Method for operating a reversing assistant for a vehicle with a coupled trailer

Abstract

Method for operating a reversing assistant (12) for a vehicle (1) with a coupled trailer (2), wherein the reversing assistant (12) performs lateral guidance of the vehicle (1) by adjusting a front wheel angle of the front wheels (6) of the vehicle (1) and by adjusting a rear wheel angle of the rear wheels (8) of the vehicle (1), comprising: - Providing (S1) a target angle (20) that specifies a target articulation angle between the vehicle (1) and the trailer (2); - Determining (S2) a target front wheel angle (21) at which an articulation angle between the vehicle (1) and the trailer (2) corresponds at least substantially to the target angle (20) by applying a front wheel angle determination criterion (22) to the provided target angle (20); - Setting (S3) and holding the determined target front wheel angle (21); - Check (S4) whether a deviation (23) greater than 0 between the articulation angle and the target angle (20) can be detected when the target front wheel angle (21) is held; - if this is the case, determine (S5) a target rear wheel angle (24) at which the deviation (23) is at least reduced by applying a rear wheel angle determination criterion (25); and - Setting (S6) the determined target rear wheel angle (24).

Description

[0001] The invention relates to a method for operating a reversing assistant for a vehicle with a coupled trailer. The invention also relates to a control device, a vehicle, and a computer program for carrying out such a method.

[0002] A vehicle can have a trailer attached to it, so that the vehicle and trailer together form a vehicle combination. When reversing, steering the combination can feel unfamiliar to the driver, especially when cornering, because, for example, the trailer moves in the opposite direction to the steering wheel movement. To at least assist the driver when reversing, the vehicle can be equipped with a reversing assistant designed to perform or at least assist lateral guidance of the vehicle during reversing.

[0003] DE 10 2017 007 289 A1 discloses a method for reversing a vehicle combination. During reversing, the front wheels of one vehicle are steered in the same direction by means of front axle steering and the rear wheels of the other vehicle are steered in the same direction by means of rear axle steering, so that the vehicle combination travels a curved trajectory in reverse.

[0004] DE 10 2014 005 681 A1 discloses a method for driver assistance during driving, in particular reversing, of a motor vehicle with a trailer coupled to the motor vehicle, wherein a display device of the motor vehicle shows a superimposition of an image from a camera arranged on the motor vehicle with a graphic representation calculated by a computing device. The image depicts at least a section of the trailer's drawbar. The graphic representation depicts at least one direction associated with an angle value relating to an articulation angle between a longitudinal axis of the motor vehicle and a longitudinal axis of the trailer, and / or at least one directional range associated with the angle value, in perspective according to the imaging geometry of the camera.A target articulation angle can be specified via a control element of the motor vehicle, whereby actuators for adjusting a steering angle on the front and / or rear axle are controlled so that the target steering angle is achieved. DE 10 2018 130 429 A1 discloses a method for supporting a reversing maneuver of a vehicle combination comprising a towing vehicle and a trailer connected to each other via an articulated coupling. The method includes a step for adjusting a rear wheel steering angle depending on an articulation angle between the towing vehicle and trailer, and a step for adjusting a front wheel steering angle depending on the articulation angle and / or the rear wheel steering angle. The magnitude of the rear wheel steering angle is limited to a maximum value. The magnitude of the front wheel steering angle is limited to a maximum value.The adjustment of the front and rear wheel steering angles is designed such that the change in the rear wheel steering angle is greater for small values ​​of the articulation angle than for large values ​​of the articulation angle.

[0005] The object of the invention is to provide a solution by means of which a reliable reversing assistant can be provided for a vehicle with a trailer attached.

[0006] The problem is solved by the subject matter of the independent patent claims. Advantageous further developments result from the dependent claims.

[0007] A first aspect of the invention relates to a method for operating a reversing assistant for a vehicle with a coupled trailer. The trailer is, for example, coupled to a trailer hitch on the vehicle. The vehicle and the trailer together form a vehicle combination. The reversing assistant is designed to provide at least lateral guidance for the vehicle. It can alternatively or additionally be designed to provide longitudinal guidance for the vehicle. The trailer is, for example, a single-axle trailer. Other trailer configurations are possible.

[0008] Lateral control of the vehicle is achieved by adjusting the front wheel angle and the rear wheel angle. The front wheels are located on the front axle of the vehicle. The rear wheels are located on the rear axle. Adjusting the front wheel angle controls the front-axle steering, and adjusting the rear wheel angle controls the rear-axle steering. The reversing assistant is therefore designed to control the front and rear wheels of the vehicle and move them into a predetermined position to steer the vehicle combination. The front and rear wheels can be controlled independently of each other; that is, the front and rear wheel angles can be different.It can be assumed that the system does not adjust the angles of the trailer wheels during operation, meaning that the reversing assistant only controls the vehicle's wheels for lateral guidance of the vehicle combination. The reversing assistant can be activated automatically or manually whenever reversing with a trailer attached is being or is about to be performed.

[0009] The procedure involves providing a target angle. The target angle specifies a desired articulation angle between the vehicle and the trailer. This desired articulation angle can alternatively be referred to as the desired articulation angle between the vehicle and the trailer. The articulation angle is the angle between a centerline of the vehicle and a centerline of the trailer. The respective centerline can alternatively be referred to as the center axis or longitudinal axis. If the two centerlines are not parallel but angled relative to each other, the articulation angle is greater than 0 degrees. In this case, the vehicle combination is traveling through a curve. When traveling straight ahead, that is, when the centerlines of the vehicle and trailer are parallel to each other, the articulation angle is essentially 0 degrees. "Essentially" here includes deviations from 0 degrees of, for example, up to 0.5 degrees, 1 degree, 2 degrees, 3 degrees, 5 degrees, or, in particular, 10 degrees.

