ELECTROHYDRAULIC STEERING CONTROL SYSTEM

Abstract

Steering system (60) for a work vehicle with a steerable wheel (14), the steering system (60) comprising: a steering input device configured to provide a first steering input configured to move the steerable wheel (14) in a first direction and a second steering input configured to move the steerable wheel (14) in a second direction; a pilot system operatively connected to the steering input device, the pilot system comprising a first control line (76) operatively connected to the first steering input, a second control line (86) operatively connected to the second steering input, a first metering pre-valve (72) operatively connected between the first control line (76) and the second control line (86), and a second metering pre-valve (82) operatively connected between the first control line (76) and the second control line (86); a controlled system operatively connected to the pilot system, the controlled system comprising a first pressure control valve (80) operatively connected to the first control line (76) and having a first pressure control valve output, a second pressure control valve (88) operatively connected to the second control line (86) and having a second pressure control valve output, and a directional control valve (102; 134) operatively connected to the first pressure control valve output and to the second pressure control valve output and having a first directional control valve output and a second directional control valve output; and a steering cylinder (108) operatively connected to the steerable wheel (14) and to the first directional control valve output and to the second directional control valve output, wherein the first directional control valve output and the second directional control valve output move the steerable wheel (14) in the first direction and the other of the first directional control valve output and the second directional control valve output move the steerable wheel (14) in the second direction.

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to a steering system for a work vehicle and a work vehicle having such a steering system configured to reduce the likelihood of a system failure resulting in an undesirable steering operation. BACKGROUND

[0002] Agricultural equipment, such as a tractor or a self-propelled combine harvester, includes an electrohydraulic steering control system for adjusting the position of one or more wheels of a vehicle to establish a direction of movement of the vehicle. Steering control systems include electrohydraulic valves that respond to a steering control signal generated by a steering device, such as a steering wheel or joystick, or to a steering control signal provided by a GPS (Global Positioning System) signal. Steering control systems often include one or more sensors configured to detect a position of the steering device or a position of the wheels relative to a frame of the vehicle. In these types of systems, a failure of an electrohydraulic valve or an incorrect steering signal to an electrohydraulic valve by the control software can trigger an undesired or unwanted steering action.Such a steering action is detected by one or more of the system sensors and evaluated by a system controller. Once the undesired steering action has been detected by the system controller, a corrective signal is generated by the system controller to prevent unintentional steering due to the error. Detecting and responding to the error takes a certain amount of time, which is often too long to prevent an undesirable result. What is needed, therefore, is a steering control system configured so that the steering action can be initiated not only by an electro-hydraulic valve or an electronic command, but must also require a steering initiation action by the vehicle driver.

[0003] US Pat. No. 4,356,759 A further discloses a hydraulic control system for a transport vehicle, in which a hydraulic fluid flow is supplied from the pressure source to the servo motor via a control hydraulic circuit. The control hydraulic circuit includes a fluid control device that is mechanically connected to the steering unit of the transport vehicle.

[0004] Furthermore, from US 5 520 262 A an electro-hydraulic steering system with a pilot-operated directional control valve is known, which is arranged between a variable displacement pump and a pair of steering cylinders.

[0005] From US 2011 / 0 132 681 A1 a control system for a vehicle steering system using electro-hydraulic fluid control valves is known.

[0006] DE 10 2008 025 154 A1 discloses a steering system with a hydraulic actuator having at least one cylinder chamber, a fluid pressure source and a device for determining a pressure prevailing in the cylinder chamber in an operating state of the system.

[0007] US 4 736 811 A also discloses a steering system for a vehicle which is electronically controlled and has a manually operated, mechanical control as a backup.

[0008] WO 93 / 004 905 A1 further discloses a steering control arrangement which has an additional auxiliary steering control device.

[0009] US 2015 / 0 021 116 A1 further discloses a steering device having first, second, third, and fourth hydraulic chambers, wherein the first and third chambers can be actuated for steering in a first direction and the second and fourth chambers can be actuated for steering in a second direction. A pump system supplies fluid to a steering system, which can be operated to supply the pressurized fluid to one or more of the first, second, third, and fourth hydraulic chambers.

