METHOD AND SYSTEM FOR THE DETERMINATION OF A STEERING ANGLE

A method and system are provided for determining the angle of steering of a vehicle, particularly an agricultural vehicle, by determining vehicle yaw rate, determining vehicle speed, determining hydraulic flow in a hydraulic steering assembly connected in parallel with a manual hydraulic steering circuit of the vehicle, and processing the yaw rate, speed, and hydraulic flow data to determine the angle of steering of the vehicle.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1shows a diagrammatic view having components of a vehicle10and components of an automated steering system40. The vehicle10has wheels12which are steered by hydraulic lines connected to a standard hydraulic steering assembly16. The hydraulic steering assembly16, which typically includes hydraulic valves and an orbital motor, is controlled by a manual steer wheel18connected therewith. In use, as the manual steer wheel18is turned (typically by an operator) the hydraulic steering assembly16actuates the hydraulic fluid in the hydraulic lines14to steer the wheels12(i.e., turn the wheels left or right, changing their angle relative to the vehicle body).

The vehicle10also includes a hydraulic pump20connected between a reservoir22and the hydraulic steering assembly16. The hydraulic pump20in the illustrated embodiment has a variable delivery rate and transfers hydraulic fluid from the reservoir22via a hydraulic hose connected to an input of the pump20labelled ‘T’ (for tank) to the hydraulic steering assembly16via a hydraulic hose connected to an output of the pump20labelled ‘P’ (for pressure). The illustrated pump20also has load sensing, labelled LS.

The automated steering system40is hydraulically connected to the vehicle10by hydraulic lines42and44connected to the existing steering lines14of the vehicle10by hydraulic line46connected to the pressure side of the hydraulic pump20, and by hydraulic line48connected to the reservoir22. Optionally, the steering system40may also be connected by hydraulic lines50and52for load sensing (from the steering assembly16and pump20, respectively).

All of hydraulic lines42,44,46,48,50, and52are hydraulically connected to a valve block54. Hydraulic line42is connected via a flow sensor56, for reasons which will become apparent. The valve block54is electrically connected, via electrical cables58, to a steering control system in the form of a steering controller60and a guidance console62. Although electrical cables58are utilised to physically connect various components, wireless communication may also be utilised in place of, or in addition to, at least some of the electrical cables. Furthermore, although the steering controller60and guidance console62are shown as separate components, it will be appreciated that they may also be integral.

The steering controller60is electrically connected to the valve block54by a pressure sensor64, the flow sensor56, and hydraulic actuator inputs66. The steering controller60is, in the illustrated embodiment, external to the cab, as indicated by dashed line68. The steering controller60and guidance console62are electrically connected via connector70. ThroughoutFIG. 1various connectors are shown. These are typically to keep the system modular, and to assist with isolating various parts or components, e.g., when servicing the system. A skilled person will recognise that they generally do not substantially affect the function of the invention (unless otherwise noted) and that they are primarily included for convenience.

The guidance console62includes a yaw rate determination unit in the form of an internal gyroscopic sensor (or ‘gyro’) indicated by72, and a speed determination unit in the form of a GNSS system. The GNSS system has one or more GNSS sensors (typically in the guidance console62) and is connected to one or more GNSS antennas74(two being illustrated inFIG. 1), which are typically mounted on the exterior of the cab to reduce signal losses and interference, and the like. With one or more readings of the position of the vehicle10over time via the GNSS system, the speed (and heading) of vehicle can be determined. Alternatively, the speed of the vehicle may be determined from instrumentation of the vehicle (e.g. by the speedometer) or from other suitable measurement techniques. The GNSS measurements may also be used to correct any bias in the gyroscopic sensor.

The guidance console62is also connected to an engage switch76and to a power source78. The power source78is preferably taken direct from a power source of the vehicle, such as from the vehicle's battery (not shown). Alternatively (or even in addition) the steering system40may have its own power storage (e.g., battery) and/or generation (e.g., solar).

When the vehicle10is being operated under manual control the steering system40is typically inactive. The steering system40may be in a standby or generally passive state, or may be actively monitoring the location of the vehicle10using GNSS, and the like, without actually interfering with the steering of the vehicle10(e.g., providing feedback to the operator but not providing any control to the vehicle).

In use, steering controller60and/or guidance console62process GNSS data from received from the GNSS antennas74to determine, among other things (e.g., the location of the vehicle), the speed of the vehicle. Additionally, the steering controller60and/or guidance console62use the gyro72to determine the yaw rate of the vehicle10. The flow sensor56can be utilised to determine hydraulic flow in hydraulic line42(as illustrated or, alternatively, in hydraulic line44). It will be appreciated that flow in line42is the reverse of the flow in line44and as the flow sensor can sense flow in both directions, a single flow sensor in either of lines42or44should be all that is required to determine flow in both hydraulic lines (for at least for this type of steering mechanism). As hydraulic lines42and44are connected to the existing steering hydraulic lines14in parallel, the flow sensor56does not sense flow in the original hydraulic steering lines14when the vehicle is under manual control (i.e., when the vehicle is being steered by the operator via the manual steer wheel18).

