Abstract:
The front cover of a transport refrigeration unit includes a plurality of hinged access doors, with each door being formed of a pair of spaced thermoplastic olefin sheets with their edges being bonded along the entire periphery of the door to form a hollow space between the sheets without a need for foam. The edges are bonded by a thermoforming process which provides strength and rigidity to the door. Additional thermoforming bonds are made at locations other than the periphery to provide further strength and rigidity. A ribbing structure is formed in one of the sheets and extends around the periphery thereof. Further ribbing may extend transversely across the sheet in non-peripheral positions.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the art of transport refrigeration units and in particular to outer protective covers for such units. 
     A typical transport refrigeration unit of the type designed for mounting on the front face of a tractor trailer unit comprises a one piece, self-contained fully refrigerant charged, prewired, refrigerant/heating unit powered by a diesel engine. In such a design the evaporator fits into a rectangular opening in the upper portion of the trailer front wall. When installed, the evaporator section is located inside the trailer; and the condensing section is outside and on the front of the trailer. The condensing section consists of an engine-compressor drive package, condenser fan, condenser coil, radiator coil, control panel, relay module, refrigerant controls, piping, wiring and associated components. 
     Structural frame members support all of the components and facilitate attaching of the unit to the trailer front face. Also supported by the structural framework is an outer cover which includes the necessary air inlet and outlet openings for cooling, and doors which may be opened to provide access to the interior of the unit for maintenance and service. 
     The access doors may include both front and side doors which should be light in weight, having adequate structural strength so as to withstand significant impacts without being damaged structurally or cosmetically, and provide an attractive appearance. They should also have sufficient torsional stiffness to hold their shape and provide adequate sound damping capabilities. Generally a composite structure with a form inner core has been used to obtain these characteristics. The use of foam adds complexity and expense to the manufacturing process. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the invention, the doors of an outer cover of a transport refrigeration unit are formed of inner and outer sheets of plastic material that are bonded by a thermoforming process at their edges to form a rigid composite structure with a hollow space between the two sheets. 
     In accordance with another aspect of the invention, the doors are made from a thermoplastic olefin material to provide superior strength and improved sound damping characteristics without the need for foam. 
     By another aspect of the invention, in addition to the edges, the inner and outer sheets are bonded at select other locations to provide improved strength and rigidity capabilities without the need for foam. 
     In accordance with another aspect of the invention, the inner sheet of a door has a plurality of C-shaped cross sectional ribs disposed therein to provide increased torsional stiffness and strength to the door. 
     In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a transport refrigeration unit having the front doors open and being fabricated in accordance with the present invention. 
         FIGS. 2A and 2B  are rear and front views of a curb side outer door in accordance with one aspect of the present invention. 
         FIG. 3  is a sectional view thereof as seen along lines E-E of  FIG. 2A . 
         FIG. 4  is a sectional view thereof as seen along lines D-D of  FIG. 2A . 
         FIGS. 5A and 5B  are sectional and partial views thereof as seen along lines H-H of  FIG. 2A . 
         FIG. 6  is a sectional view thereof as seen along lines A-A of  FIG. 2A . 
         FIG. 7  is a sectional view thereof as seen along lines C-C of  FIG. 2A . 
         FIG. 8  is a sectional view thereof as seen along lines F-F of  FIG. 2A . 
         FIGS. 9A and 9B  are rear and front views of a curb side front door in accordance with one aspect of the present invention. 
         FIG. 10  is a sectional view thereof as seen long lines C-C of  FIG. 9A . 
         FIG. 11  is a sectional view thereof as seen long lines G-G of  FIG. 9A . 
         FIG. 12  is a sectional view thereof as seen long lines D-D of  FIG. 9A . 
         FIG. 13  is a sectional view thereof as seen long lines A-A of  FIG. 9A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1  a fragmentary front part of a large transport trailer  10  is shown with a transport refrigeration unit  11  according to the invention shown mounted on the front wall  12  of the trailer. For purposes of the present description the terms “roadside” and “curbside” will be used in describing various components of the refrigeration unit and its cover. As viewed in  FIG. 1 , the right hand side of the unit will be referred to as the roadside and the left hand side of the unit as the curbside of the unit. 
