Abstract:
A trailer coupling ( 1 ) is disclosed having a first interconnection ( 2, 12 ) to a prime mover ( 4 ) and a second interconnection ( 14 ) to a trailer. A pivot mechanism which includes a universal joint ( 13 ) interconnects the first and second interconnections. The first interconnection is a frusto-conical spigot ( 2 ) and a frusto-conical sleeve housing ( 12 ). This interconnection is rigid and does not permit any movement between the prime mover and the sleeve housing ( 12 ). The universal joint ( 13 ) is rotatably mounted to permit movement between the trailer and the prime mover about a vertical axis ( 136 ), a left to right horizontal axis ( 137 ) and a front to rear horizontal axis ( 34 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Stage of PCT Application Ser. No. PCT/AU2010/000256, filed on Mar. 4, 2010, which claims priority from Australian Patent Application Ser. No. 2009901198, filed on Mar. 20, 2009, both of which are incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to trailer hitches which are used to couple a prime mover (or towing vehicle) to a trailer (or towed vehicle). 
         [0003]    Generally speaking, trailer hitches can be classified into three distinct types. One type of hitch is a turn-table hitch which is used for semi-trailers or articulated vehicles and is not of concern in relation to the present invention. 
         [0004]    The next type of hitch consists of a donut shaped device (that is to say an anulus having a substantially circular cross-section) which is arranged in a generally horizontally plane and which is connected by means of a vertical post of cylindrical cross-section (or pintle). The vertical post bearing on the inner most diameter provides the left or right turning ability, whilst the vertical post moving on the inner curve of the donut provides the ability for the prime mover and the trailer to travel over humps and across dips. This hitch suffers from two distinct disadvantages in that, firstly, it is not able to cater for the prime mover being on a piece of ground which slopes from high ground on the left to low ground of the right, whilst the trailer stands on ground which slopes from the high ground on the right to low ground on the left. Secondly, every time the towing vehicle brakes or accelerates, there is an unrestrained backwards and forwards motion of the trailer which results in the vertical post hitting either the leading interior edge or the trailing interior edge of the donut. 
         [0000]    The third type of prior art hitch takes the form of a substantially cylindrical ball which is mounted on the top of an upright support, and which receives a substantially hemispherical cup. The hemispherical cup is able to rotate about three axes of rotation relative to the center of the sphere, however, the extent of the rotation is limited because of a locking mechanism which holds the cup to the sphere. This locking mechanism involves prongs or fingers which come together under the “equator” of the sphere and thus retain the cup on the sphere. 
         [0005]    All three of these prior art devices are characterized in that the point of interconnection between the trailer coupling and the prime mover or towing vehicle is also the location of the pivoting mechanism which enables the trailer to pivot relative to the prime mover. This has the consequence that the point of interconnection between the trailer coupling and the prime mover is also the site of wear through use. An extremely dangerous consequence of this wear is that the trailer coupling may detach from the prime mover under load, particularly as a consequence of a sudden shock caused by a bump or similar. This has the extremely dangerous consequence that the trailer detaches from the prime mover and may well cause the prime mover to have an accident. 
         [0006]    The genesis of the present invention is a desire to provide a trailer coupling where the point of attachment between the prime mover and the trailer coupling is physically spaced from the pivoting mechanism which permits the trailer to pivot relative to the prime mover, and/or where the interconnection between the trailer coupling and the prime mover is substantially rigid and thus not subjected to wear. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with a first aspect of the present invention there is disclosed a trailer coupling having a first interconnection between a prime mover and said coupling, a second interconnection between said coupling and a trailer, and a pivot mechanism to permit said trailer to pivot relative to said prime mover, wherein said pivot mechanism is located intermediate said first and second interconnections and spaced from said first interconnection. 
         [0008]    In accordance with a second aspect of the present invention there is disclosed a trailer coupling for connecting a prime mover to a trailer and having a first interconnection between said prime mover and said coupling, wherein said first interconnection does not permit movement between said prime mover and said trailer coupling. 
