Abstract:
A temperature controlled railroad freight car ( 20 ) including an air flow conduit ( 98 ) and a related plenum ( 52 ) for distributing conditioned air from a refrigeration and heating unit ( 64 ) on an end wall ( 44 ) of the freight car ( 20 ), and a floor structure ( 40 ) that contributes to temperature control in a cargo space within the car ( 20 ). A diverter directs a flow of air upward into an inlet end of the plenum ( 52 ) and allows the flow to expand gradually within the plenum ( 52 ), smoothing the flow of air as it enters the plenum ( 52 ) so that it continues effectively at sufficient rates over the length of the car ( 20 ). The car ( 20 ) may include a subfloor ( 38 ) of composite construction, supporting a floor ( 40 ) that includes several tubular metal segments through which air can flow longitudinally of the car ( 20 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present application relates to temperature controlled railroad freight cars, and particularly to railroad freight car body structures incorporating air duct arrangements for circulation of air from a refrigeration or heating unit to various locations within a body of such a car while maximizing available cargo space. 
         [0002]    Temperature controlled railroad boxcars are well known, and have long used mechanical refrigeration and heating units mounted on an end wall, primarily to deliver chilled air to the interior of the car. For simplicity, the term refrigeration unit will be used herein to refer to refrigeration units, heating units, or units capable of both heating and cooling. Air from a refrigeration unit is typically forced into one end of an upper plenum extending longitudinally overhead, near the roof of the car, to deliver the conditioned air throughout the car to maintain a desired temperature throughout the cargo space in the car body. Such plenums in the past have intruded down into otherwise useable cargo space more than is desired, in order to assure sufficient air flow throughout the car body. This downward projection has also made the plenum vulnerable to damage from lift trucks moving cargo within such cars. 
         [0003]    Typically, an air circulation pattern in such a temperature-controlled car includes flow of air down from the upper plenum onto and along the sides of the cargo and the end wall of the car that is remote from the refrigeration and heating unit. Air returns along the floor to a return air intake plenum leading back up along the near end wall to the refrigeration unit. 
         [0004]    As railroad car sizes have increased it has become increasingly difficult to ensure even distribution of air throughout a railroad freight car, as needed in order to avoid uneven cooling that could damage parts of a sensitive cargo. A factor contributing to such difficulty is the desire to provide as much useable cargo space as possible within a boxcar whose size is limited by clearance along rights-of-way where the car is intended to be used. 
         [0005]    Another factor in the design of such railcars is the need to avoid excessive car weight, which would limit the weight of cargo that could be carried and add to the cost of fuel used in hauling the car. 
         [0006]    In view of these factors, it is desired to provide the necessary air circulation flow and distribution through an upper plenum that is no larger than necessary, so that it takes as little as possible of the potential cargo space within a refrigerated boxcar body, is out of the way of lift truck uprights and the like, and is not unnecessarily heavy. 
         [0007]    Along with larger cars has come the desire to use larger lift trucks to quickly load and unload such cars. Lift trucks now in such use are rated at up to 60,000 lb (27240 kilograms) per axle. It is therefore also desired to provide for such a car a floor structure that provides sufficient strength and aids efficient air circulation and thermal conduction to or from the cargo, and yet does not contribute excessive weight to the car. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides an answer to the aforementioned need for improved distribution of conditioned air within the cargo space of a temperature-controlled railroad freight car, as defined by the claims which follow. 
         [0009]    In particular, in one preferred embodiment of the present invention an air outlet port from a refrigeration unit extends through an opening in an end wall of a railroad freight car body at a distance beneath a ceiling height and is interconnected with an inflow end of an upper plenum extending closely along the ceiling toward an opposite end wall of the car body. A diverter extends slopingly upward, from a location near a lower side of the air outlet port of the refrigeration unit, into the inflow end of the plenum, smoothly directing a flow of air from the outlet port of the refrigeration unit into the inflow end of the upper plenum. The diverter preferably includes an upper shoulder located at the inflow end of the upper plenum, defining a most constricted part of a path for the flow of air from the refrigeration unit, and an inner margin portion of the diverter extends away from the shoulder at a gently sloping angle, allowing the flow of air to expand slightly as it enters into the inflow end of the plenum. 
         [0010]    In a preferred embodiment of the invention, an upper deflector is also included and provides a smoothly curved concave surface defining part of the path for the flow of air. The upper deflector extends from an end wall of the car, adjacent the inlet opening, to an upper interior surface of the upper plenum, and also contributes to smooth flow of air from the refrigeration unit into the plenum. 
         [0011]    Smooth flow of air from the refrigeration unit into the upper plenum, combined with a smooth substantially unobstructed interior shape of the upper plenum, contributes to continued smooth flow of air throughout the upper plenum over the length of the temperature-controlled car, even in a car considerably longer than previously known refrigerated cars. 
