Abstract:
An extensible draw bar for facilitating coupling of a towed vehicle to a towing vehicle. An extension may be slidably secured to a static portion of a draw bar. A lock may be secured to the draw bar and be activated and deactivated to fix and release the extension, respectively. An extender may be activated to move the extension outwardly from the static portion. The extension may be slidable with respect to the lock while the lock is activated for certain positions of the extension relative to the lock. The extension may be positionable relative to the activated lock to automatically engage the lock to fix the position of the extension relative to the static portion.

Description:
RELATED APPLICATIONS  
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application Serial No. 60/302,630 filed Jul. 2, 2001 and entitled Truck Operated Transfer System. 
     
    
     
       BACKGROUND  
         [0002]    1. The Field of the Invention  
           [0003]    This invention relates generally to the field of transfer equipment. More particularly this invention relates to an apparatus to move a body from a supporting structure onto a truck. This invention also relates to mechanisms for coupling trailers to vehicles. More particularly, the invention relates to draw bars for securing trailers to trucks.  
           [0004]    2. The Background Art  
           [0005]    In many instances cargo or equipment needs to be loaded onto trucks. These loads are generally very large and may require specialized equipment to aid in loading and unloading. Loads may be containers, dump-truck bodies, mechanical equipment such as cranes or spreaders, or the like. A special problem exists where the transfer of a load onto a truck needs to take place away from industrial equipment such as cranes, fork-lifts, or other supporting equipment. In such cases the capability to transfer the load must be relocatable to the location of the vehicle.  
           [0006]    In some situations an operator of a truck may maximize the amount of cargo hauled during a trip by carrying a load mounted on the truck as well as drawing a trailer carrying additional cargo. For example, a dump truck may tow a trailer having an additional dump truck body mounted thereto. In this manner the truck may carry more cargo to or from a work site in a single trip. In some locations local laws may limit the weight of the load a truck is allowed to carry, based on the number of axles and the spacing between axles. Thus a trailer allows a truck to carry more load than the law would normally permit the truck to carry directly.  
           [0007]    Dump trucks have long made use of such functionality by towing “pup trailers” having their own dumping body. In some cases a pup trailer may have its own hydraulics to effect dumping of a load. A dump truck may also tow a transfer trailer that does not have dumping hydraulics. The body of the transfer trailer must therefore be transferred into the dumping body on the truck in order for the load to be dumped. An advantage of a transfer trailer is that a truck can transport a large load because of the extended wheel base of the truck and transfer trailer, and yet can still have good maneuverability at the dump-site because of the short wheelbase of the dump truck. In addition the transfer trailer is made inexpensive through the elimination of hydraulic dumping hardware or other complex systems.  
           [0008]    Some transfer trailers have small roller wheels that are powered along a track by an air or even electrical motor mounted to a transfer body resting on the transfer trailer. In typical operation an operator will position the back of the truck adjacent the front of the transfer trailer. The operator then exit the truck and goes to a switch at the back of the transfer trailer. The operator will then activate a switch that powers the wheels to propel the transfer body into the truck body. In some cases the roller wheels may roll along rails on the transfer trailer. In some systems, the operator must continually apply force to the switch as the transfer body moves from the trailer frame into the truck body in order to load the transfer body. Accordingly, the operator is obliged to walk along with the transfer body as it is loaded into the truck.  
           [0009]    Such a manner of operation has many inconveniences and disadvantages. First of all, the operator must exit the safety and controlling environment of the truck in order to effect the loading of the transfer trailer body. The unprotected operator is very close to a moving object weighing many tons during the process. In addition, the amount of force that can be transferred between the transfer body roller wheels and the transfer trailer is limited by the frictional forces that the roller wheel can exert on the rails.  
           [0010]    The amount of energy available to effect the transfer is also limited by the amount of energy that can be stored on the transfer body as pressurized gas, a battery, or the like. Thus, the wheels may not be able to overcome the weight of the transfer body if the transfer trailer is inclined. Thus, it would be an advancement in the art to provide a transfer system powered by the truck, in order to provide more power and energy to effect transfer of the transfer body. It would be a further advancement in the art to provide a transfer system that could be operated from within the cab of a truck.  
           [0011]    Once the transfer body is loaded onto the truck the operator is then required to again exit the truck and unlatch the tailgate of the transfer body so the load can be dumped. The operator then must enter the cab of the truck to operate the controls for the hydraulics to dump the contents of the transfer body. Disadvantages to this manner of operation include the fact that the driver must exit the truck to unlatch the tailgate. It may also pose a safety risk, inasmuch as the load may be exerting a force on the tailgate such that when the latch is released the load may spill out creating potential for potential harm of the operator.  
           [0012]    In some applications it may be advantageous for the truck to be in motion when the latch is released, such as when the truck is being used to spread material. Thus, a further disadvantage of such a conventional system is that the transfer body cannot be used to spread material, since the tailgate cannot be unlatched while the truck is in motion. Thus it would be an advancement in the art to provide a transfer body having a tailgate latch operable from within the cab of a truck.  
           [0013]    A transfer trailer may be secured to a truck by a draw bar. The draw bar typically has a fixed length such that the truck must be positioned at a precise distance from the trailer in order for the draw bar to connect to a hitch on the truck. To accomplish this an operator will typically turn off the engine and leave the truck with the brake disengaged, the transmission in reverse gear, and the clutch engaged. The operator will then walk to the back of the truck and push a button activating the starter motor of the truck, thereby causing the truck to move toward the drawbar. The operator is thereby enabled to position the truck with sufficient precision to connect the draw bar to the truck.  
           [0014]    This manner of operation has the principle disadvantage that an operator must stand behind a truck weighing many tons and set it in motion without access to a brake. A further disadvantage is that it is not conveniently performed with trucks having automatic transmissions. Thus it would be an advancement in the art to provide a drawbar that is extensible, enabling an operator to position the truck with less precision relative to the trailer. The operator would then be able to safely engage the brake of the truck before walking behind the truck to connect the draw bar to the truck. The draw bar could then be extended to reach the hitch on the truck, compensating for imprecision in the position of the truck relative to the transfer trailer. Such an extensible draw bar would have applications for a variety of trailers, besides transfer trailers, that makes use of draw bars in order to connect to a towing vehicle.  
         BRIEF SUMMARY OF THE INVENTION  
         [0015]    An invention is disclosed in sufficient detail to enable one of ordinary skill in the art to make and use the invention. In some embodiments a transfer module may rest on a support. In some embodiments a driver mounted to a truck may engage a track secured to the transfer module. The driver may engage the track in order to draw the transfer module onto the truck. In some embodiments the truck may have a dumping body having a substantially continuous floor. The track may be mounted to a pull bar secured at the rearward end of the transfer module. The pull bar may be pivotably secured to the rearward end of the transfer module. The transfer module may be pulled inside the dumping body whereas the pull bar may be located underneath the dumping body when the transfer module is loaded onto the truck.  
           [0016]    The track may be a chain extending along the pull bar and the driver may have a sprocket configured to engage the chain. Registration members such as horns secured to the forward end of the support may serve to align the transfer module and truck. The horns may insert into tubes or cavities formed in the truck.  
