Abstract:
A device for automatically repositioning the pivot point between a fifth wheel trailer and truck. The hitch is composed of a base with integral first pivot member, two forward converging links, a second pivot member to which a spindle is attached. Pivotally attached to the spindle is a fifth wheel mount, which is pivotally attached to a fifth wheel. A pin adapter, which is attached to the hitch box of a fifth wheel trailer, eliminates rotation between the hitch box and fifth wheel assembly when hitched. This arrangement results in the trailer pivoting about the resulting center of rotation of the converging links, which is substantially forward of the pin of the trailer when in a straight-line orientation. The shifting of the pivot point distributes lateral forces from the trailer to all four wheels of the truck, thereby improving stability. During a turn, the subsequent articulation of the links results in a rearward repositioning of the pivot point, allowing sharp turns with a short bed truck.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of United States Provisional Application No. 60/703,207 filed on Jul. 28, 2005 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   REFERENCE TO SEQUENCE LISTING, A TABLE OR COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
   Not Applicable 
   BACKGROUND 
   The present invention relates generally to automatically repositioning fifth wheel hitches for use with fifth wheel trailers and towing vehicles, and particularly to fifth wheel hitches that automatically reposition the pivot point of the hitch rearward as the towing vehicle turns relative to the trailer by utilizing a rotational pivotable mechanism with four links. 
   The background information discussed below is presented to better illustrate the novelty and usefulness of the present invention. This background information is not admitted prior art. The following discussions of related art are provided as illustrative and exemplary of problems now present in the art. 
   Fifth wheel trailers and tow vehicles for fifth wheel trailers are generally well known in the art. Fifth wheel trailers are usually much longer and heavier than tent campers and travel trailers. Thus a fifth wheel trailer typically requires a tow vehicle, such as a pickup truck. The front portion of a fifth wheel trailer generally extends over the rear portion of the tow vehicle so that a portion of the trailer&#39;s weight is carried directly over the rear axle of the tow vehicle. To accommodate the weight of the trailer a special hitch assembly is required. Trailers are fitted with a hitch box which includes a support plate and a downwardly extending hitch pin. Tow vehicles are fitted with a base plate having an aperture and a latch mechanism for mounting, and securing the trailer to the tow vehicle. In presently available hitch assemblies the support plate, which is where the mechanism&#39;s single pivot point is located, rotates relative to the base plate about the hitch pin. Typically, the hitch assembly, and thus, the single vertical pivot axis, is mounted directly over or a short distance in front of the rear axle of the tow vehicle in order to maintain proper weight distribution. 
   To prevent contact between a trailer and a cab while maneuvering in tight spaces, the clearance between the pivot point and the rear of the cab must be at least half the width of the trailer. Trailers come in a variety of widths and lengths from long tractor trailers to short mini-trailers. Recreational trailers, for example, are often as much as 102 inches wide, but more typically are 96 inches and can be less. Such a recreational vehicle if routinely towed by a short bed pickup truck. Most short bed pickups have a bed that is typically only about 6 feet long. Beds that are 8 feet long are available on regular and extended cabs, as are short beds. Although the shorter bed pickups have the towing capacity to handle fifth wheel trailers, they do not have enough clearance between the axle and the rear of the cab to allow the trailer to pivot a 90 degree angle without the trailer coming into contact with the cab and potentially causing damage to the truck and injury to occupants. Generally, a fifth wheel trailer contacts the cab of a short bed pickup at angles much less than 90 degrees. 
   A number of attempts have been made to adapt fifth wheel trailers for towing by such short bed trucks, but each of these has been shown to have a significant drawback. One attempt uses a hydraulically operated sliding base to move the hitch assembly, and hence the pivot point, rearward from the cab. This assembly is likely to be expensive, difficult to maintain, and has to be driver actuated, which means the vehicle with trailer must be at rest at some safe spot off of the road. Actuating the working mechanism of this assembly requires a delay or lag time, which would mean that during an accident, such as a jackknife, the system would operate too slowly to prevent the trailer from contacting and most likely damaging the cab. 
