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TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present invention is directed to an engine compartment hood, and method of assembly thereof, for an off road work vehicle.  
         BACKGROUND OF THE INVENTION  
         [0002]    Backhoe loaders are common off road work vehicles. These vehicles are provided with a front mounted loader and a rear mounted backhoe. The lift arms of the loader are pivotally mounted to a mast extending upwardly from the supporting structure of the vehicle. A hood covering an internal combustion engine is located in front of the mast. The hood typically comprises a structurally reinforced, sheet metal top panel. To service the engine, the hood is tilted to an open position.  
           [0003]    The top wall of a hood for a backhoe loader must be impact and dent resistant. It is not uncommon for the top panel to be impacted by a rock or other debris. The present inventors have recognized that it would be desirable to provide a top wall for a hood that was impact and dent resistant while being cost effectively manufactured. The present inventors have recognized that it would be desirable to provide such a top wall for the hood that maintains a smooth aesthetically pleasing outer contour, even during extreme temperatures.  
         SUMMARY OF THE INVENTION  
         [0004]    The invention provides a hood for an off road work vehicle, and a method of assembling the hood. The hood is preferably applied to a backhoe loader. According to one aspect of the invention, a hood for an off road vehicle includes a top wall that comprises: an outer panel and an inner panel secured to the outer panel, forming a substantially enclosed shell. Preferably, one or both the inner and outer panels are composed of thermoformable polymer.  
           [0005]    The outer and inner panels are configured to form a space between the outer and inner panels when assembled, the space having an open outlet and an open inlet, the space arranged to channel air from outside the hood to inside the hood.  
           [0006]    The inner panel can comprise a plurality of laterally extending corrugations, configured to add stiffness to the hood, particularly the top wall of the hood. The outer and inner panels are adhesively secured together around a substantial portion of a perimeter of at least one of the outer and inner panels by a substantially continuous pattern of adhesive having some regions applied in a non-linear pattern, such as a zigzag or otherwise undulating form, extending longitudinally.  
           [0007]    Preferably, the inner and outer panels are composed of GE Noryl GTX PPE/PA resin, and the adhesive is composed of Essex Betaseal U-216 two-compound urethane.  
           [0008]    The regions are applied in an undulating form correspond in distance, measured between peaks of the undulating form, to a distance between corrugations of the plurality of corrugations.  
           [0009]    The hood can include sidewalls fastened to the inner top panel and having a dominant outer surface oriented substantially vertically.  
           [0010]    The inner panel can comprise a plurality of protrusions, such as dimples, extending toward the outer panel, the dimples arranged to maintain a clearance between the inner and outer panels around the dimples. The clearance between the inner and outer panels provided by the protrusions can be used to regulate a thickness of the adhesive that is applied between the inner and outer panels.  
           [0011]    The invention provides a method of forming a hood structure for an off road work vehicle, comprising the steps of: thermoforming a plastic inner panel having raised formations thereon, thermoforming an outer panel having a smooth outer surface and a contoured edge region, applying adhesive in a pattern between the inner and outer panels, and holding the inner and outer panels together until the adhesive has adequately set.  
           [0012]    The step of applying adhesive is further characterized in that the adhesive is applied between the inner and outer panels longitudinally in a non-linear pattern along lateral edge regions of the inner panel. The non-linear pattern can comprise an undulating or zigzag pattern.  
           [0013]    The invention provides a top wall for a hood that is impact and dent resistant. The invention provides a top wall for a hood that is cost effectively manufactured. The invention provides a top wall for a hood that maintains a smooth aesthetically-pleasing outer contour, even during extreme temperatures.  
           [0014]    Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a diagrammatic elevational view of an off road work vehicle incorporating the hood of the present invention;  
         [0016]    [0016]FIG. 2 is a diagrammatic longitudinal sectional view of the hood of the off road work vehicle shown in FIG. 1;  
         [0017]    [0017]FIG. 3 is a front top perspective view of the hood shown in FIG. 2, separate from the work vehicle;  
         [0018]    [0018]FIG. 4 is a bottom rear perspective view of the hood shown in FIG. 3;  
         [0019]    [0019]FIG. 5 is a front top perspective view of an inner panel of a top wall of the hood shown in FIG. 3, separate from the rest of the hood;  
         [0020]    [0020]FIG. 6 is a bottom rear perspective view of the top wall of the hood shown in FIG. 5;  
         [0021]    [0021]FIG. 7 is a front top perspective view of an adhesive pattern used between the inner panel and an outer skin of the top wall of the hood shown in FIG. 3;  
         [0022]    [0022]FIG. 7A is a bottom view of the adhesive pattern of FIG. 7 superimposed on an outline of the underside of the outer skin; and  
         [0023]    [0023]FIG. 8 is an enlarged fragmentary perspective view of an underside of the hood.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.  
