Method for operating a reversing assistance system of a vehicle and reversing assistance system

Abstract

The invention relates to a method for operating a reversing assistance system (1) for a vehicle (50), wherein the reversing assistance system enables a trajectory (20) that has already been traveled in reverse, wherein a maximum path length (21) for the trajectory (20) that has already been traveled in reverse is determined and provided by means of a control device (2) based on an expected error for the trajectory (20) that has already been traveled in reverse, wherein the maximum path length (21) is a path length for which the expected error exceeds a predetermined error threshold value (5). The invention also relates to a reversing assistance system (1) and a vehicle (50).

Description

Technical Field

[0001] The invention relates to a method for operating a reversing assistance system for a vehicle and to a reversing assistance system. The invention also relates to a vehicle. Background Art

[0002] Reversing assistance systems for vehicles are known which store the already travelled path (eg the last 50 metres) up to a maximum speed (eg 35 km / h) and can partially or automatically drive back along the already travelled path again.

[0003] Document DE 10 2015 217 555 A1 discloses a traveler, a device and a method for maneuvering assistance of the traveler. The method comprises the steps of determining a control variable and a measured variable when the traveler travels on a first distance, determining a first trajectory of the traveler for the first distance based on the control variable and the measured variable, determining a desired trajectory for the traveler relative to the first trajectory, comparing the desired trajectory with a reference trajectory traveled at an earlier time point, and if there is a sufficient degree of consistency, using the control variable and the measured variable assigned to the reference trajectory for maneuvering assistance. It can be provided that the desired trajectory corresponds to reverse driving of the traveler on the first trajectory.

[0004] From document DE 10 2014 213 074 A1, a reversing assistance system for a two-track motor vehicle with front-wheel steering is known, for returning in the rearward direction along a road section previously traveled manually in the forward direction. The reversing assistance system allows at least automatic steering of the motor vehicle during the return. The reversing assistance system is configured to determine, for different positions of the road section traveled during forward travel, the value of a first variable representing the orientation of the longitudinal axis of the vehicle during forward travel at the corresponding position, according to the distance traveled by one rear wheel and the distance traveled by the other rear wheel. In particular, the calculated values ​​of the first variable representing the orientation of the longitudinal axis of the vehicle during forward travel (with an assignment relative to the corresponding position) are stored in a data memory, and then, when reversing, these values ​​are read out from the data memory again and used to control the front-wheel steering. For different positions of the road section traveled during reverse travel, the value of a second variable representing the orientation at the corresponding position is determined, according to the distance traveled by one rear wheel and the distance traveled by the other rear wheel. During reversing, the value of a first variable characterizing the orientation of the longitudinal axis of the vehicle when moving forward at the corresponding position is compared with the value of a second variable characterizing the orientation of the longitudinal axis of the vehicle when reversing at the same position for different positions of the road section, and the front wheel steering is controlled based on the comparison. Summary of the invention

[0005] The object of the present invention is to improve a method for operating a reversing assistance system for a vehicle and a reversing assistance system.

[0006] This object is achieved according to the invention by a method having the features of claim 1 and a reversing assistance system having the features of claim 9. Advantageous embodiments of the invention are disclosed in the dependent claims.

[0007] In particular, a method for operating a reversing assistance system for a vehicle is provided, wherein the reversing assistance system at least partially automatically executes a trajectory already traveled in reverse driving, wherein a maximum path length for the trajectory already traveled in reverse driving is determined and provided by means of a control device based on an expected (or predicted) error for the trajectory already traveled in reverse driving, wherein the maximum path length is such a path length along the trajectory, that is, at this path length the expected error exceeds a predetermined error threshold.

[0008] In addition, a reversing assistance system is provided in particular, wherein the reversing assistance system can at least partially automatically execute a trajectory that has already been traveled in reverse, and the reversing assistance system includes a control device, wherein the control device is configured to determine and provide a maximum path length for the trajectory that has already been traveled in reverse based on an expected error for the trajectory that has already been traveled in reverse, wherein the maximum path length is a path length along the trajectory and in the case of this path length the expected error exceeds a predetermined error threshold.

