Abstract:
A compact, portable locking pin locator device adapted to assist the driver of a semi truck including a tractor and a trailer to locate the trailer over the tandem axle under the back end of the trailer to achieve proper weight and balance of the load carried in the trailer over the wheels of the truck.

Description:
This invention relates to a portable locking pin locator device for use by the driver of a semi truck for locating the trailer of the truck in the proper position over the tandem axle under the trailer to achieve the correct and legal weight and balance relative to the different wheel locations of the truck, namely (a) the steering wheels (steers) located at the front of the tractor of the truck, (b) the driving wheels (drives) located at the rear of the tractor and (c) the tandem axle (tandems) located at the rear of the trailer. 
   BACKGROUND OF THE INVENTION 
   Semi trucks consist of a tractor and a trailer. For legal and safety concerns the loads carried in the trailers must meet state and federal weight requirements. This can be accomplished most often by positioning the trailer over the tandems in the rear of the trailer. Weight limitations apply to the steers, the drives and the tandems. Movement of the trailer over the tandems affects the weight at all three locations, the steers, the drives and the tandems. The trailer is constructed to slide back and forth over the tandems until the proper position is achieved and then locked into that position. Two parallel rails, fastened longitudinally underneath the trailer (sometimes referred to as the main frame) are fitted over corresponding rails on the tandems (sometimes referred to as the sub-frame). Holes in the trailer rails are positioned to engage extendable pins located on the tandems through holes in the tandem axle rails. Two or four pins are generally employed to lock the trailer and tandems together. The pins are retracted to permit the trailer to slide back and forth over the tandems. The pins are extended to lock the trailer to the tandems when the proper position is achieved to meet positional weight requirements. The mechanism used to extend and retract the pins is located on the tandems and moves all of the pins simultaneously. Holes in the trailer rails are located so they can match the locations of the pins. Thus lining up a hole on one trailer rail with a locking pin on one side of the tandems will simultaneously line up with a hole on the trailer rail on the other side of the trailer with a locking pin on the other side of the tandems. 
   The difficulty of locating the trailer in the proper position over the tandems axle is that the driver sitting in the tractor cannot see the relative position of the trailer over the tandems at the back of the trailer. After selecting the locking pin hole in the trailer rails to achieve proper weight and balance, a driver working alone must climb back into the cab of the tractor and slide the trailer until he/she thinks the correct position has been acquired. This action is repeated after every move the driver makes to position the trailer over the tandems and determine the relative position of the selected hole in the trailer rail to the pins in the tandems. The driver may have to make several trips climbing in and out of the tractor before positioning the trailer over the tandems at the selected location. 
   The prior art contains many examples of means for locating the trailer of a semi truck over the tandem axle. With varying degrees of complexity the prior art accomplishes this by some sort of sensor or trigger that detects when the trailer is in proper position and turns on a switch that activates a signal that can be detected by the driver without getting out of the tractor. Some of the newer semi trucks come with built in sensors and signals so assist the driver with this task. Most of the older trucks do not. 
   U.S. Pat. No. 5,617,072 discloses a mechanism to assist the driver to position the front of the trailer over the fifth wheel assembly mounted on the tractor or the back of the trailer over the tandem axle assembly. In each case the switch is located oh the fifth wheel assembly or the tandem axle assembly while the trigger part of the signaling apparatus is attached to a suitable position on the frame or other structure of the vehicle. A light signals the driver when the proper position is achieved. 
   U.S. Pat. No. 5,460,237 discloses an air-powered actuator for retracting the locking pins and light means to signal the driver to determine that the pins are in position for retraction. It does not disclose a signal capable of determining when the locking pins are in position to engage selected holes in the trailer rail. 
   U.S. Pat. No. 5,678,834 discloses means for providing a remote indication of the positioning desired by the driver of a semi truck while the driver remains in the cab. However it does so employing a much more complicated set of components. Thus it employs a rod fitted in a tube and means for attaching one end of the combination to the tandem axle as well as means for securing the adjustment end of the rod within the tube. It also employs a spring attached at one end to the locking pin release handle. Finally it employs a separate visible indicator attached to the trailer. 
   U.S. Pat. No. 6,354,642 discloses a tool for positioning a tandem rig under a trailer of a semi truck. The tool attaches to the tandem and applies force to the handle, which unlocks the positioning pins. It then signals the driver in the cab that the positioning pins have been freed from their locked position. The tool is not designed to signal the driver when the positioning pins are in position to be locked. 