         [0009]    In accordance with a third aspect of the present invention there is also disclosed a method of interconnecting a prime mover with a trailer using a trailer coupling, said method comprising the steps of: (i) making a first interconnection between said prime mover and said coupling, (ii) making a second interconnection between said trailer and said coupling, (iii) locating a pivot mechanism between said first and second interconnections, and (iv) spacing said pivot mechanism from said first interconnection. 
         [0010]    In accordance with a fourth aspect of the present invention there is also disclosed a method of interconnecting a prime mover to a trailer using a trailer coupling, said method comprising the steps of: (a) making a first interconnection between said prime mover and said trailer coupling, and (b) making said first interconnection rigid to thereby prevent movement between said prime mover and said trailer coupling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0012]      FIG. 1  is an exploded side view of the trailer hitch of a first embodiment, 
           [0013]      FIG. 2  is a vertical cross-section taken through the assembled spigot and frusto-conical housing of  FIG. 1 , 
           [0014]      FIG. 3  is a perspective view from above and to one side of the trailer coupling of a second embodiment, and 
           [0015]      FIG. 4  is a side view of the spigot and locking cap of the trailer coupling of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    As seen in  FIGS. 1 and 2 , the trailer coupling  1  of a first embodiment is illustrated and takes the form of a spigot  2  which has a threaded shank  3  which passes through an aperture in a towbar or goose neck  4  which is part of a prime mover (not illustrated). The spigot  3  is secured to the goose neck  4  by means of a nut  5 . The spigot  2  is of frusto-conical shape and has a circumferential groove  7  and a threaded blind hole  8  in its upper end. 
         [0017]    The portion of the trailer coupling  1  which connects to the trailer (not illustrated) takes the form of a sleeve housing  12 , a universal joint  13  and a trailer coupling  14 . 
         [0018]    The sleeve housing  12  has an interior frusto-conical cavity  16  which is capable of mating with the spigot  12 . As illustrated in  FIG. 2 , the housing  12  includes a locking cap  18  having a threaded shank  19  which is dimensioned to be received by the threaded blind hole  8  in the spigot  2 . The locking cap  18  also includes a lock nut  20  and a pair of detents  22  which mate with corresponding recesses  23  in the top of the sleeve housing  12 . 
         [0019]    A spring  21  surrounds the shank  19  and is compressed by the inter-engagement of the locking cap  18  and sleeve housing  12  to assist in maintaining the locking cap  18  securely placed in its final position. 
         [0020]    With the spigot  2  secured to the goose neck  4 , the sleeve housing  12  can be placed over the spigot  2  and moved downwardly so that the frusto-conical surfaces of the spigot  2  and cavity  16  inter-engage with each other. The locking cap  18  is then rotated so as to threadably engage the threaded shank  19  of the locking cap  18  with the threaded blind hole  8  of the spigot  2 , the locking cap  18  being maintained in position by the inter-engagement of the detents  22  and the recesses  23 . The locking cap  18  is preferably provided with radial apertures  29  into which a locking pin  25  can be inserted. In this way, the locking pin  25  can be used as a lever to provide extra force to rotate the locking cap  18 . 
         [0021]    In addition, the locking pin  25  is thereafter passed through a pair of apertures  26 ,  27  in the sleeve housing  12  so as to thereby retain the locking pin  25  in the circumferential groove  7 . The locking pin  25  can be secured by any convenient means such as a spring clip or cotter pin (not illustrated in  FIG. 2 ). 
         [0022]    Preferably the sleeve housing  12  is provided with a pair of downwardly directed lugs  28  which are spaced to provide a close fit to either side of the goose neck or towbar  4  and are a further preventative mechanism to prevent rotation of the sleeve housing  12  relative to the spigot  2 . 
