Abstract:
A new apparatus for reducing sway of a trailer towed by a towing vehicle has a draw bar for linking a trailer to a vehicle, a ball for hitching the trailer to the draw bar, and a pin for hitching the draw bar to the vehicle. The apparatus also has a body that is associated with the ball in such a way that horizontal angular movement of the draw arm relative to the draw bar causes a substantially equivalent horizontal angular movement of the body relative to the draw bar. A hydraulic dampener linked to the body dampens horizontal angular movement of the body and, thereby, dampens horizontal angular movement of the trailer.

Description:
FIELD OF THE INVENTION 
     The present invention relates to trailer hitches and, more specifically, to trailer hitches for reducing or preventing a trailer, under tow, from swaying behind a towing vehicle. 
     BACKGROUND OF THE INVENTION 
     The term trailer as used herein refers to any form of towed vehicle, including an open tray trailer and a caravan. 
     Sway or oscillation of a trailer behind a vehicle is not an uncommon occurrence and can be a result of the actions of the driver, the condition of the road, other traffic, the weather or a combination of these or other factors. The results of an uncontrolled oscillation (commonly referred to fishtailing) can lead to serious damage to the trailer or vehicle and even to the occupants of the vehicle. 
     A variety of solutions have been proposed in order to resolve the problem of swaying movement of a trailer behind a vehicle. Some solutions involve controlled breaking of the trailer and other solutions involve devices for dampening the swaying movement. The present invention is directed to dampening swaying movement. 
     U.S. Pat. No. 6,283,489 to Hoog discloses an arrangement for reducing the sway of a trailer that is attached to a towing vehicle. 
     The arrangement comprises a towing beam that is disposed generally parallel to the bumper of a vehicle and has approximately the same length as the bumper. The towing beam includes a plate that extends from an extreme side of the beam, i.e. offset from a drawing arm of the trailer. The trailer is hitched to the beam by a towing arm that is modified to receive a first end of two extendible piston-type dampeners. The plate receives a second end of each piston-type dampener. Accordingly, any angular disposition of the trailer arm relative to the beam is resisted by the dampeners. 
     Although assisting to reduce sway of a trailer behind the vehicle, this arrangement suffers several draw backs. 
     The dampeners resist the extent to which the trailer can be angularly displaced relative to the vehicle in both horizontal and vertical directions. 
     In terms of restrictions on horizontal movement, this arrangement limits the extent to which the vehicle can turn around sharp corners and limits the manoeuvrability of the trailer relative to the vehicle. That is, the dampeners compress only to a certain extent at which point the dampeners form of rigid link between the vehicle and the arm of the trailer to prevent further angular displacement of the trailer relative to the vehicle. Any attempt to increase the angular displacement beyond this extent would result in destruction of the dampeners. 
     In terms of restrictions on vertical movement, the dampeners are fastened to the plate and the modified trailer by upright pins. While the pins permit the ends of the dampeners to pivot about a vertical axis of the pins, i.e. in a horizontal plane, the pins do not accommodate vertical angular movement of the vehicle relative to the trailer. Accordingly, the arrangement disclosed in Hoog does not account for pivoting the dampeners when the trailer is taken up a steep driveway, over a speed hump or down a boat ramp. 
     This arrangement also requires the dampeners to be attached either to the trailer or the vehicle each time the trailer is hitched to the vehicle. Similarly, the dampeners must be detached from the trailer or vehicle each time the trailer is unhitched from the vehicle. This is a nuisance when the trailer is frequently hitched and unhitched from the vehicle. 
     The dampeners in Hoog must be very stiff in order to resist movement of the trailer relative to the vehicle. However, if the dampeners are removed to enable unhitching of the trailer from the vehicle, the dampeners would be in a certain extended disposition. In order to refit the dampeners when hitching the trailer to the vehicle, the trailer must be disposed at the exact angular displacement relative to the vehicle when the dampeners were removed so the disposition of dampeners does not need adjustment to bridge the exact distance between the plate and the arm of the trailer. Alternatively, the disposition of the dampeners must be adjusted to bridge the exact distance between the plate and the arm of the trailer. In either case, this is a difficult task and makes the arrangement disclosed in Hoog difficult to use. 
