Abstract:
A hitch includes a control linkage having a single handle on a control bar. The control linkage doubles to provide both a positive safety feature and a movement feature to the hitch, permitting single handed operation of both the positive safety feature and the opening of the hitch with the single handle. A release throw of four inches or less opens jaws of the hitch. A latch is included which can secure the control bar in either a secured position or in a release position. A follower is secured to one of the jaws to maintain timing between the jaws, and the follower doubles as a hitch position indicator so an operator to easily visually discern the position of the hitch. By including kingpin recesses of appropriate location and depth on the jaws, the hitch can be used with or without a lube plate over the skid plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
   None. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to trailer hitches, and more particularly, to trailer hitches for fifth wheel or gooseneck type trailers supported such as in the bed of a pick-up truck and which are operated by mechanical controls. 
   Fifth wheel and gooseneck type trailers are used with pick-up trucks to support and tow a trailer by placing the weight and load of the trailer generally over the rear axle of the pick-up truck rather than over or adjacent the rear bumper. Hitches for fifth-wheel and gooseneck trailers have found a large and long-standing acceptance in the marketplace for towing a wide variety of trailers. 
   One common type of fifth-wheel trailer includes a kingpin which extends generally vertically on the leading tongue of the trailer. The hitch engages the trailer by surrounding the kingpin. One example of such a fifth-wheel hitch is disclosed in U.S. Pat. Nos. 6,846,000 and 6,935,650, which includes two movable plates or jaws which engage around the kingpin. The hitch disclosed in U.S. Pat. Nos. 6,846,000 and 6,935,650 has a control lever for moving the jaws to release the kingpin. A safety pin provides a positive locking feature which prevents unintended release of the hitch. 
   An example of a gooseneck hitch is disclosed in U.S. Pat. No. 6,533,308, which includes a pop-up ball rather than kingpin engaging jaws. The gooseneck hitch disclosed in U.S. Pat. No. 6,533,308 includes a raising/lowering linkage with a handle which extends into the rear wheel well of the pick-up truck, a convenient spot for the operator to control the operation of the hitch without climbing into the bed of the pick-up truck. 
   The average operator of a fifth-wheel or gooseneck hitch is not young, such as over 55 years old, who is perhaps not as strong and nimble as he or she once was. The controls of the hitch should be readily accessible by the operator, without requiring too much climbing or bending to access. Operation of the controls should not require the application of excessive force or torque. The hitch must be strong to securely engage the trailer, minimizing the possibility of breakage or of any way the trailer could inadvertently come loose. At the same time, the hitch should be simple to operate, so the operator has no difficulty in intentionally engaging and disengaging the trailer. The hitch should preferably be mechanically operated, so there is no possibility of a loss of power preventing operation of the hitch. The hitch must be robust and reliable, to last for carefree operation over the life of at least one vehicle, and possibly over the life of several vehicles, despite the fact that the hitch will likely be openly exposed to weather over its years or decades of use. As much as possible, the hitch should also have minimal cost and expense in manufacturing and assembly. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is a hitch, a control linkage for a hitch and a method of hitch operation. In one aspect, a single handle, with a short release throw, moves a control rod both to provide a safety function and to open the hitch. In another aspect, the control rod translates in a sleeve, and a latch is included which can secure the control bar in either a secured position or in a release position. In another aspect, a follower is secured to one of the jaws to maintain timing between the jaws, and the follower doubles as a hitch position indicator so an operator to easily visually discern the position of the hitch. By including kingpin recesses of appropriate location and depth on the jaws, the hitch can be used with or without a lube plate over the skid plate. In another aspect, the jaws are mounted with a bearing structure which is stiffer in roll than in pitch. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view from above showing a preferred embodiment of a hitch in accordance with the present invention. 
       FIG. 2  is an exploded perspective view of the hitch of  FIG. 1 . 
       FIG. 2   a  is an enlarged view of a portion of  FIG. 2 , showing the bearing components of the preferred embodiment. 
       FIG. 2   b  is an enlarged view of a portion of  FIG. 2 , showing the control linkage components of the preferred embodiment. 
       FIG. 3  is a side view of the preferred base plate. 
       FIG. 4  is a diagram of the preferred cam ramps of the base plate of  FIG. 3 . 
       FIGS. 5-10  are simplified plan views of the control linkage components, showing operation of the hitch from a closed, locked position ( FIG. 5 ), in time steps ( FIGS. 6 and 7 ) to a fully open position ( FIG. 8 ), and then in time steps ( FIGS. 9 and 10 ) before returning to the closed, locked position ( FIG. 5 ). 
