Patent Publication Number: US-11026368-B2

Title: Steering control system for harvester and methods of using the same

Description:
BACKGROUND 
     Harvesters such as windrowers, tractors, and forage harvesters, have to operate effectively in different operational modes (e.g., normal operation mode, in-field operation mode, high-speed operation mode, or the like). Typical construction for such vehicles include front ground wheels mounted on the frame at fixed angles parallel to each other and parallel to a center line of the frame and rear ground wheels mounted on a respective caster. Each of the front ground wheels is typically driven by a respective drive motor which allows variable speed in both the forward and reverse directions such that steering of the tractor is effected by a differential in speed between the front wheels with the rear wheels following the steering in a castering action. 
     Conventional harvesters generally use dual path steering for both in-field operation mode and high-speed road transport operation mode. Dual path steering generally operates by varying the speed of the two front drive wheels in order to steer the harvester. The left wheel slows while the right wheel speeds up to turn left, while the right wheel slows and the left wheel speeds up to turn right. Combined with passively castering rear wheels, this enables the conventional harvester to perform zero radius spin turns in the field, which is desirable for optimum field efficiency and maneuverability. However, during high-speed road transport operation mode (e.g., speeds greater than 24 mph) dual path steering does not provide adequate steering stability. This is due to several factors, including variable ground drive motor/pump efficiency, lack of steering feedback to the driver, dynamics of the harvester which uses the front wheels to steer with no stabilizing effect provided by the rear wheels, combinations thereof, or the like. 
     SUMMARY 
     The disclosure relates to a steering control system for a harvester that provides for stable operation during high-speed rear axle steering (e.g., road operation mode). The steering control system includes a position sensor detecting the position of a single steering cylinder associated with one caster of the windrower. Based on input from a steering wheel or device, the steering cylinder is actuated to extend or retract to steer one caster of the windrower, with the second caster providing passive damping. In some embodiments, steering cylinders are provided on both casters with the position of only one steering cylinder detected by a sensor. In such embodiments, actuation of a first steering cylinder to extend or retract results in an equal and opposite actuation of the second steering cylinder, thereby providing steering on both casters. Steering of one or both casters provides additional stability to the windrower during the road operation mode. 
     In accordance with some embodiments of the present disclosure, an exemplary steering control system for a harvester is provided. The steering control system includes a first cylinder configured to be coupled to a rear axle of the harvester at one end and an upright shaft of a first caster of the harvester at an opposing end. The steering control system includes a sensor associated with the first cylinder and in communication with a controller, the sensor detecting a position of the first cylinder. The steering control system includes a passive damper configured to be coupled to the rear axle of the harvester at one end and an upright shaft of a second caster of the harvester at an opposing end. In a road operation mode, the first cylinder is actuated by the controller to extend or retract to control steering of the first caster, and the sensor transmits data to the controller regarding the detected position of the first cylinder. The passive damper is free of sensing and provides passive damping to the second caster. 
     One end of the first cylinder is configured to be coupled to the rear axle of the harvester by a flange. In some embodiments, the first cylinder is hydraulically plumbed to a steering proportional valve for actuation of the first cylinder to extend or retract. The steering proportional valve is hydraulically plumbed to both a rod end and a barrel end of the first cylinder. The detected position of the first cylinder is representative of a position of the first caster relative to the rear axle of the harvester. 
     In some embodiments, the steering control system includes a proximity sensor configured to detect a position of the first caster relative to the rear axle of the harvester. Castering of second caster is unaffected by actuation of the first cylinder to extend or retract. In some embodiments, the sensor is at least one of an internal position sensor, an external position sensor, a potentiometer, or the like. In a field operation mode, free flow of hydraulic fluid into and out of the first cylinder provides passive damping by the first cylinder to the first caster. 
     In accordance with embodiments of the present disclosure, an exemplary steering control system for a harvester is provided. The steering control system includes a first cylinder configured to be coupled to a rear axle of the harvester at one end and an upright shaft of a first caster of the harvester at an opposing end. The steering control system includes a sensor associated with the first cylinder and in communication with a controller, the sensor detecting a position of the first cylinder. The steering control system includes a second cylinder configured to be coupled to the rear axle of the harvester at one end and an upright shaft of a second caster of the harvester at an opposing end. In a road operation mode, the first cylinder is actuated by the controller to extend or retract to control steering of the first caster, and the sensor transmits data to the controller regarding the detected position of the first cylinder. The second cylinder is free of sensing and is hydraulically coupled to the first cylinder to move in an equal and opposite direction of the first cylinder to control steering of the second caster. 
     In some embodiments, barrel ports of the first and second cylinders are hydraulically coupled together, and rod ports of the first and second cylinders are hydraulically coupled to a steering proportional valve. Actuation of the first cylinder to retract displaces fluid from a barrel end of the first cylinder into a barrel end of the second cylinder. Displacement of the fluid into the barrel end of the second cylinder actuates the second cylinder to extend in an equal magnitude to retraction of the first cylinder. 
     In some embodiments, the detected position of the first cylinder is representative of a position of the first and second casters relative to the rear axle of the harvester. In some embodiments, the steering control system includes a proximity sensor configured to detect a position of the first caster or second caster relative to the rear axle of the harvester. In some embodiments, the sensor is at least one of an internal position sensor, an external position sensor, a potentiometer, or the like. In a field operation mode, free flow of hydraulic fluid into and out of the first and second cylinders provides passive damping by the first cylinder to the first caster and the second cylinder to the second caster. 
