Abstract:
A trailer has a frame having frame-members configured to support a container, at least a pair of traction devices rotatably mounted on the frame, and a tongue configured to be mounted on a transportation device or an implement being towed by a transportation device. The frame-members may have a three-point mount configured to support a container. The container may be configured to be interchangeable with another container. The container may be an element of a seeding apparatus, the seeding apparatus mountable on the frame-members of the frame. The trailer may have a steering mechanism for the traction devices, and may be convertible between steerable and non-steerable modes. The steering mechanism may be guidance controlled. A transverse distance between the traction devices may be adjustable and/or height of the frame in relation to the ground may be adjustable. The trailer provides greater flexibility of operation under a greater variety of conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Patent Application 62/203,160 filed Aug. 10, 2015, the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD 
       [0002]    This application relates to trailers, in particular to trailers for towing behind an agricultural implement. 
       BACKGROUND 
       [0003]    Agricultural carts for transporting containers containing solid or liquid inputs are known in the industry. Such carts are typically designed for one type of application, lacking flexibility in the type of input to be carried or the conditions under which the input is to be distributed in a field. Carts with greater flexibility of operation are generally more desirable reducing the number of implements a farmer needs to purchase and reducing inventory that dealers may need to carry at any given time. 
       SUMMARY 
       [0004]    There is provided a trailer comprising: a frame having frame-members configured to support a container; at least a pair of traction devices rotatably mounted on the frame; and, a tongue configured to be mounted on a transportation device or an implement being towed by a transportation device. 
         [0005]    In one aspect, the frame-members may comprise a three-point mount configured to support a container. 
         [0006]    In one aspect, the container may be configured to be interchangeable with another container. 
         [0007]    In one aspect, the container may be an element of a seeding apparatus, the seeding apparatus mountable on the frame-members of the frame. 
         [0008]    In one aspect, the trailer may comprise a steering mechanism for the traction devices. 
         [0009]    In one aspect, the steering mechanism may be designed for row cropping applications. 
         [0010]    In one aspect, the trailer may comprise a guidance control for a steering mechanism. 
         [0011]    In one aspect, the trailer may be convertible between a steerable trailer and a non-steerable trailer. 
         [0012]    In one aspect, a transverse distance between the traction devices in the pair of traction devices may be adjustable. 
         [0013]    In one aspect, a height of the frame in relation to the ground may be adjustable. 
         [0014]    The trailer comprises a frame. The frame has a longitudinal axis in the direction of motion of the trailer as it is being towed across the ground. The longitudinal axis runs from front to rear (or rear to front) of the frame. The frame has a transverse axis that is perpendicular to the longitudinal axis and runs left to right (or right to left) of the frame. The frame may have a plurality of connected frame-members, for example longitudinally and/or transversely spaced-apart frame-members, on which the traction devices, tongue, container and/or other elements may be mounted. The frame-members may comprise any suitably strong and/or rigid material (e.g. steel, aluminum alloy) in the form of elongated structures (e.g. tubes or bars). In one embodiment, frame-members may comprise rectangular tubes. 
         [0015]    The trailer further comprises a tongue. The tongue may extend longitudinally forward of the frame and is configured to be mounted on a transportation device (e.g. a vehicle, for example a tractor) or an implement being towed by a transportation device. Such implements may include, for example, another trailer or any type of tillage or row cropping apparatus (e.g. a planter, a strip till bar, a fertilizer bar, etc.) The tongue may be a separate elongated structure rigidly mounted on the frame (for example by welding, bolting or the like) an integral extension of one or more of the frame-elements, or a combination thereof. The tongue comprises an attachment structure, preferably proximate or at a longitudinally forward end of the tongue, configured to mount the tongue on a corresponding attachment structure at a mounting point on the transportation device or implement. The attachment structure preferably provides for some degrees of freedom of motion at the mounting point. In a preferred embodiment, the tongue may comprise one or more ball hitches on pivoting knuckles. 
         [0016]    Containers may be supported on the frame-members. The containers may be mounted at one or more points on the frame-members, for example two to five mounting points. The frame-members preferably comprise three mounting points, providing a good balance between secure mounting and easy interchangeability of containers. The mounts on the frame-members may comprise apertures through which pins on the containers may be fitted. The pins may be secured in the apertures by cotter pins, or in the case where the pins are bolts they may be secured in the apertures with nuts. Other types of mounts and securement devices may be utilized, for example pin and pocket, ridge and groove mounts and the like secured with clamps, spot welds and the like. Mounting containers on the frame may be aided by mounting guides to facilitate moving the container to the correct location on the frame for mounting. The mounts may further comprise weigh scales (e.g. load cells), preferably in electronic communication with a remote display device, computer or the like, to provide an indication of the weight of the container on the frame, which facilitates understanding the levels of product in the container at any given time. The frame-members may also comprise multiple sets of mounts for mounting more than one container. 