   Another approach, employs a sliding base to move the pivot point from a front position to a rear position and requires the operator to exit the truck to manually release the locking mechanism, lock the brakes on the trailer, and then reenter the truck to drive it forward until the desired rearward position of the pivot point is reached before the trailer is able to pivot, relative to the truck, without making an undesirable contact with the cab. When preparing to drive the truck/trailer combination at highway speeds, the process is reversed to move the hitch to the forward position. While this method solves the clearance problem, it requires the operator to anticipate when sharp turns were going to be made in order to move the hitch before the fact. This system also could create a hazard if tight turns were required in a traffic situation and thus would be practically useless in an emergency. 
   Yet still another attempt, offers a sliding hitch assembly that automatically moves rearward away from the truck cab in response to pivotal movement of the trailer and the truck that typically occurs during normal driving. The sliding hitch assembly includes a sliding base plate, mounted on a pair or rods. An additional plate is attached to the hitch box of the trailer, with a key that prevents rotation between the hitch box and base plate. A lever arm extends from the base plate, and a cam follower attached to the end of the lever arm engages a stationary slot that extends substantially perpendicular to the rods. As the truck turns relative to the trailer, the rotation of the base plate causes the cam follower to move within the slot towards one of the slot ends, which in turn causes the base plate to slide back and forth along the rods. As the base plate is rotated the base plate moves between a forward position, in which the cam follower is at the center of the slot, and a rearward position, in which the cam follower is near one of the slot ends. When in the forward position, the hitch pin receiving aperture, and thus the pivot point of the trailer, is directly or slightly in front of the axle centerline. As the base plate rotates relative to the truck, the lever arm mechanism causes the base plate to slide rearwardly on the rods, moving the pivot point of the trailer away from the rear of the truck cab. The numerous components of this single pivot point device tend to make this device more prone to breakage, more costly to repair, and cause the device to be relatively expensive. 
   It is clear then that, there still exists a need for a hitch assembly that allows fifth wheel trailers to be towed without the fear of contact between the trailer and the truck where the hitch assembly provides for automatic repositioning of the effective pivot point in response to pivoting movement between the trailer and the towing vehicle and that does not require the expense, maintenance, and lag time of hydraulic systems, and that does not require the operator to exit the vehicle in order to lock or unlock the hitch assembly. 
   SUMMARY 
   The present invention, addressing all of the problems described above, teaches a rotating hitch assembly that enables fifth wheel trailers to be towed without fear that the trailer and truck will come in contact. Moreover, the rotating hitch assembly according to the principles of the invention provides for automatic forward and rearward rotational positioning and repositioning of the “effective pivot point” of a combined towing vehicle and fifth wheel trailer, thus providing for the towing vehicle and attached trailer to make sharp turns without the fear of undesirable contact between the towing vehicle and the trailer. The effective pivot point is the result of the motions of four interconnected dependent pivot points, which are brought about in response to pivoting motions between the trailer and the towing vehicle. Furthermore, the hitch according to the principle of the present invention does not require the expense, maintenance, and lag time of hydraulic systems, nor does it require the operator to exit the vehicle in order to lock or unlock the hitch assembly. While the automatic pivotal repositioning of the effective pivot point rearward facilitates sharp turns, the automatic pivotal forward shifting of the effective pivot point when the truck and trailer are in a straight orientation provides the new advantage of distributing lateral forces that are generated by the trailer between the front and rear axles of the truck, thus, improving stability. The invention provides for the rearward shifting of the effective pivot point upon turning and new forward shifting of the pivot point when the unit is traveling in a straight line, and does so using fewer components than the prior art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that these and other objects, features, and advantages of the present invention may be more fully comprehended and appreciated, the invention will now be described, by way of example only, with reference to specific embodiments which are illustrated in appended figures wherein like reference characters indicate like parts throughout the several figures. It should be understood that these figures only depict a few preferred embodiments of the present invention and are not therefore to be considered limiting in scope. Thus, the invention will be described and explained with added specificity and detail through the use of the accompanying figures, in which: 
       FIG. 1  is a top plan view of the fifth wheel hitch according to the principles of the present invention, shown installed in a truck bed (trailer omitted for clarity). 
       FIG. 2  is a side plan view of the fifth wheel hitch, as illustrated in  FIG. 1 , with trailer hitched. 
       FIG. 2   a  is a top plan view of hitch box pin and pin adapter pin engaged with pin slot preventing any rotation at that point between trailer and fifth wheel. 