     With this reference, the unit as illustrated in  FIG. 1  has the curbside front door  14 , and, the roadside front door  16  of the unit cover in their closed positions but containing the inner structural components of the unit as well as some of the components of the refrigeration unit itself. Attachment of the refrigeration unit  11  to the trailer  10  is carried out by connection of an outer peripheral planar structural steel framework illustrated generally by reference numeral  20 . It should be appreciated that this framework is not normally visible when the unit is properly installed on a trailer unit, however for purposes of illustration, at least a portion of the structural framework is illustrated in  FIG. 1 . 
     All of the component assemblies which define the outer cover of the refrigeration unit  11  are mounted to the various structural components. Each of the doors forming the lower portion of the cover are made from a tough, light-weight composite material designed to resist rust, denting, warping, fading or peeling of their outer finish. Their construction will be described in more detail hereinbelow. These components include the front curbside door  14  and the front roadside door  16  previously referred to above. They also include the curbside outer door  15  and roadside outer door  17 . 
     The front doors  14  and  16  are vertically hinged at their respective outer edges to provide a large access opening at the front of the unit. The side doors  15  and  17  are vertically hinged at their rear edges such that they pivot open from front to back. Latches  18  and  19  are provided for latching and unlatching the front roadside door  16  and side roadside door  17 , respectively 
     The upper part of the unit cover comprises a rigid front grille member  40  and a flexible support structure  41  disposed in surrounding relationship therewith. The grille member  40  is positioned in overlying relationship with the condenser heat exchanger of the refrigeration unit and is provided with a large number of openings  42  therethrough to facilitate air flow for efficient heat transfer. The support member  41  is secured to the frame  20  and the front grille is fastened to the support structure  41  by appropriate fastening means as at  44 . 
     A cover bottom panel  25  is attached to the unit for purposes of closure and to improve the aesthetics of the unit. 
     It will be appreciated therefore that the door and grille components described above are designed to cooperate to fully enclose the refrigeration unit  11  to provide protection from the environment and road hazards and to aerodynamically and aesthetically enhance the unit. 
     Referring now to  FIGS. 2-8 , the features of the curbside outer door  15  will now be described. Rear and front views of the curbside outer door  15  are shown in  FIGS. 2A and 2B , respectively. The rear edge  51  of the door  15  is planar in form and is linked to the frame by hinges  52  and  53  such that the doors  15  opens in a front-to-back relationship to thereby provide easy access to the components therein. The front edge  54  of the door  15  has angled portions  56  and  57  and a planar portion  58  as shown. The bottom edge is shown at  55 . When the door  15  is in the closed position, the planar portion  58  abuts the outer edge of the curbside front door  14 , and the angled portions  57  and  58  abut the outer edges of the grille flexible element. The bottom edge  55  abuts a bottom cover. 
     A latch mechanism  59  is provided for locking the door  15  in its closed position or for unlocking the door  15  for purposes of opening the door by rotating it on its hinges  52  and  53 . 
     Near the top of the door  15  is an opening  61  which is provided for the purpose of accommodating the attachment of a fresh air exchange feature. 
     Considering now the construction of the door  15 , it is formed of an inner sheet  62  and an outer sheet  63  of a high strength plastic material such as thermoplastic olefin (TPO). The inner and outer sheets  62  and  63  are bonded together at their edges by a thermoforming bonding process. That is, along the entirety of each of the edges  51 ,  54  and  55 , the two sheets  62  and  63  are joined by thermoforming bonding so as to thereby provide a hollow space between the two sheets. The process of joining the two sheets in this manner is often referred to as “twinning”. 
     In addition to the twinning at the perimeter of the inner and outer sheets  62  and  63 , in order to provide structural rigidity and strength to the combination, the two sheets  62  and  63  are joined by a twinning process at certain locations within the perimeter of the door. These locations are indicated by the numerals  64 ,  66  and  67  in  FIG. 2A . 
