METHOD FOR IMPROVED ESTIMATION OF THE TREAD DEPTH OF VEHICLE TIRES

Description

[0001] Vehicle tires on a vehicle and a vehicle system designed to carry out the method.

[0002] Advancing technological development and increasing digitalization are particularly affecting the field of automotive technology and vehicle tires. There is continued interest in continuously recording operating data from the components used in vehicles, for example, to continuously monitor performance and operational reliability. One important piece of information that can be monitored, for example, in vehicle tires, is the tread depth, as this value regularly correlates well with the durability and condition of the tires and can be used, for example, to determine the optimal time to replace tires.

[0003] There is fundamentally a great interest in being able to estimate and / or calculate the tread depth of tires individually for each tire during operation and as accurately as possible, so that a precise individual value for the tread depth of the tread is available for all tires of a vehicle, preferably without the driver having to determine the tread depth himself.

[0004] Various methods for estimating and / or calculating tread depth are known from the state of the art, but they have different advantages and disadvantages.

[0005] Prior art is disclosed, for example, in CN 112976956 A, EP 0972658 B1, US 9340211 B1, US 2021 / 0302272, and DE 102018200358 A. Further information on the technological background is disclosed, for example, in JP 2022052205 A, US 7762129 B2, WO 2015 / 049418, WO 2021 / 108930 A1, and WO 2021 / 201095 A1.

[0006] WO2022 / 066867 A1 discloses a method for setting indirectly determined values ​​of a tire monitoring system. The method comprises the following steps: identifying an indirectly determined value associated with a tire by a tire monitoring controller; identifying one or more tire parameters from one or more direct measuring devices by the tire monitoring controller; using the one or more tire parameters from the one or more direct measuring devices by the tire monitoring controller to set the indirectly determined value; and using the set indirectly determined value by the tire monitoring controller to indirectly determine a wear condition value for the tire.

[0007] Methods for estimating and / or calculating tread depth are particularly interesting for use in commercial vehicle fleet management. Commercial vehicles, such as trucks, regularly travel long distances and not only travel on various types of roads, such as highways or country roads, but are also frequently used across national borders and are exposed to a wide range of stresses.

[0008] For example, methods are known that allow conclusions to be drawn about the tread depth of the tire's tread by measuring the radial acceleration of a vehicle tire using an acceleration sensor on the tire's inner liner. For example, DE 102015216210 A1 discloses a method that allows the tread depth to be calculated from the radial acceleration using a system of linear equations. EP 2172759 B1 calculates the tread depth from the minimum or maximum of the time differential of the radial acceleration within a defined time interval, in particular within a time interval in which the acceleration sensor traverses the wheel contact patch.

[0009] Other methods rely on the correlation of the vehicle speed determined, for example, by GPS data, with the

[0010] Rotational speed of the vehicle tire, whereby the tread depth of the vehicle tire is derived from the initial tread depth and the change in the dynamic rolling radius, which can be obtained from the correlation of the vehicle speed with the rotational speed of the vehicle tire.

[0011] These processes usually require additional sensors in the vehicle tires or their peripherals. However, these sensors not only increase the manufacturing costs of the vehicle tires, but in many cases, sensors built into the vehicle tires are also susceptible to malfunctions caused or exacerbated by the severe mechanical stresses encountered during driving. For this reason, many vehicle tires in use today do not have additional sensors that would enable the use of such processes.

[0012] Against this background, data-based methods for estimating the tread depth of vehicle tires have been proposed, in which the tread depth of vehicle tires is calculated based on vehicle parameters, in particular the vehicle speed or the acceleration values ​​of the vehicle, as well as a set of different influencing parameters, for example the condition of the vehicle, the type of tires or the prevailing environmental conditions, whereby the number of influencing parameters included in the calculation can vary with the respective application scenario and the desired precision of the calculation.

[0013] While the methods for estimating the tread depth using acceleration sensors or GPS data in most cases allow a direct estimation of the absolute tread depth or at least generate an output that correlates with the absolute tread depth, this is generally not possible with the inherently advantageous parameter-based methods. To illustrate this, in the former methods, it is possible, metaphorically speaking, to remove a large portion of the tread from a vehicle tire by mechanical processing while the vehicle is stationary and to later register this change in the estimation process, for example, because the time-dependent radial acceleration curve or the relationship between rotational speed and vehicle speed would change accordingly.

[0014] In contrast, the inherently advantageous parameter-based methods are usually blind to any change in the profile condition caused by loads that are not entered into the calculation system as a parameter.

[0015] The inventors of the present invention have recognized in their own experiments that a significant contribution to the deviation of a tire tread condition assessment generated using a parameter-based method from the actual condition is caused, in particular, by maneuvering maneuvers, such as parking. During these maneuvers, the vehicle tires are moved relative to the often rough road surface while the vehicle is stationary or at low speeds during steering movements. The mechanical stress experienced during this process contributes noticeably to the deterioration of the tread condition, particularly in heavily loaded commercial vehicles, especially when such maneuvers are performed frequently during vehicle use.

