Abstract:
Broadly, one aspect of the present invention is an articulated combine having increased on-board grain storage capacity (e.g., 1,200 bushels) and which is composed of a forward unit having an operator&#39;s cab, an engine, a grain harvesting assembly, a grain transfer assembly, and being devoid of an on-board grain bin; and a rearward unit jointedly attached to the forward section and having, steerable and powered wheels, an on-board grain bin for receiving grain from the forward section grain transfer assembly, and a grain off-loading assembly. The grain transfer assembly, joint, and grain off-loading assembly and controls, form other aspects of the present invention.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of application Ser. No. 09/481,046, filed Jan. 11, 2000; which is divisional application of application Ser. No. 09/040,985, filed on Mar. 18, 1998, now U.S. Pat. No. 6,012,272; and is cross-referenced to application Ser. No. 09/210,331, filed Dec. 11, 1998. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
         [0002]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention generally relates to combines and more particularly to an articulated (jointed) combine which employs, inter alia, an improved joint, unloading capability, grain transfer capability, airbag suspension, straw and chaff conveyor, suspended/movable fuel tank, control/steering, and extremely large grain storage capacity.  
           [0004]    A modern agricultural combine typically unloads or transfers clean grain from its on-board storage hopper utilizing an auger of fixed length which swings out in a fixed radius and fixed elevation arc from its stowed position. The stowed position generally is pointing to the rear of the combine. The auger in turn generally is driven by a mechanical arrangement of belts, chains, clutch, and gearbox. The unload auger in most combine designs swings out to the operator&#39;s left. The auger length generally is limited by the practical distance that it can extend beyond the rear of the combine in its stowed position without creating a serious maneuvering hazard.  
           [0005]    As the size of on-board storage hoppers and capacity of combines has increased, the time required to maneuver the machine next to the grain receiving wagon or truck and the grain transfer time have become a major component of the total harvesting time. Conventional combines have a grain hopper capacity of 250 to 300 bushels and unload auger capacities of 1.9 to 2.6 bushels per second.  
           [0006]    The unload time of the hopper typically is about 2 to 3 minutes with the unload auger running at maximum speed and 1 to 2 minutes are taken to maneuver the combine into the optimum unload position next to the truck or wagon. Re-positioning the combine and running the auger at less than maximum speed are often encountered when topping off the truck or wagon which is receiving the grain. As modem combine harvesting capacities approach 3,000 bushes per hour, the unload cycle must be repeated every 8 to 10 minutes. Therefore, the total unload time or non-harvesting time is a significant reduction of total grain harvesting productivity. A grain capacity of about 600-450 bushels would permit the combine to harvest for about 1 mile, which would greatly reduce unloading cycles.  
           [0007]    This productivity loss can be countered by a second operator utilizing a tractor and grain cart following the combine back and forth through the field to unload the on-board combine storage hopper without stopping the harvesting process. Alternatively, a combine with an integrated grain cart, as disclosed in applicant&#39;s U.S. Pat. No. 5,904,365 can be utilized to reduce the number of unload cycles and at least double the rate at which grain is discharged to the receiving vehicle.  
           [0008]    Unloading combines into semi-trailer road trucks has become the prevalent practice as opposed to field wagons that were utilized in the past. These road trucks typically are parked at the side of the road and not in the field where the combine is operating. This necessary practice almost always creates an elevational difference between the two vehicles. These road trucks themselves also have widely varying heights. These two conditions create a big variation in the optimum elevation of the discharge point of the combine unloading system. Combine manufacturers have attempted to address this problem with ever-longer augers and higher fixed swing out arcs. There are, however, limits to both. This fixed point discharge point frequently ends up too high, too low, too far from the combine, or too close to the combine for optimum truck loading conditions. Such conditions require repositioning the combine with respect to the vehicle while it is unloading.  
           [0009]    Existing combine unloading systems can unload from one side of the machine only. This frequently requires 180° turns by the combine to position it on the proper side to unload the grain into the road truck. It also means that while harvesting the combine generally only can be unloaded into a moving grain cart only while traveling along the left-hand side of the unharvested crop since access to the unloader would be precluded by the unharvested crop were the combine to be located to the right of the crop.  
           [0010]    When topping off or completely filling the truck or wagon, it is necessary for the operator to inch the combine forward or backward during the process. In addition to being cumbersome, the combine must be positioned close to perfectly parallel to the receiving vehicle or a stop and reposition is necessary. Moving the auger through its fixed arc frequently cannot solve the lack of parallel orientation.  
           [0011]    An agricultural combine has multiple steering requirements. Precise control is needed as the row harvesting units such as a cornhead, are guided through the rows of grain. When the end of the field is reached, a tight turning radius is needed to proceed back across the field in order to harvest the crop immediately adjacent to the just-completed rows or round. Concomitant with its field performance, this large vehicle also must be controlled on the roadway at speeds of around 20 mph and around tight corners. Another steering associated problem is to turn multiple axle, heavily-loaded bogies with large tires in a tight radius while minimizing sliding the tires in the horizontal (particularly in the lateral) direction, which places high stresses in the suspension, piles up dirt in the field, and causes excessive tire wear.  
           [0012]    Early attempts at an articulated combine are reported in U.S. Pats. Nos. 4,317,326 and 4,414,794. The design capacity is stated to be around 360 bushels. Its unloading mechanism is limited to one side of the combine and steering is accomplished only by articulation steering cylinders. U.S. Pat No. 4,453,614 proposes a steering cylinder arrangement for an articulated combine. U.S. Pat. No. 4,204,386 proposes an articulated machine for gathering vegetables. U.S. Pat. No. 5,857,907 proposes a discharge conveyor having a secondary, variably extending conveyor attached to the terminal end of the discharge conveyor.  
           [0013]    U.S. Pat. No. 6,012,272 (the &#39;272 patent) discloses an articulated combine composed of a forward unit or bogey having an operator&#39;s cab, engine, grain harvesting assembly, grain transfer assembly, but no on-board grain storage; and a rear unit or bogey jointedly attached to the forward unit and having a steerable and powered wheel assembly, an on-board grain storage bin, and a grain off-loading assembly. Many of the industry long-felt, but unsolved needs regarding articulated combines are disclosed in the &#39;272 patent. Basic improvements thereto are the subject of this application.  
         BRIEF SUMMARY OF THE INVENTION  
         [0014]    One aspect of the present invention is a combine having increased on-board grain storage capacity. The combine includes a forward unit having an operator&#39;s cab, an engine, a grain harvesting assembly, a grain transfer assembly, and is devoid of an on-board grain bin. The combine also has a rearward unit jointedly attached to the forward section. The rearward unit has a powered wheel assembly, an onboard grain bin for receiving grain from the forward section grain transfer assembly, and a grain off-loading assembly.  