[0009] The above method and the reversing assistance system make it possible to provide the user of the reversing assistance system with feedback about the maximum path length so that the user can optimally use the reversing assistance system for its purpose. For this purpose, the error expected when driving backwards on the track that has already been driven is determined by means of a control device. The expected error is caused in particular by the sensor system used when detecting the track that has already been driven, such as the measurement error of the vehicle odometer, and by the error of the actuator system, in particular the transverse and longitudinal guidance system of the vehicle used when driving backwards on the track that has already been driven. The present invention is based on the recognition that when driving backwards, the recorded track that has already been driven can only be reproduced to a certain extent, wherein errors occur when reversing, that is, deviations from the track that has been driven forward. This error is in particular a lateral deviation from the track that has been driven forward when reversing. The lateral deviation is critical when driving on this track, because if the deviation is too large, for example, a collision with other objects beside the track (such as a parked vehicle) may occur.

[0010] A maximum path length is determined using the determined expected error, wherein the maximum path length is the path length when an error to be expected during reversing along the trajectory exceeds a predefined error threshold value.

[0011] The method and the reversing assistance system have the advantage that the user is always informed of the distance at which the vehicle can be partially or automatically retraced. Thus, in complex environments, the user can only drive forward so far that partially or automatically reversing is always possible. This increases the comfort and safety of the user when using the vehicle.

[0012] A trajectory is in particular a (temporally and / or logically) ordered set of measurement points or tuples (or sets of variables), each of which includes at least one steering angle and at least one speed of the vehicle. The speed along the trajectory can also be mapped via a value pair consisting of a distance and a timestamp to store the average speed of a trajectory segment.

[0013] In determining the expected errors, the following error sources can be taken into account in particular: the vehicle odometer and / or the measuring sensor system used when recording the trajectory (in particular even depending on the respective measuring principle used and / or the speed of the vehicle and / or corresponding measuring conditions, such as temperature, weather, etc.), errors during storage (e.g. due to quantization, etc.) and / or errors associated with the actuator system during backward travel. The errors and their correlation can be determined for the individual error sources, in particular based on empirical tests.

[0014] Parts of the reversing assistance system, in particular the control device, can be designed individually or together as a combination of hardware and software, for example as a program code executed on a microcontroller or microprocessor.

[0015] Providing the determined maximum path length can include, for example, outputting the maximum path length on a display device. The maximum path length can thus be communicated directly to the user of the vehicle. In this case, the maximum path length can be displayed, for example, as a numerical value, a bar graph and / or a Harvey sphere. The trajectory shortened to the maximum path length can also be displayed, for example, as a projection in a road map (for example in a navigation view of a navigation system) or in a camera image (for example a reversing camera system).

[0016] The vehicle is in particular a motor vehicle. However, in principle the vehicle can also be another ground, water, rail, air or space vehicle.

[0017] In one embodiment, it is provided that the path length that can be traveled backwards is limited to a certain maximum path length. This can prevent the vehicle from traveling backwards beyond a permissible error on a track that has already been traveled when using the reversing assistance system. This can increase safety when operating the reversing assistance system, in particular, because a predetermined maximum deviation from the track that has already been traveled is maintained at all times. In particular, it can be provided that the maintenance of the limitation on the maximum path length is checked by means of the control device. In particular, the control device can interrupt or end the reversing operation if the result of the check indicates that the maximum path length has been reached.

[0018] In one embodiment, it is provided that, in order to determine the expected error, the track that has been traveled is divided into track segments according to the shape, wherein the expected error of the corresponding track segment is determined at least based on the corresponding shape of the track segment and the corresponding speed (at which the track segment is traveled in the forward direction), wherein the expected error in the case of traveling backward along the backward direction of the track that has been traveled is determined by the (multiple) expected errors of multiple track segments. In this way, the error can be determined more accurately, that is, according to the shape and speed or speed curve of the track or track segment. The method is based on the recognition that the accuracy when tracking, especially traveling backward on the track that has been traveled depends to a large extent on the shape of the track or the shape of the track segment and the speed of the vehicle used on the track segment when recording the track that has been traveled. In other words, the track that has been traveled is divided into track segments according to the shape of the track and / or the shape of each individual track segment. For example, straight track segments, curved or arc-shaped track segments can be divided here. Even different curvatures or curve radii (e.g. straight ahead, different turns, S-shaped swings, 90° turns, 180° turns, etc.) can be distinguished. Errors can then be determined, for example estimated, for all trajectory segments obtained in this way, at least as a function of the shape and the speed at which they are driven. To determine the overall error, the errors determined for the individual trajectory segments are accumulated, for example, absolute errors can be determined and added up according to error propagation laws. This is done in particular starting from the end point of the already traveled trajectory or the current position of the vehicle on the already traveled trajectory.

