Abstract:
A frame and undercarriage track mounted assembly for a grain cart or manure tank unit designed to be pulled in a forward direction over and agricultural field by a farm tractor is disclosed. The invention involves a steering axle assembly that is adapted to turn dual spaced track assemblies. The steering axle is easily guided to improve the maneuverability and safety of the unit and reduce field compaction. The steering system design features compound angled kingpins that transfer some of the unit weight to assist in turns. Thus, the steering system reduces the resistance of the unit steering system to turning and the large footprint of the track assemblies minimizes ground compaction during turns.

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of application Ser. No. 12/689,903, filed Jan. 19, 2010, entitled “SELF-STEERING AGRICULTURE GRAIN CARTS AND MANURE TANKS”, and which is deemed incorporated herein by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    I. Field of the Invention 
         [0004]    The present invention relates generally to heavy agricultural vehicles that are not self-propelled, including grain carts used in harvesting grain crops and manure tanks, all of which are designed to be pulled behind farm tractors. More particularly, the invention relates to a steering axle assembly designed for grain carts and manure tank trailers that facilitates turning and maneuverability while minimizing soil loading and compaction. 
         [0005]    II. Related Art 
         [0006]    Non-motorized trailer-mounted agriculture utility vehicles in the form of grain carts and manure tanks that are designed to be pulled behind motorized vehicles, specifically farm tractors, have been used for a long period of time. Grain carts are typically used in combination with various types of combines in grain-harvesting operations in which the grain is separated from stalks in threshing and separation steps and is first collected in a grain tank in the combine from which it is discharged through a grain tank unload tube into a grain cart pulled alongside the combine. Large capacity and easy maneuverability are desirable attributes for such grain carts inasmuch as this increases the efficiency of the grain harvesting operation. While increased capacity for grain carts is desirable, it is also desirable that the implements minimize the degree to which the soil in the field is compacted by the cart, particularly when the cart is fully loaded. An example of such a cart is shown in U.S. Pat. No. 6,488,114 B1 to McMahon et al. 
         [0007]    Manure tanks have also long been used to distribute manure-containing mixtures over large field areas. The tanks, at times, are heavily laden and also must be highly maneuverable and need to have a minimum impact in terms of soil compaction when pulled through a field while applying the tank contents. 
         [0008]    One important aspect of pulled grain carts and manure tanks is the ability of such vehicles to maneuver in the field while maintaining a minimum impact on the soil over which they travel. This is directly affected by the design and operation of steerable axles on such vehicles. These vehicles typically include rear-steering axles and fixed front axles in the case of two-axle vehicles and may alternate steering and fixed axles on vehicles which have three or more axles. In addition, these vehicles must have the ability to be easily pulled down roads. 
         [0009]    A rear-steering axle assembly which utilizes an offset kingpin arrangement is shown in U.S. Pat. No. 6,267,198 B1. That axle is particularly suited for rear steering on a grain harvesting combine. 
         [0010]    Presently, the trend is toward, and the market is demanding, higher and higher capacity grain carts and manure tanks. Whereas, grain carts having a capacity of 1500 bushels were considered high capacity, the size requirement has risen to 2000 bushels or more and manure tanks may have a capacity of 12,000 gallons. Thus, the load carried by the vehicle may be over 50 tons in addition to the weight of the vehicle itself. 
         [0011]    While progress has been made, particularly as loads increase, there has developed and remains a need for steering axles that improve the steering function for better maneuverability and safer operation and which also reduce the impact of the vehicle on the soil including field compaction to thereby allow for higher capacity loads. 
         [0012]    In addition to wheeled vehicles, systems supporting such vehicles on track assemblies could further reduce the average soil loading thereby reducing soil compaction effects. However, it has not been practical to support heavy grain carts and manure tanks or other large agricultural containers using track-mounted vehicles because of the difficulties in maneuvering tracks in the field as the tracks lack a steering mechanism and must rely on skid steering that severely disturbs the soil under the tracks. Thus, it is also desirable that a system be devised that would enable such heavy agriculture vehicles to be supported on dual track systems that can be steered in a conventional manner. 