[0010] Furthermore, DE 10 2006 007 783 A1 discloses an electro-hydraulic standby steering system for a work machine.

[0011] DE 203 04 336 U1 further discloses a servo system for a vehicle with a steering linkage, a steering gear, a steering wheel connected to a control hydraulic motor, a modulator pump connected in parallel with the control hydraulic motor and capable of providing a hydraulic flow.

[0012] None of the cited documents discloses a steering system having the features of the present invention. SUMMARY

[0013] The object to be achieved with the invention is to provide an electronically controlled electrohydraulic steering system that overcomes electrohydraulic or electrical failures of a steering control system that trigger an undesired steering operation.

[0014] This object is achieved by a steering system having the features of claim 1 and a work vehicle having the features of claim 10. Advantageous further developments are the subject of the dependent claims.

[0015] In one embodiment of the invention, a steering system for a work vehicle having a steerable wheel is provided. The steering system includes a steering input device configured to provide a steering input for moving the steerable wheel, and a pilot system operatively connected to the steering input device. The pilot system includes a control line operatively connected to the steering input device. A controlled system includes a directional control valve operatively connected to the control line and having a pilot-operated control valve output. A steering cylinder is operatively connected to the steerable wheel and the controlled control valve output, the steering cylinder being configured to move the steerable wheel in response to the controlled control valve output.

[0016] According to the invention, a steering system having the features of claim 1 is provided for a work vehicle with a steerable wheel.

[0017] According to the invention, there is also provided a work vehicle having the features of claim 10, comprising a steerable wheel, a steering input device configured to provide a steering input for moving the steerable wheel, and a steering system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above-mentioned aspects of the present invention and the manner of obtaining them will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention in conjunction with the accompanying drawings, in which: Fig. 1 is a side elevational view of a work vehicle, and in particular an agricultural vehicle such as a tractor. Fig. Figure 2 is a simplified schematic diagram of an electro-hydraulic control system for a steerable wheel work vehicle. Fig. 3 is an embodiment of an electro-hydraulic steering control system. Fig. 4 is another embodiment of an electro-hydraulic steering control system. DETAILED DESCRIPTION

[0019] To promote an understanding of the principles of the novel invention, reference will now be made to the embodiments described herein and illustrated in the drawings, and specific language will be used to describe them. It is to be understood, however, that no limitation on the scope of the novel invention is intended thereby, and that such changes and further modifications in the illustrated devices and methods, and such further applications of the principles of the novel invention as therein illustrated, will normally be contemplated by those skilled in the art to which the novel invention pertains.

[0020] Fig. 1 is a side view of an agricultural work vehicle, and more particularly, a tractor 10 having a frame 12 supported on a pair of front wheels 14 and a set of rear wheels 16. An operator's cab 18 is mounted to the frame 12 and contains various controls for the work vehicle so that they are within reach of a seated or standing operator. In one aspect, these controls may include a steering wheel 20. An engine 22 is mounted to the frame 12 below a housing 24 and provides power to driven components of the tractor 10. The engine 22 is configured, for example, to drive a transmission (not shown) coupled to drive the front wheels 14 at various selected speeds and in either forward or reverse mode.In other embodiments, the rear set of wheels is driven to move the tractor, or all wheels are driven in a four-wheel drive mode to move the tractor 10.

[0021] While the described embodiments are described with reference to a tractor, other work vehicles are conceivable in addition to agricultural work vehicles, including construction vehicles, forestry vehicles, lawn care vehicles, and road vehicles such as those used for snow plowing, salt spreading, or vehicles with towing capability.

[0022] The cab 18 defines an operator workstation 26 supported by the frame 12. The cab 18 also includes a seat 28 for seating the operator. The operator workstation 26, in various embodiments, includes one or more operator interfaces, a steering wheel, a joystick, an accelerator pedal, and a PTO control device for engaging or disengaging the PTO. Pedals for a brake and clutch are also disposed in the cab 18, but are not shown.