     In accordance with embodiments of the present disclosure, an exemplary harvester is provided. The harvester includes a frame, at least one front axle comprising first and second front wheels pivotally mounted to the front axle, at least one rear axle comprising first and second casters pivotally mounted to the rear axle, and a steering control system. The steering control system includes a first cylinder coupled to the rear axle at one end and an upright shaft of the first caster at an opposing end. The steering control system includes a sensor associated with the first cylinder and in communication with a controller, the sensor detecting a position of the first cylinder. The steering control system includes a passive damper coupled to the rear axle at one end and an upright shaft of the second caster at an opposing end. In a road operation mode, the first cylinder is actuated by the controller to extend or retract to control steering of the first caster, and the sensor transmits data to the controller regarding the detected position of the first cylinder. The passive damper is free of sensing and provides passive damping to the second caster. Castering of second caster is unaffected by actuation of the first cylinder to extend or retract. 
     In accordance with embodiments of the present disclosure, an exemplary harvester is provided. The harvester includes a frame, at least one front axle comprising first and second front wheels pivotally mounted to the front axle, at least one rear axle comprising first and second casters pivotally mounted to the rear axle, and a steering control system. The steering control system includes a first cylinder coupled to the rear axle at one end and an upright shaft of the first caster at an opposing end. The steering control system includes a sensor associated with the first cylinder and in communication with a controller, the sensor detecting a position of the first cylinder. The steering control system includes a second cylinder coupled to the rear axle at one end and an upright shaft of the second caster at an opposing end. In a road operation mode, the first cylinder is actuated by the controller to extend or retract to control steering of the first caster, and the sensor transmits data to the controller regarding the detected position of the first cylinder. The second cylinder is free of sensing and is hydraulically coupled to the first cylinder to move in an equal and opposite direction of the first cylinder to control steering of the second caster. 
     In accordance with embodiments of the present disclosure, an exemplary method of steering a harvester is provided. The method includes coupling a first cylinder to a rear axle of the harvester at one end and an upright shaft of a first caster of the harvester at an opposing end. The method includes associating a sensor with the first cylinder, the sensor in communication with a controller and detecting a position of the first cylinder. The method includes coupling a passive damper to the rear axle of the harvester at one end and an upright shaft of a second caster of the harvester at an opposing end, the passive damper being free of sensing. In a road operation mode, the method includes actuating the first cylinder by the controller to extend or retract to control steering of the first caster, and transmitting data to the controller regarding the detected position of the first cylinder. The method includes providing passive damping to the second caster with the passive damper. 
     Any combination and/or permutation of embodiments is envisioned. Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To assist those of skill in the art in making and using the disclosed steering control systems, reference is made to the accompanying figures, wherein: 
         FIG. 1  is a perspective view of a windrower with an exemplary steering control system of the present disclosure; 
         FIG. 2  is a perspective view of a windrower with an exemplary steering control system of the present disclosure; 
         FIG. 3  is a perspective view of a rear axle of a windrower with an exemplary steering control system of the present disclosure; 
         FIG. 4  is a detailed view of a steering assembly of an exemplary steering control system of the present disclosure; 
         FIG. 5  is a detailed view of a damping assembly of an exemplary steering control system of the present disclosure; 
         FIG. 6  is a top view of an exemplary steering control system of the present disclosure in a left turn operation; 
         FIG. 7  is a top view of an exemplary steering control system of the present disclosure in a right turn operation; 
         FIG. 8  is a detailed view of a steering assembly of an exemplary steering control system of the present disclosure; 
         FIG. 9  is a static image of a hydraulic circuit of an exemplary steering control system of the present disclosure; 
         FIG. 10  is the hydraulic circuit of  FIG. 9  in a field operation mode; 
         FIG. 11  is the hydraulic circuit of  FIG. 9  in a straight path operation mode; 
         FIG. 12  is the hydraulic circuit of  FIG. 9  in a right turn operation mode; 
         FIG. 13  is the hydraulic circuit of  FIG. 9  in a left turn operation mode; 
         FIG. 14  is a perspective view of an exemplary steering control system of the present disclosure; 
         FIG. 15  is a detailed view of an exemplary steering control system of the present disclosure; 
         FIG. 16  is a detailed view of an exemplary steering control system of the present disclosure; 
         FIG. 17  is a top view of an exemplary steering control system of the present disclosure in a left turn operation; 
         FIG. 18  is a top view of an exemplary steering control system of the present disclosure in a right turn operation; 
         FIG. 19  is a static image of a hydraulic circuit of an exemplary steering control system of the present disclosure; 
         FIG. 20  is the hydraulic circuit of  FIG. 19  in a field operation mode; 
         FIG. 21  is the hydraulic circuit of  FIG. 19  in a straight path operation mode; 
         FIG. 22  is the hydraulic circuit of  FIG. 19  in a right turn operation mode; 
         FIG. 23  is the hydraulic circuit of  FIG. 19  in a left turn operation mode; and 
         FIG. 24  is a static image of a hydraulic circuit of an exemplary steering control system of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various terms relating to the methods and other aspects of the present disclosure are used throughout the specification and claims. Such terms are to be given their ordinary meaning in the art unless otherwise indicated. Other specifically defined terms are to be construed in a manner consistent with the definition provided herein. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. 
     The term “more than 2” as used herein is defined as any whole integer greater than the number two, e.g., 3, 4, or 5. 
     The term “plurality” as used herein is defined as any amount or number greater or more than 1. In some embodiments, the term “plurality” means 2, 3, 4, 5, 6 or more. 
     The terms “left” or “right” are used herein as a matter of mere convenience, and are determined by standing at the rear of the machine facing in its normal direction of travel. Likewise, “forward” and “rearward” are determined by the normal direction of travel. “Upward” and “downward” orientations are relative to the ground or operating surface as are any references to “horizontal” or “vertical” planes. 