       FIG. 11  is a cross-sectional view of a portion of the preferred hitch in the closed, locked position, taken along lines  11 - 11  of  FIG. 5 . 
       FIG. 12  is a cross-sectional view of the same portion of the preferred hitch in the fully open position, taken along lines  12 - 12  of  FIG. 8 . 
       FIG. 13  is a simplified cross-sectional elevational view of the hitch about a kingpin, showing the release position of the controlled jaw in dashed lines. 
       FIG. 14  is a simplified cross-sectional elevational view of the hitch about a kingpin with a lube plate over the skid plate, showing the release position of the controlled jaw in dashed lines. 
   

   While the above-identified drawing figures set forth one or more preferred embodiments, other embodiments of the present invention are also contemplated, some of which are noted in the discussion. In all cases, this disclosure presents the illustrated embodiments of the present invention by way of representation and not limitation. Numerous other minor modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. 
   DETAILED DESCRIPTION 
   As shown in  FIGS. 1 and 2 , a preferred embodiment of a hitch  20  in accordance with the present invention includes a support frame  22  which permits attachment of the hitch  20  into the bed of a pick-up truck (not shown). A skid plate  24  provides the top surface of the hitch  20  and defines a king-pin receiving slot  26 . The skid plate  24  may embody an ornamental design such as described in U.S. patent application Ser. No. 29/257,292 , now issued at U.S. Pat. No. D560,143, assigned to the assignee of the present invention and incorporated by reference. Two jaws  28 ,  30  are positioned under the skid plate  24  and are used as a kingpin retention structure to engage the kingpin  32  (shown in  FIGS. 13 and 14 ) of a towed vehicle (not shown). The jaws  28 ,  30  are rotationally attached each on a hub  34 . One of the jaws is a controlled jaw  28 , moveable in the height direction on its hub  34 , while the other jaw is a fixed height jaw  30 . A linkage  36  controls operation of the jaws  28 ,  30 , with the linkage  36  being operable via a handle  38 . The jaws  28 ,  30  are supported by and protected in a jaw housing  40 , which in turn is supported by the support frame  22 . The jaw housing  40  has a kingpin opening  42  on its aft wall. 
   As better shown in  FIG. 2 , the preferred support frame  22  generally includes legs  44  and a bearing structure  46 , with the bearing structure  46  supported by a bearing undercarriage  48 . The preferred legs  44  are provided as identical right and left side legs, and provide an appearance of right to left and front to back symmetry to the hitch  20 . The bearing undercarriage  48  mounts between the right and left side legs  44 . For instance, the legs  44  may embody the ornamental design described in U.S. patent application Ser. No. 29/257,291, now issued as U.S. Pat. No. D572,633, assigned to the assignee of the present invention and incorporated by reference. If desired, the frame  22  may permit fore and aft, height, and side-to-side flexibility in mounting position. A basic frame structure is disclose in U.S. Pat. Nos. 6,846,000 and 6,935,650 to Grinde et al., owned by the assignee of the present invention and incorporated herein by reference. The present invention is disclosed and explained as an improvement of the hitch and frame structure of U.S. Pat. Nos. 6,846,000 and 6,935,650, but the various aspects of the invention can be used with a wide variety of other hitch and frame structures. 
   The preferred bearing structure is a shaft-supported spherical bearing  46  to permit angular movement in all directions (other than elevation) of the skid plate  24  and jaws  28 ,  30 , enabling the hitch  20  to permit angled pitch and roll movement of the kingpin  32  as the vehicle traverses over hills, across side slopes, around corners, etc., when the trailer rides on an undulating roadplane behind the towing vehicle. The bearing undercarriage  48  supports the bearing shaft  46  at several locations along its length. 
   The bottom of the jaw housing  40  is provided by a base plate  50  as shown in  FIGS. 2 ,  2   a  and  3 . A peripheral side wall  52  fixedly attaches to the base plate  50  such as through a bolted or welded connection. The bearing structure  46  preferably biases the jaw housing  40  toward an aligned position, wherein the jaw housing  40  (and the jaws  28 ,  30  mounted therein) are in a plane parallel to a bottom attachment plane defined by the legs  44  of the frame  22 , i.e., parallel to the plane of the bed of the truck into which the hitch  20  is attached. 
