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CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 14/457,519 filed Aug. 12, 2014, which is a divisional of U.S. patent application Ser. No. 13/277,333, filed Oct. 20, 2011, now U.S. Pat. No. 8,991,936, which is a continuation of U.S. patent application Ser. No. 12/335,114, filed Dec. 15, 2008, now U.S. Pat. No. 8,042,875; the entire disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to dump bodies on trucks. More particularly the present invention relates to dump bodies which are pivotally mounted such that the front may be elevated and the contents removed by gravity through a chute located in a rear tailgate. Specifically, the present invention relates to an improvement in coal chutes which enhances the longevity and operability by means of an easily replaceable coal chute door within an elastomeric track. 
         [0004]    2. Background Information 
         [0005]    Many trucks have a bed or body that is lifted upwardly relative to the vehicle to unload materials by gravity from within the bed. Dump bodies for industrial use, such as dump trucks and coal trucks, typically employ a tailgate which is pivotally mounted to the top of the side walls of the dump body and extends across the width of the bed, such that it may swing between an open and closed position as the front of the dump body varies in elevation. 
         [0006]    These rear tailgates oftentimes include a center door assembly called a “coal chute”. The coal chute is substantially narrower than the rear tailgate and includes a door that can be selectively opened or closed. Common coal chute designs involve sliding the door up and down within tracks mounted in the sidewalls of the chute. Using a pivot arm, the user draws the door upwards along the chute door track before the bed of the dump truck is lifted. As the bed is lifted, the material within the bed exits through the coal chute in a contained and controlled stream that can be fed directly onto a ditch, intake basin, or onto a conveyor belt. 
         [0007]    Due to the enormous tonnage carried by such trucks and the abuse to the walls of such truck bodies, the retaining chute door and the door track is subjected to distorting forces and are oftentimes broken or dented by movement of the material within the dump body or through the chute itself. When the cute door or track becomes distorted, the chute&#39;s effectiveness is diminished as the door cannot form a proper seal or slide within the track. Therefore gravel, coal, sand or other particulate matter can escape through the resulting gap. Consequently, it is not uncommon for the chute door to become unusable and require replacement or repair. 
         [0008]    Replacing or repairing parts of the chute is very time consuming and expensive. Typical chutes have welded tracks, pivot arms, plates, and various other components. The chute assembly itself is welded onto the tailgate and difficult to remove. Furthermore, when the chute door or track is repaired or replaced, these items must be re-welded to the tailgate body, adding more time and expense to the process of replacing or repairing a part of the chute. 
         [0009]    Therefore, the need exists for a center door assembly for a dump bed which includes easily replaceable and repairable parts, which parts are not welded to the tailgate so disassembly and reassembly time and expense will be minimized. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    One object of the invention is to provide an easily replaceable door on a center door assembly for a dump bed. 
         [0011]    A further object of the invention is to provide a chute assembly which employs elastomeric material for the tracks which slidably receive the edges of the chute door therein to provide a removable insert to receive the edges of the chute door and facilitate removal of the chute door from within the tracks for repair or replacement. 
         [0012]    It is the object of the invention to provide a tailgate having a center door assembly which remains in alignment without degradation of the seal therebetween. 
         [0013]    Another object of the invention is to provide a tailgate and center door assembly which is positively secured to prevent inadvertent gate openings. These features are obtained by the center door assembly for a dump bed of the present invention, the general nature of which includes a center door assembly for a dump bed comprising: a frame adapted to be mounted in a wall of a dump bed; a pair of opposite and spaced apart channels defined by said frame; at least one insert removably mounted in one of said channels; a retractable door having a pair of edges slidably received in the at least one insert; and movable linearly between a closed position and an open position; an axle rotatably mounted with respect to the frame; a pivot linkage having a spaced apart first and second end, wherein the first end is secured to the axle and the second end is secured to the door; and a handle for rotating the axle whereupon rotation of the axle slidably moves the door between the closed position and the open position through the pivot linkage; and wherein said insert when removed from the channel enables the door to be removed from the frame. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    A preferred embodiment of the invention, illustrated of the best mode in which Applicant contemplates applying the principles, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims. 