           [0015]    Another aspect of the present invention is directed to a joint for a powered articulated vehicle, such as a combine for joining a forward unit to a rearward unit. The joint includes an upper frame member carried by the forward unit and having a recess on its lower side and a lower frame member carried by the forward unit, having a recess on its upper side, and being spaced-apart vertically below the upper frame member so that the recesses are in vertical registration. The joint further includes a shaft carried by the rearward unit and a bearing retainer assembly carried by the end of the shaft and disposed between the recesses. The bearing assembly includes an outer annulus surmounting an inner hub which hub is connected to the shaft with thrust bearings inserted between the annulus and said hub, whereby the inner hub co-rotates with shaft with respect to the outer annulus. The bearing assembly also includes a pair of nibs carried by the outer annulus which nibs reside in the upper and lower recesses and which nibs are associated with tapered roller bearings so that the outer annulus co-twists with the shaft respect to the forward unit. Uniquely, the joint is stiff in the vertical plane through the longitudinal axis formed along the forward unit frame members and the rear unit shaft, i.e., around the pitch axis. It will be appreciated that the upper and lower frame members could be carried by the rearward unit and the shaft carried by the forward unit and the novel joint would function the same as with the configuration set forth above.  
           [0016]    A further aspect of the present invention is an improved articulated combine comprising a forward unit connected by a joint to a rearward unit. The improvement for transferring clean grain from the forward unit to the rearward unit includes the rearward unit carrying an onboard grain bin and having a front wall that has a horizontal slot therein. The front wall retains a horizontally elongate grain transfer trough affixed thereto which trough is curved with its center of curvature congruent with the center of articulation of the combine. The trough is in communication with the bin via the slot. The forward unit carries a grain transfer assembly of a fixed elongate discharge chute that empties into the rearward unit trough while the forward and rearward units are being turned about the joint.  
           [0017]    A still further aspect of the present invention is a grain unloading assembly for unloading clean grain from a combine grain bin, wherein a combine harvests grain and cleans it to provide the clean grain. Such grain unloading assembly includes a vertical flighted conveyor that is adapted to operate in either direction. Also included is a housing in which the vertical flighted conveyor is disposed. The housing is fitted at its top with a bin spout, a discharge spout, a moveable door that permits communication of the flighted conveyor either with the bin spout or with the discharge spout. A first opening at the bottom of the housing is covered with a moveable door for permitting grain in the bin to be moved into the housing for conveying by the flighted conveyor. A second opening at its bottom of the housing is for permitting clean grain to be passed into the housing from the combine.  
           [0018]    Yet another aspect of the present invention is an unload assembly for unloading clean grain from a combine grain bin. This unload assembly includes a distal frame nested within a proximal frame. The distal frame is extensible from and retractable into the proximal frame. The distal frame has a discharge end for discharging grain. The proximal frame has a feed end for receiving grain from the grain bin and a distal end from which the nested distal frame extends and retracts. This unload assembly further includes a conveyor system that includes a first fixed pulley located at the feed end of the proximal frame. A second fixed pulley is located at the discharge end of the distal frame. A third fixed pulley is located at the distal end of the proximal frame. A fourth moveable pulley is disposed within the proximal frame intermediate the first and third fixed pulleys. The conveyor extends from the first pulley to the second pulley to the fourth pulley to the third pulley and back to the first pulley.- A fifth pulley may be employed near the first pulley to increase the wrap angle of the conveyor belt around the first pulley. This arrangement permits the conveyor to extend as the distal conveyor extends and retracts as the distal conveyor retracts by movement of the fourth pulley.  
           [0019]    Still a yet further aspect of the present invention is a straw and chaff spreader for mounting in association with a grain cleaner of a combine. This spreader includes a pair of generally horizontally-disposed, outwardly rotating, cleated conveyors disposed to receive straw and chaff discharged from the grain separator and cleaner of a combine.  
           [0020]    A yet further aspect of the present invention is an airbag suspension for a vehicle having a vehicle frame having an axle (stub or through axle) extending therefrom. A longitudinal beam is affixed to the axle that carries at least one wheel. An airbag assembly includes an upper plate extending from the vehicle frame, a lower plate affixed to the longitudinal beam, and an airbag disposed between the upper and lower plates. The lower plate carries a pair of vertical blocks having vertical slots. A pair of cams is carried by the upper plate and rides in the vertical slots.  
           [0021]    Another aspect of the present invention is a steering system for an articulated vehicle having a joint that connects a forward unit and a rearward unit and at least one articulation cylinder to provide a turning force at the joint. The steering system includes an operator speed and direction mechanism whereby an operator can direct the desired direction of the vehicle. A power source is provided for driving pumps adapted to drive motors and cylinders. The forward unit has tractive wheels (tired or tracked) powered by one or more motors. Each motor has a transducer for measuring its rotational speed and direction. The rearward unit has a pair of tractive endless tracks or tired wheels each powered by a separate motor. Each motor has a transducer for measuring its rotational speed. A programmable controller receives the rotational speed measurements (for over-speed control) and pressures from all of the transducers and operator steering commands from the speed and direction mechanism, and responds with suitable outputs. Actuators receive the controller outputs and adjust the output of each of the motors powering the rearward unit tracks/wheels.  
           [0022]    A still further aspect of the present invention is an improved combine having a fuel tank, and which includes an overhead rail from which the fuel tank is suspended and an optional actuator connected to the fuel tank for moving the fuel tank forwardly and rearwardly. Desirably, though, the fuel tank can be moved forwardly and rearwardly by hand.  
           [0023]    A still further aspect of the present invention is a method for articulating an articulated vehicle at a rest position wherein the vehicle is composed of a forward unit and a tracked rearward unit having a pair of powered tracks. The forward and rearward units are connected by a joint and an articulation cylinder. The method powers up only one track while simultaneously actuating the articulation cylinder.  