         [0012]    As another aspect of the invention, one preferred embodiment includes an underframe of steel construction, a thermally insulating subfloor of composite materials, and a thermally conductive floor including a weight bearing conduit structure including several longitudinally extending parallel tubes, to carry air back toward the refrigeration unit from the far end of the car body. 
         [0013]    As a further aspect of the invention, one preferred embodiment of such a floor may include weight-bearing segments that fit interlockingly together side by side atop the subfloor. 
         [0014]    As yet a further aspect of the invention, one preferred embodiment of such a floor is arranged to facilitate cleanout and repairs in portions most likely to be damaged during use. 
         [0015]    The foregoing and other features of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0016]      FIG. 1  is a side elevational view of a temperature controlled railroad boxcar which includes one preferred embodiment of the present invention. 
           [0017]      FIG. 2  is a side elevational view of a portion near a first end of the car shown in  FIG. 1 , with the near side cut away to expose the interior of the car, showing a part of a pattern of flow of air from the refrigeration unit to the cargo space within the car and back to the refrigeration unit. 
           [0018]      FIG. 3  is a side elevational view of a portion near the other end of the car shown in  FIG. 1 , with the near side cut away to expose the interior of the car, showing another part of the pattern of flow of air from the refrigeration unit to the cargo space within the car and back to the refrigeration unit. 
           [0019]      FIG. 4  is a sectional view toward a first, or “A” end of the car, taken along line  4 - 4  of  FIG. 1 . 
           [0020]      FIG. 5  is a sectional view toward a second, or “B” end of the car, taken along line  5 - 5  of  FIG. 1 . 
           [0021]      FIG. 6  is an isometric view from a point above and to one side of the car shown in  FIG. 1 , and looking toward the “A” end of the car, showing a preferred arrangement of a plenum adjacent the ceiling of the car and an air discharge port for a refrigeration unit carried on the “A” end of the car. 
           [0022]      FIG. 7  is a view of a portion of  FIG. 2  at an enlarged scale, showing details of the inflow end of the upper plenum and associated structures. 
           [0023]      FIG. 8  is a partially cutaway sectional view, taken along line  8 - 8  in  FIG. 1 , showing a portion of the floor, subfloor, and subframe structures of the car. 
           [0024]      FIG. 9  is a view of a detail of  FIG. 8  at an enlarged scale, showing construction of an end wall and a side wall. 
           [0025]      FIG. 10  is a sectional view, at an enlarged scale, taken along line  10 - 10  in  FIG. 8 , showing a portion of the structure of the subfloor and floor of the temperature-controlled car. 
           [0026]      FIG. 11   a  is a sectional view taken along  11 - 11  in  FIG. 8  at an enlarged scale, showing the construction of the floor and subfloor of the car. 
           [0027]      FIG. 11   b  is a detail view at an enlarged scale of a portion of  FIG. 11   a , showing an area of intersection of a subfloor portion with a side wall of the car. 
           [0028]      FIG. 12  is an exploded view, at an enlarged scale, of portions of the extruded aluminum floor shown in  FIG. 11 . 
           [0029]      FIG. 13  is a partially cutaway top plan view of a longitudinally central portion of the car, showing provision for gaining access to the tubular structure of the floor for cleaning and repair. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Referring now to  FIGS. 1-8  of the drawings which form a part of the disclosure herein, a temperature-controlled railroad freight car  20  has an underframe structure  22  which may include a center sill  24 , a pair of side sills  26 , and a pair of body bolsters  28  each supported by a wheeled truck  30 . Cross-bearers  32  extend from the center sill to each of the side sills  26 , and crossties  34 , of lighter construction, extend similarly at spaced-apart locations between those of the body bolsters  28  and cross-bearers  32 . Longitudinal stringers  36  are spaced apart between the side sills  26  and center sill  24  and are carried by the bolsters  28 , cross-bearers  32  and crossties  34 , assisting in supporting a subfloor  38  and a floor  40  that rests on the subfloor  38 . An end sill  41  is located at each end of the car body, interconnecting the opposite side sills  26  that extend the entire length of the car between the end sills. 
         [0031]    Side walls  42  and end walls  44  and  46  are supported by the underframe and, extend upwardly above the floor  40  to a roof  48 . The subfloor  38 , end walls  44 ,  46 , side walls  42 , and roof  48  are of a thermally insulating construction. The floor  40 , inner faces of the side walls and end walls, a ceiling  50 , and an upper plenum  52  suspended beneath the ceiling  50 , define an enclosed cargo space  53 . Doorway openings  54  are provided in the side walls  42 , and may be closed by conventional insulated doors  56 . Construction of the side walls  42  and floor  40  may be largely conventional, in connection with one aspect of the car  20 . 
