BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to school bus seats and more particularly to a structural member used to reinforce seat joints and thereby control the location and degree of deformation of the seat back upon rear impact by an object. 
         [0003]    2. Description of the Problem 
         [0004]    School bus seats are built to meet many differing customer specifications. For example, some bus seats must accommodate three point safety belts by providing a compatible upper back rest, other specifications call for a universal child restraint attachment equipped lower frame, while still others provide standard DOT (United States Department of Transportation) seat backs. Alternatively, customers can specify seats in different widths or heights and can demand various strength requirements. School bus passenger seats vary in height and width resulting in different seat back performance characteristics. FMVSS (Federal Motor Vehicle Safety Standard) 222 requirements dictate the seat back deflection be controlled to fall within a specified window of force versus deflection. The specified window has minimum as well as maximum limits for this deflection. 
         [0005]    Differing customers&#39; specifications have required substantially or entirely different component sets. The need to supply such component sets has even occurred relative to completed vehicles that have been put into service where the vehicle has been moved from one state or municipality to another, based on differing requirements of the new jurisdiction. The variability in size has contributed to varying component sets meant to meet strength standards. Multiple tubes, brackets and gussets are incorporated into welded seat assembly. Components were added to the various seat assemblies until the resulting design was compliant. Various seat widths and heights may use different hardware based on these changes. Therefore, seats have exhibited additional variation in component parts to meet the FMVSS 222 requirements. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides for placing the variability relating to seat back strength and the degree of allowed deflection under force to be focused into one reinforcement component. In a modular seat frame the seat back has its foundation in an aisle riser and a wall riser, and includes a perimeter frame provided by a partial perimeter tube mounted at opposed ends in necks extending from the aisle riser and wall riser. A reinforcement member fits into the neck/partial perimeter tube joint. The length of the reinforcement member can be varied, and the reinforcement member itself weakened at some point along its length to vary the strength and allowed deflection under rear impact of the seat back. In the preferred embodiment the length of the reinforcement member can be varied, as well as features such as holes can be added to limit the strength, and increase the amount of energy that is absorbed at the joint. It also allows control of where the bending takes place. This allows common frames to be used across height and width variation, with their resulting differences in the amount of loads that they will absorb. 
         [0007]    Additional effects, features and advantages will be apparent in the written description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0009]      FIG. 1  is a perspective view of a school bus. 
           [0010]      FIG. 2  is a perspective view of a prior art school bus seat frame. 
           [0011]      FIG. 3  is a perspective view of a modular school bus seat frame incorporating the present invention as installed in a vehicle. 
           [0012]      FIG. 4  is an exploded view of the school bus seat frame illustrated in  FIG. 4 . 
           [0013]      FIG. 5  is an exploded view of a joint between a riser and a seat back perimeter tube in which the reinforcement element of the present invention may be placed. 
           [0014]      FIG. 6  is a perspective view of the reinforcement element of the invention. 
           [0015]      FIG. 7  is an exploded view of a joint between a riser and a seat back perimeter tube illustrating an alternative location for positioning the reinforcement element during assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring now to the drawings and in particular to  FIG. 1 , a school bus  10  with which the present invention is advantageously used is illustrated. The seat frames of the present invention are installed in the interior  18  of the bus. 
         [0017]      FIG. 2  illustrates a prior art seat frame  20  in which a closed, multi-piece full perimeter tube  26 , which is closed on it self and forms an “L” outlining a base and seat back for the bus seat frame  20 . A full perimeter tube  26  is supported by an aisle riser  22  and a wall riser  24 . An internal frame  28  and a back seat support  30  are nestled within the closed perimeter tube  26 . Excluding the risers  22 ,  24 , virtually none of the components are reusable should seat specifications, such as width, or height of the seat back be changed. Internal frame  28  parallels portions of the perimeter tube  26 , reinforcing the sides of the perimeter tube and adding a seat back bottom brace  34  and a cross member  32  to give the frame  20  rigidity. 