[0010] The target angle is set manually by a vehicle user, particularly the driver. The reversing assistant then assumes that the target angle is the articulation angle at which the vehicle should be oriented relative to the trailer while reversing. Therefore, the reversing assistant will at least attempt to set and maintain this target angle when operating. Alternatively or additionally, the target angle can be set automatically, for example, based on a calculated driving trajectory for the vehicle combination.

[0011] The procedure involves determining a target front wheel angle at which the articulation angle between the vehicle and the trailer corresponds at least substantially to the target angle. "Substantially" in this context refers to a deviation between the articulation angle and the target angle of, for example, up to 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 10 degrees, 15 degrees, or, in particular, 20 degrees. The target front wheel angle is determined by applying a front wheel angle determination criterion to the provided target angle. The front wheel angle determination criterion comprises at least one algorithm and / or at least one rule, the execution of which, based on the provided target angle, calculates how the vehicle's front wheels should or must be turned to achieve the target angle at least substantially.The front wheel angle determination criterion is based at least on the finding that each target angle within a specified target angle range, which is specified for the combination and achievable with the combination, can be assigned exactly one front wheel angle, so that when the front wheels are in a position within the front wheel angle, the articulation angle of the combination corresponds exactly to the target angle.

[0012] The procedure involves setting and maintaining the determined target front wheel angle. The vehicle's front wheels are controlled and thus turned or moved in such a way that they assume a front wheel angle that corresponds, at least substantially, to the target front wheel angle. "Substantially" includes, for example, inaccuracies that may depend on the accuracy of the front axle steering. These inaccuracies can be, for example, up to 0.5 degrees, 1 degree, 2 degrees, 3 degrees, or, in particular, 5 degrees. The front wheels are thus moved into a predetermined position that corresponds to the target front wheel angle.

[0013] However, errors can occur when determining and / or setting the target front wheel angle, resulting in the determined target front wheel angle not being exactly the front wheel angle at which the target angle is achieved, or the set front wheel angle deviating from the target front wheel angle. Reasons for this can include inaccuracies in measuring the current articulation angle and / or the distance between the trailer hitch and a trailer wheel axle, if this distance is only estimated and not measured or specified. Therefore, for example, a steering command for setting the target front wheel angle might be determined and implemented that doesn't quite achieve the target angle. Fine-tuning or adjustment may then be necessary to bring the articulation angle into line with the target angle.

[0014] The procedure involves checking whether a deviation greater than zero can be detected between the articulation angle and the target angle at the maintained target front wheel angle. The deviation can be specified, for example, in degrees or as a percentage. The procedure determines whether the driven front wheels have already succeeded in reaching the target angle, i.e., setting it correctly. If a deviation greater than zero is detected between the current articulation angle of the vehicle combination and the target angle, a target rear wheel angle is determined at which the deviation is at least reduced. The target rear wheel angle is determined by applying a rear wheel angle determination criterion. This criterion can be designed analogously to the front wheel angle determination criterion. The rear wheel angle determination criterion can, for example, be applied to the target angle.The rear wheel angle determination criterion includes at least one algorithm and / or at least one rule, in the execution of which the rear wheel angle is determined that is to be set or must be set in order to reduce, in particular eliminate, the previously recorded deviation between articulation angle and target angle.

[0015] The method involves adjusting the determined target rear wheel angle. The vehicle's rear wheels are controlled in such a way that the rear wheel angle corresponds to the determined target rear wheel angle. According to the invention, a coarse adjustment of the articulation angle of the vehicle combination is thus carried out using the front wheels by setting the determined target front wheel angle, and subsequently, if necessary, a fine adjustment or correction is made using the rear wheels by setting the determined target rear wheel angle. This reliably ensures that the target angle is set and, in particular, maintained during reversing. A reliable reversing assistant is therefore provided for a vehicle with a coupled trailer.

[0016] The procedure is carried out, for example, by means of a vehicle control unit. This control unit can operate the reversing assistant. It can control the vehicle's front-axle and rear-axle steering, meaning it can adjust the target front wheel angle by steering the front wheels and the target rear wheel angle by steering the rear wheels. The control unit can therefore access the vehicle's front and rear wheels. Control of the trailer wheels is not required. The procedure is thus independent of any technical equipment on the trailer. The vehicle can perform the procedure independently. The procedure can, for example, be understood as a computer-implemented process.During the execution of the procedure, in particular during the setting of the target front wheel angle and / or the target rear wheel angle, the vehicle can be moved, i.e. it can, for example, drive in reverse.

[0017] One embodiment provides that when the determined target rear wheel angle is set, the target front wheel angle is maintained. The front wheels thus remain at the set target front wheel angle while the rear wheels are moved to the target rear wheel angle, and in particular, are held at the set target rear wheel angle. The method therefore does not involve alternating between controlling the front and rear wheels; rather, the front and rear wheels can be adjusted simultaneously or held at a set wheel angle. The term "maintained" means, for example, that the target front wheel angle is kept constant. This clarifies that no further change to the front wheel angle is intended to perform the fine adjustment with the rear wheels. This can contribute to particularly precise fine-tuning.