[0019] In this context, it is particularly taken into account during the accumulation that the overall error can be reduced if the movement along the trajectory section is opposite.

[0020] The accumulated error values ​​obtained by taking into account the further approaching trajectory segments are compared with a predefined error threshold. If the error threshold is exceeded, the trajectory segment considered in particular in the previous step is used as a reference for determining the maximum path length, so that the maximum path length includes the path lengths of all trajectory segments considered in the previous steps.

[0021] In an alternative embodiment, it is provided that, in order to determine the expected error, the track that has been traveled is divided into track segments according to the shape, wherein, based on at least the corresponding shape of the track segment and the speed when traveling through the corresponding track segment in the forward direction, the number of measuring points representing the corresponding track segment is determined or set, wherein the maximum path length and / or the predetermined error threshold value are provided in the form of the maximum number of measuring points. The method of dividing the track that has been traveled into individual track segments is similar to the above-mentioned embodiment. However, the track segments obtained in this way are represented by a set number of measuring points respectively. This can also be done when recording the track that has been traveled. For example, the number of measuring points detected and / or recorded (a tuple composed of at least one steering angle and at least one speed) can be set according to the steering angle and the speed (when recording). The setting of the number of measuring points representing the corresponding track segment is carried out at least based on the corresponding shape of the track segment and the speed of traveling in the corresponding track segment in the forward direction. Here, this is particularly carried out in such a way that the greater the number of measuring points, the higher the complexity of the track segments considered respectively. Therefore, a straight track segment can be represented in sufficient detail by two measuring points, whereas a curved track segment with a very small curve radius requires a larger number of measuring points to fully represent it. The maximum path length and / or the predetermined error threshold are defined in particular by setting the maximum number of measuring points. Here, the method is based in particular on the number of measuring points used to represent the entire track segment being selected so that the error contribution of each measuring point can remain essentially unchanged. Here, the more complex the track segment, the greater the number of measuring points, and therefore the greater the corresponding error contribution of the track segment to the total error when driving backwards on a track that has already been driven. The maximum error can be limited by specifying the maximum number of measuring points. The maximum path length can then be determined by the predetermined number and the corresponding number of measuring points for all track segments. The maximum path length is in particular the path length in which the number of measuring points exceeds the maximum number of measuring points.

[0022] In one embodiment, it is provided that, in order to determine the expected error or the number of measuring points of a track segment, the value for the respectively expected error is retrieved from a table as a function of the respectively determined shape and the corresponding speed. In this way, the corresponding error for different combinations of shape and speed can be determined quickly. The entries of such a table can be determined empirically, for example, for different combinations of shape (for example, for curves with different curve radii) and speed. The empirically determined table is then stored in a memory of the control device so that the control device can access it when applying the method.

[0023] In one embodiment, it is provided that a classification and / or pattern recognition is performed to determine the shape of the trajectory segment. This allows errors to be estimated even for unknown shapes. The trajectory segments are then classified, in particular, according to different shape classes. The errors can then be determined or estimated based on the respectively assigned shape class. This is done, for example, with the aid of a classification device. For example, even machine learning and artificial intelligence methods can be used here.

[0024] In one specific embodiment, it is provided that the maximum path length that can still be stored is determined and outputted as a function of the remaining storage capacity of the memory in which the already traveled path is stored. The user of the reversing assistance system thus additionally receives information about how much longer the already traveled path can still be, so that the already traveled path can still be partially or automatically traveled backwards with the aid of the reversing assistance system. This further increases the comfort and safety when operating the reversing assistance system.

