STEERING METHOD FOR AN AGRICULTURAL MACHINE
Patent Information
- Application Number
- DE102023131189
- Authority / Receiving Office
- DE · DE
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-11-09
- Publication Date
- 2025-05-15
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
The present invention relates to a steering method for an agricultural machine according to the preamble of claim 1, an agricultural machine according to the preamble of claim 13, a gear set according to the preamble of claim 14 and a control device for an agricultural machine according to the preamble of claim 15.Agricultural machines which are towed by a tractor during field processing have long been known, and self-propelled agricultural machines which are controlled by a driver during field processing. These machines can also be moved in the same way during transfer drives or road drives, i.e. on the way from or to the field, i.e. either pulled by the tractor or steered by the driver in a self-propelled manner. In towed agricultural machines, the brake can be supplied with energy and controlled from the towing vehicle. If present, this also applies to steerable axles of the towed agricultural machine. In addition, autonomous agricultural machines are also increasingly being used, which have their own drive and steering and perform the field processing independently, without control commands of a driver. Since these vehicles cannot perform a transfer trip autonomously in road traffic, they must be loaded onto a low loader, for example, which is complicated and increases the costs for the entire deployment.It has already been proposed to attach an autonomous agricultural machine to a towing vehicle for a transfer trip, for example via a drawbar. It is possible to steer the agricultural machine even without steering commands from the tractor vehicle. For this purpose, a drawbar angle of the drawbar relative to one of the vehicles can be detected, for example, by means of sensors. It is likewise possible to detect forces acting on the agricultural machine via inertial sensors. By means of these or other sensory measurements it can be determined how the agricultural machine moves in relation to the lane of travel of the towing vehicle and, if necessary, corrections can be made by the steering of the agricultural machine. However, the optimal steering strategy depends on various factors. Thus, the dimensions of the agricultural machine can change, for example by means of different coupled attachments. Even with the same dimensions, different steering strategies may be advantageous in different driving situations or traffic situations.It is the object of the invention to optimize the steering of a agricultural machine attached to a towing vehicle during road travel.The object is achieved with a steering method having the features of independent claim 1.For this purpose, a steering method for an agricultural machine is provided which is attached to a towing vehicle which travels along a towing vehicle lane during road travel, wherein:starting from a plurality of possible steering modes of the agricultural machine, a steering mode is defined for at least a part of the road travel,determining kinematic data which describe a kinematic of the agricultural machine based on sensory measurement,determining lane information relating to the towing vehicle based on sensory measurement and matching the kinematic data therewith,depending on the result of the matching and depending on the currently defined steering mode, steering commands for at least one steerable axle of the agricultural machine are automatically determined in order to steer the agricultural machine in a manner adapted to the tractor vehicle lane, andthe agricultural machine is automatically steered by the steering commands.The agricultural machine can also be referred to as an agricultural working machine. It can be, in particular, a harvesting machine such as a forage harvester, a combine harvester, a baler or a loading truck. However, it could also be, for example, a counter, a plough, a fertilizer spreader, a manure barrel or the like. The agricultural machine is configured for field processing, for example for ploughing, fertilizing, mowing, ettes, crop material pick-up or the like. It may include at least one attachment coupled to a vehicle body as needed, the vehicle body itself being configured for no specific type of field machining. It is also considered in the sense of the invention as an agricultural machine if no attachment is coupled during road travel. The agricultural machine can also be a trailer which is towed by a tractor during field processing. In this case, it is also towed on a road or transfer trip. The agricultural machine can, however, also have its own travel drive which drives it both during field processing and during road travel. It can be designed in particular as an autonomous vehicle which is configured to perform field processing without control commands of a driver or operator. However, it would also be conceivable for the agricultural machine to have a guide stand or a driver's cab and to be controllable by a driver as required. However, in the course of the steering method according to the invention, automatic steering takes place, as will be explained below.In the method according to the invention, the agricultural machine is attached to a towing vehicle during a road travel, which towing vehicle travels along a towing vehicle lane. The term "road travel" is not to be interpreted as being strictly speaking here and also refers to travel on unpaved paths. It is used interchangeably herein to mean "transfer travel", i.e. a travel from or to the place of use. The towing vehicle itself can be an agricultural machine, but it can also be another vehicle, for example a truck. Normally, the towing vehicle is a motor vehicle with its own drive, but it could also be, for example, a trailer without its own drive, which in turn is towed. It may be a vehicle that is steered by a driver or an autonomous vehicle. The towing vehicle travels along a route or lane, which is referred to herein and hereinafter as the towing vehicle lane. The towing vehicle lane may depend on short-term steering actions of a driver or an autonomous steering system and may be subject to potentially continuous changes. It can therefore only be predicted to a limited extent for the future. The agricultural machine is attached to the towing vehicle, which generally means that the towing vehicle moves in front and pulls the agricultural machine during forward travel. When driving backwards, the agricultural machine is pushed by the towing vehicle. The agricultural machine is attached, that is to say it is mechanically connected to the towing vehicle, but not rigidly but rather movably. The connection between the towing vehicle and agricultural machine has at least one degree of freedom. Inter alia, due to the at least one degree of freedom, the agricultural machine does not necessarily travel along the towing vehicle lane. Optionally, the towing vehicle can actuate a brake system of the agricultural machine and / or supply the agricultural machine with energy. However, this could also use its own energy store and / or an own energy generator in order to provide energy in mechanical, hydraulic, electrical or other form.According to one step of the method according to the invention, a steering mode is defined for at least part of the road travel, starting from a plurality of possible steering modes of the agricultural machine. It can also be said that a steering mode of the agricultural machine or a steering mode for the agricultural machine is set. The steering mode decides how the agricultural machine is steered. It characterizes and determines the steering behavior of the agricultural machine. The steering mode may include one or more steering parameters that are set. After its definition, the steering mode is maintained for at least a portion of the road trip. That is, it applies to a certain period of time or a distance. These may be set in advance or may be variable. In the latter case, the set steering mode is maintained until further. The steering mode that is set is one of a plurality of possible steering modes of the agricultural machine and is selected from these. Overall, different numbers of steering modes may be provided. If the respective steering mode can be described by a steering parameter which can be varied quasi-continuously, a number of possible steering modes which are quasi "infinite" would result. The number is in practice limited to a finite but possibly very large value. The steering mode may be set within a control