         [0017]    Containers are preferably interchangeable on the frame to provide for a modular system. The containers may be directly and removably mounted on the frame or the containers may be mounted in a separate container retaining structure and the container retaining structure removably mounted on the frame. Container retaining structures may comprise, for example, interconnected struts configured to receive and secure the container within a network of the struts. It is an advantage of the present trailer that the containers may be a wide variety of types of containers, especially for agricultural product, and still be interchangeable on the same trailer. The containers may be for solid or liquid product, for example, bins, hoppers, boxes, tanks and the like. The product may be fertilizer, seed, anhydrous ammonia, pesticide, herbicide, lime or the like. The containers may be pressurized or non-pressurized. The containers may be accompanied by metering devices for metering product from the container into spreaders. Spreaders associated with the container may comprise liquid or solid product spreaders, for example liquid spray mechanisms, spinners for particulate materials or air delivery mechanisms (e.g. air lines and/or booms and the like) for particulate materials. In one embodiment, the container is a seed bin for cover seeding in association with other parts of a seeding apparatus, for example an air seeder. The trailer is particularly useful as an agricultural applicator cart. 
         [0018]    The trailer further comprises at least a pair of traction devices rotatably mounted on the frame to permit movement of the trailer on the ground. The traction devices may comprise wheels, belts, tracks or the like and any combination thereof. Wheels are preferred. The traction devices are preferably located on either side of the frame. The traction devices may be mounted on one or more axles, the one or more axles mounted on the frame. One or more traction devices may be mounted on one axle on one side of the trailer. One traction device per axle per side of the trailer is common, but using two or more traction devices per axle per side may lower soil compaction and/or increase carrying capacity of the trailer. Preferably, the traction devices are mounted on stub axles and opposed stub axles mounted on an axle bar connecting the stub axles. The stub axles are preferably circular in cross-section so that the traction devices can readily rotate. The stub axles may comprise hubs onto which the traction devices, especially wheels, may be removably mounted. The axle bars may be of any cross-sectional shape and may be transversely in line or out of line with the stub axles when the traction devices are straight. The axle bars may be formed of one or more of the frame-members of the frame. The stub axles are preferably mounted on the axle bar such that the stub axles, traction devices and any mounting assembly for mounting the stub axles and traction devices on the axle bar may rotate thereby causing the trailer to turn. Such rotational motion assists with a steering mechanism as described below. Where the trailer comprises just two opposed traction devices, the container mounting points are preferably arranged on the frame-members so that the container&#39;s center of gravity is over the axle bar. 
         [0019]    The trailer may be non-steerable or may comprise a steering mechanism for the traction devices. In one embodiment, a steering mechanism ensures that the traction devices stay between crop rows and track properly behind the transportation. Keeping the traction devices between crop rows is particularly important in row cropping applications. The steering mechanism may be entirely mechanical, or may further comprise hydraulic or electric actuators. In one embodiment, the steering mechanism is entirely mechanical comprising mechanical linkages. 
         [0020]    Any suitable steering mechanism may be employed. For example, the traction devices on each side of the trailer may be steered by separate 4-bar linkage assemblies, where each 4-bar assembly comprises four linkages pivotally connected in a quadrilateral, and each 4-bar assembly is controlled by separate longitudinal control rods extending forward and connected to the transportation device or implement. 
         [0021]    However, the steering mechanism preferably comprises a 5-bar linkage assembly in which five linkage arms are connected at pivot points so that the linkages may move relative to each other. In one embodiment, three of the five linkage arms are length adjustable. In one embodiment, two of the linkages comprise mounting assemblies for pivotally mounting the stub axles (and therefore the traction devices) on the axle bar. The stub axles on the mounting assemblies are able to pivot on the axle bar thereby turning the traction devices. One of the linkages comprises the axle bar, which is rigidly mounted on the frame or is a part of the frame. The other two linkages comprise tie rods, each tie rod pivotally mounted on respective mounting assemblies to permit pivoting of the mounting assemblies at the connection between the tie rods and the mounting assemblies. The tie rods may be pivotally connected at a pivot plate to form the 5-bar steering mechanism. The pivot plate may be pivotally connected to the transportation or an implement by one or more control rods, the one or more control rods pivotally connected to the pivot plate proximate first ends of the control rods and pivotally connected to the transportation or implement proximate second ends of the control rods. In such an arrangement, turning of the transportation or implement causes longitudinal movement of the one or more control rods, causing pivoting of the pivot plate. Pivoting of the pivot plate causes the tie rods to translate (e.g. by pushing one tie rod and pulling the other tie rod), causing the stub axles to pivot thereby turning the traction devices of the trailer in response to the turning of the transportation or implement. 
         [0022]    The trailer may also be readily convertible between steerable and non-steerable modes by disabling the steering mechanism. In one embodiment, the 5-bar steering mechanism particularly facilitates the conversion by simply locking the pivot plate to prevent the pivot plate form turning. Locking the pivot plate may be accomplished, for example, with a pin-in-hole arrangement, a clamp arrangement or any other suitable arrangement. Disconnecting the one or more control rods from the pivot plate and/or the transportation or implement would further assist in the conversion from steerable to non-steerable mode. Where more than one control rod is used, disconnecting all of the control rods may be required. Unlocking the pivot plate and reconnecting the one or more control rods would return the trailer to steerable mode. 