         [0023]    Returning now to  FIG. 1 , the trailer coupling  14  takes the form of a connector plate  31  which includes apertures  32  which enable the trailer coupling  14  to be bolted to a corresponding plate (not illustrated but conventional) mounted at the apex of the trailer yoke. The trailer coupling  14  also has a longitudinal axle  34  which is threaded at its rear end  35  and provided with a pair of Y-shaped arms  36  at its leading end. The Y-shaped arms  36  form part of a substantially conventional universal joint  13  which is provided with a grease nipple  39 . 
         [0024]    The longitudinal axle  34  is mounted within a pair of bushings  40 ,  41  located within a hollow cylinder  42  which is welded to the connector plate  31 . Two polyurethane washers  44 ,  45  are located at opposite ends of the hollow cylinder  42  and a metal washer  46  and nut  47  are mounted on the rear end  35  of the axle  34 . The nut  47  compresses the polyurethane washers  44  and  45  and provides a sealed space which can be filled with grease via grease nipples  49 . The bushings  40 ,  41  each have an interior aperture which is cylindrical and an exterior shape which is substantially rectangular to thereby ensure that the bushings  40 ,  41  do not themselves rotate but instead the axle  34  rotates within the bushings  40 ,  41 . 
         [0025]    The universal joint  13  is entirely conventional in construction having two pairs of Y-shaped arms  36 ,  37  (only one of the Y-shaped arms  37  being illustrated in  FIG. 1 ). The free ends of the Y-shaped arms  36 ,  37  carry threaded plugs  38  which retain the internal universal joint mechanism. Extending between the Y-shaped arms  36  is a vertical axis  136  which enables the prime mover to turn from left to right and the trailer coupling  1  to pivot about the vertical axis  136  as the trailer follows the left or right movements of the prime mover. 
         [0026]    In addition, extending between the Y-shaped arms  37  is a substantially horizontal axis  137 . The pivoting movement of the universal joint  13  about the horizontal axis  137  enables the prime mover to pass over dips and bumps and have the trailer follow faithfully behind. Furthermore, the extent of angular movement about the vertical axis  136  and the horizontal axis  137  typically exceeds approximately 210 degrees so in respect of these two pivoting movements the trailer coupling  1  is far superior to any of the prior art types of trailer coupling. 
         [0027]    Furthermore, the longitudinal axis  34  constitutes a front to rear axis about which the trailer is able to pivot relative to the prime mover. This enables the prime mover to be positioned on ground which slopes, for example, from high ground on the left to low ground on the right whereas the trailer can be positioned on ground which slopes in the opposite direction namely from tow ground on the left to high ground on the right. Such pivoting movement is not provided at all in the donut type prior art trailer coupling and is only provided to a limited extent in the spherical ball and hemispherical cap type of prior art trailer coupling, because of the need for the cap to be secured to the ball. However, in the arrangement illustrated in  FIG. 1 , essentially a 360 degree movement is possible although in practice movements of the order of less than 30 degrees are to be expected. 
         [0028]    It will also be apparent that longitudinal movement between the prime mover and the trailer occasioned by the prime mover accelerating and decelerating or braking is taken up by the ability of the polyurethane washers  44 ,  45  to be compressed and expand after being compressed. 
         [0029]    Furthermore, upward or downward loads of the trailer on the prime mover (caused by the trailer load center of gravity being respectively behind or in front of the trailer ground engaging wheels) are resisted by the  2  and sleeve housing  12 . 
         [0030]    Turning now to  FIGS. 3-4 , a second embodiment of the present invention is illustrated in which like parts to those of the first embodiment are designated by the same number. 
         [0031]    It will be seen from  FIG. 3  that the locking cap  18  instead of being provided with detents  22  is provided with a ratchet and pawl mechanism in which the pawl  52  mates with recesses  53  in the locking cap  18 . Alternatively, as illustrated in  FIG. 4 , the locking cap  18  instead of being provided with recesses  53  can be provided with a series of ramps  54  which engage the pawl  52 . 
         [0032]    The foregoing describes only two embodiments of the present invention and modifications, obvious to those skilled in the motor vehicle arts, can be made thereto without departing from the scope of the present invention. 
         [0033]    The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “including” or “having” and not in the exclusive sense of “consisting only of”.