[0016] According to the inventors' assessment, the parameter-based methods known from the prior art, which calculate an estimate of the tread condition, particularly based on parameters such as the distance traveled and / or the vehicle speed, are generally unable to accurately represent the loads experienced by vehicle tires during maneuvering maneuvers when estimating the tread condition. This also extends to other driving situations, such as very tight and correspondingly usually very slow cornering, as can occur, for example, in urban areas. Many of the parameter-based methods known from the prior art register such maneuvering maneuvers as stationary phases or low-speed phases and thus often consider the corresponding times to be "tire-friendly," even though the vehicle tires actually experience noticeable stress in practice.

[0017] The primary object of the present invention was to eliminate or at least mitigate the disadvantages of the prior art described above.

[0018] In particular, it was an object of the present invention to provide a method for estimating the tread depth of vehicle tires, with which the tread depth of vehicle tires can be estimated reliably and efficiently, wherein the susceptibility to errors of the method should be reduced compared to the prior art.

[0019] It was an object of the present invention that in particular the influence of shunting maneuvers, such as parking maneuvers or cornering, can be better taken into account.

[0020] It was an object of the present invention that the method to be specified should be highly compatible with existing methods for estimating the tread depth of vehicle tires and should allow for efficient correction of the tread depths estimated using these existing methods. Therefore, it was a desirable requirement that the method to be specified should not only allow for an improvement in the estimation quality of parameter-based methods, but also enable a more efficient implementation of other methods for estimating tread depth, with a particular aim of reducing the computational effort.

[0021] In particular, it was an object of the present invention that the method to be specified should be particularly resource-saving and executable with the lowest possible requirement of computing capacity, so that the method to be specified should be particularly efficient to be executed with the data processing device integrated in a vehicle.

[0022] Furthermore, it was desirable that the specified method should place as few demands as possible on the additional sensor technology required, with particular emphasis on eliminating the need for additional sensors installed in the vehicle's tires. Ideally, the specified method should also be able to access sensors that are already present in the vehicle or in the vehicle's peripherals.

[0023] Furthermore, it was an object of the present invention to provide a vehicle which is specifically designed to carry out the method to be specified.

[0024] The inventors of the present invention have now found that the objects described above can be achieved if, in a method for estimating the tread depth of vehicle tires, typically in addition to an existing method for estimating the tread depth, in particular a parameter-based method, the time-dependent orientation of the vehicle is also detected via an orientation sensor when the vehicle is moving, in that the tread depth information stored for the vehicle tires, which can be determined, for example, via the complementary method for estimating the tread depth of the vehicle tire during driving times, is corrected depending on the detected change in the orientation of the vehicle, as defined in the claims.

[0025] In other words, the method according to the invention provides a possibility that improves the result of indirect tire tread depth determination by taking into account the wear in the quasi-stationary state during maneuvering operations. In particular, in combination with parameter-based methods for estimating the tread depth of vehicle tires, the disadvantages of the prior art when taking maneuvering maneuvers into account can be advantageously compensated for. Furthermore, advantages also arise when combined with other estimation methods, for example the acceleration- and / or GPS-based methods disclosed above. Even if these fundamentally enable an estimation of the absolute tread quality, they use too few computational resources to reduce the required computing capacity and / orTo improve the quality of the estimation, the previously estimated profile depths stored in the memory unit of the electronic data device for the previous estimation interval are often used. The correction of the temporarily stored profile depth information within the scope of the method according to the invention thus allows the input of a more precise initial value into the subsequent estimation process, thereby reducing the required computing capacity and further improving the overall accuracy of the estimation.

[0026] The above-mentioned objects are thus achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0027] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus particularly preferred. Likewise preferred are embodiments in which a feature of one embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred vehicle systems result from the features of preferred methods.

[0028] The invention particularly relates to a method for estimating the tread depth of vehicle tires in a vehicle, comprising the method steps: a) moving the vehicle in a time interval, b) detecting the time-dependent alignment of the vehicle with an alignment sensor in the time interval, and c) correcting tread depth information stored for a vehicle tire of the vehicle on a storage unit of an electronic data processing device as a function of the detected change in the alignment of the vehicle in the time interval.

[0029] The method according to the invention is used to estimate the tread depth of vehicle tires on a vehicle, optionally in combination with another estimation method, which in particular maps the change in tread depth outside of maneuvering maneuvers, for example, during regular driving. However, at least theoretically, the sole use of the method according to the invention is also conceivable, particularly for work vehicles where, due to their specific intended use, maneuvering maneuvers contribute particularly significantly to tire wear.

[0030] Due to the more accurate estimation quality when taking maneuvering maneuvers into account, the method according to the invention is particularly suitable for use with vehicles that, for example, are exposed to particularly pronounced tire wear due to a high axle load during maneuvering maneuvers. An example of a method according to the invention is therefore a commercial vehicle, preferably a truck, a truck trailer, or a bus, preferably a truck or a truck trailer.

[0031] Those skilled in the art will understand that the method according to the invention serves, in particular, to compensate for the additional loads on vehicle tires that occur during everyday use. Typically, the method according to the invention will be used when the vehicle is moving in road traffic.