unit that performs various functions associated with the steering of the agricultural machine. It can advantageously be part of the agricultural machine, but it could optionally also be arranged wholly or partly externally, for example on the towing vehicle. It can also have a plurality of spatially separated components. Functions of the control unit can be implemented partly in software. The determination of the steering mode within the control unit does not necessarily mean, however, that the determination is carried out by the control unit.According to a further step of the method, kinematic data are determined based on sensory measurement, which describes a kinematic of the agricultural machine. The kinematic data are ascertained on the basis of sensory measurement, i.e. on the basis of a measurement by means of at least one sensor. Different sensors can be used, as will be explained below. The respective sensor can be arranged on the agricultural machine or integrated therein. In principle, it would also be conceivable for it to be an external sensor. The kinematic data are based on the sensory measurement, which includes the possibility that the kinematic data are also identical to measurement values obtained by the measurement or are connected thereto in a trivial manner. In particular, however, the kinematic data can be calculated, which is based, for example, on a linking of measured values. It could also be a temporal integration, for example, in order to determine a speed and, if appropriate, a position from a one- or multi-dimensional acceleration, wherein initial values need to be specified which do not result from the integration. In any case, the kinematic data describes a kinematic system of the agricultural machine, that is to say the movement of the agricultural machine and / or its current spatial arrangement. The kinematic data can be determined by the above-mentioned control unit. The control unit can receive wirelessly or by wire measured values from the above-mentioned at least one sensor and optionally further data. The steering mode can also be established within the control unit.Kinematic data are preferably determined which describe a location, a speed, an acceleration, an orientation, an angular speed and / or an angular acceleration. In particular, the respective kinematic data can describe all six of the mentioned variables. The mentioned variables are classically associated with the term kinematics and describe the position, including the orientation, and the change over time of the same. The speed and the acceleration correspond to the first and second time derivatives of the location. Each of the mentioned sizes is normally an at least two-dimensional size, optionally also a three-dimensional size. A two-dimensional location can be characterized by an X and a Y coordinate, a three-dimensional location additionally by a Z coordinate. The angular velocity and the angular acceleration correspond to the first and second time derivatives of the orientation. Each of these quantities is at least one-dimensional, insofar as an orientation etc. within a plane is viewed. However, it is also possible to consider two- or three-dimensional orientations, etc., which can be characterized by two or three angles. An example would be yaw angle, roll angle, and pitch angle.Furthermore, lane information relating to the towing vehicle is determined on the basis of sensory measurement and the kinematic data are hereby matched. The sensory measurement mentioned here is also carried out by means of at least one sensor. It is possible that at least one sensor and / or the measured values supplied by it are used completely or partially both for determining the kinematic data and for determining the lane information. The lane information can also be determined by the control unit. The lane information relates to the towing vehicle and is thus associated with the towing vehicle lane. However, they normally do not allow an exact description of the tractor vehicle lane, for example due to measurement errors of numerical inaccuracies or other influences. In any case, the tractor vehicle lane can be characterized at least to a limited extent and approximately on the basis of the lane information. The determined kinematic data can be matched with this lane information. This comparison provides a statement about how the agricultural machine is positioned in relation to the towing vehicle lane and / or how it moves in relation to the towing vehicle lane. Since the towing vehicle lane is generally not exactly known, the result of the matching is necessarily also generally not exactly. However, certain inaccuracies are acceptable and do not compromise the functional principle of the steering method according to the invention.In a further method step, depending on the result of the matching and depending on the currently defined steering mode, steering commands for at least one steerable axle of the agricultural machine are automatically determined in order to steer the agricultural machine in a manner adapted to the tractor vehicle lane. This method step can in turn be carried out by the control unit. The agricultural machine may have one or more steerable axles. The respective axle is steerable by at least one actuator, wherein the actual steering angle can be checked by an associated sensor. In the case of a plurality of steerable axles, steering commands can be determined for all axles. The steering commands can be digital or analog signals. In each case, a steering command contains information about the respective steering angle of the steerable axle. The steering commands are determined in order to steer the agricultural machine adapted to the tractor vehicle lane. "Adapted to the vehicle lane" does not necessarily mean that the agricultural machine is intended to follow the vehicle lane as exactly as possible. In any case, however, the tractor vehicle lane forms an orientation for the steering of the agricultural machine. The steering commands are determined as a function of the result of the adjustment. This means that the comparison is used to decide how to steer the agricultural machine, based on the determined kinematic data, in order to achieve or maintain the intended adaptation to the towing vehicle lane (insofar as it is known on the basis of the lane information). The determination also takes place depending on the steering mode. That is to say that with the same lane information and the same kinematic data, different steering commands can be determined depending on which steering mode has been set. Here and below, the formulation "depending on" always means that there is at least one dependency on the stated variable.This always includes the possibility that a dependence on at least one further variable is additionally given. The formulation is thus synonymous with "at least partially depending on".In a further step, the agricultural machine is automatically steered by the steering commands. This can also be done by the above-mentioned control unit, which for this purpose can be connected wirelessly or by wire to at least one steering actuator, which is assigned to the at least one steerable axle.The advantage of the steering method according to the invention is that automatic steering of the agricultural machine according to demand is possible via the defined steering mode. This can be adapted to different situations and / or different conditions by defining a suitable steering mode. The steering behavior of the agricultural machine is therefore not fixedly predefined, which could be suboptimal depending on the situation, but rather can be adapted flexibly.One specific embodiment provides that the ascertained lane information corresponds to a calculation lane of the towing vehicle and the kinematic data corresponds to an actual lane of the agricultural machine, the actual lane being matched to a setpoint lane, which is derived from the calculation lane as a function of the currently defined steering mode, and the steering commands being ascertained as a function of the result of the matching. The calculation lane would ideally be identical to the towing vehicle lane or to a portion thereof. In reality, there is generally a deviation from the tractor vehicle lane, which is acceptable, however, within certain limits. The calculation lane can be determined up to the current point in time, but it can also be extrapolated into the future for a certain time. The latter may be useful in particular in the case of a reverse travel in which the agricultural machine moves in front of the towing vehicle to a certain extent. The actual lane is either part of the kinematic data