       FIG. 3  is a front plan view of the fifth wheel hitch, shown installed in a truck bed, with trailer hitched. 
       FIG. 4  is a sectional view of first pivot member and associated links, pins and bearings. 
       FIG. 5  is a sectional view of the second pivot member and associated links, pins and bearings. 
       FIG. 6  is a sectional view of a connecting link and associated pivot members, pins and bearings. 
       FIG. 7  is a sectional view of the mounting hardware for the fifth wheel hitch. 
       FIG. 8  is a bottom plan view of the fifth wheel pin adapter. 
       FIG. 9  is a side plan view of the fifth wheel pin adapter. 
       FIG. 10  is an exploded side view of the fifth wheel hitch box and fifth wheel pin adapter. 
       FIG. 11  shows an assembled side view of the fifth wheel hitch box and fifth wheel pin adapter. 
       FIG. 11   a  illustrates a view looking up at the pin adapter plate attached to the fifth wheel hitch box. 
       FIG. 12  is a top sectional view of the fifth wheel assembly, with the latch assembly closed. 
       FIG. 13  is a top sectional view of the fifth wheel assembly, with the latch assembly open. 
       FIG. 14  is a sectional view of the fifth wheel assembly, fifth wheel pin adapter and fifth wheel hitch box. 
       FIG. 15  is a top plan view of the second pivot member and related components. 
       FIG. 16  is a top plan view of the fifth wheel hitch, shown in a slight turn of the truck and trailer (trailer shown in phantom). 
       FIG. 17  is a top plan view of the fifth wheel hitch, shown in a partial turn of the truck and trailer (trailer shown in phantom). 
       FIG. 18  is a top plan view of the fifth wheel hitch, shown in a full turn of the truck and trailer (trailer shown in phantom). 
       FIG. 19  is a side plan view of the height adjustment section of the second pivot member, shown in the lowest height position. 
       FIG. 20  is a side plan view of the height adjustment section of the second pivot member, shown in the highest height position. 
       FIG. 21  is a side plan view of an alternate embodiment of the fifth wheel assembly and associated components. 
       FIG. 22A  is a rear plan view of an alternate embodiment of the fifth wheel assembly and associated components, with the clamping jaws shown in a closed position. 
       FIG. 22B  is a rear plan view of an alternate embodiment of the fifth wheel assembly and associated components, with the clamping jaws shown in an open position. 
       FIG. 23A  is a top plan view of an alternate embodiment of the fifth wheel assembly, with the clamping jaws shown in an open position. 
       FIG. 23B  is a top plan view of an alternate embodiment of the fifth wheel assembly, with the clamping jaws shown in a closed position. 
       FIG. 24  is a bottom plan view of an alternate embodiment of the fifth wheel assembly, with the clamping jaws shown in a closed position. 
   

   A LIST OF REFERENCE NUMBERS AND RELATED PARTS OF THE INVENTION 
   
       
         10  Fifth wheel hitch member that is affixed to a towing vehicle, also referred to as a first hitch member. 
       P 1  and P 2  denote the two pivoting points of first element  14  of base  12 . 
       P 3  and P 4  denote the two pivoting points of second element  20  of base  12 . 