           [0024]    Advantages of the present invention include a combine design, preferably an articulated combine, which enables grain storage capacity of between 500 and 1,000 bushels or more. Another advantage is an articulated combine which can unload clean grain to either side and which is controlled by a unique control system. A further advantage is a unique steering system for an articulated combine. These and other advantages will be readily apparent to those skilled in this art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:  
         [0026]    [0026]FIG. 1 is a side elevational view of the novel combine (or harvester) with, inter alia, extra large storage capacity, straw and chaff conveyor, novel joint, clean grain transfer ability, and unloading capacity;  
         [0027]    [0027]FIG. 2 is a side elevational view of the other side of the novel combine depicted in FIG. 1. fitted with caster wheels at the rear of the front unit;  
         [0028]    [0028]FIG. 3 is an overhead view of the combine depicted in FIG. 1;  
         [0029]    [0029]FIG. 4 is a rear view of the rear unit of the combine depicted in FIG. 1;  
         [0030]    [0030]FIG. 5 is a sectional view taken along line  5 - 5  of FIG. 1;  
         [0031]    [0031]FIG. 6 is a sectional view taken along line  66  of FIG. 5 showing a plan view in greater detail of joint  22 ;  
         [0032]    [0032]FIG. 7 is a sectional view taken along line  7 - 7  of FIG. 6;  
         [0033]    [0033]FIG. 8 is a sectional view like that taken along line  7 - 7 , but of a preferred embodiment of the joint of FIG. 6;  
         [0034]    [0034]FIG. 9 is a sectional view taken along line  9 - 9  of FIG. 8;  
         [0035]    [0035]FIG. 10 is an overhead view of the straw and chaff conveyor system fitted at the rear of the front unit of the novel combine;  
         [0036]    [0036]FIG. 11 is a side cut-away view of the rear unit of the novel combine showing the grain transfer system between the front and rear units and the grain handling system aboard the rear grain bin unit;  
         [0037]    [0037]FIG. 12 is a rear cut-away view of the rear unit of the novel combine showing part of the grain handling system aboard the rear grain bin unit;  
         [0038]    [0038]FIG. 13 is a side cut-away view of the hydraulic nested grain off-loading assembly in its retracted position;  
         [0039]    [0039]FIG. 14 is a side cut-away view of the hydraulic nested grain off-loading assembly in its extended position;  
         [0040]    [0040]FIG. 15 is a partial side elevational view of a joystick used to control the clean grain transfer assembly depicted in FIGS. 13 and 14;  
         [0041]    [0041]FIG. 16 is a top view of the joystick shown in FIG. 15;  
         [0042]    [0042]FIG. 17 is a schematic of the hydraulic vertical control for the clean grain transfer assembly of FIGS. 13 and 14;  
         [0043]    [0043]FIG. 18 is a schematic of the hydraulic swing control for the clean grain transfer assembly of FIGS. 13 and 14;  
         [0044]    [0044]FIG. 19 is a schematic of the hydraulic telescoping control for the clean grain transfer assembly of FIGS. 13 and 14;  
         [0045]    [0045]FIG. 20 is a schematic of the hydraulic speed control for the clean grain transfer assembly of FIGS. 13 and 14;  
         [0046]    [0046]FIG. 21 is a side elevational view of the novel suspension system of the rear grain bin unit;  
         [0047]    [0047]FIG. 22 is a sectional view taken along line  22 - 22  of FIG. 15;  
         [0048]    [0048]FIG. 23 is a sectional view taken along line  21 - 21  of FIG. 15;  
         [0049]    [0049]FIG. 24 is a side elevational view of a combine like that depicted in FIG. 1, except that the rear unit is wheeled rather than fitted with an endless track;  
         [0050]    [0050]FIG. 25 is a rear elevational view of the combine in FIG. 24;  
         [0051]    [0051]FIG. 26 is an overhead view of the combine in FIG. 24;  
         [0052]    [0052]FIG. 27 is a partial sectional view of the suspension system of the combine in FIG. 24;  
         [0053]    [0053]FIG. 28 is a simplified overhead schematic of the turning geometry for a wheeled rear unit embodiment of the present invention; and  
         [0054]    [0054]FIG. 29 is a schematic of the hydraulic steering system for the novel articulated combine. 
     
    
       [0055]    The drawings will be described in detail below.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0056]    The present invention provides basic improvements to the &#39;272 patent articulated combine, which disclosed solutions to many problems associated with modem farming combines by providing a harvester that can unload readily on either side and to virtually any height road truck. The disclosed harvester retains the increased capacity of harvested grain carrying capacity from about 200-300 bushels in conventional combines to about 500-1,200 bushels utilizing the rearward-only grain bin, because the rearward unit has more capacity (space) than there is in a grain bin located over a front axle. This is important because the capacity of a typical road semi-trailer is 1,000 bushels. This means that the disclosed combine can fill an entire road truck from its on-board grain bin in a single unloading. Moreover, a unique, unloading system permits unloading of clean grain from the rearward grain bin unit out to either side of the combine. Such increased grain storage capacity is possible because the grain bin is located on the rearward unit, which permits a much lower center of gravity to be designed into the rearward unit.  
         [0057]    In order to ensure that the extra weight can be easily maneuvered by the novel harvester, the rearward unit has powered and steerable wheels that are supported by a unique airbag suspension system. A new dean grain transfer assembly for transferring clean grain from the forward unit to the rearward cart bin unit also is disclosed. An improved two-axis joint interconnects the forward and rearward units. Straw and chaff from the harvesting assembly is discharged to either side by a unique dual conveyor system. “Wheels” or “wheeled” for present purposes includes both wheels that are fitted with tires (pneumatic tires) and wheels that are fitted with endless tracks.  
         [0058]    Referring initially to FIGS. 1, 2 and  3 , innovative combine  10  generally includes forward unit  12  and rearward unit  14 . Forward unit  12  is seen to include cab  15  in which the operator is seated, cornhead or small grainhead  16 , engine compartment  18  (two cooling fan air inlets shown in the drawings), and powered non-steerable wheel pair  20 . In the alternative embodiment in FIG. 2, forward unit  12  is fitted with caster wheel pair  19  located at the rear of forward unit  12 . Rearward unit  14  is interconnected to forward unit  12  via joint assembly  22  and clean grain is transferred from forward unit  12  to rearward unit  14  via clean grain transfer assembly  24 . Rearward unit  14  is seen to include clean grain unloading system  26  in its stored position and in phantom in two possible raised unloading positions in FIG. 3, grain bin  28 , and powered endless tracks  30  and  32 . Use of a dual track system supporting grain bin  28  on rearward unit  14  contributes to the capability of grain bin  28  holding upwards to 1,200 bushels of grain. Providing the grain bin capacity only on rearward unit  14  translates into a lower center of gravity for grain bin  28  which also enables such higher storage capacity and provides more even weight distribution per axle. Importantly, at about 600-650 bushel capacity of grain bin  28 , combine  10  could harvest, for example, a cornfield for one mile before unloading. Capacity in excess of requirement means that combine  10  can harvest for even greater distances before unloading.  
         [0059]    As seen in FIG. 2, fuel tank  34  is carried suspended by rail  36  and is moveable from a forward to a rearward position as indicated by arrow  38 . Movement of suspended fuel tank  34  ensures access to, for example, hydraulic lines and other components should such access be necessary, desirable, or convenient. Such fuel tank movement also enables weight shifting of forward unit  12 , should such weight shifting also be necessary, desirable, or convenient.  
         [0060]    As seen in FIG. 4, grain bin  28  is fitted with ladder  40  for operator access to the interior of grain bin  28 . Grain bin  28  also is fitted a pair of light arrays,  42  and  44 , as the combine may traverse roadways in order to access field to harvest. Other items of interest in this rear view of the combine will be discussed later in connection with other features of the novel articulated combine.  
         [0061]    Referring to FIGS. 5, 6 and  7  that illustrate joint  22 , initially, it will be observed that a pair of steering cylinders,  46  and  48 , are seen in FIG. 5 to connect forward unit  12  to rearward unit  14  of articulated combine  10 . Such steering cylinders are conventionally used to assist in the steering of articulated vehicles and are provided here for such steering use in the present articulated combine design. Now, with respect to the two-axis joint, pipe  50  is attached to rearward unit  14  at one end and is constructed as a round pipe or structural tube. Shaft  52  extends from pipe  50  towards forward unit  12  and is inserted into bearing retainer assembly  60  which is inserted between upper frame member  54  and lower frame member  56 . These frame members  54  and  56  are bolted to forward unit  12  via bolts  58   a - d ; although, other attachment means certainly can be envisioned. Each frame member  54  and  56  has an inner recess that confronts the corresponding recess in the other and into which is inserted bearing retainer assembly  60 .  