       SUMMARY OF THE INVENTION 
       [0013]    By means of the present invention, there is provided a steerable axle assembly designed for utility agriculture vehicle units in the form of grain carts and manure tanks designed to be pulled in a forward direction over an agricultural field by a motorized farm tractor. The invention involves an axle assembly that is easily guided to improve the maneuverability and safety of the unit and reduce field compaction. The steering system design reduces the amount of weight of the unit concentrated on kingpins and transmitted through the wheels to the ground during turns. Thus, the steering system reduces the resistance of the unit steering system to turning and minimizes ground disturbance and compaction during turns. The steering system improves the performance of rear-steering grain carts and manure tank units having two axles and larger versions of such units with multiple alternating steering and non-steering axles. 
         [0014]    One embodiment of the steerable axle assembly of the invention includes a pair of spaced kingpin receiver arrangements supported by a common central axle member, a spindle receiver carried by each kingpin receiver and a spindle mounted in each spindle receiver, each such spindle being adapted to carry a wheel. A kingpin is mounted in each kingpin receiver and each kingpin receiver is disposed in the structure such that a kingpin mounted in the kingpin receiver is positioned at a compound acute angle with the common central axle member, the angle being both directed inward toward the central axle member and rearward of the central axle member. Each of the spindle receivers is mounted to pivot about a kingpin. An arrangement is provided for connecting the spindle receivers together so that they operate in unison. This may be a hydraulic connection or a tie rod arrangement. In a turn, the kingpin angle causes the outward spindle in the turn to travel in an arc that pivots upward and forward to thereby facilitate the turning of the steering axle. 
         [0015]    A damping device such as a hydraulic cylinder may be provided to bias the self-steering axle toward a neutral position in which the wheel alignment is returned to a straight ahead direction as the axle assembly comes out of a turn situation. 
         [0016]    The self-steering axle assembly of the invention may be paired with a non-steering axle assembly to support a frame for supporting a grain cart or manure tank with the self-steering axle being the rear axle in the assembly. Larger vehicles may be provided with more than one self-steering axle. These include vehicles with three axles in which the front and rear axles are steering axles and the intermediate axle is non-steering and even larger units, for example, ones having four axles wherein the front, second and fourth axles are self-steering and the third axle is non-steering, etc. 
         [0017]    In an alternate embodiment, the steering system of at least one steering axle in the grain cart or manure tank unit can incorporate mechanically controlled steering arrangement using a drive line shaft attached to the drawbar of a conveying vehicle such as a tractor. 
         [0018]    In a further embodiment, the axle assemblies, particularly the steering axle assemblies, are adapted to be used with track assemblies used to support heavy agriculture vehicles. The track assemblies are designed to be incorporated into heavy vehicles such as dual-track grain cart and manure tank vehicles. The steering axle assemblies for track-mounted vehicles are similar to those of the other embodiments first described above modified to adapt to steer spaced track assemblies in dual track support systems. This enables the use of wide track dual tracks in a steerable arrangement which greatly increase support area to thereby reduce field compaction loading and allow for higher capacity loads. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the drawings wherein like reference characters depict like parts: 
           [0020]      FIG. 1  is an exploded view of a steering kingpin system constructed in accordance with the invention; 
           [0021]      FIG. 2  is a view of the steering kingpin system of  FIG. 1  assembled attached to a fragment of a vehicle frame; 
           [0022]      FIG. 3  is a rear elevational view of an assembled steering axle system for a wheeled vehicle with a tie rod connector; 
           [0023]      FIG. 4  is a top view of an assembled steering axle system similar to that of  FIG. 3  with parts removed for clarity; 
           [0024]      FIG. 5  is a rear elevational view of an alternative embodiment of an assembled steering axle system in accordance with the invention; 
           [0025]      FIG. 6  is a top view of a tandem assembly showing hydraulic connections and additional non-steering wheels; 
           [0026]      FIGS. 7A-7F  show top views ( 7 A,  7 C,  7 E) and rear views ( 7 B,  7 D,  7 F) of a steering kingpin system illustrating a left turn ( 7 A and  7 B), a straight or neutral position ( 7 C and  7 D) and a right turn ( 7 E and  7 F) with respect to a pulled vehicle illustrating an action of the kingpin steering axle system of the invention; 
           [0027]      FIG. 8  represents a bottom perspective view of an alternative embodiment of a steerable axle system with mechanically controlled steering; 