     The term “about” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, ±1%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, ±0.1%, ±0.09%, ±0.08%, ±0.07%, ±0.06%, ±0.05%, ±0.04%, ±0.03%, ±0.02% or ±0.01% from the specified value, as such variations are appropriate to perform the disclosed methods. 
     The term “harvester” as used herein is defined as a machine that consolidates and/or packages material so as to facilitate the storage and handling of the material for later use. In some embodiments, the harvester is used to harvest agricultural material. In some embodiments, the harvester is a windrower, a forage harvester, lawn mower or a combine including a baling mechanism. In some embodiments, the harvester is a self-propelled windrower. 
     The term “material” as used herein is defined as a numerous individual items that are harvested or collected by the harvester. In some embodiments, the material is agricultural crop, such as hay or silage. In some embodiments, the material is biomass. 
     The term “drive system” or “steering system” as used herein is defined as an assembly, hydraulic or mechanical arrangement that allows for control of the front and/or rear wheels of the harvester. 
     The term “information” as used herein is defined as data values attributed to parameters. In some embodiments, information is digital and/or analog information. In some embodiments, information is the current operable mode of the harvester. In some embodiments, warning information can be audio and/or visual information. In some embodiments, warning information is information that is capable of alerting an operator that an action may need to be taken. 
     Discussions herein utilizing terms such as, for example, “processing,” “computing,” “calculating,” “determining,” or the like, may refer to operation(s) and/or process(es) of a computer, a computing platform, a computing system, or other electronic computing device, that manipulate and/or transform data represented as physical (e.g., electronic) quantities within the computer&#39;s registers and/or memories into other data similarly represented as physical quantities within the computer&#39;s registers and/or memories or other information storage medium that may store instructions to perform operations and/or processes. 
     Some embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment including both hardware and software elements. Some embodiments may be implemented in software, which includes but is not limited to firmware, resident software, microcode, or the like. 
     Furthermore, some embodiments may take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For example, a computer-usable or computer-readable medium may be or may include any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, or harvester. In some embodiments, the harvester includes a software system with executable code that executes different hydraulic states based on operator steering of the harvester. In some embodiments, the disclosure also relates to a computer software product with executable code that automatically toggles between or through different hydraulic states based on operator steering of the harvester. The software program product may be on any medium or a component of a system optionally configured for update or install into the software of an existing harvester. 
     In some embodiments, the medium may be or may include an electronic, magnetic, optical, electromagnetic, InfraRed (IR), or semiconductor system (or apparatus or device) or a propagation medium. Some demonstrative examples of a computer-readable medium may include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a Random Access Memory (RAM), a Read-Only Memory (ROM), a rigid magnetic disk, an optical disk, or the like. Some demonstrative examples of optical disks include Compact Disk-Read-Only Memory (CD-ROM), Compact Disk-Read/Write (CD-R/W), DVD, or the like. 
     In some embodiments, the disclosure relates to a processing system including a processing device suitable for storing and/or executing program code and may include at least one processor coupled directly or indirectly to memory elements, for example, through a system bus. The memory elements may include, for example, local memory employed during actual execution of the program code, bulk storage, and cache memories which may provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution. In some embodiments, the memory is capable of storing preferred settings or information about steering of the harvester. In some embodiments, the system includes one or a plurality of sensors to detect the steering selected by the operator. The sensors may be hard wired to one or more wires creating a physical connection to one or a plurality of controllers and/or are active sensors can be activated and used over a WiFi hotspot, Bluetooth® or other internet connection with controllers capable of receiving such remote signals. 
     In some embodiments, input/output or I/O devices (including but not limited to keyboards, displays, pointing devices, etc.) may be coupled to the system either directly or through intervening I/O controllers. In some embodiments, I/O devices may be coupled to the system directly or to I/O controller by an I/O bus (cables and or wires which connect the devices and enable the information to pass therebetween). In some embodiments, network adapters may be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices, for example, through intervening private or public networks. In some embodiments, modems, cable modems and Ethernet cards are demonstrative examples of types of network adapters. Other suitable components may be used. Any sensor disclosed herein may function on any disclosed harvester by integration into one or more data processing systems of the harvester. For example, in some embodiments, the disclosure relates to a data processing system including executable software program product configured for sending and receiving information about the steering of the harvester. In some embodiments, the system may be configured by the operator to transition the harvester between different hydraulic states in synchrony or substantial synchrony to operator-initiated steering of the harvester. In some embodiments, the data processing system of the harvester transitions the harvester between different hydraulic states in synchrony or substantial synchrony to operator-initiated steering of the harvester depending upon real-time information sent to a controller by a sensor that monitors the steering wheel actuation. 
     The term “real-time” and the phrase “in real-time” as used herein are defined as a way of describing a process, event, or action that occurs simultaneously with the process of actively operating a harvester. In some embodiments, various sensors continuously sense information about the steering operation of the harvester and transmit that information to a controller in real-time. In some embodiments, an operator may adjust values or thresholds for one or more hydraulic states in real-time through the operator interface by accessing the system electronically and inputting one or a plurality of values. 
     Many of the fastening, connection, processes and other means and components utilized in this disclosure are widely known and used in the field of the disclosure described, and their exact nature or type is not necessary for an understanding and use of the disclosure by a person skilled in the art, and they will not therefore be discussed in significant detail. Furthermore, the various components shown or described herein for any specific application of this disclosure can be varied and the practice of a specific application of any element may already be widely known or used in the art by persons skilled in the art and each will likewise not therefore be discussed in significant detail. 