that is determined or it is identical to these kinematic data. Here too, on account of measurement errors, numerical errors and other influences, there may be a deviation between the actual lane and the actually traveled lane of the agricultural machine, which is likewise acceptable within certain limits, however. The actual lane can also be determined up to the current point in time or extrapolated into the future for a certain time. In the latter case, it can be used, for example, to take the basis that the steering angle of the at least one steerable axle is not changed with respect to the current state. A desired lane for the agricultural machine is determined, which is derived from the calculation lane. It can be identical to the calculation lane, but can also deviate from it in a anticipated manner, for example in order to realize a lateral offset in a curve. In this case, the setpoint lane is derived from the calculation lane as a function of the steering mode. That is, depending on the steering mode, different target lanes can be derived from a specific calculation lane. By matching the target lane with the actual lane, it is possible to determine how the agricultural machine has to be steered in order to move in the intended manner relative to the towing vehicle. Since the setpoint lane is derived from the calculation lane, an (indirect) comparison with the calculation lane also takes place here. The steering commands are then determined in accordance with a possible deviation of the actual lane from the target lane.According to one embodiment, the steering mode is determined at least in part by a user input. That is, a user decides which steering mode he currently keeps appropriate and makes a corresponding input via a user interface. The user interface may be disposed on the agricultural machine. Advantageously, however, it should either be mobile, i.e. arranged on a smartphone, tablet or the like, for example, or it should be arranged on the towing vehicle. It can be connected wirelessly and / or by wire to the agricultural machine, for example to the above-mentioned control unit. The determination of the steering mode can optionally take place completely by user input in this embodiment.According to a further embodiment, the steering mode is at least partially automatically set. Automatic means that the definition takes place without the intervention of a user and the user is thus excluded from the selection of the steering mode. The automatic selection can be made by the above-mentioned control unit.Mixed forms are also conceivable, wherein the selection is effected only partially by the user input. For example, in certain situations, at least one steering mode may be disabled so that it cannot be selected by the user. It would also be conceivable for different steering modes to be automatically selected depending on the situation, which appear as one and the same steering mode from the point of view of the user. That is, the user makes a selection, whereby, for example, some steering parameters are defined, while other steering parameters are automatically defined without the user being able to influence this and possibly without he actually detecting this. In this case, the fine tuning of the steering mode could be effected automatically to a certain extent. It would also be conceivable that the user can freely decide on the steering mode in certain situations, while the selection is made automatically in other situations. The latter can be done to relieve the user. However, safety reasons for this would also be conceivable. For example, the user may select a steering mode which then remains active until further. In certain circumstances, the steering mode may then be automatically deactivated and a different steering mode selected instead.It is preferably provided that at least a re-establishment of the steering mode is made possible during the road travel, in particular that the re-establishment takes place during the road travel. That is, the steering mode is not set for the entire road travel, but a renewed setting, that is, a change of the steering mode, takes place during the road travel.According to one embodiment, the agricultural machine is connected to the towing vehicle, for example, via two mutually movable coupling parts, one of which is rigidly connected to a vehicle body of the towing vehicle and the other of which is rigidly connected to a vehicle body of the agricultural machine. For example, a ball joint, pin joint, or the like would be conceivable. Another embodiment provides that the agricultural machine is connected to the towing vehicle by a tow bar that transmits tension and pressure and is pivotably connected both on the side of the towing vehicle and on the side of the agricultural machine. The drawbar can normally be considered a rigid body, although it is possible that, for example, even during normal operation, a slight elastic deformation of the drawbar takes place. In any case, the drawbar does not have in itself flexible areas or joints. However, it is conceivable that the drawbar is manually or actuatorally adjustable, for example length adjustable, wherein it could consist of two telescopically connected parts. The drawbar connects the towing vehicle to the agricultural machine and transmits a tractive force when driving forwards and a compressive force when driving backwards from the towing vehicle to the agricultural machine. The drawbar can be a separate component which is temporarily connected to the towing vehicle and agricultural machine for the purposes of road travel. It can also be permanently integrated into the towing vehicle or the agricultural machine, wherein it is pivotably connected to a vehicle body of the respective vehicle. The connection to the respective other vehicle can be established via a clutch (for example, ball-head clutch etc.). In any case, the drawbar is pivotably connected on both sides, wherein at least one-dimensional pivotability is provided, i.e. pivotability about a one-dimensional angle in the horizontal plane. In addition, an at least limited pivotability in the vertical direction is normally also provided, so that a two-dimensional pivotability can be referred to. The drawbar can be pivoted in each case free of restoring forces; however, it would also be possible for it to be connected to the towing vehicle and / or to the agricultural machine via at least one spring element.It is possible here that in at least one steering mode a front axle of the agricultural machine is positively steered by the drawbar. This means that in the corresponding steering mode-possibly also in all steering modes-a drawbar angle of the drawbar with respect to the vehicle body of the agricultural machine specifies a steering angle of the front axle. The corresponding positive steering can be realized mechanically, which includes the possibility of a fluid-mechanical, for example hydraulic or pneumatic, coupling. However, a sensor-actuator coupling could also be provided, having at least one sensor which detects the drawbar angle, and at least one actuator which adjusts the steering angle. In this case, the actuator could be controlled by the control unit such that a specific value of the drawbar angle always corresponds to a specific value of the steering angle.As explained above, the kinematic data as well as the lane information are based on a sensory measurement for which different types of sensors can be used. In particular, the kinematic data and / or the lane information can be determined based on a measurement by at least one inertial sensor, an angle sensor for determining a drawbar angle and / or a position sensor for determining a relative position of the towing vehicle to the agricultural machine.An inertial sensor is configured to determine inertial measurements. These inertial measurements correspond to at least one multi-dimensional acceleration, including both two-dimensional and three-dimensional accelerations. Apart from a (translatory) acceleration, an inertial sensor can also measure an angular acceleration, i.e. a change over time in an angular speed. One or more inertial sensors may form an inertial measurement device. An inertial sensor can be arranged on the agricultural machine, on the drawbar or on the towing vehicle. In this case, it is of course possible to provide a plurality of inertial sensors, of which in each case at least one is arranged on the agricultural machine and at least one is arranged on the drawbar and / or on the towing vehicle. At least in some embodiments, the inertial sensor may also be referred to as an inertial measurement unit (IMU).An angle sensor may