Abstract:
An improved tailgate assembly for a truck body is provided. The tailgate assembly including a gate portion that is pivotally supported between a pair of opposing side beams for movement relative to the side beams between an operative and an inoperative position. Each of the side beams is pivotally attached to a respective side wall of the dump body such that the side beams and gate are movable relative to the truck body between an in-service, closed position wherein the gate portion encloses a rear end of the dump body and an out-of-service position wherein the gate portion is positioned adjacent a forward end of the dump body. The assembly also including a pivoting assembly for moving the gate portion between the operative and inoperative positions. The pivoting assembly is actuated as the side beams carry the gate portion to the out-of-service position and operable to pivot the gate portion relative to the side arms toward the forward end of the dump body from the operative to the inoperative position.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to heavy-duty off-road trucks and, more particularly, to a tailgate assembly for these trucks. 
     BACKGROUND OF THE INVENTION 
     Certain working environments, such as coal mines, can require the use of rear dump off-road trucks to haul loads having different material densities. Since the optimal volumetric capacity for a truck body varies based on the density of the material to be hauled, such hauling operations can be difficult to conduct efficiently. For example, in the case of a coal mine, off-road trucks may be used to haul both coal, which has a relatively lighter density, and overburden (i.e. the earth otherwise removed in a coal mining operation), which has a relatively heavier density. If the heavier density overburden is hauled in trucks having bodies with a volumetric capacity designed to haul coal, the load can substantially exceed the gross vehicle weight rating of the truck if the body is filled to capacity. Conversely, if a truck having a relatively smaller body designed to haul overburden is used to haul coal, the load of lighter weight coal will not come close to reaching the maximum allowable payload capacity of the truck. 
     One way in which to address this issue is to provide a group of trucks, with relatively larger dump bodies, which are dedicated to hauling coal and a separate group of trucks, which have relatively smaller dump bodies, dedicated to hauling overburden. However, having trucks which are exclusively dedicated to hauling one particular material substantially reduces the overall truck fleet flexibility. 
     In order to permit off-road trucks used in working environments such as coal mines to be used in a more flexible manner, the dump bodies can be equipped with a selectively deployable tailgate assembly which can be used to adjust the volumetric capacity of the dump body. In particular, the dump body of the truck can be equipped with a tailgate assembly rotatable between a closed, in-service position at the rear of the truck body and an out-of-service position at the front of the truck body. With such a tailgate assembly, to increase the effective volumetric capacity of the truck body for hauling relatively lighter density material such as coal, the truck can be loaded with the tailgate in the closed, in-service position. Arranging the tailgate at the rear of the truck body increases the effective volumetric capacity of the truck body by preventing material from spilling out of the rear of the truck body. To lower the effective volumetric capacity of the truck body for hauling relatively heavier density material such as overburden, the truck can be loaded with the tailgate in the out-of-service position. When the tailgate is arranged in the out-of-service position at the front of the truck body, excess material loaded into the dump body will spill out of the open rear end of the body thereby minimizing the risk of overloading the truck body with the heavier overburden material. 
     Accordingly, such selectively deployable tailgate assemblies allow the effective volumetric capacity of a truck body to be selectively adjusted to permit a truck to efficiently haul loads of different volumes and material densities. As will be appreciated, the ability to selectively adjust the volumetric capacity of the dump body eliminates the need to provide differently sized trucks for hauling lighter density materials and heavier density materials. 
     One problem with such tailgate assemblies, however, is that when the tailgate is in the out-of-service position it can pose an obstacle to the loading operation. More specifically, when the tailgate is in the out-of-service position, the center rear portion of the tailgate, which extends between the two tailgate side beams, is oriented such that it extends upward and towards the rear end of the dump body overhanging the open top of the dump body. In this position, as material is being loaded into the dump body, the center rear portion of the tailgate is susceptible to being struck by the loading equipment or possibly by the actual material being loaded into the body. This can result in significant damage to the tailgate assembly necessitating costly repairs or even replacement. Moreover, the impact of a collision with the tailgate potentially could also damage the loading equipment. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Accordingly, in view of the foregoing, a general object of the present invention is to provide a dump body for a heavy-duty, off-road truck having a selectively deployable tailgate assembly which enables the truck to efficiently haul loads of varying volumes and material densities. 