     The arrangement disclosed in Hoog further requires a modification to be made to the vehicle and/or trailer to properly fit the arrangement and thereby have a sway-reducing effect. The need to modify the trailer and the vehicle contributes to an increased cost of using this arrangement. This is disincentive financially and modifications to the vehicle may be insightly. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with providing a sway dampening apparatus that alleviates, at least in part, one more of the above problems. 
     The present invention provides an apparatus for reducing sway of a trailer towed by a towing vehicle, the apparatus comprising:
         (a) a draw bar for linking a trailer to a vehicle, the draw bar having a first end and a second end;   (b) first means for hitching a draw arm of the trailer to the draw bar;   (c) second means for hitching the draw bar to the vehicle;   (d) a body associated with the first means such that horizontal angular movement of the draw arm relative to the draw bar causes a substantially equivalent horizontal angular movement of the body relative to the draw bar; and   (e) means linked to the body for dampening horizontal angular movement of the body and, thereby dampening horizontal angular movement of the trailer relative to the vehicle.       

     The dampening means is part of the apparatus and the apparatus is able to be located between a trailer and a towing vehicle to hitch the trailer to the vehicle Accordingly, the apparatus avoids the need to modify the trailer or the vehicle by fixing additional attachments to the trailer or vehicle that receive the dampening means. Therefore, the apparatus can be hitched to the vehicle with standard conventional trailer hitches and trailers are able to be hitched to the vehicle with standard conventional trailer hitches. Additionally, the apparatus enables trailers to be hitched to the vehicle and unhitched from the vehicle without having to couple dampening means to or uncouple dampening means from the trailer or vehicle. 
     By location of the apparatus between the trailer and the vehicle, the apparatus does not interfere with the horizontal or vertical angular displacement of the trailer relative to the vehicle. Therefore, the apparatus does not need to be removed when tight cornering or manoeuvring of the trailer is required, such as during parking the trailer or driving on roads with steep bends. Additionally, the ability of the apparatus to accommodate vertical angular movement of the trailer relative to the vehicle ensures that the apparatus is not limited to a select range of towing applications. 
     More preferably, the first and second means hitching means is conventional or standing hitching means. For example, the first means may comprise a tow ball or a pintle. 
     The body preferably includes a formation for coupling the body to the draw arm such that the horizontal angular movement of the draw arm relative to the draw bar causes the body to move with the draw arm. 
     Preferably the formation comprises a pair of spaced members that define a slot in which the draw arm is locatable, whereby the members are positioned closely adjacent to the draw arm when the draw arm is located in the slot such that horizontal angular movement of the draw arm drives a corresponding movement of the body through the member and such that the draw arm is free to move in the slot through a vertical angular displacement. 
     The members may be selectively positionable relative to each other to vary the width of the slot. 
     Preferably, the members are operable to clamp the draw arm. 
     Preferably the body comprises a platform that is pivotably mounted to the first means or to the draw bar at the first means for horizontal angular movement relative to the draw bar and the members comprise posts extending from the platform. 
     The dampening means is preferably mounted to the draw bar and the platform such that horizontal angular movement of the body relative to the draw bar due to movement of the draw arm relative to the vehicle causes the dampening means to resist the horizontal angular movement. 
     Preferably, the dampening means comprises a piston-type dampener and one end of the dampener is attached to the platform and the other end of the dampener is attached to the draw bar such that horizontal angular movement of the platform changes a distance between the ends of the dampener and causes the dampening means to resist the horizontal angular movement. 
     Preferably, the draw bar comprises a main bar and a side bar and one end of the dampener is attached to the side bar. 
     The resistance provided by the dampener is preferably adjustable. 
     The resistance may be controlled manually. Alternatively, a control means may control the resistance of the dampening means. 
     Preferably, the resistance is controlled by the control means in response to the speed of the vehicle and/or weight of the trailer. 
     Preferably, the control means controls the resistance such that the resistance is low at low vehicle speeds and the resistance is high at high vehicle speeds. 
