Abstract:
A system is described for attenuating intermittent forces at the interconnection between a towing vehicle and a trailer. The system includes a linear rocking member suspended between the towing vehicle and the trailer, a shock absorber between the linear rocking member and the vehicle, and a pendulum having a fulcrum connected to the vehicle and a swinging component rotationally connected to the linear rocking member, and a fastening device connecting the linear rocking member to the trailer to be towed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based upon, and claims priority from, my Provisional Application No. 60/761,693, filed Jan. 23, 2006. 

   FIELD OF THE INVENTION 
   This invention relates to economical techniques for alleviating and attenuating the longitudinal surges and vertical shocks that are transferred through a conventional hitch connecting a trailer and a towing vehicle. 
   BACKGROUND OF THE PRIOR ART 
   A trailer and a towing vehicle are two relatively independent entities that are interconnected by a hitching device. The trailer and the vehicle each have their own center of gravity, and when in motion each is subjected to its own pitch, yaw, and roll motions. Because of these differing motions by the trailer and towing vehicle, the interconnection between them is subjected to numerous intermittent jerking forces in addition to the motivational force exerted by the towing vehicle on the trailer. These unsteady, irregular and rapidly changing jerking forces are very undesirable. They cause annoyance and discomfort to drivers and their passengers. They place further burdens on the suspension systems of the trailer such that the contents of the trailer can be jostled and damaged. They cause wear and tear on every component of both the trailer and towing vehicle. It is clear that any attenuation of these jerking forces will result in a smoother and better ride which is safer for the occupants of the vehicle and also for the cargo in the trailer. 
   Prior art includes a multitude of systems for attenuating these jerking forces. Many of these systems are quite elaborate and require numerous springs and/or other shock absorbing devices. Thus, they can be prohibitively expensive. Other simpler systems dampen longitudinal surges but not vertical shocks. Still others dampen vertical shocks but not longitudinal surges. 
   Because of either the expense involved or a limitation on effectiveness, most of the hitches in use on the road today do not have any capacity to attenuate intermittent jerking motions and forces. An economical technique for attenuating a significant portion of these jerking motions and forces is clearly needed. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a novel arrangement of components featuring a linear rocking member normally centered on the hitch, parallel with the longitudinal axis of the towing vehicle, and suspended between the towing vehicle and the trailer. For hitches that are located forward of the rear axle of the towing vehicle including those for gooseneck trailers and most fifth-wheel arrangements, the linear rocking member is suspended on one end from a short pendulum and supported on the other end by an air spring or other means for absorbing mechanical energy. The ball of a standard ball and socket type of trailer hitch, or the receiving receptacle for the king pin of a fifth wheel type of hitch, is rigidly attached to the linear rocking member near or at the center of the linear rocking member. 
   For hitches located behind the rear axle of the towing vehicle, the linear rocking member is supported near or at the center by an air spring or other means for absorbing mechanical energy. The front end of the linear rocking member is suspended on an inverted pendulum and the trailer hitch ball is rigidly attached to the rear end of said linear rocking member. 
   For all hitches, whether behind or ahead of the rear axle of the towing vehicle, the pendulum provides for limited longitudinal displacement between the trailer and towing vehicle such that longitudinal surges in either direction can be attenuated. Both the hitch weight of the trailer and the air spring dampen these longitudinal surges. Vertical shocks are attenuated by the air spring. It is also noted herein that further damping of longitudinal surges can be achieved by restricting the pendulum action with other shock absorbing means such as encasing the pendulum rod ends in spring rubber or elastomeric material. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a configuration of the present invention that is suitable for use with a ball and socket type of hitch located forward of the rear axle of the towing vehicle such as those generally used on gooseneck trailers. 
       FIG. 2  illustrates a configuration of the present invention that is suitable for use with a kingpin type of trailer hitch, which is also located forward of the rear axle of the towing vehicle. 
       FIG. 3  illustrates a configuration of the present invention that is suitable for use with a ball and socket type of hitch located behind the rear axle of the towing vehicle. These hitches are known as receiver hitches or as bumper hitches. 
       FIG. 4  is a cross-section of the pendulum subassembly and illustrates a simplified technique for making a short sturdy pendulum. 
       FIG. 5  illustrates another embodiment of a shock attenuation system which is useful in the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the present invention suitable for use with a ball and socket hitch located forward of the rear axle of the towing vehicle is illustrated in  FIG. 1 . Linear rocking member  10  is supported at one end  10 A by air spring  11 . Zerk  12  is the air inlet valve for air spring  11 . Bolts  13  attach air spring  11  to linear rocking member  10 . Ball  14  can be welded to linear rocking member  10  at location  15 . 
   Fulcrum rod  16  with fulcrum cylindrical bushings  17 , and swinging rod  18  with cylindrical bushings  19 , are parts of a short sturdy pendulum further illustrated in  FIG. 4 . The internal diameter of cylindrical bushing  17  is a clearance fit with fulcrum rod  16 . The internal diameter of swing bushing  19  is a clearance fit with swinging rod  18 . Fulcrum rod  16  is supported at its ends by buttress plates  20 . The holes  21  in buttress plates  20  are circular and are clearance fits with fulcrum rod  16 . Buttress plates  20  have arcuate slots  22  that serve to limit the travel of swinging rod  18 . Bushings  19  are welded or otherwise securely attached to bushings  17 . In  FIG. 4  this attachment is shown as welds  28  and  29 . 