[0023] The user interface includes a plurality of operator-selectable buttons configured to enable the operator to control the operation and function of the tractor 10. The user interface, in one embodiment, includes a user interface screen having a plurality of user-selectable buttons for selecting from a variety of commands or menus, each of which is selectable via a touchscreen with a display. In another embodiment, the user interface includes a plurality of mechanical buttons and a touchscreen. In another embodiment, the user interface includes a screen and only mechanical buttons. A communications antenna 30 is carried by the cab 18 and provides for the transmission and reception of signals transmitted wirelessly.In one embodiment, the communication antenna 30 is a GPS antenna configured to receive and transmit global positioning data from and to a GPS satellite, as is known to those skilled in the art.

[0024] Fig. Figure 2 is a simplified schematic diagram of the work vehicle and a steering control system embodying the invention. In the illustrated embodiment, the steered front wheels 14 are steerable by the steering wheel 20 located in the cab 18. A steered wheel 14 angle sensor 32 senses the angular position of the wheels 14 relative to the frame 12 and includes an output line 33 coupled to an electronic control unit or controller 34. A steering wheel angle sensor and input device 26 are operatively connected to the steering wheel and connected via signal lines to the controller 34 and the hydraulic valve assembly 46. A wheel speed sensor 36 includes an output line 38 coupled to the controller 34 and provides a wheel speed signal. In other embodiments, the wheel speed is alternatively provided by a sensor connected to the rear wheels.Vehicle speed could alternatively be provided by processing GPS signals. In one embodiment, wheel speed sensor 36 is used to provide a speed of the work vehicle. Antenna 30 is operatively connected to a communications circuit 40, which is operatively coupled to controller 34. A GPS unit 42 provides a vehicle position signal to controller 34.

[0025] Communication circuitry 40 is configured to transmit signals generated by controller 34, which, in some applications, are generated in response to information submitted by an operator via the user interface at driver workstation 26. A memory / processor 44 is operatively connected to controller 34 and configured to store information. In various embodiments, memory / processor 44 is internal memory located within controller 34 or in an externally located memory / processor 44.

[0026] The controller 34 is configured to execute software instructions located in the memory / processor storage 44. The software includes one or more specific applications, components, programs, objects, modules, or instruction sequences, typically referred to as "program code." The program code includes one or more instructions located in the memory and other storage devices that execute control algorithms to adjust the position of the wheels 14 in light of, for example, the sensor position of the wheels 14 provided by the angle sensor 32, commands from the driver via the steering wheel 20, or GPS signals.

[0027] In some embodiments, communication circuitry 40 is used for internal communication between devices or circuits located within the work vehicle. In still other embodiments, communication circuitry 40 provides unidirectional or bidirectional communication to and from antenna 30 and to and from GPS unit 42.

[0028] The controller 34, in various embodiments, comprises a computer, a computer system, or a programmable device, e.g., a single-user or multi-user computer. In other embodiments, the controller 34 comprises one or more processors (e.g., microprocessors) and associated internal memory, including random access memory (RAM), comprising the memory of the controller 34, as well as any additional memory levels, e.g., cache memory, non-volatile or backup memory (e.g., programmable or flash memory), read-only memory, etc. Additionally, the memory may comprise a memory location physically located at a different location than the processing devices and may include any cache memory in a processing device, as well as any memory capacity used as virtual memory, e.g.,stored on a mass storage device or other computer connected to the controller 34 via the communication circuit 40. The mass storage device may include a cache or other data space, which may include databases.

[0029] The steering control system further includes a valve assembly 46 having one or more hydraulic circuits, including various hydraulic valves, such as electrically controlled valves, and various hydraulic and electrical lines. The valve assembly 46 receives a boost pressure and a working pressure from various pumps, including a pump 48 and a pump 50. In certain embodiments, pump 48 is configured as a lower-pressure boost pump, and pump 50 is configured as a higher-pressure steering pump.