     The dampening means may comprise a piston-type dampener comprising a fluid-filled body, a ram that extends into the body to define two chambers within the body, the ram having one or more than one aperture for the flow of fluid between the chambers and wherein the resistance of the dampener is controlled by adjusting the rate of fluid flow between the chambers. 
     More preferably, the fluid flow rate between the chambers is adjustable by controlling the size of the one or more than one aperture in the ram. 
     In an alternative form, the dampener may comprise a ram that cooperates with a wall disposed within the body to define two chambers within the dampener and the wall forms a channel for fluid flow between the two channels and wherein the resistance of the dampener is controlled by a valve located in the channel. 
     The valve may be manually adjusted or may be electronically adjusted from a remote location. 
     Electronic adjustment of the valve may comprise linking the valve to a solenoid for control by the control means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an apparatus in accordance with a first embodiment of the present invention. 
         FIG. 2  is a top plan view of the apparatus of  FIG. 1 . 
         FIG. 3  is a top plan view of a second embodiment of an apparatus in accordance with the present invention. 
         FIG. 4  is a side plan view of an adaptor of the apparatus in  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a body of the apparatus in  FIG. 3 . 
         FIGS. 6A ,  6 B and  6 C and  6 D are schematic cross-sectional views of hydraulic dampeners of the apparatus in  FIGS. 1 and 3 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     An apparatus in accordance with a first embodiment of the present invention is illustrated in  FIG. 1 . 
     The apparatus comprises a draw bar  10 , a first means for hitching a draw arm of a trailer to the draw bar  10  in the form of the conventional tow ball  4  and a second means for hitching the draw bar to the vehicle in the form of a locking pin (not shown). The apparatus further comprises a body in the form of a turntable  3  and a dampening means in the form of a shock absorber  11 . 
     The draw bar  10  is formed of tubular steel in a square cross-section and in a dimension to slidably fit in a conventional sleeve hitch  7  for linking a draw bar to a vehicle. 
     It will be appreciated however that materials other than steel may be used to form the draw bar  10  provided the materials have sufficient strength for towing a trailer. Additionally, the draw bar  10  may have an alternative shape depending on the form of the first means and the second means for hitching the draw bar  10  to the vehicle and to the trailer. 
     The lock pin locks the draw bar  10  in the sleeve  7  attached to the vehicle. The tow ball  4  is located on an end of the draw bar  10  opposite to the end of the draw bar  10  that fits within the sleeve  7 . 
     The turntable  3  has a generally flat plate structure with an aperture through which a neck portion  4   a  of the tow ball extends. The turntable  3 , therefore, is able to rotate about the neck portion  4   a  of the tow ball  4 . The turntable  3  includes upstanding posts  5  with outwardly divergent ends to guide a tow ball coupler  15  ( FIG. 4 ) over the tow ball  4 . 
     The spacing of the posts  5  is adjustable to define a slot of variable width between the posts  5 . Adjustment of the spacing of the posts  5  enables the posts  5  to be brought into close proximity to respective sides of a draw arm  14  of a trailer ( FIG. 2 ) to reduce free play in movement of the arm  14  relative to the turntable  3 . Preferably, however, the posts  5  clamp the arm  14  to avoid all free play. Alternatively, a clamp may be substituted for the posts  5  to capture the arm  14 . 
     The slot defined between the posts  5  is bound on three sides by the posts  5  and the turntable  3  and is open on the remaining side to receive the arm  14  of a trailer. The open space allows unrestricted movement of the arm through a vertical angular displacement relative to the turntable  3  and the draw bar  10 . Accordingly, vertical angular movement of the trailer relative to the vehicle is unrestricted so the apparatus can remain linked to the trailer and vehicle for use with vertically undulating terrain, such as over speed humps, and when transitioning between terrain of different inclinations, such as inclined driveways and boat ramps. 
     The turntable includes an upstanding lug  2  to which is attached a first end of the shock absorber  11 . The lug is positioned such that the longitudinal axis of the dampener is slightly ahead of the tow ball  4  on the vehicle side of the draw bar  10 . 
     The draw bar includes a side bar in the form of a beam  6  that extends generally perpendicularly from the draw bar  10  and includes an upstanding lug  1  near the free end of the beam  6 . A second end of the shock absorber  11  is fixed to the lug  1 . 