[0032] The method according to the invention is used in particular to consider driving maneuvers in which a pronounced pivoting movement of the vehicle and correspondingly extensive steering movements occur, while the center of gravity of the vehicle moves only comparatively slightly or the vehicle travels at a low speed. An example of a method according to the invention is one in which the movement of the vehicle in the time interval includes or consists of a maneuvering movement or parking movement, preferably a maneuvering movement.

[0033] The movement of the vehicle in the time interval comprises a change in the orientation of the vehicle by 15° or more, preferably 30° or more, particularly preferably 45° or more, relative to the longitudinal axis of the vehicle, wherein the change in orientation occurs at an average vehicle speed of 10 km / h or less, preferably 5 km / h or less, particularly preferably 2.5 km / h or less, and wherein the change in orientation occurs at a maximum change in the position of the vehicle's center of gravity of 20 m or less, preferably 10 m or less, particularly preferably 5 m or less.

[0034] In order to implement the intended correction in the method according to the invention, the time-dependent orientation of the vehicle is detected, which can expediently be done relative to the vehicle's longitudinal axis. In this case, the method according to the invention involves detecting the time-dependent orientation of the vehicle and detecting the orientation of the vehicle's longitudinal axis.

[0035] The vehicle's orientation is detected using an orientation sensor. A preferred method according to the invention is one in which the orientation sensor is an electronic orientation sensor, and the orientation sensor is preferably a component of the electronic data processing device or is connected to the electronic data processing device in a signal-conducting manner.

[0036] Based on their general technical knowledge, those skilled in the art will be aware of suitable orientation sensors with which the relative orientation of the vehicle and any changes therein can be detected. Corresponding orientation sensors are commercially available from various suppliers. In the inventors' opinion, orientation sensors which detect the orientation of the vehicle relative to the Earth's magnetic field or the Earth's rotation axis are particularly suitable. Accordingly, a method according to the invention is preferred, wherein the orientation sensor detects the orientation of the vehicle relative to the Earth's magnetic field. A method according to the invention is particularly preferred, wherein the orientation sensor comprises a magnetic compass or a Hall sensor. Additionally or alternatively, a method according to the invention is preferred, wherein the orientation sensor detects the orientation of the vehicle relative to the Earth's rotation axis.In this respect, a method according to the invention is preferred, wherein the orientation sensor comprises a gyrocompass.

[0037] Within the scope of the method according to the invention, the orientation of the vehicle is determined using the orientation sensor as time-dependent information. In accordance with expert understanding, this serves to register changes in the orientation of the vehicle that arise during the movement of the vehicle. One advantage of the method according to the invention can be seen in the fact that good results can be achieved even with greatly reduced sampling rates, for example, less than 1 Hz. This is due in particular to the fact that corresponding shunting maneuvers, especially in commercial vehicles, regularly take place on a comparatively long time scale, so that shunting processes can usually be determined reliably even with comparatively greatly reduced sampling rates.A method according to the invention is expedient in which the detection of the time-dependent orientation of the vehicle is carried out at a measurement frequency of 0.1 Hz or more, preferably 0.2 Hz or more, particularly preferably 0.5 Hz or more. Additionally or alternatively, a method according to the invention is preferred in which the detection of the time-dependent orientation of the vehicle is carried out at a measurement frequency of 5 Hz or less, preferably 2 Hz or less, particularly preferably 1 Hz or less.

[0038] The above definition states that the movement of the vehicle occurs within a time interval to which the detection of the time-dependent orientation of the vehicle is also related. In accordance with the expert's understanding, this expresses that the movement, the detection, and the subsequent correction are related to the same time interval. This time interval can, in principle, be freely selected by the person skilled in the art, although it is expedient to dimension the time interval such that, for example, an observed maneuvering operation falls entirely within this time interval.

[0039] In method step c) of the method according to the invention, the tread depth information stored for a vehicle tire of the vehicle is corrected, wherein the correction is carried out as a function of the previously detected change in the alignment of the vehicle.

[0040] A change in the vehicle's alignment, possibly detected during the time interval, is achieved in the method according to the invention by correcting stored tread depth information. This tread depth information can, for example, have been obtained by a complementary estimation method, in particular a parameter-based indirect estimation method, and / or can in turn be an input parameter for a downstream indirect estimation method, as disclosed below. The step of correcting the stored tread depth information is carried out in the method according to the invention by an electronic data processing device.

[0041] The inventors propose that both the electronic data processing device including the storage unit and, in principle, the orientation sensor can either be implemented as part of the vehicle or provided by a separate device. In accordance with the understanding of those skilled in the art, it is important that an orientation sensor provided by a separate device is also arranged in such a way that a change in the orientation of the vehicle can be detected by implementing the method according to the invention, for example, by positioning a separately implemented device inside the vehicle.Furthermore, if the electronic data processing device and the alignment sensor are separated from each other by the design of the vehicle system, for example, because one component is part of the vehicle and the other component is provided by a separate device, it is important that these two components can communicate with each other. This is possible, for example, via an electronic communication unit using Bluetooth or other radio technology. It is conceivable, for example, that the electronic data processing device or its storage unit is formed by a "cloud" in which the tread depth information is stored, so that it is only visible to the fleet manager, for example.