determine angle measurement values that correspond to a drawbar angle, i.e., a relative angle of the drawbar with respect to a vehicle body of the agricultural machine. Alternatively or additionally, an angle sensor can also be used for measuring the relative angle between the drawbar and the towing vehicle. The term "relative angle" as used herein includes both a one-dimensional angle measurement in which only how far the drawbar pivots horizontally left and right is determined, and a two-dimensional angle measurement in which also how far the drawbar pivots vertically up and down is measured. The orientation of the drawbar relative to the towing vehicle and / or the agricultural machine can under certain circumstances be determined with high precision using the angle measurement values of an angle sensor. By including the geometric dimensions of the drawbar, it is thereby possible, for example, to determine the position of a hinge point on the towing vehicle based on the position and orientation of the agricultural machine, without having to resort to sensors on the towing vehicle. This information can be combined with other sensor data in order to understand the position and / or movement of the towing vehicle as a whole.A position sensor can ascertain position measurement values which correspond to a relative position of the towing vehicle with respect to the agricultural machine. The position sensor can be designed, for example, as an ultrasonic sensor, radar sensor or lidar sensor. It can also be designed as a camera (which can optionally also be sensitive to infrared), wherein specific structures on the towing vehicle are identified by means of image recognition and the relative position is recognized by means of the arrangement and apparent size thereof within the camera image. For this purpose, information about the geometry of the towing vehicle must naturally be stored on the part of a corresponding evaluation unit. Different types of position sensors may also be combined with one another. A position sensor can be used to compensate for any drift of an inertial measurement device. Alternatively or additionally, at least one position sensor could also be arranged on the towing vehicle.A further option is an orientation sensor which ascertains orientation measured values which correspond to an orientation of the agricultural machine and / or of the towing vehicle with respect to the surroundings thereof. For example, while an IMU may only provide information about a change in orientation, the orientation sensor may measure the orientation as such. This is a type of "absolute" indication of orientation with respect to the environment. In two dimensions, the orientation specification corresponds, for example, to a direction of the sky. Such an orientation can be determined, for example, by means of a gyro compass, which represents a solution that is in principle reliable but cost-intensive. A magnetometer using the earth's magnetic field to measure orientation would be less expensive, although potentially prone to failure.The inertial measurement devices do not allow direct position measurement and also do not allow direct measurement of a distance travelled. This information can only be determined by two (numerical) integrations of the accelerations, which can generally lead to numerical errors that increase over time. This disadvantage can be compensated for by an additional sensor being designed as a distance sensor which determines distance measurement values which correspond to a distance covered by the agricultural machine and / or the towing vehicle. The distance sensor can also be referred to as odometer and the distance measurement values can be referred to as odometry data. In this case, the number of revolutions of a wheel is normally measured and multiplied by its known rolling circumference in order to determine the distance covered. Such a travel distance sensor can be arranged on the agricultural machine and / or on the towing vehicle.A preferred embodiment provides that the steering mode is defined as a function of geometry data which describe a geometry of the towing vehicle, the drawbar and / or the agricultural machine. Such geometry data may correspond to a length of the towing vehicle, the drawbar and / or the agricultural machine, or to an axle distance, a vehicle width, a track width or other characteristics, for example. This can also be information about the relative position of specific components of a vehicle, for example the relative position of two sensors with respect to one another. The geometry data may be more or less complex. For example, a vehicle could be characterized merely by length, width and optionally height, but a detailed three-dimensional model could also be stored, having a plurality of characteristic points of the vehicle, similar to a polygonal approximation. The geometry data can be stored in the control unit, which performs the corresponding calculations, or can be transmitted from an external source to the control unit. For example, the position of a clutch on the towing vehicle can be deduced from the drawbar angle of the drawbar if the length of the drawbar and its connection to the agricultural machine are known. It is possible that drawbars of different lengths are used in combination with one and the same agricultural machine, or that a drawbar of adjustable length is used. It would also be possible to combine towing vehicles with different geometries with an agricultural machine, which could be relevant in order to prevent a collision between the towing vehicle and the agricultural machine, for example, when cornering. The geometry data are preferably at least partially automatically adapted. This could be achieved, for example, by wired or wireless communication between the towing vehicle and / or drawbar on the one hand and the agricultural machine on the other hand, whereby the towing vehicle and / or drawbar are identified or at least geometry data are made accessible. In particular, it is preferred that changing geometry data of an adjustable drawbar are adapted. That is, as the dimensions of the drawbar change, the geometry data is also changed.Generally, the adaptation of the geometry data can take place automatically and / or according to a user input. In the latter case, it could be provided that the user actually inputs numerical values characterizing geometric dimensions. For improved user-friendliness, it can also be provided that the user makes a simple input which, for example, identifies a specific model whose geometry data are stored in a database and are then used for the adaptation. In the case of automatic adaptation, geometry data could be determined by sensory measurement, which, however, may be complicated or even unreliable. In contrast, an automatic recognition of a specific model, the geometry data of which are stored, or an above-described transmission of geometry data, is advantageous.According to one embodiment, the agricultural machine has a vehicle body to which at least one attachment can be coupled, wherein geometry data of the agricultural machine are adapted as a function of at least one attachment coupled to the vehicle body and the steering mode is correspondingly defined. The attachment can be designed for different types of field machining. It can be connected, for example, to a hoisting mechanism of the agricultural machine. In addition to a mechanical connection, an energy-transmitting connection can also be produced, for example an electrical, hydraulic or pneumatic connection. A wireless or wired data connection can also be established between the vehicle body and the attachment. In the present embodiment, the geometry data are adjusted depending on whether an attachment is coupled to the vehicle body and / or which attachment is coupled. It will be appreciated that the overall dimensions of the agricultural machine will depend substantially on whether an attachment is coupled and on its dimensions. This in turn has an influence on which steering maneuvers the agricultural machine can execute without problems or without risk. Under certain circumstances, a current position of the attachment can also be taken into account, provided that a plurality of positions are possible which lead to significantly different overall dimensions of the agricultural machine.If the attachment is attached to that side of the agricultural machine at which it is connected to the towing vehicle via the drawbar, a length adjustment of the drawbar can also be carried out depending on the attachment. If an attachment is coupled, a greater drawbar length must be selected than without an attachment. That