         [0025]    A work vehicle  10  is illustrated in FIG. 1 in the form of a backhoe loader. Such a work vehicle is described for example in U.S. Pat. Nos. 6,460,644 and 5,125,716 both herein incorporated by reference. The work vehicle  10  is provided with a supporting structure  12  and ground engaging means  14  comprising wheels, which support and propel the supporting structure  12 . Although the ground engaging means  14  on the illustrated embodiment are wheels, the present invention could also be used on tracked work vehicles having steel or rubber tracks. The supporting structure  12  is provided with a vertically extending mast  16 . A first work implement  20  comprising a loader is operatively mounted to the mast  16  and the supporting structure  12 . A second work implement  22  comprising a backhoe is mounted to the back  18  of the supporting structure  12 . The operation of the work vehicle  10  and the operation of the first and second work implements  20  and  22  are controlled from the operator&#39;s cab  24 .  
         [0026]    The loader  20  comprises lift arms  28  and a bucket  30 . The lift arms  28  are pivotally mounted to the mast  16  to pivots  26 . The lift arms  28  are provided with lift arm hydraulic cylinders  32  for lifting arms  28  relative to supporting structure  12 . The lift arm cylinders  32  are pivotally coupled to the supporting structure  12  at pivots  33 . The bucket  30  is pivotally mounted to the end of the lift arms  28 . The bucket  30  is provided with a bucket-tilt hydraulic cylinder  34  for tilting the bucket  30  relative to the lift arms  28 .  
         [0027]    An internal combustion engine, not shown, powers the work vehicle. The internal combustion engine is mounted to the front of the supporting structure  12 .  
         [0028]    As shown in FIG. 2, the front of the supporting structure  12  is also provided with upwardly extending support flanges  52 , shown in fragmentary fashion. The radiator and associated grille for the engine are mounted to the support flanges  52 .  
         [0029]    The internal combustion engine is housed by hood  60 . The hood comprises two sidewalls  62  and a top wall  64  joining the sidewalls  62 . In its closed position, the hood extends longitudinally between the support flanges  52  and the mast  16 , so that the front edge  66  of the hood  60  is adjacent to the upstanding support flanges  52  and the rear edge  68  of the hood is adjacent to the mast  16 . The sidewalls  62  of the hood  60  are mounted to pivot brackets  70 . The pivot brackets  70  are pivotally mounted to the front of the supporting structure  12  at pivots  72 . Pivots  72  adjoin the support flanges and define a pivot axis that passes through the support flanges  52 .  
         [0030]    The interior surface of each sidewall  62  is provided with an integral, arcuate guide  96 . These guides  96  contact the sidewalls of the grille support flanges  52  to guide pivotal movement of the hood  60 . The front of each arcuate guide  96  is provided with a cylindrical nylon button, not shown, which engages the sidewall of the grille support flanges  52  when the hood  60  is in its closed position. One or more hydraulic cylinders  94  and counterbalance springs  92  are operatively connected between the support flanges  52  and the pivot brackets  70  to control opening and closing of the hood. Mechanisms which support opening and closing of the hood are described in U.S. Pat. No. 6,460,644, herein incorporated by reference.  
         [0031]    The present invention is particularly directed to the construction of the hood  60 . FIGS. 3 and 4 illustrate the top wall  64  of the hood being fabricated of two separate pieces, an inner panel  102  and an outer panel or skin  104 . The inner and outer panels  102 ,  104  are preferably composed of polymer, preferably composed of GE Noryl GTX PPE/PA resin, in an extrusion state for thermoforming processes. Each panel  102 ,  104  can have a nominal thickness of about {fraction (3/16)} inch.  
         [0032]    The outer panel  104  provides a smooth, lightweight and paintable surface  105  (FIG. 3). The inner panel  102  includes ridges and formations for accepting fasteners and for forming stiffening, latching and an engine air intake duct. In order to provide a construction that is durable, rigid, high-temperature resistant and has a low temperature impact strength, the two panels  102  and  104  are fixed together to form a shell, the shell preferably being a unified structural member.  