           [0028]      FIG. 9A  is a front perspective view of another embodiment of an assembled steering axle system similar to that illustrated in  FIGS. 1-4  adapted to steer a vehicle supported on spaced track assemblies; 
           [0029]      FIG. 9B  is a reduced top or plan view of the steering axle system of  FIG. 9A ; 
           [0030]      FIG. 9C  is an end elevational view taken from  FIG. 9B ; 
           [0031]      FIG. 9D  is a rear elevational view of the steering axle system of  FIG. 9B ; 
           [0032]      FIG. 10A  is an exploded view of a track arrangement for use with the steering axle system of  FIGS. 9A-9D ; 
           [0033]      FIG. 10B  is a perspective view of the track arrangement of  FIG. 10A  assembled with the track belt removed; 
           [0034]      FIGS. 10C ,  10 D and  10 E are top, end and side views of the assembled track of  FIG. 10B ; 
           [0035]      FIG. 10F  is an internal side view with parts removed of the assembled track and the track belt in place showing tensioning central devices, a damping cylinder, and bogey wheel pivot members; 
           [0036]      FIGS. 11A-11C  are perspective, and enlarged top and rear elevation view of a steering axle and dual track assembly in accordance with the invention assembled with track belts removed; 
           [0037]      FIGS. 12A-12D  are rear perspective, top, rear elevation and side elevation views of a vehicle frame supported on spaced, steered, dual track arrangements; 
           [0038]      FIGS. 13A-13C  depict the operation of a track carriage on flat and uneven terrain (shown with the track removed; 
           [0039]      FIG. 14A  is a top view of a further embodiment of an assembled steering axle system shown in a turning configuration; 
           [0040]      FIG. 14B  is a top view of the assembly of  FIG. 14A  shown in a straight aligned configuration; 
           [0041]      FIGS. 15A and 15B  are top rear perspective views of the assembled steering axle system of  FIGS. 14A and 14B  shown in a turning and straight aligned configuration, respectively; 
           [0042]      FIGS. 16A and 16B  are bottom rear perspective views of the assembled steering axle embodiment of  FIGS. 14A and 14B , depicted in a turning and straight aligned mode, respectively; 
           [0043]      FIGS. 17A ,  17 B,  17 C and  17 D are top, rear elevation, detail and end views of the assembled steering axle embodiment of  FIGS. 14A and 14B  showing turning and kingpin mounting angles; 
           [0044]      FIGS. 18A-18C  depict axle end views corresponding to turning in both directions (A and B) and with straight ahead alignment (c); 
           [0045]      FIG. 19  is a schematic diagram of a hydraulic system for coordinating front and rear steering axles in accordance with the invention; 
           [0046]      FIGS. 20A and 20B  are front perspective views of a manure tank mounted on a steerable track supported chassis assembly and a wheel supported chassis, respectively; 
           [0047]      FIG. 21  is a front elevational view of a grain cart mounted on a steerable track chassis; 
           [0048]      FIG. 22  is a rear elevational view of the grain cart of  FIG. 21 ; and 
           [0049]      FIG. 23  is a right side elevational view of the grain cart of  FIG. 22 . 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    In accordance with the following detailed description, several embodiments associated with the present inventive concepts are presented. These embodiments are intended as examples of such concepts, but are not intended to limit the scope of the present invention in any manner as variations within the confines of the inventive concepts may occur to those skilled in the art. 
         [0051]    As used herein, the term “axle assembly” refers to a set of opposed spaced assemblies for carrying wheels or track carriages aligned on opposite sides of a vehicle frame, whether or not they are connected by a common member. Thus, the spaced assemblies may enjoy a common axle tube or other possibly unconnected mounting arrangement. The axle assemblies may be steering in which the wheels can pivot about kingpins or non-steering in which the wheels assume a fixed position. Steering axle assemblies include a connecting member or other arrangement to coordinate the turning of both wheels in unison. 
         [0052]      FIG. 1  depicts an exploded view of a typical kingpin steering system, generally at  100 , which represents one of a pair of opposed symmetrically constructed assemblies that make up a steering axle assembly in accordance with the invention. The kingpin steering system further includes a kingpin receiver assembly  102  and a spindle receiver  104 . A spindle and wheel assembly is shown at  106 , including a spindle  108  and a wheel  110  mounted on the spindle. The kingpin receiver assembly further includes spaced, generally parallel, kingpin receiving members  112  and  114 , which hold and position an angled kingpin  116  and also accommodate the spindle receiver  104 . They also provide bearing surfaces for the assembly to operate. A lip seal member is shown at  118  on the lower bearing surface and a nut  120  secures the kingpin in place. It should also be noted that the nut clamps the upper plate  112  to the lower plate  114  causing the load of the weight of the unit to be carried more evenly. 