           [0017]    In some embodiments the transfer module may be embodied as a transfer dumping body having a tailgate. A latching system may enable an operator to latch and unlatch the tailgate of the transfer dumping body. In some embodiments an actuator may drive the movement of the latching system. In some embodiments the actuator may serve to both latch and unlatch the tailgate of the transfer dumping body as well as the tailgate of the dumping body mounted on the truck. In certain embodiments a locking systems may maintain the tailgates of the transfer dumping body and truck-mounted dumping body latched. In certain embodiments the locking systems may maintain themselves locked without the continuous application of force. In certain embodiments a locking system may be embodied as an over-center lock taking advantage of the toggle position of a linkage forming part of the locking system.  
           [0018]    A trailer may have a draw bar secured thereto. A truck hitch may secure near a free end of the draw bar. In certain embodiments an extension may be adjustable with respect to the remaining portion of the draw bar. In certain embodiments a lock may be activated to fix the position of the extension relative to the remainder of the draw bar. In certain embodiments the lock may be embodied as pins or posts secured to a pneumatic piston. The pneumatic piston may fix the position of the extension relative to the remaining portion by forcing a pin, post, or the like, into an aperture formed in the free end. In certain embodiments an extender may provide the force to drive the extension outwardly from the remaining portion in order to extend the length of the draw bar. In certain embodiments the extender may be a pneumatic piston acting on the extension.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The foregoing and other objects and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which:  
         [0020]    [0020]FIG. 1 is a perspective view of a transfer system in accordance with the invention;  
         [0021]    [0021]FIG. 2 is a perspective cutaway view showing components of the transfer system in accordance with the invention;  
         [0022]    [0022]FIG. 3 is lower quarter perspective view of a transfer module and track with various alternative track embodiments in accordance with the invention;  
         [0023]    [0023]FIG. 4 is a side elevation view of a transfer system in accordance with the invention;  
         [0024]    [0024]FIG. 5 is a side elevation view of a transfer system with the trailer and draw bar oriented in preparation for engagement of the truck and support in accordance with the invention;  
         [0025]    [0025]FIG. 6 is a side elevation view of a transfer system with the truck and support engaged with one another in accordance with the invention;  
         [0026]    [0026]FIG. 7 is a partial cutaway side elevation view detailing the disposition of various components of the transfer system when engaged in accordance with the invention;  
         [0027]    [0027]FIG. 8 is a side elevation view of a transfer system with the transfer module loaded onto the truck in accordance with the invention;  
         [0028]    [0028]FIG. 9 is a partial cutaway side view detailing the disposition of the various components of the transfer system when the transfer module is loaded onto the truck;  
         [0029]    [0029]FIG. 10 is a side elevation view of a transfer system having an alternative embodiment of a support in accordance with the invention;  
         [0030]    [0030]FIG. 11 is a bottom, rear quarter perspective view of an alternative embodiment of a track and pull bar in accordance with the invention;  
         [0031]    [0031]FIG. 12 is a is a perspective cutaway view showing an alternative embodiment of a truck body in accordance with the invention;  
         [0032]    [0032]FIG. 13 is a cutaway perspective view of a transfer system which does not have a dumping body secured to the truck;  
         [0033]    [0033]FIG. 14 is a cutaway perspective view showing alternative embodiments for a driver in accordance with the invention;  
         [0034]    [0034]FIG. 15 is a cutaway perspective view of a transfer system having a track mounted on the truck in accordance with the invention;  
         [0035]    [0035]FIG. 16 is a partial side elevation view of the apparatus of FIG. 15 showing the disposition of the various components of the apparatus when the support and transfer module are initially engaged with the truck in accordance with the invention;  
         [0036]    [0036]FIG. 17 is a partial side elevation view of the apparatus of FIG. 15 showing the disposition of the various components of the apparatus as the transfer module is being moved onto the truck;  
         [0037]    [0037]FIG. 18 is an exploded view of the components of a latching system and a locking system for a transfer module tailgate in accordance with the invention;  
         [0038]    [0038]FIG. 19 is an exploded view of the components of a latching system and a locking system for a truck-mounted dumping body tailgate in accordance with the invention;  
         [0039]    [0039]FIGS. 20A and 20B are side elevation views of an over-center lock in accordance with the invention;  
         [0040]    [0040]FIG. 21 is a side elevation of latching and locking systems for use with transfer module and truck-mounted dumping body tailgates, with the transfer module tailgate locked in a closed position in accordance with the invention;  
         [0041]    [0041]FIG. 22 is a side elevation of latching and locking systems for use with a transfer module and truck-mounted dumping body tailgates, with the latching systems in unlocked positions in accordance with the invention;  
         [0042]    [0042]FIG. 23A is a schematic representation of an electrical system for use in accordance with the invention  
         [0043]    [0043]FIG. 23B is a schematic representation of a hydraulic system suitable for use in accordance with the invention;  
         [0044]    [0044]FIG. 23C is a schematic representation of a pneumatic system for use in accordance with the invention;  
         [0045]    [0045]FIG. 24 is a partial perspective view of an extensible draw bar in accordance with the invention;  
         [0046]    FIGS.  25 A-C are cross sectional views illustrating the manner of operation of a lock suitable for use with an extensible draw bar in accordance with the invention;  
         [0047]    [0047]FIG. 26 is a partial perspective view of an alternative embodiment of an extensible draw bar in accordance with the invention;  
         [0048]    [0048]FIG. 27 is a partial perspective view of an alternative embodiment of an extensible draw bar in accordance with the invention; and  
         [0049]    FIGS.  28 A- 28 C are side elevation views showing a manner of operation of an extensible draw bar in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0050]    It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in FIGS. 1 through 28C, is not intended to limit the scope of the invention. The scope of the invention is as broad as claimed herein. The illustrations are merely representative of certain, presently preferred embodiments of the invention. Those presently preferred embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.  
         [0051]    Those of ordinary skill in the art will, of course, appreciate that various modifications to the details of the Figures may easily be made without departing from the essential characteristics of the invention. Thus, the following description of the Figures is intended only by way of example, and simply illustrates certain presently preferred embodiments consistent with the invention as claimed.  
         [0052]    Referring to FIG. 1, an apparatus  10  may comprise a truck  12  and a transfer module  14 . The transfer module  14  may rest on a support  16 . The support  16  may be embodied as a trailer  18  towable by a truck  12 . In certain embodiments the trailer  18  may have a draw bar  20  secured to the trailer  18 . The draw bar may serve to couple the trailer  18  to the truck  12 . The truck  12  may have a body  22  secured to a frame  24 .  
         [0053]    A longitudinal direction  26   a  may be defined as being parallel to the direction of travel of a truck  12 . A lateral direction  26   b  may be defined as being substantially parallel to a supporting surface under the truck  12  and perpendicular to the longitudinal direction  26   a . A transverse direction  26   c  may be defined as being substantially orthogonal to both the longitudinal direction  26   a  and the lateral direction  26   b.  The directions  26   a - 26   c  may also be considered to be axes  26   a - 26   c , accordingly rotation may be defined in terms of rotation about an axis parallel to an axis  26   a - 26   c.    