   In the preferred embodiment, the base plate  50  includes three extension bars  54 ,  56 ,  58  for alignment biasing: a central extension bar  54 , a fore extension bar  56  and an aft extension bar  58 . The extension bars  54 ,  56 ,  58  all preferably extend radially relative to the center of the spherical bearing  46 . In the preferred configuration, the extension bars  56 ,  54 ,  58  are one behind the other, in a fore-aft plane perpendicular to the base plate  50  (i.e., a generally vertical fore-aft plane). 
   A bottom elastomeric pad  60  is provided which mates around the central extension bar  54 , biasing the central extension bar  54  back toward an aligned position. The bottom elastomeric pad  60  is retained in a bottom pad housing  62 , which attaches to the bearing undercarriage  48  and keeps the bottom elastomeric pad  60  in a generally constant position relative to the bearing undercarriage  48 . When the jaw housing  40  is not in the aligned position, the central extension bar  54  causes compression of the bottom elastomeric pad  60  in the direction that the central extension bar  54  is out of alignment. The bottom elastomeric pad  60  responds against the compression force, biasing the central extension bar  54  horizontally, in a radial direction relative to the longitudinal axis of the central extension bar  54 , back toward the aligned vertical position, in the exact radial direction needed for alignment. 
   A fore elastomeric pad  64  mates around the fore extension bar  56 , and an aft elastomeric pad  66  mates around the aft extension bar  58 . The fore and aft elastomeric pads  64 ,  66  are received between two cross-members  68  of the bearing undercarriage  48 . The fore and aft elastomeric pads  64 ,  66  have a width which matches the width of the opening between the two cross-members  68 . However, in contrast to the bottom elastomeric pad  60  as constrained by the bottom pad housing  62 , the cross-members  68  permit the fore and aft elastomeric pads  64 ,  66  to slide in the fore and aft directions. 
   The bottom elastomeric pad  60  provides an alignment biasing force which is generally consistent both in pitch and in roll of the towed trailer relative to the towing vehicle. For instance, a 2° roll offset of the base plate  50  creates an alignment force in the bottom elastomeric pad  60  of the same magnitude as a 2° pitch offset of the base plate  50 , though the 2° roll offset creates a sideways force while the 2° pitch offset creates a fore-aft force. All 2° offsets which are combinations of pitch and roll will also provide a compression force in the bottom elastomeric pad  60  of the same general magnitude, just in the proper direction for alignment. 
   In contrast to the relatively equal pitch and roll forces provide by the bottom elastomeric pad  60 , the fore and aft elastomeric pads  64 ,  66  provide essentially no pitch alignment force. When the towing vehicle traverses over hills and valleys with no side slope, the hitch  20  will allow pitch offset in which the fore and aft elastomeric pads  64 ,  66  will not compress but will merely slide fore and aft between the cross-members  68 . When the towed trailer rolls relative to the towing vehicle, the roll will cause the fore and aft elastomeric pads  64 ,  66  to compress and providing a horizontally sideways correction force. Thus, the fore and aft elastomeric pads  64 ,  66  cause the hitch  20  to be stiffer against roll than against pitch. The higher roll stiffness is illustrated in  FIG. 3  by the arrows, wherein the larger arrows  70  indicate the compressive force which can be provided by the elastomeric pads  60 ,  64 ,  66  and the lined arrows  72  represent the translation in the pitch direction without compression permitted by the fore and aft elastomeric pads  64 ,  66 . The amount of roll stiffness and the amount of pitch stiffness can be easily selected by a worker skilled in the art by appropriately sizing the bottom elastomeric pad  60  relative to the fore and aft elastomeric pads  64 ,  66 , and by selecting the moment arm of each of the elastomeric pads  60 ,  64 ,  66  on their respective extension bars  54 ,  56 ,  58 . 
   The shape of the bottom elastomeric pad  60 , the opening  74  of the bottom elastomeric pad  60  for receiving the central extension bar  54 , and the cross-sectional shape of the central extension bar  54  are preferably all square just for ease of manufacturing and assembly. The shape of the fore and aft elastomeric pads  64 ,  66 , the openings  76  of the fore and aft elastomeric pads  64 ,  66  for receiving the fore and aft extension bars  56 ,  58 , and the cross-sectional shape of the fore and aft extension bars  56 ,  58  are preferably all square just for ease of manufacturing and assembly. The hitch  20 , including the bottom and fore and aft elastomeric pads  60 ,  64 ,  66 , does not provide a significant alignment force in the yaw direction, as the kingpin  32  is cylindrical and transmits essentially no yaw force to the jaws  28 ,  30 . 