           [0015]      FIG. 1  is a side elevational view of a dump truck and dump body shown in the raised position; 
           [0016]      FIG. 2  is a perspective view of the center door assembly of the present invention mounted on a tailgate of a dump body and shown in the closed position; 
           [0017]      FIG. 3  is an enlarged perspective view of the center door assembly with parts cut away; 
           [0018]      FIG. 4  is front elevational view of the center door assembly in the closed position; 
           [0019]      FIG. 5  is a rear elevational view of the center door assembly in the closed position; 
           [0020]      FIG. 6  is an enlarged sectional view taken on line  6 - 6  of  FIG. 4 ; 
           [0021]      FIG. 7  is an exploded perspective view of the center door assembly as shown in  FIG. 2 ; 
           [0022]      FIG. 8  is a perspective view with the linkage assembly removed from the frame and chute door; 
           [0023]      FIG. 9  is a perspective view of the door linkage assembly; 
           [0024]      FIG. 10  is an exploded perspective view of the center door assembly with the linkage assembly removed; 
           [0025]      FIG. 11  is a perspective view of the center door assembly with the outer cover plate and the door linkage assembly removed; 
           [0026]      FIG. 12  is a front elevational view of the center door assembly as shown in  FIG. 11  with portions broken away to show the elastomeric tracks; 
           [0027]      FIG. 13  is an enlarged sectional view taken on line  13 - 13  of  FIG. 12 ; 
           [0028]      FIG. 14  is an enlarged sectional view of the encircled portion of  FIG. 13 ; 
           [0029]      FIG. 15  is a front elevational view similar to  FIG. 12  of the center door assembly with parts cut away and with the door in the raised open position; 
           [0030]      FIG. 16  is an enlarged sectional view taken on line  16 - 16  of  FIG. 15 ; 
           [0031]      FIG. 17  is a view similar to  FIG. 16  with the insert being deformed; 
           [0032]      FIG. 18  is a view similar to  FIG. 17  with the insert being partially removed from the channel; 
           [0033]      FIG. 19  is a front elevational view similar to  FIGS. 12 and 15  with parts cut away and the door in the open position and the lower inserts shown in phantom being removed; 
           [0034]      FIG. 20  is a view similar to  FIG. 19  with the door in the closed position and the upper inserts shown in phantom being removed; 
           [0035]      FIG. 21  is a view similar to  FIG. 20  after removal of the door and with the door being moved laterally within the supporting tracks; 
           [0036]      FIG. 22  is an enlarged sectional view taken along line  21 - 21 . 
       
    
    
       [0037]    Similar numbers refer to similar parts throughout the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    The center door assembly of the present invention is generally indicated at  1 , and is shown in  FIGS. 1-22 . Center door assembly  1  is typically disposed in a rear tailgate wall  7  of a dump bed  5  of a vehicle  3  as shown in  FIGS. 1 and 2 . 
         [0039]    Referring to  FIGS. 3 ,  4 ,  5 , and  6 , door assembly  1  includes a rectangular frame  9  having top and bottom ends  19  and  21  respectively, first and second sides  18  and  20  respectively, an inner cover plate  11  secured to frame  9  by a weld  14  ( FIG. 6 ), and an outer cover plate  13  externally secured to frame  9  with a plurality of bolts  15  or other type of fasteners. Outer cover plate  13  extends in a spaced parallel relationship with respect to inner cover plate  11 . Outer cover plate  13  extends from top end  19  of frame  9  to the general longitudinal midpoint of frame  9 , indicated by dot dash line  12  in  FIG. 4 . As shown in  FIG. 5 , inner cover plate  11  is generally longer and extends past line  12 . Frame  9  includes a U-shaped channel  17  extending around the periphery of frame  9 , and is shaped to receive tailgate wall  7  for securing center door assembly  1  to dump bed  5 . 
         [0040]    Frame  9  further includes a pair of U-shaped channels  23  ( FIGS. 14 ,  16 ,  17 , and  18 ) extending longitudinally along each side  18  and  20  of frame  9 , each terminating in a notch  27  proximate bottom end  21  of frame  9 . Each channel  23  slidably receives a pair of elastomeric inserts  24  conforming to the shape of channels  23  ( FIGS. 6 ,  13 - 16 ). Inserts  24  are sized to slidably receive side edges  22  of a chute closure door  25  therein. Door  25  has a generally flat planer plate shape and is sized to extend between each side  18  and  20  within inserts  24  and extending approximately one-half the longitudinal length of frame  9 . Door  25  is slidably movable between cover plates  11  and  13  between an open position as shown in  FIG. 15  and a closed position as shown in  FIG. 12 . A pair of lobes  33  are attached to and extend from adjacent a bottom edge of door  25  as shown in  FIGS. 10 and 11 . Each lobe  33  is formed with a hole  35 , the purpose of which is described below. 
         [0041]    Referring to  FIGS. 13 ,  14 , and  16 , elastomeric inserts  24  have a general U-shaped cross-sectional configuration having a pair of spaced legs  34  extending from an end wall  36 . Each insert  24  includes a door receiving recess  26 , a bend recess  28  formed in end wall  36 , and a D-shaped protruding nub  30  sized to fit into a corresponding D-shaped recess  32  formed in one of the legs of U-shaped channel  17  of frame  9 . 