         [0018]    Referring to  FIG. 3 , an assembled modular school bus seat frame  40  is illustrated supported in part from the floor  42  (shown in phantom) and along interior bus wall  44  (shown in phantom) from a chair rail  62  formed along the interior wall  44 . Support from the floor  42  is provided by an aisle riser  46 . Support from the wall  44  is provided by a wall riser  48 . Aisle riser  46  and wall riser  48  differ from the aisle risers and floor risers known from the art illustrated in  FIG. 2  in that they form more of the seat frame than is traditional in school bus applications. Both the aisle riser  46  and the wall riser  48  are modified to function as frame elements, in part by inclusion of necks  50  which provide bases of support for an open ended, partial perimeter tube  52  used to define the top and sides of a seat back portion of frame  40 . The partial perimeter tube  52  is an upside down U shaped structural member mounted at opposite ends in necks  50  and defines the top and sides of the seat back. Suspended on and within the partial perimeter tube  52  is a seat back panel  54 . Extending between and fitted into the aisle riser  46  and the wall riser  48  are front and back latitudinal supports  60  and  56 . Supports  56  and  60  come in varying lengths to support seats of varying widths and fit into the risers to form joints. Risers  46  and  48  are molded elements with interior (i.e. facing) sides which are contoured to reinforce the riser. 
         [0019]      FIG. 4  is an exploded view of the modular seat frame  40  which shows the major structural members of the seat frame. Necks  50  provide the location of the junction between the ends of the seat back perimeter tube  52  and the risers and are the locations where variable length reinforcement members  64  are located upon assembly of the seat frame  40 . Necks  50  are C-channel sections extending upwardly from the upper rearward areas of aisle riser  46  and wall riser  48  and formed during the stamping process used to fabricate the risers. The open faces of the necks  50  face one another. Partial perimeter tube  52  fits by its opposite ends into the necks  50 . The joints formed by joining the ends of the perimeter tube  52  to the necks  50  are reinforced by addition of reinforcement members  64  which fit into the neck  50  sandwiched between the tube  52  and the interior of the necks  50 . Bolts  66  are inserted through the walls of the necks  50 , reinforcement members  64  and the ends of perimeter tube  52  to complete the assembly. 
         [0020]    Back panel  54  includes a partial perimeter lip  74  by which the panel is attached to tube  52 . Risers  46 ,  48  include inner face contours  76  which position the ends of rear and front supports  56 ,  60 . Risers  46 ,  48  have integral inwardly turned flanges  78  along their top and front edges. In addition, risers  46 ,  48  have a back edge flange  71 , which are also inwardly turned. Flanges  71  and  78  provide surfaces against which opposite surfaces of the front and rear cross members  60 ,  56  may be placed to be secured by self pierce rivets (not shown), or other methods such as low temperature welding. Front cross member  60  is substantially formed in three panels, front panel  61 , intermediate panel  63 , and top panel  65  with panel  63  being intermediate to panels  61  and  65 . The angle between panels  61  and  65  corresponds to the angle between the front and top edge sections of flange  78 , allowing the cross member to be brought into contact with both portions of the flange concurrently. Panel  63  intersects both panels  61  and  65  obliquely along the respective interior side (i.e. the underside of the member relative to the risers) and positioned between the two panels functions as a cross brace between the flange  78  portions. 
         [0021]    Rear cross member  56  incorporates two major sections, a top section  57  and a back section  59 . The ends of top section  57  and back section are angled (essentially a right angle) to allow them flush mating of the sections to the under surface of the top portion of flange  78  and the forward surface of flange  71 . Self pierce rivets (not shown), glue or welding are used to connect the member to the riser. 
         [0022]    Aisle riser  46  includes legs which support the structure from the floor. A plate  68  is provided for securing fasteners between the riser  46  and a vehicle floor. Wall riser  48  includes an attachment lip  72  allowing securing of the wall riser to a wall support. Plate  68  and washer  70  are provided as part of the attachment process. 