   The present invention differs substantially from the above in several ways. First the switch assembly is a single piece that attaches to a single location on the trailer rail. When the switch reaches the selected locking pin location to achieve proper weight and balance in the trailer, it turns on the signal that alerts the driver that the trailer is in the selected position for extending the locking pins. Additionally the Locking Pin Locator comes in a small compact carrying case for easy storing. Being more portable and compact than its prior art alternatives, it performs this function in an inexpensive and simple manner. 
   SUMMARY OF THE INVENTION 
   The heart of the present invention comprises a switch assembly fitted inside a pipe whose outside diameter is threaded for about half its length and a mounting bracket with a threaded hole sized to receive the threaded end of the pipe. A pressure sensitive ball or dome shaped switch extends outward from the threaded end of the pipe. The switch assembly includes wiring (hereinafter referred to as a cable) that completes a circuit including a signaling apparatus, preferably a battery and a light. The mounting bracket employs magnets to facilitate attachment to the slide rail of the trailer. The switch is sized to fit into a one of the many holes in a trailer slide rail used to lock the trailer in the position selected to achieve the desired weight and balance of the load over the wheels. A carrying case with a padded interior to house the foregoing components and provide a platform for the light completes the invention. Magnets can be affixed to the carrying case to make it possible to attach the case directly to the side of the trailer or to one of the cross members located underneath the trailers main frame. 
   To use the present invention, the first step is to release the locking pins. Then the switch assembly, which includes the mounting bracket, is taken out of the case and attached to a locking pin hole on the trailer slide rail anywhere between the locking pin on the front of the tandem axle and the back of the tandem axle. When a light is employed as the signal, the case can be placed on the ground or attached to the trailer using magnets on the outside of the case in a position that makes the light on the case visible to the driver sitting in the cab of the tractor. The pipe is then rotated clockwise into the hole in the mounting bracket until the switch on the end of the pipe contacts the tandem slide rail and turns on the light. The pipe is then rotated counter clockwise away from the tandem slide rail just far enough for the light to go out. The switch assembly is now ready to be moved to the selected hole in the trailer slide rail to achieve the desired weight and balance. The cable extending from the switch assembly to the case can be attached to side of the trailer using a wire clip to prevent the cable from contacting the wheels or any part of the tandem when the trailer is moved. When the driver moves the trailer toward the locking pin, the switch will eventually come in contact with a reinforcement plate fitted over the tandem slide rail at the locking pin location. The pressure on the switch provided by the raised reinforcement plate will turn on the light and alert the driver to stop immediately since the trailer is at the selected position to extend the locking pins. The bracket is then removed and replaced in the case. Finally the locking pins can be extended to the locked position. 
   The unexpected recognition that the raised reinforcement plate located alongside a locking pin hole on the tandem axle rail can be used to turn on a signal available to the driver is the creative basis for the present invention. In the event that the reinforcement plate is attached to the inside of the tandem slide rail, the procedure must be reversed. The driver will calibrate the switch assembly at the desired hole location on the trailer slide rail until the signal is on and then slide the trailer until the ball/dome enters the hole at the locking pin and the pressure on the switch is released and signal is turned off. In this variation a rolling ball switch is preferred to reduce wear and tear when the ball moves along the tandem slide rail. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a typical semi truck including a tractor and a trailer. 
       FIGS. 2 and 3  are front and side views of the tandem axle assembly attached to a cutout of the trailer. 
       FIG. 4  is an exploded perspective view of the device of the present invention depicting its various components. 
       FIG. 5  is an exploded perspective view of the switch assembly depicting its various components. 
       FIG. 6  is a dismantled view of the slide rails to highlight the reinforcement plates around the locking pin holes. 