         [0032]    Preferably, as may be seen with reference also to  FIGS. 2 ,  3 ,  4  and  5 , the roof  48  of the car may be of composite construction, including a skin sheet  57  of corrugated sheet steel, for example  13  gauge steel panels pressed to the desired shape and welded together, and which is preferably cambered to promote runoff of precipitation. A layer  58  of thermal insulation material such as a closed cell plastic foam is fastened to the skin sheet  57  and may have a depth  60  of about six inches (7.6 cm), below which smooth ceiling panels  62  of fiber reinforced plastic are located. 
         [0033]    In a preferred embodiment of the temperature-controlled railcar  20 , the roof  48  is manufactured as an assembly of composite materials that can be placed atop and fastened to the end walls  44 ,  46  and side walls  42  as a single module during the process of assembling the car  20 . A fiber-reinforced polymeric resin liner including the substantially flat ceiling panels  62  of fiber reinforced plastic is attached to the skin  57  to form an enclosed space between the skin  57  and the liner. That space is filled with poured-in-place urethane foam insulation and cured, with the roof  48  assembly held in a suitable press to maintain the required shape. 
         [0034]    A refrigeration unit  64  is mounted on the outer side of the end wall  44  at an “A” end of the car, and a fuel tank  66  for the refrigeration unit  64  may be supported by the underframe  22  of the car beneath the refrigeration unit. 
         [0035]    A refrigeration unit opening  68  is provided in the “A” end wall  44  to receive an inwardly directed portion of the refrigeration unit  64  and to permit air from within the cargo space  53  to enter into the refrigeration unit  64  through a lower portion of the refrigeration unit opening  68 , to be chilled or heated as may be needed, and to allow the refrigerated (or heated) air from the refrigeration unit  64  to be delivered into the car for distribution as necessary within the cargo space  53 . The top  70  of the refrigeration unit opening  68  is spaced downward a distance  72  such as 1 inch (2.5 cm) beneath the height of the ceiling  50 . The refrigeration unit opening  68  may have a height  74  of 46 inches (116.8 cm), for example, in order to accommodate any of various commercially available refrigeration units. 
         [0036]    An upper, or air inlet opening portion  76  of the refrigeration unit opening  68  extends down to the structure of the top  78  of a return air plenum  80  extending up from the floor  40  along the interior of the end wall  44 . Air can return through the return air plenum  80  to the supply air opening  82  or intake of the refrigeration unit  64 . The upper or air inlet opening portion  76  of the refrigeration unit opening  68 , above the top  78  of the return air plenum  80 , receives the air outlet port  84  of the refrigeration unit, from which a flow of air proceeds toward the interior of the cargo space  53  within the car body  20 . The air outlet port  84  is defined by the refrigeration unit  64  and may have, for example, a height  86  of 4⅞ inches (11.9 cm) and a width  88  of 30 13/16 inches (78.1 cm) in a refrigeration unit available from the Carrier Corporation. 
         [0037]    A general pattern of air circulation is shown by the arrows  89  in  FIGS. 2 ,  3 ,  6 , and  7 . The upper plenum  52  extends along the underside of the ceiling  50  from a location adjacent the “A” end wall  44  of the car toward the opposite, or “B”, end wall  46  of the car. Bottom panels  90  and side panels  92  of the upper plenum  52  are perforated, beginning from a point a predetermined distance  94 , such as 8 feet, from the “A” end wall and thence along the length  96  of the upper plenum  52  to a location near the “B” end wall  46 . Perforations may be circular holes 1 inch (2.5 cm) in diameter arranged in line with center-to-center spacings  99  of 6 inches (15.2 cm) in the side panels  92 , as shown in  FIG. 2 , in one preferred embodiment. In the plenum bottom panel  90 , the holes  97  may be arranged in staggered transversely extending rows with holes spaced apart by a distance  99 ′ of about 14¾ inches (37.5 cm) in a row and with rows spaced apart by a distance  99 ″ of about 18 inches (45.7 cm), as shown in  FIG. 6 , to allow air to escape from the upper plenum  52  in an evenly distributed fashion. 
         [0038]    A conduit  98  extends downwardly along the interior side of the “B” end wall  46  toward the floor  40 , and passageways  100  are defined longitudinally through the floor  40  toward the “A” end beneath cargo (not shown) that may be resting on the floor  40 , to complete a circulation route for air, collecting and leading the flow of air back toward the “A” end of the car body after it has absorbed heat from the cargo and from the ceiling  50 , walls  42 ,  44 , and  46 , and floor  40 . The return flow of air through the floor  40  makes that air available near the “A” end of the car  20  to be drawn into the refrigeration unit  64  and again chilled for circulation again within the cargo space. Air which has escaped from the upper plenum  52  through the perforations described above flows over the upper surfaces and along the side surfaces of cargo contained in the cargo space  53 , and is then conducted forward within the car, along the floor  40  and at least partially through the air passageways  100 , toward the “A” end. The return air plenum  80  receives the forward-flowing air from the passageways  100 , or through openings  101  in the sides of the return air plenum  80 , and conducts it into the supply air, or intake, opening  82  of the refrigeration unit. 