         [0023]    The trailer may also comprise guidance control of steering. Guidance control of steering may be accomplished in any suitable way, including methods known in the art. In one embodiment, a global navigation satellite system (GNSS), especially with real time kinematic (RTK) enhanced function, may be used. In one particular embodiment, a linear distance may be determined between a fixed point on the pivoting tongue of the trailer and a fixed point on the attachment structure of the transportation device or implement to which the tongue is attached. The linear distance may be correlated to the position of a global navigation satellite system (GNSS) receiver (e.g. a global positioning system (GPS) receiver) relative to a pre-mapped line of travel pre-programmed into both an auto-steer functionality of the transportation device and a secondary guidance system for the trailer itself. A controlled actuator (e.g. a servo-controlled hydraulic cylinder) may override pivoting of the tongue to return the trailer to tracking along the pre-mapped line of travel. The controlled actuator may be activated by a guidance system controller. To implement guidance control in the steering mechanism, actuators (e.g. hydraulic cylinders and/or electric actuators) may be used instead of linkage arms in the steering mechanism and the action of the actuators controlled according to GNSS input to steer the trailer on the pre-mapped line of travel. Alternatively, mechanical linkage arms in the steering mechanism may be equipped with in-line linkage compensating actuators (e.g. electric linear actuators and/or hydraulic cylinders), which may be activated to partially or completely move the traction devices in response to GNSS input or, for side hill tracking, provide a correction amount to keep the trailer on the pre-mapped line of travel. 
         [0024]    In a particularly preferred embodiment, transverse distance between the traction devices (e.g. wheel-to-wheel distance) may be adjustable in order to accommodate differing axle lengths of the transportation or implement, or to more generally ensure that the traction devices of the trailer ride between crop rows. Adjustment of the transverse distance may be accomplished mechanically or by using hydraulic or electric actuator arrangements. In one embodiment, an axle may comprise one or more disconnectable connection points into and out of which one or more spacers may be inserted or removed to lengthen or shorten the axle. Where the trailer comprises a steering mechanism, certain connections in the steering mechanism may need to be lengthened or shortened to accommodate the change in transverse distance. Where the steering mechanism comprises actuators, the stroke length can be readily adjusted to accommodate the change in transverse distance, whereas with mechanical elements of the steering mechanism, length adjustable rods may be used to accommodate the change in transverse distance. Further, pivoting points in the steering system, for example the pivot plate in the 5-bar mechanism described above, may need to translate longitudinally to accommodate the change in transverse distance. 
         [0025]    It is a particular advantage of a 5-bar steering mechanism that the tie rods may be pivotally connected to a common pivot plate and that arrangements for adjusting the transverse distance may be located between the pivot point of each tie rod on the pivot plate and the pivot point of each tie rod on the stub axle mounting assemblies. Therefore, the lengths of the tie rods may be changed to accommodate the change in transverse distance without affecting the ability of the trailer wheels to correctly track behind traction devices of the transportation or implement during a turn. 
         [0026]    In another particularly preferred embodiment, height of the trailer in relation to the ground may be adjustable. Height adjustment may be conveniently accomplished by mounting one or more axles, and therefore the traction devices, at different vertically-spaced locations on the frame or by using hydraulic or electric actuators (e.g. hydraulic cylinders or liner actuators) to move an axle vertically. In one embodiment, stub axles to which the traction devices are mounted may be configured for mounting at different vertically-spaced locations on mounting plates proximate each end of a transverse axle bar rigidly mounted on the frame. As with any changes in the transverse distance, where the trailer comprises a steering mechanism, certain connections in the steering mechanism may need to be lengthened or shortened to accommodate the change in height of the trailer in relation to the ground. 
         [0027]    Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
           [0029]      FIG. 1A  depicts a plan view of a trailer being towed behind an agricultural implement. 
           [0030]      FIG. 1B  depicts a side view of the trailer depicted in  FIG. 1A . 
           [0031]      FIG. 2  depicts a side view of the trailer depicted in  FIG. 1A  with a seed bin mounted on the trailer. 
           [0032]      FIG. 3  depicts a side view of the trailer depicted in  FIG. 1A  with a liquid product tank mounted on the trailer. 
           [0033]      FIG. 4  depicts a side view of the trailer depicted in  FIG. 1A  with a spinner spreader box mounted on the trailer. 
           [0034]      FIG. 5A  depicts a side view of the trailer depicted in  FIG. 1A  with a granular fertilizer bin mounted on the trailer. 
           [0035]      FIG. 5B  depicts is a rear perspective view of the trailer depicted in  FIG. 5A  further showing an air boom spreader for granular fertilizer in association with the granular fertilizer bin. 
           [0036]      FIG. 6A  depicts a plan view of a frame of a trailer. 
           [0037]      FIG. 6B  depicts a magnified view of a region A of the frame depicted in  FIG. 6A . 
           [0038]      FIG. 7  depicts a plan view illustrating how a tongue of the trailer depicted in  FIG. 1A  is hitched to an implement. 
           [0039]      FIG. 8A  depicts a rear isometric view of a trailer having a pair of opposed wheels separated by a shorter transverse distance. 
