Abstract:
One aspect of the present invention relates to a steering system for an articulated tracked combine composed of (i) a forward unit having a pair of differentially-connected powered non-steering wheels or tracks and (ii) a tracked rearward unit having powered steerable tracks. This steering system includes a pivoting articulation joint interconnecting the forward unit and the rearward unit. The rearward unit is fitted with a differential tracked steering system in steering connection with an operator steering wheel for steering of the articulated tracked combine. Optionally, such novel steering system includes a pair of steering articulation cylinder assemblies connected between the forward unit and the rearward unit. An angle sensor is mounted at the joint for sensing the relative position of the forward unit and the rearward unit. Another sensor is mounted at the steering wheel to sense its position. A controller is connected with the angle sensor and with the steering wheel sensor for monitoring their concordance and for activating the steering articulation cylinder assemblies when the concordance varies by a threshold value in order to re-establishes the concordance within the threshold value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is cross-referenced to Applicant&#39;s application Ser. No. 09/040,985, filed on Mar. 18, 1998, now U.S. Pat. No. 6,012,272 the disclosure of which is expressly incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to combines and more particularly to a tracked articulated (jointed) combine with improved tracked steering system capability. 
     Tracked vehicles, which utilize metallic sectioned tracks or rubber traction belts, have been steered historically by establishing a speed differential between the endless tracks on opposite sides of the vehicle. Means causing the track on the right side of the vehicle to stop or run slower than the track on the left side of the vehicle causes the vehicle to turn to the right and vice versa if the progress of the left track is retarded. Such turning regimen initially was accomplished by clutch/brakes affixed to the individual tracks for retarding movement of the track. Such a steering regimen results in abrupt steering changes and in the retarded track sliding sideways with a resulting dirt pile being established on the outside of the sliding track and high stress on the vehicle suspension. 
     Another tracked vehicle steering system is a proportion steering system. This steering system for tracked vehicles causes a speed differential to be created between the two tracks rather than retarding one of the tracks. This “differential steering” system was an improvement in that the turns were less abrupt, less dirt was piled up because sliding of the inside track was less, and the suspension system was subject to less stress, as some power was being applied to both tracks during the turn. A common implementation of a differential steering system involved driving each track with its own hydraulic motor with the relative flow of hydraulic fluid in a hydrostatic transmission arrangement being diverted to either track utilizing a diverter/divider valve controlled by the vehicle operator. The two hydraulic motors, then, provided both propulsion and steering. In a straight-ahead direction, both motors receive the same percentage of the total flow of fluid from the hydrostatic pump. To perform a turn to the right, say, the percentage of the total hydraulic fluid or oil flow to the right side motor is decreased with a simultaneous and concomitant increase in oil flow to the left side motor. A reverse flow is used for a left turn. 
     Differential steering also can be achieved by utilizing a hydraulic motor which, when receiving flow from a steering wheel activated pump, applies power to a mechanical differential which is connected to both tracks. Such a steering system is shown in Caterpillar Company brochure # YEDA 3003 (September 1997). 
     While differential steering represents a definite improvement in the art of tracked vehicle steering, such systems are not without their own problems and limitations. To be effective in guiding a vehicle, particularly an articulated combine, the differential steering system depends on both endless tracks or belts encountering relatively the same traction conditions. Since these vehicles operate in agricultural fields with widely varying soil and soil moisture conditions, a wide differential of track traction can be encountered from one side of the vehicle to the other. 
     Such differential traction problem is illustrated by the following example. The vehicle operator desires to turn the combine to the right and, accordingly, turns the steering wheel to the right. The ground, however, is firmer and less slippery on the right side of the vehicle under the right track or belt than under the left side. The differential steering system causes the left side track to speed up and the right side track to slow down to effect a turn to the right. However, because the right side track has more traction than the left, increasing the speed (power) of the left track merely causes it to “spin” in the loose soil or mud and it will be overpowered by the slower turning, but better tractioned, right track. The net result of these circumstances is that the vehicle will slide or turn left when the operator is calling for a right turn even though the steering system is trying to turn the vehicle to the right. Moreover, this slide or turn (drift) to the left will continue until the left side track encounters soil with at least as good, or better traction than the right side track. At this point in the turn, however, the operator has probably strongly “oversteered” to the right and the left track is running much faster than the right. When the left track encounters firm soil, the vehicle will lunge to the right before the operator can recover. 