   As one alternative to elastomeric pads  60 ,  64 ,  66 , the alignment force for the bearing structure  46  could be provided by other biasing members, such as springs. Elastomeric pads work well for the alignment force because they can provide the compression force in all directions, which ever direction is needed to make the correction into alignment. 
   As better shown in  FIGS. 2   b  and  6 - 12 , the jaws  28 ,  30  are operated by a control rod  78  through the linkage  36 . The handle  38  is at the proximal end of the control rod  78 , bent at an angle relative to the longitudinal axis of the control rod  78 . With the handle  38 , an operator can easily apply a translational motion pulling or pushing the control rod  78  along its longitudinal axis. The control rod  78  generally translates between a closed position, wherein the control rod  78  extends over the controlled jaw  28 , and a release position wherein the control rod  78  is pulled back off the surface of the controlled jaw  28 . 
   The control rod  78  extends through a slotted sleeve  80 . The slotted sleeve  80  provides support for the control rod  78 , maintaining the control rod  78  on its longitudinal axis. The slotted sleeve  80  can be directly supported by the frame  22 , but more preferably is rigidly attached to the jaw housing  40  to move with the jaws  28 ,  30  and jaw housing  40  on the bearing structure  46 . A slot  82  on the slotted sleeve  80  allows an attachment link  84  to extend through the slotted sleeve  80  and connect to the control rod  78 . 
   A spiral lift cam  86  is positioned on the hub  34  underneath the controlled jaw  28 . The spiral lift cam  86  operates essentially as disclosed in U.S. Pat. Nos. 6,846,000 and 6,935,650. The base plate  50  includes a mating opening  88  for the spiral lift cam  86 . The mating opening  88  has one or more ramps  90 , which cooperate with ramps  92  on the bottom of the spiral lift cam  86 . The preferred profile for the ramps  90  is shown in  FIG. 4 , which shows two opposing ramps operating over a throw of about 78°, and then has a 25° landing dwell. 
   As best shown in  FIGS. 2   b ,  11  and  12 , a compression spring  94  biases the controlled jaw  28  and the underlying spiral lift cam  86  downward. When the spiral lift cam  86  is pivoted about the hub  34 , the ramps  92  on the bottom of the spiral lift cam  86  ride up the ramps  90  on the mating opening  88 , raising the spiral lift cam  86  and the controlled jaw  28  above it against the compression spring  94 . 
   The preferred attachment link  84  includes an attachment pin  96  and an attachment bar  98 . The attachment pin  96  extends through the control bar  78  and resides in the slots  82  of the slotted sleeve  80 . The attachment bar  98  pivotally connects the attachment pin  96  to the spiral lift cam  86 . A distal end of the attachment pin  96  is connected to a tension spring  100 . The tension spring  100  extends through a tension spring window  102  in the jaw housing wall  52 , and the opposite end of the tension spring  100  biases off a tension spring mount  104  fixed on the jaw housing  40 . The attachment bar  98  extends through an attachment bar window  106  on the jaw housing  40 . The size of the attachment bar window  106  should permit side-to-side angular movement of the attachment bar  98  and the spiral lift cam  86  as the control linkage  36  moves between the closed and release positions. The size of the attachment bar window  106  should also permit some angular up-and-down movement of the attachment bar  98  as the spiral lift cam  86  rises or lowers relative to the fixed height of the slotted sleeve  80 . When the control bar  78  is pulled or pushed within the slotted sleeve  80 , the attachment pin  96  translates with the control bar  78 . The attachment bar  98  then torques the spiral lift cam  86  about the movable jaw hub  34 . The tension spring  100  biases the control bar  78  toward the closed position, with the spiral lift cam  86  nesting downward in the mating opening  88 . 
   A latch  108  permits the control bar  78  to be secured at either the closed position or at the release position. The preferred latch  108  is hinged relative to the slotted sleeve  80  with a hinge pin  110 , and includes an interference flat  112  which mates with either a closed latch recess  114  or a release latch recess  116  on the control bar  78 . The latch  108  can then be held downward into an interference position, mating with either the closed latch recess  114  or the release latch recess  116 , with a safety pin  118 . With the latch  108  in the interference position, the latch  108  prevents translation of the control bar  78 . If desired, the latch  108  may be either biased open or biased closed such as with a spring (not shown), which would minimize rattling of the latch  108  in the interference position during towing and affect how the latch  108  moves into and out of the interference position. However, the preferred embodiment allows the latch  108  to freely rotate about the hinge pin  110  under only gravitational forces, which lightly bias the latch  108  either toward the interference position or toward an open position depending upon where the latch  108  is released in its hinged arc. 