           [0040]      FIG. 8B  depicts a rear isometric view of the trailer of  FIG. 8A  where the opposed wheels are separated by a longer transverse distance. 
           [0041]      FIG. 9A  depicts a magnified view of one embodiment for extending transverse distance between opposed wheels of the trailer of  FIG. 8A  to the arrangement depicted in  FIG. 8B . 
           [0042]      FIG. 9B  depicts a reverse view of the embodiment depicted in  FIG. 9A  including a wheel mounted on a hub. 
           [0043]      FIG. 10A  depicts a rear isometric view of a trailer having one wheel removed to illustrate where a height of the trailer frame in relation to the ground may be adjustable at an axle. 
           [0044]      FIG. 10B  depicts a magnified orthogonal view of a region B of the axle illustrated in  FIG. 10A . 
           [0045]      FIG. 11A  depicts a side view of the trailer of  FIG. 10A  showing three positions to which the height of the frame may be adjusted in relation to the ground. 
           [0046]      FIG. 11B  depicts a rear view of the trailer of  FIG. 10A  showing three positions to which the height of the frame may be adjusted in relation to the ground. 
           [0047]      FIG. 12A  depicts a plan view of a trailer having one embodiment of a steering mechanism for a pair of opposed wheels on the trailer. 
           [0048]      FIG. 12B  depicts the trailer of  FIG. 12A  where transverse distance between the opposed wheels has been increased. 
           [0049]      FIG. 13A  depicts a plan view of the trailer of  FIG. 12A  in a ten degree turn. 
           [0050]      FIG. 13B  depicts a plan view of the trailer of  FIG. 12A  in a twenty degree turn. 
           [0051]      FIG. 13C  depicts a plan view of the trailer of  FIG. 12A  in a thirty degree turn. 
           [0052]      FIG. 14A  depicts a plan view of an overlay of the trailer of  FIG. 12A  when the trailer is tracking straight (solid lines) in comparison to when the trailer is turning (dashed lines). 
           [0053]      FIG. 14B  depicts a plan view of an overlay of the trailer of  FIG. 12B  when the trailer is tracking straight (solid lines) in comparison to when the trailer is turning (dashed lines). 
           [0054]      FIG. 15A  depicts a plan view of the trailer of  FIG. 12A  hitched to transportation while in a turn showing how the wheels of the trailer track with respect to the wheels of the transportation. 
           [0055]      FIG. 15B  depicts a plan view of the trailer of  FIG. 12B  hitched to transportation having a wider wheel base while in a turn showing how the wheels of the trailer track with respect to the wheels of the transportation. 
           [0056]      FIG. 16A  depicts a plan view of a trailer steerable with only one control rod. 
           [0057]      FIG. 16B  depicts a plan view of a trailer steerable with only one control rod and where transverse distance between the opposed wheels has been increased. 
       
    
    
     DETAILED DESCRIPTION 
       [0058]    Referring to  FIG. 1A  and  FIG. 1B , a trailer  100  is depicted being towed behind an agricultural implement  5 . The agricultural implement  5  is in turn being towed by a vehicle (not shown), for example a tractor. The trailer  100  comprises a frame  101  comprising longitudinally oriented rectangular tubes  102  and a transversely oriented rectangular tube  103  welded together to form a supporting structure for a container. The frame  101  further comprises an axle bar  105  welded to the longitudinally oriented rectangular tubes  102 , the axle bar  105  also comprising a rectangular tube and providing additional structural support for the frame  101 . A pair of opposed wheels  106  are rotatably mounted on the axle bar  105 . A tongue  104  is formed from a pair of converging longitudinally oriented rectangular tubes  107  meeting at hitch  108 . Each of the converging longitudinally oriented rectangular tubes  107  are rigidly connected (e.g. by welding, bolting or the like) to respective longitudinally oriented rectangular tubes  102  by angled braces  109 . Hitch  108  comprises a pair of ball hitch receivers, one at the end of each tube  107 , fitted with knurled knuckles to permit relative movement of the tongue  104  to the implement  5 . 
         [0059]    The trailer  100  may be interchangeably equipped with a variety of containers as shown in  FIG. 2  to  FIG. 5 .  FIG. 2  shows the trailer  100  outfitted with a seed bin  110 . The seed bin  110  is secured in a superstructure  111  designed to contain the seed bin  110  and to permit mounting of the superstructure  111  on the frame  101  of the trailer  100 . The seed bin  110  is accompanied by an air blower  112 , which is part of an air delivery system for delivering seed to seed applicators located on the agricultural implement  5 . Air lines which deliver the seed are not shown.  FIG. 3  shows the trailer  100  outfitted with a liquid tank  120 . The liquid tank  120  is contained in a superstructure  121  configured to be mounted on the frame  101  of the trailer  100 . Liquid lines in fluid communication with the liquid in the liquid tank  120  are not shown.  FIG. 4  shows the trailer  100  outfitted with a spinner spreader box  130 . The spinner spreader box  130  is mounted on the frame  101  and tongue  104  of the trailer  100 . The spinner spreader box  130  is associated with a spinner spreader  132 , which delivers granular product contained in the box  130  to the environment.  FIG. 5A  and  FIG. 5B  show the trailer  100  outfitted with a granular fertilizer bin  140 . The granular fertilizer bin  140  is contained on a superstructure  141  configured to be mounted on the frame  101  of the trailer  100 . As seen in  FIG. 5B , air booms  142  associated with the granular fertilizer bin  140  may be configured to deliver granular fertilizer from the bin  140  to the environment. 