[0030] Control signals, for example, hydraulic and electrical signals, are received by the valve assembly 46 from one or more controllers, referred to herein as the controller 34, via a signal line 52. Control signals are also received from the combined steering wheel angle sensor / metering pump 26 via a signal line 53 by the valve assembly 46. The signal line 52, which is depicted as a single line in various embodiments, includes one or more signal lines for transmitting electrical signals to and from the hydraulic and electrical valves of the valve assembly 46.

[0031] Fig. Figure 3 illustrates one embodiment of an electro-hydraulic steering system 60 that includes the steering wheel 20 operatively coupled to a drive shaft 62 connected to an input metering device 64, such as a gear, vane, piston, or any other type of positive displacement pump. The metering device 64 includes a first port 66 and a second port 68, each of which directs a flow of pressurized fluid in response to movement of the drive shaft 62 about a longitudinal axis of rotation. A steering command angle sensor 70 is operatively connected to the steering wheel 20, the drive shaft 62, or the metering device 64 and configured to provide a steering command angle signal to determine a position of the steering wheel 20 and ultimately an indication of a desired angle of one or all of the steered wheels.The steering command angle sensor 70 is operatively connected to the controller 34 to provide the steering angle command signal.

[0032] Port 66 is operatively connected to the metering control flow bypass throttle valves controlled by the controller 34 via control lines 74 and 84. Port 66 also provides a pressurized fluid flow to pressurize a control line 76, which is operatively connected to a pilot-operated first pressure regulating valve 80. In the same manner, port 68 is operatively connected to the metering control flow bypass throttle valves controlled by the controller 34 via control lines 74 and 84. Port 68 also provides a pressurized fluid flow to pressurize a control line 86, which is operatively connected to a second pilot-operated pressure regulating valve 88.

[0033] The metering pilot valves 72 and 82, in various embodiments, are either normally open or normally closed when the system is not operating. In a specific embodiment, one of the metering pilot valves 72 and 82 is a normally open valve and the other is a normally closed valve so that in the event of a general electrical or hydraulic failure, the steering response is neither the least responsive nor the most aggressive. In the illustrated embodiment, the metering pilot valve 72 is normally closed and the metering pilot valve 82 is normally open. Each of the metering pilot valves 72 and 82 are continuously variable valves in which the amount of flow through the valve is adjusted by the controller 34 via control lines 74 and 84.

[0034] Pilot line 76 and pilot line 86 are operatively connected to a low-pressure source 81, which includes an oil pan 83. A valve 85 is coupled between pilot lines 76 and 86 to ensure that the pilot system remains full of fluid. The external pressure source could be a separate pump, flow from another unrelated system on the work vehicle, or from a pressure reducing valve connected to a main source of steering flow, such as pump 110.

[0035] The metering device 64 directs the fluid flow and consequently adjusts the fluid pressure in both the control line 76 and the control line 86. The level of fluid pressure in either fluid line is a direct result of the direction of the steering determined by the metering device 64.

[0036] A check valve 87 and a pressure relief valve 89 ensure that the pressure in the pilot system does not exceed predetermined allowable limits. The pressure relief valve 89 is operatively connected to the oil pan 83. When the input metering device 64 is embodied as a positive displacement pump, rotation of the steering wheel in a first direction, for example, a clockwise direction, as shown, allows the orifice 68 to provide a positive flow of fluid into the control line 86. At the same time, a negative flow of fluid occurs into the orifice 66. Counterclockwise rotation of the steering wheel, as shown, causes a positive flow of fluid into the control line 76 and a negative flow of fluid into the orifice 68.

[0037] The fluid pressure in each of the control lines 76 and 86 is adjusted by each of the metering pilot valves 72 and 82 in response to control signals generated by the controller 34 and transmitted via the control lines 74 and 84. By controlling the amount of pressure in each of the control lines 76 and 86, the pressure signal is provided to the pilot-operated first pressure control valve 80 and the second pilot-operated pressure control valve 88.