         [0039]    The ceiling  50  is preferably adhesively attached to the underside of the roof  48  as an integral part thereof, and is preferably constructed of generally flat horizontal panels  62  of fiber reinforced polymeric resin, which can be amply stiff, are of lighter weight than previously utilized metal ceiling panels, and can be interconnected with each other in smooth joints, providing a generally smooth and flat ceiling surface as the upper interior surface of the upper plenum  52 . 
         [0040]    The bottom panels  90  of the upper plenum  52  are similarly flat and located parallel with the ceiling panels  62 , providing a wide plenum with smooth interior surfaces and a smaller height than that of similarly located plenums in previously known cars. The height  102  of the upper plenum  52  is preferably less than 4 inches (10.2 cm) and more preferably is about 3 15/16 inches (10.0 cm), while the width  104  of the upper plenum  52  is preferably relatively great, to spread the flow of air over the width of the cargo space, and may, for example, be about 88 13/16 inches (225.6 cm). 
         [0041]    In a preferred embodiment of the upper plenum  52 , the bottom panels  90  of the plenum are of a stiff fiber reinforced resin sheet material having a nominal thickness of 0.075 inch (0.19 cm) and the sides  92  of the upper plenum  52  are of easily flexible urethane resin sheet material adhesively attached to the ceiling  50  and the plenum bottom panels  90 . A central support web or a plurality of small support strips  106  of similar flexible material may be used to support the median portions of the plenum bottom panels  90 , although the plenum bottom panels  90  are preferably rigid enough to be largely self supporting and remain substantially flat and parallel with the ceiling  50 . The flexibility of the plenum sides  92  and support strips  106  permits the bottom panels  90  simply to move up if bumped by a lift truck or cargo during loading or unloading of the car, and to move back down into place undamaged when the offending item has been removed. The car  20  may be constructed to provide an interior height of 11 feet, 9 inches (3.58 m) between the floor  40  and the upper plenum  52 , while remaining within the limitations of AAR Plate F and providing acceptable thermal insulation. 
         [0042]    The conduit  98  defined along the “B” end wall  46  for downward flow of air has a cross sectional area which is smaller than that of the interior of the upper plenum. While the conduit  98 , as shown in  FIG. 5 , extends across most of the width  148  of the “B” end wall  46 , a vertical conduit wall  107  is spaced apart from the interior surface of the insulated “B” end wall of the car by a distance  108  of, for example, only 1½ inches (38 mm), which is about one-third the height  102  of the upper plenum  52  mentioned previously. The flow of air down through the conduit  98  along the interior face of the “B” end wall  46  is thus comparatively restricted, generating some back pressure against the flow of air through the upper plenum  52  and requiring some of the flow of air into the upper plenum  52  to flow out of the upper plenum  52  through the perforations in the sides  92  and bottom panels  90  of the upper plenum. 
         [0043]    Nevertheless, in order for the air to be distributed as evenly as is necessary throughout the interior of the cargo space  53  within the car  20 , it is desired for the flow of air through the upper plenum  52  to proceed unimpeded and smoothly toward the “B” end of the car. 
         [0044]    Because of the location of the air outlet port  84  in the refrigeration unit  64 , the top of the air outlet port  84  is spaced downward from the top  70  of the refrigeration unit opening  68  in the “A” end wall  44  of the car body by a distance  109  of about 2 inches (5.1 cm). Because the height  86  of the air outlet port  84  of the refrigeration unit  64  is greater than the height  102  of the upper plenum  52 , the bottom  110  of the air outlet portion  84  is thus located at a distance below the ceiling  50  and also below the plenum bottom panel  90 . In order to promote the desired smooth flow through the interior of the upper plenum  52 , the flow of air from the air outlet port  84  through the end wall  44  at the “A” end of the car  20  must be diverted upward to the inflow end  112  of the upper plenum  52 , but diversion must be accomplished without causing turbulence that would interfere with the flow of air through the interior of the upper plenum  52  toward the opposite, or “B”, end of the car  20 . Accordingly, a diverter  114  is mounted atop a transverse structural member  116  that extends across the width of the interior of the car at the top of the return air plenum  80  at the “A” end, as may be seen in  FIGS. 4 ,  6 , and  7 . 