         [0060]      FIG. 6A  and  FIG. 6B  show the frame  101  of the trailer to further illustrate a three-point mount for supporting containers on the trailer and facilitating the interchange of containers. Each of the longitudinally oriented rectangular tubes  102  and the transversely oriented rectangular tube  103  of the frame  101  comprises a mounting tab  145  through which mounting apertures  146  are formed (only one of two mounting apertures  146  is labeled on each mounting tab  145 ). The mounting tabs  145  are fixedly secured to the rectangular tubes  102 ,  103 , for example by welding, and the mounting apertures  146  are configured to receive downwardly depending pins or bolts attached to the container or the superstructure for the container. The mounting tabs  145  on the longitudinally oriented rectangular tubes  102  may be located at or proximate to the rear end of the tubes  102 , while the mounting tab  145  on the transversely oriented rectangular tube  103  may be conveniently located proximate a transversely central point to provide an approximately isosceles triangular three-point mount for the containers. The locations of the mounting apertures  146  and the pins or bolts on the container or superstructure are preferably selected so that the center of gravity of the container is over the axle bar  105 . Further, having more than one mounting aperture  146  per mounting tab  145  simplifies and provides flexibility in mounting the container on the frame  101 . While two mounting apertures  146  are shown, more than two apertures in any suitable pattern on the mounting tab  145  may be provided. The container may be mounted on the trailer with the aid of a mounting rack or a forklift, and guide structures may be associated with the mounting apertures  146  to guide the pins or bolts toward the mounting apertures  146  as the container is being mounted on the frame  101 . The pins or bolts may be secured in the mounting apertures  146  by any suitable device, for example cotter pins, nuts and the like. 
         [0061]      FIG. 7  provides a magnified view of how the tongue  104  of the trailer is hitched to the implement  5 . The hitch  108  at the front ends of the converging longitudinally oriented rectangular tubes  107  comprises to ball receivers for receiving two hitch balls protruding upwardly form hitch plate  6  mounted on hitch tube  7 , where hitch tube  7  is removably mounted on two hitch struts  8  using brackets, which is in turn removably mounted on a rear bar  9  of implement  5  also using brackets. As discussed in more detail below, if the trailer in one embodiment comprises a 5-bar steering mechanism, control rods  451  of the steering mechanism may be pivotally mounted at pivot mount  10  on hitch plate  6  so that turning of the implement  5  will either cause the control rods  451  to translate longitudinally rearward or forward depending on whether the implement is turning left or right. 
         [0062]    As shown in  FIG. 8A  and  FIG. 8B , in one embodiment, transverse distance between opposed wheels  206   a ,  206   b  of a trailer  200  may be adjustable. In  FIG. 8A  where the wheels  206   a ,  206   b  are separated by a shorter transverse distance, opposed stub axles  211   a ,  211   b  are removably mounted directly on opposed ends of a transverse axle bar  205 . To increase the transverse distance between the wheels  206   a ,  206   b , the stub axles  211   a ,  211   b  may be dismounted from the axle bar  205  and axle inserts  212   a ,  212   b  may be inserted between respective stub axles  211   a ,  211   b  and the axle bar  205 , as depicted in  FIG. 8B . The axle inserts  212   a ,  212   b  may have the same length to extend the distance from the axle bar  205  to the stub axles  211   a ,  211   b  by the same amount, but in some applications it may be desirable for the axle inserts  212   a ,  212   b  to have different lengths. In some applications it may be desirable to insert an axle insert on one side of the trailer but not on the other side. Axle inserts of different lengths may be provided to be able to adjust the transverse distance between the opposed wheels by different amounts. In some embodiments, the axle inserts may be length adjustable actuators (e.g. hydraulic cylinders or linear actuators) so that the transverse distance between opposed wheels may be finely and/or independently controlled without the need to dismount the stub axles from the axle bar. 