[0038] Because the metering pilot valve 72 and the metering pilot valve 82 have an orifice size controlled by the controller 34 and provide the appropriate amount of pressure in the control lines 76 and 86, these valves are considered part of a pilot system. The pilot system also includes the fixed orifices or restrictors 92 and 96, the external low-pressure source 81, the metering pump 64, and the other described valves that build fluid pressure in the control lines 76 and 86. In other embodiments, the pilot system includes a fewer or greater number of devices. The pilot system output lines, control lines 76 and 86, are connected to the pressure control valves 80 and 88, which control a flow and directional control valve that ultimately controls the direction of the wheels. The pressure control valves 80 and 88 are considered a pilot-operated system.

[0039] The flow generated by the metering pump 64 at the orifice 68 along the control line 86 not only moves to a control portion 90 of the pressure control valve 88, but some flow attempts to move through to the orifice 66 of the metering pump 64, through a restriction 92 and 96 and the metering pilot valves 72 and 82, rather than pressurizing the control portion 90 of the pressure control valve 88. This bypass flow creates pressure on the control portion 94 of the pressure control valve 80. The pressure control valve 88 then provides an output pressure generally proportional to the pressure applied to its control portion 90. The pressure control valve 88 includes an output control portion 91.

[0040] Similarly, the flow generated by the metering pump 64 at orifice 66 along control line 76 not only moves to a control portion 94 of the pressure control valve 80, but some flow attempts to move through to the orifice 68 of the metering pump 64, through a restriction 96 and 92 and the metering pilot valves 82 and 72, rather than pressurizing the control portion 94 of the pressure control valve 80. This bypass creates pressure on the control portion 90 of the pressure control valve 88. The pressure control valve 88 then provides an output pressure generally proportional to the pressure applied to the control portion 94. The pressure control valve 80 includes an output control portion 93.

[0041] Each of the pressure control valves 80 and 88 generates an output pressure at pressure outputs 98 and 100, respectively. The pressure output 98 is operatively connected to a pilot-operated flow and directional control valve 102 at a first control portion 104. In one embodiment, the directional control valve 102 is a three-position pilot-operated control valve. The pressure output 100 is operatively connected to the directional control valve 102 at a second control portion 106. Fluid pressure provided at either the first or second control portions 104 and 106 causes the valve spool to move from a center position to flow oil to a steering cylinder 108, which moves the wheels 14 in a direction determined by the steering device 20. A valve position sensor 109 is configured to determine the position of the spool of the directional control valve 102 and provide the determined position as a signal to the controller 34.The position of the steering cylinder 108 is identified by a cylinder position sensor 111. The identified position of the steering cylinder 108 is provided to the controller 34. Alternatively, a wheel steering angle sensor could be used instead of the steering cylinder position sensor. Both the cylinder position sensor 111 and the angle sensor 32 are considered control output sensors.

[0042] By specifying a difference between the input control area 90 and an output control area 91 of the pressure control valve 88, and also for the output control area 93 of the directional control valve 102, a control pressure for the directional control valve 102 is provided that is higher than the output pressure provided by the metering pump 64. In this way, steering handwheel torques can be reduced.

[0043] In the illustrated embodiment, pressure control valves 80 and 88 are pilot-operated pressure reducing / limiting valves. In another embodiment, pressure control valves 80 and 88 are configured as pilot-operated pressure relief valves by directly connecting a flow source to the control portions of directional control valve 102.

[0044] A hydraulic pump 110 is operatively connected to the directional control valve 102, which, when activated by the first or second control portions 104 and 106, supplies fluid under pressure to move the steering cylinder 108. The hydraulic pump 110 is operatively connected to the pressure control valves 80 and 88. An oil pan 112 includes a fluid source for use by the pump 110. Each of the pressure control valves 80, 88 and directional control valve 102 includes fluid outlets that discharge excess fluid to the oil pan 112 when it is not necessary to adjust the position of the steering cylinder 108. The pump 110 is generally considered a high-pressure source of fluid.

[0045] The output pressure from the pressure control valve 88 is applied to the control portion 106 of the directional control valve 102, causing it to move from its center position, which in turn causes oil to flow to the steering cylinder 108 and thus turn the steerable wheels. It is generally desirable to have a position-responsive steering system in which the position of the steering cylinder 108 (and the steered wheels) is generally proportional to the rotational position of the steering wheel from a center point. In one embodiment, position-responsive steering is achieved by controlling or preventing the bypass of control flow through ports 92 and 96 by controlling the metering pilot valves 82 and 72. The metering pilot valves 82 and 72 are controlled by the controller 34.