   The fixed height jaw  30  is preferably biased toward an open position. In the preferred embodiment, a torsion spring  120  is mounted about the fixed height hub  34 , providing a biasing force from a torsion spring mount  122  fixed on the jaw housing  40  to a side of the fixed height jaw  30 . 
   A follower  124  is mounted on the fixed height jaw  30  in a configuration for cooperating with the controlled jaw  28 . The preferred follower  124  is formed from bent bar stock which is welded or otherwise fixedly secured to the fixed height jaw  30 . The follower  124  causes the controlled jaw  28  to open with the opening of the fixed height jaw  30 . A stop  126  is provided which stops the controlled jaw  28  from rotating past the closed position. The follower  124  and the stop  126  together ensure that the two jaws  28 ,  30  do not get “out-of-time” wherein one jaw in the open position nests in the other jaw in the closed position. 
   A viewing opening  128  in the fore side of the jaw housing  40  permits operator viewing of the follower  124  from the cab of the vehicle. The slots  82  in the slotted sleeve  80  permit operator viewing of marked portions of the control rod  78 . For instance, green dots may be painted on the control rod  78  and on the follower  124  which are only visible when the fixed height jaw  30  is rotated back into the closed position and when the control rod  78  is in the closed position indicating that the controlled jaw  28  is positioned downward beneath the distal end of the control rod  78 . In its preferred configuration, the position indicator dot(s) is/are viewable from the forward side of the hitch  20 , so the operator can check the position indicator from the cab of the pick-up truck prior to driving with the towed vehicle, thereby ensuring that the kingpin  32  is locked in the hitch  20 . The operator should only drive with a towed vehicle after checking to make sure the position indicator is “green” signifying that the hitch  20  is locked closed. A yellow dot may be painted on the control rod  78  which is visible through the sleeve  80  only when the control rod  78  is in an intermediate position indicating that the controlled jaw  28  is ready to receive the kingpin  32 . A red dot may be painted on the control rod  78  which is visible only when the controlled jaw  28  is fully opened into the release position, signifying that the hitch  20  will not lock about a kingpin  32  but rather is uncoupled from the kingpin  32 . 
   Operation of the hitch  20  is explained with reference to  FIGS. 5-12 . As shown in  FIG. 5 , the hitch  20  is depicted as beginning in a closed, locked position. The controlled jaw  28  is biased downward by the compression spring  94 . The controlled jaw  28  is further positively held downward by the control bar  78  extending over the top surface of the jaw  28 . With the controlled jaw  28  in its downward position, it mates with the fixed height jaw  30  and cannot pivot or open. With the control bar  78  in place positively securing the controlled jaw  28  down, there is no possibility of the controlled jaw  28  rising up out of plane with the fixed height jaw  30  to an unsecured position. The control bar  78  is biased by the tension spring  100  to an extended position (to the right in  FIG. 5 ). The follower/position indicator  124  is in its forward position, visible to an operator in the cab of the vehicle to signify that the jaws  28 ,  30  are closed and secured. The latch  108  is closed into an interference position, and held closed by the safety pin  118 . 
   When the operator of the hitch  20  wants to release the trailer from the hitch  20 , first the safety pin  118  is pulled, and the latch  108  is opened. Then the control handle  38  is pulled as shown by arrow A in  FIG. 6 . The operator must pull sufficiently hard to overcome the biasing force of the tension spring  100 , but the handle  38  extends at a right angle to the pull direction, making it easy for an operator transmit a significant pull force to intentionally overcome the spring bias when desired. As the control handle  38  begins to move, the attachment bar  98  pulls the spiral lift cam  86  and the spiral lift cam  86  begins to rotate about the hub  34 . The spiral lift cam  86  rotates towards the landing dwell without lifting, until the control bar  78  has been retracted (translated) beyond the top surface of the controlled jaw  28 . 
   Once the control bar  78  clears the top surface of the controlled jaw  28 , the ramps  92  on the spiral lift cam  86  ride up the ramps  90  in the base plate  50 , lifting the spiral lift cam  86  and the controlled jaw  28  against the compression spring  94 . The pull force must now overcome the combined force of both the tension spring  100  and the compression spring  94  (through the ramp angle), as well as the gravitational force on the controlled jaw  28  and the spiral lift cam  86 . However, the tension spring  100  and the compression spring  94  need not have high spring constants, so a pull force on the order of 5 to 25 pounds can open the hitch  20 .  FIG. 6  shows the hitch  20  during the opening motion just after the spiral lift cam  86  has begun rising. At this point, if the operator releases pull on the handle  38  without completing a full release stroke, the hitch  20  will react to the forces of the tension spring  100  and the compression spring  94  and return to the closed position of  FIG. 5 . 