is to say that the geometry data of the drawbar can also optionally be adapted as a function of at least one attachment coupled to the vehicle body.Particularly preferably, when identifying an attachment, the geometry data of the agricultural machine are automatically adapted. This means that an attachment is identified and the geometry data are then automatically adapted, i.e. without further user input. The identification itself, on the other hand, can be effected by user input. That is, the user could specify by input that a particular attachment is coupled without having to know or specify the geometry data thereof. However, it is also conceivable for the identification to take place automatically, for example by wireless or wired communication between the attachment and the above-mentioned control unit, which can be integrated into the vehicle body of the agricultural machine. According to a plug-and-play principle, such automatic identification with automatic adaptation of the geometry data enables a particularly user-friendly application which substantially excludes human errors. As explained above, the geometry data of the drawbar can be adapted together with the geometry data of the agricultural machine, which can likewise take place automatically in this embodiment.According to one embodiment, in at least one steering mode, a movement range of the towing vehicle is determined on the basis of the lane information and geometry data of the towing vehicle, and the steering commands are determined on the basis of the movement range and the geometry data of the agricultural machine. The movement range is a two- or three-dimensional range through which the towing vehicle moves along the towing vehicle lane. In a two-dimensional consideration, it is neglected that the towing vehicle can have different horizontal dimensions depending on height. The same applies to the agricultural machine. Two-dimensional viewing is sufficient for many applications. The movement region is traversed by the towing vehicle to a certain extent and it can be assumed that this region can also be traversed by the agricultural machine without risk. This is used in the present embodiment to define an appropriate desired travel route in combination with the geometry data of the agricultural machine.An option already mentioned above is that in at least one steering mode the target travel route corresponds to the calculation travel route, so that the agricultural machine ideally exactly follows the travel route of the towing vehicle. However, such a steering mode could lead to problems, in particular in the case of a agricultural machine that is loaded in the longitudinal or transverse direction. When driving around a curve, the agricultural machine could collide with stationary objects, for example a arch of a door, a traffic sign, a house corner, etc., if it exactly follows the travel route of the towing vehicle. Therefore, in a development of the method, it is provided that, in at least one steering mode, a range of movement of the agricultural machine is bounded at least on one side by the range of movement of the towing vehicle. "One side" means here either on the left side or on the right side with respect to a transverse axis of the agricultural machine. Since the boundary is relevant in particular when cornering, one can also speak of a boundary inside the curve or outside the curve. In some cases, a bilateral limitation can be realized. In other cases, only one-sided limiting is possible. The range of movement of the agricultural machine is limited on one side (for example on the left or on the inside of the curve) by the range of movement of the towing vehicle. That is, the range of movement of the towing vehicle is determined with the aid of the calculation travel route, and the target travel route is then determined in such a way that the range of movement of the agricultural machine does not project beyond the range of movement of the towing vehicle on one side. If, for example, a stationary object is located on the inside of the curve in the case of cornering, the corresponding steering mode can ensure that the agricultural machine passes the object without collisions, provided that the towing vehicle has done this.One embodiment provides that at least one steerable axle is locked depending on the steering mode. That is, in at least one steering mode, the steerable axle is locked, typically in a center or neutral position, while in at least one other steering mode it is enabled for steering. That is, in the corresponding steering mode, the axle is deflected to the right or left as needed.One possibility is that the steering mode is defined as a function of an amount of a travel speed and / or the presence of a reverse travel. Both can take place in response to a user input. Preferably, it is carried out automatically. The travel speed can be a travel speed of the towing vehicle and / or of the agricultural machine itself, wherein the difference due to the coupling is generally negligible. In general, a more powerful and / or more sensitive steering of the agricultural machine is advantageous at low travel speeds, while a less sensitive steering contributes to stabilization at higher travel speeds. For these or other reasons, it may be useful to establish a different steering mode at higher speeds. In particular, at least one steerable axle can be locked as a function of the travel speed. Above a defined limit speed, a change can be made to a steering mode in which the corresponding axle (for example the rear axle) is locked, whereby the agricultural machine and the combination as a whole can be stabilized. A plurality of speed ranges can also be distinguished, for example a low, a medium and a high speed range. A determination depending on the presence of a reverse travel may also be advantageous. This can relate to a reverse travel of the towing vehicle and / or of the agricultural machine, which in turn are almost always present simultaneously on account of the coupling. In this embodiment, a different steering mode is set in a reverse travel than in a forward travel. Different strategies are conceivable, wherein it may be advantageous in particular to lock a steerable axle during a reverse travel, while the latter is released for the steering during a forward travel.The object is furthermore achieved by a agricultural machine which is configured to be attached to a towing vehicle which travels along a towing vehicle lane during road travel and which has a control device which is configured to:starting from a plurality of possible steering modes of the agricultural machine, it is possible to define a steering mode for at least part of the road travel,determining kinematic data, which describe a kinematic of the agricultural machine, based on sensory measurement,determining lane information relating to the towing vehicle based on sensory measurement and thereby matching the kinematic data,automatically determining steering commands for at least one steerable axle of the agricultural machine as a function of the result of the matching and as a function of the currently defined steering mode in order to steer the agricultural machine in a manner adapted to the tractor vehicle lane, andsteering the agricultural machine automatically by the steering commands.The terms mentioned have already been explained above with reference to the steering method according to the invention and are therefore not explained again. Advantageous embodiments of the agricultural machine according to the invention correspond to those of the steering method according to the invention.The control device normally comprises a plurality of components which can be arranged spatially separated from one another. In particular, it can have at least one sensor for carrying out the sensory measurement, and a control unit which can be spatially separated from the sensor. The control unit can be configured to enable the determination of the steering mode, to ascertain the kinematic data, to ascertain the lane information and / or to ascertain the steering commands. Also, at least one steering actuator for steering at least one axle may be considered part of the control device.The object is also achieved by a combination having a towing vehicle and a agricultural machine which is attached to the towing vehicle during road travel, which vehicle travels along a towing vehicle lane, wherein the combination has a control device which is configured to:starting from a plurality of possible steering modes of the agricultural machine, it is possible to define a steering mode for at least part of the road travel,determining kinematic