         [0045]    A preferred embodiment of the diverter  114  includes a narrow base flange  118  mounted upon and attached to the transverse structural member  116  and extending away from the “A” end wall  44 . An upwardly sloped front face portion  120  extends from the base flange  118  toward the ceiling  50  and away from the interior face of the end wall  44  at the “A” end, at an angle  121  preferably in the range of 40°-60° and most preferably equal to about 45° to the plenum bottom panel  90 . An uppermost portion of the diverter  114 , at the top of the front face portion  120 , defines a shoulder  122 , and beyond the shoulder  122  an inner margin portion  124  extends further away from the “A” end wall  44  into the inflow end  112  of the upper plenum  52 , extending away from the shoulder  122  at a gentle downward slope, such as an angle  125  in the range of 3-6 degrees and preferably of about four degrees to the plenum bottom panel  90 . The shoulder  122  and the inner margin portion  124  may be considered to be a flow transition portion of the diverter  114 . 
         [0046]    A flow of air from the outlet port  84  of the refrigeration unit  64  is forced to follow the sloping front face  120  of the diverter  114  upward to and through a most restricted area, or throat, near the inflow end  112  of the upper plenum  52 , at the location of the shoulder  122 . The available area for flow of air into the upper plenum  52  then expands gradually along the gently sloping inner margin portion  124  toward the interior of the upper plenum  52  and the “B” end of the car  20 . A blocking panel  123  aligned with each side panel  92  seals the space above the diverter  114  to the upper plenum  52  at each side. 
         [0047]    Preferably, in addition to the diverter  114  an upper deflector panel  126  is also provided and extends generally horizontally from the interior face of the “A” end wall toward the “B” end wall from the top of the refrigeration unit opening  68  defined through the “A” end wall  44 , thus at a small distance beneath the ceiling  50 , to a location approximately above the interior face of the refrigeration unit  64  and the lower, front margin  128  of the diverter  114 . From that location, the upper deflector  126  extends arcuately upward and away from the “A” end wall  44  toward a location on the ceiling  50  at the inflow end  112  of the upper plenum  52 , in a downwardly facing, concave shape, appearing in side view in  FIGS. 2 and 7  as a partial cylinder. The upper deflector  126  thus aids in smoothly directing the flow of air from the outlet port  84  of the refrigeration unit  64  into the inflow end  112  of the upper plenum, and in gradually reducing the space available for the flow of air to a minimum located approximately at the location of the shoulder  122 . 
         [0048]    Both the diverter  114  and the upper deflector  126  may be of fiber reinforced plastic resin sheet material, in order to minimize the weight of the car  20 . 
         [0049]    As a result of the arrangement of the diverter  114  and upper deflector  126 , the air from the refrigeration unit  64 , which initially flows generally horizontally from the outlet port  84 , is diverted upward by the sloping front face  120  of the diverter  114 . The flow of air is shaped further by the concave lower face of the upper deflector  126 , and is then redirected to a horizontal flow into the inflow end  112  of the upper plenum. The flow is slightly constricted by the shoulder  122  at the top of the forward face of the diverter  114  and is thereafter allowed to expand gradually as it accelerates and proceeds along the gently sloping inner margin portion  124  of the diverter  114  as shown by the arrow  127 . The air thus moves smoothly in a suppressed turbulent state in a generally horizontal direction through the upper plenum  52  toward the “B” end of the car body as it leaves the diverter  114 . This construction permits an interior length of the cargo space  53  of as much as 72 feet, 3 inches (22.02 m) between the conduit  98  at the “B” end and the return plenum  80  at the “A” end. 
         [0050]    Since the upper plenum  52  is essentially airtight near the input end  112  and for a distance toward the “B” end of the car, until the pattern of perforation is encountered, a distance  94  of about 8 feet from the end wall  44  at the “A” end of the car  20 , the flow of air continues within the upper plenum  52  toward a region of gradually decreasing pressure extending toward the “B” end, created as air is exhausted from the upper plenum  52  through the perforations along the sides  92  and bottom panel  90  of the upper plenum  52  to flow over and around cargo toward the floor  40 . Because the interior surfaces of the plenum  52  are generally planar and smooth, rather than being obstructed by raised joints or ribs extending transversely across the upper plenum  52  to provide stiffness as in previously utilized ceiling panels and plenum panels, the smooth flow of air continues from the “A” end to the “B” end of the car body relatively free from turbulence. 