         [0054]    The truck  12  may define a forward end  28  and a rearward end  30 . In certain embodiments the truck body may be embodied as a dumping body  32 , or dump-truck body  32 , having a tailgate  34 . The tailgate  34  may be secured to the body  32  by pivots  36 . An arm  38  may be secured to the tailgate  34  and to an actuator  40 . The actuator  40  may be used to open the tailgate  34  to facilitate dumping.  
         [0055]    In certain embodiments the transfer module  14  may be embodied as a dumping body  42 . The dumping body  42  may have a forward end  44  and a rearward end  46 . The trailer  18  may have stops  48  formed to engage the rearward end  46  of the trailer  18  to prevent the body  42  from sliding off the trailer  18 . The body  42  may also have a tailgate  50  secured to the body  42  by pivots  52 . In certain embodiments the draw bar  20  may have a pintle ring  54  secured thereto. The pintle ring  54  may engage a pintle hitch  56  secured to the truck  12 .  
         [0056]    Referring to FIGS. 2 and 3, in certain embodiments the transfer module  14  may have a track  60  secured thereto. The track  60  may engage a driver  62  secured to the truck  12 . In certain embodiments, the track  60  may be secured to a pull bar  64  secured to the rearward end  46  of the transfer module  14  and extending toward the forward end  44 . In certain embodiments the pull bar  64  may be secured to the transfer module  14  by means of a pivot  66 . A pivot  66  may be embodied as a bolt  68  or pin  68 , or other structure  68 , extending through apertures  70  in the transfer module  14  and through the pull bar  64 . Alternatively, a pivot  66  may be embodied as studs  68 , or a pin  68 , either fixedly or pivotably secured to the pull bar  64  and extending through an aperture  70  or apertures  70  in the transfer module  14 . A rest  72 , or restraint  72 , may be secured to the support  14  to support the pull bar  64 , capturing the pull bar  64  and preventing the pull bar  64  from falling further toward the ground. The pull bar  64  may rotate, or pivot, about a number of axes, for example, the pull bar  64  may pivot about an axis substantially parallel to a lateral axis  26   b.    
         [0057]    The support  16  may have registration members  74  secured thereto, which may engage registration members  76  secured to the truck  12 . The registration members  74 ,  76  may serve to ensure adequate alignment of the truck  12  and transfer module  14  when the transfer module  14  is being transferred on to and off of the support  16 . The registration members  74 ,  76  may align the truck  12  and transfer module  14  in the longitudinal direction  26   a  and the lateral direction  26   b.  In certain embodiments the registration members  70  may be embodied as a horn  78 , or horns  78 , extending from the forward end  44  of the support  16  along a longitudinal direction  26   a.  The horn  78 , or horns  78 , may engage receivers  80  shaped to permit insertion of a horn  78  while still substantially forcing alignment of the truck  12  and transfer module  14 . In certain embodiments, a horn  78  may have a tapered end  82  to serve as a pilot to accommodate misalignment during insertion into a receiver  80 .  
         [0058]    In certain embodiments a lock  84  may secure to the truck  12  and lock the transfer module  14  to substantially fix its position relative to the truck  12 . The lock  84  may comprise a pin  86  actuated by a hydraulic piston  88 , pneumatic piston  88 , or the like. The pin  86  may insert into an aperture  90  formed in the transfer module  14 . In one embodiment, the aperture  90  may be formed in the pull bar  64 .  
         [0059]    The driver  62  may be embodied as a motor  98 , such as a hydraulic motor  98 , electric motor  98 , pneumatic motor  98 , or the like, having a drive wheel  100 . In certain embodiments the track  62  may be embodied as either a rigid or flexible member  62 , such as a rack or a chain  102 . The chain  102  may be secured along the length of the pull bar  64 , or may be secured only near the free end  104  and near the secured end  106  of the pull bar  64 . Accordingly the drive wheel  100  may be embodied as a sprocket  108  for engaging the chain  102 . The rest  72  may have a notch  110  to facilitate engagement of the sprocket  108  with the chain  102 .  
         [0060]    In certain embodiments, the transfer module  14  may have rollers  120  secured thereto to facilitate transfer of the transfer module  14 . The support  14  may have rails  122  to guide the transfer body  14  during transfer. Accordingly, the rollers  120  may have flanges  124  to maintain the rollers on the rails  122 . The truck  12  may likewise have rails  126 , along which the rollers  120  may roll. Alternatively, the transfer module  14  may simply be dragged onto the truck  12  without the benefit of rails  122 ,  126 , rollers  120 , or both.  
         [0061]    The track  60  may have various embodiments. For example, the track  60  may be a belt  132  secured near the free end  104  and near the secured end  106  of the pull bar  64 . The belt  132  may be secured at a distance  134  from the pull bar  64  in order to permit the insertion of a roller (e.g. idler) or other mechanism to increase friction between the drive wheel  100  and the belt  132 .  
         [0062]    The track  60  may also be embodied as a rack  136  formed along the pull bar  64 . Alternatively, the track may be a surface  138 , or surfaces  138 , formed on the pull bar  64  for engaging the drive wheel  100 . The pull bar  64  may have a tapered end  140  to facilitate initial engagement with the drive wheel  100  and to accommodate misalignment between the pull bar  64  and the drive wheel  100 . The surface  138 , or surfaces  138 , may be toothed, perforated, stepped, textured, roughened, coated, treated, or the like to enhance friction between a surface  138  and the drive wheel  100 . In certain embodiments the track  60  may be mounted to the truck  12 . Accordingly the pull bar  64  may have a hook  142   a , hooks  142   a  and  142   b,  or a ring  142 , aperture  142 , or other structure  142  for engaging a track  60 .  
         [0063]    Referring to FIGS. 4 and 5, a draw bar  20  may be secured to a trailer  18  by a pivot  143  allowing the draw bar  20  to be positioned as shown in FIG. 4 when towing a trailer  18 , and positioned as shown in FIG. 5 when transferring a transfer module  14  onto the truck  12 . During the process of transferring a transfer module  14 , the truck  12  and trailer  18  are typically positioned relative to one another as shown in FIG. 4. An operator may detach the pintle ring  54  from the hitch  56  and pivot the draw bar  20  out of the way into the position of FIG. 5. The operator will then back the truck toward the support  14  as shown in FIG. 5.  
         [0064]    Referring to FIG. 6, the operator may back the truck  12  toward the support  14  such that the horns  78  insert into the receivers  80 . The track  60  is then positioned proximate the driver  62 . For embodiments having a driver  62  embodied as a hydraulic motor  98 , the motor hydraulics may be switched to allow the drive wheel  100  to spin freely as the free end  104  of the draw bar  64  is forced over the drive wheel  100  during insertion.  
         [0065]    A trailer lock  144  may function in conjunction with the stops  48  to secure the transfer module  14  to the trailer  18 . In certain embodiments the trailer lock  144  may automatically lock the transfer module to the trailer  18  upon transfer of the transfer module  14  onto the trailer  18 . The lock  144  may also be configured to automatically disengage the transfer module  14  when a truck  12  backs up against the trailer  18 . Alternatively the lock  144  may be manually disengaged when the transfer module  14  is being transferred off the support  16 .  