[0046] In one embodiment, controller 34 monitors signals from steering command angle sensor 70, valve position sensor 109, and cylinder position sensor 111 when all are in use. In one possible control algorithm, steering command angle sensor 70, valve position sensor 109, and cylinder position sensor 111 are monitored, and metering pilot valves 82 and 72 are controlled such that directional control valve 102 generates flow to steering cylinder 108 to provide position-dependent steering. In this control scheme, there is an inner control loop using valve position sensor 109 and steering command angle sensor 70, and an outer control loop between cylinder position sensor 111 and steering command angle sensor 70.The inner control loop is used by the controller 34 to monitor the rate of rotation of the steering device 20 via the steering command angle sensor 70 and to monitor the position of the directional control valve 102 via the valve position sensor 109. In response to these sensor outputs, the metering pilot valves 72 and 82 are adjusted to produce flow approximately providing position-sensitive steering for given output / input characteristics of the directional control valve 102. The outer control loop is used by the controller to monitor the position of the steering device 20 via the steering command angle sensor 70 and to monitor the position or angle of the steered wheel via the cylinder position sensor 111 in order to make additional adjustments to the control of the metering pilot valves 72 and 82 to improve the accuracy of the position-sensitive steering.

[0047] In one embodiment, when the steering cylinder 108 reaches a stop or is prevented from moving further due to an overload, the metering pre-valves 82 and 72 are closed to provide tactile feedback to the operator that the steering has either reached its limit or is locked.

[0048] In another embodiment, the control algorithm is designed to include a variable steering ratio either as a function of vehicle speed, turning angle, or another parameter. For example, under moderate speed driving conditions of approximately 16 kilometers per hour (km / h), as determined by signals from a wheel speed or GPS sensor, the control algorithm could be written such that three (3) complete revolutions of the steering wheel 20 result in the steerable wheels turning from far left to far right. However, at lower and higher speeds, the control algorithm could be written such that the internally encoded parameters result in a full left-to-right turn with only one and a half (1.5) revolutions and five (5) revolutions of the steering wheel 20, respectively.Similarly, it would be possible to change the control parameters as a function of the angle of the steerable wheel to affect the steering ratio rather than the vehicle speed. Similarly, it would be possible to change the control parameters from an external input provided by the attached or towed device or from a driver-entered setting to effect more or less responsive steering. The means of achieving this are well known to those skilled in the art of control software development.

[0049] In still other embodiments, the steering system includes one or more fluid temperature sensors to identify fluid temperature(s) that can be used to improve performance.

[0050] Fig. Figure 4 illustrates another embodiment of an electro-hydraulic steering control system 120 with an external steering controller that uses an electronic guidance system, such as one that uses GPS or line tracking signals. In this embodiment, the steering control system is Fig. 3 is configured to include additional pilot valves to provide integrated, cost-effective external control. The devices associated with both embodiments of the Fig. 3 and Fig. 4 are identified by the same element numbers and different or additional devices are re-identified.

[0051] As in Fig. As shown in Figure 4, the steering control system 120 includes the capability of external steering control, such as guidance systems based on GPS (Global Positioning System) signals. In this embodiment, the steering system is configured to include additional control valves to provide integrated, cost-effective external control.

[0052] A means for providing an integrated external control capability as in Fig. 4, includes the addition of external flow valves 122, 124, 126, and 128. A relief valve 130 and a pressure reducing valve 132 are provided to allow the pump 81 to keep the main steering system pilot circuit filled with fluid and also to provide a pressure and flow source for external control. Alternatively, the pressure and flow source for external control may be provided by supplying the pressure and flow through a pressure reducing valve connected to the high-pressure pump 110. The GPS unit 42 is operatively connected to the controller 34, as shown in Fig. 2 shown.