[0018] Another embodiment involves moving the steering wheel when adjusting the target front wheel angle. However, the steering wheel remains stationary when adjusting the target rear wheel angle. This approach is based on the understanding that the driver recognizes or registers the adjustment of the front wheels because the steering wheel moves. This movement of the steering wheel, independent of any manual steering input, can be perceived as irritating. In contrast, the driver does not recognize or register the adjustment of the rear wheels by any movement of the steering wheel, as it does not move when the rear wheels are being steered. For this reason, a rear wheel angle adjustment is particularly suitable for fine-tuning, as this can be repeated while reversing without the driver being confronted with a moving steering wheel.This means that the driver can drive in a particularly relaxed manner with the reversing assistant activated, as the steering wheel no longer moves after the target front wheel angle has been set.

[0019] Furthermore, one embodiment provides that, when setting the target front wheel angle, a temporal profile of the articulation angle, as well as a first limit articulation angle profile and a second limit articulation angle profile, are determined. The temporal profile of the articulation angle describes a change in the articulation angle during the setting and, if applicable, the maintenance of the target front wheel angle. The temporal profile of the articulation angle can alternatively be referred to as the articulation angle profile. The temporal profile begins with a starting articulation angle, which, for example, existed between the vehicle and the trailer when the reversing assistant was activated, i.e., when the target angle was specified. If, for example, the vehicle was initially aligned straight ahead, i.e., an articulation angle of 0 degrees was present, the starting articulation angle can be 0 degrees. This is only one example; other starting articulation angles for the temporal profile of the articulation angle are possible.The angle of articulation over time can be determined, for example, from camera data from a rear-view camera of the vehicle. The articulation angle may be subject to error in this example, depending, for instance, on the accuracy of the rear-view camera and / or the evaluation algorithm used to determine the articulation angle from the camera data.

[0020] The first limiting buckling angle curve begins with an initial buckling angle that is greater than the initial buckling angle of the time-dependent buckling angle by a predetermined initial buckling angle interval. This initial buckling angle can alternatively be referred to as the upper initial buckling angle. The predetermined initial buckling angle interval can, for example, be 5 degrees. Larger or smaller initial buckling angle intervals are possible. The second limiting buckling angle curve begins with a second initial buckling value that is smaller than the initial buckling angle of the time-dependent buckling angle by a predetermined second buckling angle interval. This second initial buckling angle can alternatively be referred to as the lower initial buckling angle. The predetermined second buckling angle interval can also be, for example, 5 degrees. Larger or smaller second buckling angle intervals are possible. The two buckling angle intervals can differ from each other.For example, if the starting angle of the time course of the bend angle is 20 degrees, the first limit bend angle course can start at a first starting bend angle of 25 degrees and the second limit bend angle course at a second starting bend angle of 15 degrees.

[0021] The two limit angle curves describe the temporal evolution of an expected articulation angle at a set target front wheel angle. In other words, two curves, the first and second limit angle curves, are calculated, indicating how the vehicle combination would behave with a different starting articulation angle when the determined target front wheel angle is set. For example, the first limit angle curve is expected to approach the actual articulation angle more quickly than the second limit angle curve. Compared to the actual articulation angle and the first limit angle curve, the second limit angle curve is expected to reach the target angle with a delay. Essentially, the first and second limit angle curves represent two boundaries within which the articulation angle, i.e., its temporal evolution, is expected to occur.After a predetermined time, all three curves, i.e., the temporal curve of the buckling angle, the first limiting buckling angle curve, and the second limiting buckling angle curve, will approach the target angle and, in the long term, at least essentially achieve it.

[0022] The system considers the difference between the first and second limiting angle curves. As soon as this difference falls below a predefined first threshold, the target front wheel angle is considered reached. This first threshold might be, for example, 1 degree, 2 degrees, 3 degrees, 4 degrees, or, in particular, 5 degrees. Once the deviation between these two thresholds, and thus between the two limiting angle curves, is relatively small, the target angle is assumed to have been reached. Consequently, it can be assumed that the target front wheel angle has been set and can now be maintained. Upon reaching the distance corresponding to the first threshold, a steady state is assumed in which the target angle is essentially achieved.Once this steady state is considered reached, further adjustment of the articulation angle via the vehicle's front wheels alone is no longer desired, and the target rear wheel angle is determined and set. This illustrates a simple approach to reliably determine when the deviation between the articulation angle and the target angle should be checked.

[0023] Another embodiment involves determining the temporal progression of the articulation angle, the first limit articulation angle progression, and the second limit articulation angle progression, as described above. As soon as the difference between the first limit articulation angle progression and the second limit articulation angle progression is less than a predefined second limit value, the permissible change in the front wheel angle to achieve the target front wheel angle is reduced compared to the previous procedure, where any change in the front wheel angle was allowed. Additionally, a further target rear wheel angle is determined, which is set during the remaining adjustment of the target front wheel angle and contributes, at least in part, to achieving the target angle. The further target rear wheel angle and the target rear wheel angle are different rear wheel angles. They can differ from each other or, if necessary, be the same.The described procedure results in a reduction in the influence of the front wheels on the articulation angle once the second limit is reached, while the influence of the rear wheels begins. The second limit is, for example, 3 degrees, 4 degrees, 5 degrees, 7 degrees, or, in particular, 10 degrees. The second limit can be the same as the first limit or differ from it. In a preferred example, the second limit is greater than the first. As the difference between the two limit articulation angle curves decreases after reaching the second limit, the permissible change in the front wheel angle can be continuously or incrementally reduced, and / or the further target rear wheel angle can be continuously or incrementally increased.The process thus involves a transition from lateral control using only the front wheels to lateral control using both the front and rear wheels, before fine-tuning of the articulation angle is achieved solely using the rear wheels. This is particularly convenient, as it minimizes the driver's transition from steering input indicated by turning the steering wheel to steering input not indicated by the steering wheel.