         [0063]      FIG. 9A  and  FIG. 9B  show magnified views of one embodiment of an extended axle and wheel arrangement on one side of the trailer  200 . The other side of the trailer  200  may comprise a similar arrangement. In the extended arrangement depicted in  FIG. 9A  and  FIG. 9B , the axle bar  205  is rigidly connected to the stub axle  211   a  though the axle insert  212   a . An axle bar mounting plate  221   a  may be rigidly attached to an end of the axle bar  205 , for example by welding or being formed integrally with the axle bar  205 , and the axle bar mounting plate  221   a  may be removably mounted to a first insert mounting plate  222   a , for example by bolting. The first insert mounting plate  222   a  may be rigidly attached to a first end of the axle insert  212   a , for example by welding or being formed integrally with the axle insert  212   a . A second end of the axle insert  212   a  may comprise a second insert mounting plate  223   a , which may also be rigidly attached the axle insert  212   a . The second insert mounting plate  223   a  may be removably attached, for example by bolting, to a stub axle mounting plate  224   a , which may be part of a stub axle assembly  225   a . In this embodiment, to change the distance between the wheels, the axle insert  212   a  may be removed by unbolting the stub axle mounting plate  224   a  from the second insert mounting plate  223   a  and then unbolting the first insert mounting plate  222   a  from the axle bar mounting plate  221   a . The stub axle mounting plate  224   a  may then be bolted directly to the axle bar mounting plate  221   a , or an axle insert of different length may be bolted between the axle bar mounting plate  221   a  and the stub axle mounting plate  224   a.    
         [0064]    In addition to the stub axle mounting plate  224   a , stub axle assembly  225   a  may comprise the stub axle  211   a  housed and secured in axle collar  226   a  by a bolt  227   a . The axle collar  226   a  may be supported in apertures in collar support brackets  228   a  and the bolt  227   a  may further serve to prevent the axle collar  226   a  from slipping out of the collar support brackets  228   a . The collar support brackets  228   a  may be rigidly fixed to the stub axle assembly  225   a , or in the case where the trailer  200  comprises a steering mechanism, the collar support brackets  228   a  may be mounted on a rotatable spindle  229   a  rotatably mounted on the stub axle assembly  225   a . The rotatable spindle  229   a  may be connected to the steering mechanism to permit turning the wheel  206   a , for example by connecting a tie rod to rotatable spindle  229   a . The wheel  206   a  may be removably mounted on a wheel hub  231   a , which may be mounted on the stub axle  211   a  in any usual way, preferably with the use of bearings in the wheel hub  231   a  to permit easy rotation of the wheel hub  231   a  on the stub axle  211   a.    
         [0065]      FIG. 10A ,  FIG. 10B ,  FIG. 11A  and  FIG. 11B  illustrates one embodiment of a trailer  300  in which a height of a frame  301  above the ground may be adjusted. Adjustment of the height in this embodiment may be accomplished by changing the relative heights of stub axles  311   a ,  311   b  to an axle bar  305  on the trailer  300 . While the stub axles  311   a ,  311   b  and wheels  306  remain at the same height, the axle bar  305  and the frame  301  of which the axle bar  305  is a part may be raised or lowered in relation to the stub axles  311   a ,  311   b . Details of how height adjustment in this embodiment may be accomplished are best illustrated in  FIG. 10B .  FIG. 10B  illustrates an axle arrangement on one side of the trailer  300 , but the other side of the trailer  300  may comprise a similar arrangement. 
         [0066]    With reference to  FIG. 10B , the stub axle  311   a  may be mounted in a stub axle assembly  325   a , and a wheel removably mounted on a wheel hub  331   a  rotatably mounted on the stub axle  311   a . The stub axle assembly  325   a  may further comprise a stub axle mounting plate  324   a , the stub axle mounting plate  324   a  comprising a plurality of bolt holes arranged in rows  331 ,  332 ,  333 . Three rows of bolt holes  331 ,  332 ,  333  are labeled and each row comprises three bolt holes. More or fewer rows of bolt holes and/or bolt holes per row may be used if desired, but at least two rows of bolt holes and two bolt holes per row are generally desirable. The stub axle mounting plate  324   a  may be mounted on the axle bar  305  at an axle bar mounting plate  321   a . The axle bar mounting plate  321   a  may also comprise a plurality of bolt holes arranged in rows  334 ,  335 ,  336 ,  337 ,  338 . Five rows of bolt holes  334 ,  335 ,  336 ,  337 ,  338  are labeled and each row comprises three bolt holes, although the rows of bolt holes  335 ,  336 ,  337  are not seen in  FIG. 10B  as they are hidden behind the stub axle mounting plate  324   a . More or fewer rows of bolt holes and/or bolt holes per row may be used if desired, but at least two bolt holes per row is generally desirable for security and the number of rows of bolt holes depends on the number of height settings that are desired. In  FIG. 10B , five rows of bolt holes  334 ,  335 ,  336 ,  337 ,  338  on the axle bar mounting plate  321   a  and three rows of bolt holes on the stub axle mounting plate  324   a  provides for at least three height settings, although another two height settings for a total of five height settings are possible if only two rows of bolt holes are used to secure the stub axle mounting plate  324   a  to the axle bar mounting plate  321   a .  FIG. 11A  and  FIG. 11B  illustrate three height settings achievable by the height adjustable axle arrangement depicted in  FIG. 10B . 
         [0067]    Securing of the two mounting plates  324   a ,  321   a  together may be accomplished by aligning the rows of bolt holes, inserting bolts through the aligned bolt holes and then using nuts to secure the bolts in the bolt holes.  FIG. 10B  illustrates an intermediate height setting where the rows of bolt holes  331 ,  332 ,  333  in the stub axle mounting plate  324   a  are aligned with the rows of bolt holes  335 ,  336 ,  337  in the axle bar mounting plate  321   a.    