[0053] Each of the external electronic flow valves 122, 124, 126 and 128 includes control lines operatively connected to a controller 34, which in this embodiment is configured with a different or additional set of control instructions than the controller 34 of Fig. 3. Flow valves 126 and 128 in this embodiment provide redundancy against inadvertent external control in the event of a failure of flow valves 122 and 124. In other embodiments, flow valves 126 and 128 are not included. In the illustrated embodiment, flow valves 122 and 124 are depicted as directional / flow control valves. In other embodiments, flow valves 122 and 124 are pressure reducing / limiting valves.

[0054] A switch 135 is operatively connected to the controller 34. Actuation of the switch in accordance with the controller 34 results in a first state indicating that the work vehicle is to be operated in a manual mode and a second state indicating that the work vehicle is to be operated in an external control mode, i.e., the GPS mode. In one embodiment, the switch 135 is located at the operator workstation 26 for use by the operator. The operator moves the switch from one state to the other to signal the controller 34 that the work vehicle is in the manual control mode or the external control mode. Additionally, movement of the steering wheel, as indicated by the steering command angle sensor 70, will cause the controller 34 to switch the control mode from the external to the manual mode.

[0055] Since the steering control system 120 includes the use of the external controller to adjust the steering cylinder 108, a pilot-operated flow and directional control valve 134 includes a first control portion 136 operatively connected to the control line 98 and a second control portion 138 operatively connected to the control line 100. The control portions 136 and 138 provide the same function as the control portions 104 and 106. Fig. 3. In this embodiment, the directional control valve 134 includes two additional control sections, control sections 140 and 142. The control section 142 is operatively connected to the flow valve 126, and the control section 140 is operatively connected to the flow valve 128. A valve position sensor 143 identifies the position of the directional control valve 134.

[0056] In another embodiment, directional control valve 134 does not include control sections 140 and 142. Instead, pressure control valves 80 and 88 each include an additional control section (not shown) connected to one of the outputs of flow control valves 126 and 128. In this case, flow control valves 122 and 124 are configured as pressure-reducing relief valves.

[0057] For normal steering using an input to the steering device 20, each of the flow valves 122, 124, 126, and 128 is in a de-energized position, diverting any control pilot pressure provided by the pump 81 to the drain 83. Steering is performed as described with respect to Fig. 3 described.

[0058] During an external control mode of the embodiment of Fig. 4, which includes the additional control areas 140 and 142 of the directional control valve 134, the flow valves 122, 126, 124, and 128 are controlled by the controller 34. In the alternative configuration with the additional control areas on the pressure control valves 80 and 88, one or both of the metering pre-valves 72 and 82 are held in the open position.

[0059] To perform externally controlled rotation in one direction, the valve 126 is energized to connect the output of the flow valve 122 to an external control portion 142 of the directional control valve 134 or to the pressure control valve 88 if that configuration is used. The flow valve 122 is then energized, sending oil to move the directional control valve 134 directly, or via an increase in the output pressure from the pressure control valve 88, so that the flow is directed to the steering cylinder 108. The electronic control of the flow valve 122 is achieved by closing a control loop around the desired angle of rotation and cylinder position sensor 111 and possibly the valve position sensor 143 in a manner similar to that for the embodiment of Fig. 3. Rotation of the wheels in the opposite direction is achieved in a similar manner by energizing the flow valves 128 and 124.

[0060] In additional embodiments, an additional external steering valve, such as directional control valve 134, is provided to operatively connect to the illustrated vehicle steering system.