         12  Base of hitch  10   
         14  First element of base  12  having two pivoting points. 
         16  Connecting link 
         18  Connecting link 
         20  Second element of base  12  having a second set of pivoting points. 
         22  Mounting spindle 
         24  Fifth wheel mount 
         26  Fifth wheel assembly 
         28  Pin adapter 
         30  Hitch box 
         32  Fifth wheel trailer 
         34  First leg member of base  12   
         36  Second leg member of base  12   
         38  Third leg member of base  12   
         40  Fourth leg member of base  12   
         42  Distal end of leg  34   
         44  Distal end of leg  36   
         46  Distal end of leg  38   
         48  Distal end of leg  40   
         50  Mounting pin for leg  34   
         52  Mounting pin for leg  36   
         54  Mounting pin for leg  38   
         56  Mounting pin for leg  40   
         58  Hitch pin for mounting pin  50   
         60  Hitch pin for mounting pin  52   
         62  Hitch pin for mounting pin  54   
         64  Hitch pin for mounting pin  56   
         66  Frame of truck 
         68  Aperture in truck bed 
         70  Truck bed 
         72  Bearing bore in first element  14   
         74  Bearing bore in first element  14   
         76  Bearing bore in first element  14   
         78  Bearing bore in first element  14   
         80  Centerline of bearing bores  72  and  74   
         82  Centerline of bearing bores  76  and  78   
         84  Horizontal centerline of base  12   
         86  Pivot member bearing for bearing bore  72   
         88  Pivot member bearing for bearing bore  74   
         90  Pivot member bearing for bearing bore  78   
         92  Pivot member bearing for bearing bore  76   
         94  Pivot pin for bearings  86  and  88   
         96  Pivot pin for bearings  90  and  92   
         98  Rearward bore of connecting link  18   
         100  Rearward bore of connecting link  16   
         102  Hitch pin for pivot pin  94   
         104  Hitch pin for pivot pin  96   
         106  Rear bore of connecting link  18   
         108  Rear bore of connecting link  16   
         110  Front bore of link connecting link  16   
         112  Front bore of link connecting link  18   
         114  Vertical centerline of second element  20   
         116  Pivot pin for bearings  124  and  126   
         118  Pivot pin for bearings  128  and  130   
         120  Hitch pin for pivot pin  116   
         122  Hitch pin for pivot pin  118   
         124  Bearing in bore  132   
         126  Bearing in bore  134   
         128  Bearing in bore  136   
         130  Bearing in bore  138   
         132  Bearing bore in second element  20   
         134  Bearing bore in second element  20   
         136  Bearing bore in second element  20   
         138  Bearing bore in second element  20   
         140  Centerline of bearings  124  and  126   
         142  Centerline of bearings  128  and  130   
         144  Left side of second element  20   
         146  Right side of second element  20   
         148  Front portion of second element  20   
         150  Vertical flange of second element  20   
         152  Vertical flange of second element  20   
         154  Apertures in flanges  150  and  152   
         156  Bolt for flanges  150  and  152   
         158  Bolt for flanges  150  and  152   
         160  Nuts for bolts  156  and  158   
         162  Pivotal mounting surface of spindle  22   
         164  Nut for spindle  22   
         166  Centerline of spindle  22   
         168  Centerline of fifth wheel assembly  26   
         170  Machine screws for attaching pin adapter  28   
         172  Base plate for pin adapter  28   
         174  Rearward pin of pin adapter  28   
         178  Aperture in base plate  172   
         180  Hitch box pin of trailer  32   
         182  Bottom surface of hitch box  30   
         184  Slotted portion of fifth wheel assembly  26   
         186  Wheel well of truck  234   
         188  Wheel well of truck  234   
         190  Shoulder of bearings  86 ,  88 ,  90  and  92   
         192  Centerline of rear axle of truck  234   
         194  Longitudinal centerline of trailer  32   
         196  Center bore of fifth wheel mount  24   
         198  Hitch pin for fifth wheel assembly  26   
         200  Hitch pin for fifth wheel assembly  26   
         202  Mounting portion of spindle  22   
         204  Spindle portion of mounting spindle  22   
         206  Mounting yoke for fifth wheel mount  24   
         208  Mounting yoke for fifth wheel mount  24   
         210  Flat surface of fifth wheel assembly  26   
         212  Mounting bar for fifth wheel assembly  26   
         214  Mounting bar for fifth wheel assembly  26   
         216  Latch mechanism for fifth wheel assembly  26   