         [0062]    Bearing retainer assembly  60  has a pair of nibs or ears which fit into frame member  54  and  56  recesses and which ride on tapered roller bearing  62   a - 62   b  to provide sideways movement to units  12  and  14  via pipe  50 . Such sideways movement permits combine  10  to be steered. A hole penetrates through bearing retainer assembly  60  into which a reduced-diameter threaded end of shaft  52  fits and is secured via nut  64 . Now, thrust bearings  66  and  68  fit into counterbores that adjoin the hole through bearing retainer assembly  60  and which thrust bearings permit shaft  52  to rotate and which, thus, enables units  12  and  14  to rotate with respect to each other. Such rotation permits units  12  and  14  to traverse uneven terrain during harvesting or other movement of combine  10 . Note, however, that pipe  50  and shaft  52  are not permitted to move in a vertical direction due to the unique construction of joint assembly  22 . Thus, a unique dual axis joint has been disclosed. I should be understood that the connection of joint  22  could be the reverse of that connection depicted in FIGS. 5, 6, and  7 . That is, pipe  50  could be attached to forward unit  12  rather than rearward unit  14 .  
         [0063]    A modified version of the joint depicted in FIGS. 6 and 7 has now been designed and is illustrated in FIGS. 8 and 9. It utilizes the features of joint  22  of FIGS. 6 and 7, except that additional thrust bearings have been added to take up the additional separational forces that joint  22  sees due to taped roller bearings  62  and  66 . Also, the joint in FIGS. 8 and 9 has been rotated 180° so shaft  52  now is connected to forward unit  12 , rather than to rearward unit  14  via pipe  50 , as is shown in FIGS. 6 and 7. Also, frame members  54  and  56  are removably attached to frame member  59  that is connected to rear unit  14 . Additionally, spacers  51  are held in place by threaded bolts  53  and  55 , which fit through holes in frame members  54  and  56 , respectively. The basic construction of the joint in FIGS. 8 and 9 is like that for joint  22 , except that frame members  54 / 56  have apertures into which flanged plug assemblies  70  and  72  are placed and held securely by threaded members  74  and  76 , respectively. Recesses adjacent the apertures in frame members  54 / 56  contain races into which thrust bearings  78  and  80 , respectively fit and are retained by the flared heads of flanged plugs  70  and  72 . Flanged plug assemblies  70  and  72  include spacers (not shown in the drawings) to ensure that tapered roller bearings  62  and  66  are not excessively pre-loaded when flanged plugs  70  and  72  are tightened and washers (not shown in the drawings) are provided for the flanges of plugs  70  and  72  to bear against when tightened.  
         [0064]    Regarding to the novel two-axis joint as disclosed in the &#39;272 patent, unique to joint  22  is that it is a “single point” joint. That is, joint  22  is designed to be only about a foot or so high. No other structural connection between forward unit  12  and rearward unit  14  is required by dint of the design of joint  22 . That is not to say that other structural connection cannot be made between forward unit  12  and rearward unit  14 , but that no other structural connection is necessary. In fact, it is a positive advantage that no other structural interconnection is needed between the two units because the combine designer has greater flexibility in locating equipment, lines, feeders, etc. because of the single point joint design disclosed herein.  
         [0065]    Referring now to FIG. 10, the description will commence with the transfer of clean grain from forward unit  12  to grain bin  28  and will be completed with off-loading of the grain into, e.g., a semi-truck. In this regard, clean grain and straw and chaff separately exit from grain cleaner assembly  82  (which is quite conventional). The straw and chaff falls down onto dual conveyors  84  and  86  that are separately driven by hydraulic motors  88  and  90 , respectively. Alternatively, conveyors  84  and  86  could be driven by a single motor with appropriate gearing, belts, or the like, providing for the movement of the non-driven conveyor either in the same direction or in the opposite direction from the driven conveyor. Conveyors  84 / 86  also can be seen in FIGS.  1 - 3  to be located above joint assembly  22 . In normal operation where combine  10  is traveling through the field harvesting grain, conveyors  84  and  86  each rotate so as to throw the straw and chaff outwardly from combine  10 . During a turn, it may be advantageous to not bunch up straw and chaff under the rear wheels of rearward unit  14 , so both conveyors can be set to throw the straw and chaff to the side of combine  10  that is opposite the direction of the turn. Since conveyors  84 / 86  desirably are separately powered, they can be rotated in the same direction or in opposite directions. Regardless of the direction of their turning, conveyors  84 / 86  ensure that the straw and chaff will not fall down on joint assembly  22  nor bunch up directly underneath combine  10  for rearward unit  14  to traverse over.  
         [0066]    The clean grain from the grain cleaning operation aboard forward unit  12  travels to clean grain transfer assembly  24  (see FIGS.  1 - 3  and  11 ). Referring especially to FIG. 11, it will be observed that clean grain passes down fixed elongate discharge chute  92  into elongate horizontal trough  94  that is connected to the forward wall of grain bin  28 . From FIG. 3, it can be seen that the front of trough  94  is curved (or arcuate) to match the radius of curvature of articulation of combine  10 . Such curvature ensures that fixed chute  92  always will empty clean grain into trough  94  even while combine  10  is turning (articulating). Now front wall  96  of grain bin  28  has slot  98  that permits clean grain in trough  94  to be passed to the inside (or cavity) of bin  28 . The design of clean grain transfer assembly  24  is simple in that gravity is used to feed the clean grain from forward unit  12  into trough  94  via chute  92 . Gravity also ensures that the clean grain in trough  94  passes through slot  98  into grain bin  28 .  
         [0067]    The clean grain passing through slot  98  enters vertical conveyor system  100  that passes the clean grain into bin  28  and also to clean grain off-loading assembly  26 . As such, vertical conveyor assembly  100  is central to proper grain handling within grain bin  28 . To that end, vertical conveyor system  100  includes flighted (paddled) conveyor  102  disposed within housing assembly  104 . Conveyor  102  is driven by hydraulic motor  106  (see FIG. 4) and its direction is reversible and its speed is variable. At the top of conveyor assembly  100  are a pair of discharge chutes,  108  and  110  (which will be described later). Moveable door  112  powered by hydraulic cylinder  115  (see FIG. 2) permits clean grain to be discharged either by chute  108 , chute  110  or both with the direction of conveyor  102  being coordinated with the position of door  112 . With door  112  in the position shown in FIG. 11, conveyor  112  would be set to rotate in the counterclockwise direction by motor  106  (the direction of rotation is given with respect to FIG. 11, as direction of movement is determined by the position of the observer). Grain entering housing  104  via slot  98  would be discharged into grain bin  28 . When door  112  is moved into the dashed line position and the direction of conveyor  102  reversed, grain would be discharged through chute  110  into unload assembly  26 , which will described in detail below. It is possible to unload bin  28  while harvesting as also will be described below. Due to all the grain being dumped into bin  28  through chute  110 , top leveling augers also can be provided to even out the clean grain stored in grain bin  28 .  