Claims

[1] Steering system (60) for a work vehicle with a steerable wheel (14), the steering system (60) comprising: a steering input device configured to provide a first steering input configured to move the steerable wheel (14) in a first direction and a second steering input configured to move the steerable wheel (14) in a second direction; a pilot system operatively connected to the steering input device, the pilot system comprising a first control line (76) operatively connected to the first steering input, a second control line (86) operatively connected to the second steering input, a first metering pre-valve (72) operatively connected between the first control line (76) and the second control line (86), and a second metering pre-valve (82) operatively connected between the first control line (76) and the second control line (86); a controlled system operatively connected to the pilot system, the controlled system comprising a first pressure control valve (80) operatively connected to the first control line (76) and having a first pressure control valve output, a second pressure control valve (88) operatively connected to the second control line (86) and having a second pressure control valve output, and a directional control valve (102; 134) operatively connected to the first pressure control valve output and to the second pressure control valve output and having a first directional control valve output and a second directional control valve output; and a steering cylinder (108) operatively connected to the steerable wheel (14) and to the first directional control valve output and to the second directional control valve output, wherein the first directional control valve output and the second directional control valve output move the steerable wheel (14) in the first direction and the other of the first directional control valve output and the second directional control valve output move the steerable wheel (14) in the second direction. [2] The steering system (60) of claim 1, further comprising a steering command angle sensor (70) operatively connected to the steering input device, a valve position sensor (109; 143) operatively connected to the directional control valve (102; 134), and one of a cylinder position sensor (111) operatively connected to the steering cylinder (108) and an angle sensor (32) of a steered wheel (14), wherein each of the steering command angle sensor (70), the valve position sensor (109; 143), the cylinder position sensor (111), and the angle sensor (32) of the steered wheel (14) provides a signal to adjust a position of the first metering pilot valve (72) and a position of the second metering pilot valve (82). [3] The steering system (60) of claim 2, further comprising a controller (34) operatively connected to the first metering pre-valve (72) and the second metering pre-valve (82), the controller (34) comprising a processor and a memory (44), the memory (44) configured to store program instructions, and the processor configured to execute the stored program instructions to: adjusting a position of the first metering pre-valve (72) and the second metering pre-valve (82) to move the directional control valve (102; 134) in a first direction; adjusting a position of the first metering pre-valve (72) and the second metering pre-valve (82) to move the directional control valve (102; 134) in a second direction opposite to the first. [4] The steering system (60) of claim 3, further comprising a first flow valve (122, 126) having a first control output and a second flow valve (122, 126) having a second control output, and the directional control valve (134) further comprising a third control portion (142) operatively connected to the first control output and a fourth control portion (140) operatively connected to the second control output. [5] Steering system (60) according to one of claims 1 to 4, characterized by that the first control line (76) is functionally connected to a first control area (104; 136) of the directional control valve (102; 134) and the second control line (86) is functionally connected to a second control area (106; 138) of the directional control valve (102; 134). [6] Steering system (60) according to one of claims 1 to 5, characterized bythat the first metering pre-valve (72) is normally open or normally closed and the second metering pre-valve (82) is normally open or normally closed. [7] Steering system (60) according to one of claims 5 or 6, characterized by that the first pressure control valve (80) is functionally connected to the first control line (76) and to the first control area (104; 136) of the directional control valve (102; 134) and the second pressure control valve (88) is functionally connected to the second control line (86) and to the second control area (106; 138) of the directional control valve (102; 134). [8] The steering system (60) of claim 4 or claim 4 and any one of claims 5 to 7, wherein the controller (34) is operatively connected to the first metering pre-valve (72), the second metering pre-valve (82), the first flow valve (122, 126) and the second flow valve (124, 128), the controller (34) comprising a processor and a memory (44), the memory (44) being configured to store program instructions, and the processor being configured to execute the stored program instructions to: to identify one of a manual control mode and an external control mode; and both the first metering pre-valve (72) and the second metering pre-valve (82) or activate both of the first flow valves (122, 126) and the second flow valves (124, 128) in response to the identified control mode. [9] The steering system (60) of claim 8, further comprising a steering command angle sensor (70) operatively connected to the steering input device, a valve position sensor (143) operatively connected to the directional control valve (134), and a cylinder position sensor (111) operatively connected to the steering cylinder (108), wherein each of the steering command angle sensor (70), the valve position sensor (143), and the cylinder position sensor (111) provides a signal to adjust a position of the first flow valve (122, 126) and a position of the second flow valve (124, 128). [10] Work vehicle, comprising: a steerable wheel (14); a steering input device configured to provide a steering input to move the steerable wheel (14); and a steering system (60) according to any one of claims 1 to 9, operatively connected to the steerable wheel (14) and the steering input device.

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