         [0023]      FIGS. 5 and 6  illustrated the variable length reinforcement member  64  and its use to construct a joint having controllable deformation and flexure characteristics. As already noted, reinforcement member  64  fits sandwiched between the perimeter tube  52  and necks  50  of risers  46  and  48  (only riser  46  is illustrated, though the member would typically be used identically with riser  48 ). The length of the reinforcement members  52  can be varied, and features such as holes  92  can be added to limit the members&#39; strength, and increase the amount of energy that is absorbed at the joint. This further allows control of where bending takes place during a rear impact against the seat frame  40 . Frames  40  can now be built which exhibit variation in height and width, with the differences in loads that they experience under conditions of impact handled by changes in the reinforcement member  64 . The risers are typically an aisle riser  46  and a wall riser  48 , though nothing would prevent use of the invention with a full width seat using opposed wall risers or a seat built on two aisle risers. Hence, in the claims the risers are referred to as first and second risers without differentiation regarding which type of riser is used. 
         [0024]    In one embodiment, reinforcement member  64  is a three sided sleeve having opposed legs  90  and an open face, with examples positioned on the ends of perimeter tube  52  by welds  100 . After introduction of the ends of perimeter tube into risers  50 , the reinforcement member  64  is sandwiched between a lower riser stamping ( 46 ,  48 ) and the upper seat partial perimeter tube  52  with its open face aligned with the open side of the neck  50  in which it is situated. Thus the member  64  is located at the joint formed between the necks  50  and the ends of the partial perimeter tube  52 . It overlaps the tube  52  of the upper frame, and extends above the joint for a distance that is varied according to the loading characteristics that are required. It can also be extended downward. Holes  92  are provided through which bolts  66  can be positioned and which strategically weaken the reinforcement member  64  at the desired locations. Members  64  are positioned to align holes  92  with holes  122  (see  FIG. 7 ) through the ends of partial perimeter tube  52  and with holes  104  through the necks  50 . In the embodiment illustrated in  FIG. 5 , member  64  is also attached to tube  52  using spot MIG (Metal in Inert Gas) welds. In effect, the seat frame can be tuned for strength characteristics between the lower seat and the seat back frame, and the degree of allowed deformation controlled, with the use of only two reinforcement members. 
         [0025]      FIGS. 5 and 6  illustrated the variable length reinforcement member  64  and its use to construct a joint having controllable deformation and flexure characteristics. As already noted, reinforcement member  64  fits sandwiched between the perimeter tube  52  and necks  50  of risers  46  and  48  (only riser  46  is illustrated, though the member would typically be used identically with riser  48 ). The length of the reinforcement members  52  can be varied, and features such as holes  92  can be added to limit the members&#39; strength, and increase the amount of energy that is absorbed at the joint. This further allows control of where bending takes place during a rear impact against the seat frame  40 . Frames  40  can now be built which exhibit variation in height and width, with the differences in loads that they experience under conditions of impact handled by changes in the reinforcement member  64 . The risers are typically an aisle riser  46  and a wall riser  48 , though nothing would prevent use of the invention with a full width seat using opposed wall risers or a seat built on two aisle risers. Hence, in the claims the risers are referred to as first and second risers without differentiation regarding which type of riser is used. 
         [0026]    In its preferred embodiment, reinforcement member  64  MIG welded to the inside of neck  50  with its open side coinciding with the open side of the neck. Both neck  50  and reinforcement member  64  are three sided sleeves and an open face. Upon assembly, the reinforcement member becomes sandwiched between the lower riser stamping ( 46 ,  48 ) and the upper seat partial perimeter tube  52  as in the prior embodiment. Again the member  64  is located at the joint formed between the necks  50  and the ends of the partial perimeter tube  52 . It overlaps the tube  52  of the upper frame, and extends above the joint for a distance that is varied according to the loading characteristics that are required. It can also be extended downward. Holes  92  of the reinforcement member  52  are provided through which bolts  66  can be positioned and which strategically weaken the reinforcement member  64  at the desired locations. Members  64  are positioned to align holes  92  with holes  122  through the partial perimeter tube  52  and with holes  104  through the necks  50 . Member  64  is also attached to the inside of neck  50  using spot MIG (Metal in Inert Gas) welds. 
         [0027]    While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.
A modified seat frame provides a seat back frame mounting reinforcement which can be conveniently varied in length and strength to vary the allowed degree of deflection and energy absorption provided by the seat back upon rear impact.