         [0068]    The axle bar  305 , and thus the frame of the trailer, may be raised in relation to the ground by bolting the rows of bolt holes  331 ,  332 ,  333  in the stub axle mounting plate  324   a  to higher rows of bolt holes  336 ,  337 ,  338  in the axle bar mounting plate  321   a . The axle bar  305 , and thus the frame of the trailer, may be lowered in relation to the ground by bolting the rows of bolt holes  331 ,  332 ,  333  in the stub axle mounting plate  324   a  to lower rows of bolt holes  334 ,  335 ,  336  in the axle bar mounting plate  321   a . Spacing between the rows of bolt holes in the stub axle mounting plate and between the rows of bolt holes in the axle bar mounting plate, as well as spacing between the individual bolt holes in the rows may be regularized to ensure that the bolt holes between the two mounting plates readily align at all desired height settings. While this embodiment has been described with reference to bolts and bolt holes, other structures may be used to mount the axle bar  305  at different heights in relation to the stub axle  311   a , for example clamps, unthreaded pins, and the like. 
         [0069]    Comparing  FIG. 10B  to  FIG. 9A  it is evident that the same structures used for mounting the stub axles on the axle bar may facilitate both height adjustment ( FIG. 10B ) and adjustment of the transverse distance between the wheels ( FIG. 9A , ‘width’ adjustment). In a trailer that combines both height and width adjustment, the axle bar mounting plate and the first and second insert mounting plates may be the same in size and bolt hole configuration so that the stub axle mounting plate may be mounted at a desired height setting whether or not an axle insert is employed. Further, the stub axle assembly may be the same whether or not height and/or width adjustment is desired. Thus, the description related to the structure of the stub axle assembly in  FIG. 9A  is equally applicable to the stub axle assembly in  FIG. 10B . 
         [0070]    A trailer  400  having a steering mechanism  450  for the wheels  406   a ,  406   b  is depicted in  FIG. 12A ,  FIG. 12B ,  FIG. 13A ,  FIG. 13B ,  FIG. 13C ,  FIG. 14A ,  FIG. 14B ,  FIG. 15A ,  FIG. 15B ,  FIG. 16A  and  FIG. 16B . The trailer  400  comprises a frame  401 , a tongue  404  a hitch  408  at a forward end of the tongue  404  for hitching to an agricultural implement, an axle bar  405  which is part of the frame  401 , first and second stub axle assemblies  425   a ,  425   b  removably mounted on the axle bar  405  and comprising stub axles  411   a ,  411   b , and wheel hubs  431   a ,  431   b  rotatably mounted on the stub axles  411   a ,  411   b  and adapted to receive the wheels  406   a ,  406   b . The stub axle assemblies  425   a ,  425   b  are the same as the stub axle assembly described in connection with  FIG. 9A . In  FIG. 12B , transverse distance between the wheels is increased by the insertion of two axle inserts  412   a ,  412   b  between the axle bar  405  and respective stub axle assemblies  425   a ,  425   b  in a manner as previously described. 
         [0071]    The steering mechanism  450  may comprise five ‘bars’ linked into a pentagon at five locations and controlled by one or more control rods  451 . The one or more control rods  451  may extend longitudinally between a pivot plate  455  proximate a rear of the trailer  400  and the hitch plate  6  mounted on the hitch tube  7  of the transportation or implement towing the trailer  400 . The one or more control rods  451  may be pivotally mounted on the pivot plate  455  at one or more control rod pivot points  452 , and may be pivotally mounted on the hitch plate  6  at one or more pivot mounts  10 . 
         [0072]    The ‘bars’ of the 5-bar mechanism may comprise a first tie rod  456   a , a second tie rod  456   b , a first stub axle linkage  457   a , a second stub axle linkage  457   b  and a ‘bar’ comprising the axle bar  405 , stub axle assemblies  425   a ,  425   b  and any axle inserts  412   a ,  412   b  when taken all together may be considered a single rigid ‘bar’ in the 5-bar mechanism. The first tie rod  456   a  and second tie rod  456   b  are pivotally linked together at pivot points  454  on the pivot plate  455 . The first tie rod  456   a  is pivotally linked to the first stub axle linkage  457   a  at a pivot point  458   a . The second tie rod  456   b  is pivotally linked to the second stub axle linkage  457   b  at a pivot point  458   b . The first stub axle linkage  457   a  is pivotally connected to the first stub axle assembly  425   a  at a first spindle  429   a . The second stub axle linkage  457   b  is pivotally connected to the second stub axle assembly  425   b  at a second spindle  429   b.    