     This steering limitation can be mitigated somewhat in a tractor application by reducing the load from the towed implement by raising it until more equal left/right soil conditions are encountered. However, the operator of a combine does not have this option since he cannot reduce the load and must follow precisely the rows or position of the crop to be harvested. 
     Thus, it will be readily apparent that there exists a real need for improving the steering of tracked vehicles in general and of tracked combines specifically. 
     BRIEF SUMMARY OF THE INVENTION 
     Broadly, one aspect of the present invention relates to a steering system for an articulated tracked combine composed of (i) a forward unit having a pair of powered non-steering wheels or tracks (fitted with a differential in their axle) and (ii) a tracked rearward unit having powered steerable tracks. This steering system includes a pivoting articulation joint interconnecting the forward unit and the rearward unit. The rearward unit is fitted with a differential tracked steering system in steering connection with an operator steering wheel for steering of the articulated tracked combine. 
     Another aspect of the present invention is directed to a steering system for an articulated tracked combine composed of (i) a forward unit having a pair of powered non-steering wheels or tracks and (ii) a tracked rearward unit having steerable tracks, wherein steering of said combine is effected by an operator steering wheel in steering connection with the rearward unit tracks. Such novel steering system includes a pair of steering articulation cylinder assemblies connected between the forward unit and the rearward unit. An articulation joint interconnects the forward unit and the rearward unit. An angle sensor is mounted at the joint for sensing the relative position of the forward unit and the rearward unit. Another sensor is mounted at the steering wheel to sense its position. A controller is connected with the angle sensor and with the steering wheel sensor for monitoring their concordance and for activating the steering articulation cylinder assemblies when the concordance varies by a threshold value in order to re-establishes the concordance within the threshold value. 
     Advantageously, the controller publishes the output of each sensor to the operator so that the operator knows the relative position of the two units at all times. Also, a manual override also is desirably provided so that the operator can actuate the articulation steering cylinder assemblies as is necessary, desirable, or convenient. Additionally, the operator can call for a combination steering approach by using the articulation steering cylinder assemblies full time. Finally, the operator can manually articulate the tracked combine by actuating the articulation steering cylinder assemblies. Thus, a multitude of steering options are available to the operator of the novel articulated tracked combine of the present invention. 
     Advantages of the present invention include the ability to readily steer the tracked combine in conventional fashion desirably using a conventional differential tracked steering system. Another advantage is the concomitant ability to overcome slippage of a track during such differential steer automatically so that the operator need only concentrate on steering the combine where desired. A further advantage is the ability of the operator to assist the differential tracked steering system by manually actuating the articulation steering cylinder assemblies. These and other advantages will be readily apparent to those skilled in the art based on the instant disclosure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a side elevational view of the novel combine (or harvester) with rearward unit tracked drive; 
     FIG. 2 is an overhead view of the combine depicted in FIG. 1; 
     FIG. 3 is a sectional view taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a schematic of the hydraulic steering system for the novel tracked articulated combine; and 
     FIG. 5 is a side elevational view of another embodiment of the novel combine depicted in FIG. 1 where the forward unit is tracked. 
    
    
     The drawings will be described in detail below. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the articulated combine utilizing both tracks and pneumatic tires as disclosed in U.S. Pat. No. 6,012,272 (&#39;272 patent) (cited above), it is preferable to steer the combination vehicle utilizing a differential steering system on the track type belts and wheels supporting the rearward grain carrying unit. The rearward unit will be heavily loaded and differential steering minimizes the horizontal sliding of the traction belts. The articulation joint of the combine is equipped with conventional steering cylinder assemblies appropriate for steering an articulated vehicle by conventional applying force to either side of the articulation joint. The joint, however, is unrestricted; that is, it is a freely moveable joint. Steering control over the forward unit, then, relies on the steerable tracks of the tracked rearward unit. 
     In soil conditions where the traction of both belt drives is acceptable for successful differential steering, the articulation steering cylinder assemblies will be in a “float” or passive mode. In this case, the entire vehicle will be steered by the differential steering on the rear belts. When the rearward until is differentially steered, it will cause the articulation joint to change its angle and point the front of the combine or vehicle in the desired direction. However, when soil conditions are encountered which present different traction possibilities to the drive belts and the differential steering drift, slide or opposite desired turn problem begins to appear, the articulation joint steering cylinder assemblies are used to overcome the problem. 