     Windrowers and tractors, such as self-propelled windrowers, are well known in the agricultural industry, and the instant invention can be used with substantially any of such machines. Reference is made, for example, to U.S. Pat. Nos. 9,101,090 and 8,020,648; that illustrate such windrowers, the disclosures of which are incorporated herein by reference in their entireties. Embodiments of the present invention are particularly well suited, but in no way limited to, use with windrowers. The present invention may also find utility in agricultural harvesters including, for example, a self-propelled windrower, a forage harvester, cotton harvester or a lawn mower. Embodiments of the present disclosure are particularly well suited, but in no way limited to, use with any vehicle with a front and rear steer system. 
     In some embodiments, the method is performed by a harvester comprising a crop supply chamber, a crop gating system, and one or more sensors. In some embodiments, the one or more sensors are capable of determining a range of information, including, but not limited to, one or a combination of: the size of a bale in the bale chamber (diameter and/or weight), the position of the tailgate, the position of the control arm, the position of the rear wall, and the position of the crop gating system. In some embodiments, the one or more sensors are in electronic communication with one or more controllers. In some embodiments, sensors can be used to determine that the caster cylinders are fully retracted or extended. 
       FIG. 1  shows a perspective view of an exemplary windrower  100 . The windrower  100  generally includes front wheels  102 ,  104  rotatably mounted to a frame  106 . The windrower  100  includes a cabin  108  mounted to the frame  106 . The cabin  108  is configured and dimensioned to receive an operator, and has a plurality of controls for operation of the windrower  100 , such as controlling a header  110  attachable to the front  112  of the windrower  100 , controlling movement of the windrower in a forward direction  114 , and controlling movement of the windrower  100  in a reverse direction  116 . 
     At the rear  118 , the windrower  100  includes casters  120 ,  122  rotatably mounted on opposing sides of a rear axle  124  of the frame  106 . The windrower  100  includes two independent caster wheels  126 ,  128  mounted to the respective casters  120 ,  122 , one on the left-hand side and one on the right-hand side of the windrower  100 . The windrower includes a steering control system  130  including a damping assembly  132  (e.g., a passive damper, shock absorbers, or the like) and a steering assembly  134  (e.g., a hydraulic steering cylinder) mounted to the frame  106 . As will be discussed in greater detail below, the damping assembly  132  provides damping functionality to one of the casters  120 ,  122 , and the steering control system  130  provides steering functionality to the other caster  120 ,  122 . As such, only one of the casters  120 ,  122  is damped and the other caster  120 ,  122  is steered. Although illustrated as located on the left-hand and right-hand sides, it should be understood that the position of the damping and steering assemblies  132 ,  134  could be reversed. 
       FIGS. 2 and 3  show perspective views of the windrower  100  and rear axle  124  of the windrower with the steering control system  130 .  FIGS. 4 and 5  show detailed views of the steering and damping assemblies  134 ,  132  of the steering control system  130 . The damping assembly  132  includes a passive damper  136  (e.g., a shock absorber, a shimmy damper, or the like) pivotably coupled at one end to an arm  138  and pivotably coupled at the opposing end to a flange  140 . The damper  136  passively damps the oscillation of the caster  120  without providing any steering action of the caster  120 . The opposing end of the arm  138  is rigidly coupled to the top of an upright shaft  142  and is rotatable about a pivot axis defined by the upright shaft  142  (e.g., the pivot axis of the caster  120 ) with the caster  120 . The shaft  142  and the arm  138  thereby rotate together with the caster  120 . The opposing end of the flange  140  is fixedly coupled to the axle  124  and does not pivot. The upright shaft  142  pivots within the axle  124  with the flange  140  remaining in a fixed, rigidly mounted position on the axle  124 . The rigid position of the flange  140  allows for the extension and retraction of the damper  136  as the assembly of the arm  138 , the shaft  142 , and the caster  120  rotates about the axis of the shaft  142 . The extension and retraction of the damper  136 , in turn, provides damping to the caster  120 . 
     The steering assembly  134  includes a steering cylinder  144  (e.g., a hydraulic cylinder) pivotably coupled at one end to an arm  146  and pivotably coupled at the opposing end to a flange  148 . The cylinder  144  can be hydraulically actuated to extend or retract, thereby providing steering to the left-hand side caster  122 . The opposing end of the arm  146  is rigidly coupled to the top of an upright shaft  150  and is rotatable about a pivot axis defined by the upright shaft  150  (e.g., the pivot axis of the caster  122 ) with the caster  122 . The shaft  150  and the arm  146  thereby rotate together with the caster  122 . The opposing end of the flange  148  is fixedly coupled to the axle  124  and does not rotate with the shaft  150 . The arm  146  is rigidly coupled to the shaft  150 , with the shaft  150  rigidly connected to the caster  122 . The arm  146 , the shaft  150 , and the caster  122  thereby rotate within the upright of axle  124  about the axis of the shaft  150 . The steering assembly  134  includes one or more sensors  152  capable of detecting the position or amount of extension/retraction of the cylinder  144 , and transmits data corresponding to the position of the cylinder  144  to a controller module  154  as feedback regarding steering of the caster  122 . 
     Hydraulic lines  156 ,  158  (e.g., pressure and vent lines) connect the cylinder  144  to a steering proportional valve  160 . Hydraulic lines  162 ,  164  connect the steering proportional valve  160  to respective blocking valves  166 ,  168 . Hydraulic line  170  connects the steering proportional valve  160  to a steering pump  172 . Hydraulic line  174  connects the steering proportional valve  160  to hydraulic line  176 , which connects to tank  178 , and hydraulic line  176  connects the blocking valves  166 ,  168  to a tank  178 . The hydraulic lines can be actuated to extend or retract the cylinder  144 . Extension or retraction of the cylinder  144  results in pivoting of the caster  122  at the upright shaft  150 , allowing for steering of the caster  122 . The steering control system  130  thereby provides for single wheel rear axle steering of the windrower  100 . 