         218  Rear open portion of fifth wheel assembly  26   
         220  Latch bar of mechanism  216   
         222  Handle of mechanism  216   
         224  Trigger bar of mechanism  216   
         226  Retaining plate of mechanism  216   
         228  Latch bar spring of mechanism  216   
         230  Trigger bar spring of mechanism  216   
         232  Centerline of the truck  234 . 
         234  Truck 
         236  Intersection of centerline of trailer  194  and centerline of truck  232   
         238  Line delineated by pivot bores  72  and  76   
         240  Retaining pin of mechanism  216   
         242  Aperture in latch plate  220   
         244  Aperture in fifth wheel assembly  26   
         246  Finger aperture in trigger  224   
         248  Truck cab 
         250  Pivot pin for retaining plate  226   
         252  Centering springs for first hitch member  10   
         254  Alternate fifth wheel assembly 
         256  Widened pin slot in alternate assembly  254   
         258  Clamping screw of alternate assembly  254   
         260  Left clamp jaw of alternate assembly  254   
         262  Right clamp jaw of alternate assembly  254   
         264  Crank of alternate assembly  254   
         266  Threaded portion of clamping screw  258   
         268  Threaded portion of clamping screw  258   
         270  Pin slot in alternate assembly  254   
         272  Latch bar of alternate assembly  254   
         274  Sleeve bearing for clamping screw  258   
         276  Sleeve bearing for clamping screw  258   
         278  Flange in alternate assembly  254  for sleeve bearing  274   
         280  Flange in alternate assembly  254  for sleeve bearing  276   
     
  
   It should be understood that the figures are not necessarily to scale. In certain instances, details which are not necessary for an understanding of the present invention, or which render other details difficult to perceive, may have been omitted. 
   DEFINITIONS 
   Fifth wheel hitch, as used herein, refers to the combined elements attached to a towing vehicle, such as a short bed pickup truck, and a fifth wheel trailer allowing for coupling of and rotational movement between the towing vehicle and fifth wheel trailer.
 
Centerline of fifth wheel assembly, as used herein, refers to the line about which the fifth wheel assembly rotates fore and aft relative to the fifth wheel mount.
 
Centerline of rear axle of truck, as used herein, refers to the line about which the rear wheels of the truck rotate.
 
Centerline of spindle, as used herein, refers to the line about which the fifth wheel mount rotates side to side relative to the spindle portion of mounting spindle.
 
Centerline of the truck, as used herein, refers to the longitudinal line midway between the right and left sides of the truck at road level.
 
Longitudinal centerline of trailer, as used herein, refers to the longitudinal line midway between the right and left sides of the trailer at road level.
 
   DETAILED DESCRIPTION 
   This invention relates to a “fifth wheel” hitch for use with a fifth wheel trailer and a towing vehicle. To use a fifth wheel hitch there is a hitch part on the trailer that is receivable by a hitch part on the towing vehicle. The fifth wheel hitch of the present invention provides for a trailer/towing vehicle to be able to make tight turns, such as those that are required when parking, backing up, and turning a corner on a narrow roadway without the fear of unwanted contact between trailer and truck. Additionally, the fifth wheel hitch of the present invention provides for improved road stability of the truck/trailer combination. Furthermore the fifth wheel hitch as taught herein provides for automatically repositioning of the turning pivot point of the combination trailer/truck. 
   In a preferred embodiment, as illustrated in  FIGS. 1-3 , fifth wheel hitch member  10 , also referred to as first hitch member, is affixed to the towing vehicle. First hitch member  10  has four independent but related pivot points P 1 , P 2 , P 3  and P 4 , the combined pivoting action of which defines the “effective pivot point” between the trailer and the truck. First hitch member  10  comprises base  12  which supports and is integral to first element  14  having two pivoting points P 1  and P 2  and second element  20  of base  12  having two pivoting points P 3  and P 4 . One end of first member  14  is pivotally attached to a first end of connecting link  16  and an opposing end of first member  14  is pivotally attached to a first end of connecting link  18 . A second end of connecting link  16  is pivotally attached to one end of second element  20  and a second end of connecting link  18  is connected to an opposing end of second element  20 . Also attached to second element  20  is mounting spindle  22  which is attached to fifth wheel mount  24  which is attached to fifth wheel assembly  26  (see  FIGS. 1 and 2 ). 