data, which describe a kinematic of the agricultural machine, based on sensory measurement,determining lane information relating to the towing vehicle based on sensory measurement and thereby matching the kinematic data,automatically determining steering commands for at least one steerable axle of the agricultural machine as a function of the result of the matching and as a function of the currently defined steering mode in order to steer the agricultural machine in a manner adapted to the tractor vehicle lane, andsteering the agricultural machine automatically by the steering commands.The terms mentioned have already been explained above with reference to the steering method according to the invention and are therefore not explained again. Advantageous embodiments of the combination according to the invention correspond to those of the steering method according to the invention.Again, the control device normally comprises a plurality of components which can be arranged spatially separated from one another. As described above, this can include at least one sensor, a control unit and at least one actuator. The control device is preferably arranged at least partially on the agricultural machine and can in particular be arranged exclusively on the agricultural machine. However, it can also be arranged partially on the towing vehicle and / or-if present-on the drawbar. In such a case, parts of the control device may communicate with each other wirelessly or in a wired manner.The object is also achieved by a control device for controlling an agricultural machine, which is attached to a towing vehicle, which travels along a towing vehicle lane, during a road trip, wherein the control device is configured to:starting from a plurality of possible steering modes of the agricultural machine, it is possible to define a steering mode for at least part of the road travel,determining kinematic data, which describe a kinematic of the agricultural machine, based on sensory measurement,determining lane information relating to the towing vehicle based on sensory measurement and thereby matching the kinematic data,automatically determining steering commands for at least one steerable axle of the agricultural machine as a function of the result of the matching and as a function of the currently defined steering mode in order to steer the agricultural machine in a manner adapted to the tractor vehicle lane, andsteering the agricultural machine automatically by the steering commands.The terms mentioned have already been explained above with reference to the steering method according to the invention and are therefore not explained again. Advantageous embodiments of the control device according to the invention correspond to those of the steering method according to the invention. Possible components of the control device and its arrangement have been explained with reference to the agricultural machine according to the invention and the combination according to the invention.The invention is described below with reference to figures. The figures are merely exemplary and do not limit the general inventive concept. They show FIG. 1 shows a top view of a road intersection and of a combination according to the invention comprising a towing vehicle and a agricultural machine having a control device according to the invention; FIG. 2 is a block diagram of components of the control device and information transmitted between the control devices; FIG. 3 is a plan view of the road intersection with different lanes; FIG. 4 is a top view of a road with the combination and a driving lane and two movement regions; and FIG. 5 shows a flow chart of a steering method according to the invention for steering the agricultural machine from FIG. 1.FIG. 1 shows a top view of a road intersection with a first road 50 and a second road 51. In this case, the towing vehicle 30, which is illustrated as a tractor in this example, travels along a towing vehicle travel route Rz, which is illustrated as a long dashed line in FIGS. 1, 3 and 5. Agricultural machine 10 has a front axle 14 and a rear axle 15, which are each actively steerable by means of a front steering actuator 24 and a rear steering actuator 25 (illustrated in the block diagram in FIG. 2 ). The axles 14, 15 are arranged on a vehicle body 26. Various attachments 27 can optionally be coupled to these. The drawbar 20 is pivotably connected to the towing vehicle 30 at a front articulation point 33 and pivotably connected to the agricultural machine 10 at a rear articulation point 21. It is pivotable in the mentioned articulation points 21, 33. It transmits at least tensile and compressive forces parallel to its extension direction. No steering commands are transmitted to the agricultural machine 10 by the towing vehicle 30.In order to be able to steer the axles 14, 15 of the agricultural machine 10 in such a way that it adapts itself in a provided manner to the movements of the towing vehicle 30, a control device 1 is provided, the components of which are shown together in the block diagram in FIG. 2. The control device 1 includes a control unit 22 which is arranged on the agricultural machine 10 and an inertial measurement device 11 which in this case has two inertial sensors 12 spaced apart from one another. The inertial sensors 12 transmit, to the control unit 22, inertial measurement values M A, which correspond to a multi-dimensional acceleration and a multi-dimensional angular acceleration. The inertial measurement values M A received by the two inertial sensors 12 are in principle redundant with respect to one another, which is used to perform a calibration and to correct possible measurement errors.The agricultural machine 10 can optionally have further sensors 13, 16-19. For example, an orientation sensor 13, which can be designed as a magnetometer, can be used to determine orientation measured values Mo that correspond to an orientation, i.e. spatial orientation, of the agricultural machine 10. Position sensors 16 can ascertain position measurement values M P which correspond to a relative position of the towing vehicle 30 to the agricultural machine 10. These position sensors 16 could be designed, for example, as radar or lidar sensors. Finally, a distance sensor 19, which can also be referred to as odometer, can determine distance measurement values Ms, which correspond to a distance traveled by agricultural machine 10. Furthermore, a speed sensor 18 is provided, which can measure the direction and amount of a speed of the agricultural machine 10 via a rotational speed of a wheel of the rear axle 15. Finally, an angle sensor 17 is arranged at the rear articulation point 21. This determines angle measurement values Mw, which correspond to a drawbar angle of the drawbar 20 with respect to the agricultural machine 10. The angle measurement values Mw can also be transmitted wirelessly or by wire to the control unit 22. FIGS. 1 and 2 show a plurality of sensors, which are not normally all used together. However, a plurality of different types of sensors may serve to improve the precision of the control device 1.The agricultural machine 10 has a first user interface 23 and the towing vehicle 30 has a second user interface 31. A user input E can be made via each of the user interfaces 23, 31. Both user interfaces 23, 31 are connected wirelessly or by wire to the control unit 22.The control device 1 performs a steering method according to the invention, which will now be explained with reference to the flow chart in FIG. 5 and additionally with reference to FIGS. 2, 3 and 4. In a first step S 100, the control unit 22 is initialized, in which vehicle body geometry data G F of the vehicle body 26 of the agricultural machine 10, towing vehicle geometry data Gz of the towing vehicle 30 and drawbar geometry data G D of the drawbar 20 are loaded. In this case, the towing vehicle geometry data Gz can be transmitted by the towing vehicle 30 or, after identification of the towing vehicle 30, can be loaded from a database to which the control unit 22 has access. The vehicle body geometry data G F is first used to set agricultural machine geometry data G L of the agricultural machine 10.The geometry data G D, G F, G L, G Z can describe different aspects of the geometry, for example length, width, wheel alignment, track width, arrangement of the articulation points 21, 33, etc. In addition, initial values A are determined, in particular the initial position and orientation of the agricultural machine 10, its speed and angular speed. The latter are normally equal to zero, since the initialization is typically carried out at a standstill. The initial position of agricultural