     The problem is sensed by comparing an angle sensor mounted at the articulation joint and the position of the steering wheel. If the differential steering system on the drive belts or tracks is not able to establish or maintain the proper turn angle at the articulation joint the operator is requesting due to poor traction, the vehicle steering controller will command the articulation joint steering cylinder assemblies to be energized and force the steering angle requested by the operator through the steering wheel. A manual switch also is provided to allow the operator to energize the joint cylinder assemblies to assist in steering when he foresees a problem. In the “automatic” mode, the articulation joint cylinder assemblies will be de-energized when an acceptable match between the steering wheel position and the joint angle sensor has been maintained for a reasonable and adjustable period of time. 
     Referring initially to FIGS. 1 and 2, innovative combine  10  generally includes forward unit  12  and rearward unit  14 . Forward unit  10  is seen to include cab  15  in which the operator is seated, cornhead or small grainhead  16 , engine compartment  18  (fan discharge shown in the drawings), and powered non-steerable wheel pair  20 . 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 grain cleaning and transfer assembly  24  seen in FIG.  2 . Rearward unit  14  is seen to include clean grain unloading system  26  in its stored position, grain bin  28 , and powered and steerable tracks  30  and  32 . Use of a tracked configuration of powered and steerable tracks supporting grain bin  28  on rearward unit  14  contributes to the capability of grain bin  28  holding upwards to 1,200 bushels of grain or more. 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. 
     Operation of cornhead or small grainhead  16 , clean grain unloading system, grain bin  28 , and like units of combine  10  is accomplished inventively as disclosed in applicant&#39;s &#39;272 patent (cited above). Thus, an exhaustive discussion of these components and their operation is omitted here. 
     Joint  22  as depicted in FIG. 3 also is disclosed in applicant&#39;s &#39;272 patent (cited above). A pair of steering cylinder assemblies&#39;,  46  and  48 , is seen to connect forward unit  12  to rearward unit  14  of articulated tracked combine  10 . Such steering cylinder assemblies are conventionally used to assist in the steering of articulated vehicles and are provided here for auxiliary steering use in the present articulated tracked 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 because it is in the chaff/straw flow path from grain cleaning and transfer assembly  24 . 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 shown bolted to forward unit  12 , although other attachment means certainly can be envisioned. Joint sensor  61  senses the position of joint assembly  22  (i.e., the relative position of forward unit  12  to rearward unit  14 ). Other joint configurations can be used as is necessary, desirable, or convenient. 
     Of importance to the present invention, however, are the problems inherent in the steering of tracked vehicles in general and in the steering of tracked combines in particular. Operation of tracks  30  and  32  for steering purposes preferably is accomplished by differential steering, as described above. Were rearward unit  14  standing alone, steering of it would be routine. However, inventive combine  10  has forward unit  12  affixed thereto via joint assembly  22 . Thus, bearing retainer assembly  60  permits shafts  50 / 52  to rotate or pivot freely thereabouts with provision for bearings as described in applicant&#39;s &#39;272 patent (cited above). Of importance is that joint assembly  22  permits units  12  and  14  to freely move with respect to each other therethrough. Thus, steering of combine  10  (and, thus, forward unit  12 ) is accomplished by tracks  30 / 32  and their differential steering system. Since forward unit  12  can move freely via joint  22 , steering of rearward unit  14  to the left via tracks  30 / 32  will cause forward unit  12 , and, hence, combine  10 , to veer to the right, and vice versa. Such steering scheme forms one aspect of the present invention. 
     This steering scheme, along with supplemental steering schemes, which form additional embodiments of the present invention, are set forth in FIG.  4 . The combine operator in cab  15  steers combine  10  via steering wheel  62  which activates valve  64  which is fed hydraulic fluid via line  66  at, say, 2,000 psi, and also is connected to reservoir  68  via line  70 . During normal operation when tracked combine  10  is proceeding in a straight ahead direction, hydraulic fluid or oil is fed from valve  64  via line  72  to diverter valve  74  which proportions the hydraulic fluid equally between left track  32  motor  76  via line  78  and right track  30  motor  80  via line  82 . 
     Power is supplied to motors  76 / 80  from propulsion hydrostatic pump  84  via line  86 . Pump  84  is connected to operator motion control lever  85  and in turn is powered from the engine of combine  10  which also powers via line  90  motor  88  which powers wheel pair  20  of forward unit  12 . During such straight ahead movement of combine  10 , cylinder assemblies  46 / 48  are in a “float” mode, that is, they exert no influence over units  12  and  14  and their corresponding servo valve is centered. Steering in this mode is entirely controlled by rear tracks  30 / 32  differential drive system and freely pivotable joint  22 . 