[0024] Furthermore, in one embodiment, it can be provided that it is checked whether the distance between the first limit articulation angle profile and the second limit articulation angle profile is smaller than a predetermined third limit value. The third limit value is smaller than the second limit value. As soon as this is the case, that is, as soon as the distance is smaller than the predetermined third limit value, the target front wheel angle is considered reached, so that the target rear wheel angle is determined and provided. This completes the transition with the reduced change in the front wheel angle and the setting of the further target rear wheel angle. From the point at which the third limit value is reached, the target front wheel angle can, for example, be kept constant, and the articulation angle can be further approximated to the target angle using only the target rear wheel angle. The third limit value can, for example, correspond to the first limit value. Alternatively, it can differ from it.This clarifies when the advantageous fine-tuning using the rear wheels takes place at the latest.

[0025] According to an additional embodiment, instead of checking whether a deviation greater than zero between the articulation angle and the target angle can be detected at the maintained target front wheel angle, a temporal profile of the front wheel angle is recorded. The temporal profile of the front wheel angle is adjusted or fitted using a predefined function. This involves, for example, applying a filter to the temporal profile of the front wheel angle. The temporal profile of the front wheel angle describes how the front wheel angle behaves, and in particular, how it changes, when the target front wheel angle is set. The function approximates the temporal profile of the front wheel angle; that is, it approximates the temporal profile of the front wheel angle and / or follows it with at least local deviations.

[0026] The target rear wheel angle is now determined to at least reduce any deviation between the front wheel angle over time and the adjusted function. Here, reaching the target front wheel angle is not required to then check whether the articulation angle can still be further approximated to the target articulation angle solely based on the rear axle steering. Instead, fine-tuning of the articulation angle using the rear wheels occurs repeatedly, and in particular continuously, while the target front wheel angle is being set at the front wheels. This can be understood as an alternative approach in which deviations and / or jumps in the front wheel angle over time can be corrected by adjusting the rear wheels. Compared to the previously described embodiments, this may be more complex to configure, but it represents a reliable alternative for achieving the target angle.

[0027] Another embodiment involves checking, after setting the determined target front wheel angle, whether the deviation between the articulation angle and the target angle is increasing again. As soon as the deviation exceeds a predetermined deviation limit, a corrective target front wheel angle is determined and set, at which the deviation is reduced again. Thus, even if, for example, the target front wheel angle has been set and initially only the deviation between the articulation angle and the target angle has been reduced by adjusting the target rear wheel angle, over time the deviation between the articulation angle and the target angle may again become so large that reducing the deviation using the front wheels is advisable.In such a situation, the articulation angles can be subsequently corrected and brought closer to the target angle by adjusting the front wheels, i.e., by setting the correction front wheel angle, which deviates from the actual front wheel angle. Reasons for the increasing deviation can include, for example, measurement errors and / or unexpected trailer dynamics. It is therefore quite possible that the front wheel angle will no longer be kept constant, but will be actively controlled and thus changed to compensate for and correct the deviation. The procedure described above can essentially be repeated in this context. Subsequent adjustments to the target front wheel angle are therefore possible and at least contribute to making the procedure even more reliable.

[0028] According to a preferred embodiment, it is provided that it is checked whether the determined target front wheel angle is greater than a predetermined limit front wheel angle. For example, the front axle steering may be limited so that maximum front wheel angles of plus / minus 30 degrees or 35 degrees are adjustable. If a target front wheel angle is determined that is greater than the limit front wheel angle, this would be the case in this example for front wheel angles above 30 degrees or 35 degrees, respectively. A front wheel angle of 40 degrees, for example, may not be adjustable. If the determined target front wheel angle is greater than the predetermined limit front wheel angle, the limit front wheel angle is set, and an additional rear wheel angle is determined and set to at least reduce the additional deviation between the articulation angle and the target angle resulting from the set limit front wheel angle instead of the determined target front wheel angle.For example, the remaining 5 degrees in the example above can be compensated for by appropriately controlling the rear wheels. For instance, there could be a predefined limit angle for the rear wheels, perhaps plus / minus 5 or 10 degrees. The additional rear wheel angle cannot then exceed this limit, meaning that there may also be system limits regarding the rear wheel angles that cannot be overcome. Essentially, the coarse adjustment of the articulation angle using the front wheels can be supplemented by a contribution from the rear wheels, if necessary. This makes the process even more reliable.

[0029] Furthermore, in one embodiment, it is provided that, to determine the target front wheel angle and / or the target rear wheel angle, at least one distance between a trailer axle and a trailer coupling of the vehicle is taken into account. This distance is estimated, for example, by querying or requesting the driver or another user, particularly in the vehicle. The driver may be asked and / or required to manually specify the distance, for example, by operating a control element. The control element may be, for example, a button, a knob, a switch, a rotary push-button, and / or an element on a touchscreen. Alternatively or additionally, the distance can be specified by voice input.Alternatively or additionally, the distance can be determined, or in particular estimated, from camera data from a rear-view camera on the vehicle and / or sensor data from a radar device, lidar device, and / or ultrasonic sensor mounted at the rear of the vehicle. Furthermore, or alternatively, other data relating to the vehicle, the front-axle steering, and / or the rear-axle steering can be taken into account. Ultimately, this makes it clear that uncertainties in setting the target angle can also arise from estimations, but are nevertheless necessary to, for example, estimate and account for the dynamics of the trailer.