     A more specific object of the present invention is to provide a dump body for a heavy-duty, off-road truck having a selectively deployable tailgate which minimizes potential interference with the loading of heavier density material into the dump body. 
     A related object of the invention is to provide a tailgate assembly as characterized above which minimizes the risk of damage to the tailgate assembly and dump body caused by possible over loading of heavier density material into the dump body/onto the rear dump off road truck. 
     Another object of the invention is to provide a tailgate assembly as characterized above which provides controlled and consistent movement of the tailgate assembly between in-service and out-of-service positions. 
     These and other features and advantages of the invention will be more readily apparent upon reading the following description of a preferred exemplary embodiment of the invention and upon reference to the accompanying drawings wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a heavy-duty, off-road truck showing the dump body in the lowered position and an illustrative tailgate assembly constructed in accordance with the present invention in the in-service, closed position. 
     FIG. 2 is a side view of the heavy-duty, off-road truck of FIG. 1 showing the dump body in the raised position and the tailgate assembly in the in-service, open position. 
     FIG. 3 is a side view of the heavy-duty, off-road truck of FIG. 1 showing the dump body in the raised position and the tailgate assembly approaching the out-of-service position. 
     FIG. 4 is an enlarged partial side view of the heavy-duty, off-road truck of FIG. 1 showing the tailgate assembly approaching the out-of-service position with the center rear portion of the tailgate in the operative position. 
     FIG. 5 is a side view of the heavy-duty, off-road truck of FIG. 1 showing the dump body in the raised position and the tailgate assembly in the out-of-service position with the center rear portion of the tailgate in its inoperative position. 
     FIG. 6 is side view of the heavy-duty, off-road truck of FIG. 1 showing the dump body in the lowered position and the tailgate assembly in the out-of-service position with the center rear portion of the tailgate in its inoperative position. 
     FIG. 7 is an enlarged partial side view of the heavy-duty, off-road truck of FIG. 1 showing the tailgate assembly in the out-of-service position with the center rear portion of the tailgate in the inoperative position. 
     FIG. 8 is an enlarged partial side view of the heavy-duty, off-road truck of FIG. 1 showing the tailgate assembly in the in-service, closed position with the center rear portion of the tailgate secured in the operative position. 
     FIG. 9 is an enlarged partial rear end view of the heavy-duty, off-road truck of FIG. 1 showing the tailgate assembly in the in-service, closed position and the center rear portion of the tailgate secured in the operative position. 
     FIG. 10 is an enlarged partial side view of an alternative embodiment of the present invention showing the dump body in the lowered position and the tailgate assembly in the out-of-service position with the center rear portion of the tailgate in its inoperative position. 
    
    
     While the invention will be described and disclosed in connection with certain preferred embodiments and procedures, it is not intended to limit the invention to those specific embodiments. Rather it is intended to cover all such alternative embodiments and modifications as fall within the spirit and scope of the invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now more particularly to FIG. 1 of the drawings there is shown an illustrative heavy-duty off-highway truck  10  having a dump body  12  and a tailgate assembly  14  constructed in accordance with the teachings of the present invention. The truck  10  includes a chassis  16  which is supported on a plurality of tires  17  and to which the dump body  12  is attached for pivotal movement about an axis  18  between a lowered position (FIG. 1) for receiving and transporting a load of light density material and a raised position (FIG. 2) for dumping the load. In the illustrated embodiment, the dump body  12  is moved between the lowered and raised positions by actuation of a hydraulic dump cylinder  19  carried on the chassis  16  of the truck  10 . The dump body  12  is generally constructed of steel panels which define the shape of the dump body and beams which form the structural framework for the dump body. 