         [0051]    Referring to  FIGS. 8 and 9 , each side wall  42  rests atop and extends upwardly from a respective one of the side sills  26 , with a sheet steel outer skin sheet  131  supported by a plurality of upright side posts  132  spaced apart at intervals between corner posts  134 . A doorway frame  136  is incorporated, and all of the side posts  132 , corner posts  134  and doorway frame members  136  are securely fastened to the outer skin sheet  131  as by welding. The end walls  44  and  46  also include steel skin sheets  131  and extend upward to join the roof  48  at each end of the car  20 . As an interior face of each side wall  42 , corrugated fiber-reinforced plastic panels  138  are fastened, as by suitable adhesives or nails, to nailing strips  140  of non-metallic material fastened, as by bolts or other suitable fasteners, to each of the side wall posts  132 . Flat interior panels  137  are mounted in the end walls  44  and  46 . Spaces within the side walls  42 , between the skin  131  and panels  138  are preferably filled with foamed-in-place insulating foam resin  139 , such as closed cell urethane foam, and the spaces between the skin  131  and interior panels  137  of the end walls  44  and  46  are filled preferably with foam blocks. 
         [0052]    At the top of each side wall  42  and extending longitudinally along the entire length  141  of the car body  20  is a top chord assembly  142  having an exterior structural layer  144  of sheet steel incorporating a horizontal leg, a downwardly angled diagonal leg, a small inwardly protruding L-shaped portion, and a downwardly extending leg that mates with and is parallel with outer sheet  131  of the side wall. The roof assembly  48  fits between the top chords  142  with the margins of the steel skin  57  of the roof extending above and along the horizontal portions of the top chord assemblies  142 . An arcuate wall closure panel  146  extends from the top of the wall  42 ,  44 ,  46  on the interior of the car, to the ceiling panel  62  defining the bottom side of the roof structure  48 , and the space between the wall closure panel  146  and the top chord outer structural member  144  is filled with insulating closed cell foam, preferably foamed in place. 
         [0053]    The upper plenum  52  extends to the “B” end wall  46  of the car body with a uniform interior height  102  and is there interconnected to the vertical conduit  98 , which carries the remainder of the air flow downward from the plenum  52  and along the interior face of the end wall  46  at the “B” end of the car body and connects the adjacent end of the upper plenum  52  to the end of the floor  40 . 
         [0054]    The floor  40 , as shown also in  FIGS. 10 and 11  is supported by the composite subfloor  38 , and includes a weight bearing tubular support structure  150  resting on and fastened to the subfloor  38  and defining the longitudinally extending parallel air pathways  100 . The tubular support structure  150  is unified and covered by a set of floor plates  152  connected to and extending over the entire length and width of the assembled tubular support structure  150 . 
         [0055]    As mentioned briefly above, the underframe of the car is preferably of welded steel construction. The stringers  36 , which may be steel I-beams, rest atop the transversely extending cross-bearers  32  and crossties  34 , and extend longitudinally, spaced apart from each other and parallel with the side sills  26  and center sill  24 , between the body bolsters  28  and between each body bolster  28  and the nearby end sill  41 . Preferably the stringers  36 , body bolsters  28 , and center sill  24  all include generally horizontal top surfaces that are all substantially coplanar, and the subfloor  38 , preferably of composite construction, rests atop those coplanar surfaces. 
         [0056]    In a preferred construction of the car body, the composite subfloor  38  includes a bottom panel  156  of fiber reinforced plastic resin, 0.1 inch (2.5 mm) thick, for example, and extends horizontally and rests atop the stringers  36  and center sill  24 , attached to their coplanar horizontal top surfaces by a suitable adhesive, such as Normount V2800 bonding tape. 
         [0057]    The bottom panel  156  of the subfloor  38  rests on an upwardly offset outwardly extending steel sheet margin mount  157  which rests atop upper flanges of the side sills  26 , as shown in  FIG. 11 . Rectangular support tubes  158  of fiber reinforced plastic, preferably about 5 inches (12.7 cm) high and 4 inches (10.2 cm) wide, with tube sidewall thickness  160  of ⅜ inch (9.5 mm) and top and bottom wall thicknesses  162  of ¼ inch (6.4 mm) extend transversely, across the width  148  of the car body, establishing a vertical spacing distance between the bottom panel  156  and top panels  166  of similar fiber-reinforced plastic resin material. The tubes  158  are spaced evenly apart from one another along the length of the interior of the car body, with a regular spacing  164  of, for example, eighteen inches (45.7 cm) center-to-center. The tubes  158  are filled preferably with closed cell polymeric resin foam, for example, a urethane foam having a density of 1.16×10 −3  lb/in. 3  (0.032 g./cm 3 ). The spaces between the tubes  158  are occupied by closed cell resin foam insulating material preferably having a similar density and preferably installed in the form of urethane foam blocks  167 . 