   Additionally, base  12  provides mounting means for securely mounting hitch  10  to bed  70  of truck  234  between wheel wells  186  and  188  (see  FIG. 1 ) where centerline  168  of fifth wheel assembly  26  is slightly forward of centerline  192 , of the rear axle of the truck. The mounting means assembly of base  12  comprises four mounting leg assemblies: first leg member  34  with mounting pin  50  secured with hitch pin  58  at distal end  42 , second leg member  36  with mounting pin  52  secured with hitch pin  60  at distal end  44 , third leg member  38  with mounting pin  54  secured with hitch pin  62  at distal end  46 , and fourth leg member  40  with mounting pin  56  secured with hitch pin  64  at distal end  48 . Rigid attachment of mounting pins  50 ,  52 ,  54  and  56  to truck frame  66  is illustrated in  FIG. 7 , where mounting pin  56  can be seen extending through aperture  68  of truck bed  70  to be securely attached to truck frame  66 . It is to be understood that a variety of readily available mounting methods well known in the art or to be known, may be substituted for the method illustrated in  FIG. 7  without departing from the principles of the present invention. As illustrated in  FIGS. 1-3 , are proximate ends of legs  34 ,  36 ,  38 , and  40  rigidly attached to first element  14 . As illustrated in  FIGS. 1 and 4 , first element  14  is of a generally symmetrical V-shape with vertically oriented pairs of bearing bores  72 ,  74  and  76 ,  78  at opposing corners. Bearing bores  72  and  74  are coaxial, as are bearing bores  76  and  78 . Centerlines  80  and  82  of bearing bore pairs  72 ,  74  and  76 ,  78  are parallel to each other and are perpendicular to horizontal centerline  84  of base  12 .  FIG. 4  also shows first member bearings  86 - 88  and  92 - 90  inserted in the bearing bores with shoulders  190  of the bearings facing toward horizontal centerline  84  of first element  14 . Left pivot pins  94  and right pivot pin  96  are inserted into respective left and right pairs of bearings  86 - 88  and  92 - 90 , respectively, through rearward bores  98  and  100  of connecting links  18  and  16  ( FIGS. 1 and 2 ), which are pivotally connected to first element  14 . Left and right pivot pins  94  and  96  are secured by hitch pins  102  and  104 , respectively. Connecting links  18  and  16  each have bores on a first end for accepting pivot pins  94  and  96 . Links  16  and  18  are equal in length and the distance between rear bore  100  and front bore  110  (see  FIG. 6 ) is slightly longer than one half the distance between bores  72  and  76  of first element  14 . 
   Pin adapter  28  illustrated in FIGS.  2  and  8 - 11 , attaches to hitch box  30  of the second hitch member that is fixedly attached to fifth wheel trailer  32 . During turns (see  FIGS. 16-18 ), the hitch connection created by these components automatically repositions the pivot point of the hitched trailer rearward, resulting in the necessary clearance between truck cab  248  and trailer  32  that is required for making tight turns without damaging contact between the truck cab and trailer. An additional benefit is that when the truck-trailer is going straight, first element  14 , second element  20 , and converging links  16  and  18  place the effective pivot point forward, thereby distributing any lateral forces generated by the towed trailer, between the front and rear wheels of the truck, enhancing stability. 
     FIG. 5 , a sectional view, illustrates second element  20  which is symmetrical about its vertical centerline  114 . The frontward ends of connecting left and right links  16  and  18  are connected to respective left and right front ends  144  and  146  (see  FIG. 15 ) of T-shaped element  20 , using left and right pivot pins  116  and  118 , secured by hitch pins  120  and  122 . The pivot pins are inserted through respective bearings  124 ,  126 ,  128 , and  130  and received in bearing bores  132 ,  134 ,  136 , and  138  of second element  20 . Left bearing bores  132  and  134 , of second element  20 , are coaxial as are right bearing bores  136  and  138 . The centerlines  140  and  142  of the bearing bores are parallel to each other and are equally spaced on opposite sides of vertical centerline  114  of second element  20 . The distance between bores  132  and  138  of second element  20  is slightly shorter than the distance between the bores  72  and  76  of first element  14 . 