     In this case, the dump body  12  comprises a pair of opposing sidewalls  20 , a front wall  22  (or front slope) and a floor  24 . The dump body  12  further includes a canopy  26  which is integrally connected to the top end of the front wall  22  and extends over the cab of the truck  10 . The illustrated tailgate assembly includes a pair of laterally spaced, parallel side beams  28  between which a center rear portion  30  of the tailgate is supported. Each side beam  28  is pivotally connected to a respective one of the sidewalls  20  of the dump body  12  by a pivot pin  32  so as to allow the side beams to rotate relative to the dump body  12 . 
     In the illustrated embodiment, the truck  10  is generally symmetrical about its longitudinal axis. Accordingly, as will be appreciated, many of the elements identified in the side views of FIGS. 1-10 have complementary elements arranged on the opposite side of the truck  10 . For ease of references herein, the present invention will only be described in connection with the side of the truck shown in FIGS. 1-10. However, it will be appreciated that in one embodiment of the invention complementary elements are provided on the side of the truck that is not shown. 
     To permit the effective volumetric capacity of the dump body  12  to be selectively adjusted to accommodate loads of different material densities, the tailgate assembly  14  is movable relative to the dump body between an in-service, closed position (FIG. 1) and an out-of-service position (FIGS.  5  and  6 ). In the in-service closed position, the tailgate assembly  14  is in a lowered position with the center rear portion  30  of the tailgate extending between the opposing sidewalls  20  and, when being loaded, closing off the rear end of the dump body  12  as shown in FIG.  1 . With the rear end of the dump body  12  closed off, the volumetric capacity of the dump body is increased for more efficient hauling of lighter density material such as coal. In the out-of-service position, the tailgate assembly  14  is in a resting position with the center rear portion  30  of the tailgate arranged on the canopy  26  of the dump body  12  thereby opening up the rear end of the dump body as shown in FIGS. 5 and 6. Thus, the dump body  12  can be quickly and easily converted to a lower effective volumetric capacity for hauling relatively heavier density materials such as overburden, simply by moving the tailgate assembly  14  into the out-of-service position. Additionally, to facilitate rear dumping of lighter material when the dump body  12  is moved to the raised position, the tailgate assembly  14  moves into an in-service, open position as shown in FIG. 2 wherein the center rear portion  30  of the tailgate is pivoted upward relative to the rear end of the dump body into an intermediate position between the in-service, closed and out-of-service positions. 
     For moving the tailgate assembly  14  between the various positions, in the illustrated embodiment, two different tailgate actuation assemblies are provided. The first tailgate actuating assembly, generally referenced as  34 , is responsible for rotating the tailgate assembly  14  between the in-service, closed (FIG. 1) and in-service, open (FIG. 2) positions. The first tailgate actuation  34  assembly comprises, in this instance, a cable or chain  36  and a solid link  37  that interconnects the truck chassis  16  and the side beam  28  of the tailgate assembly. The chain  36  and solid link  37  produce a torque on the tailgate assembly  14  that rotates the tailgate assembly between the in-service, closed (FIG. 1) and in-service, open (FIG. 2) positions as the hydraulic dump cylinder  19  pivots the dump body  12  between the raised and lowered positions. 