       FIG. 6  is a top view of the steering control system  130  in a left turn operation. Arrow  180  represents the direction of rotation of the caster  122  as actuated by the steering assembly  134 . In the left turn operation, the steering assembly  134  is hydraulically controlled to retract the cylinder  144 .  FIG. 7  is a top view of the steering control system  130  in a right turn operation. Arrow  182  represents the direction of rotation of the caster  122  as actuated by the steering assembly  134 . In the right turn operation, the steering assembly  134  is hydraulically controlled to extend the cylinder  144 . In both left and right turn operations, steering of the windrower  100  is controlled by a combination of the front wheel dual-path steering and the left-hand side rear wheel steering assembly  134 , while the right-hand side wheel passively casters to follow the control of steering with the damping assembly  132  providing passive damping during castering. 
     The exemplary steering control system  130  therefore provides for active steering control to one of the two rear wheels on the windrower  100 , while the other rear wheel remains passively castering during the rear axle steering mode. Steering of one of the rear wheels, particularly during high-speed operation, provides additional stability to the front drive dual-path steering system rather than providing primary steering control. Thus, rather than providing the primary steering control of the windrower  100 , steering of one of the rear wheels assists in stabilizing the system overall during high-speed and normal operation modes of the windrower  100 . 
     As compared to conventional windrowers, the windrower  100  includes a steering cylinder  144  coupled to one of the casters  120 ,  122  that allows for directional control of the caster  120 ,  122 , while the other caster  120 ,  122  maintains a traditional shimmy damper configuration without active steering control. The cylinder  144  uses the sensor  152  (e.g., internal cylinder position sensor, external position sensor, radial potentiometer, proximity sensor, or the like) to determine and transmit the radial position of the caster  122  to a controller. A control valve manifold can be used to extend and retract the steering cylinder  144 . A steering pump  172  can be used to provide pressure/flow to the manifold, and valves and lines can provide a path for flow to return to tank  178  during field operation. An electronic steering wheel/device position sensor can be used to provide operator commanded steering wheel/device position to the controller, with such data used by the controller to calculate and execute the commanded steering position (e.g., extension or retraction of the cylinder  144 ) via a control algorithm. 
     The windrower  100  can remain in front drive dual-path steering during the different operation modes of the windrower  100 , with the rear steering acting to supplement or assist in stabilizing operation of the windrower  100 . In some embodiments, steering in the field can be provided only by the front drive dual-path steering, while the rear axle steering can function along with the dual-path steering during high-speed (e.g., road) operation mode. As noted above, the steering cylinder  144  connects to an arm  146  attached to the top of the upright shaft  150  (e.g., a caster vertical pivot shaft) at one end and the rear axle  124  (via the flange  148 ) at the opposing end. 
     The rod and barrel ports of the cylinder  144  can be plumbed to the proportional steering valve  160 . The hydraulic lines to the steering cylinder  144  have blocking valves  166 ,  168  to tank  178  that are normally open, allowing free flow of fluid into and out of the cylinder  144  during field operation. Blocking valves  166 ,  168  are provided to block flow back to tank  178  in the rear axle steering mode. When all blocking valves  166 ,  168  are blocking flow back to tank  178 , the movement of the steering cylinder  144  can be controlled by the steering valve  160 . 
     In the field/free castering operation mode, all blocking valves  166 ,  168  are actuated into the open position, allowing free flow of fluid into and out of the steering cylinder  144 . The steering cylinder  144  is extended and retracted based on the caster  122  position due to steering control from the front drive wheels. The steering valve  160  remains in the centered or closed position during this operation. The steering cylinder  144  acts as a caster damper during the field operation mode as the flow of fluid into and out of the cylinder  144  provides a viscous damping force on the steered caster  122 . The non-steered caster  120  receives damping force from the passive shimmy damper  136  during field operation. 
     In the rear axle steering operation, the operator selects rear axle steering operation through the operator console in the cab or another command switch (e.g., at a user interface). The operator can be prompted to drive straight forward in order to orient the steered caster  122  and rear wheel  128  behind the rear axle  124  as this is this orientation of the caster  122  during rear axle steering operation. In some embodiments, a proximity sensor  153  can be incorporated into the steering assembly  134  to detect and transmit data to the controller regarding the position of the caster  122  and/or wheel  128  relative to the rear axle  124  (see  FIG. 4 ). In some embodiments, a similar proximity sensor can be disposed on the caster  120  to detect and transmit data to the controller regarding the position of the caster  122  and/or wheel  126  relative to the rear axle  124 . For example, a magnetic sensor on the caster  122  and a fixed target on the rear axle  124  can be used to sense when the caster  122  is in a position behind the rear axle  124  prior to initiating the rear axle steering operation. 
       FIG. 8  is a detailed view of the steering assembly  134 . As noted above, in some embodiments, a proximity sensor  121  can be rigidly coupled to the axle  124  via the casing for the shaft  150 . In some embodiments, the sensor  121  can be disposed within an opening of a flange extending from the casing for the shaft  150 . A target  123  can be rigidly coupled to the caster  122 . The target  123  can rotate with rotation of the caster  122  with the sensor  121  detecting the target  123  only when the caster  122  has rotated behind the axle  124 . Upon detection of the target  123  with the sensor  121 , the rear axle steering operation can be initiated. 