[0030] Another embodiment provides that the front and rear wheels are adjusted independently of each other. In a preferred example, the target front wheel angle and the target rear wheel angle are not the same. Typically, they differ. For example, the front wheels may have a positive angle and the rear wheels a negative angle relative to, say, a position of the wheels parallel to the vehicle's centerline. The front and rear wheels are thus independent of each other, making it reliably possible to achieve the target angle.

[0031] In an additional embodiment, the articulation angle is determined by evaluating camera data from at least one camera on the vehicle. This camera data describes at least part of the trailer. In a preferred example, the camera that captures the data and transmits it to the control unit for evaluation is the vehicle's rear-view camera. Alternatively or additionally, camera data from the vehicle's side cameras, such as those located in the side mirrors, can be used, provided they can capture at least part of the trailer. This demonstrates that the method can be performed using the vehicle's sensors without the need for external data.

[0032] Another aspect of the invention relates to a control device for a vehicle. The control device is configured to perform the method described above. The control device carries out the method. The control device includes, for example, a processor unit. This can include at least one microprocessor, microcontroller, FPGA (Field Programmable Gate Array), and / or DSP (Digital Signal Processor). Furthermore, it can include program code, which can alternatively be referred to as a computer program product. The program code can be stored in a data memory of the processor unit.

[0033] Another aspect of the invention relates to a vehicle. The vehicle is designed to perform, or performs, the method described above. The vehicle can be a motor vehicle, for example a passenger car, a truck, a bus, a motorcycle, and / or a moped. The motor vehicle can have the control device described above.

[0034] Another aspect of the invention relates to a computer program product. The computer program product is a computer program. The computer program product comprises instructions which, when the program is executed by a computer, such as the vehicle's control units, cause it to perform the steps of the method according to the invention.

[0035] The embodiments described in connection with the method according to the invention, both individually and in combination with one another, apply accordingly, where applicable, to the vehicle according to the invention, the control device according to the invention, and the computer program product according to the invention. The invention comprises combinations of the described embodiments.

[0036] This shows: Fig. 1 a schematic representation of a vehicle and trailer combination; Fig. 2 a schematic representation of the team made of Fig. 1 with angled trailer; Fig. 3. A schematic representation of a signal flow graph of a method for operating a reversing assistant; Fig. 4. A schematic representation of the temporal progression of a bending angle; and Fig. 5 shows a schematic representation of the time course of a target front wheel angle.

[0037] The figures contain identical components labelled with the same reference symbols.

[0038] Fig. Figure 1 shows a vehicle 1 to which a trailer 2 is coupled. The coupling is achieved, for example, by means of a trailer hitch 3. The vehicle 1 and the trailer 2 together form a vehicle combination 4. The vehicle 1 has a front axle 5 with front wheels 6 and a rear axle 7 with rear wheels 8. The trailer 2 is shown here as a single-axle trailer 2, which has a trailer axle 9 with trailer wheels 10. Trailers 2 with other configurations are possible.

[0039] In Fig. 1. Several distances or lengths L are shown. The distance L f describes a distance between the front axle 5 and the rear axle 7 of the vehicle 1. The distance L hdescribes the distance between the rear axle 7 and the trailer hitch 3. The distance Lt indicates the distance between the trailer wheel axle 9 and the trailer hitch 3.

[0040] Vehicle 1 has a control device 11. This device can be used to operate a reversing assistant 12. The reversing assistant can control at least the lateral guidance of vehicle 1, and thus of the vehicle combination 4, during reversing, by adjusting the front wheel angles of the front wheels 6 and the rear wheel angles of the rear wheels 8. In addition, the reversing assistant 12 can, in one example, also provide longitudinal guidance for vehicle 1, and thus of the vehicle combination 4, during reversing.

[0041] Vehicle 1 can have at least one camera 13, which is configured here as a rear-facing camera. This camera can at least partially capture the trailer 2. In a preferred example, the camera 13 can capture the trailer 2 completely.

[0042] Fig. 2 shows the team of 4 from Fig. 1 with an articulation angle Φ greater than 0 degrees. The articulation angle describes an angle between a vehicle centerline 14 of vehicle 1 and a trailer centerline 15 of trailer 2. Furthermore, a front wheel angle δ is also present. r The angle δ is shown for the front wheels 6, which here describes an angle between a parallel 16 to the vehicle centerline 14 and a wheel alignment 17. Additionally, a rear wheel angle δ is shown for the rear wheels 8. rThe diagram shows an angle between the parallel 16 to the vehicle centerline 14 and the wheel alignment 17. It is clear that the front wheels 6 and the rear wheels 8 can be adjusted independently of each other.

[0043] Fig. Figure 3 shows the steps of a procedure for operating the reversing assistant 12. The procedure is carried out, for example, using the control device 11 of the vehicle 1. In a procedure step S1, a target angle 20 is provided, which specifies a target articulation angle between the vehicle 1 and the trailer 2. The target angle 20 is entered, for example, by a driver of the vehicle 1 in the vehicle 1 and is the angle at which the vehicle 1 is to reverse. For example, the target angle 20 can be set to the Fig. 2 sketched buckling angles Φ correspond.