[0025] In one embodiment, it is provided that a starting point on the already traveled track can be set or determined, wherein, after the starting point is set, the path length from the current position of the vehicle on the already traveled track to the set starting point is determined, wherein the determined path length is compared with the determined maximum path length, and wherein, if the determined path length is greater than the maximum path length, a warning is generated and output. In this way, the user of the reversing assistance system can be warned when the already traveled track can no longer be completely driven backwards to the determined starting point ("point of no return"). This is particularly advantageous in demanding driving situations (e.g. very narrow parking spaces, lack of turning possibilities, etc.). The warning can be performed visually, acoustically and / or tactilely. In addition, it can be provided that the set starting point is displayed in a display device (e.g. a navigation display of a navigation system). The warning can alternatively be designed as an indicator information to draw the attention of the vehicle user to the feasibility of using the reversing assistance system.

[0026] In one embodiment, it is provided that after the start of recording the already travelled track, the already travelled path length is determined, wherein the difference between the determined maximum path length and the already travelled path length is determined and output. In particular, the remaining path length can be estimated based on the remaining error up to a predetermined error threshold value. For this purpose, for example, the backward calculated error of the already travelled track is calculated in the above-described manner. From the difference between the calculated error and the predetermined error threshold value, the difference between the determined maximum path length and the already travelled path length can be estimated.

[0027] In one specific embodiment, it is provided that after the start of the recording of the travelled trajectory, the length of the travelled path is determined and output.

[0028] It can be provided that a situation in which a reversing assistance system is used is identified, wherein an indication message is generated and outputted in order to draw the attention of the vehicle user to the feasibility of using the reversing assistance system. The identification of this situation can be carried out, for example, by means of a control device or alternatively or additionally even by means of a surrounding perception system and / or a surrounding recognition system, in particular by means of a surrounding recognition device. Alternatively or additionally, the situation can even be identified based on map data, for example, depending on the vehicle position (using, for example, a navigation system, map data from a background server, based on swarm data / usage characteristics of other users, etc.). For example, the following situations can be identified in this case: blind alleys with no turning possibility, narrow parking spaces or parking lots.

[0029] In one embodiment, it is provided that if a situation is detected in which the reversing assistance system can be used, a starting point on the already traveled trajectory is set (or determined). This setting is performed in particular by means of a control device.

[0030] One situation is, for example, that based on the map data the vehicle is in a blind alley or is driving from a public transport space into a private area (e.g. private property, parking space, parking lot) and a bottleneck is detected by means of the control device and / or the surroundings recognition device. The bottleneck can be predefined by means of a stored width and length. The beginning of the blind alley or the transition from the public transport space to the private area can additionally be automatically set as the starting point.

[0031] In this case, a warning message is output to the driver as soon as reverse gear is engaged or the distance from the current position of the vehicle on the already traveled trajectory to the automatically set starting point is greater than the maximum distance. The warning message can be output acoustically, visually and / or haptically, for example by outputting a message and / or highlighting the feasibility of activating the reversing assistance system.

[0032] The further features with respect to the design of the reversing assistance system are derived from the description of the design of the method. The advantages of the reversing assistance system are respectively the same as the advantages in the design of the method.

[0033] Furthermore, in particular a vehicle is provided which comprises at least one reversing assistance system according to one of the described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below according to preferred embodiments with reference to the accompanying drawings.

[0035] Figure 1 A schematic diagram showing an embodiment of a reversing assist system;

[0036] Figure 2 A flow chart of an embodiment of a method for operating a reversing assistance system for a vehicle is shown in FIG.