     When the controller receives data from the sensor  152  that the steering cylinder  144  is in the steering straight position, the blocking valves  166 ,  168  can be actuated to shift and block all flow into and out of the steering cylinder  144 . Blocking flow into and out of the steering cylinder  144  creates a closed circuit where the retraction and extension of the steering cylinder  144  (and thereby the steering direction of the steered caster  122 ) is controlled by the steering valve  160 . To steer the rear wheel  128 , the operator can input a steering command by turning the steering wheel/device to a desired position. A steering sensor receives data corresponding with the steering command (e.g., the amount of rotation of the steering wheel, the input desired rotation of the windrower  100 , or the like). In some embodiments, the steering sensor can be electronically coupled to the steering wheel/device. The controller uses the position data received from the steering sensor to command a steering angle of the rear axle steering cylinder  144  with position sensing. Thus, the controller can extend or retract the steering cylinder  144  as needed to achieve the desired input at the steering wheel/device, with the sensor  152  detecting and transmitting the position of the steering cylinder  144  (and thereby the caster  122 ) to the controller. 
       FIG. 9  is a static image of a hydraulic circuit  200  of the steering control system  130 . The hydraulic circuit  200  includes a relief valve  202 , a steering pump  204 , a steering wheel or device position sensor  206 , and a controller  208 . The hydraulic circuit  200  includes a tank  210 , a return to tank blocking valve  212 , a return to tank blocking valve  218 , and a steering proportional directional valve  220 . The hydraulic circuit  200  includes a steering cylinder  216  and a cylinder position sensor  214 . 
       FIG. 10  is the hydraulic circuit  200  in an in-field operation mode. The blocking valves  212 ,  218  are opened, allowing free flow of hydraulic fluid into and out of the steering cylinder  216  and back to tank  210 . Steering of the windrower  100  is controlled by the front drive wheel dual-path steering system only (e.g., without steering from the cylinder  216 ). 
       FIG. 11  is the hydraulic circuit  200  in a straight path operation mode. The steering proportional directional valve  220  is centered with the steering cylinder  216  centered (e.g., partially extended). Steering of the windrower  100  is controlled by a combination of the front drive wheel dual-path steering and the rear axle steering from the cylinder  216 . The desired steering position can be provided to the controller  208  by a steering wheel or device position sensor  206 , while the actual rear wheel position feedback can be provided to the controller  208  by the steering cylinder position sensor  214  (e.g., on the left-hand side caster as shown in  FIGS. 1-6 ). 
       FIG. 12  is the hydraulic circuit  200  in a right turn operation mode. The steering proportional directional valve  220  is shifted to extend the steering cylinder  216 , resulting in the windrower  100  turning right. Steering of the windrower  100  is controlled by a combination of the front drive wheel dual-path steering and the rear axle steering from the cylinder  216 . The desired steering position can be provided to the controller  208  by a steering wheel or device position sensor  206 , while the actual rear wheel position feedback can be provided to the controller  208  by the steering cylinder position sensor  214  (e.g., on the left-hand side caster as shown in  FIGS. 1-6 ). 
       FIG. 13  is the hydraulic circuit  200  in a left turn operation mode. The steering proportional directional valve  220  is shifted to retract the steering cylinder  216 , resulting in the windrower  100  turning left. Steering of the windrower  100  is controlled by a combination of the front drive wheel dual-path steering and the rear axle steering from the cylinder  216 . The desired steering position can be provided to the controller  208  by a steering wheel or device position sensor  206 , while the actual rear wheel position feedback can be provided to the controller  208  by the steering cylinder position sensor  214  (e.g., on the left-hand side caster as shown in  FIGS. 1-6 ). 
       FIGS. 14-16  are perspective and detailed views of an exemplary steering control system  300  of the present disclosure. The steering control system  300  can be substantially similar in structure and function to the steering control system  130  except for the distinctions noted herein. Therefore, like reference numbers refer to like structures. Particularly, rather than having a steering assembly associated with only one caster, the steering control system  300  includes a steering assembly associated with each of the casters with only one of the steering assemblies being actuated to steer the rear wheels and the other steering assembly moving in an equal and opposite direction from the first steering assembly. 
     The steering assembly  134  on one of the casters  122  includes the sensor  152  in communication with the controller  154  such that the detected position of the caster  122  (based on the extension/retraction of the cylinder  144 ) can be used to control the cylinder  144  to achieve the desired steering of the windrower  100 . Rather than a passive damper, the steering control system  300  includes a second steering assembly  302  at the other caster  120 . The steering assembly  302  includes a steering cylinder  304  capable of being hydraulically actuated to extend or retract, thereby adjusting the rotational position of the caster  120 . 
     Rather than having a sensor associated with the steering cylinder  304 , the steering assembly  302  can be hydraulically coupled to the steering assembly  134  such that actuation of the steering cylinder  144  to extend or retract automatically actuates the steering cylinder  304  to extend or retract in an equal and opposite direction. The extension or retraction of the steering cylinder  304  is therefore directly tied to actuation of the steering cylinder  144  and is dependent on the single sensor  152  of the steering control system  300 . Both steering cylinders  144 ,  304  are actuated to steer the casters  120 ,  122 , with the position of only one of the casters  120 ,  122  being measured by the sensor  152  (e.g., a master/slave arrangement with the steering cylinder  144  acting as the master component and the steering cylinder  304  acting as the slave component). 
     Each of the steering cylinders  144 ,  304  is coupled to the steering proportional valve  160  via hydraulic lines  306 ,  308 . The steering cylinders  144 ,  304  are coupled to each other by a hydraulic line  310 , which is further coupled to a blocking valve  312  by a hydraulic line  314 . The steering proportional valve  160  is coupled to blocking valves  316 ,  318  by hydraulic lines  320 ,  322 . Each of the blocking valves  312 ,  316 ,  318  is coupled to tank  178  by a hydraulic line  176 , and the steering proportional valve  160  is coupled to tank  178  by a hydraulic line  324 . The steering proportional valve  160  is further coupled to the steering pump  172  by hydraulic line  170 . 