[0044] In process step S2, a target front wheel angle 21 is determined such that the articulation angle between the vehicle 1 and the trailer 2 corresponds at least substantially to the target angle 20. The target front wheel angle 21 is determined by applying a front wheel angle determination criterion 22 to the provided target angle 20. This can be done, for example, based on the following equation for the articulation angle rate, i.e., the time derivative of the articulation angle Φ: ϕ˙=−1ltsin(ϕ)vx−1lf(lhltcos(ϕ)+1)(tan(δf)−tan(δr))vx+1ltcos(ϕ)tan(δr)vx

[0045] With I t for L t , I f for L f and I n for L h as well as the speed v x .

[0046] In process step S3, the determined target front wheel angle 21 is set and maintained. This means that the front wheels 6 are brought to the determined target front wheel angle 21, thereby setting the target front wheel angle 21. In process step S4, it is then checked whether a deviation 23 greater than zero between the articulation angle and the target angle 20 can be detected while the target front wheel angle 21 is maintained. If this is the case and the deviation 23 is greater than zero, a target rear wheel angle 24 can be determined in process step S5, which at least reduces the deviation 23. The target rear wheel angle 24 can be determined by applying a rear wheel angle determination criterion 25. In process step S6, the determined target rear wheel angle 24 is then set. This means that the rear wheels 8 are brought to a corresponding angle.

[0047] When setting the determined target rear wheel angle 24, it may be intended that the target front wheel angle 21 remains constant. It may generally be the case that when setting the target front wheel angle 21, or generally when setting any front wheel angle, the steering wheel of vehicle 1 is moved, whereas the steering wheel of vehicle 1 remains stationary when setting the target rear wheel angle 24, and thus when setting any rear wheel angle.

[0048] A process step S7 can be performed, which can follow process step S2. In process step S7, for example, it is checked whether the determined target front wheel angle 21 is greater than a predefined limit front wheel angle 40. If this is the case, the limit front wheel angle 40 can be set using the front wheels 6, and an additional rear wheel angle 41 can be determined and set so that an additional deviation 23 between the articulation angle and the target angle 20, resulting from the set limit front wheel angle 40 instead of the set determined target front wheel angle 21, can at least be reduced. Afterwards, process step S4 can be performed, for example.Therefore, if an angle limit (limit front wheel angle 40) exists for the target front wheel angle 21 and this would be exceeded, the steering of the vehicle 1 can be influenced by means of the rear wheels 8, in particular even before the target rear wheel angle 24 is determined and set in process steps S5 and S6, by using the rear wheels 8 and the additional rear wheel angle 41.

[0049] Fig. Figure 4 illustrates one or more ways in which it can be determined that the setting of the target front wheel angle 21 is complete and that, for example, the verification in process step S4 should now take place. When setting the target front wheel angle 21, a time-dependent profile 26 of the articulation angle is considered. In addition, a first limit articulation angle profile 27 and a second limit articulation angle profile 28 are determined and considered. The first limit articulation angle profile 27 begins with a first starting articulation angle 30, which is greater than a starting articulation angle 29 of the time-dependent profile 26 by a predetermined first articulation angle interval 32. The second limit articulation angle profile 28 begins with a second starting articulation angle 31, which is smaller than the starting articulation angle 29 by a second predetermined articulation angle interval 33. The first articulation angle interval 32 and the second articulation angle interval 33 can be the same or different.The angle intervals 32, 33 are, for example, 5 degrees.

[0050] Both limit angle curves 27, 28 describe, for example, a time course 26 of an expected articulation angle at a set target front wheel angle 21. As soon as the distance 43 between the first limit angle curve 27 and the second limit angle curve 28 is less than a predefined first limit value 34, the target front wheel angle 21 can be considered to have been reached. Then, for example, process step S4 can be carried out.

[0051] Alternatively, it can be checked whether the distance 43 between the two limit articulation angle profiles 27, 28 is smaller than a predetermined second limit value 35. As soon as or if this is the case, a front wheel angle change that is still permissible to achieve the target front wheel angle 21 is reduced compared to before, and a further target rear wheel angle 24 is determined, which is set during the remaining adjustment of the target front wheel angle 21 so that it at least contributes to achieving the target angle 20. This is done, for example, until a third limit value 36 is reached that is smaller than the second limit value 35. As soon as this is the case, the target front wheel angle 21 can be considered reached, so that process step S4 can be carried out. Here, purely by way of example, the first limit value 34 is equal to the third limit value 36.

[0052] Fig.Figure 5 shows an alternative procedure for omitting the check in process step S4. Here, a time-dependent profile 37 of the front wheel angle is recorded and adjusted using a predefined function 38. The target rear wheel angle 24 is determined to at least reduce any deviation 23 between the time-dependent profile 37 of the front wheel angle and the adjusted function 38.

[0053] It may be provided that, after setting the transmitted target rear wheel angle 24 in process step S6, it is checked whether the deviation 23 between the articulation angle and the target angle 20 increases again. As soon as this deviation exceeds a predefined limit value, a corrective target front wheel angle can be determined and set, at which the deviation 23 is reduced again. Therefore, a further change to the front wheel angle may occur after process step S6 if this is necessary due to deviations 23.

[0054] When determining the target front wheel angle 21 and / or the target rear wheel angle 24, that is, when applying the front wheel angle determination criterion 22 or the rear wheel angle determination criterion 27, at least the distance L can be determined. t This will be taken into account. This will be assessed in particular.

[0055] The articulation angle can be determined, for example, by evaluating camera data from camera 13 of vehicle 1. Except for the acquisition of the camera data, all process steps in a preferred example are carried out by means of the control device 11.