         [0058]    The fiber-reinforced plastic top panels  166  rest atop the rectangular tubes  158  and foam blocks  167  and are fastened to the rectangular tubes by adhesive bonding tape, such as Ashland Chemical 8000/6660. Each top panel  166  preferably extends the full width  148  of the interior of the car body and extends longitudinally a distance equal to a multiple of the spacing  164  of the transversely extending support tubes  158 , except for a smaller panel at each end of the car body, where the floor  40  and subfloor  38  would never be subjected to as great a weight loading as where a lift truck can be located inside the car  20 . At the base of each side wall  92 , flexible elastic filler and seal members  168 , seen best in  FIG. 11   b , are provided between a plastic resin spacer  169  at the base of the side wall  42  and the adjacent margins of the subfloor  38 . 
         [0059]    As may be seen in  FIGS. 11   a  and  12 , the floor  40 , resting atop the subfloor  38 , includes a top plate  152  resting on the tubular support structure  150  of weight bearing support elements defining parallel tubes  172  extending longitudinally along the subfloor  38  and functioning as the passageways  100  for flow of air from the “B” end of the car  20  toward the “A” end. 
         [0060]    A narrow channel  174  extends longitudinally along each side of the floor  40  at the base of the adjacent side wall  42 , and the floor  40  includes sets of holes  176  aligned with each other and extending laterally inward about one-third the width of the floor  40 , toward the central longitudinal axis of the car and communicating between adjacent passageways  100 . The sets of holes  176  are spaced apart along the length  141  of the car at regular intervals  178 , of, for example, one foot (30.5 cm), allowing air which has flowed downward within the cargo space  53  from the upper plenum  52  into the channel  174  to pass laterally inward into the parallel tubes  172  to be carried away longitudinally of the car body from the “B” end toward the “A” end of the car. 
         [0061]    The refrigeration unit return air intake plenum  80  is connected to the floor  40  at the “A” end of the car body to carry the air upward from the floor  40  and thus back into the intake opening  82  in refrigeration unit  64 . The floor  40  thus plays an integral part in forming the path for circulation of the air to maintain the desired temperature within the cargo space  53  and thus to protect the cargo carried within the car. 
         [0062]    The tubular support structure  150  of the floor  40  is preferably constructed as a group of extruded aluminum alloy segments  180 , each preferably including a pair of complete tubes  182 ,  184  and a pair of horizontal arms  186 ,  188  extending laterally from the tube  184 , one at the top and one at the bottom of the extruded segment  180 . The segments  180  could also be designed to have the arms extending in opposite directions away from the tubes  182 ,  184 , or to have only a single complete tube, or more than the two complete tubes  182 ,  184  of the segment  180  as shown herein. 
         [0063]    Each segment  180  thus includes three upstanding parallel load bearing side wall members  190 ,  192 ,  194  extending between and interconnecting a generally planar bottom member  196  with a generally planar top member  198  that is parallel with the bottom member. Each segment  180  may have a height of about 3 inches (76 cm), with each wall member  190 ,  192 ,  194  having a thickness of 3/16 (0.48 cm), and the top and bottom members each having a thickness of about ⅛ inch (0.32 cm), for a floor  40  designed to carry a loading of 60,000 lb per lift truck axle. The tube side wall members  190 ,  192 ,  194  are interconnected with the top and bottom members  196 ,  198  in smoothly radiused connection zones, making each parallel tube segment a rigid, strong structure, in which each of the upright side wall members  190 ,  192 ,  194  is a weight bearing member capable of transmitting forces between the top and bottom members  196 ,  198  and capable of withstanding lateral components of forces acting on the floor structure  40 . 
         [0064]    The segments  180  are designed to interlock with each other when properly placed alongside each other, so that the segments  180  lying parallel with each other can be securely integrated into a single unified floor  40 . This is preferably accomplished by providing a groove  200  along an upper shoulder of each segment  180 , adjacent an outer tube side wall  190 , and by providing a flange  202  having a sloping outer surface, extending out from the bottom of the same tube side wall  190 . At the opposite side, shown at the left of each segment in  FIG. 12 , the upper horizontal arm  186 , extending parallel with and as an extension of the top member  198 , includes a downwardly projecting rib  204  that fits interlockingly into the groove  200 . 
         [0065]    The lower horizontal arm  188  extends a slightly smaller distance away from the adjacent tube side wall  194  than does the upper arm  186 , and an upwardly sloping lip  206  is provided as the outer margin of the lower horizontal arm  188 . The lip  206  fits snugly against the sloping outer surface of the flange  202  of an adjacent segment  180  when the rib is engaged with the groove of that adjacent segment  180  and the two adjacent segments are both supported on a planar surface such as the top panel  166  of the subfloor  38 . As shown in  FIG. 11 , a number, for example four, of the parallel floor segments  180  having holes  176  through their tube side walls  190 ,  192 ,  194  are preferably aligned with one another, with the holes  176  aligned with one another along each lateral side of the floor. Air flowing through the tubes  172  of those segments  180  toward the “A” end can draw more air into the tubes  172 , by Venturi action, from the channels  174  along the sides of the floor  40 . 