   The longer surfaces of each slot  22  are two concentric circular arcs whose center is at the center of holes  21 , which is also the center of the fulcrum. The width of slot  22  is equal to the difference in radii of the two concentric arcs and is a clearance fit with the diameter of swinging rod  18 . The length of slot  22  governs the swing of the pendulum and is such that the allowable limits for lateral motion of air springs  11  are not exceeded. The ends of slot  22  are circular arcs with radii slightly larger than the radii of swinging rod  18 . 
   Bushing  23  is welded to the end  10 B of linear rocking member  10 . The internal diameter of cylindrical bushing  23  is a clearance fit with swinging rod  18 . 
   Buttresses  20  are connected to base  24 , which in turn is connected to the bed of the towing vehicle with apparatus  25 , which is adapted to fit the hitch of the towing vehicle. 
   Stop  26  secured to buttress plate  20  serves to limit counterclockwise rotation of the linear rocking member  10 . Stop  27  on base plate  24  serves to limit clockwise rotation of the linear rocking member  10 . These rotations correspond to pitch motions of the towing vehicle and also of the trailer when the trailer is in the normal position of alignment with the towing vehicle. 
     FIG. 2  illustrates a second embodiment of the invention suitable for use with a kingpin type of trailer hitch. Kingpin trailer hitches are also located forward of the rear axle of the towing vehicle. In this embodiment, the linear rocking member  10 C can be an inverted channel. Air springs  11 , zerk  12 , and bolts  13  are the same as described above in connection with  FIG. 1 . Fulcrum rod  16  with cylindrical bushings  17  swinging rod  18  with cylindrical bushings  19  form a pendulum of the type shown and described in connection with the embodiment of  FIG. 1 . On end of linear rocking member  10 C is welded to bushing  23  on rod  18 . Buttresses  20 A are secured to plate  24 A, and apparatus  25 A is adapted to connect the entire apparatus to the hitch of the towing vehicle. 
   Receiving mechanism  14 A is for receiving and releasably securing the kingpin of the trailer to be towed. Rotation on shaft  14 B allows pitch motions of the trailer with respect to the towing vehicle. Rotation at point  14 C allows limited roll motions of the trailer with respect to the towing vehicle. Kingpin receiving mechanism  14 A normally has a latching mechanism that is not shown in  FIG. 2  for reasons of clarity. 
     FIG. 3  illustrates the third embodiment of the invention wherein the hitch is located behind the rear axle of the towing vehicle. For this embodiment, the positions of air spring  11  and ball  14  on linear rocking member  10 D are interchanged such that ball  14  is on the rearward end of the linear rocking member  10 D and air spring  11  is near the midpoint of the linear rocking member  10 D. For this third embodiment, the pendulum mechanism comprised of fulcrum rod  16 , cylindrical bushings  17 , swinging rod  18 , and swinging bushings  19 , is inverted with slots  22  on top and fulcrum hole  21  on the bottom, and linear rocking member  10  is cantilevered. A receiver tube  25 B is mounted to the base  24 B with bolts  28 . Holes  29  allow for vertical adjustability of the receiver tube  25 B. The receiver tube is of a standard size to fit standard receiver hitches mounted on the towing vehicle. 
     FIG. 4  is a typical cross-section through the pendulum mechanism of the invention and illustrates a method of constructing the pendulum mechanism. Fulcrum cylindrical bushing  17  is welded to swing cylindrical bushing  19  at locations  28  and  29  forming a short sturdy arm for the pendulum. 
   In operation, air spring  11  provides for vertical travel through the hitch and the pendulum mechanism provides some variation in the longitudinal distance between the towing vehicle and the trailer. Together they provide for some relative displacement between towing vehicle and trailer in any combination of vertical and longitudinal directions. Both the restoring forces of the pendulum and air pressure within air spring  11  attenuate intermittent forces in various combinations of these two directions. Because a straight line between the center of gravity of the towing vehicle and the center of gravity of the trailer will rarely pass through the pivot points of the hitch, almost all intermittent forces through the hitch will be some combination of vertical and longitudinal forces and both air spring  11  and the pendulum mechanism will work to attenuate them. 
   In  FIG. 5  there is illustrated another embodiment of the system of the invention. In this embodiment, further damping of longitudinal surges during towing is achieved by restricting the pendulum action using a damper system  30  comprising a rubber or elastomeric member. The rubber or elastomer member  32  (having an opening  32 A therethrough) is positioned on each end of the pendulum rod  18 . The rubber or elastomer member is captured or secured within a steel box or frame  31  having an aperture  31 A for mounting bolt  34 . The bolt  34  is passed through hole  33  in buttress member  20  and secured with a threaded nut  34 A. A cover may be secured over the outside of the box  31 . The rubber serves to dampen the movement of the pendulum rod  18  so as to alleviate the shocks of sudden starts or stops of the towing vehicle. 
   Other variants are possible without departing from the scope of this invention.