         [0068]    To continue with the flow of clean grain, once clean grain enters bin  28 , it is stored there until it is required to be discharged. Referring to FIGS. 3, 5,  11 , and  12 , the first step is clean grain discharge commences with a unique floor design that includes drag paddles  114  and  116  that are powered by hydraulic motor  118  (see FIG. 4) that can be accessed via door  120  at the rear of grain bin  28 . Drag paddles  114 / 116  essentially create a fluidized bed of grain that is fed from bin  28  through moveable door  122  that is powered by hydraulic cylinder  124  (see FIG. 11) and into housing  104 . It will be appreciated that augers or the like could replace drag paddles  114 / 116 ; although, the flatness of paddles permits bin  28  to have a flat floor which increases the grain capacity of bin  28 . In order to prevent the grain in bin  28  from stopping the movement of drag paddles  114 / 116  and in order to meter grain to such drag paddles, adjustable inverted-V floor assembly  126  is stationed just above drag paddles  114 / 116  (see FIGS. 3 and 12). Moveable doors or the like could substitute therefor. It will be appreciated that each inverted-V (e.g., V  128 ) retains a pair of adjustable louvers (e.g., louvers  130  and  132 ) that can finely adjust the openings between each inverted-V. Such louver arrangement provides for precise metering of grain from bin  28  to drag paddles  114 / 116 . Louvers  130 / 132  can be adjusted manually; although, hydraulic adjustment could be provided.  
         [0069]    Now that drag paddles have pulled/pushed the clean grain into housing  104 , if conveyor  102  rotated in a clockwise direction with door  112  actuated to the dashed line position (i.e., chute  108  closed and chute  110  open), then clean grain in bin  28  will be conveyed by conveyor  102  up through housing  104  and be discharged via chute  110  onto clean grain unloading system  26 . Should combine  10  be harvesting field grain while off-loading is progressing, then not only will grain housed within grain bin  28  be off-loaded (unloaded), but so too will clean grain entering housing  104  via slot  98  from grain transfer system  24 . Thus, the novel combine has the capability of harvesting and unloading grain concurrently. Once clean grain in grain bin  28  has been off-loaded, door  112  is moved to its position as shown in FIG. 11 and conveyor  102  reversed in its direction of travel to then throw clean grain back into bin  28 .  
         [0070]    Clean grain unloading system  26  (see FIGS. 2 and 13) includes nested conveyor assembly  134 , which includes distal frame  136  with grain chute  137  nested within proximal frame  138 . Housed within frames  136 / 138  is cleated (or flighted) endless conveyor belt  140 . Nested conveyor assembly  134  rests on cradle  142  that is formed from a shaft (not seen in the drawings) and rollers, such as roller  144  (see FIG. 3). Cradle  142  permits the nested conveyor assembly  134  to move along its longitudinal axis with respect to cradle  142  when combine  10  articulates. Rotational power is not supplied to conveyor assembly  134  when no clean grain unloading is taking place so that it is in a float or relaxed mode; thus, permitting conveyor assembly  134  to be rotated by cradle  142  when combine  10  articulates. Chute  110  transfers clean grain through an aperture in proximal housing  138  directly above the pivot point, pivot assembly  146  (see FIGS. 13 and 14), for conveyor assembly  134  so that the transfer location does not change as the conveyor rotates from side to side during unloading.  
         [0071]    Nested conveyor assembly  134  is lifted by pistons  148  and  150 , which are attached to cable  152  that runs through snatch block  154  which in turn is connected to rearward unit  14  by frame assembly  156  (see FIGS. 2 and 3). Such lifting mechanism also has its pivot point in line with the axis of rotation of conveyor assembly  134  so that conveyor assembly  134  does not change height as it is rotated from side to side, such as is shown in phantom in FIG. 3. Such lifting mechanism&#39;s connection to rearward unit  14  is moment decoupled to prevent conveyor assembly  134  from twisting as it rotates by means of the universal attachment of snatch block  154  which is permitted to move in all three axes. Alternatively, rod end Heim joints could be placed at the ends of an adjustable rod in place of cable  152 .  
         [0072]    Referring to FIGS. 2, 11,  13 , and  14 , nested conveyor assembly  134  is rotated from side-to-side by wheel or sprocket  158  that is supported by shaft  159  for rotation of sprocket  158 , a chain that encircles sprocket  158  (not readily seen in the drawings), and hydraulic motor  160  which pulls the chain through a small sprocket (also not readily seen in the drawings). Conveyor assembly  134  is supported by pivot assembly  146 , which permits conveyor assembly  134  to be inclined upwards. The center of wheel  158  establishes both the axis of rotation and the axis of inclination of conveyor assembly  134 . Pivot assembly  146  includes a shaft disposed vertically through its center hub, which shaft is supported by an outer hub that is tied to rearward unit  14  via structure  162 . Additional structural stability and support (not shown in the drawings) for wheel  158  is provided by cam follower-type rollers that are disposed under the periphery of wheel  158  and tied to structure  162 . This additional support can be helpful as the conveyor rotates which causes a torque load to be introduced into the center support shaft at various angles.  
         [0073]    Endless conveyor  140  is driven by hydraulic motor  164  (see FIG. 2), which connects to drive pulley  166  (see FIGS. 13 and 14). From fixed drive pulley  166 , belt  140  goes to stationary pulley  168  located in distal frame  136 , back to moveable pulley  170 , to fixed pulley  172 , to idler pulley  174 , and back to drive pulley  166 . Note that moveable pulley  170  is located between fixed pulleys  166  and  172 . As distal frame  136  is extended from proximal frame  138  by hydraulic motor  151  associated with pinion  153  and rack  155 , pulley  170 , which otherwise is biased inwardly, moves from a position such as is illustrated in FIG. 13 to a position such as is illustrated in FIG. 14. Hydraulic motor  151  is mounted at the distal end of proximal frame  138  along with pinion  153 . Rack  155  is mounted at the proximal end of distal frame  136  and is driven by pinion  153  to extend/retract distal frame  136 . Chute  137  in turn extends from its home position to an extended position so that clean grain can be unloaded, for example, into a waiting semi-trailer. Frames  136  and  138  preferably are shrouded or covered to aid in grain retention during operation of belt  140 .  