[0037] Figure 3 A flow chart of a further specific embodiment of a method for operating a reversing assistance system for a vehicle is shown in FIG. DETAILED DESCRIPTION

[0038] Figure 1 , a schematic diagram of an embodiment of a reversing assistance system 1 is shown. The reversing assistance system 1 is arranged in a vehicle 50. The reversing assistance system 1 enables a trajectory 20 that has been traveled backward. For example, the recording of the trajectory 20 can be started manually or automatically when the vehicle 50 has a speed lower than, for example, 35 km / h. For example, a trajectory 20 with a length of 50 meters can be recorded. In order to record the trajectory 20, sensor data 10 of a sensor system 51 of the vehicle 50 are collected and recorded. The sensor system 51 detects in particular at least one steering angle and at least one speed of the vehicle 50. It can be provided that control data of an actuator system 52 of the vehicle 50, such as data of longitudinal and lateral control, are also recorded. In addition, other data, such as position data of the vehicle, control data of the actuator system and / or sensor data of sensors of the vehicle, can also be recorded when driving the trajectory 20.

[0039] The reversing assistance system 1 comprises a control device 2. The control device 2 comprises a computing device 3 and a memory 4. The recorded already traveled trajectory 20 is stored in the memory 4. In order to travel the already traveled trajectory 20 backwards, the control device 2 controls an actuator system 52 of the vehicle 50 accordingly.

[0040] The control device 2 is configured to determine and provide a maximum path length 21 for the trajectory 20 that has been traveled backwards as a function of the expected error for the trajectory 20 that has been traveled backwards. In this case, the maximum path length 21 is the path length in which the expected error exceeds a predetermined error threshold 5. The error threshold 5 is input externally to the reversing assistance system 1 or is alternatively already stored in the memory 4 of the control device 2. The maximum path length is determined, in particular, based on a reference to Figure 2 and Figure 3 The following is an explanation of the implementation method.

[0041] The determined maximum distance length 21 is then output, for example, on a display device 53 of the vehicle 50 in order to make it available to the user.

[0042] It can be provided that the path length that can be traveled backwards is limited to a certain maximum path length 21. For this purpose, when traveling backwards, the track 20 that has already been traveled is only opened up to the certain maximum path length 21.

[0043] Provision can be made to determine and output the maximum still storable path length 22 by means of the control device 2 as a function of the remaining storage capacity of the memory 4 in which the already traveled trajectory 20 is stored. The still storable path length 22 can be output, for example, on a display device 53 of the vehicle 50.

[0044] It can be provided that a starting point 11 on a trajectory 20 that has already been traveled can be set or set, wherein, after setting the starting point 11, the path length from the current position of the vehicle 50 on the trajectory 20 that has already been traveled to the set starting point 11 is determined with the help of the control device 2, wherein the determined path length is compared with a determined maximum path length 21, and wherein, if the determined path length is greater than the maximum path length 21, a warning 23 is generated and output.

[0045] It can be provided that, if a situation is detected in which the reversing assistance system 1 can be used, a starting point 11 is set on the already travelled trajectory 20 .

[0046] It may be provided that after the start of recording of the travelled trajectory 20 , the travelled path length 24 is determined by means of the control device 2 , wherein a difference 25 between the determined maximum path length 21 and the travelled path length 22 is determined and output.

[0047] It may be provided that after the start of the recording of the travelled trajectory 20 , the travelled path length 24 is determined and output.

[0048] It can be provided that the already traveled trajectory 20 and / or the maximum path length 21 and / or the maximum path length 22 that can still be stored and / or the already traveled path length 24 and / or the difference 25 are outputted graphically on the display device 53 so that the user can understand them more easily. In this case, numerical values ​​and / or bar graphs and / or Harvey spheres can be used for the display.

[0049] Figure 2 A flow chart of an embodiment of a method for operating a reversing assistance system for a vehicle is shown in FIG.

[0050] The method starts from the fact that the track that has been traveled has been recorded. This recording itself can also be part of the method.

[0051] In method step 100 , the already traveled track is divided into track segments. This is done based on the shape of the respective track segment and the speed at which the respective track segment is completed.

[0052] In this case, it can be provided that a classification and / or pattern recognition is carried out to determine the shape of the track segment. Machine learning and artificial intelligence methods can be used in this regard. The result is, for example, a classification into different classes consisting of a combination of shape and speed. The shape includes, for example, the curvature or curve radius of different track segments (e.g. straight ahead, different turns, S-shaped swings, 90° turns, 180° turns, etc.).