         [0066]    Referring to FIG. 7, with the truck  12  positioned relative to the transfer module  14  as shown in FIG. 6, the pull bar  64  may be positioned over the driver  62 . The track  60  may also engage the drive wheel  100 . For embodiments of the apparatus  10  having a drive wheel  100  embodied as a sprocket  108 , the pivoting of the draw bar  64  relative to the transfer module  14  may allow the free end  104  of the pull bar  64  to be forced up over the teeth of the sprocket  108  and then fall down toward the sprocket  108  with the chain  102  engaged with the teeth of the sprocket  108 . In embodiments of the apparatus  10  having a truck body  22  embodied as a dumping body  32 , the driver  62  is typically positioned below the floor  146  of the body  32 . This may be the case for other embodiments of a truck body  22  having a continuous floor  146  that cannot conveniently have transfer hardware such as a driver  62  secured thereto.  
         [0067]    Referring to FIGS. 8 and 9, the driver  62  may be activated to exert a force on the track  60  to draw the transfer module  14  onto the truck  12  as shown in FIG. 8. The lock  84  may be activated during the transfer of a transfer module  14  into a truck  12 . The lock  84  may be continuously activated during the transfer process without effectively locking the position of the transfer module  14  into the truck  12  until the transfer module  14  is substantially completely transferred.  
         [0068]    In embodiments of the apparatus  10  having a locking pin  86  actuated by a piston  88 , the piston  88  may push the pin  86  against a structure of the transfer module  14 , allowing the transfer module  14  to slide by until a locking aperture  90  reaches a position near the piston  88 . The piston  88  may then force the pin  86  into the aperture  90  effectively locking the transfer module  14  into the truck  12 .  
         [0069]    In embodiments of the apparatus  10  wherein the locking aperture  90  is formed in the draw bar  64 , the locking pin  86  may slide along the draw bar  64  as the transfer module  14  is being transferred into the truck  12  until the locking aperture  90  is positioned such that the pin  86  inserts into the locking aperture  90 , as shown in FIG. 9. As shown in FIG. 9, for truck bodies  12  having continuous floors  146  the pull bar  64  is typically drawn into the envelope of the truck underneath the floor  146  while the transfer module  14  is drawn into the envelope of the truck above the floor  146 .  
         [0070]    Referring to FIG. 10, a support  16  may be embodied as a pedestal  148 . A pedestal  148  may allow transfer modules  14  to be stored at a height  150  such that they may be loaded into a truck  12  in the same manner as a transfer module  14  stored on a trailer  18 . In this manner a municipality, or other organization or individual, may purchase a single truck  12  and have several types of transfer modules  14  stored on pedestals  148 . A transfer module  14  may have any one of several functionalities and may accordingly be embodied as a spreader  152 , dumpster  152 , container  152 , garbage-truck body  152 , crane  152 , or the like. In this manner an organization may derive more functionality from a single truck  12 .  
         [0071]    Referring to FIGS.  11 - 13 , the pull bar  64  may be disposed in a variety of configurations. For example, the pull bar  64  may be fixedly, rather than pivotably, secured to the transfer module  14 . The pull bar  64  shown in FIG. 11 may also be formed without a chain  102 , but may rather have a surface  138 , or surfaces  138 , for engaging a drive wheel  100 . A floor  146  of a truck body  32  may have a channel  156  formed therein as in FIG. 11. The channel  156  may accommodate a pull bar  64  that is fixedly secured to the transfer module  14 . Alternatively a truck  12  may not have a floor  146 , but rather, merely a frame  24  having rails  126 , as shown in FIG. 12.  
         [0072]    Referring to FIG. 13, a driver  62  may be disposed in a variety of configurations. For example, a driver  62  may have a drive wheel  100  embodied as a gear  160  having involute gear teeth  162  suitable for engaging a track  60  embodied as a rack  136 . The normal operation of a gear  160  having involute gear teeth  162  results in a force exerted on the mating gear directed from the axis of rotation of the gear  160  toward the point of contact with the mating gear teeth.  
         [0073]    Accordingly, a retainer  164  may be needed to maintain the rack  136  in contact with the gear  162 . A retainer  164  may be embodied as a roller  166  spaced apart from the drive wheel  100 , such that the draw bar  64  extends between the drive wheel  100  and roller  166  with the roller  166  urging the draw bar  64  into the drive wheel  100  during transfer of a transfer module  14 .  
         [0074]    A roller  166  may have an actuator  168 , such as a piston  168 , solenoid  168 , or the like. The actuator  168  may be activated to position the roller  166  opposite the drive wheel  100  during transfer and moved out of the way of the free end  104  of the pull bar  64  during insertion.  
         [0075]    A track  60  may be embodied as a belt  132 . Accordingly, a drive wheel  100  may be embodied as a drive roller  170 . A roller  166  may be used to press the belt  132  against the roller  170 . The roller may insert between the pull bar  64  and the belt  132 . An actuator  168  may be used to move the roller  166  out of the way of the pull bar  64  during insertion and between the pull bar  64  and the belt  132  during transfer. A drive roller  170  may have flanges  172  to maintain the belt  132  substantially centered on the drive roller  170 .  
         [0076]    In certain embodiments of an apparatus  10 , the track  60  may be embodied as surfaces  138  formed on the pull bar  64 . Accordingly, the drive wheel  100  may be embodied as a drive roller  170 . A retainer  164  may be used to press the pull bar  64  onto the drive wheel  100 . The retainer  164  may move the roller  166  along a substantially transverse direction  26   c . Thus the force exerted on the pull bar  64  can be controlled using the actuator  168 .  
         [0077]    In certain uses the transfer of a transfer module  14  into or out of a truck may take place on uneven terrain. Accordingly, the transfer module  14  may not be adequately aligned with the truck  12 . The support  16  may likewise be at an angle relative to the truck  12 . Such variability in orientation may cause variations in the angle that the pull bar  64  makes with the truck  12 .  
         [0078]    A roller  166  positioned a fixed distance away from the drive wheel  100  may be able to accommodate only small variations in the angle of the pull bar  64  relative to the truck  12 . An actuator  168  that has a range of motion parallel to a transverse direction  26   c  enables the application of a force to urge the draw bar  64  onto the drive wheel  100 . In the case where the draw bar is at an angle with respect to the truck, the actuator  168  may be forced to move the roller  166  in order to accommodate the angle. However, because the motion of the draw bar  64  is parallel to the direction of motion of the actuator  168 , no bending or breakage of hardware results.  
         [0079]    For example, an actuator  168  may be a hydraulic piston  168 . Application of pressurized hydraulic fluid to the piston will result in a constant force exerted on the pull bar  64 . Should the pull bar  64  be angled wrong it will exert a force on the roller  166 . If the force exerted by the pull bar  64  is greater than the force exerted by the piston  168 , the piston  168  will merely be extended from its cylinder until the force exerted by the pull bar  64  on the roller is equal to the force exerted by the hydraulic piston  168 .  
         [0080]    An actuator  168  may also be a biasing spring  168  that urges the roller onto the drive wheel  100 . The free end  104  of the pull bar  64  may have a tapered end  140  such that the pull bar  64  may be piloted between the roller  166  and the drive wheel  100  when the truck  12  is backed up to the support  16 .  