         [0074]    With respect to operation of clean grain unloading system  26 , reference is made to FIGS. 15 and 16 which show the unique joystick control system of the &#39;272 patent which can be adapted to control the present unloading system. Initially, joystick  200  is fitted with finger toggle switches  202 ,  204 ,  206 , and button  208 . The operator&#39;s fingers activate toggle switch  202  that causes unloading system  26  to move vertically up and down. Switch  204  conveniently is thumb activated and is an on-off switch for unloading system  26 . Switch  206  is a combine inching switch; that is, it causes combine  10  to move slowly forward or backward to place spout  137  exactly where the operator desires. Such slow movement is known as “inching” in this field. Button  208  is a “home” button that means that unloading system  26  is returned to its stored position as shown in FIG. 3, for example.  
         [0075]    Another capability of joystick  200  is that it can move forward, backward, and laterally left and right. These movements cause unloading system  26  to extend (say, forward movement of joystick  200 ), retract (backward movement), swing to the left (left movement), and swing to the right (right movement). Finally, joystick  200  is rotatable to control the speed of the belt  140  of unloading system  26 .  
         [0076]    Joystick  200  accomplishes the described movements of unloading system  26  by signaling electrohydraulic valves with a signal sent to manually adjustable flow control valves for, say, movement of unloading system  26  up/down, left/right, in/out, and home. Joystick  200  signals a proportional servo valve for on/off and conveyor speed (e.g., activates a linear electric servo that moves a pump swash plate). Joystick  200  signals the propulsion system of combine  10  in order to inch the combine forward or reverse by by-passing the normal operator speed control of the vehicle. It should be obvious that the novel combine takes advantage of the hydraulic system already in place in conventional combines and extends their use in order to power desirably the unloading system  26  and tracks  30  and  32 . Other power means, of course, could be employed; however, hydraulic power tends to be more reliable.  
         [0077]    In the unloading or off-loading mode, belt  140  always is actuated first and turned off last in order to minimize any plugging problems. Next, the direction of vertical conveyor  102  is reversed from the grain harvesting mode and its speed is increased. Door  122  is opened and grain fed by gravity to conveyor  102  until a sensor indicates that the amount of gravity fed grain slows down. At this point, drag paddles  114 / 116  are activated to feed conveyor  102 .  
         [0078]    Implementation of such joystick movements of unloading system  26  is displayed in FIGS.  17 - 19 . Referring initially to FIG. 17, lines  210  and  212  are connected to a source of voltage (say,  12  volts supplied by the combine). Contacts  214  and  216  are joystick  200  contacts for raising and lowering, respectively, conveyor assembly  134  of unloading system  26 . Ground  217  is provided in conventional fashion. Upon closure of one of joystick contacts  214  or  216 , bi-directional valve with adjustable flow  218  is fed hydraulic fluid at, say, 2,000 psi from a hydraulic pump which feeds rod and cylinder assemblies (pistons)  148 / 150  via lines  220  and  222  with oil returned to reservoir  224  via line  226 . Assembly  134 , then, raises and lowers unloading system  26  (conveyor assembly  134 ).  
         [0079]    Referring to FIG. 18, lines  228  and  230  run to joystick contacts  232  and  234  which actuate bi-directional valve with adjustable flow and float  236  which actuates motor  160  for swinging unloading system  26  either left or right. Ground  238  and return line  239  to reservoir  224  are provided in conventional fashion. A rod and cylinder or other means could be substituted for motor  160 .  
         [0080]    Referring to FIG. 19, lines  240  and  242  run to joystick contacts  244  and  246  which actuate bi-directional two flow valve (slow/fast speed)  248  which actuates motor  151  for extending distal frame  136  from its nested position within frame  138 . Ground  250  and return line  254  to reservoir  224  are conventionally provided. A rod and cylinder or other means could be substituted for motor  151 .  
         [0081]    Referring to FIG. 20, the unload system speed control is shown. Specifically, combine engine  256  is connected via line  258  to pump  260 , which is a variable displacement pump. Pump  258  is in fluid (oil or hydraulic fluid) communication with motor  106 , which runs vertical conveyor assembly  102 , via lines  262  and  264  that form a hydrostatic loop. Pump  260  is controller/actuated via joystick  200  as follows. Line  266  runs through on/off switch  268  and combine speed potentiometer  270  (actuated by joystick  200 ) to servo controller  272 , which in turn is connected via line  274  to servo actuator  276  that is connected to pump  260  via line  278  for moving the swash plate of pump  260  to control the speed and direction of vertical conveyor assembly  102  via motor  106 . Line  280  runs through on-off switch  282  and unload speed potentiometer  284  to servo controller  272  (also actuated by joystick  200 ). Now, line on/off switch  268  is on (and switch  282  off) when combine  10  is not in an unloading mode, i.e., the combine is idle or harvesting grain. Switch  282  is turned on (and switch  268  off) when the operator desires to off-load grain from combine  10 . In this manner, the operator can control the speed of vertical conveyor assembly  102  via motor  106 . It will be appreciated that the function of switches  268  and  282  could be combined into a single switch unit.  
         [0082]    When the operator desires to off-load grain from grain bin  28 , the operator also needs to control drag paddles  114 - 1116  and belt  140 . This is accomplished via on/off switch  281  (controlled by joystick  200 ) in line  283  that runs to solenoid-operated valve  284  that is disposed in line  286 . Valve  284  is actuated by pump  288  that is powered by engine  256  via line  290 . Now, line  286  from valve  284  runs to hydraulic motor  164 , which runs belt  140 , with the oil in line  286  returning to tank  292 . On/off switch  294  (also controlled by joystick  200 ) in line  295  runs to solenoid-operated valve  293  that is disposed in line  291  that branches from line  286 . Line  291  runs to hydraulic motor  118  that runs drag paddles  114 - 116 , with the oil returning to tank  292 . At this point in the description it should be noted that reservoir  224  is notated on the drawings as the reservoir for all hydraulic fluid circuits. Obviously, additional reservoirs could be used as is necessary, desirable, or convenient.  
         [0083]    The novel airbag suspension system now will be described with specific reference to FIGS.  21 - 23  for an endless track system; although, such airbag suspension system can be adapted for tired wheels (see FIGS.  24 - 27  and the description thereof) and for a variety of articulated vehicles (e.g., other farm vehicles, earth moving equipment (bull dozers, excavators, cranes), buses, mining equipment, etc.) in addition to combines. Endless track system  298  generally includes endless metallic sectioned or rubber traction belt  30  is seen to be mounted around drive wheel  300  (wheel and hydraulic motor assembly) and idler wheel  302 . Additional intermediate idler wheels  304 - 312  are conventional in use, location, and function, and generally ensure contact of track  30  with the ground. Track system  298  is connected to frame member  314  of grain bin  28  (see FIG. 12) by stub axle  316 . Another endless track system  296  (see FIG. 23) is disposed opposite track system  298 , but will not be described in detail herein as it is a mirror image of track system  298 . Track system  296  is supported by frame  315  as seen in FIG. 12.  