[0056] Overall, the examples demonstrate steering wheel stabilization using rear-axle steering when reversing with a trailer 2. Typically, rear-axle steering is used to achieve larger articulation angles without trailer 2 breaking away.

[0057] Given the vehicle and trailer geometry, the change in articulation angle (articulation rate) is determined by the front and rear wheel angles and the vehicle speed (see the formula above). In the following, we assume that the vehicle speed is constant (or consider the change in articulation angle per unit distance traveled). Then, the articulation rate depends only on the front and rear wheel angles.

[0058] The basic idea behind many reversing assistants is to define the requested articulation angle rate (target angle 20) as a function of the articulation angle, and in particular, the articulation angle error. The problem here is that there is only one equation but two degrees of freedom: the rear wheel angle and the front wheel angle. Therefore, either one of the two wheel angles must be fixed, or a fixed relationship between the two wheel angles must be defined to obtain a unique solution.

[0059] Simple approaches are here: 1.) Priority on front wheel angle: a) Set the rear wheel angle to 0 and calculate the front wheel angle b) Limit the front wheel angle to the maximum range (limit front wheel angle 40°) c) Calculate the rear wheel angle using the limiting front wheel angle of 40° as the angle of the front wheel. 2.) Priority on rear wheel angle: Similar to 1.) but reversed, for example by first setting the front wheel angle to 0. 3.) Fixed relationship between front and rear wheel angles, for example a fixed distance to the virtual rear axle

[0060] Reversing with a trailer 2 is a major challenge for most drivers. The main reasons for this are the counterintuitive steering, the unstable behavior of the trailer 2, and poor visibility. "Trailer Backing Assist" is an assistance function that supports the driver when reversing with a trailer 2. The driver selects a target angle 20, and the assistance system controls the steering so that the desired target angle 20 is reached and maintained. Since the articulation angle is unstable when reversing, the steering must constantly and very quickly adapt to any deviation 23 from the articulation angle. This rapid movement of the steering wheel feels quite unpleasant to the driver and is particularly noticeable when a constant articulation angle needs to be maintained. According to the invention, these small and rapid steering wheel movements are to be reduced or even eliminated by means of the rear-axle steering.

[0061] The basic idea is as follows: In most vehicles 1, the front wheels 6 are mechanically connected to the steering wheel. In contrast, the angles of the rear wheels 8 are controlled only via an electric motor (steering-by-cable). Therefore, a change in the rear wheel angle is not perceptible at the steering wheel. The aim is to filter out the small and rapid wheel angle adjustments from the requests for the front wheel angles and compensate for errors using the rear wheels. A) Stationary state only: The simplest suggestion is to steer trailer 2 according to approach 1) until the current articulation angle is close enough to the target angle 20. Once the current articulation angle is close enough to the target angle 20, the stationary front wheel angle (constant) is requested, while the articulation angle is maintained at the target angle 20 using the rear wheels 8. B) Saturating requirement of the front wheel angle: Due to system errors, an incorrect trailer hitch length, errors in measuring the articulation angle, and other factors, it is possible that with a fixed target angle 20, the target angle 20 is never reached, but rather the articulation angle converges to a smaller or larger angle. In this case, we may never achieve the stable state of proposal A). On the other hand, with the convergence of the control device 11, the desired front wheel angle also converges towards a specific front wheel angle (target front wheel angle 21) and then only oscillates around it. The front wheel angle has then reached a stable state, which we detect by using a filter such as an IIR low-pass filter. Once the steady state has been detected, the front wheel angle is fixed, and control is once again left to the rear wheels 8. C) For A) and B), fuzzy logic can be used, meaning that an interpolated angle between the fixed and the calculated front wheel angle is assumed for the front wheel angle. An angle closer to the fixed front wheel angle is used if the articulation angle approaches the target angle of 20° (for 1)) or if the calculated front wheel angle requirement has fewer deviations (for 2)). D) A low-pass filter is generally used for the requested front wheel angle or front wheel angular velocity. The rear wheels handle the rest. 8.

[0062] A practical example could be: a) Start with a coupling angle of -30 degrees (trailer 2 to the left of vehicle 1) and drive in reverse at a constant speed. b) The user requests a target angle of 20 degrees from 0 degrees. c) To reduce the articulation angle, the control device 11 requests a large positive front wheel angle (steering to the left, for example at 32 degrees) and a 0 degree rear wheel angle. d) The bending angle increases towards zero. e) The closer the articulation angle is to zero, the smaller the front wheel angle can be in order to still have a positive articulation angle rate. f) Both the front wheel angle and the articulation angle approach zero. g) Asymmetries of the trailer 2, uneven ground, delays, measurement errors, and the instability of the trailer 2 when reversing cause the articulation angle to fluctuate around zero (remaining in the range [-0.5 degrees, 0.5 degrees]). The control device 11 constantly counteracts this to bring the articulation angle back to zero (remaining in the range [-1 degree, 1 degree]). h) Determine that the stable state has been reached. i) Demanding a front wheel angle of 0 degrees and using only the rear wheel angle for steering. The steering wheel does not move at all, as the rear axle 7 is controlled via the steering system using a cable.