         [0081]    Alternatively, the weight of the pull bar  64  may be sufficient to maintain the urge the pull bar  64  against the drive wheel  100  such that enough friction is developed between the track  60  and drive wheel  100  to enable the drive wheel  100  to transfer force to the transfer module  14  effective to move the transfer module  14  to and from the truck  12 . In some embodiments the weight of the pull bar  64  may be enough to maintain a rack  136  in mating engagement with a gear  160  even while the gear  160  is driving the rack  136 .  
         [0082]    The driver  62  and lock  84  may be disposed in a variety of configurations. For example, the axis of rotation of the drive wheel  100  of the driver  62  may be substantially parallel to a transverse axis  26   c.  An actuator  168  may, accordingly, move substantially in a lateral direction  26   b.  The lock  84  may rely on a piston  88  to move the locking pin  86  along a transverse direction  26   c,  accordingly the locking aperture  90  may extend through the pull bar  64  in a transverse direction  26   c.    
         [0083]    Referring to FIGS.  15 - 17 , a track  60  may be positioned on the truck  12  rather than on the transfer module  14 . In certain embodiments of an apparatus  10 , the track  60  may be embodied as a conveyor  178  extending from proximate the rearward end  46  toward the forward end  44  of the truck  12 . The conveyor  178  may be driven by the hydraulic motor  98 . The conveyor  178  may be a chain  180 , belt  182 , or the like. A conveyor  178  may have a dog link  184 , or dog  184 , having one or more protrusions or side pieces  186  on either one or both sides of the chain  180 , a cross bar  188  may extend therebetween.  
         [0084]    The cross bar  188  is typically secured to the side pieces  186  such that it is positioned a distance  190  away from the chain. Alternatively the side pieces  186  may be replaced by a single hook  186 , or post  186 , protruding from the dog link  184  for engaging a hook  142 , aperture  142 , ring  142 , or the like, formed on the pull bar  64 .  
         [0085]    Conveyors  178  embodied as belts  182  may have a dog  184  with side pieces  186  embodied as two links  194  having one end pivotably secured to the cross bar  188  and the other end secured to one of two bands attached to the belt  182  in order to allow the belt to wrap around a roller, such as a drive roller  170 .  
         [0086]    A dog  184  may be positioned as shown in FIG. 16 at the time the truck  12  backs up to the transfer module  14 . The driver  60  may be activated to move the dog  184  to the position shown in FIG. 17. As the dog  184  moves from the position of FIG. 16 to the position of FIG. 17 the cross bar  188  catches the hook  142   a,  or other protrusion, structure, or aperture. The driver  60  may then drive the dog  184  toward the forward end  44  of the truck  12  in order to load the transfer module  14  onto the truck  12 . The driver may likewise be reversed to cause the cross bar  188  to catch the hook  142   b,  or other protrusion, structure, or aperture, and drive the transfer module  14  toward the rearward end  46  of the truck  12  in order to unload the transfer module  14 .  
         [0087]    Referring to FIG. 18, a transfer module  14  having a tailgate  50  may have a latching system  200  secured to either side of the transfer module  14 . The latching system  200  shown in FIG. 18 illustrates one side of the latching system  200 , the other side of the latching system  200  may be substantially the mirror image of the side illustrated in FIG. 18. A latching system  200  may comprise a latch  202  for maintaining a tailgate  50  closed.  
         [0088]    A locking system  204  may be used to both actuate the latch  202  and to maintain the latch  202  in a position suitable for retaining the tailgate  50 . A latch  202  may have an arm  206  for retaining a structure on the tailgate  50  in order to hold the tailgate  50  closed. In certain embodiments the arm may retain a rod  208 , post  208 , or other structure  208 , extending from the tailgate  50 .  
         [0089]    A catch  210  may secure to the transfer module  14 . The catch  210  may serve to register the rod  208  with respect to the transfer module  14 . In certain embodiments the catch  210  may be or include a notch  212  formed to receive the rod  208 , post  208 , or other structure  208 .  
         [0090]    The latch  204  may be either fixedly or pivotably secured to a pivot  216  or shaft  216 . The shaft  216  may be pivotably or fixedly secured to the transfer module  14 . For embodiments having a latch  204  fixedly secured to the shaft  216 , the shaft  216  is typically pivotably secured to the transfer module  14 . For embodiments having a latch  204  pivotably secured to the shaft  216  the shaft  216  may be either pivotably or fixedly secured to the transfer module  214 .  
         [0091]    A crank  220  may be either fixedly or pivotably secured to the pivot  216 . For embodiments having a crank  220  and latch  204  pivotably secured to the pivot  216 , the crank  220  may also secure to the latch  204  such that relative rotation therebetween is substantially prevented. A pin  222  may pivotably secure the free end  224  of the crank  220  to the end  226  of a hook  230 .  
         [0092]    A roller  238  may be rotatably secured to the hook  230  by a pin  234 . The end  240  of the hook  230  may be secured with a pin  242  to the free end  244  of a toggle link  246 . The toggle link  246  may be fixedly secured to a pivot  248 , or shaft  248 , pivotably secured to the transfer module  14 . Alternatively, the toggle link  246  may be pivotably secured to the shaft  248  and the shaft  248  may then be either pivotably or fixedly secured to the transfer module  14 .  
         [0093]    A spring  250  may serve to predictably position the roller  238  for engagement in order to change the state of the locking system  204 . The spring  250  typically urges the hook  230  into a position to engage a driving surface, or the like, which may serve to force the hook locking system  204  into a variety of positions. The spring  250  may bias the hook  230  in a variety of directions in order to accomplish its purpose.  
         [0094]    For example, a spring  250 , such as a torsion spring  250  or the like, may have one end  252   a  engaging the hook  230  and the other end  252   b  engaging the transfer module  14  to urge the end  240  of the hook  230  downward substantially in the transverse direction  26   c . Alternatively, the spring  250  may have one end  252   a  engaging the toggle link  246  and the other end  252   b  engaging the transfer module  14  biasing the toggle link  246  to rotate about the pivot  248 , effectively urging the end  240  of the hook  230  downward substantially in the transverse direction  26   c . The spring  250  may also have one end  252   a  engaging the hook  230  and the other end  252   b  engaging the toggle link  246  with the spring loaded to cause the hook  230  to rotate relative to the toggle link  246 , effectively urging the hook  230  downward substantially in the transverse direction  26   c.    
         [0095]    Referring to FIG. 19, A truck  12  having a body  22  with a tailgate  34  may have a latching system  258  having latches  260  located on either side of the truck  12  and locking systems  262  on either side  263  of the truck  12 . A locking system may provide for locking of the position of a latch  260  relative to the truck  12 . The locking system  262  may also provide for the actuation of the latch  260 . A latch  260  may have an arm  264  for engaging a rod  266 , post  266 , or other structure  266  extending from the sides of the tailgate  34 .  
         [0096]    Catches  268  maybe formed on the truck  12  for receiving the rods  266 . The rods  266 , or posts  266 , may be held between the arms  256  and the catches  268  when the tailgate  34  is being held closed. In certain embodiments a catch  368  may have a notch  270  for retaining a rod  266 , or post  266 . The latch  260  may be either fixedly or pivotably attached to a pivot  272 . The pivot  272  may be either fixedly or pivotably secured to the truck  12 . For embodiments of an apparatus  10  having a latch  260  fixedly secured to the pivot  272 , the pivot  272  is typically pivotably secured to the truck  12 .  