         [0033]    It is important that the effects of thermal expansion be accounted for in the attachment of the outer panel with the inner panel. Since the hood is subjected to both ambient and engine temperatures simultaneously, a great temperature differential can exist through a thickness of the assembled hood top wall  64 . To allow for expansion and contraction, and to improve structural rigidity of the hood, shaped ribs  112  (FIG. 4) and stiffeners  113  are provided by corrugations of the inner panel  102 . The ribs have substantially squared U-shaped cross sections while the stiffeners have substantially V-shaped cross sections.  
         [0034]    The outer skin  104  is adhesively attached to the inner panel  102  as explained below. The adhesive is preferably composed of Essex Betaseal U-216 two-compound urethane.  
         [0035]    As illustrated in FIGS. 4 and 5, the inner panel  102  includes the stiffeners  113  and ribs  112 . In the described embodiment, the stiffeners  113  are interspersed with the ribs  112 , the ribs  112  and stiffeners  113  being spaced apart along a length of the inner panel  102 . The ribs extend across a lateral dimension of a top portion  102   a  of the inner panel  102  and down each side portion  102   b ,  102   c  of the inner panel. The stiffeners  113  extend across a lateral dimension of the top portion  102   a  of the inner panel  102 .  
         [0036]    As illustrated in FIGS. 6 and 8, side portions  112   a ,  112   b  of the ribs include faster nut receptacles or seats  112   c  open facing downward. A fastener nut  114  can be fed into the receptacles  112   c  through a side passage  112   d  and thereafter be engaged by a threaded fastener  115 , threaded in an upward direction through a hole (not shown) in the seat  112   c.    
         [0037]    Step offs or stepped bosses  118  are also provided spaced apart along the side portions  102   b ,  102   c  of the inner panel  102 . The bosses  118  can also include faster nut receptacles or seats  118   a  open facing downward. A fastener nut  120  can be fed into the receptacles  118   a  through a side passage  118   b  and thereafter receive a threaded fastener  122  threaded in an upward direction through a hole (not shown) in the seat  118   a.    
         [0038]    The hood sidewalls  62  are fastened to the hood by the fasteners  115 ,  122  that engage the fastener nuts  114 ,  120  along the side portions  102   b ,  102   c . The holes in the seats  112   c ,  118   a  are elongated or made oval in the longitudinal direction and the fasteners are permitted to slide longitudinally within the holes to accommodate differential thermal expansion between the top wall  64  and the sidewalls  62  of the hood.  
         [0039]    As illustrated in FIGS. 5 and 6, a steel frame  130  is fit onto a top side  131  of the inner panel  102  and beneath the outer panel  104 . The frame  130  includes substantially vertical, inverted U-shaped bents  132 , 134  having substantially vertical legs  132   a ,  134   a  and horizontal lateral legs  132   b ,  134   b , connected together by two longitudinally-extending tie bars  136 ,  138 . The lateral leg  134   b  of the rear most U-shaped bent  134  includes a deflected portion  134   c  to clear an exhaust pipe area  141 .  
         [0040]    As viewed in FIG. 5, the steel frame  130  fits onto a trough region  142  of the top side  131  of the inner panel  102 . A raised support plateau  144  of the inner panel  102  is also located within the trough region  142 . The bents  132 ,  134  and the tie bars  136 ,  138  are adhesively secured in place to the top side  131  of the inner panel  102 . A linear pattern of adhesive can be used between the members of the frame  130  and the top side  131 .  
         [0041]    As shown in FIG. 4, one of two vertical, three sided partitions  142  is fastened to each of the bents  132 ,  134  using four fasteners  144  (two shown). The bents  132 ,  134  are fastened to the sidewalls  62  using four fasteners  144  over a louvered air opening  146  on the respective sidewall  62  (see the louvered air opening  146  on the sidewall  62  in FIG. 3). One of two end walls  148  closes the bottom of each of the three sided partitions  142 .  
         [0042]    The mirror image identical, three sided partition  142  and end wall  148  are fastened together and to the bents  132 ,  134  and the respective side wall  62  in substantially identical fashion to the right side shown, and is located on the near side wall  62  in registry with the louvered air opening  146 . Each combination of the three sided partition  142 , the end wall  148 , the respective side wall  62  and louvered air opening  146  form a partial vertical air duct  150   a ,  150   b  on one side of the hood  60 .  