[0053] In method step 101, the expected error is determined for all trajectory segments. In particular, it is provided that, in order to determine the expected error for a trajectory segment, a value for the respective expected error is retrieved from a table as a function of the respectively determined shape and the corresponding speed. The table has been determined in advance, for example based on empirical tests. The table is stored, for example, in a memory of the control device of the reversing assistance system. For each combination of shape and speed, the control device of the reversing assistance system can then retrieve from the table the corresponding expected error when driving backwards for the trajectory segment under consideration.

[0054] In method step 102, the errors determined in each case for the trajectory segments are accumulated step by step by means of an error propagation method in order to be able to determine the total error. For example, the absolute errors can be added according to the error propagation law for this purpose. This is done starting from the end point of the trajectory that has already been traveled.

[0055] After each additional trajectory segment is added, a check is performed in method step 103 to determine whether the determined expected (total) error exceeds a predetermined error threshold. If the expected error does not exceed the predetermined error threshold, method step 102 is repeated and additional trajectory segments are added.

[0056] If, on the other hand, the expected error exceeds a predetermined error threshold, the maximum path length of the trajectory already traveled for the backward drive is determined in method step 104. In this case, it can be provided, for example, that the path lengths of the already added trajectory segments are added up and provided as the maximum path length. Alternatively, it can also be provided that the last added trajectory segment is not taken into account when determining the maximum path length, because a predetermined error threshold is exceeded after or due to the addition of this trajectory segment.

[0057] In method step 105, the determined maximum path length is output, for example on a display device of the vehicle. It can also be provided that the path length that can be driven backwards is limited to the determined maximum path length.

[0058] Figure 3 A flow chart of an embodiment of a method for operating a reversing assistance system for a vehicle is shown in FIG.

[0059] The method starts from the fact that the track that has been traveled has been recorded. This recording itself can also be part of the method.

[0060] In method step 200 , the already traveled track is divided into track segments. This is done based on the shape of the respective track segment and the speed at which the respective track segment is completed.

[0061] In this case, it can be provided that a classification and / or pattern recognition is carried out to determine the shape of the track segment. Machine learning and artificial intelligence methods can be used in this regard. The result is, for example, a classification into different classes consisting of a combination of shape and speed. The shape includes, for example, the curvature or curve radius of different track segments (e.g. straight ahead, different turns, S-shaped swings, 90° turns, 180° turns, etc.).

[0062] In method step 201, the number of measuring points representing the respective track segment is set. This is done at least as a function of the respective shape of the track segment and the speed at which the respective track segment is traveled in the forward direction. It is provided in particular that, in order to determine the number of measuring points, a value for the number is retrieved from a table as a function of the respectively determined shape and the respective speed. The table has been determined in advance, for example based on empirical tests. The table is stored, for example, in a memory of a control device of a reversing assistance system. For each combination of shape and speed, the control device of the reversing assistance system can then call up from the table the corresponding number of measuring points required when driving backwards on the track segment under consideration. It is assumed here that each measuring point has essentially the same contribution to the total error.

[0063] In method step 202 , the respectively specified number of measuring points of the track section is added up step by step in order to be able to determine the total number of measuring points. This is done starting from the end of the track that has already been traveled.

[0064] After each additional trajectory segment is added, a check is performed in method step 203 to determine whether the number of measurement points determined exceeds a predetermined maximum number of measurement points. The predetermined maximum number of measurement points corresponds in particular to a predetermined error threshold. If the number of measurement points determined does not exceed the predetermined maximum number, method step 202 is repeated and additional trajectory segments are added.

[0065] If, however, the determined number does not exceed a predetermined maximum number, the maximum path length of the already traveled trajectory for the backward drive is determined in method step 204. In this case, it can be provided, for example, that the path lengths of the already added trajectory segments are added up and provided as the maximum path length. Alternatively, it can also be provided that the last added trajectory segment is not taken into account when determining the maximum path length, because after or by adding this trajectory segment, the predetermined maximum number of measuring points is exceeded.

[0066] In method step 205, the determined maximum path length is output, for example on a display device of the vehicle. It can also be provided that the path length that can be driven backwards is limited to the determined maximum path length.