         [0084]    Each track system  296 / 298  has a pair of airbag suspension systems, e.g.,  318  and  320  airbag systems (nominal rating of, e.g., 10,000 pounds) for track system  298 . Referring specifically to airbag system  320 , airbag  322  will be seen to be retained by upper plate member  324  that is connected to frame member  314  and rests on lower plate assembly  326 . Lower plate assembly  326  is connected to walking beam  328 , which is supported by stub axle  316 . Lower plate assembly  326  has a pair of upstanding forward and rearward members,  330  and  332 . Each upstanding member  330 / 332  has a race or slot in which rides a cam follower, e.g., cam follower  334  for upstanding member  330 . Cam follower  334  (and the other cams not visible in the drawings) are connected to upper plate member  324  are free to move vertically, but are restrained from moving horizontally. Thus, the cam followers dramatically reduce the large moment in the axle caused by the tracks sliding as combine  10  turns. Note should be taken that while stub axle  316  can be located at the longitudinal center of grain bin  28 , it may be advantageous to locate it forward of such center of gravity so that grain bin  28  always is lifting up on joint  22 . Also, walking beam  328  with its mounting only by stub axle  316  permits about a 12 inch rise and fall of each of its ends, i.e., wheels  300  and  302  can move ±12 inches to accommodate uneven terrain.  
         [0085]    The same type of airbag suspension system can be adapted for tired wheels as was described for tracked wheels. Reference is made to FIG. 24 in this regard whereat articulated combine  350  is shown to have its rearward unit  352  supported by tired wheels  354  and  356  on one side, and on the other side by tired wheels  358  and  360  (see also FIGS. 25 and 26). Each tired wheel  354 / 356 / 358 / 360  is separately powered by a hydraulic motor  362 / 364 / 366 / 368 , respectively. Each forward tired wheel also is designed to be turned about 15° by a hydraulic cylinder arrangement as seen in FIG. 26 wherein cylinder  394  is seen connected from beam  384  to knuckle  396  for tired wheel  358  and cylinder  397  is seen connected from beam  382  to knuckle  398 . Cylinders  394  and  397  are hydraulically actuated and can be integrated into the steering system of combine  10 .  
         [0086]    Tired wheels  356  and  358  are joined together by tie rod assembly  391 , which connects knuckle  396  with knuckle  398 . Tie rod assembly  391  passes through grain bin  28  at about its center, that is, where beams  382  and  384  are attached to axles  378  and  380 , respectively, in order to minimize the affect that the ups and downs that tired wheels  356  and  358  would generate as combine  10  traversed over uneven ground. Finally, spring assemblies  393  and  395  are mounted in associated with tired wheels  360  and  354 , respectively, and bias tired wheels  360  and  354  to a neutral or straight-ahead configuration. Tired wheels  360  and  354  are permitted to rotate slightly during a turn of combine  10  and spring assemblies  393  and  395  return the wheels to a straight-ahead position.  
         [0087]    The reason for permitting rear tired wheels  354  and  360  to “free-wheel” rotate slightly during a turning of front tired wheels  356  and  358  is due to the geometry of turning an articulated vehicle. This can be seen by referring to FIG. 28 wherein an overhead simplified schematic of combine  350  is seen to include forward unit  351 , having one set of wheels, and rearward unit  352 , have two pairs of wheels. Now, during a turn of articulated combine  350 , each set of wheels must be on an arc that meets at center  502  of the radius of the turn. The corresponding radii for each set of wheels are identified by radius  504  for the wheels of forward unit  351 , radius  506  for tired wheel  358 , radius  508  for tired wheel  356 , radius  510  for tired wheel  360 , and radius  512  for tired wheel  354 . One consequence of the turning geometry is permitting rear tired wheels  354  and  360  to rotate slightly to conform to the turning radius, with spring assemblies  393  and  395  biasing them back into a straight position. Another consequence is that front tired wheels  356  and  358  can be turned along the same radius and still an acceptable turning scheme would be present; although, their radii are slightly different. Structuring a steering control system, then, accommodates the turning geometry illustrated in FIG. 28.  
         [0088]    The airbag suspension system still is used; albeit in a slightly modified condition. That is, airbags  370 / 372 / 374 / 376  are retained by frames and utilize cam follower assemblies,  386 ,  388 ,  390 , and  392 , as described above. Stub axles  378  and  380  support walking beams  382  and  384 , respectively, which in turn support the airbag assemblies. Thus, each tired wheel  354 / 3561358 / 360  has the ability to rise and fall, for example, ±12 inches, to accommodate uneven terrain. FIG. 27 illustrates such construction in greater detail and taken in conjunction with FIG. 26. The remainder of operation of articulated combine  350  is the same as described above with respect to articulated combine  10 .  
         [0089]    Now, with respect to steering and controlling articulated combine  10 , several unique problems are encountered. Prior art articulated vehicles typically use hydraulic cylinders mounted across the articulation joint to produce steering force. The cylinders are controlled by a rotary valve mechanically connected to a steering wheel that is positioned by the operator to achieve the desired turn or vehicle direction. This system is used primarily on wheeled (tired) vehicles that have one axle in front of the joint and one behind the joint, such as an agricultural tractor; or two axles behind the joint, such as a mining truck. Typically, the wheels on the axle, which are powered, are connected together and receive power from a mechanical differential. The differential permits a speed difference to be created between the two tired wheels which speed difference is required to turn with a reasonable amount of force from the articulation cylinders. To initiate a turn in such an articulated vehicle, its also is necessary to slide or rotate the portion of the tires that are in contact with the ground or supporting surface. This generally is feasible since the contact patch or portion of the tire diameter in contact with the supporting surface generally is relatively small with respect to the diameter and width of the tires. Such tire sliding or rotating usually can be accomplished with a reasonable amount of force from the steering cylinders at the articulation joint.  
         [0090]    In an articulated combine wherein the rear module is supported by endless tracks powered by individual motors, such as is disclosed in application Ser. No. 09/210,331, cited above, the steering forces are quite different from the tired vehicle just described. The endless tracks provide a much larger contact patch than do tires and, therefore, a much higher resistance to sliding or rotating them is encountered when a turn is initiated. The contact patch area also is elongated, which further increases the force required from the articulation cylinders to initiate a vehicle turn and to recover from a turn, which maneuver also requires sliding of the tracks laterally to position the vehicle in a straight alignment.  
         [0091]    The steering forces are increased further when individual motors are used to power the tracks, rather than a single motor and a mechanical differential to interconnect the two tracks. When individual motors on each track are used, such motors typically receive hydraulic power from a common supply, whether such supply is one pump or two pumps that are interconnected at their output ports. The common supply is necessary in a conventional system to ensure that the motors will share the propulsion load since they are mechanically interconnected by the supporting surface under the vehicle. The common supply provides the same pressure to all motors, which means that each motor will produce the same torque or thrust when the system is in equilibrium and the vehicle is moving in a straight line. In order to initiate a turn, the steering cylinders must provide sufficient force to change the arc of travel of the tracks and establish an inside track and an outside track relationship that establishes a speed differential between the two tracks. The cylinders must overcome the natural tendency of the motors to run at the same speed and to share equally the tractive effort required to move the vehicle. The cylinders must force an articulation angle that forces a portion of the tractive load to move to the inside track, which causes the pressure to go down in the outside track due to its mandated increase in speed. Hydraulic fluid flow to the outside track motor increases immediately following the path of least resistance until the pressure in the two motors equalizes. This process occurs any time the articulation angle changes during a turn of the vehicle. The steering cylinders, therefore, must not only have sufficient force to slide or rotate the tracks, but also to create a backpressure differential between the two motors. The motors, thus, are resisting both the initiation of a turn and a recovery from a turn.  