         [0043]    As illustrated in FIGS. 5 and 6, each air duct  150   a ,  150   b  communicates air upwardly into a plenum  156  formed by the trough region  142  of the inner panel  102  and the overlying outer panel  104 . The plenum  156  channels air into a round duct  160  formed on the inner panel  102 , which is ducted into the air inlet of the internal combustion engine (not shown). The air flows between the vertical legs  132   a ,  134   a  of the adjacent bents  132 ,  134  and over the horizontal tie bars  136 , 138 . The air flows converge from opposite directions, and flow into the round duct  160 .  
         [0044]    As illustrated in FIGS. 4 and 5, spring loaded latch element  174  is mounted onto a rearward-facing vertical wall  176  of the inner panel  102  using two fasteners  180 . A backing plate  182  (FIG. 5) can be used to strengthen the mounting. A hood release linkage  184  is operatively connected to the latch element  174  and extends laterally to penetrate through the inner and outer panels  102 ,  104 , and terminates in a hand-operated hood release lever or pull  186  (FIGS. 3). The latch element  174  is self-latching to the mast  16  or other stationary part upon closing of the hood  60 , and is manually released to open the hood  60  by use of the release lever or pull  186 .  
         [0045]    [0045]FIGS. 5, 7 and  7 A illustrate an advantageous pattern of adhesive  220  is applied between the outer skin  104  and the inner panel  102  that facilitates the differential expansion and contraction between the inner and outer panels and prevents the differential expansion from causing a corrugated or wavy appearance on the outside surface  105  of the outer panel  104  of the hood.  
         [0046]    The pattern of adhesive  220  is shown which will sufficiently bond the top skin  104  with the inner panel  102  but which will allow the inner panel  102  to flex longitudinally without separating from the outer skin  104  or causing a wrinkling or corrugation of the outer skin  104  that is visible from outside the hood  64 . In practice, it may be more effective to apply the adhesive during assembly to the bottom surface of the upper panel  104 , rather than to the upper surface of the inner panel  102 . In this regard, an etching or other marking of the adhesive pattern can be applied to the inside of the outer panel  104  as a guide for the application of the adhesive to the outer panel  104 .  
         [0047]    [0047]FIG. 7 illustrates the adhesive pattern  220  in isolation from the outer skin  104  and the inner panel  102 . Inner longitudinal edges  220   a ,  220   b , and  220   c  of the pattern  220  have undulations  236  which are matched to adjacent ends of the stiffeners  113  formed in the inner top panel  102  as shown in FIG. 5. The undulations  236  can be in a substantially zigzag pattern with rounded or squared peaks  238 . The longitudinal distance d 1  between adjacent peaks  238  is approximately equal to the distance d 2  between stiffeners that are adjacent to the respective adjacent peaks.  
         [0048]    As illustrated in FIG. 8, in order to space the inner panel  102  from the outer panel  104 , a plurality of dimples or bumps  230  are formed on the inner panel  102  that extend toward the outer panel  104 . A pre-selected spacing between the inner panel  102  and the outer panel  104  serves to increase the rigidity of the shell formed by the inner and outer panels  102 ,  104  and also sets a uniform adhesive gap to achieve a uniform layer thickness of adhesive  220  when the panels  102 ,  104  are assembled. The dimples  230  have a height of about 3 mm above the surrounding surface of the inner panel  102 . The dimples are spaced about 2-4 inches apart longitudinally and laterally. The inner panel  102  can also include similar dimples  232 , about 3 mm tall, that are arranged below the frame  130  to set an adhesive thickness between the frame  130  and the inner panel  102 .  
         [0049]    Although the dimples  230 ,  232  are shown extending from the inner panel  102 , a similar protrusion could be provided instead on the outer panel extending toward the inner panel and both are encompassed by the invention.  
         [0050]    The embodiment described above provides a top wall for a hood that is impact and dent resistant. The embodiment described above provides a top wall for a hood that is cost effectively manufactured. The embodiment described above provides a top wall for a hood that maintains a smooth aesthetically-pleasing outer contour, even during extreme temperatures.  
         [0051]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Summary:
A hood for an off road work vehicle includes a thermoformed polymer outer top panel having a smooth outer surface, a thermoformed inner panel, the inner panel having laterally extending corrugations, and a pattern of adhesive arranged between the inner and outer top panels. The inner and outer top panels are secured together by the pattern of adhesive, the pattern of adhesive comprising non-linear longitudinally extending regions spaced apart and straddling a longitudinal centerline of the inner top panel. The non-linear regions can be undulating or zigzag regions.