[0067] List of reference numerals:

[0068] 1 Reversing Assist System

[0069] 2 Control device

[0070] 3 Memory

[0071] 4 Computing Devices

[0072] 5 Error Threshold

[0073] 10 Sensor Data

[0074] 11 Starting Point

[0075] 20 Tracks that have been traveled

[0076] 21 Maximum path length

[0077] 22 Path length that can still be stored

[0078] 23 Warning

[0079] 24 Length of the path traveled

[0080] 25 Difference

[0081] 50 Transportation

[0082] 51 Sensor System

[0083] 52 Actuator system

[0084] 53 Display device

[0085] 100-105 Methods and Steps

[0086] 200-205 Methods and Steps

Claims

1. A method for operating a reversing assistance system (1) for a vehicle (50), wherein: A reversing assistance system at least partially automatically executes a trajectory (20) travelled backwards, wherein a maximum path length (21) for the trajectory (20) travelled backwards is determined and provided by means of a control device (2) based on an expected error for the trajectory (20) travelled backwards, wherein the maximum path length (21) is such a path length along the trajectory (20) that the expected error exceeds a predetermined error threshold value (5) at this path length, wherein the path length that can be travelled backwards is limited to the determined maximum path length (21), wherein in order to determine the expected error, the trajectory (20) travelled is divided into trajectory segments according to shape, wherein the number of measuring points representing the respective trajectory segment is determined based on at least the respective shape of the trajectory segment and the speed at which the respective trajectory segment is travelled in the forward direction, wherein the maximum path length (21) and / or the predetermined error threshold value (5) are predetermined in the form of a maximum number of measuring points.

2. The method according to claim 1, characterized in that In order to determine the expected error, the already traveled trajectory (20) is divided into trajectory segments according to their shapes, wherein the expected error of the corresponding trajectory segment is determined at least based on the corresponding shape of the trajectory segment and the speed when the corresponding trajectory segment is traveled in the forward direction, wherein the expected error in the case of traveling backward along the already traveled trajectory (20) in the backward direction is determined by the expected errors of multiple trajectory segments.

3. The method according to claim 1 or 2, characterized in that In order to determine the expected error of a trajectory segment or the number of measuring points, a value for the respectively expected error is retrieved from a table as a function of the respectively determined shape and the respective speed.

4. The method according to claim 1, characterized in that The maximum path length (22) that can still be stored is determined and outputted based on the remaining storage capacity of a memory (3) in which the already traveled trajectory (20) is stored.

5. The method according to claim 1, characterized in that A starting point (11) on a track (20) that has already been traveled can be set or is set, wherein after setting the starting point (11), a path length from a current position of a vehicle (50) on the track (20) that has already been traveled to the set starting point (11) is determined, wherein the determined path length is compared with a determined maximum path length (21), and wherein, if the determined path length is greater than the maximum path length (21), a warning (23) is generated and output.

6. The method according to claim 1, characterized in that If a situation is detected in which the reversing assistance system (1) can be used, a starting point (11) is set on the already travelled trajectory (20).

7. A reversing assistance system (1), wherein: The reversing assistance system (1) is capable of at least partially automatically executing a reverse travel of a trajectory (20) that has already been traveled, the reversing assistance system comprising a control device (2), wherein the control device (2) is configured to determine and provide a maximum path length (21) for the trajectory (20) that has already been traveled, based on an expected error for the reverse travel, wherein the maximum path length (21) is such a path length along the trajectory (20) that the expected error exceeds a predetermined error threshold value (5) at this path length, wherein the path length that can be traveled backwards is limited to the determined maximum path length (21), wherein in order to determine the expected error, the trajectory (20) that has already been traveled is divided into trajectory segments according to shape, wherein the number of measuring points representing the respective trajectory segment is determined based on at least the respective shape of the trajectory segment and the speed at which the respective trajectory segment is traveled in the forward direction, wherein the maximum path length (21) and / or the predetermined error threshold value (5) are predetermined in the form of a maximum number of measuring points.

8. A vehicle having at least one reversing assistance system according to claim 7.

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