   The vertical distance between the upper and lower pivot bores of first and second elements  14  and  20  along with the vertical height of connecting links  16  and  18  form four parallel couple joints for carrying the pin weight of the hitched trailer.  FIGS. 3 and 15  show front portion  148  of second element  20  consisting of two vertically oriented flanges  150  and  152 .  FIG. 2  illustrates series of apertures  154  for fastening mounting spindle  22  via bolts  156  and  158 . Bolts  156  and  158  are secured with nuts  160 .  FIG. 14  illustrates mounting spindle  22  consisting of mounting portion  202  sized to fit between vertically oriented flanges  150  and  152  of second element  20  (as illustrated in  FIG. 15 ) and apertures  154  for accepting bolts  156  and  158  bolting mounting spindle  22  to second member  20 . In addition, mounting spindle  22  consists of spindle portion  204 , which provides pivotal mounting surface  162  ( FIG. 14 ) for fifth wheel mount  24 , which is held in place by nut  164 . As illustrated in  FIGS. 2 ,  3  and  14 , fifth wheel mount  24  is essentially flat with centrally located bore  196  (see  FIG. 14 ), for pivotal attachment to spindle  204 , and two mounting yokes  206  and  208  (see  208  in  FIG. 3 ) located at the ends for pivotally mounting fifth wheel assembly  26  (see  FIG. 2 ). Fifth wheel assembly  26  includes flat surface  210  ( FIG. 12 ), two mounting bars  212  and  214 , latch mechanism  216 , and slotted portion  184 , which is open on rear portion  218 , allowing hitching of trailer  32 . Fifth wheel assembly  26  is held in place by two hitch pins  198  and  200  (see  FIG. 1 ). As illustrated in  FIGS. 1 and 14 , pivots at centerlines  166  and  168  allow for fore and aft as well as side to side pivoting between truck  234  and trailer  32 . Latch mechanism  216  consists of latch bar  220 , handle  222 , trigger bar  224 , retaining plate  226 , latch bar spring  228  and trigger bar spring  230 . 
     FIGS. 8 and 9  illustrate the structure of pin adapter  28 , which consists of base plate  172 , rearward pin adapter pin  174 , and aperture  178  for receiving hitch box pin  180 .  FIG. 10  illustrates hitch box  182  and hitch box pin  180  fixedly attached to trailer  32  ready to receive pin adapter  28  that is positioned for attachment to plate  172 .  FIG. 11  illustrates hitch box pin  180  received through aperture  178  of plate  172  of pin adapter  28  and pin adapter  28  now rigidly fastened to the bottom surface of hitch box  182  with attachment means  170 , which in this example are machine screws. As illustrated in  FIGS. 2A ,  11 A,  14  and  16 , when fastened, hitch box pin  180  and pin adapter pin  174  lie in a line coincident with longitudinal centerline  194  (see  FIG. 2A ) of trailer  32 , and when the trailer is hitched to the truck, pins  174  and  180  engage with pin slot  184  (as illustrated in  FIGS. 1 ,  2 A, and  14 ) of fifth wheel assembly  26  and are held in position by latch bar  220  (see  FIG. 14 ) preventing any rotation between trailer  32  and fifth wheel  26 . The result is that all rotational pivoting between the truck and the trailer takes place within the four-link mechanism comprised of first and second elements  14  and  20  and two connecting links  16  and  18 , as described above. As illustrated in  FIGS. 1 and 3 , the four-link mechanism is normally held in a centered position by two springs  252 . This aids the hitching process as well as preventing the mechanism from moving about when the truck is driven without a trailer. 
     FIG. 16  illustrates that when the trailer-truck is beginning a turn, the effective pivot point of the hitch is located at the intersection of centerline  194  of trailer  34  and centerline  232  of truck  234 . The effective pivot point is indicated by point  236  on  FIG. 16 . As the turn sharpens (see  FIGS. 17 and 18 ), the front end of the connecting link,  16  in this case, is on the outside of the turn, rotating past line  238  delineated by pivot bores  72  and  76  of first element  14 . At the same time first element  14  allows clearance for second element  20  to pass through line  238 . The total amount of rearward shifting of the pivot point of the trailer is dependant upon the size of the four link mechanism ( 14 ,  16 ,  18 , and  20 ) and the longitudinal distance from second pivot member bearing bores  132  and  138  to the centerline of the forward pin of fifth wheel assembly  168 . 
   When hitching, the truck is backed into a position in line with the trailer and somewhat ahead of it. Fifth wheel lever  222  is then pulled laterally to an open position as shown in  FIG. 13 . Referring to  FIGS. 12 and 13 , as lever  222  is pulled laterally, it slides latch bar  220  with it, until retaining pin  240  passes by the hooked portion of retaining plate  226 , which pivots on pin  250 . At this point, retaining plate  226 , held in position by spring  230 , engages with retaining pin  240 , thereby holding it in an open position as shown in  FIG. 13 . The truck is then backed under the pin of the trailer such that pin  180  slides into slot  184  of fifth wheel assembly  26 . As illustrated in  FIGS. 12 ,  13 , and  14 , when pin  180  strikes release trigger  224 , retaining plate  226  rotates and latch bar  220  is released. As pin  180  reaches full engagement into fifth wheel assembly  26 , latch bar  220  slides to a closed position behind it, moved by latch bar spring  228 . The position of the latch plate can be locked in position, with a pin or a pad lock inserted into apertures  242  and  244 . 