     As will be seen in  FIG. 3 , at the periphery of the opening  61 , the inner and outer sheets  62  and  63  are joined, or twinned, around the entire periphery of the opening  61  as shown by the rib at  64 . 
     Near the central area of the structure, it will be seen in  FIG. 2A  that the twinning rib as shown at  66  extends substantially ⅓ of the length of the structure. This can be seen in the cross-sectional view of  FIG. 4 . Because of the central location and the length of the twinned rib  66 , this rib adds substantially to the strength and rigidity of the combination. 
     In the area framing the latch mechanism  59 , the two sheets  62  and  63  are joined by the continuous twinning rib  67  as shown in  FIGS. 5A and 5B . 
     In addition to the twinning rib as described hereinabove, the inner sheet  62  also has a built in rib structure  68 , having a C-shaped cross section which is provided around the entire perimeter (i.e. inwardly offset from each of the edges  51 ,  54  and  55 ). This rib structure  68  is shown in  FIGS. 3 ,  4  and  5  as described hereinabove, as well as in  FIGS. 6 ,  7  and  8 . 
     In addition to the continuous perimeter rib structure  68  as described hereinabove, horizontal rib structures  69 ,  71  and  72  have the same C-shaped cross section as the rib structure  68  and add further strength and torsional rigidity to the combination. 
     Having described the curbside outer door  15 , the curbside front door  14  will now be described. The door  14  is shown from the inner side and outer side in  FIGS. 9A and 9B , respectively. 
     The curbside front door  14  has an outer edge  73 , an inner edge  74 , a top edge  76  and a bottom edge  77 . Similar to the curbside outer door  15  as described hereinabove, the front door  15  comprises an inner sheet  78  and an outer sheet  79  which are joined, or twinned together at their edges  73 ,  74 ,  76  and  77  to form a rigid hollow structure. Again, the edges are formed along their entire length by a thermoforming bonding process. Again, the material is a plastic material and preferably a thermoplastic olefin (TPO). 
     Located near the outer edge  73  is a pair of spaced hinges  81  and  82  for pivotally attaching the door  14  to the frame of the cover. Both the curbside outer door  15  and the roadside outer door (not shown) are hinged at their outer edges such that their inner edges  74  open forwardly. The lip  83  on the inner edge  74  extends inwardly and mates in an overlapping relationship with a similar lip on the roadside front door, with the curbside front door closing first and the roadside door having its lip overlapping the lip  83  of the curbside front door  14 . A latch on the roadside front door secures the two doors in the closed position and allows them to be opened for purposes of gaining access to the internal components. 
     In addition to the twinning at the perimeter of the door  14 , there are additional twinning ribs established at locations other than the perimeter as shown at  84  and  86 . The twinning rib  84  is disposed horizontally and extends about half way across the width of the door  14 . The cross sectional view of this rib  84  is shown in  FIG. 10 . 
     The twinning rib  86  is disposed vertically, and is located near the outer edge  73  as shown in  FIG. 9A . The cross-sectional view of the twinning rib  86  is shown in  FIG. 11 . 
     Similar to the twinning rib in the curbside outer door  15 , the twinning ribs  84  and  86  provide torsional rigidity and strength to the curbside front door  14 . 
     In order to provide further torsional stiffness and strength to the front door  14 , a rib structure  87  having a C-shaped cross section is provided near the periphery (i.e. spaced inwardly from the edges  73 ,  74 ,  76  and  77 ) as shown in  FIG. 9A , in a manner similar to that of the rib structure of the curbside outer door as described hereinabove. These ribs  87  are shown in cross-sectional views in  FIGS. 10 and 11  as described hereinabove, as well as in  FIGS. 12 and 13 . 
     Only the curbside doors have been described above. However, it should be understood that the roadside doors are substantially the same and therefore, the discussion should be considered relevant to them as well.