         [0042]    Referring to  FIGS. 3 ,  4 , and  6 , and shown particularly in  FIGS. 7 and 9 , a pivot linkage assembly indicated generally at  37  is removably secured to frame  9 . Pivot linkage  37  includes an axle  39  secured at each end by a pillow block bearing  41 . Each block bearing  41  extends outwardly from frame  9  and is comprised of a first and second blocks  43  and  45  each having a half-moon recess  42 . First block  43  is welded to frame  9  proximate top end  19  and includes a pair of threaded receiving holes  47 . Second block  45  is removably secured to first block  43  by means of a pair of threaded bolts  49  extending through holes  51  formed in second block  45  and into threaded receiving holes  47 . Pivot linkage  37  is further comprised of a crank arm  53  having annular mounting bosses  55  secured to axle  39  by welding or other attachment means. Crank arm  53  extends from axles  39  and terminates in a crank handle  57  sized to be manipulated by a user&#39;s hand. 
         [0043]    A pair of lift arms  59  extend from and are welded to axle  39  intermediate pillow block bearings  41 . Each lift arm  59  is pivotally connected to a U-shaped bracket  61  by a bolt  63 , each bracket  61  forming a bottom threaded hole  62  for receiving a first end  65  of a threaded stud bolt  67  therein. Bolt  67  extends to second threaded end  69  which is received in a threaded receiving hole  70  of a second U-shaped bracket  71 . Each bracket  71  is pivotally attached to lobe  33  by a removable bolt  73  secured by a cotter pin  75 . A securing handle  64  extends from one bolt  63 . 
         [0044]    In operation, as shown in  FIG. 1 , center door assembly  1  is located in tailgate wall  7  of dump bed  5  on truck  3  with chute closure door  25  in the closed position ( FIG. 21 ). A material  2  (not shown) such as stones, sand, mulch, or any other matter which is typically transported by truck within a dump bed, is loaded into dump bed  5 . Truck  3  moves material  2  to the desired material deposit location and positions tailgate wall  7  to release material  2  in the desired location. The user slidably moves chute closure door  25  from a closed position to an open position ( FIG. 15 ) and locks door  25  in the open position by turning handle  64  ( FIG. 4 ). Dump bed  5  then is extended from a generally horizontal position to an angled position with the ground which allows the gravitational force to pull material  2  towards tailgate wall  7  within dump bed  5 . Material  2  is dumped out of dump bed  5  through the opening defined by frame  9  and the open position of coal chute door  25  in tailgate wall  7 . After the desired amount of material  2  is dumped, dump bed  5  is returned to the horizontal position. Handle  64  is loosened to unlock coal chute door  25 . The user then moves coal chute door  25  from an open position to a closed position by pivotal movement of crank arm  53  in preparation for loading dump bed  5  with material  2 . 
         [0045]    Pivot linkage assembly  37  allows the user to slidably move coal chute door  25  between open and closed positions. As shown in  FIGS. 3 and 4 , axle  39  extends between pillow block bearings  41  which allow axle  39  to rotate within half moon recess  42  of each bearing  41 . Crank arm  53  is secured to one end of axle  39  and rotates axle  39  when crank handle  57  is moved by a user. The rotation of axle  39  rotates lift arms  59  which are secured to axle  39  at one end. At the opposite end, lift arms  59  are engaged with first U-shaped bracket  61  which rotates about bolt  63 . First U-shaped bracket  61  extends to receive threaded stud bolt  67  which extends to be received by second U-shaped bracket  71 . Second U-shaped bracket  71  is pivotally engaged with lobe  33  about a removable bolt  73 . 
         [0046]    To move chute closure door  25  from a closed to an open position, the user rotates crank arm  53  causing axle  39  to rotate. Axle  39  raises lift arms  59  which pivot about bolt  63 , pulling first U-shaped bracket  61 , stud bolt  67  and second U-shaped bracket  71  in an upward direction. The movement of these elements within pivot linkage assembly  37  results in an upward force on lobes  33  which transfers the force to chute closure door  25 , drawing door  25  upwards. 
         [0047]    Each sidewall  22  of chute closure door  25  is slidably received by door receiving recesses  26  formed in inserts  24 . Inserts  24  fit in U-shaped channel  23  formed in frame  9 . One desired property of the material comprising inserts  24  is to reduce the difficulty of sliding chute closure door  25  by providing a low friction coefficient between door  25  and inserts  24 . To this end, inserts  24  are typically made from Teflon® or other similar low friction material. As upward force is applied to door  25  and sidewalls  22  thereof, door  25  slides within receiving recesses  26  formed in inserts  24 . The sliding movement is guided by the general shape of U-shaped channels  23  and recesses  26 , and is generally co-planer with tailgate wall  7 . When door  25  is in the open position, the hole through tailgate wall  7  is exposed and material may exit dump bed  5 . When door  25  is in the closed position, the hold through tailgate wall  7  is sealed and material will not exit dump bed  5 . 