         [0053]    The spindle receiver  104  includes an integral hollow spindle tube  122  for receiving a corresponding spindle member  108 . The assembly further includes a series of thrust washers  124  that carry the vertical load of the vehicle and an o-ring  126  that is mounted beneath the thrust washers to seal the upper bearing surface from the environment. An attachment plate  128  cooperates with members  130  using fasteners (not shown) to attach the assemblies  104  and  106  together. 
         [0054]    In this embodiment, the kingpin receiver assemblies are attached by intermediate structural members to a common central axle member or axle tube  132  and a fluid-operated, preferably hydraulic, steering cylinder  134  is provided having the rod end  136  mounted to the spindle receiver  104  using tab  138 . The other end of the cylinder is connected to a member  140  fixed to the axle tube  132 , as shown in  FIG. 4 . 
         [0055]    The hydraulic cylinder  134  is actually a damping cylinder which performs two functions. First, it controls the speed at which the steering system turns and, second, the hydraulic cylinder has three hydraulic connections at  142 ,  144  and  146  and is pressurized to center the steering system, that is, it urges the system to assume a neutral or aligned straight forward position to allow the unit to back up or to be transported down a road easily, for example, with the spindles in what amounts to a locked position. 
         [0056]    This embodiment also includes a tie rod  148  connected between the spindle receivers  104 , one connector of which is shown at  150 . The tie rod forces the spindle receivers to operate (pivot) in unison by mechanical connection. 
         [0057]    The system of  FIG. 1  is shown assembled in  FIG. 2  and attached to a fragment of a vehicle frame at  152 . 
         [0058]      FIGS. 3 and 4  show rear elevational and top views of steering axle assemblies in accordance with the embodiment of  FIGS. 1 and 2 . As can be seen from the figures, a key feature of the kingpin steering system of the invention lies in the mounting disposition of the kingpins. The kingpins are disposed at a compound acute angle with the common axle tube or other support member such that the kingpins are disposed to extend in a rearward and inward manner rather than being mounted in a conventional vertical plane. An important aspect of the invention is the mounting of the kingpins at a compound angle that allows the spindles to travel in an arc that wants to pivot up and forward with the weight of the unit resting on the bearing surfaces. The tie rod  148  that connects the left kingpin steering system, including the left spindle assembly, shown at  160  in  FIGS. 3 and 4 , with the right kingpin steering system  162  using respective connectors  164  and  166 , as shown in  FIG. 4  causes the spindles to operate in unison. This is further illustrated in the turning, straightening and opposite direction turning sequences depicted in  FIGS. 7A-7F . Easy turning and relief of stress on the kingpins is accomplished as the spindle receivers, and so the spindles rotate in a plane perpendicular to the non-vertical disposition of the kingpins, rather than in a flat trajectory accommodated by the normal vertical disposition of kingpins. 
         [0059]    In addition, this configuration reduces ground traveling in turns and further enables the vehicle to accommodate larger tires, typically up to two meters in diameter or greater, thereby reducing ground loading even more. 
         [0060]      FIG. 5  is a top view of an alternative embodiment of an assembled single steering axle system in accordance with the invention. The steering axle is shown generally at  170  and includes spaced symmetrically opposed and otherwise identical kingpin steering assemblies for steering as at  172  and  174  that include compound angled kingpins  176  and  178  respectively. The kingpins are attached to the frame and coordinated by two separate hydraulic cylinders  180  and  182  supplied from a common hydraulic fluid line  184  and common connector  186 . The common hydraulic connection enables the cylinders  182  and  182  to act in the manner of a tie rod to coordinate the turning of assemblies  172  and  174  as was the case with the damping cylinder of  FIGS. 1-3 , the cylinders  182  and  182  act to return the assemblies to a forward directed position. Fragments of frame members are shown at  188  and  190  with cross brace  192  and shock absorbing suspension devices are shown at  194  and  196 . 
         [0061]      FIG. 6  is a top view of a tandem axle assembly also showing similar hydraulic connections. The steering axle assembly is shown generally at  200  and includes steering spaced, opposed symmetrically constructed kingpin assemblies at  202  and  204 . These assemblies are attached to structural members  206  and  208 , respectively, which, in turn, attach to a common structural member  210 . This system also features a pair of hydraulic steering cylinders  212  and  214 . Cylinder  212  connects a corresponding pivoting spindle receiver  216 , to a structural member  206  using a plate member  218 . Likewise, cylinder  214  connects pivoting spindle receiver  220  with member  208  using a member  222 . The cylinders  212  and  214  are provided with hydraulic fluid from a common source  224  in a manner that coordinates both cylinders to operate together and also pressurizes the cylinders to center to stabilize the steering system so that it favors locking the spindles in a forward position. 