machine 10 can be selected, for example, as the origin of the coordinates or can be initialized with another standard value, and its orientation can likewise be initialized with an angle of 0° or another standard value. However, it would also be possible to determine the orientation via the orientation sensor 13. The orientation of the drawbar 20 can be determined by means of the angle sensor 21. The position of the tractor 30 can be determined at least with respect to the front articulation point 33 by means of the angle sensor 17 in combination with the geometry data of the drawbar 20. Alternatively or for improving the accuracy, the position sensors 16 could also be used, which optionally also allow a direct determination of the orientation of the towing vehicle 30.Thereafter, it is checked in step S110 whether an attachment 27 is coupled to the vehicle body 26 as schematically shown in FIG. 4. If yes, the type of attachment 27 is identified in step S120, and attachment geometry data G A is automatically loaded in step S130. The identification can be effected by wireless or wired communication between the attachment 27 and the control unit 22, wherein the attachment geometry data G A can also be transmitted. In step S140, the agricultural machine geometry data G L is updated including the attachment geometry data G A. If agricultural machine 10 has a plurality of coupling positions (for example lifting mechanisms) for attachments 27, a plurality of attachments 27 can be taken into account in steps S 120 to S 140. If no attachment 27 is coupled, the steps mentioned are skipped.In step S 150, the magnitude of the speed is ascertained by means of the speed sensor 18 and it is ascertained on the basis of the sign of the speed whether there is a reverse travel. In step S 160, it is queried whether a user input E has occurred via one of the user interfaces 23, 31, which has an influence on the steering mode L.In step S 170, the steering mode L is specified. For example, the user can select a steering mode in which the agricultural machine 10 follows the towing vehicle lane Rz of the towing vehicle 30 as exactly as possible, which is explained below with reference to FIG. 3. Alternatively, the user may select a steering mode in which a towing vehicle movement range BZ through which the towing vehicle 30 moves represents a one-sided boundary of a agricultural machine movement range BL, which is explained below with reference to FIG. 4. It could also manually select that one of the axles 14, 15 should remain locked, or that both axles 14, 15 are steered. A further possibility would be to choose that the front axle 14 should be positively steered by the drawbar 20 or should be steerable independently of it. Alternatively or in addition to manual setting, the steering mode L may be set automatically. A possible criterion for an automatic determination would be, for example, the exceeding of a limit value of the travel speed. Below this limit, both axles 14, 15 could be steered for better maneuverability, while above the limit, the rear axle 15 is locked in order to stabilize the agricultural machine. Even in the presence of a reverse travel, the rear axle 15 could be locked automatically. In addition, the steering mode L, which can also be described by one or more steering parameters, can depend on the towing vehicle geometry data Gz of the towing vehicle 30, the drawbar geometry data G D of the drawbar 20 and the agricultural machine geometry data G L of the agricultural machine 10, as is indicated in FIG. 2. All of this geometry data can affect how to steer the agricultural machine 10. In particular, the steering mode L may depend on the presence of an attachment 27 and its attachment geometry data G A.After the steering mode L has been established, measured values M A, M O, M P, M S, M W are measured by means of various sensors 12, 13, 16, 17, 19 in step S 180 and are sent to the control unit 22, as shown in the block diagram in FIG. 2. This calculates kinematic data of agricultural machine 10 in step S 190. In particular, a current speed and angular speed and a current position and orientation can be calculated by numerical integration of the acceleration or angular acceleration determined on the basis of acceleration measured values M A wherein initial values A are required. It is also possible to include travel distance data Ms of the travel distance sensor 19 in order to specify the ascertained value for the current position, or orientation data Mo of the orientation sensor 13 in order to improve the precision of the ascertained orientation. Based on this, an actual lane R I of agricultural machine 10, which is shown as a dot-dash line in FIG. 3, is calculated as part of the kinematic data.Furthermore, in a step S 200, which could also be carried out before step S 190 or simultaneously therewith, lane information relating to the towing vehicle 30 is determined. There are different possibilities for this purpose. For example, a lateral acceleration of agricultural machine 10 can be used to infer a change in the direction of travel of towing vehicle 30, both qualitatively and quantitatively. The precision can be improved if at least the angle sensor 17 and / or the position sensors 16 are additionally included, the measured values of which can be read in in step S 180. By combination with the known agricultural machine geometry data G L, towing vehicle geometry data Gz and drawbar geometry data G D it is possible to determine the position, orientation, speed and angular speed of the towing vehicle 30 from this. In any case, a calculation lane R B can be determined, which is shown as a short dashed line in FIG. 3. Due to various influences such as measurement errors and numerical errors, the calculation lane R B partially deviates from the actual towing vehicle lane R F. However, the deviation is slight and does not impair the basic function of the control device 1. In particular, in the case of a reverse travel, the calculation lane R B can also be extrapolated for the future.Based on the calculation lane R B and based on the currently defined steering mode L, a desired lane Rs for the agricultural machine 10 is determined in step S 220. In the example shown in FIG. 3, this is identical to the calculation lane R B i.e. it is provided that the agricultural machine 10 follows exactly in the lane of the towing vehicle 30. Alternatively, it would also be conceivable for the setpoint lane to be determined in such a way that a agricultural machine movement range B L is bounded on one side by the towing vehicle movement range Bz. In the example shown in FIG. 4, a right-hand boundary is provided in the direction of travel, so that the agricultural machine movement range B L represented by a dotted line is bounded on the outside of the curve by the towing vehicle movement range Bz represented by a dashed line. This ensures that, when traveling around a curve of the road 50, the agricultural machine 10 does not collide with a house 52 standing close to the road 50. In such a case, which corresponds to its own steering mode L, the towing vehicle movement range Bz is first ascertained in a step S 210 on the basis of the calculation lane R B and the towing vehicle geometry data Gz. In addition, based on the agricultural machine geometry data G L the target lane Rs is determined such that the agricultural machine moving range B L is limited as described. It is understood that the target lane Rs (omitted for reasons of clarity in FIG. 4 ) no longer corresponds to the calculation lane R B as a result.In a further step S220, the desired lane Rs is matched with the actual lane R I. In step S 230, steering commands K 1, K 2 for the steerable axles 14, 15 are ascertained depending on the result of the matching and depending on the steering mode L. These steering commands K 1, K 2 naturally serve to make the actual lane R I coincide with the desired lane Rs. Depending on the steering mode L, "actual" steering commands K 1, K 2 can be generated only for one axle 14, 15, while the other axle 14, 15 remains locked in a central position. The steering commands K 1, K 2 could also be generated in such a way that the front axle 14 is positively steered by the drawbar 20 so that a specific drawbar angle always corresponds to a specific steering angle of the front axle 14. In a further step S 240, the agricultural machine 10 is steered by means of the steering actuators 20, 21 in accordance with the steering commands L 1, L 2. In step S250, it is checked whether the road travel has been completed. If yes, the method ends. If no, the process returns to step S 150 and the described steps are repeated.