         [0097]    A latch  260  may have a driving surface  274  on the latch  260  to engage the roller  238  secured to the hook  230 . A stop  276  may also be either formed with or secured to the latch  260  near the driving surface. The stop  276  may then catch the roller  238  as the transfer module  14  is inserted into the truck  12  and also serve to drive the locking system  204  into a locked position.  
         [0098]    A crank  278  may be either fixedly or pivotably secured with respect to the pivot  272 . For embodiments of the apparatus  10  having a latch  260  that is pivotably secured to the pivot  272 , the crank  278  may be secured to the latch  260  such that relative rotation of the crank  278  with respect to the latch  260  is substantially prevented. For embodiments wherein the latch is fixedly attached to a pivot  272  pivotably secured to the truck  12 , the crank  278  is typically fixedly secured to the pivot  272 .  
         [0099]    A crank  278  may have a free end  280  pivotably secured, by a pin  282 , or some other fastener  282 , to the end  284  of a hook  286 . An end  288  of the hook may be pivotably secured with a pin  290 , or other fastener  290 , to the free end  292  of a toggle link  294 . The toggle link  294  may be fixedly secured to a shaft  296  extending across the truck  12  substantially in a lateral direction  26   b.  The shaft  296  may be rotatably secured to the frame  24  of the truck  12 . A crank  298  may be fixedly secured to the shaft  296 . The free end  300  of the crank  298  may engage an actuator  302 , such as a hydraulic piston  304 , or the like. Alternativley, the crank  298  may be embodied as a gear  298  which may engage a gear  306  driven by a motor  308 .  
         [0100]    Referring to FIGS. 20A and 20B, a locking system  204 ,  262  may make use of the toggle position of the various components of the system  204 ,  262  in order to provide a self locking system  204 ,  202 . For example a toggle link  246 ,  294 , may be forced to rotate from the position shown in FIG. 20A to the position shown in FIG. 20B. The rotation of the toggle link  246 ,  294  may require rotation through an angular region  324  where the distance between the end  240 ,  288  and the end  226 ,  284  of the hook  230 ,  286  must exceed the undeformed length of the hook  230 ,  286  in order for the end  226 ,  284  to be moved therethrough. Thus, it requires that a force sufficient to deform a hook  230 ,  286  be exerted on the toggle link  246 ,  294  in order to move the hook  230 ,  286  into and out of the position of  19 B. The end  226 ,  284  may need to be restrained from moving in order for the rotation of the toggle line  246 ,  294  to cause deformation of the hook  230 , 286 . A catch  210 ,  268  may interfere with the arm  206 ,  264  in order to constrain rotation of the latch  202 ,  260 , effectively restraining the end  226 ,  284  of a hook  230 ,  286 .  
         [0101]    The curvature  326  of the hook may facilitate locking by preventing further rotation in a direction  328  of a toggle link  246 ,  294  once the hook  230 ,  286  has been moved through the angular region  324 . The curvature  326  allows the end  240 ,  288  to be moved through the angular region  324  without interference with the pivot  248  or shaft  296 . However, once the toggle link  246  has moved through the angular region  324 , the hook  230 ,  286  will interfere with the pivot  248 , or shaft  296 , to prevent further substantial rotation in a direction  328 .  
         [0102]    Typically a hook  230 ,  286  and toggle link  246 ,  294  will be loaded substantially in a direction  328 . It can readily be seen that such loading cannot result in a rotational force sufficient to move a toggle link  246 ,  294  out of the position of FIG. 19B into the position of FIG. 19A. Thus, the toggle link  246 ,  294  and hook  230 ,  286  are effectively locked in position and require no constant exertion of force to be maintained locked. The toggle link  246 ,  294  and hook  230 ,  286  can therefore be used to move a structure, such as a latch  202 ,  260 , through an angle  330  and lock it in place.  
         [0103]    Referring to FIGS. 21 and 22, upon transfer of a transfer module  14  into a truck  12  the roller  238  may be positioned adjacent the driving surface  274 . The hook  230  and toggle link  246  may be in a locked position, maintaining the arm  206  of the latch pressed against the catch  210 , maintaining the tailgate  50  closed as shown in FIG. 21. The hook  286  and toggle link  294  may likewise be in a locked position.  
         [0104]    The actuator  302  may exert a force on the crank  298  in a direction  334 , thereby causing the shaft  296  to rotate the toggle link  294  and hook  286  out of the locked position of FIG. 21. The hook  286  may then exert a force on the crank  278 , causing the driving surface  274  to push against the roller  238 . The force exerted on the roller  238  may then force the hook  230  and toggle link  246  out of the locked position of FIG. 21. The force exerted on the hook  230  may be transferred through the hook  230  to the crank  220 , opening the latch  202  and releasing the rod  208 , or post  208 , effectively allowing the tailgate  50  to open as shown in FIG. 22.  
         [0105]    The actuator  302  may exert a force on the crank  298  in a direction  336 , thereby causing the shaft  296  to rotate the toggle link  294  and hook  286  into the locked position of FIG. 21. The hook  286  may then exert a force on the crank  278 , causing the stop  276  to push against the roller  238 . The force exerted on the roller  238  may then force the hook  230  and toggle link  246  into the locked position of FIG. 21. The force exerted on the hook  230  may be transferred through the hook  230  to the crank  220 , closing the latch  202  and engaging the rod  208 , or post  208 , effectively closing the tailgate  50  as shown in FIG. 21.  
         [0106]    The actuator  302  may also serve to latch and unlatch the tailgate  34  of the body  32 . The actuator  302  may cause the hook  286  and toggle link  294  to move to the locked position of FIG. 21 thereby locking a rod  208 . In the absence of a transfer module  14  loaded onto the truck  12 , the latch may then move to secure the rod  266  , or post  266 , secured to the tailgate  34  between the arm  264  of the latch  260  and the catch  270 . In a like manner the actuator  302  may move the hook  286  and toggle link  294  to the open position of FIG. 2B and release the rod  266 , or post  266 , from the arm  264  of the latch  260 . In this manner the same actuator  302  may latch and unlatch both of the tailgates  34 ,  50 .  
         [0107]    Referring to FIGS.  23 A- 23 C, the pneumatic and hydraulic components of the apparatus  10  may be controlled by an electrical system  348  shown schematically in FIG. 23A. The electrical system  348  may be powered by a power source  346 , such as a battery  346 . The hydraulic components of the apparatus  10  may form part of a hydraulic system  348  shown in FIG. 23B. The hydraulic system  348  may be powered by a pressure source  350 , such as a hydraulic pump  350  associated with the truck  12 . The pneumatic components of the apparatus  10  may form part of a pneumatic system  352  shown in FIG. 23C. The pneumatic system  352  may be powered by a pressure source  354 , such as a compressor  354  on the truck  12 .  