As shown inFIG. 2, when in use the vehicle steering system40determines vehicle yaw rate data (step100), vehicle speed data (step110), and hydraulic flow data (step120). Although these steps (100,110, and120) as shown in parallel, it will be appreciated that one or more of the steps may also, be in series. The determined data (from steps100,110, and120) is subsequently processed (step130), by the steering controller60and/or guidance console62, and the angle of the wheels12is determined (step140). The determined steering angle of wheels12may then be utilised in control systems to assist in automatically operating the vehicle10.

FIG. 3, which is much likeFIG. 2, further shows that the vehicle yaw rate data (determined at step200) and vehicle speed data (determined at step210) are utilised in an embodiment to either initially generate an estimate of the absolute angle of the wheels12, or to refine an existing estimate of the absolute angle of the wheels12(step230). The hydraulic flow data (determined at step220) is then utilised to estimate a relative angle (step240).

The estimated relative angle (from step240) relies upon direct measurement of hydraulic flow from flow sensor56, but only provides a relative angle measurement as the flow sensor56is only able to determine changes in hydraulic flow, and not the absolute angle of the wheels12. Furthermore, as the flow sensor56does not sense any flow when the vehicle10is under manual control (i.e. the wheels12are being driven solely by the steering assembly16) the angle of the wheels when the steering system40is engaged is not known (from the flow sensor). The estimate of absolute steering angle (from step230) and the estimate of relative steering angle since inception of the system (from step240) are then processed in combination (at step250) to determine a high accuracy estimate of the actual angle of the wheels12relative to the vehicle10. As the absolute estimate of the steering angle is refined over time (step230), coupled with any accurate estimate of any relative changes (step240), the accuracy of the determined wheel angle is also increased.

FIG. 4shows a broad flow chart of an automatic steering system method. Initially, the vehicle is under manual steering (step300), and stays in this state until automatic steering is engaged (at step310). When the steering system40is engaged (at step310), typically by the engage switch76being actuated by an operator, the yaw rate and speed of the vehicle is determined (step320) and an initial estimate of the absolute steering angle is calculated (step330). Once the initial estimate of steering angle has been calculated (step330), the automatic steering system is enabled (step340).

Once enabled (step340), the speed, yaw rate, and flow rate are determined (step350) to refine the steering angle estimate (step360). In practice, the refining step (360) uses subsequent determinations of yaw rate and speed data to refine the absolute angle estimate and flow data from the flow sensor56to adjust for relative angle changes since the system was engaged (step310).

The steering controller60then processes the steering angle data, together with other relevant data (e.g. speed, location, inclination, and the like), and outputs control signals to steer the vehicle (e.g., to keep the vehicle on a predetermined route) (step370). The automatic steering system40continually refines the angle estimates (step360) and controls the steering of the vehicle (step370) until disabled (step380). Once disabled, the vehicle reverts back to manual steering control (back to step300).

With reference toFIG. 1, the steering system40is engaged by actuating the engage switch76, at which stage the guidance console and/or steering controller process yaw rate data from the gyro72and speed determinable from the GNSS antennas74to generate an initial estimate of the absolute angle of the wheels12. Once the initial estimate has been generated the steering controller60can start to issue control signals to actuate the valve block54(via electrical cable58and hydraulic actuator inputs66). The valve block54routes hydraulic fluid as necessary to steer the wheels12of the vehicle10(e.g., by applying hydraulic pressure to line42or44in order to turn the wheels12to a desired angle).

By utilising yaw rate, speed, and hydraulic flow in the automatic steering circuit, the system is able to accurately determine the steering angle without having the associated difficulties of installing direct mechanical sensors.

Having the flow sensor56in parallel with added hydraulic lines42,44means that the flow sensor56does not sense hydraulic flow when the vehicle is under manual control (i.e., no flow is sensed unless there is electro-hydraulic activation via the valve block54). This results in the flow sensor56only being able to determine relative changes in steering while the steering system is engaged. However, by having the flow sensor in parallel with the main steering lines manual steering is unaffected in the event of a flow sensor failure (e.g., in a blocked state). This not only improves the safety of the system over typical hydraulic flow sensor only systems, but also does not require safety valves to be fitted in parallel around the flow sensor. Advantageously, the system provides substantially the same accuracy as previous flow metered systems, while providing easier installation, and increased reliability and safety.

The steering angle may be determined and utilised as the angle of a vehicle wheel relative to the body of a vehicle, as a curvature that the vehicle is travelling along, and the like. It will be appreciated that the steering angle determination may be applied to various types of vehicles including, for example, Ackermann style (as illustrated inFIG. 1), rear wheel steer, articulated, skid steer, and the like.

It is to be understood that the terminology employed above is for the purpose of description and, unless explicitly stated otherwise, should not be regarded as limiting.

As would be appreciated by a skilled person, the components of the vehicle10are typically all provided by an existing vehicle and, accordingly, there may be variations between the types and configurations of these components between different vehicles and manufacturers (and the like). As would be apparent to the skilled person the underlying principals and spirit of the invention should still apply, even if minor modifications or adaptations are required.

Use of the terms ‘determine’ and ‘estimate’ are not to be given a strict interpretation and, in fact, could be used interchangeably (that is, a determination may be an estimate, and an estimate may be a determination).

Where the context permits, reference to an integer or a component or step (or the like) is not to be interpreted as being limited to only one of that integer, component, or step, but rather could be one or more of that integer, component, or step etc.

In this specification, the terms ‘comprises’, ‘comprising’, ‘includes’, ‘including’, or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.