Caster wheel orientation sensor assembly

A system for sensing the angular position of a caster wheel includes a sensor mounted on a bearing which supports a shaft aligned with the rotational axis of the caster. A target on the shaft is detected by the sensor which generates signals indicative of the presence or absence of the target. The position of the target is coordinated with the position of the caster wheel such that the signals are indicative of the angular position of the caster wheel. The target may be a groove extending partially around the shaft and a remaining ungrooved portion of the shaft.

FIELD OF THE INVENTION

This invention relates to caster sensor systems for vehicle steering control.

BACKGROUND

Harvesters such as windrowers, tractors, and forage harvesters, have to operate effectively in different operational modes (e.g., field mode and high-speed mode for road transport). 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 each 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 harvester is effected by a difference in speed between the front wheels with the rear wheels following the steering in a castering action. This is known as “differential steering”.

Conventional harvesters generally use differential steering for both in-field operation mode and high-speed road transport operation mode. Differential 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, stability concerns arise during high-speed road transport (e.g., speeds greater than 24 mph) when only differential steering is used. 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. Stability at higher speeds may be increased by actively steering of one or both of the rear wheels. However, to prevent damage to the structural and mechanical components associated with the rear wheels it is advantageous to determine the angular orientation of the wheels relatively to the rear axle, and allow the switch from caster operation to active steering of the rear wheels only when the rear wheels are in a known position trailing the rear axle. There is clearly a need for a system which determines the orientation of rear castering wheels and permits the mode of vehicle steering to change only when the castering wheels are properly oriented.

SUMMARY

In one aspect the invention concerns a caster wheel orientation sensor assembly. In an example embodiment the assembly comprises a wheel arm having first and second ends oppositely disposed. A wheel is attached to the first end of the wheel arm. The wheel is rotatable about a first axis. A shaft is fixedly attached to the second end of the wheel arm and is oriented transversely to the first axis. A sensor target is positioned on the shaft. A bearing defines a bore. The shaft is received within the bore. The shaft is rotatable about a second axis oriented coaxially with the bore. A sensor is mounted on the bearing. The sensor is adapted to sense a presence or absence of the sensor target upon rotation of the shaft and generate signals indicative of the presence or the absence of the sensor target.

In an example embodiment the sensor target comprises a groove extending about a portion of a circumference of the shaft. In a practical example the groove subtends an angle between 270° and 300° about the shaft. In a particular example the groove subtends an angle of 285° about the shaft. In a further example, the groove may have a uniform depth over its entire extent, or the groove may have a non-uniform depth. In an example embodiment the groove comprises a first portion having a depth which increases with distance about the circumference, a second portion having a uniform depth, and a third portion having a depth which increases with distance about the circumference. In this example the second portion is positioned between the first and third portions. By way of further example the depth of the first portion and the depth of the second portion may increase linearly with the distance about the circumference. In another example embodiment the sensor target comprises a recess in the shaft. By way of further example, the recess comprises a flat surface. In a particular example embodiment the flat surface extends across a chord of a cross section of the shaft.

In an example embodiment the groove is positioned within the bearing and may also be positioned distal to the second end of the wheel arm. In an example embodiment the sensor comprises a proximity sensor. In a practical example the sensor may be a Hall effect sensor, a capacitive sensor, an inductive sensor, an optical sensor or an ultrasonic sensor.

The invention further encompasses a shaft orientation sensor assembly. In an example embodiment the assembly comprises a shaft having a groove extending about at least a portion of a circumference thereof. A bearing defines bore in which the shaft is received. The shaft is rotatable about an axis oriented coaxially with the bore. A sensor is mounted on the bearing proximate to the groove. The sensor is adapted to sense a depth of the groove upon rotation of the shaft and generate signals indicative of the depth of the groove.

An example sensor assembly according to the invention may further comprise a wheel arm having first and second ends oppositely disposed. A wheel is attached to the first end of the wheel arm. The wheel is rotatable about a wheel axis. The shaft is fixedly attached to the second end of the wheel arm and oriented transversely to the wheel axis in this example. In a further example embodiment the groove is positioned within the bearing and also may be positioned distal to the second end of the wheel arm.

In an example embodiment the sensor comprises a proximity sensor including examples such as Hall effect sensors, capacitive sensors, inductive sensors, optical sensors and ultrasonic sensors.

The invention also encompasses a harvester having a caster wheel orientation sensor system. In an example embodiment the harvester comprises a chassis and a first wheel arm having first and second ends oppositely disposed. A first wheel is attached to the first end of the first wheel arm. The first wheel is rotatable about a first wheel axis. A first shaft is fixedly attached to the second end of the first wheel arm and is oriented transversely to the first wheel axis. A sensor target is positioned on the shaft. A first bearing defines a first bore. The first shaft is received within the first bore. The first shaft is rotatable about a first shaft axis oriented coaxially with the first bore. The first bearing is mounted on the chassis. A sensor is mounted on the first bearing. The sensor is adapted to sense a presence or absence of the sensor target upon rotation of the first shaft and generate signals indicative of the presence or the absence of the groove. A controller is mounted on the chassis. The controller is adapted to receive the signals.