   

   LIST OF REFERENCE NUMERALS 
   
       
         1  Semi truck 
         2  Tractor 
         3  Trailer 
         4  Tandem axle 
         5  Trailer cross member 
         6  Typical hole in trailer slide rail 
         7  Trailer slide rail 
         8  Tandem slide rail 
         9  Reinforcement plate 
         10  Mounting bracket 
         11  Threaded center hole of bracket 
         12   a ,  12   b ,  12   c ,  12   d  Magnets 
         13  Switch 
         14  Locking pin 
         15  Threaded end of pipe 
         16  Cable 
         17  Switch assembly 
         18  Light assembly 
         19  Battery clip 
         20  Foam insert 
         21  Case 
         22  Locking pin release handle 
         24  Switch sub-assembly 
         25   a ,  25   b ,  25   c ,  25   d  Screws 
         26  Threaded pipe 
         27   a ,  27   b  Magnet holes 
     
  
   DETAILED DESCRIPTION 
     FIG. 1  pictures the basic components of a semi-truck  1 , namely a tractor  2 , a trailer  3  and a tandem axle  4 .  FIGS. 2 and 3  provide more detailed pictures of the back end of the trailer  3  coupled to the tandem axle  4  both from the front and the side as well as the mechanism  23  by which the pins are extended and retracted.  FIGS. 2 and 3  are essentially reproductions of FIGS. 1 and 2 of U.S. Pat. No. 5,460,237 but omit details pertinent to the invention described and claimed in the patent. The patent also provides a more detailed description of the structure of the trailer and tandem axle and the means by which they are slidably connected employing matching pairs of slide rails and pins. The present invention is useful for trucks described in the patent albeit for a somewhat different purpose than the invention described and claimed in the patent. The invention of the patent helps to disconnect locking pins that are difficult to retract because of added friction brought about for example when the truck is standing on an uneven surface. The present invention helps to locate the trailer over the tandem axle so the pins can be extended to lock the tandem axle in the selected position under the trailer. 
     FIG. 6  depicts the disassembled trailer and tandem axle slide rails and provides a clear view of the reinforcement plates around the locking pin holes on one of the tandem axle slide rails. 
   The preferred operational configuration of the present invention, pictured in exploded perspective form in  FIG. 4 , is manufactured by George Risk Industries, Inc. of Kimball, Nebr., and comprises a case  21  (part # 8624), a foam insert  20  (part #8585), a switch assembly  17  (part # 10-137-009), an LED light assembly  18  (part # 10-137-010), a battery clip  19  (part # 5395), and a 9V battery (not shown). A label (part # 8586) and a cardboard cover (part # 8588) (not shown) are added for commercialization. 
   The preferred operational configuration of the switch assembly is pictured in  FIG. 5  and comprises the bracket  10  (part # 8582), the switch sub-assembly  24  (part # 10-137-008), the magnets  12   a ,  12   b ,  12   c ,  12   d  (part # 5942) and the screws  25   a ,  25   b ,  25   c ,  25   d  (part # 6915) which attach the magnets  12   a ,  12   b ,  12   c ,  12   d  to the bracket  10 . The switch sub-assembly comprises a threaded pipe  26 , a pressure sensitive plunger type micro switch  13 , and a cable  16 . 
   The switch assembly  17  is assembled by inserting the switch  13  attached to an 8 ft. long cable  16  (part # 248) into the ¾ in. diameter, 2 in. long threaded PVC pipe  26  (part # 8581) so the active end of the switch  13  extends just beyond the threaded end  15  of pipe  26  and filling the pipe  26  with epoxy (Acamine hardener and Epon resin). The unthreaded end of pipe  26  provides a handle for turning the pipe  26 . The threaded end  15  is screwed into the threaded center hole  11  in the plastic bracket  10 . Four magnets  12   a ,  12   b ,  12   c ,  12   d  are attached to the bracket  10  in counter-bored holes  27   a ,  27   b ,  27   c ,  27   d  in the bracket  10  using screws  25   a ,  25   b ,  25   c ,  25   d.    
   The main assembly is housed in the plastic carrying case  21 . The foam insert  20  holds all of the components in place. Cutouts are provided for the LED light assembly  18 ; the switch assembly  17  and the battery clip  19 . The cable  16  is fed through a hole in a clip (not shown) and tied off for strain relief. The clip is suitable for attaching the light assembly  18  to the side of the trailer. The components are hooked together in series under the foam and protected with heat shrink tubing. The final unit is tested and the label and cardboard wrapping attached for retail sale. 
   Alternatively an audible or radio transmitted signal can be substituted for the light signal. If a radio-transmitted signal is employed, the driver will need a receiver in the tractor. 
   The foregoing provides both a general description and a specific description of the preferred embodiment of the invention. It should be understood that various substitutions, variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention as further delineated in the following claims.