     Now, when the operator wants to turn combine  10  to the right (right chosen arbitrarily for purposes of illustration), the operator turns steering wheel  62  to the right which actuates valve  64  and via line  72  diverter valve  74  now proportions more hydraulic fluid to motor  80  (right track  30 ) and a lesser amount of fluid to motor  76  (left track  32 ). This differential hydraulic fluid flow causes rearward unit  14  to turn to the left and, via joint  22 , forward unit  12  (and, hence, combine  10 ) to the right because wheel pair  20  is fitted with a differential in the axle which connects such wheel pair. When the turn is complete, the operator returns steering wheel  62  to its neutral position which results in diverter valve  74  equalizing the flow of hydraulic fluid to motors  76  and  80 , resulting in combine  10  returning to straight ahead movement. 
     During such a turn, steering wheel sensor  92  sends a signal to steering controller  94  via line  96  which controller also publishes the position of joint  22  as determined by joint sensor  61  (see FIG. 3) in joint position display  98  which is connected to controller  94  via line  100 . Joint sensor  61  also sends a signal to controller  94  via line  95 . So long as joint sensor  61  and steering wheel sensor  92  are within a threshold value, steering of combine  10  can be accomplished solely by means of the differential steering associated with tracks  30 / 32 . The threshold value is a measure of the difference in readings between steering wheel sensor  92  which represents where the operator has determined that combine  10  should be going during a turn and joint sensor  61  which represents where combine  10  actually is going during a turn. When this differential becomes too large (exceeds the threshold value), collective action is required in order for combine  10  to follow the turn outlined by the operator via steering wheel  62 . Such corrective action will be described below. 
     Now, controller  94  also is fitted with several switches namely, switch  102  for continuous mode operation, switch  104  for manual/automatic mode operation, and switches  106 / 108  for manual articulation to the left and light, respectively. These modes also will be described below. 
     When corrective action is required because sensors  61  and  92  indicate that track  30  is slipping during the right hand turn with a consequent difference between these sensors readings above a pre-determined threshold value, in the continuous mode of controller  94  as set by the operator via switch  102 , controller  94  sends a signal via line  110  to articulate servo valve  112  which is powered by a source of, say, 2,000 psi hydraulic fluid, via line  114  with return line to reservoir  68  (or another suitable hydraulic fluid reservoir) provided conventionally. Such signal causes valve  112  to transmit hydraulic fluid via line  116  to line  120  to extend left cylinder  46  and retract right cylinder  48  for augmenting the right hand turn called for by the operator. For a left hand turn, valve  112  sends fluid via line  122  to line  124  to retract left hand cylinder  46  and extend right hand cylinder  48 . Returning to the right hand turn illustration, cylinder assemblies  46 / 48  by being activated, force combine  10  to turn to the right, thus overcoming the slippage of track  30 . Once concordance between sensors  61  and  92  have been re-established, cylinder assemblies  46 / 48  work in concert with tracks  30 / 32  differential steering system to complete tile turn. 
     Alternatively, the operator could activate switch  104 , which would engage cylinder assemblies  46 / 48  to work full time during turning of combine  10 . Yet another alternative available to the operator is to activate switch  106  to manually articulate combine  10  to the right via steering articulation cylinder assemblies  46 / 48 , or switch  108  to manually articulate combine  10  to the left via steering articulation cylinder assemblies  46 / 48 . Thus, the operator has a multitude of steering modes available to steer articulated tracked combine  10 . 
     Referring to FIG. 5, innovative combine  126  generally includes forward unit  128  and rearward unit  130 , which are similar in construction to combine  10  depicted in FIG. 1, except for the tracks. Forward unit  128  and rearward unit  130  each are fitted with track systems  132  and  134 , respectively. Such track systems are the QUADTRAC™ tracks of Case Corporation (Racine, Wis.), such as is illustrated in their STEIGER® 9300 Series 4WDs brochure (1996). The remainder of operation of combine  126  is like that described in connection with FIGS.  1 - 4 . 
     It will be appreciated that the foregoing description is illustrative of how the present invention can be practiced, but it should not be construed as limiting the present invention. Finally, all citations referred to herein are expressly incorporated herein by reference.