         [0092]    The described problem can be reduced by using the differential steering techniques in conjunction with articulation cylinders as disclosed in application Ser. No. 091210,331, cited above. An implementation of such improved technique is described below in connection with FIG. 29.  
       System Elements  
       [0093]    A power source, which typically is an internal combustion engine disposed in forward unit  12  and which drives hydraulic pumps, which in turn function as a controlled source of power for hydraulic motors and cylinders.  
         [0094]    A support and tractive means on the front unit (e.g., wheel pair  20 ) powered by a hydraulic motor driving through a mechanical differential; although, use of individually driven tracks and tires can be used.  
         [0095]    An articulation joint (e.g., articulation joint assembly  22 ) that includes at least one articulation cylinder and rod assembly (e.g., hydraulic cylinder  46  or  48 ) to provide turning force wherein the cylinder is powered by a steering valve directing the flow from a hydraulic pump. The steering valve is controlled by the operator using a steering device, such as a wheel, or can be controlled by an automatic guidance system.  
         [0096]    A support and tractive means for rearward unit  14  (e.g., endless track assembly  298 ). Usually, there are two such track assemblies separately and independently powered by individual hydraulic motors, which receive power from a pair of hydraulic pumps, each dedicated to a single hydraulic motor. Each motor includes a transducer or sensor that measures the rotational speed of the motor and provides that information to a control system.  
         [0097]    A programmable controller (e.g., CPU), which receives steering and propulsion information from measurement transducers, performs preprogrammed or adaptive logic functions, and directs propulsion and steering elements to implement the vehicle maneuvers commanded by the operator or automatic guidance system.  
         [0098]    An actuator, which receives commands form the programmable controllers and adjusts the output of the hydraulic pumps powering endless track assembly  298  (and a similar assembly on the other side of rearward unit  14 ) to cause the motors to execute the operator&#39;s desired vehicle maneuvers. These actuators typically are digital stepping motors that are adjusting the pump mechanism, which sets its output. In a typical hydrostatic pump, this mechanism is called a swash plate, which sets the stroke of the pistons that determines the output flow of the pump.  
       System Characteristics  
       [0099]    Motor speed is determined by the oil flow rate from the pump.  
         [0100]    Motor torque is determined by the pressure applied to it up to the setting on the relief valve, which opens at a preset pressure and allows hydraulic fluid to bypass the motor and flow back to the reservoir.  
         [0101]    The load the motor is seeing at any point in time determines the pressure in the hydrostatic pump/motor loop. The swash plate in the pump is establishing a flow rate to the motor. The pump will attempt to always maintain that flow rate and the pressure rises or subsides as needed to keep the motor rotating at a speed to accept that flow.  
         [0102]    It is, therefore, possible to make multiple motors load share or accept a disproportionate share of the total system load by controlling the pressure of the hydraulic fluid flowing to them. This assumes that traction will allow the load share or shift to occur, which dictates a speed limiting control loop since the individual pumps are not cross-connected. If the motor is speeded up by increasing the pressure to it in order for the motor to take on a greater load and the track powered by such motor cannot achieve sufficient traction, the motor will overspeed. The only controllable variable in the pump is flow by changing the swash plate. However, motor pressure/torque/speed can be controlled, assuming sufficient traction is available and the motor is sized adequately to overcome the load placed on it, by controlling the flow of hydraulic fluid the pump is trying to force through it.  
       System Objectives  
       [0103]    To cause the motors to share the forward or reverse propulsion load within ±5% when the steering load on the articulation cylinders is less than a defined amount, say, 1,000 psi.  
         [0104]    To assist the articulation cylinders to execute a turn whenever the cylinder pressure in either direction goes above 1,000 psi. Note: 1,000 psi is exemplary, but based upon results of testing the articulated tracked combine disclosed herein. Such figure may vary once further acceleration or starting on grade testing is undertaken. In this situation, the pressure reference may not be as stable as speed and likely will change with the load.  
         [0105]    The foregoing system elements, characteristics, and objectives are embodied in FIG. 29. Specifically, inputs to micro-controller  400  include left steering pressure signal  402  and right steering pressure signal  404  from steering valve  406 , which is actuated by the operator rotating steering wheel  408 . Signals  402 / 404  also are fed to left articulation cylinder  46  and right articulation cylinder  48  with lines  410  and  412  supplying the necessary interconnection between cylinders  46 / 48  and lines  410 / 412 . Such interconnection is the primary steering mechanism for articulated combine  10 .  
         [0106]    The operator indicates the desired speed of combine  10  through lever  414  which is connected by line  416  to front axle pump  418  which drives front motor drive  420 . Lines  422  and  424  interconnect pump  418  and motor  420  with lines  426  and  428  providing two more inputs to controller  400 . Potentiometer  430  provides a reference signal via line  432  to controller  400 . Left track pump  434  powers left track motor  436  via lines  438  and  440 , from which signals  442  and  444  are sent to controller  400 . Line  446  provides yet another input to controller  400  from left track motor  436 . Right track pump  448  powers right track motor  450  via lines  452  and  454 , from which signals  456  and  458  are sent to controller  400 . Line  460  provides yet another input to controller  400  from right track motor  436 . Finally, controller  400  communicates with left track pump  434  via line  462  and with right track pump  448  via line  464 . All equipment is conventional in nature and design.  
         [0107]    One condition that requires special attention for a tracked articulated combine is when the operator desires to commence movement (forward or reverse) from a standing or stop position with the steering wheel in a turning mode. Such initial turning movement requires tracks  30 / 32  to slide from rest, which requires a great amount of force/torque to overcome the consequent track friction with the ground. The above-described steering scheme can accommodate such conditions by initiating the turn with the articulation cylinders augmented by powering up only the outside track.  
         [0108]    While combine  10  has been described as having non-steerable wheels, it should be appreciated that combine  10  can be designed to have steerable front wheels. Thus, steering of combine  10  can result from one or a combination of steerable forward unit wheels, articulation cylinders, and steerable (e.g., by speed differential or by wheel turning) rearward tracks (or tired wheels).  
         [0109]    Finally, it should be appreciated also that some and/or all of the hydraulic motors, valves, pumps, and the like, can be replaced by pneumatic motors and associated equipment, electric motors and associated equipment, or by any other power generating device or system, so long as the design and operation remains with the precepts of the present invention.  
         [0110]    While the invention has been described with reference to a preferred embodiment, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. In this application all units are in the metric system and all amounts and percentages are by weight, unless otherwise expressly indicated. Also, all citations referred herein are expressly incorporated herein by reference.