   If the operator continues pulling on the handle  38 , the control linkage  36  will continue to pull the spiral lift cam  86  clockwise (as shown in  FIG. 7 ) which continues to raise the controlled jaw  28  to an elevation where it clears the fixed height jaw  30 . The total release of the hitch  20  is achieved in a handle throw of only about 3 to 6 inches and preferably a complete handle throw of 4 inches or less. 
   Once the controlled jaw  28  clears the fixed height jaw  30 , the torsion spring  120  on the fixed height jaw  30  biases the fixed height jaw  30  open, pivoting counterclockwise about the fixed height hub  34 . Due to this rotation, the follower  124  contacts the controlled jaw  28  in the position shown in  FIG. 7 . The stop  126  is most important at this time, as it prevents the controlled jaw  28  from the possibility of pivoting counterclockwise into an out-of-time position with respect to the fixed height jaw  30 . Additionally, friction between the spiral lift cam  86  and the controlled jaw  28  creates the tendency for the controlled jaw  28  to pivot in the same direction as the spiral lift cam  86 , clockwise. With the controlled jaw  28  prevented from counterclockwise rotation due to the stop  126  and started in the clockwise direction due to friction with the spiral lift cam  86 , the follower  124  readily continues the opening of the controlled jaw  28  under the force of the torsion spring  120 . The hitch  20  opens and tends to “eject” the formerly held kingpin  32 , so the hitch  20  can be driven away from the towed vehicle and its kingpin  32 . 
   If desired, the hitch  20  may be secured in this fully open position by closing the latch  108  and securing the latch  108  with the safety pin  118 . In many instances, the weight of the trailer and the frictional reluctance of the trailer to move (for a “heavy load”) will be greater than the opening force provided by the torsion spring  120 . That is, the hitch  20  will not eject a heavy load upon reaching the release position. In such cases, merely raising the controlled jaw  28  to the release position will not by itself open the hitch  20 , and releasing of the pull force on the handle  38  prior to closing the latch  108  into the release recess  116  will cause the hitch  20  to revert back to the closed position of  FIG. 5  under the force of the tension spring  100  and the compression spring  94 . With the hitch  20  held in the fully open position, the spiral lift cam  86  holds the controlled jaw  28  up and out-of-plane with the fixed height jaw  30 , and the jaws  28 ,  30  will not unintentionally reclose around a kingpin  32 . With a heavy load, the operator may use the “held open” position to drive the towing truck out from under the kingpin  32  of the heavy load, causing the hitch  20  to spring open to the position of FIG.  8 . If desired, the operator may also take advantage of the “held open” hitch position during reattachment of the towed kingpin  32  to the hitch  20 , i.e., while positioning the trailer and kingpin  32  to the general vicinity desired relative to the hitch  20 . So long as the hitch  20  is in the “held open” position of  FIGS. 8 and 12  (either due to force on the handle  30  or to the latch  108  engaging the release recess  116 ), there is no possibility of the controlled jaw  28  moving downward into a locked position. 
   Once the kingpin  32  is no longer in the hitch  20 , the torsion spring  120  fully opens the jaws  28 ,  30  to the release position shown in  FIGS. 8 and 12 . Once the fixed height jaw  30  is open, the rear corner of the fixed height jaw  30  prevents the controlled jaw  28  from moving back downward despite the biasing force of the compression spring  94 . Typically after some time has passed after releasing the kingpin/trailer, the operator may desire to use the hitch  20  again. Opening of the latch  108  out of the release recess  116  (or releasing pull on the handle  38  without ever closing the latch  108 ) causes the handle  38  to translate back toward the controlled jaw  28  to the “load” position shown in  FIG. 9 . The force of the tension spring  100  moves the control bar  78  until the distal end of the control bar  78  contacts the controlled jaw  28 . The spiral lift cam  86  has lowered back down relative to the base plate  50 , but the controlled jaw  28  is still held at an elevated position due to the underlying fixed height jaw  30 . The force of the torsion spring  120  keeps the jaws  28 ,  30  open even though the tension spring  100  and the compression spring  94  are biasing the controlled jaw  28  toward a closed position. However, this force balance is readily overcome when a kingpin  32  is pressed into the hitch  20 . The kingpin  32  (shown in  FIGS. 13 and 14 ) provides a pushing force K which is used to push the jaws  28 ,  30  backward until they close around the kingpin  32 , to the position shown in  FIG. 10 . Once the jaws  28 ,  30  are aligned about the kingpin  32 , the controlled jaw  28  clears the fixed height jaw  30 , and the compression spring  94  forces the controlled jaw  28  downward into the plane of the fixed height jaw  30  and into engagement with the fixed height jaw  30 . Once the controlled jaw  28  moves downward under the force of the compression spring  94 , the control rod  78  is free to complete its movement over the controlled jaw  28  to the position shown in  FIGS. 5 and 11 . With the controlled jaw  28  in the “down” position, the follower/position indicator  124  is again visible through the view window to an operator in the cab of the pickup truck. Once the kingpin  32  is in place and engaged within the jaws  28 ,  30 , the operator can close the latch  108 , again creating positive interference between the latch  108  and the control rod  78  to prevent the control rod  78  from unintended movement. 