         [0062]    In this embodiment, note that the kingpins  226  and  228  are disposed at the same angle as those enumerated with respect to the previously described embodiments. Additional non-steering or fixed position assemblies are shown at  230  and  232 , which are also structurally attached to the forward portion of common member  210  through an intermediate structure. As can be seen from the drawing, the assemblies  230  and  232  are fixed in a neutral or straightforward position. 
         [0063]      FIG. 8  represents a bottom perspective view of an alternative embodiment of a steerable axle system that employs mechanically controlled steering. The system, shown generally at  300 , includes angled kingpin steering systems at  302  and  304  with common tie rod  306 . The kingpin steering system  304  includes a spindle receiver  308  connected at  310  to a second tie rod  312  which, in turn, is attached at  314  to an eccentric steering arm  316  instead of to a hydraulic cylinder, as shown in the embodiment of  FIGS. 1-4 , for example. The steering arm  316  is attached to a steering shaft  318  that rotates and operates the eccentric steering arm  316 . The shaft  318  is held by bearings as at  320  and extends to be connected by a universal joint  322  to a drive line shaft  324 . The drive line locks and controls the amount of steering available in the axle system and is, in turn, connected via a second universal joint  326  to the draw bar of a tractor or other motorized pulling vehicle. In this manner, the act of the tractor turning transfers the necessary torque to the steering axle to rotate the system in the correct amount in the direction. Both kingpin assemblies are coordinated via the connection with common tie rod  306  and the kingpins are set at an angle as per previous embodiments. 
         [0064]    Another embodiment of a steering axle system in accordance with the invention is depicted in  FIGS. 9A-9D . That system is adapted to steer a vehicle supported on pairs of spaced track assemblies rather than wheels. The steering axle is shown generally at  400  and includes a pair of spaced compound-angled kingpin receiving arrangements  402  and  404  which are similar to those depicted in  FIGS. 1-4  mounted to an axle assembly which includes a tube or common central structural axle member  406  and plate member  407 . This embodiment uses a hydraulic coordinating system which includes a central plate member  408  secured to structural member  406  and pivotally connected to the blind ends of a pair of hydraulic cylinders  410  and  412  at  414  and  416 . The rod ends of cylinders  410  and  412  are pivotally connected to gusset plate members  418  and  420 , respectively, which are connected to spindle assemblies  422  and  424  and operate to pivot the spindle assemblies in unison based on a fluid control system, as will be described, to control the speed at which the steering system turns. The fluid control system also may coordinate to turn both axles of a dual axle steering system and to urge the system to assume a neutral or aligned straight forward position when desired. The spindle assemblies  422  and  424  pivot about dual angled kingpins  426  and  428  and carry heavy integral spindle steering rod members  430  and  432 , respectively.  FIG. 9D  depicts the relative inward directed angles of the kingpins about which the spindles rotate. The preferred angles of the kingpins are also discussed further below. 
         [0065]      FIG. 10A  depicts an exploded view of one track arrangement in accordance with the invention. The track is one of a pair of spaced steered track assemblies which are designed to be associated with and connected to an axle assembly such as that shown in  FIGS. 9A-9D . The assembly includes a track belt  450 , which may be a continuous belt. One model uses a belt that is thirty-six inches (91.4 cm) wide made of heavy gauge rubber. Pairs of spaced idler wheels  452  which may be 30 inches (76.2 cm) in diameter flank pairs of spaced bogey wheels  454 , which may be 16 inches (40.6 cm) in diameter, and these are combined to operate each inside track belt  450 . 
         [0066]    The assembly further includes a track carriage main arm  456  with associated bogey rocker arm  458 , hydraulic tension adjusting and damping cylinder  460 , track tensioning spindles  462 , front and rear track arm members  464  and  466 . Opposed hub members  470  and  472  are associated with each pair of spaced idler and bogey wheels. 
         [0067]    The track carriage main arm  456  includes a steering spindle receiving opening  474  flanked by a pair of half ring retaining members  476 . Main arm  456  further includes a connected pivoting section  478  connect to pivot at  480 . The pivoting connection of the two arm sections enables the two outer sets of idler wheels  452  to be displaced up and down relative to each other in response to uneven ground. As best depicted in FIGS.  10 F and  13 A- 13 C, the sets of bogey wheels are carried and connected by bogey rocker arm  458  which, has an attached gusset  482  that, in turn, is pivotally connected at  484  to pivoting connecting arm member  478  which, as indicated, is pivotally connected to main arm  456  at  480 . This arrangement enables the sets of bogey wheels  454  to pivot in unison and independent of the sets of idler wheels  452  in response to uneven ground making the entire track quite flexible. 