[0042] In the inventors' opinion, the embodiment in which the electronic data processing device and / or the orientation sensor, preferably both of these components, are provided by a separate mobile terminal is particularly preferred. Advantageously, these corresponding mobile terminals are usually already available to vehicle drivers and can thus be used with an appropriate computer program product to carry out the method according to the invention. In addition, modern mobile terminals usually have suitable orientation sensors which, for example, when a mobile phone is arranged in the interior of the vehicle, can ensure detection of the change in orientation that can be used for the method according to the invention. A method according to the invention is thus conceivable, wherein the vehicle comprises the electronic data processing device and / or wherein the vehicle comprises the orientation sensor.

[0043] However, a method according to the invention is preferred, wherein the electronic data processing device is a component of a device separate from the vehicle, preferably a mobile terminal or a central server network, wherein, in the case of an alignment sensor designed as a component of the vehicle, the vehicle comprises an electronic communication unit for wireless communication with the electronic data processing device in the separate device. Additionally or alternatively, a method according to the invention is also preferred, wherein the alignment sensor is a component of a device separate from the vehicle and arranged in the vehicle, preferably a mobile terminal, wherein, in the case of a data processing device arranged in the vehicle, the vehicle preferably comprises an electronic communication unit for wireless communication between the alignment sensor and the electronic data processing device.

[0044] In process step c), profile depth information is corrected. The following explains in more detail how this profile depth information, which will later be corrected, may have been obtained beforehand. However, at this point, the focus will initially be on the profile depth information itself and the applied correction.

[0045] In the simplest case, the profile depth information can be determined by previously performed manual measurement and stored on the storage unit, wherein it is preferred if the profile depth information was previously estimated by means of an estimation method, wherein the profile depth information can also in turn be the result of a method according to the invention in which the output of a first run is used as input in a subsequent method.

[0046] Tread depth information can, in principle, be any information suitable for quantifying the condition of the tread depth of a vehicle tire. Tread depth information, which represents the absolute depth of the tire tread at a predetermined location or the average tread depth across multiple measurement positions, is particularly important. The absolute tread depth of the center groove is particularly relevant in practice.

[0047] With knowledge of the present invention, a person skilled in the art can correct the tread depth information stored in the memory unit in a manner suitable for the application and can do so in particular with the requirements of the method used to obtain the tread depth information. However, the inventors have succeeded in identifying particularly preferred correction methods in this regard. These embodiments have in common that the dimensioning of the necessary correction operation can be designed by a person skilled in the art on the basis of empirical data. For example, the additional tire wear occurring during maneuvering maneuvers can be determined as an empirical value in a test setup or under real road conditions on corresponding vehicles. In this way, the correction can be used to take into account the influence of the maneuvering maneuvers on the tread depth orthe condition of the tread of the vehicle tires, particularly depending on other tire parameters, such as the rubber composition or tire pressure.

[0048] In a first embodiment of the method according to the invention, it is conceivable, for example, that the stored profile depth information is corrected proportionally to the extent of the detected change in alignment, i.e., that the correction of the stored profile depth information is more pronounced, the greater the detected change in alignment was in the time interval. Accordingly, this is a method according to the invention, wherein the profile depth information stored on the storage unit is corrected proportionally to the change in alignment detected in the time interval.

[0049] Here, the inventors propose that the profile depth information, which typically has the unit of length, for example, "mm," be corrected by a correction value A, which is proportional to the integral of the detected changes in the vehicle's alignment. The proportionality factor can be determined empirically or experimentally. Accordingly, a method according to the invention is preferred, wherein the profile depth information stored in the storage unit is corrected by subtracting a variable correction value A, wherein the variable correction value A is proportional to the integral of the change in the vehicle's alignment detected in the time interval.

[0050] Additionally or alternatively, the correction can also be performed in such a way that the profile depth information is only corrected by a predefined correction value when the detected alignment change exceeds a certain threshold. For example, this allows only those maneuvers to be considered that involve a minimal change in position and for which a certain impact on the profile condition is to be expected. This allows smaller alignment changes to be ignored, allowing the process to be carried out in a particularly resource-efficient manner.Accordingly, a method according to the invention is preferred, wherein the profile depth information stored on the storage unit is corrected by subtracting a predetermined correction value B if the change in the orientation of the vehicle detected in the time interval fulfills a predetermined criterion, in particular a predetermined minimum change in the orientation below a predetermined maximum change in the mean vehicle position in the time interval.

[0051] The inventors propose that, in the further development of the embodiment described above, a classification approach can also be used for correcting the tread depth information, in which specific change profiles of the vehicle alignment are classified into different classes of a classification, in particular taking into account other parameters such as vehicle speed and / or the change in the mean position of the vehicle's center of gravity, but also taking into account other influencing factors such as the wheelbase. This essentially corresponds to the detection of specific maneuvering maneuvers depending on the experienced change, so that each corresponding movement class, i.e. each type of maneuvering maneuver, can be assigned a predetermined corrective action. For example, a detected cornering maneuver can be associated with a different correction value C than a parking maneuver.To implement this embodiment, a method according to the invention is preferred, wherein the correction in method step c) comprises the following sub-steps: . c1) Classifying the detected change in the orientation of the vehicle into two or more movement classes of a classification, c2) Correcting the stored profile depth information by a movement class-specific correction value C depending on the classification, wherein the movement class-specific correction value C is predetermined for the movement classes of the classification.