         [0048]    As material  2  is loaded and unloaded, stress is applied to the elements comprising door assembly  1 . Chute door  25  including sidewalls  22  thereof may become damaged or dented, hindering the sliding movement of door  25  within door receiving recess  26 . A distortion of the general planar shape of door  25  typically renders door  25  unable to open or close as recesses  26  closely conform to the shape of sidewalls  22  to slidable hold door  25  within frame  9 . If door  25  becomes damaged, it must be replaced. However, door  25  is typically very difficult to replace. Parts within a typical center door assembly are welded and fixedly attached to one another, making removal of the center door very difficult. Center door assembly  1  provides for a method to easily replace elements within assembly  1 . The elements comprising center door assembly  1  are held in position by easily removable parts allowing a user to disassemble and reassemble center door assembly  1 . 
         [0049]    The method for removing pivot linkage assembly  37  from center door assembly  1  is shown in  FIGS. 7 and 8 . First, threaded bolts  49  are removed from threaded receiving hole  47  and hole  51  within pillow block bearings  41 . This allows first block  43  to be separated and removed from second block  45 , releasing axle  39 . Second, cotter pins  75  are removed from bolts  73 . Bolts  73  are then free to be removed from second U-shaped brackets  71  and lobes  33 , releasing second U-shaped brackets  71  from center door assembly  1 . As shown in  FIG. 8 , pivot linkage assembly  37  may then be removed from center door assembly  1 . As shown in  FIG. 9 , pivot linkage assembly  37  is a sub-assembly which is easily removed as a unit from center door assembly  1 . This exposes the area behind assembly  37  and further facilitates removal of the elements comprising center door assembly  1 . 
         [0050]    As shown in  FIG. 10 , center door assembly  1  is further disassembled by removing bolts  15  which releases outer cover plate  13 . Bolts  15  are common hex-head type screws which fit typical wrenches. With outer cover plate  13  removed, door  25  is exposed ( FIGS. 11 and 12 ). As shown in  FIG. 15 , door  25  is manually lifted in the direction of arrow “A” to move center door assembly  1  into the open position. This exposes inserts  24 A at lower notch  27  in U-shaped channels near bottom end  21  of frame  9 . The exposing of inserts  24 A allow a user to manually grasp insert  24  at notch  27 . As shown in  FIGS. 17 and 18 , the user manually distorts legs  34  of insert  24  in the direction of arrow “B”. This bending is facilitated by bend recess  28  formed in end wall  36  of insert  24 , which reduces the bend strength of insert  24  by providing a ready crease in the material. As legs  34  of insert  24  are bent inwardly, D-shaped nub  30  is released from D-shaped recess, allowing insert  24  to slide out of U-shaped channel  23  in the direction of arrow “C” at bottom end  21  of frame  9 . As shown in  FIG. 19 , inserts  24 A are manually pulled out of U-shaped channels  23  proximate bottom end  21  of frame  9  in the direction of arrow “C”. Inserts  24 A are fully extracted and may be replaced if worn or damaged. 
         [0051]    As shown in  FIG. 20 , door  25  is then manually lowered to the closed position by moving door  25  in the direction of arrow “D”. The process of removing inserts  24 A is then repeated for inserts  24 B. Door  25  is now less restrained within U-shaped channels  23  because the space occupied by inserts  24  is empty. As shown in  FIG. 21 , to remove door  25 , it is manually moved in the direction of arrow “E”. This exposes sidewall  22 B as it retracts from U-shaped channel  23 . As shown in  FIG. 22 , sidewall  22 B is free to move in the direction of arrow “F”, releasing the entire door  25  from center door assembly  1 . 
         [0052]    Door  25  and inserts  24  may then be replaced or fixed to restore center door assembly  1  to workable condition. To install the elements of center door assembly  1 , the removal process is simply reversed. Elements are added and secured by the same process, allowing the user to quickly and easily fix the elements within assembly  1 . The truck owner may replace elements such as door  25  with common tools and without breaking welds or welding parts back into place. This dramatically eases the replacement of parts within assembly  1 . 
         [0053]    In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. 
         [0054]    Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described.

Summary:
A center door assembly for a dump bed and a method for removing the door from the dump bed. A frame is mounted in a wall of the dump bed and has a pair of opposite and spaced apart channels. A pair of elastomeric inserts are removably mounted in the channels. A retractable door has a pair of edges slidably received in the inserts and is movable linearly within the channels between a closed position and an open position. A pivot linkage assembly is operatively connected to the door for linearly moving the door between the closed and open positions. The elastomeric inserts are removed from the channels through a bottom opening in the channels providing lateral space between the channels to enable the door to be removed from the frame. The elastomeric inserts are provided with bend areas enabling them to be compressed for removal from the channels.