       FIG. 17  is a top view of the steering control system  300  in a left turn operation. Arrow  180  represents the direction of rotation of the caster  122  as actuated by the steering assembly  134 , and the direction of rotation of the caster  120  as actuated by the steering assembly  302  tied to the steering assembly  134 . In the left turn operation, the steering assembly  134  is hydraulically controlled to retract the cylinder  144 , and the cylinder  304  of the steering assembly  302  is hydraulically controlled to extend in an equal and opposite direction to the cylinder  144  due to fluid connection of the barrel ends of the cylinders  144 ,  304 .  FIG. 18  is a top view of the steering control system  300  in a right turn operation. 
     Arrow  182  represents the direction of rotation of the caster  122  as actuated by the steering assembly  134 , and the direction of rotation of the caster  120  as actuated by the steering assembly  302  tied to the steering assembly  134 . In the right turn operation, the steering assembly  134  is hydraulically controlled to extend the cylinder  144 , and the cylinder  304  of the steering assembly is hydraulically controlled to extend in an equal and opposite direction to the cylinder  144 . In both left and right turn operations, steering of the windrower  100  is controlled by a combination of the front wheel dual-path steering and the rear wheel steering assemblies  134 ,  302 , with the right-hand side steering assembly  302  controlled based on the left-hand side position sensor  152 . 
     The steering control system  300  therefore provides for rear axle steering of the windrower  100  with cylinders  144 ,  304  hydraulically coupled to move in equal and opposite directions during operation with the position of only one cylinder  144  measured to control the steering action of the rear wheels. The steering control system  300  is capable of providing stability to the windrower  100  during high-speed operation with directional control of the rear wheels without necessitating multiple position sensing cylinders  144 ,  304 . As noted above, the windrower  100  includes two steering cylinders  144 ,  304  for each respective caster  120 ,  122 . Only one of the cylinders  144  includes a means for the controller  154  to determine the radial position of the caster  122  (e.g., an internal cylinder position sensor, an external position sensor, a radial potentiometer, or the like). 
     A control valve manifold can be used to extend and retract the steering cylinders  144 ,  304 . A steering pump  172  can provide pressure or flow to the manifold, and valves and lines can provide a path for flow to return to tank  178 . An electronic steering wheel/device position sensor can be used to provide an operator commanded steering wheel/device position to the controller  154  which, in turn, can be used to calculate and execute the commanded steering position via a control algorithm (e.g., the amount of extension or retraction of the cylinder  144 ,  304 ). 
     The windrower  100  can retain the front drive dual-path steering for all operations, with the steering control system  300  assisting in stabilizing operation of the windrower  100  in at least the high-speed operation mode. For example, steering in the field can be provided only by the front drive dual-path steering, while the rear axle steering functions along with the dual-path steering during high-speed road mode operation. The cylinders  144 ,  304  connect to respective arms  146 ,  138  attached to the top of the caster vertical pivot shaft at one end and the rear axle  124  of the windrower  100  at the other end (via flanges  148 ,  140 ). 
     The barrel ports of the cylinders  144 ,  304  can be plumbed together, while the rod ports can be plumbed to the proportional steering valve  160 . The hydraulic lines to the steering cylinders  144 ,  304  include blocking valves  312 ,  316 ,  318  to tank  178  that are normally open, allowing free flow of fluid into and out of the cylinders  144 ,  304  during field operation. The blocking valves  312 ,  316 ,  318  are provided to block flow back to tank  178  in the rear axle steering mode. When all blocking valves  312 ,  316 ,  318  are blocking flow back to tank  178 , movement of the steering cylinders  144 ,  304  can be controlled by the steering valve  160 . 
     Such arrangement results in retraction of a first cylinder (e.g., cylinder  144 ) causing fluid to be displaced from the barrel end of the first cylinder and into the barrel end of the second cylinder (e.g., cylinder  304 ). The fluid displacement actuates the second cylinder to extend an equal amount that the first cylinder retracts when the proportional valve  160  shifts to retract the first cylinder. The setup allows a position sensor  152  to be provided on only one steering cylinder for providing steering cylinder position feedback to the controller  154 . 
     In the field/free castering operation mode, all blocking valves  312 ,  316 ,  318  are opened, allowing free flow of fluid to and from the steering cylinders  144 ,  304 . The steering cylinders  144 ,  304  extend and retract based on the caster  120 ,  122  position due to the steering control from the front drive wheels. The steering valve  160  remains in the centered or closed position during such operation. The steering cylinders  144 ,  304  act as caster dampers during field operation as the flow of fluid into and out of the cylinders  144 ,  304  provides a viscous damping force. 
     In the rear axle steering operation mode, the operator can select the rear axle steering operation through an operator console, user interface or other command switch. The operator can be prompted to drive the windrower  100  straight forward in order to orient the casters/rear wheels behind the rear axle  124  as this is the orientation of the casters  120 ,  122  during the rear axle steering operation. In some embodiments, one or more proximity sensors can be used to detect the position of the casters  120 ,  122  relative to the rear axle  124 . When the controller  154  receives data indicating that the sensing cylinder  144  is in the steering straight position, the blocking valves  312 ,  316 ,  318  can be shifted to block all flow into and out of the steering cylinders  144 ,  304 , creating a closed circuit in which the retraction of a steering cylinder on one side causes an equal and opposite extension of the steering cylinder on the other side of the windrower  100 . 