Claims

[1] Method for operating a reversing assistant (12) for a vehicle (1) with a trailer (2) attached, wherein the reversing assistant (12) performs lateral guidance of the vehicle (1) by adjusting a front wheel angle of the front wheels (6) of the vehicle (1) and by adjusting a rear wheel angle of the rear wheels (8) of the vehicle (1), comprising: - Providing (S1) a target angle (20) that specifies a target articulation angle between the vehicle (1) and the trailer (2); - Determining (S2) a target front wheel angle (21) at which an articulation angle between the vehicle (1) and the trailer (2) corresponds at least substantially to the target angle (20) by applying a front wheel angle determination criterion (22) to the provided target angle (20); - Setting (S3) and holding the determined target front wheel angle (21); - Check (S4) whether a deviation (23) greater than 0 between the articulation angle and the target angle (20) can be detected when the target front wheel angle (21) is held; - if this is the case, determine (S5) a target rear wheel angle (24) at which the deviation (23) is at least reduced by applying a rear wheel angle determination criterion (25); and - Setting (S6) the determined target rear wheel angle (24). [2] Method according to claim 1, characterized by , that when the determined target rear wheel angle (24) is set, the target front wheel angle (21) is maintained. [3] Method according to any one of the preceding claims, characterized by , that when the target front wheel angle (21) is set, a steering wheel of the vehicle (1) is moved, but when the target rear wheel angle (24) the steering wheel remains stationary. [4] Method according to any one of the preceding claims, characterized by, that when setting the target front wheel angle (21), a time profile (26) of the articulation angle as well as a first limit articulation angle profile (27) and a second limit articulation angle profile (28) are determined, wherein the first limit articulation angle profile (27) begins at a first starting articulation angle (30) which is greater than a starting articulation angle (29) of the time profile (26) of the articulation angle by a predetermined first articulation angle distance (32), and the second limit articulation angle profile (28) begins at a second starting articulation angle (31) which is smaller than the starting articulation angle (29) of the time profile (26) of the articulation angle by a predetermined second articulation angle distance (33), and both limit articulation angle profiles (27, 28) describe a time profile (26) of an expected articulation angle at the set target front wheel angle (21),wherein as soon as a distance (43) between the first limit buckling angle profile (27) and the second limit buckling angle profile (28) is less than a predetermined first limit value (34), the target forward bearing angle is deemed to have been reached. [5] Method according to any one of claims 1 to 3, characterized by, that when setting the target front wheel angle (21), a time profile (26) of the articulation angle as well as a first limit articulation angle profile (27) and a second limit articulation angle profile (28) are determined, wherein the first limit articulation angle profile (27) begins at a first starting articulation angle (30) which is greater than a starting articulation angle (29) of the time profile (26) of the articulation angle by a predetermined first articulation angle distance (32), and the second limit articulation angle profile (28) begins at a second starting articulation angle (31) which is smaller than the starting articulation angle (29) of the time profile (26) of the articulation angle by a predetermined second articulation angle distance (33), and both limit articulation angle profiles (27, 28) describe a time profile (26) of an expected articulation angle at the set target front wheel angle (21),wherein as soon as a distance (43) between the first limit articulation angle profile (27) and the second limit articulation angle profile (28) is less than a predetermined second limit value (35), a front wheel angle change that is permitted to achieve the target front wheel angle (21) is reduced and a further target rear wheel angle (24) is determined, which is set during the remaining adjustment of the target front wheel angle (21) and at least contributes to achieving the target angle (20). [6] Method according to claim 5, characterized by , that it is checked whether the distance (43) between the first limit articulation angle profile (27) and the second limit articulation angle profile (28) is smaller than a predetermined third limit value (36) which is smaller than the second limit value (35), wherein as soon as this is the case, the target front wheel angle (21) is considered to have been reached, so that the target rear wheel angle (24) is determined and set. [7] Method according to any one of the preceding claims, characterized by , that instead of checking whether the deviation (23) of a large 0 between the articulation angle and the target angle (20) can be detected at the held target front wheel angle (21), a time course (37) of the front wheel angle is recorded and adapted with a predefined function (38) and the target rear wheel angle (24) is determined in order to at least reduce a deviation (23) between the time course (37) of the front wheel angle and the adapted function (38). [8] Method according to any one of the preceding claims, characterized by , that after setting the determined target rear wheel angle (24) it is checked whether the deviation (23) between the articulation angle and the target angle (20) increases again, whereby as soon as this is greater than a specified deviation limit value, a correction target front wheel angle is determined and set, at which the deviation (23) is reduced again. [9] Method according to any one of the preceding claims, characterized by , that it is checked whether the determined target front wheel angle (21) is greater than a specified limit front wheel angle (40), wherein if this is the case, the limit front wheel angle (40) is set and an additional rear wheel angle (41) is determined and set in order to at least reduce an additional deviation (23) between the articulation angle and the target angle (20) due to the set limit front wheel angle (40) instead of the determined target front wheel angle (21). [10] Method according to any one of the preceding claims, characterized by , that when determining the target front wheel angle (21) and / or the target rear wheel angle (24), at least a distance between a trailer wheel axle (9) of the trailer (2) and a trailer coupling (3) of the vehicle (1) is taken into account, in particular estimating this distance. [11] Method according to any one of the preceding claims, characterized by , that the front wheels (6) and the rear wheels (8) are adjusted independently of each other. [12] Method according to any one of the preceding claims, characterized by , that the articulation angle is determined by evaluating at least camera data from a camera (13) of the vehicle (1), wherein the camera data at least partially describe the trailer (2). [13] Control device (11) for a vehicle (1), wherein the control device (11) is configured to perform a method according to one of the preceding claims. [14] Vehicle (1) designed to perform a method according to any one of claims 1 to 12. [15] Computer program product comprising instructions which, when executed by a computer, cause it to perform a method according to any one of claims 1 to 12.

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