Abstract:
Mobile towers of an irrigation system have drive wheel assemblies that propel the towers along the ground. At least certain of the wheel assemblies may comprise dual wheels that share a common axis of rotation but are separately driven by their own drive motor. By driving the two separate wheels in unison but with their own individual drive shafts, increased ground-engaging surface area can be obtained without a consequential increase in load for any one motor.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to the field of agricultural irrigation systems and, more particularly, to an improved drive wheel assembly for the mobile towers of such systems.  
       BACKGROUND AND SUMMARY  
       [0002]     It is known in the art to provide the mobile, water conduit-supporting towers of irrigation systems with drive wheels that propel the towers over ground to be irrigated. Typically, such towers include at least a pair of wheel assemblies at the base of the tower, each assembly comprising a single drive wheel powered by an electric or hydraulic motor.  
         [0003]     It would be desirable in some instances to increase the ground-engaging surface area or “foot print” of each wheel assembly, such as where the wheel assemblies are steerable. However, providing larger tires or attaching special enlarged traction structures to the existing wheels necessarily increases the load on their existing drive motors and gearboxes, which can cause the units to malfunction or fail prematurely.  
         [0004]     The present invention achieves the desired increase in surface area through the provision of a separately driven second wheel for each wheel assembly. Both wheels of each assembly are driven in unison and at the same speed but by separate drive motors. Preferably, the two wheels share a common axis of rotation but have separate drive shafts that are driven by separate motors. In one preferred form of the invention, the two wheels are disposed in closely spaced apart, side-by-side relationship. Preferably, the wheels are supported on a yoke having an upright, rotatable spindle and a pair of upright, laterally spaced legs that depend from the spindle at its lower end. The drive motors and gearboxes for the two wheels are duplicates of one another and are electrically interconnected. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a fragmentary, schematic illustration of a center pivot irrigation system employing an auxiliary corner span, the steerable tower of the corner span employing wheel assemblies constructed in accordance with the principles of the present invention;  
         [0006]      FIG. 2  is an enlarged, fragmentary isometric view of the steerable tower of the corner span in  FIG. 1  illustrating in more detail the wheel assemblies of such tower;  
         [0007]      FIG. 3  is a horizontal cross-sectional view through one of the wheel assemblies taken at a location above the drive motors thereof and looking downwardly; and  
         [0008]      FIG. 4  is a fragmentary, vertical cross-sectional view of a wheel assembly illustrating details of construction. 
     
    
     DETAILED DESCRIPTION  
       [0009]     The present invention is susceptible of embodiment in many different forms. While the drawings illustrate and the specification describes certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments.  
         [0010]     Although the principles of the present invention have utility with respect to a variety of irrigation systems, they are particularly beneficial when applied to systems wherein at least certain of the wheel assemblies are steerable. For example, steerable wheels are typically used on the auxiliary corner span of a center pivot system wherein the corner span is steered into difficult-to-reach comers of the field as the main span sweeps in a circular path around the primary portion of the field. One such system is disclosed in U.S. Pat. No. 5,695,129 owned by the assignee of the present invention and hereby incorporated by reference into the present specification. Accordingly, in the description which follows, the invention is disclosed byway of example in connection with steerable wheel assemblies and, in particular, the steerable wheel assemblies of the corner span of a center pivot irrigation system.  
         [0011]      FIG. 1  illustrates a center pivot irrigation system  10  having a main span  12  and an auxiliary or corner span  14 . Main span  12  is connected at its inner end to a central pivot (not shown), and corner span  14  has a pivotal connection  16  at its inner end with the outer end of main span  12 . A water supply conduit  18  stretches along the main span  12  and corner span  14  for supplying water to a number of distribution heads (not shown). Main span  12  has non-steerable towers  20  supporting a main section  22  of conduit  18 , while corner span  14  has a steerable tower  24  supporting a conduit section  26  that is hingedly interconnected with main section  22  at or adjacent pivot  16 . Non-steerable towers  20  are each provided with single-wheel drive wheel assemblies  28  and  30 , while steerable tower  24  is provided with dual-wheel drive wheel assemblies  32  and  34 .  
         [0012]     As illustrated in  FIG. 2 , steerable tower  24  comprises a somewhat generally H-shaped frame  36  having a pair of upright, tubular legs  38  and  40  that are interconnected across their upper ends by a cross pipe  42 . Wheel assemblies  32 ,  34  are disposed at the lower ends of legs  38 ,  40 . As illustrated in  FIGS. 2 and 4 , in one preferred embodiment each wheel assembly  32 ,  34  includes a yoke  44  comprising an upright spindle  46  and a pair of wheel supports in the form of laterally spaced, generally upright legs  48  and  50  fixed to the lower end of spindle  46 . Spindles  46  are rotatably received within legs  38 ,  40  and at their upper ends are operably connected through gearboxes  52  in a well known manner to a common electric or hydraulic steering motor  54  that is operable to swivel spindles  46  about their upright axes in unison and in equal amounts so as to steer wheel assemblies  32  and  34 .  
         [0013]     Referring also now to  FIG. 3 , it will be seen that each wheel assembly  32 ,  34  includes a set of dual wheels  56  and  58  supported by the yoke  44  of the wheel assembly. In one preferred embodiment, wheels  56 ,  58  are closely spaced apart in side-by-side relationship between the legs  38 ,  40 . Wheels  56  and  58  are both rotatable about a common axis of rotation  60 , but each has its own axle  62  that is mechanically separate from the axle of the other wheel. Thus, wheels  56  and  58  are not structurally fixed to one another as in the case of conventional dual wheels, but are instead capable of independent rotation relative to each other. As is conventional, each wheel  56 ,  58  may include a pneumatic tire  64  mounted on a hub  66  that is fixed to the end of axle  62  in a suitable manner, such as by lug bolts (not shown). The two axles  62  associated with each wheel assembly  32 ,  34  project laterally inwardly from their respective yoke legs  48 ,  50  toward one another and in axial alignment with each other.  
         [0014]     Each axle  62  comprises the output shaft of a right angle gearbox  68  secured to the inside face of yoke leg  48  or  50  at its lower end. An input shaft  70  of gearbox  68  is operably coupled via a U-joint driveline  72  to a combined drive motor and gearbox unit  74  of conventional construction that is supported on a horizontally extending arm  76  projecting generally parallel with the path of travel of wheels  56 ,  58 .  
         [0015]     Although drive motors  74  for each wheel assembly  32 ,  34  are mechanically separate from one another and each drives its own wheel, drive motors  74  are electrically connected in such a manner that they operate simultaneously and at the same speed. Consequently, each motor  74  is burdened with the load of only one wheel  56  or  58 , yet the effective ground-engaging wheel surface area obtained by each wheel assembly  32 ,  34  is double that provided by prior wheel assemblies having only a single wheel. Consequently, the benefits of dual drive wheels are obtained without the detriment of increased loading on any single drive motor.  
         [0016]     It is to be noted that although drive motors  74  have been described as electric motors and connected in a circuit in such a manner that all motors  74  operate in unison, such motors may also comprise hydraulic motors that would be plumbed in such a manner that they too would operate in unison. It will be seen, therefore, that the principles of the present invention apply to hydraulic driving means as well as electric means, although electric means are the preferred embodiment.  
         [0017]     The inventor(s) hereby state(s) his/their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his/their invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.