In an example embodiment the sensor target comprises a groove extending about a portion of a circumference of the shaft. In a practical example the groove may subtend an angle between 270° and 300° about the shaft. Further by way of example the groove may subtend and angle of 285° about the shaft. In particular example embodiments the groove may have a uniform depth over its entire extent or the groove may have a non-uniform depth. By way of example, the groove may comprise a first portion having a depth which increases with distance about the circumference, a second portion having a uniform depth, and a third portion having a depth which increases with distance about the circumference. In an example the second portion is positioned between the first and third portions. By way of example the depth of the first portion and the depth of the second portion increase linearly with the distance about the circumference.

In an example embodiment the groove is positioned within the first bearing and may also be positioned distal to the second end of the wheel arm. By way of example the sensor may comprise a proximity sensor such as a Hall effect sensor, a capacitive sensor, an inductive sensor, an optical sensor or an ultrasonic sensor.

In an example embodiment the harvester may further comprise a second wheel arm having first and second ends oppositely disposed. A second wheel is attached to the first end of the second wheel arm. The second wheel is rotatable about a second wheel axis. A second shaft is fixedly attached to the second end of the second wheel arm and is oriented transversely to the second wheel axis. A second bearing defines a second bore. The second shaft is received within the second bore. The second shaft is rotatable about a second shaft axis oriented coaxially with the second bore. An actuator acts between the chassis and one of the first and second shafts. The actuator is adapted to rotate one of the first and second shafts for steering the harvester. The controller is adapted to prevent the actuator from rotating the one of the first and second shafts upon receipt of the signals from the sensor indicative of the presence or the absence of the sensor target. In an example embodiment of a harvester the sensor target comprises a recess in the shaft. By way of further example, the recess comprises a flat surface. In a particular example the flat surface extends across a chord of a cross section of the shaft.

DETAILED DESCRIPTION

FIG. 1shows an example embodiment of a harvester, in this example a windrower10according to the invention. Windrower10comprises a chassis12on which two powered wheels14(not visible) and16and two unpowered casters18and20are mounted via a rear axle22. As is well understood, windrower10is powered by a diesel or gasoline engine which drives hydraulic pumps which in turn drive hydraulic motors which supply motive power to the powered wheels14and16as well as the cutter head24mounted on chassis12. Windrower10can be steered in two different modes as disclosed in U.S. patent application Ser. No. 16/200,324, titled “Steering Control System for Harvester and Methods of Using the Same”, filed Nov. 26, 2018 and hereby incorporated by reference herein. In the “field mode”, the casters18and20rotate freely about their respective caster axes26and28, and steering is effected by turning the powered wheels14and16at different speeds, the direction of the turn being toward the slower moving wheel. In the “high speed mode”, used for travel over roads, the steering is augmented by actively steering at least one of the casters (caster18in this example). Active steering of the caster18increases the stability of the harvester10in turns and is effected via a steering actuator30. As shown in detail inFIG. 2, steering actuator30in this example comprises a hydraulic actuator which acts between the rear axle22and a steering arm32of the caster18. As shown inFIG. 1, it is further advantageous to damp the rotation of the non-steering caster20about caster axis28using a damper, such as a shock absorber34for enhanced stability.

Switching from field mode steering (free caster rotation of caster18) to high speed mode (active steering of caster18) cannot be permitted unless the caster wheels36and38are “behind” (rearward) of the rear axle22as shown inFIG. 1. To prevent switching in the absence of the required caster positions a sensor assembly and control system are used.

An example sensor assembly40according to the invention is shown inFIGS. 1 and 3. Sensor assembly40comprises a wheel arm42having respective first and second ends44and46oppositely disposed. Caster wheel36is attached to the first end44of wheel arm42, the caster wheel being free to rotate about a wheel axis48. A shaft50is fixedly attached to the second end46of the wheel arm42. Shaft50is oriented transversely to the wheel axis48. A bearing52is mounted on the rear axle22, which, in turn, is mounted on chassis12. In this example bearing52comprises a tube54which defines a bore56which receives the shaft50. Shaft50is rotatable within bore56about a shaft axis58which is oriented coaxially with bore56and also coincides with caster axis26. Note that for proper caster action the wheel axis48trails the caster and shaft axes26and58as established by the geometry of wheel arm42. Rotation of the wheel arm42about the caster axis26can thus position the caster wheel36forward or reward of the rear axle22, and this position of the caster wheel determines whether or not the steering mode may be switched from the field mode (free rotation about the caster axis26) to the high speed mode (active steering of caster18). The position of the caster wheel36relative to the rear axle22may be determined by the angular orientation of the shaft50using a sensor60. In an example according to the invention, sensor60may be a proximity sensor, for example, a Hall effect sensor, a capacitive sensor, an inductive sensor, an optical sensor or an ultrasonic sensor. In a practical design for a harvester, inductive sensors are advantageous for their dependability and robustness.