         [0068]    The terrain following versatility characteristic of the track assemblies of the invention is illustrated in  FIGS. 13A-13C  which depict a track on level ground  490  in  FIG. 13A , and on different uneven ground patterns in  FIGS. 13B  ( 492 ) and  13 C ( 494 ). 
         [0069]      FIGS. 10B-10F  depict views of the track arrangement of  FIGS. 10A  in assembled form at  500  with the track belt removed except in the view of  FIG. 10F  which illustrates the internal workings including the damping cylinder and track tensioning devices which are located between the pairs of spaced idler and bogey wheels. 
         [0070]      FIGS. 11A-11C  illustrate perspective, top and rear elevation views of a pair of track modules similar to those of  FIGS. 10A-10F  assembled with a steering axle into a steerable dual track unit  510  including a steering axle  512  connecting a pair of assembled track arrangements  500  shown with the track belts removed for clarity. The modular track arrangements are connected to be steered by the heavy spindle rod members of the steering axles. A plurality of such units are used as undercarriage supports for the chassis frame of a heavy grain cart, manure tank or the like. 
         [0071]      FIGS. 12A-12D  show perspective, top, end elevation and side elevation views of an assembled vehicle  520  without a mounted container, but including a plurality of steerable track modules assembled with belts or treads in place at  522  in spaced relation with steering axles  512  to form dual track units. Spaced dual track units provide undercarriage support to support a heavy structural frame or chassis  530  for a heavy container such as a manure tank grain cart or similar heavy container. 
         [0072]    Thus,  FIG. 12A  is a perspective view of an assembled vehicle  520  suitable for carrying a grain cart, manure tank or similar large, heavy vehicle implement unit including the tracks, chassis  522 , frame  530  and a yoke assembly  532  with a hitch  534  for attachment to a farm tractor or other towing vehicle. The heavy structural frame  530  is attached to an undercarriage arrangement that includes spaced front and rear spaced self-steering axle assemblies  512  which, connect between and steer the pairs of spaced track assemblies  522 . The chassis frame  530  further includes main longitudinal support members  536  and  538  spanned by end transverse cross members  540  and  542  and shaped intermediate cross members  544  and  546 . The cross members  544  and  546  are shaped to receive the lower portion of a grain cart or tank body or the like. Support pads are shown at  548 . 
         [0073]    In this illustrated embodiment, both sets of track assemblies are steering sets which gives the vehicle the most flexibility for maneuvering in an agricultural field. Other embodiments of the vehicles can be built in which only one of the dual track sets or units, self steers. In addition, the number of steerable or fixed dual track sets can be varied depending on the vehicle size. The views depict the vehicle in a turning disposition in which the front and rear dual track units turn in opposite directions to aid in reducing the overall turning radius of the vehicle. This feature is described in greater detail below. 
         [0074]    An important aspect of the track-mounted embodiment is that it provides a combination of large area support for the unit in the form of a plurality wide track supports which reduces the unit area loading and thus reduces soil compaction; but it also provides a self-steering aspect to the track assemblies that avoids the undesirable and destructive effects of skid steering conventionally present with track supported vehicles. 
         [0075]    The large self-steering footprints of the tracks also enable the use of grain carts, manure tanks or similar vehicles that carry larger payloads without increasing soil compaction or disruption. Thus, ten or twelve thousand (10,000-12,000) gallon tanks weighing over 100,000 lbs. (45,351 kg) fully loaded or 2500 bushel grain carts can easily be accommodated. For example, each track may present a footprint surface 36 inches (91.4 cm) wide by 72 inches (183 cm) long or 18 ft 2  or 2592 in 2  (1.67 m 2 ). In this manner, a load of 100,000 lbs. (45,351 kg) supported on four track units yields a per square inch in loading of only about 9.65 lbs. (4.14 kg) per in 2 . This is much lower loading than would be available with conventional tires, which present a much smaller footprint or contact area, and therefore allows a much higher vehicle capacity at a comparable soil loading. 