   When the trailer is to be unhitched, the fifth wheel lever is pulled laterally into an open position (see  FIGS. 12 and 13 ). As the truck is pulled forward relative to the trailer, trigger  224  once again is struck by pin  180 , releasing latch bar  220 , which closes after pin  180  passes by it. If desired, latch plate  220 , when in an open position, can be released by pulling laterally on finger aperture  246 . A variety of readily available latching mechanisms that are well known in the art and those that are yet to be known may be substituted for the mechanism shown without deviating from the principles of the present invention. 
   As illustrated in  FIGS. 19 and 20 , the height of fifth wheel assembly  26  can be adjusted. This is accomplished by removing nuts  160  ( FIG. 3 ) and bolts  156 ,  158 , raising or lowering spindle  22 , and re-inserting bolts  156 ,  158  and nuts  160  in different mounting apertures  154  thereby achieving the desired height. 
     FIGS. 21 through 24  show an alternate fifth wheel assembly  254 . The purpose of this alternate is to allow for hitching when the centerline of the truck and the centerline of the trailer are at an angle to each other. Typically, when hitching, the front supporting jacks, or landing gear, on a fifth wheel trailer can allow for some front to back movement without damage. If the trailer is hitched at an angle, the landing gear is loaded from side to side and can be damaged. The present invention has two points of contact between the fifth wheel assembly and the pin adapter. If the truck and the trailer are not properly aligned, the engagement of hitch box pin  180  and pin adapter  28  to the fifth wheel assembly will tend to generate lateral forces on the front of the trailer. To avoid this problem alternate fifth wheel assembly  254  can be used. Referring back to the drawings, alternate fifth wheel assembly  254  is similar to the fifth wheel assembly  56 , with the addition of widened pin slot  256 , clamping screw  258 , left and right clamp jaws  260  and  262 , and crank  264  for rotating clamping screw  258 . Clamping screw  258  is suspended on sleeve bearings  274  and  276  that are fitted into flanges  278  and  280 , which are rigidly attached to base  282  of alternate fifth wheel assembly  254 . Clamping screw  258  has right hand threads on one side  266  and left hand threads on other side  268 , so as to move jaws  260  and  262  in opposite directions from each other and at the same rate. In the closed position ( FIGS. 23B ,  22 A and  24 ) jaws  260  are centered with respect to fifth wheel slot  270 . In use, crank  264  is rotated so as to move the jaws away form each other to an open position as shown in  FIGS. 23A and 22B . With the jaws open, the trailer can then be hitched in a normal fashion, engaging hitch box pin  180  into slot  270  until latch bar  272  is closed behind it ( FIG. 23A ). The landing gear of the trailer can then be raised until it clears the road surface. After the landing gear is raised, crank  264  is rotated until jaws  260  and  262  are in a closed and centered position as illustrated in  FIGS. 23B ,  22 A and  24 . During this closing of the jaws portion of the hitching process, pin adapter plate  172  slides along top surface  284  of fifth wheel base  282  and any angular differences ( FIG. 23A ) between fifth wheel assembly  254  and hitch box pin  180  and pin adapter  28  are eliminated. The front end of the trailer may also move laterally as pin adapter  28  and fifth wheel assembly  254  align with each other. At this point the hitching process is complete. When unhitching, the clamping jaws can be left in a closed position as long as the truck is being driven straight forward relative to the trailer. If not, jaws  260  and  262  can be opened ( FIGS. 22B and 23A ) to allow for unhitching at an angle as allowed by the clearance of widened portion  256  of pin slot  270 . It is also noted that clamping screw  258  could be driven by an electric motor, controlled by a switch, connected to the truck electrical system, thereby eliminating crank  264 . 
   The foregoing description, for purposes of explanation, used specific and defined nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details presented are not required in order to practice the invention and are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Those skilled in the art will recognize that many changes may be made to the features, embodiments, and methods of making the embodiments of the invention described herein without departing from the spirit and scope of the invention. The invention is limited only by the claims.