   As best shown in  FIGS. 13 and 14 , the vertical dimensions of the hitch  20  as it engages the kingpin  32  are quite important to ensure that the hitch  20  and jaws  28 ,  30  are appropriately strong to support the load of the kingpin  32  during towing. For instance, an upward force on the kingpin  32  will transmit to the jaws  28 ,  30  and then from each jaw  28 ,  30  to its hub  34  as a bending moment. To support bending moments at the connection between the jaws  28 ,  30  and the hubs  34 , each of the jaws  28 ,  30  have a collar  130 ,  132  around its hub  34  (and inside the respective springs  94 ,  120 ) that, in the preferred embodiment has an inside diameter of about 25 mm and a height of at least about 27 mm. The two jaws  28 ,  30  mate to form a circular central opening for receiving a 50.8 mm (2 inch) diameter neck  134  on the standard kingpin  32 . To transmit the towing force from the hubs  34  to the jaws  28 ,  30 , the jaws  28 ,  30  are formed of 1045 steel and have a preferred height or thickness t of 16 mm. The spiral cam ramps  90 ,  92  have a lift height of cam action  1  which raises the controlled jaw  28  18 mm so the controlled jaw  28  will readily clear the fixed height jaw  30  upon opening. While the neck  134  of standard kingpins has a 36.5 mm height which will permit the full 34 mm range of contact (16 mm thickness plus 18 mm height change) of the controlled jaw  28 , placement of the kingpin  32  at different heights relative to the hitch  20  can upset the mating relationship in height between the jaws  28 ,  30  and the kingpin  32 . For instance, one common application is to insert a lube plate  136  around the kingpin  32  so the lube plate  136  rides on the skid plate  24 , reducing or minimizing the need to grease the skid plate  24 . The lube plate  136  may be formed of a strong bearing material, at a thickness of no more than 3/16 of an inch. The additional height of the lube plate  136  raises the kingpin  32  relative to the jaws  28 ,  30 . 
   To account for the potential variance in height of the kingpin  32  relative to the jaws  28 ,  30 , the jaws  28 ,  30  have kingpin receiving recesses  138 ,  140  defined therein. On the bottom side of the fixed height jaw  30  and the bottom side of the controlled jaw  28 , a kingpin receiving recess  138  is defined, shaped to mate with the kingpin  32  upon entry and removal of the kingpin  32  from the hitch  20 . The preferred bottom side kingpin receiving recesses  138  are 2 mm deep. On the top side of the controlled jaw  28 , a topside kingpin receiving recess  140  is defined, shaped to mate with the kingpin  32  upon entry and remove of the kingpin  32  from the hitch  20 . The preferred top side kingpin receiving recess  140  is about 5 mm deep. With the bottom side and top side receiving recesses  138 ,  140 , the contact area of the controlled jaw  28  on the kingpin  32  has a contact height h on the kingpin  32  which is no greater than 10 mm, such as about 8.75 mm. Even when this controlled jaw  28  is raised 18 mm (to the height shown by dashed lines  28   a ) to clear the height of the fixed height jaw  30 , the full range of contact of the controlled jaw  28  on the kingpin  32  is 28 mm or less, allowing use of a lube plate  136  of up to about 3/16 inch (4.5 mm). By having the narrow contact height, the kingpin  32  can be secured within the jaws  28 ,  30  at different heights relative to the hitch  20  depending upon whether a lube plate  136  is or is not present 
   In considering the operation of the preferred embodiment, the numerous advantages of the present invention become apparent. One significant advantage is that the invention in one aspect permits single-handed manipulation of a single control (handle  38 ) to provide both the safety function and the hitch movement function. The handle  38  is moved through a first range of travel throughout which it positively secures the controlled jaw  28  at the closed position. Until the handle  38  is pulled a sufficient distance that the control bar  78  no longer overlies and contacts the top side of the controlled jaw  28 , there is no possibility of the controlled jaw  28  moving upward and no possibility of inadvertent release of the hitch  20 . The same handle  38  is then moved through a second range of travel throughout which it lifts the controlled jaw  28  to the release position. The operator can readily open the hitch  20  using a single hand, by undoing the latch  108  and with a simple movement of the handle  38 . 
