , or front segment, a mid/rear rail  24 , or middle segment, and a rear/rear rail  26 , or rear segment. 
         [0020]    The front segment  22  extends from a rocker panel  28  to the middle segment  24 . The middle segment  24  extends from the front segment  22  in a horizontal direction to the rear segment  26 . The middle segment  24  in the illustrated embodiment of  FIG. 2  is 171 mm above a centerline of the frame of the passenger compartment. A front/mid bend  30 , which may also be referred to herein as a front juncture or a front stress riser, is provided between the front segment  22  and the middle segment  24 . A spare tire  32  is shown in phantom lines in  FIG. 2 . 
         [0021]    A mid/rear bend  36 , which may also be referred to as a mid/rear juncture or rear stress riser herein, is provided at the juncture of the middle segment  24  and the rear segment  26 . In the improved design, the fuel tank  38  is located between the wheel housings  20  in the area of the front segment  22 , the front/mid bend  30  and the middle segment  24 . With the fuel tank being located further rearward in the vehicle compared to the prior art (as shown in  FIG. 1 ), there is a greater need for added crush space between the fuel tank  38  and the rear bumper beam  12 . 
         [0022]    Referring to  FIG. 3 , the rear portion of the vehicle  10  is shown that includes the rear bumper beam  12  and the spare tire compartment  16 . The rear rail  18  is shown to include the front segment  22 , middle segment  24 , and rear segment  26 . The rear rail  18  spans the wheel housing  20  and is connected on its front end to the rocker panel  28 . A front stress riser  30  is provided between the front segment  22  and middle segment  24  and a rear stress riser  36  is provided between the middle segment  24  and the rear segment  26 . 
         [0023]      FIG. 3  is a bottom perspective view and shows a rear sub-frame arm  40  that is connected between a front sub-frame arm connector  42  and a rear sub-frame arm connector  44 . The front sub-frame connector  42  is secured to the rear rail  18  near the rocker panel  28 . The rear sub-frame arm connector  44  is connected to the rear rail  18  just in front of the rear stress riser  36 . The rear sub-frame arm  40  provides additional strength and reinforces the rear rail  18  in an area spanning the front segment  22  and the middle segment  24 . The rear sub-frame arm  40  reinforces the rear rail  18  in front of the rear stress riser  36  and facilitates allowing the rear segment  26  to hinge downwardly in a rear collision, as will be described more specifically below with reference to  FIGS. 4A-4D . 
         [0024]    Referring to  FIG. 4A-4D , a series of CAE simulations of a rear collision applied to the vehicle body shown in  FIG. 2  is illustrated.  FIG. 4A  depicts the rear rail assembly at 0 milliseconds, prior to the rear end collision.  FIG. 4B  shows the rear rail structure at 20 milliseconds,  FIG. 4C  shows the rear rail structure assembly at 60 milliseconds, and  FIG. 4D  shows the rear rail assembly at 120 milliseconds after the rear end collision. 
         [0025]    The portions of the vehicle illustrated in  FIGS. 4A-4D  include the rear rail  18 , the wheel housing  20  and the rear bumper  12 . The rear rail includes the front/rear rail  22 , mid/rear rail  24  and rear/rear rail  26 . The front/mid bend  30  is provided between the front segment  22  and the middle segment  24 . The mid/rear bend  36  is provided between the middle segment  24  and the rear segment  26 . 
         [0026]    Referring to  FIG. 4A , the spare tire compartment  16  extends from the rear end of the rear rail  18  to an intermediate location on the middle segment  24  prior to a rear-end collision. The passenger compartment is generally indicated by reference numeral  48  and is located above the rocker panel  28  and in front of the wheel housing  20 . 
         [0027]    Referring to  FIG. 4B , the result of the rear end collision is shown at the 20 millisecond point at which the rear bumper  12  is impacted and causes an initial bending at the rear stress riser  36 . At this point, the spare tire compartment  16  is shown as it begins to be rotated or hinged downwardly. 
         [0028]    Referring to  FIG. 4C , the result of the rear end collision is shown at the 60 millisecond point at which the offset at the front/mid bend  30  and the offset at the mid/rear bend  36  cause the rear rail to deform at the front stress riser  30  and the rear stress riser  36 . The spare tire compartment  16  including the spare tire  32  is rotated to move the rear portion  50  of the spare tire compartment  16  below the front portion  52  of the spare tire compartment  16 . 
         [0029]    Referring to  FIG. 4D , the result of the rear end collision is shown at the 120 millisecond point with the tire being rotated to a greater extent. The rear portion  50  of the spare tire compartment  16  is shown below the front portion  52  of the spare tire compartment  16 . Also as shown in  FIG. 4D , dual bends in the rear rail  18  cause the front/rear rail  22  to hinge relative to the rocker panel  28  causing the mid/rear rail  24 , or middle segment, to raise during the rear end collision event. Raising the mid/rear rail results in less intrusion into the passenger compartment  48  compared to the prior art, as shown in  FIG. 1 . 
         [0030]    Referring to  FIG. 5A , the vehicle  10  made according to the prior art design shown in  FIG. 1  is shown after a 50 mph 70% offset Movable Deformable Barrier (MDB) rear impact test. The spare tire  32  is shown to be compressed axially between the bumper beam  12  and the rear axle  53 . A front portion  54  of the spare tire  32  is shown engaging the rear axle  53  and a rear portion  56  of the spare tire  32  is shown being engaged by the bumper  12 . The spare tire  32  remains in a horizontal orientation aligned with the rear bumper  12 . The crush space between the original bumper location and the rear axle  53  in a simulated test was 254 mm. 
         [0031]    Referring to  FIG. 5B , the vehicle  10  made according to the embodiment of  FIG. 2  is shown after a 50 mph 70% MDB rear impact test. The spare tire is shown rotated (or hinged downwardly) with the front portion  54  of the spare tire  32  above the rear portion  56  of the spare tire  32 . The crush space between the original bumper location and the rear axle  53  in a simulated test was 371 mm. The increase in crush space with the embodiment of  FIG. 2  is predicted to be more than a 45% increase compared to the design shown in  FIG. 5A . 
         [0032]    The embodiments described above are specific examples that do not describe all possible forms of the disclosure. The features of the illustrated embodiments may be combined to form further embodiments of the disclosed concepts. The words used in the specification are words of description rather than limitation. The scope of the following claims is broader than the specifically disclosed embodiments and also includes modifications of the illustrated embodiments.