Claims
Steering method for a agricultural machine (10) which is attached to a towing vehicle (30) which travels along a towing vehicle lane (Rz) during a road travel, wherein: - starting from a plurality of possible steering modes (L) of the agricultural machine (10), a steering mode (L) is established (S170) for at least part of the road travel, - kinematic data which describe a kinematic system of the agricultural machine (10) are determined (S190) on the basis of sensory measurement (S180), - lane information relating to the towing vehicle (30) is determined (S200) on the basis of sensory measurement (S180), and the kinematic data are matched with it (S220), - depending on the result of the matching and depending on the currently defined steering mode (L), steering commands (K 1, K 2) for at least one steerable axle (14, 15) of the agricultural machine (10) are automatically determined (S 230) in order to steer the agricultural machine (10) in a manner adapted to the towing vehicle lane (R F) and - the agricultural machine (10) is automatically steered by the steering commands (K 1, K 2) (S 240).Steering method according to Claim 1, characterized in that the ascertained lane information corresponds to a calculation lane (R B) of the towing vehicle (30), and the kinematic data corresponds to an actual lane (R I) of the agricultural machine (10), wherein the actual lane (R I) is matched (S220) to a setpoint lane (R S) which is derived from the calculation lane (R B) as a function of the currently defined steering mode (L), and the steering commands (K 1, K 2) are ascertained (S240) as a function of the result of the matching.Steering method according to one of the preceding claims, characterized in that the steering mode (L) is at least partially defined (S170) automatically by a user input (E) and / or at least partially.Steering method according to one of the preceding claims, characterized in that the agricultural machine (10) is connected to the towing vehicle (30) by a tow bar (20) which transmits tension and pressure and is pivotably connected both on the side of the towing vehicle (30) and on the side of the agricultural machine (10).Steering method according to one of the preceding claims, characterized in that the kinematic data and / or the lane information are determined on the basis of a measurement by at least one inertial sensor (12), an angle sensor (17) for determining a drawbar angle and / or a position sensor (16) for determining a relative position of the towing vehicle (30) to the agricultural machine (10).Steering method according to one of the preceding claims, characterized in that the steering mode (L) is defined (S170) as a function of geometry data (G A, G D, G F, G L, G Z) which describe a geometry of the towing vehicle (30), the drawbar (20) and / or the agricultural machine (10).Steering method according to one of the preceding claims, characterized in that the agricultural machine (10) has a vehicle body (26) to which at least one attachment (27) can be coupled, wherein geometry data (G L) of the agricultural machine (10) are adapted (S140) as a function of at least one attachment (27) coupled to the vehicle body (26), and the steering mode (L) is correspondingly defined (S170).Steering method according to one of the preceding claims, characterized in that, when an attachment (27) is identified (S120), the geometry data (G L) of the agricultural machine (10) are automatically adjusted (S140).Steering method according to one of the preceding claims, characterized in that, in at least one steering mode (L), a movement range (Bz) of the towing vehicle (30) is determined (S210) on the basis of the lane information and geometry data (Gz) of the towing vehicle (30), and the steering commands (K 1, K 2) are determined (S230) on the basis of the movement range (B Z) and the geometry data (G L) of the agricultural machine (10).Steering method according to one of the preceding claims, characterized in that, in at least one steering mode (L), a movement range of the agricultural machine (10) is bounded at least on one side by the (Bz) of the towing vehicle (30).Steering method according to one of the preceding claims, characterized in that at least one steerable axle (14, 15) is locked as a function of the steering mode (L).Steering method according to one of the preceding claims, characterized in that the steering mode (L) is defined as a function of an amount of a travel speed and / or of the presence of a reverse travel.Agricultural machine (10) which is configured to be attached to a towing vehicle (30) which travels along a towing vehicle lane (Rz) during a road trip, and which has a control device (1) which is configured to: - based on a plurality of possible steering modes (L) of the agricultural machine (10), enable a determination (S170) of a steering mode (L) for at least part of the road trip to be made (S190) - based on sensory measurement (S180), determine kinematic data which describe kinematic characteristics of the agricultural machine (10), - based on sensory measurement (S180), determine lane information relating to the towing vehicle (30) (S200) and adjust the kinematic data therewith (S220), - depending on the result of the matching and depending on the currently defined steering mode (L), automatically determine (S 230) steering commands (K 1, K 2) for at least one steerable axle (14, 15) of the agricultural machine (10) in order to steer the agricultural machine (10) in a manner adapted to the tractor vehicle lane (Rz), and - automatically steer (S 240) the agricultural machine (10) by the steering commands (K 1, K 2).A combination (5) comprising a towing vehicle and a agricultural machine (10) which is attached to the towing vehicle (30) which travels along a towing vehicle lane (Rz) during a road trip, wherein the combination comprises a control device (1) which is configured to: - based on a plurality of possible steering modes (L) of the agricultural machine (10), enable a determination (S170) of a steering mode (L) for at least part of the road trip to be made (S190) - based on sensory measurement (S180), determine kinematic data which describe kinematic characteristics of the agricultural machine (10), - based on sensory measurement (S180), determine lane information relating to the towing vehicle (30) (S200) and adjust (S220) the kinematic data therewith, - depending on the result of the matching and depending on the currently defined steering mode (L), automatically determine (S 230) steering commands (K 1, K 2) for at least one steerable axle (14, 15) of the agricultural machine (10) in order to steer the agricultural machine (10) in a manner adapted to the tractor vehicle lane (Rz), and - automatically steer (S 240) the agricultural machine (10) by the steering commands (K 1, K 2).Control device (1) for controlling an agricultural machine (10) which is attached to a towing vehicle (30) which travels along a towing vehicle lane (Rz) during a road travel, wherein control device (1) is configured to: - based on a plurality of possible steering modes (L) of the agricultural machine (10), enable a determination (S170) of a steering mode (L) for at least part of the road travel, - based on sensory measurement (S180), determine (S190) kinematic data which describe a kinematic system of the agricultural machine (10), - based on sensory measurement (S180), determine (S200) lane information relating to the towing vehicle (30) and adjust (S220) the kinematic data therewith, - depending on the result of the matching and depending on the currently defined steering mode (L), automatically determine (S 230) steering commands (K 1, K 2) for at least one steerable axle (14, 15) of the agricultural machine (10) in order to steer the agricultural machine (10) in a manner adapted to the tractor vehicle lane (Rz), and - automatically steer (S 240) the agricultural machine (10) by the steering commands (K 1, K 2).