         [0073]    With reference to  FIG. 12A ,  FIG. 12B ,  FIG. 13A ,  FIG. 13B ,  FIG. 13C ,  FIG. 14A ,  FIG. 14B ,  FIG. 15A ,  FIG. 15B ,  FIG. 16A  and  FIG. 16B , operation of the steering mechanism  450  is as follows. When the implement is turning, hitch tube  7  on the implement acquires a non-orthogonal angle with the longitudinal axis of the trailer  400  causing the one or more control rods  451  to translate longitudinally. Longitudinal translation of the one or more control rods  451  is towards the rear of the trailer  400  for control rods  451  disposed to an inside of the turn with respect to a central longitudinal axis of the trailer, and is towards the front of the trailer  400  for control rods  451  disposed to an outside of the turn with respect to a central longitudinal axis of the trailer  400 . Translation of the one or more control rods  451  causes the pivot plate  455  to pivot about a vertical axis through the pivot plate  455 . Pivoting of the pivot plate  455  causes the tie rods  456   a ,  456   b  to translate transversely and somewhat longitudinally while pivoting about the pivot points  454  on the pivot plate  455 . Transverse translation of the tie rods  456   a ,  456   b  causes the stub axle linkages  457   a ,  457   b  to translate arcuately about vertical axes though spindles  429   a ,  429   b  thereby rotating the spindles  429   a ,  429   b . As described in connection with  FIG. 9A , the spindles  429   a ,  429   b  are ultimately connected to the stub axles  411   a ,  411   b , therefore rotation of the spindles  429   a ,  429   b  causes the stub axles  411   a ,  411   b  and the wheels  406   a ,  406   b  thereon to turn in a direction opposite the turning of the hitch tube  7 , as best illustrated in  FIG. 13A ,  FIG. 13B  and  FIG. 13C . Because the stub axle assemblies  425   a ,  425   b  and any axle inserts  412   a ,  412   b  are rigidly connected to the axle bar  405 , which is a part of the frame  401  of the trailer  400 , rotation of the spindles  429   a ,  429   b  must cause turning of the wheels  406   a ,  406   b  as the trailer  400  itself is much more difficult to move and acts essentially as a weight against which the rotating action of the spindles  429   a ,  429   b  can effect turning of the stub axles  411   a ,  411   b  and the wheels  406   a ,  406   b.    
         [0074]    The steering mechanism  450  described herein is easily adaptable to configurations of the trailer  400  having an increased transverse distance between the wheels  406   a ,  406   b . As illustrated in  FIG. 13B , the transverse distance between the wheels may be increased by inserting two axle inserts  412   a ,  412   b  between the axle bar  405  and respective stub axle assemblies  425   a ,  425   b  in a manner as previously described. To accommodate the effective increase in length of the axle, the length of the tie rods  456   a ,  456   b  may also be increased. Lengthening the tie rods may be accomplished by replacing the tie rods, by using hydraulic or linear actuators, or by using length adjustable tie rods, for example telescoping rods based on a threaded rod-in-tube arrangement. Stub axle linkages  457   a ,  457   b  remain a fixed length. Effective lengthening of the axle may also cause the pivot plate  455  to translate longitudinally in its position. Adjusting the length of the one or more control rods  451  may be required to accommodate translation of the pivot plate  455 . Adjusting the length of the one or more control rods  451  may be accomplished by replacing the control rods, by using hydraulic or linear actuators, or by using length adjustable control rods, for example telescoping rods based on a threaded rod-in-tube arrangement. 
         [0075]    Changing the transverse distance between the trailer wheels is important for keeping the wheels between crop rows when crop row spacing changes and the transportation or implement has wheels that are spaced for the new spacing of the crop rows. In prior art steerable trailers, changing the effective length of the axle prevents the steering mechanism from properly tracking the trailer&#39;s wheels behind the wheels of the transportation or towing implement while the trailer is turning. Instead of properly and smoothly tracking behind the transportation&#39;s or implement&#39;s wheels, the wheels of the trailer tend to skid sideways in turns. Such behavior may arise from the way the steering linkages and pivot points are arranged in relation to the effective lengthening of the axle. With the steering mechanism  450  described herein, effective lengthening of the axle on one side of the trailer  400  occurs between the pivot points  458   a  and  454  in the 5-bar mechanism and on the other side occurs between the pivot points  458   b  and  454  in the 5-bar mechanism. As illustrated in  FIG. 15A ,  FIG. 15B ,  FIG. 16A  and  FIG. 16B , the existence and generally central location of the pivot plate  455  permits adjusting the lengths of the tie rods  456   a ,  456   b  when the effective axle length is increased while maintaining the ability of the trailer wheels  406   a ,  406   b  to track properly behind wheels  16   a ,  16   b  of the transportation, even when only one control rod  451  is used in the steering mechanism  450  (see  FIG. 16A  and  FIG. 16B ). 
         [0076]    The trailer  400  may be readily convertible between a steerable trailer and a non-steerable trailer in a number of ways, for example by disconnecting the one or more control rods  451  from the pivot mounts  10  and reconnecting the one or more control rods  451  to a rigid portion of the trailer  400  (e.g. the tongue  404 ) to prevent the pivot plate  455  from pivoting, by disconnecting the one or more control rods  451  from the pivot plate  455  and securing the pivot plate  455  (e.g. to the frame  401 ) so that the pivot plate  455  cannot pivot, or by disconnecting the tie rods  456   a ,  456   b  from the pivot plate  455  and reconnecting the tie rods  456   a ,  456   b  to a non-movable portion of the trailer  400  (e.g. the frame  401 ). 
         [0077]    The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.