[0052] Particularly preferred is a method according to the invention, wherein the classification of the detected change in the orientation of the vehicle in sub-step c1) takes place taking into account the vehicle speed and / or the change in the mean position of the vehicle's center of gravity. Additionally or alternatively, particularly preferred is a method according to the invention, wherein the two or more movement classes are selected from the group consisting of maneuvering movements, parking movements, and cornering, preferably selected from the group consisting of maneuvering movements and parking movements.

[0053] The method according to the invention is already advantageous when used for only one vehicle tire of a vehicle. However, one skilled in the art will understand that it is preferable to apply the method according to the invention to essentially all of the vehicle tires of the vehicle. Accordingly, a method according to the invention is preferred, wherein all of the tread depth information stored for the vehicle tires of the vehicle in the storage unit is corrected depending on the detected change in the vehicle's alignment over the time interval.

[0054] The inventors propose that the corrected tread depth information obtained in the method according to the invention can be output at the end of the method, for example, to a central database of a fleet management system. However, in the opinion of the inventors, the immediate reproduction of corresponding status information to the vehicle driver, as can be done, for example, via a display, is preferred in order to keep the vehicle driver optimally informed about the tire condition at all times. Accordingly, a method according to the invention is preferred, additionally comprising the method step: d) outputting information about the corrected tread depth information of the vehicle tire via an output unit, preferably via an electronic display device.

[0055] As explained above, it is fundamentally irrelevant for the method according to the invention how the profile depth information to be corrected within the scope of the method was previously determined. However, in light of the above disclosure, the person skilled in the art will understand that it is particularly preferred to use the method according to the invention to correct profile depth information that was previously calculated using a profile depth estimation method. Thus, a method according to the invention is preferred in which the profile depth information stored on the storage unit is calculated using an indirect profile depth estimation method performed by the electronic data processing device.

[0056] In accordance with the expert understanding, an indirect tread depth estimation method is a method in which the tread depth of a vehicle tire is not measured immediately, i.e. directly, for example by optical methods, but in which the tread depth of a vehicle tire is estimated indirectly by evaluating other measurement parameters, whereby the type of measurement parameters required and the complexity of the calculation operations depend on the type of indirect tread depth estimation method.

[0057] Corresponding indirect profile depth estimation methods are generally known to those skilled in the art and are disclosed, for example, in the prior art cited above. From these methods, the skilled person selects a suitable indirect profile depth estimation method in light of the available parameters and the available computing capacity.

[0058] Describing these methods in detail, which differ greatly in nature and functionality, would go beyond the scope of this article. However, preferred indirect profile depth estimation methods and their preferred configurations are defined in more detail below. Furthermore, reference is made to the relevant state of the art.

[0059] Estimating the tread depth using the indirect tread depth estimation method is expediently performed by an electronic data processing device, preferably the electronic data processing device that also performs the correction operation in the method according to the invention. In other words, this is preferably a method according to the invention, wherein the electronic data processing device is configured to estimate the tread depth of the vehicle tire using an indirect tread depth estimation method and to store it as tread depth information on the storage unit.

[0060] In principle, the method according to the invention is particularly suitable for interaction with indirect tread depth estimation methods in which each new estimate of the tread depth is based on a previously estimated value, which in particular increases accuracy and reduces the required computational effort. These methods, which include, in addition to the parameter-based estimation methods disclosed further below, some alternative estimation methods known from the prior art, benefit from the fact that the final tread depth of the preceding estimation step included in the next estimation step is corrected within the framework of the method according to the invention as a function of the detected change in the vehicle's alignment in order to obtain the most reliable initial values ​​possible for the next estimation step.Accordingly, a method according to the invention is preferred, wherein the indirect profile depth estimation method is carried out for two or more driving sections, wherein the final profile depth estimated for the previous driving section at the end of the previous driving section is used for the initial profile depth at the beginning of the second or further driving section, wherein the final profile depth is corrected, if necessary, as a function of the detected change in the orientation of the vehicle in the time interval of the driving section.

[0061] The method according to the invention has a particularly positive effect on the accuracy of the tread depth estimation result when correcting tread depth information obtained using a parameter-based approach. These methods have in common that they estimate the tread depth in particular as a function of the distance traveled, whereby, depending on the respective variant of the tread depth estimation method, external parameters, for example, temperature or road conditions, are also taken into account. Accordingly, a method according to the invention is preferred, wherein the indirect tread depth estimation method comprises adapting an initial profile value of the vehicle tire, stored in the memory unit, for a driving section as a function of the distance traveled.