     The second tailgate actuation assembly, generally referenced as  38 , is responsible for moving the tailgate assembly  14  between the in-service, open and out-of-service positions. In the illustrated embodiment, the second tailgate actuation assembly  38  comprises an actuating cylinder  40  having one end pivotally connected to the dump body  12  and the other end pivotally connected to a cam lever  42  as shown in FIGS. 2,  3  and  5 . The cam lever  42 , in turn, is connected to the dump body  12  via a pivot pin and includes a cam roller  44  which can be brought into engagement with a slot  46  disposed in the tailgate side beam  28  when the tailgate assembly is in the in-service, open position. Specifically, after the tailgate assembly  14  is rotated to the open, in-service position by the first tailgate assembly  34 , the actuating cylinder  40  is extended so as to rotate the cam lever  42  and bring the cam roller  44  into initial engagement with the slot  46  as shown in FIG.  2 . Further extension of the actuating cylinder  40  causes the cam lever  42  to rotate and the cam roller  44  to move within the slot  46  so as to produce a torque on the tailgate assembly  14  which rotates the tailgate assembly from the in-service, open position (FIG. 2) to the out-of-service position (FIGS. 3,  5  and  6 ). Once the tailgate assembly  14  reaches the out-of-service position, the engagement of the cam roller  44  with the slot  46  locks the tailgate assembly in place thereby preventing any unintentional and uncontrolled swinging movement of the tailgate back into the in-service, open position. Additional details regarding the actuation assemblies and the tailgate assembly are described in U.S. Pat. Nos. 5,474,363 and 5,887,914 the disclosure of which is incorporated herein by reference. 
     In accordance with one important aspect of the present invention, the tailgate assembly  14  is adapted such that when the tailgate is in the out-of-service position, the center rear portion  30  of the tailgate is positioned so as to minimize any obstruction posed by the tailgate center rear portion  30  to the loading of material into the dump body  12  as shown in FIG.  6 . Thus, the likelihood that either the loading equipment or possibly the material being loaded will inadvertently collide with, and damage, the tailgate assembly  14  is substantially reduced. In particular, unlike previous designs, when the tailgate assembly  14  of the present invention is in the out-of-service position, the center rear portion  30  of the tailgate is arranged and oriented such that it does not project or extend into the space above the open top of the dump body as shown in FIG.  6 . 
     To this end, the center rear portion  30  of the tailgate assembly  14  is supported between the two side beams  28  for rotation about an axis extending perpendicular to the side beams between its own respective operative (see, e.g., FIG. 1) and inoperative positions (see, e.g., FIGS.  6  and  7 ). In this instance, the center rear portion  30  of the tailgate is supported on a pair of pivot pins  48  each of which is received in a respective one of the side beams  28  so that the center rear portion  30  is pivotable relative to the side beams about the axis defined by the pivot pins  48 . In the operative position, the center rear portion  30  of the tailgate is oriented such that when the tailgate assembly  14  is in the in-service, closed position the center rear portion closes off the rear end of the dump body  12  as shown in FIG.  1 . In the inoperative position, the center rear portion  30  of the tailgate is pivoted with respect to the tailgate side beams  28  such that the center rear portion will not overhang the open top of the dump body  12  when the tailgate assembly is in the out-of-service position as shown in FIG.  6 . 
     To move the center rear portion  30  of the tailgate between the operative and inoperative positions, the tailgate includes a pivoting assembly  50  which actuates as the tailgate assembly rotates between the in-service and out-of-service positions. In the illustrated embodiment, the pivoting assembly includes a heel portion  52  which is fixed to the center rear portion  30  of the tailgate. As the tailgate assembly  14  approaches the full out-of-service position (FIGS.  3  and  4 ), a cam roller  54  on the end of the heel portion  52  engages a complementary cam surface  56  on a seat  58  arranged, in this case, on the interior surface of the side wall  20  of the dump body  12  adjacent the canopy  26 . As the tailgate assembly  14  continues to rotate, the movement of the cam roller  54  over the seat  58  caused by rotation of the tailgate assembly  14  towards the full out-of-service position produces a torque on the hinged center rear portion  30  of the tailgate. This torque rotates or pivots the center rear portion  30 , in a counterclockwise direction with respect to the drawings, away from the open top of the dump body  12  into the inoperative position (FIGS.  5 - 7 ). Similarly, when the tailgate assembly  14  rotates from the out-of-service position back to the in-service position, the movement of the cam roller  54  over the cam surface  56  on the seat  58  permits the weight of the center rear portion  30  to pivot it back into the operative position in a controlled manner. 