As shown inFIG. 3, the sensor60is mounted on the bearing52(tube54) such that it has access to the bore56and thus the shaft50thereby allowing the sensor to determine the position of the shaft50and thus of the caster wheel36(see alsoFIG. 1) relative to the caster axis26. In this example embodiment shaft50is configured to provide a target which is readily detectable by the sensor60. In the example embodiment shown inFIGS. 4 and 5the sensor target62comprises a groove64which extends about only a portion of the circumference of the shaft50, leaving a remaining portion66of the shaft at a larger diameter. Proximity sensor60can thus easily detect the presence or absence of the groove64. The extent of the groove64relative to the ungrooved portion66can be adjusted depending on which element (groove64or ungrooved portion66) is used to indicate the range of angular positions of the caster wheel36over which active steering of a caster is permitted or forbidden. For a practical design as shown inFIGS. 4 and 5, the ungrooved portion66is used to indicate the angular range of positions of the caster wheel wherein active steering is permitted. For such a design the groove64may subtend an angle between about 270° and about 300° about shaft50, with a subtended angle of about 285° being advantageous. Fixing the subtended angle of groove64also establishes the subtended angle of the ungrooved portion66. Note that the shaft50must be attached to the wheel arm42with the groove64and ungrooved portion66oriented relatively to both the sensor60and the caster wheel36such that the sensor senses the true position of the caster wheel relative to the rear axle22. It is further advantageous to position the sensor target62(groove64and ungrooved portion66) within the bearing52(tube54) and distal to the second end46of wheel arm42to prevent fouling of the sensor target and damage to the sensor60.

FIG. 6shows the shaft50used in the example caster wheel orientation sensor assembly embodiment ofFIGS. 4 and 5wherein the groove64has a uniform depth68over its entire extent around shaft50.FIG. 7shows another example shaft50wherein the groove70has a non-uniform depth. Groove70comprises a first portion72having a depth74which increases with distance about the circumference of shaft50; a second portion76having a uniform depth78, and a third portion80having a depth82which also increases with distance about the shaft's circumference. In this example the depths74and82of the first and third portions increase linearly with distance around the circumference of shaft50, it being understood that other functional relations between the depth and position around the circumference of shaft50are also feasible.

FIG. 8shows another embodiment of a sensor target84which takes the form of a continuous groove86having a varying depth88over its entire extent around shaft50. In this example embodiment the sensor may be adapted to sense the depth of the groove and generate signals indicative of the depth. The varying depth may then be coordinated with the position of the caster wheel36to provide a range of values over which active steering is permitted or not permitted.

FIG. 9shows another embodiment of a sensor target81which comprises a recess83in the shaft50. In this example recess83comprises a flat surface85situated below the circumferential surface of shaft50. Flat surface85extends across a chord87of the shaft's cross section89in this example.

Operation of the caster wheel orientation sensor assembly is described with reference to the windrower10shown inFIG. 1. In this example the sensor60and the steering actuator30operate on the same caster18(see alsoFIGS. 2 and 3), it being understood that the sensing and steering functions could be split between the two casters18and20, or sensors60could be positioned on both casters, or both casters could be actively steered. To switch from field mode steering (free rotation of casters18and20) to high speed mode (active steering of caster18) an operator will activate the caster steering control system90via a control input (lever or switch) from the windrower cab92. In this example the caster steering control system90is a hydraulic system as disclosed in U.S. patent application Ser. No. 16/200,324. During field mode operation the caster steering control system90allows free flow of hydraulic fluid through the system and steering actuator30which permits the free rotation of the caster18. However, once the high speed mode of operation is invoked, the control system regulates the flow of hydraulic fluid to the steering actuator30to apply forces to the caster18consonant with the steering inputs to the powered wheels14and16. Before the high speed steering mode can be invoked however, a controller94, in communication with and adapted to receive signals from the sensor60, must determine if the casters18and20are in a position wherein the caster wheels36and38are behind the rear axle22. Communication between the sensor60and the controller94may be via wire as indicated by sensor cable96, or wirelessly via one of a number of wireless communication protocols. This determination is made when the controller94evaluates the signals generated by the sensor60indicative of the position of the caster wheels. In this example, sensor60detects either the presence (FIG. 4) or the absence (FIG. 5) of the ungrooved portion66of shaft50. If, for example, the signals indicate the presence of the ungrooved portion66, and the ungrooved portion is sized and positioned on the shaft50relative to the position of the sensor60, the caster wheel36and the rear axle22such that the caster wheels36and38are behind the rear axle22when the ungrooved portion is detected, then the controller94will permit the switch into the high speed mode of active steering by permitting control of the various valves of the caster steering control system90which regulate the flow of hydraulic fluid to the steering actuator30to apply steering forces to the caster18. If, however, the signals from the sensor60indicate that the groove64is detected, then the controller will not permit the switch and the caster steering control system90will remain in field mode. The controller94may signal this status to the operator via a light or a gauge in the cab92, allowing the operator to move the windrower10forward to bring the casters18and20into a trailing position behind the rear axle so the high speed mode of operation may be invoked. The controller94could be, for example, a stand-alone controller, such as a programmable logic controller mounted on the windrower, or, its functions could be performed by specific algorithms within the steering control system of the windrower.