         [0076]      FIGS. 14A  through  FIG. 18C  depict a variety of views of an arrangement of steering axles and details or fragments similar to that shown in  FIGS. 9A-9D . A steering axle assembly is shown generally at  600  in a turning configuration in  FIGS. 4A ,  15 A and  16 A, and in a straight tracking disposition in  FIGS. 14B ,  15 B and  16 B. Similar to other embodiments, the steering axle assemblies  600  include compound-angled kingpin receiving arrangements  602  and  604  mounted at the ends of a common axle tube or heavy central structural axle assembly  606 . In this embodiment, a pair of heavy round spindle steering rod members  608  and  610  are carried in reinforced mounting structures in the form of spindle receiver assembles  612  and  614  that are mounted to rotate about kingpins  616  and  618 , respectively. These are similar to assemblies  104 ,  160 ,  216 , etc. previously described. As with previously described embodiments, the spindle receiver structures are identical opposed structures located at the ends of the axle assembly  606  and include a pair of shaped members in the form of an outer member  620 ,  622  and an inner member  624 ,  626  that carry and fasten an outer tube  628 ,  630  to the assembly. Heavy plate members  632 ,  634  are fixed to the shaped members. Reinforcing gusset structures  636 ,  638  stabilize the structure. The kingpin receiving arrangements  602  and  604  are connected to the central structural axle assembly by heavy retaining members that include top members  640  and  642  and bottom members  644  and  646  ( FIGS. 16A and 16B ). These, in turn, are connected to the central structural axle assembly  606  by heavy shaped connecting members  648  and  649 . 
         [0077]    A reinforced central plate member  650  is connected to the main structural axle assembly reinforced by opposed reinforcing side gussets  652 ,  653 . Each steering axle includes a pair of fluid operated double-acting cylinders  654  and  656  which are pivotally attached between plate member  650  and plate members  632  and  634 , respectively, with the rod ends connected to plates  632  and  634 . Thus, cylinder  654  includes a base or blind end pivotally attached to plate  650  at  658  and a rod end pivotally attached to a plate  632  at  660  and cylinder  656  has a base or blind end pivotally attached to plate  650  at  662  and a rod end pivotally attached to a plate  634  at  664 . Each cylinder includes three fluid connections, a rod connection (R), a base connection (B) and a common connection (C) that function as will be described. 
         [0078]    Each steering axle also includes a pair of spaced heavy shock-absorbing container support arrangements shown at  670  and  672  with connections at  674  and  676 , respectively, between sets of plates  678  and  680 , which are fixed to the main axle assembly  606 . The members  670  and  672  are designed to connect to a grain cart, bin or tank support structure. The support arrangements  670  and  672  are, thus, pivotally mounted to the axle assembly arrangement  606  at their bottom ends and include top connectors  682  and  684 . Pairs of inner and outer chassis connecting shaped strut members  686 ,  688  and  690 ,  692  connect the axle assembly to chassis members. 
         [0079]      FIGS. 17A-17B  depict top and rear elevational views of the axle assembly of  FIGS. 14A and 14B .  FIGS. 17C and 17D  depict certain details.  FIG. 17B  shows a kingpin side angle directed toward the center of the axle of 15° from vertical and  FIG. 17D  shows a kingpin angle of 7.24° from the vertical toward the rear of the axle assembly. The inward directed angle of the kingpins distributes a portion of the vertical weight of the vehicle as a horizontal force which, in turn, assists the turning rotation of the spindle rod steering members  606  and  608  when the vehicle turns according to the direction of travel of the towing vehicle. The rear-directed angle assists in returning the axle to straight tracking after a turn. While an angle of about 15° inward directed kingpin angle and an angle of about 7°, preferably 7.24°, rearward directed appears to be optimal, inward directed angles in the range of from about 13° to about 17° produce satisfactory results and a rearward directed angle in the range of 6° to 9° will also produce satisfactory results. 
         [0080]      FIG. 19  depicts a schematic drawing of a hydraulic system diagram for coordinating the steering of an embodiment of a track vehicle having two spaced steering axles as shown in  FIGS. 12A-12D . A front vehicle axle includes double-acting cylinders  802  and  804  and a rear axle includes double-acting cylinders  806  and  808 . The axles are configured as in the embodiment of  FIGS. 14A-14B . 