[0062] According to the inventors, a corresponding indirect tread depth estimation method that can be combined particularly efficiently with the method according to the invention is one based on the determination of so-called abrasion severity numbers while taking into account a plurality of influencing parameters. Corresponding methods are known to those skilled in the art in isolation from the prior art. A preferred method according to the invention is one in which the indirect tread depth estimation method is selected from the group consisting of methods for indirect tread depth estimation by calculating the forces acting on the vehicle tires during a driving section from vehicle driving parameters, preferably by determining abrasion severity numbers while taking into account a plurality of influencing parameters.

[0063] The inventors can also specify preferred embodiments for the preferred parameter-based profile depth estimation method to be combined with the method according to the invention, which the person skilled in the art can use as a guide when implementing the invention.

[0064] In particular, a method according to the invention is preferred, wherein the indirect profile depth estimation method is a method for indirect profile depth estimation by calculating abrasion sharpness numbers, comprising the method steps: w) driving the vehicle along a predetermined driving distance in a driving section, x) determining a plurality of driving parameters of the vehicle while driving in the driving section, y) calculating the forces acting on the vehicle tires in the driving section based on the determined driving parameters and determining an abrasion severity number assigned to the driving section from the calculated forces, taking into account a plurality of influencing parameters, wherein the influencing parameters are selected from the group consisting of vehicle parameters, environmental parameters and tire parameters, wherein the influencing parameters comprise at least information about the tread material of the vehicle tire and about the initial tread depth at the beginning of the driving section, and z) estimating the final tread depth at the end of the driving section for the vehicle tire based on the respective initial tread depth at the beginning of the driving section, taking into account the respective abrasion severity number.

[0065] The driving according to method step w) takes place over a predetermined driving distance, whereby the time or distance between the beginning and the end of the predetermined driving distance is referred to as the driving section. The driving section is the temporal or spatial interval in which an estimate of the tread depth is made. The person skilled in the art understands that the length of the driving section correlates with the data quality that can be fed into the indirect tread depth estimation method. Even if it would be possible in principle to create very short driving distances such as 100 m, the inventors propose that the predetermined driving distance should not be chosen too short to enable a particularly reliable determination of the driving parameters.This allows any measurement errors and uncertainties in determining the driving parameters to be balanced out over time, and special events during the driving section, such as heavy emergency braking, have a proportionally less significant impact. Accordingly, an indirect tread depth estimation method is preferred, with the predetermined driving distance being in the range of 0.5 to 20 km, preferably in the range of 1 to 10 km.

[0066] Also preferred is an indirect tread depth estimation method, wherein the vehicle comprises one or more driving parameter sensors for determining a plurality of driving parameters of the vehicle while driving. Consequently, an indirect tread depth estimation method is preferred, wherein the plurality of driving parameters comprises one or more, preferably two or more, preferably three or more, particularly preferably all, driving parameters selected from the group consisting of lateral acceleration, longitudinal acceleration, Z-acceleration, and vehicle speed.

[0067] With regard to the quality of the data obtained and the immediacy of the determination in the driving section, it is, in the inventors' opinion, particularly advantageous if the driving parameters are determined at least partially, preferably essentially completely, via vehicle-internal sensors, whereby these are often available in modern vehicles anyway, so that already available sensors can be incorporated in a synergistic manner into the indirect tread depth estimation method for estimating the tread depth.Accordingly, an indirect tread depth estimation method is preferred, wherein the vehicle comprises one or more driving parameter sensors for determining a plurality of driving parameters of the vehicle during travel, and / or wherein the determination of the plurality of driving parameters of the vehicle is carried out by one or more driving parameter sensors of the vehicle, wherein the driving parameter sensors are preferably selected from the group consisting of speed sensors and acceleration sensors.

[0068] The inventors propose that time-dependent position data of the vehicle, such as those accessible via GPS, can also be efficiently utilized in the indirect tread depth estimation method. In a particularly preferred embodiment, this data can be used to verify and / or correct the driving parameters determined by vehicle sensors, for example, by comparing a speed measured in the vehicle with the speed determined from time-dependent position data of the vehicle, for example, to compensate for errors in the vehicle-side sensors. Alternatively, in less preferred embodiments of the indirect tread depth estimation method, all driving parameters required for the method can also be determined from the time-dependent position data.In summary, an indirect tread depth estimation method is preferred, wherein the determination of the plurality of driving parameters of the vehicle is carried out by evaluating time-dependent position data, preferably GPS data, or is supported thereby, preferably supported thereby, wherein the time-dependent position data are preferably obtained by an electronic position determination unit.

[0069] Those skilled in the art will understand that the vehicle's driving parameters are determined during the driving segment, and that the word "during" here refers to a continuous determination at multiple points in time during the driving segment. According to the expert's understanding, the calculation of the time-dependent forces becomes more precise the higher the temporal resolution in the data acquisition. As is common practice in sensor and measurement technology, the vehicle's driving parameters are determined at a specific frequency that indicates how often the respective driving parameter is determined per second. Very high acquisition frequencies enable a particularly advantageous temporal resolution of the driving parameters, but also generate more storage requirements on the memory unit of the electronic data processing device or require more bandwidth in wireless transmission, and can increase energy consumption.In practice, it is therefore often expedient to keep the detection frequencies relatively low. However, the inventors propose lower limits for the detection frequencies that allow for a favorable and precise estimation in every case. An indirect tread depth estimation method is preferred in this regard, wherein the determination of the majority of the vehicle's driving parameters is carried out for each driving parameter using a detection frequency assigned to the driving parameter. The detection frequency is preferably 4 Hz or more, particularly preferably 6 Hz or more, particularly preferably 12 Hz or more.