         [0066]    Other segments  180 , for example six segments in the middle of the width of the floor  40 , are closed; that is, they have no holes  176  through the tube side wall members  190 ,  192 ,  194 , and each tube  172  of those parallel segments  180  forms a closed path extending from the conduit  98  at the “B” end of the car  20  to the “A” end and thence into the return air plenum  80  leading to the supply air intake  82  of the refrigeration unit  64 . 
         [0067]    Extending along the outermost elongate segment  180  along each longitudinally extending side margin of the floor  40  is a respective flanged hold-down member  208  or  210 , which may also be of extruded aluminum. A first, or right side hold-down member  208  corresponds to and mates with the tube side wall  190  on the closed side of a tubular segment  180 , while the other hold-down member  210  is of a different form, in order to mate appropriately with the two horizontal arms  186 ,  188  extending laterally from the side of a segment  180  at the opposite, or left side of the floor  40 , as shown in  FIGS. 11 and 12 . A first, or right side hold-down member  208  thus includes a short laterally extending arm  212  with a downwardly extending rib  214 , as well as a downwardly facing sloped surface  216 , near the bottom end of its upright portion, that fits matingly against the sloping outer surface of the flange  202  at the bottom of the tube side wall  190 . An adjoining horizontally outwardly extending fastening flange  218  that can be fastened to the subfloor  38  on which the floor is supported, using suitable mechanical fasteners, such as blind Huck™ fasteners  220  spaced appropriately apart along the length of the floor  40  and extending through the flange  218 , the top panel  166 , and the top flange of the adjacent support channel  221 , shown in  FIGS. 11   a  and  11   b . The channel  221  may be of fiber reinforced plastic filled with insulating foam and closes off the outboard ends of the transverse tubes  158 . 
         [0068]    At the opposite, or left, side of the floor  40  as shown in  FIG. 12 , a second, or left side, extruded hold-down member  210  serves both as a hold-down and as a weight bearing closure member for the segment  180  along which it is located. The hold-down member  210  in a preferred embodiment includes a pair of parallel upright members each similar in thickness to one of the tube side walls  190 ,  192 ,  194 . At a top end the left side hold-down member  210  includes a groove  220  to receive the downwardly facing rib  204  of the top horizontal arm  186  of an adjacent tubular floor segment  180 . An inner side of a base portion of the hold-down member  210  has a laterally extending rib  222  above an inner flange  224  with a sloping outer face similar to the face of the flange  202  on each segment  180 . The rib  222  and the sloping face of the inner flange  224  together define a groove for receiving the upwardly sloping lip  206  of the bottom horizontal arm  188  of the adjacent tubular floor segment  180 . A wider, outwardly extending fastening flange  226  extends laterally away from the base and serves to receive fasteners  220  to attach the left hold-down unit  210  to the subfloor preferably in the same fashion as the fastening flange  218 . Holes  176 ′ in the hold-down members  208 ,  210  are aligned with the holes  176  in the tube side walls  190 ,  192 ,  194  of the adjacent floor segments  180 . 
         [0069]    Atop the assembled group of tubular segments  180  and preferably seated in notches  228  in upper margins of the hold-down members  208 ,  210  are an array of top plate members  152 , preferably of metal such as aluminum plate embossed or rolled with a suitable non-skid surface. Alternatively, a stainless steel top plate  152  with a suitable non-skid surface, although heavier, might be used if preferred because of its better durability. The top plates  152  are also fastened to each of the several segments  180  of the tubular support structure  150  by suitable fasteners such as blind Huck™ fasteners  220  extending through corresponding openings in the floor top plates  152  and the top members  198  of the segments  180 , thus fastening together the adjacent tubular segments  180  of the floor  40  as a unified structure. 
         [0070]    In most portions of the floor  40  adjacent ones of the top plates  152  meet along joint lines spaced apart from the interconnects between adjacent tubular segments  180 . Smaller top plate sections  152 ′ are located adjacent the doorways  54  of the car  20 , as shown in  FIG. 13 . Each top plate section  152 ′ is removable, as by grinding away the head of its fasteners  220 , and the underlying tubular segments  180  are arranged with respective ends along transversely extending lines  234  and  236  to permit removal and replacement of tubular segments  180 ′ aligned with the doorways  54 , where floor damage is most likely to result, and to facilitate cleaning of the tubes  172 . Additionally, at each end of the car  20  smaller floor top plates  230  are supported on more widely spaced underlying channels  238  and are held by removable fasteners such as threaded bolts  232 , to facilitate cleanout of the tubes  172  of the tubular segments  180  after removal of the segments  180 ′. 
         [0071]    The terms and expressions that have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.