   A second advantage involves the fact that opening of the hitch  20  involves translation (pulling and/or pushing) of the handle  38  rather than pivoting or torqueing of the handle  38 . Operators are able to impart greater forces in pulling and/or pushing a handle  38  than they can impart in turning or twisting of the handle  38 . Even if the operator does not have great hand strength, the forces of the tension spring  100  and the compression spring  94  can be overcome by imparting translational forces on the handle  38 . 
   A related advantage results from the orientation of forces. Operation of the hitch  20  involves raising and lowering the controlled jaw  28 . However, it is difficult for many operators to impart a strong raising force without standing over the handle  38  to be raised or straining the operator&#39;s back. The preferred embodiment does not require the operator to impart any vertical force, but rather converts the operator&#39;s horizontal force on the handle  38  to a vertical force on the controlled jaw  28 . The horizontal forces imparted by the operator are in push and pull directions relative to where the operator usually stands beside the hitch  20  during operation of the hitch  20 , enabling the operator to readily lean into the direction of push or pull and thereby more easily impart a greater force. 
   Another force orientation benefit is achieved in the interaction between the spiral lift cam  86  and the controlled jaw  28 . Namely, friction between the spiral lift cam  86  and the controlled jaw  28  tends to pivot the controlled jaw  28  in the same direction (clockwise or counterclockwise) that the spiral lift cam  86  pivots. The spiral lift cam  86  and the controlled jaw  28  both open by clockwise motion and both close by counterclockwise motion. By having the spiral lift cam  86  and the controlled jaw  28  moving in the same direction, the frictional forces help to open and close the controlled jaw  28  as desired, which helps minimize the possibility that the controlled jaw  28  might become “out-of-time” with the fixed height jaw  30 , i.e., helps avoid the situation wherein one jaw in the open position interlocks with the other jaw in the closed position. 
   Another related advantage results from the short stroke or throw length of the handle  38  of the present invention in opening the hitch  20 . The total release of the hitch  20  is achieved in a handle throw of only about 3 to 6 inches and preferably a complete handle throw of 4 inches or less. The small handle throw necessary to move the hitch  20  from the closed position to the release position is important when one considers the small confines of the bed of the pick-up truck in which the hitch  20  is installed. With a small throw of four inches or less, the hitch  20  can be release by most operators without needing to climb into the bed of the pick-up truck. Even though the handle  38  is pulled outward on the side of the hitch  20 , the short throw length enables the hitch  20  to be mounted into beds of all standard sizes, with the kingpin opening  42  centrally mounted relative to the bed, and still provide sufficient clearance between the handle  38  and the box of the pickup truck throughout the handle throw. 
   The torsion spring  120  in the preferred embodiment provides another advantage. The torsion spring  120  biases the kingpin retention structure provided by the jaws  28 ,  30  open when the controlled jaw  28  is raised to the release position. Accordingly, in light load or no load situations, the hitch  20  “springs” open once the release position of the handle  38  is reached. It is very clear to the operator when the handle  38  has been pulled far enough to release the hitch  20 . After the hitch  20  has “sprung” open, it will not close again until after both the handle  38  is released back to the load position and the spring force of the torsion spring  120  is overcome by moving the kingpin  32  forward in the kingpin receiving slot  26 . 
   Another separate advantage of the preferred embodiment involves the follower/position indicator  124 . The operator can readily check to see when the hitch  20  is in the closed, secured position. The position indicator  124  is viewable from the cab of the pick-up truck, so the operator can look over his or her shoulder and check the position indicator as needed, such as immediately after driving over a bump in the road. 
   Another advantage of the preferred embodiment involves the sleeve arrangement for the control rod  78 . The sleeve  80  strengthens the control rod  78  against bending or misalignment. The additional stability and strength that the sleeve  80  provides to the control rod  78  are particularly important in cases when the control rod  78  is inadvertently stepped on or otherwise contacted at an angle to its longitudinal direction of motion. 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. As just one example, the single handed operation of present invention can be readily applied to a wide variety of hitch structures.