         [0108]    A switch  358  may be closed to apply a voltage to a tailgate valve  60 , opening the valve  60  and enabling hydraulic fluid to enter the cylinder  40 , the cylinder thereby raises the tailgate  34  of the dumping body  32 . A transfer mode switch  362  may be moved to a position  364   a  in order to apply a voltage to the free wheel valve  366 . By opening the valve and thereby directing the flow of hydraulic fluid to bypass the motor  98  allowing the motor to be spun freely by the track  60  forced over the drive wheel  100 . The transfer mode switch  362  may be moved to a position  364   b  to apply a voltage to a lock pin valve  368 . Opening the valve  368  and enabling pressure to be applied to the cylinder  88  causes the lock pin  86  to press against some structure of the transfer module  14  or to force itself into a locking aperture  90 .  
         [0109]    The positioning of the transfer mode switch  362  to the position  364   b  may also cause a voltage to be applied to retainer valve  370 . Opening a valve  370  and enables pressurized gas to cause the piston  168  to force the retainer  164  against a pull bar  64  to enhance friction between a drive wheel  100  and the track  60 . An override switch  372  may be used to cut off voltage from both the free wheel valve  366  and the retainer  164 . This may enable a user to disengage the locking pin  86  from the transfer module  14  when the transfer module  14  is being transferred out of the truck  12 .  
         [0110]    The engage mode switch  374  may have positions  376   a ,  376   b . The engage mode switch  374  may be placed in position  376   b  to permit the application of voltage to a light in the cab of a truck  12 , thereby alerting the operator that a transfer module  14  is safely locked onto the truck  12 . The transfer mode switch  362  and engage mode switch  374  may be coupled by a linkage  378  such that whenever the switch  362  is in the position  364   a  the switch  374  is in position the  364   a.  Whenever the switch  362  is in the position  364   b  the switch  374  is in position  364   b.  Thus, the light  380  will not turn on unless the lock pin valve  368  is open.  
         [0111]    A dump switch  382  may control the flow of hydraulic fluid to the hoist  383 . The dump switch  382  may have two positions  384   a ,  384   b . The switch  382  may be located in position  384   a  in order to apply a voltage to the dumping valve  386 . Opening the valve  386  pressurizes the hoist  383  to dump the load of the dumping body  32 .  
         [0112]    The undump switch  388  may have two positions  388   a ,  388   b . The switch  388  may be positioned in a position  390   a  in order to apply a voltage to the undumping valve  392 . Opening the valve  392  enables the hoist  382  to de-pressurize, allowing the dumping body  32  to rest on the frame  24  of the truck  12 . The switches  382 ,  388  may also have positions  384   c ,  390   c  resulting in an open circuit between the power source  346  and the valves  386 ,  392 . The dump switch  382  and undump switch  388  may be coupled by a linkage  394  such that the switch  382  is in one of the positions  384   a - 384   c  whenever the switch  388  is in one of the positions  390   a - 390   c , respectively.  
         [0113]    A transfer switch  396  may have positions  398   a - 398   c . The switch  396  may be located in a position  398   a  in order to apply a voltage to a transfer in valve  400 . Opening the valve  400  pressurizes the hydraulic motor  98  in a direction causing the transfer module to be transferred onto the truck  12 . The switch  396  may be located in the position  398   b  in order to apply a voltage to a transfer out valve  402 . Opening the valve  402  pressurizes the motor  98  such that the transfer module  14  is transferred off the truck  12 .  
         [0114]    A tailgate lock switch  404  may be closed to apply a voltage to the tailgate lock valve  406 , opening the valve  406  and causing the actuator  302  to open the tailgate latches  202  and  260 . In certain embodiments, the actuator  302  may have a bias such that when the valve  406  is open, the actuator  302  moves the latches  202 ,  260  into locked positions as in FIG. 21.  
         [0115]    A lock sensor  408  may follow the position of the lock  84  and restrict the operation of the other components of the hydraulic system  348  and pneumatic system  352 . For example the lock sensor  408  may be in a position  410   a  when the lock pin  86  is engaged with the aperture  90 . Placing the sensor  408  in a position  410   a  enables the light  380  to turn on indicating that the transfer module  14  is safely locked onto the truck  12 . The placement of the sensor  408  in position  410   a  may also enable a voltage to be applied to the dump valve  386  in order to open it and dump a load from the truck  12 .  
         [0116]    The sensor  408  may be placed in a position  410   b  indicating that the lock pin  86  has not fully engaged the aperture  90 . Placing the sensor in position  410   b  may prevent the application of voltage to the light  380  and dumping valve  386 , preventing the dumping of a transfer dumping body  42  not properly locked onto the truck  12 .  
         [0117]    Referring to FIG. 23, a draw bar  20  may have an extension  450  slidably secured to a static portion  452 . The extension  450  may be adjustable with respect to the static portion  252  in order to vary the distance  454  between the pintle ring  54  and the static portion  452 . The adjustability of the distance  454  may provide for easier securement of a trailer  18  to a truck  12 . The adjustability may provide for the truck  12  to be positioned with the pintle hitch  56  located within a large region rather than at a specific point and still allow for the pintle ring  54  to be placed on the pintle hitch  56 . The extension  450  may have arms  456   a ,  456   b , or a single arm  456 , which may slide along a guide  458  secured to the static portion  452 .  
         [0118]    The guide  458  may be embodied as sleeves  460   a ,  460   b , or a single sleeve  460  secured to arms  462   a ,  462   b  of the static portion  452 . The arms  456   a ,  456   b , or arm  456 , may slide within the sleeves  460   a ,  460   b , or sleeve  460 , in order to provide adjustability of the distance  454 . A lock  464  may fix the position of the extension  450  with respect to the static portion  452 . An extender  466  may move the extension  450  with respect to the static portion  452 .  
         [0119]    In certain embodiments the extender  466  may be a pneumatic piston  467 , hydraulic piston  467 , electric actuator  467 , or the like. The pneumatic piston  467  may exert a force on a cross beam  468  secured to both of the arms  456   a ,  456   b . In certain embodiments an operator may control the flow of air to the piston  467  in order to control extension of the extension  450 . In some embodiments an operator will open a valve or the like in order to allow pressurized gas, or the like, to contact the piston  467 . The cross beam  468  may serve to provide stiffness to the extension  450  and ensure that the arms  456   a ,  456   b  move simultaneously. The arms  456   a ,  456   b  may have apertures  470  formed therein to receive locking pins or the like to fix the position of the extension  450  with respect to the static portion  452 . In certain embodiments there may be a plurality of apertures  470  formed along an arm  456   a  and along an arm  456   b . This may enable the pintle ring  454  to be fixed at a variety of lengths  454  from the static portion  452 .  
         [0120]    In operation, an operator may disengage the lock  464  such that the extension  450  is free to move with respect to the static portion  452 . The operator may extend the extension  450  to the pintle hitch  56  and secure the pintle ring  54  thereto. The operator may then activate the lock  164 . The lock  164  may then automatically engage, fixing the position of the extension  450  with respect to the static portion  452  as the operator backs the truck  12  toward the trailer  18 .  