[0070] In process step y), the time-dependent forces acting on the respective vehicle tires during the driving section are first calculated from the determined driving parameters. In relation to the coordinate system commonly used in the vehicle tire industry, this is done, for example, with reference to the force components Fx(t), Fy(t), and Fz(t), i.e., the time-dependent forces in the longitudinal direction, transverse direction, and radial Z-direction. The calculation of these forces from the driving parameters, in particular the determined accelerations, is possible for the expert based on their specialist knowledge, adapting the methodology to the respective requirements, in particular to the precision of the determination.In addition to comparatively simple calculation algorithms, reference-based methods can also be used, which rely on comparison with previously recorded reference measurements or reference simulations. Approaches that rely on machine learning are also possible. In the majority of cases, however, the person skilled in the art will resort to simulation methods such as those commonly used in the industry to calculate forces. For this purpose, the person skilled in the art has access to a variety of commercially available software solutions, which the person skilled in the art can adapt to their requirements if necessary. An indirect tread depth estimation method is therefore also preferred, whereby the forces acting on the vehicle tires during the driving section are calculated based on the determined driving parameters by an electronic data processing device using a simulation program.

[0071] From the forces acting on the respective vehicle tires during the driving section, a measure of the load on the vehicle tires during the driving section can be determined, which influences the wear. This key figure indicates how strong – i.e., sharp – the mechanical load on the vehicle tire was during the driving section and how high the expected wear is. Against this background, it is expedient to refer to the abrasion severity index in the context of the indirect tread depth estimation method. In accordance with expert understanding, however, in the practical implementation of the indirect tread depth estimation method, the exact name of this parameter is just as irrelevant as the programming implementation of the parameter. For example, it is conceivable that the abrasion severity index has different dimensions depending on the calculation method or is even generated as a set of several abrasion severity indexes.In accordance with the expert understanding, the only relevant factor for the abrasion severity number is that the abrasion severity number is a measure of the abrasion-relevant mechanical load of the respective vehicle tire, determined from the calculated time-dependent forces, which it experienced during the driving section.

[0072] In the indirect tread depth estimation method, the forces acting on the vehicle tire during the driving section are calculated, as well as the abrasion severity index assigned to the driving section, based on the calculated forces, each taking into account a plurality of influencing parameters. These influencing parameters, which are vehicle parameters, environmental parameters, and tire parameters, thus influence the calculation of the forces and / or the calculation of the abrasion severity index assigned to the driving section. The inventors consider it expedient for the preferred indirect tread depth estimation method that these influencing parameters should always include information about the tread material of the vehicle tire and the initial tread depth at the beginning of the driving section, which, as explained above, can in turn be obtained after correction in the method according to the invention.

[0073] In this case, according to the inventors' assessment, the vehicle parameters are expediently considered predominantly, or in some cases even exclusively, when calculating the forces acting on the vehicle tires during the driving section. The vehicle parameters, e.g., information on the chassis characteristics, can be included as input in the simulation of the forces. In contrast, the environmental parameters and tire parameters are more likely to be considered when determining the wear severity index, for example, because the effect of an abrasion severity index is determined in light of the prevailing ambient temperatures and the tire type, e.g., winter tires.

[0074] When considering vehicle parameters, an indirect tread depth estimation method is preferred, wherein the vehicle parameters are selected from the group consisting of information on the wheelbase, track width, vehicle weight, wheel load, tire camber, slip angle, drive type, and drive concept. When considering vehicle parameters, an indirect tread depth estimation method is preferred, additionally or alternatively, wherein the vehicle parameters are provided depending on the vehicle type and / or vehicle configuration, preferably on the memory unit of an electronic data processing device.

[0075] According to the inventors, taking environmental parameters into account is particularly advantageous when the environmental conditions expected in an application scenario differ significantly from those for which the indirect profile depth estimation method was optimized, for example, because reference measurements were conducted in regions with a temperate climate, but the indirect profile depth estimation method is to be used in a tropical or arctic region. Furthermore, taking environmental parameters into account is expedient when larger variations in environmental conditions are to be expected in the application scenario, for example, as a result of pronounced seasonal changes. According to the inventors, this can be taken into account particularly easily in many cases, for example, as scaling factors for the resulting abrasion, which can be obtained, for example, from reference measurements under different environmental conditions.An indirect tread depth estimation method is thus preferred, wherein the forces acting on the vehicle tires during the driving section and / or the abrasion severity index assigned to the driving section are calculated, preferably the abrasion severity index assigned to the driving section is determined from the calculated forces, taking into account one or more, preferably two or more, particularly preferably three or more, environmental parameters. A third method according to the invention is preferred in this respect, wherein the environmental parameters are selected from the group consisting of information on the ambient temperature, the surface condition, and the weather.