         [0081]    Each of the corresponding front and rear cylinders has three port connections including a rod end port connection (R), a base end port connection (B) and a common port connection (C). The ports of front steering axle cylinders are designated R 1 , B 1  and C 1 , and the ports of rear steering axle cylinders are designated R 2 , B 2  and C 2 . The base ends of front and rear cylinders  802  and  806 , shown on the left side of the schematic drawing, and  804  and  808 , shown on the right side of the schematic drawing, are connected together by respective lines  810  and  812 . The common parts are likewise connected by lines  822  and  824 . The rod ends of front axle cylinders  802  and  804  are connected together by a common line  814 ; likewise the rod ends of rear axle cylinders  806  and  808  are connected together by a common line  816 . Optionally, fluid accumulators represented at  818  and  820  may be included in lines  814  and  816  respectively to dampen unequal external effects in the terrain encountered by the vehicle. The front axle cylinders and rear axle cylinders through their rod end and base end connections form a closed loop system that operates to coordinate the steering of the front and rear axles as will be explained. As indicated, connections Cl and C 2  of cylinders  802  and  804 ; and cylinders  809  and  808  are connected together by lines  822  and  824 , respectively. Lines  822  and  824  are both connected to a common source of high pressure hydraulic fluid in line  826 . 
         [0082]    In operation and according to the schematic view of  FIG. 19  in which fluid flow is denoted by arrows, both the front and rear axles are in the process of steering the vehicle to the left. The rod end of cylinder  804  extends causing fluid to be displaced into line  814 . The fluid enters port R 1  of cylinder  802  to retract rod end of cylinder  802 . The combination causes both of the associated front tracks to turn to the left. This action also displaces fluid into line  810  from the base port of cylinder  802  to the base port of cylinder  806  which causes rod end of cylinder  806  to tend to extend. This, in turn, displaces fluid into line  816  from port R 2  of cylinder  806  and into port R 2  of cylinder  808  causing the rod end to retract. Fluid is displaced from the base port B 2  of cylinder  808  to the base port B 1  of cylinder  804 , along line  812 , accordingly. Thus, the rear tracks turn to the right. The result is that the front axle is caused to turn to the left and the rear axle is caused to turn to the right as illustrated in  FIGS. 12A-12D , as viewed from the rear of the illustrated chassis. The simultaneous turning of both axles greatly reduces the overall required turning radius of the vehicle. In a right turn situation, the opposite flow will occur. When the turn is completed the steering axles will straighten on their own. 
         [0083]    High pressure fluid line  826  is used to lock the front and rear axles in a straight position when this is required, as for allowing an empty vehicle to be backed when required. 
         [0084]    As with other embodiments, the angled kingpins of the track-mounted vehicle will cause the axles to track in a straight line until the prime moving pulling tractor or other motorized vehicle changes direction to a sufficient degree to overcome the two kingpin angles. It is the weight of the vehicle on the self-steering mechanism that provides the force for the axle to steer the tracks in the direction urged by the pulling vehicle. In the preferred arrangement, both axles steer thereby greatly reducing the turning radius of the tank or cart or other heavy container carried on the chassis. 
         [0085]    The coordination of the cylinder system of each axle keeps the tracks on a common axle coordinated or in tune as well as would occur with a solid connecting rod while also allowing some variation or cushioning in the system. As indicated, the fluid system further causes the rear axle to turn in a direction opposite to that of the front axle thereby doubling the degree of turning obtained to reduce the overall turning radius of the vehicle. Accumulators provide a degree of damping in the system. It will also be appreciated that the accumulators may be used to enable a greater variation between the amount of turning angle of the front and rear axles to accommodate field obstacles or other problems that prevent identical degrees of turning for both front and rear track systems. 
         [0086]      FIG. 20A  shows a perspective view of a fully assembled manure tank vehicle  700  mounted on a dual steerable track chassis system in accordance with the invention.  FIG. 20B  shows the same type of implement at  710  mounted on a steerable wheeled system. The greatly increased ground contact surface of the track system is evident. 
         [0087]      FIGS. 21-23  depict front, rear and side views of a vehicle according to the invention in the form of a grain cart body  750  mounted on a steerable track vehicle chassis. As previously indicated, the grain cart, when loaded, weighs many tons and the track system aids in both turning and reducing local ground loading. An unloading assembly is shown at  752 . 
         [0088]    It will be appreciated that the steering axle track-mounted arrangement of the present invention lends itself for use with any combination of steering and non-steering axles in grain carts and manure tanks or the like designed to be pulled in a forward direction by a motorized conveyance. 
         [0089]    This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use embodiments of the example as required. However, it is to be understood that the invention can be carried out by specifically different devices and that various modifications can be accomplished without departing from the scope of the invention itself.