     Once the tailgate assembly  14  reaches the in-service, closed position (FIG.  1 ), the center rear portion  30  is held in place by a holding mechanism comprising, in this case, seats  60  (FIGS. 8 and 9) arranged at the rear end of the dump body  12  which engage the center rear portion  30  and prevent it from pivoting outward. 
     To ensure that the center rear portion  30  of the tailgate rotates properly between the operative and inoperative positions, the tailgate assembly  14  includes elements which limit the range of movement of the center rear portion  30  relative to the tailgate side beams  28  as the tailgate assembly moves between the in-service and out-of-service positions. More specifically, in the illustrated embodiment, a stop  62  is provided adjacent the free end of the tailgate side beam  28  which limits clockwise (with reference to the drawings) pivoting movement of the center rear portion  30 . Thus, as the tailgate assembly  14  moves between the in-service and out-of-service positions, the stop  62  prevents the weight of the center rear portion  30  from causing it to rotate out of the operative position as shown in FIGS. 2 and 3. By preventing such rotation, the stop  62  ensures that the cam roller  54  will properly engage the cam surface  56  on the seat  58  as the tailgate assembly  14  approaches the out-of-service position (FIGS. 3 and 4) and that the center rear portion will be in the operative position when the tailgate assembly reaches the in-service, closed position (FIGS.  1  and  8 ). 
     Additionally, in the illustrated embodiment, the heel portion  52  is configured so as to include an edge defining a stop surface  64  which engages the cam surface  56  (see, e.g., FIGS. 4 and 7) when the center rear portion  30  reaches the inoperative position. The stop surface  64  on the heel portion  52  further includes an extended portion  66  on the opposing side of the tailgate pivot axis (defined by the pivot pins  48 ) from the cam roller  54  which limits counterclockwise rotation of the center rear portion  30  past the inoperative position. Thus, the extended portion  66  of the stop surface  64  prevents the center rear portion  30  from over-rotating past the inoperative position and into an orientation in which it cannot rotate back into the operative position as the tailgate assembly  14  moves back to the in-service position. Additionally, the pressure in the actuating cylinder  40  prevents the center rear portion  30  from inadvertently rotating back into the operative position. 
     In an alternative embodiment, a cable, chain  68  or the like can be used to limit counterclockwise rotation of the center rear portion  30  as opposed to providing an extended portion  66  of the stop surface  64  on the opposing side of the center rear portion&#39;s pivot axis from the cam roller  54 . As shown in FIG. 10, the cable or chain  68  is attached at one end to the tailgate side beam  28  and at the opposing end to the center rear portion  30 . As will be appreciated, the chain or cable  68  is of a suitable length so as to allow the center rear portion  30  to rotate to the inoperative position while preventing it from rotating too far in the counterclockwise direction. Moreover, the chain or cable  68  provides the additional advantage that it can be designed to break if the loading equipment collides with the center rear portion during a loading operation. This allows the center rear portion to pivot counterclockwise thereby helping to lessen some of the force of the collision, preventing more serious damage to the tailgate assembly. 
     From the foregoing it can be seen that a selectively deployable tailgate assembly is provided which includes a pivotable center rear portion of the tailgate and a relatively simple and reliable mechanism for automatically pivoting the center rear portion of the tailgate into an inoperative position as the tailgate assembly rotates into the out-of-service position. When the center rear portion of the tailgate is in the inoperative position it is oriented such that it does not project into the space above the open top of the dump body and thereby minimizes obstructions to the loading of material into the dump body. Thus, the tailgate assembly of the present invention substantially reduces the risk of damage to tailgate assembly during the loading operation as compared to prior tailgate assembly designs. 
     All of the references cited herein, including patents, patent applications, and publications, are hereby incorporated in their entireties by reference. 
     While this invention has been described with an emphasis upon preferred embodiments, it will be obvious to those of ordinary skill in the art that variations of the preferred embodiments may be used and that it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the following claims.