     The angular disposition of the shock absorber  11  relative to the draw bar  10  is affected by two competing factors. Advantageously, the shock absorber  11  is as close to perpendicular to the draw bar  10  as possible to maximize the draught of the shock absorber  11  and, therefore, the resistive effect of the shock absorber  11 . Accordingly, when the amplitude of the sways is small, such as when the trailer starts swaying, the resistive effect of the shock absorber  11  has a greater impact. This factor, however, must be balanced with the need to position the lug  2  and the shock absorber  11  so interference with the turning capabilities of the vehicle relative to the trailer are not adversely affected. Preferably, the shock absorber  11  is disposed at an angle of 30-80° horizontally relative to the draw bar  10 . 
     The shock absorber  11  comprises a hydraulic dampener of any conventional form or may comprise any one of shock absorbers  11   a  to  11   d  ( FIGS. 6A to 6D ). 
     A trailer is hitched to the apparatus by locating the ball coupler  15  of the trailer arm  13  on the tow ball  4  ( FIG. 2 ). The posts  5  are spaced sufficiently to receive the trailer arm  14  between with little free play such that horizontal movement of the trailer relative to the vehicle, arising from the vehicle navigating a bend in the road or a trailer swaying behind the vehicle, causes the trailer arm  14  to contact one of the posts  15  and rotate the turntable  3 . Rotation of the turntable  3  changes the distance between lugs  1  and  2  and thereby causes the shock absorber  11  to extend or contract. The shock absorber  11  resists movement of the turntable  3 . In turn, movement of the trailer arm and trailer relative to the vehicle about a horizontal angle is, therefore, resisted. 
     Depending upon the size of the trailer and the weight carried in the trailer, the apparatus may include a second arm  6  and second shock absorber  12  (dashed lines in  FIG. 2 ) to increase the resistance forces on the turntable  3  and therefore reduce horizontal angular movement of the trailer arm  14  and the trailer relative to the vehicle. 
     Incorporation of the shock absorber  11  into the apparatus provides, in essence, a self-contained apparatus that can be simply fitted between a trailer and a vehicle. Significant modifications to the trailer or vehicle in order to fit the apparatus are avoided. Additionally, the tow ball  4  and locking pin enable the apparatus to be fitted to conventional hitching arrangements of trailers and vehicles. 
     As the apparatus is self-contained, there is no need to detach the shock absorber from a vehicle or trailer in order to decouple the trailer from the vehicle. The consequence of this is that there is no need to adjust the extension of the shock absorber to fit the distance between connection points of the shock absorber to a vehicle and/or a trailer. 
     Instead of adjusting the shock absorber  11  in order to obtain the requisite spacing between connection points of the shock absorber to the vehicle and/or trailer, it is necessary to ensure that the trailer and vehicle are returned to the angular displacement that they were at when the trailer was unhitched from the vehicle. The apparatus avoids this problem because the shock absorber  11  is not decoupled from the vehicle and/or trailer. 
     A second embodiment of the invention is illustrated in  FIG. 3 . This embodiment is the same all respects to the first embodiment described above, save for the turntable  3 . 
     The turntable does not include posts  5 , but instead has an upstanding seat  16  comprising three walls in a U-configuration. 
     In order for the trailer arm to interact with the seat  16 , and adaptor in the form of a housing  13  is fitted over the ball coupler  15  ( FIG. 4 ). When the trailer arm  14  is hitched to the apparatus with the ball coupler  15  located on the tow ball  4 , the housing  13  fits closely in the seats  16  so that horizontal angular movement of the trailer arm  14  is translated to the seat  16  and in turn, through the turntable to the shock absorber  11 . 
     The housing  15  has a generally rectangular shape that is complimentary to the U-configuration of the seat  16  to ensure the interaction between the trailer arm  14  and seat  16 . The housing  15  is applied to the arm  14  by a friction-fit or by a snap-fit and comprise any suitable rigid material for linking movement of the trailer to the shock absorber  11 . 