     To steer the rear wheels, the operator can make a steering input command by turning the steering wheel or device to a desired position. Such position can be sensed by a steering sensor coupled to the steering wheel or device. The controller  154  can use the detected position of the steering wheel or device to command a steering angle of the rear axle steering cylinder  144  with position sensing. For example, the controller  154  can actuate the steering cylinder  144  to extend or retract to achieve the desired steering with the position sensor  152  providing feedback to the controller  154  regarding actuation of the cylinder  144 . 
     Because the cylinder  144  includes the position sensor  152  and the cylinder  304  does not, the controller  154  uses the position data from the position sensor  152  for adjustments of both cylinders  144 ,  304 . For example, the cylinder  144  can be actuated to extend by shifting the steering valve  160  to retract the cylinder  304 . As a further example, if the input command necessitates that the cylinder  144  be retracted, the steering valve  160  can shift to retract the cylinder  144  which, in turn, extends the cylinder  304  due to the barrel ports of the cylinders  144 ,  304  being plumbed together. In some embodiments, the steering valve  160  can hydraulically connect only to the rod ends of the steering cylinders  144 ,  304  with no direct fluid communication with the barrel ends of the steering cylinders  144 ,  304 . 
     As such, the steering control system  300  allows for one position sensing cylinder  144  to determine the radial position of the caster  122 , while the second caster  120  and cylinder  304  do not necessitate position sensing. The steering valve  160  acts directly on only the rod end of the cylinder  144 , reducing the flow requirement for a comparable system in which valves act on both the rod and barrel ends (e.g., due to the reduced volume of the rod end compared to the barrel end). It should be understood that the position sensing can be on either the cylinder  144  or cylinder  304 . 
     In some embodiments, the steering valve can act on the barrel end of the cylinders, the rod end port of the steering cylinders can be plumbed together rather than the barrel ends or the like. In some embodiments, a proximity sensor can be used on the non-position sensing side to confirm that the non-sensing side is centered when entering the rear axle steering operation. For example, a magnetic sensor and a fixed target that is sensed only when the caster is in the proper rear axle steering straight orientation can be used. Alternatively, an active calibration can take place to enter the rear axle steering mode by prompting the operator to drive straight forward for a predetermined distance after the position sensing caster is in a straight orientation position. At such point, all blocking valves can block flow from the steering cylinders to tank and the system  300  can be a closed circuit with rear axle steering active. 
       FIG. 19  is a static image of a hydraulic circuit  400  of the steering control system  300 . The hydraulic circuit  400  includes a relief valve  402 , a steering pump  404 , a steering wheel or device position sensor  406 , and a controller  408 . The hydraulic circuit  400  includes a tank  410 , return to tank blocking valves  414 ,  420 ,  424 , and a steering proportional directional valve  422 . The hydraulic circuit  400  includes steering cylinders  412 ,  418  and a cylinder position sensor  416  associated with only the steering cylinder  418 . 
       FIG. 20  is the hydraulic circuit  400  in an in-field operation mode. The blocking valves  414 ,  420 ,  424  are opened, allowing free flow of hydraulic fluid into and out of the steering cylinders  412 ,  418  and back to tank  410 . Steering of the windrower  100  is controlled by the front drive wheel dual-path steering system only (e.g., without steering from the cylinders  412 ,  418 ). 
       FIG. 21  is the hydraulic circuit  400  in a straight path operation mode. The steering proportional directional valve  422  is centered with the steering cylinders  412 ,  418  centered (e.g., partially extended). Steering of the windrower  100  is controlled by a combination of the front drive wheel dual-path steering and the rear axle steering from the cylinder  418 . The desired steering position can be provided to the controller  408  by a steering wheel or device position sensor  406 , while the actual rear wheel position feedback can be provided to the controller  408  by the steering cylinder position sensor  416  (e.g., on the left-hand side caster as shown in  FIGS. 14-18 ). 
       FIG. 22  is the hydraulic circuit  400  in a right turn operation mode. The steering proportional directional valve  422  is shifted to retract the steering cylinder  412  which, in turn, extends the steering cylinder  418 , resulting in the windrower  100  turning right. Steering of the windrower  100  is controlled by a combination of the front drive wheel dual-path steering and the rear axle steering from the cylinder  418 . The desired steering position can be provided to the controller  408  by a steering wheel or device position sensor  406 , while the actual rear wheel position feedback can be provided to the controller  408  by the steering cylinder position sensor  416  (e.g., on the left-hand side caster as shown in  FIGS. 14-18 ). 
       FIG. 23  is the hydraulic circuit  400  in a left turn operation mode. The steering proportional directional valve  422  is shifted to retract the steering cylinder  418  which, in turn, extends the steering cylinder  412 , resulting in the windrower  100  turning left. Steering of the windrower  100  is controlled by a combination of the front drive wheel dual-path steering and the rear axle steering from the cylinder  418 . The desired steering position can be provided to the controller  408  by a steering wheel or device position sensor  406 , while the actual rear wheel position feedback can be provided to the controller  408  by the steering cylinder position sensor  416  (e.g., on the left-hand side caster as shown in  FIGS. 14-18 ). 
       FIG. 24  is a static image of an alternate hydraulic circuit  500  of the steering control system  130 . The hydraulic circuit  500  includes a relief valve  502 , a steering pump  504 , and a tank  506 . The hydraulic circuit  500  includes a return to tank blocking valve  508 , and a steering proportional directional valve  510 . The hydraulic circuit  500  includes a steering cylinder  512  and a cylinder position sensor  514 . 
     While exemplary embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the present disclosure. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the present disclosure.