         [0121]    Referring to FIGS.  25 A- 25 C, a lock  464  may have an actuator  471  for engaging and disengaging the lock  464 . In certain embodiments the actuator  471  may move the lock  464  from the state shown in FIG. 25A to the state shown in FIG. 25C. In certain embodiments the actuator  471  may be embodied as a pneumatic piston  472  and cylinder  474 . Alternatively, the actuator  471  may be embodied as a hydraulic piston  472  and cylinder  474 , electric actuator  474 , or the like. In certain embodiments the lock  464  may be secured to the guides  458 . In other embodiments the lock  464  may be secured to the arms  456   a ,  456   b , or arm  456 . A pin  476  may be secured to the piston  472  and a pin  478  secured to the cylinder  474 .  
         [0122]    The cylinder  474  may be pressurized and force the piston  472  to move outwardly from the cylinder  474 . In certain embodiments an operator may pressurize the cylinder  474  by opening a valve, or the like, to allow pressurized gas to enter the cylinder  474 . The motion of the piston  472  may drive the pin  476  into an aperture  479  formed in the sleeve  460   a  and the aperture  470  formed in the arm  456   a . The pin  478  may move into an aperture  479  formed in the sleeve  460   b  and the aperture  470  formed in the arm  456   b , as shown in FIG. 25B. When the apertures  470  are not aligned with the pins  476 ,  478 , as shown in FIG. 25C, the pins  476 ,  478  may press against the arms  456   a ,  456   b  until the arms  456   a ,  456   b  are moved into position such that the apertures  470  are aligned with the pins  456   a ,  456   b , at that point, the pins  476 ,  478  will be forced into the apertures  470 . This may allow for the extension  450  to be drawn out in order to facilitate coupling with a trailer  18 .  
         [0123]    The cylinder  474  may then be pressurized and the truck  12  backed toward the trailer  18  such that the arms  456   a ,  456   b  are pushed along the sleeves  460   a ,  460   b  until the pins  476 ,  478  are aligned with the apertures  470 . The pins  476 ,  478  may then insert into the apertures  470  effectively fixing the position of the extension  450  relative to the static portion  452  such that the truck  12  can now tow the trailer  18  .  
         [0124]    In certain embodiments the arms  456   a ,  456   b , or arm  456   a , may be formed as rectangular tubes. The locking pins  476 ,  478  may be responsible for transferring loads from the extension  450  to the static portion  452 . The pins  476 ,  478  may, therefore, exert very large forces on the arms  456   a ,  456   b , or arm  456   a . Accordingly, a bushing  480  may be inserted into an aperture  470  and extend across the vacant area of the tube to help distribute loads from a locking pin  476 ,  478  across both sides of the tube.  
         [0125]    The actuator  471  may be slidably mounted with a guide  482 . The guide  482  may be embodied as slots  484  receiving pins  485 . The slots  484  may be formed in flanges  486  secured to the actuator  471 . Alternatively, the guide  482  may be embodied as rails  487  extending between the sleeves  460   a ,  460   b . The actuator  471  may be secured to the rails and slide substantially freely therealong.  
         [0126]    Alternatively, the guide  482  may be embodied as a channel  487  extending between the sleeves  460   a ,  460   b  with the actuator  471  sliding therealong. The pins  484  may be fixed to supports  488  extending between the arms  462   a ,  462   b  of the static portion  452 . The pins  484  may secure the actuator  471  to the supports  488  while still permitting the pins  484  to slide along the slots  485 .  
         [0127]    The pin  476  may have a stop  490  formed thereon. The stop  490  may be embodied as a shoulder  491 , snap ring  491 , or other suitable structure  491 . The stop  490  may serve to prevent the pin  476  from inserting completely into the aperture  479 . In normal operation the piston  472  will continue to be forced outwardly from the cylinder  474 . The stop  490  will push against the sleeve  460   a  causing the cylinder  474  and the pin  478  to slide along the guide  522  toward the sleeve  460   b  until the pin  478  inserts sufficiently into the aperture  479  of the sleeve  460   b.    
         [0128]    In certain embodiments a pad  496  may absorb the impacts of the stop  490  against the sleeve  460   a . In certain embodiments a flange  494 , or shoulder  494 , may be formed on the pin  478 . The flange  494  may be forced against a pad  496  as the cylinder is pushed along the guide  482 . The pad  496  may serve to absorb impacts between the flange  494  and the sleeve  460   b.    
         [0129]    A return mechanism  498  may return the lock  464  to the state illustrated in FIG. 25A. In certain embodiments the return mechanism  498  may be embodied as a spring  500  having one end  502   a  secured to the flange  486  and the other end  402   b  secured to the sleeve  460   a . Alternatively, the spring  500  may be a compression spring  500  having one end  502   a  secured to the flange  486  and the other end  502   b  secured to the sleeve  460   b . Likewise, a biasing spring  504  may tend to draw the piston  472  into the cylinder  474 . In actual operation, the biasing spring  504  may return the piston  472  to the position of FIG. 25A when pressure ceases to be exerted on the piston  472 .  
         [0130]    Referring to FIG. 26, an extension  450  and lock  464  may be disposed in a wide range of configurations. In certain embodiments, the lock  464  may be secured to the extension  450  rather than to the static portion  452 . The guide  522  may be embodied as channels  506   a ,  506   b  secured to the arms  462   a ,  462   b  of the static portion  452 . In embodiments having the lock  464  secured to the extension  450 , the pins  476 ,  478  may extend through the apertures  470  in the arms  462   a ,  462   b  whether or not the cylinder  474  is pressurized.  
         [0131]    Referring to FIG. 27, in certain embodiments, the extension  450  may have a single arm  456 . The extension  450  may slide within a single sleeve  460  formed in the static portion  452 . In certain embodiments a support  522  may also have a sleeve  524  to further guide the motion of the arm  456  and resist twisting and bending.  
         [0132]    The lock  464  may still be have a cylinder  474  and may be fixedly secured to the support  522 . The lock  464  may drive a pin  476  into an aperture  470  formed in the arm  456 . In certain embodiments the sleeve  524  may have apertures  528  formed therein. The pin  476  may accordingly extend through the aperture  528  and into the aperture  470  in order to lock the extension  450  relative to the static portion  452 .  
         [0133]    An extension  450  and static portion  452  may be used as shown in FIGS.  28 A- 28 C. A truck  12  may park near the pintle ring  54  as shown in FIG. 28A. An operator may disengage the lock  464 , permitting the extension  450  to be drawn out in a direction  534  and the pintle ring  54  placed over the hitch  56 . In certain embodiments the extender  466  may be activated to provide a force tending to extend the extension  450  from the static portion  452 .  
         [0134]    The operator may then activate the lock  464  by, for example, pressurizing the cylinder  474 . With the cylinder  474  pressurized and the extension in the position shown in FIG. 28B, the pins  476 ,  478 , or pin  476 , will press against the arms  456   a ,  456   b , or arm  456 . The operator may then back the truck  12  toward the trailer  18  in a direction  536 .  
         [0135]    As the extension  450  is pushed toward the static portion  452 , the lock  464  eventually engages by, for example, forcing the pins  476 ,  478 , into the apertures  470  in the arms  456   a ,  456   b  as the apertures  470  become aligned with the pins  478 ,  476 . The lock  464  may, alternatively, force a single pin  476  into a single aperture  470  in an arm  456  as the pin  476  becomes aligned with the aperture  470 . The truck  12  and trailer  18  are then positioned suitable for towing as shown in FIG. 28C.  
         [0136]    The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.