     One form of shock absorber  11 A suitable for use in the first and second embodiments described above is illustrated in  FIG. 6A . 
     The shock absorber  11 A comprises a generally cylindrical fluid-tight body  20  with an aperture through which a piston  30  extends. The piston  30  comprises a ram  32  and a head  34  that defines two chambers within the body. The head  34  includes apertures  36  through which fluid can flow between the two chambers upon movement of the ram  30  relative to the body  20 . 
     While the shock absorber  11 A is suitable for the invention, the resistance provided by the shock absorber  11 A is constant, i.e. a given applied force is always met with the same resistance force. Accordingly, the resistance experience by a trailer is the same at low speeds and at high speeds of a vehicle for a given sway movement. If the resistance is too low, swaying of the trailer at high speeds will not be appropriately dampened. However, if the resistance is too high, removability of the trailer is reduced at low vehicular speeds, such as when navigating sharp bends in roads or parking the vehicle and trailer. Additionally, shock absorber  11 A cannot be adjusted to account for differences in the size and weight of a trailer which, in part, dictate the level of resistance required. 
     Shock absorber  11 B ( FIG. 6B ) enables the resistance to be adjusted. The shock absorber includes a body  20 , a piston  40  with a ram  42  and a head  48 . The ram  42  includes a metering pin  44  that is threaded for interacting with a thread on the ram  42 . Orifices  46  in the ram  42  are disposed adjacent the head  48  and communicate with a tapered aperture  45 . The flow rate of fluid through the tapered aperture  45  and orifices  46  is controlled by adjusting the position of the metering pin  44  within the tapered aperture  45 . The position of the pin is adjusted by rotating the pin such that the threads on the pin  44  and the ram  42  cause the pin  44  to extend or to retract in the tapered aperture  45 . 
     An alternative shock absorber  11 C that enables adjustment of resistance provided by the shock absorber is illustrated in  FIG. 6C . The shock absorber  11 C comprises a body  20  and a piston  50  with a ram  52  and a head  54 . The shock absorber  11 C further include a wall  56  that defines a fluid flow channel  58  such that upon movement of the piston  50  fluid is caused to flow between chambers  59  and  59 A through the channel  58 . 
     Fluid flow through the channel  58  is controlled by a valve  55  that is adjustable. The valve  55  is manually adjustable to increase fluid flow and thereby decrease resistance of the shock absorber  11 C or to decrease fluid flow and thereby increase the resistance of the shock absorber  11 C. 
     A further alternative form of shock absorber  11 D is illustrated in  FIG. 6D . The shock absorber  11 D comprises a body  20  and piston  60  with a ram  62  and a head  64 . The shock absorber  11 D further includes a wall  66  that defines a fluid flow channel  68 . Fluid flows through the channel when the shock absorber  11 D is extended or contracted. The fluid flow through the channel  68  is controlled by a valve  65 . The valve  65  is, in turn, controlled by a solenoid  67  that is actuated by a control module  63 . The control module  63  enables the solenoid  67 , and hence, the resistance of the shock absorber  11 D to be controlled electronically. Such electronic control may be remote from the shock absorber  11 D, such as in the cabin of the vehicle. Accordingly, the shock absorber  11 D may be controlled by a user in response to the size and weight of the trailer and the speed of the vehicle. 
     Alternatively, the control module  63  may be linked to a computer of the vehicle for control according to a range of parameters, including speed of the vehicle and the condition of the road. 
     For example, the control module  63  may be operated to control the valve  65  to prevent all fluid flow through the channel  68 , thereby locking the trailer in a selected position behind the vehicle. For example, this enables greater control at high speeds when the effects of sway are more prevalent and more serious and, assist with controlling the direction of the trailer when reversing. 
     The position of the piston in the shock absorber  11 , and thus the angle of the towed trailer, can be monitored by sensors placed either on the shock absorber  11  or turntable  3 . Indication of the position of the trailer assists in preventing trailer sway and also provides an indication to the driver when the trailer is being reversed by the vehicle of where the trailer is relative to the vehicle. 
     Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other country. 
     Many modifications may be made to the preferred embodiment of the present invention as described above without departing from the spirit and scope of the present invention.