[0076] An indirect tread depth estimation method is preferred, wherein the environmental parameters are obtained at least partially by one or more environmental sensors of the vehicle and / or wherein the further environmental parameters are obtained at least partially by comparing time-dependent position data, preferably GPS data, with spatially resolved environmental data, wherein the time-dependent position data are preferably obtained by an electronic position determination unit.

[0077] According to the inventors, at least two tire parameters should already be taken into account in the indirect tread depth estimation method, namely the information about the tread material of the vehicle tire and the initial tread depth of the vehicle tire at the beginning of the driving section.

[0078] The inventors believe that the first of these tire parameters is important because the material properties of the tread are largely responsible for the expected wear. The tread material can be taken into account, in particular, by comparing it with reference measurements on similar or identical tread materials, for example, when a reference wear behavior is determined for one or more characteristic materials in reference experiments under suitable wear severity values, possibly under specific ambient or road temperatures.Accordingly, an indirect tread depth estimation method is also preferred, wherein the information about the tread material of the vehicle tire includes information about physicochemical properties of the tread material, preferably about the glass transition temperature of the polymer used in the tread and / or about the abrasion resistance of the tread, preferably about the abrasion resistance of the tread.

[0079] The second of these tire parameters is important because the respective wear rate also depends on the current tread depth. This is often attributed to the varying stiffness of the individual tread blocks depending on the tread depth and the resulting different "snap-out behavior" when leaving the ground contact patch. In particular, synergistic advantages are evident in combining the indirect tread depth estimation method with the method according to the invention, which allows corrected tread depth information to be used as improved starting values ​​for the estimation.

[0080] The advantage of taking this tire parameter into account is that it does not usually involve any additional effort, since the initial tread depth at the beginning of the driving section will in most cases be used as the starting value for calculating the final tread depth anyway, since information on absolute tread depths is often preferred in practice over merely relative changes.

[0081] To obtain the information required for the indirect tread depth estimation method regarding the initial tread depth of the vehicle tire at the beginning of the driving section, the inventors envisage two options in particular. Determining the initial tread depth at the beginning of the driving section by actual measurement, for example, manually by the driver, regularly yields particularly accurate results in estimating the subsequent final tread depth. However, since this approach is only practical for the first driving section of each journey, this method is less preferred. An indirect tread depth estimation method, in which the initial tread depth is measured at the beginning of the driving section before the driving section, is particularly preferred for certain applications with high demands on the precision of the estimation.

[0082] However, particularly with regard to the workload of the vehicle driver, it is preferred if the result of a first estimate in the indirect tread depth estimation method, which is optionally corrected in the method according to the invention in order to take into account, for example, maneuvers that have taken place, is subsequently used as a starting point in the subsequent driving section, which can advantageously be carried out to the extent that the initial input of the initial tread depth only takes place once, for example when changing tires, and the indirect tread depth estimation method subsequently continues to work with values ​​that it has previously received as a result of an estimate, wherein these values ​​are preferably corrected in the method according to the invention depending on the detected change in alignment of the vehicle.Accordingly, an indirect profile depth estimation method is particularly preferred, wherein the method is carried out for two or more driving sections, wherein the final profile depth estimated for the previous driving section at the end of the previous driving section is used for the initial profile depth at the beginning of the second or a further driving section, wherein the final profile depth is corrected, if necessary, as a function of the detected change in the orientation of the vehicle in the time interval of the driving section.

[0083] In addition to the tire parameters that should always be considered, it may be useful to consider additional tire parameters to further increase precision. An indirect tread depth estimation method is preferred, wherein the calculation of the forces acting on the vehicle tire during the driving section and / or the determination of the wear severity index assigned to the driving section, preferably the determination of the wear severity index assigned to the driving section, is carried out taking into account three or more, preferably four or more, particularly preferably five or more, tire parameters.

[0084] An indirect tread depth estimation method is preferred, wherein the tire parameters are selected from the group consisting of information on tire size, tire pressure, tread geometry, and tire stiffness. Additionally or alternatively, a third method according to the invention is preferred, wherein the tire parameters are provided depending on the tire type and / or the tire configuration of the vehicle tires, preferably on the memory unit of an electronic data processing device.

[0085] In process step z) of the indirect tread depth estimation method, the final tread depth at the end of the driving section is estimated based on the initial tread depth at the beginning of the driving section, taking into account the respective abrasion severity number, and can be stored as tread depth information.

[0086] A multitude of options are available to the person skilled in the art for this purpose. The estimation can be carried out, for example, by comparison with data recorded in reference measurements for vehicle tires with corresponding abrasion severity numbers, whereby, for example, a relative change in the tread depth and / or a reduction in the tread depth by an absolute value and / or a resulting final tread depth can be obtained. In this respect, an indirect tread depth estimation method is preferred, wherein the reference vehicle tires essentially correspond to the tire parameters of the vehicle tires to be evaluated in the indirect tread depth estimation method with regard to at least one, preferably with regard to the majority, particularly preferably with regard to all, tire parameters, preferably at least with regard to the tread material.In this respect, an indirect tread depth estimation method is additionally or alternatively also preferred, wherein the reference abrasion sharpness number is calculated in a reference method which essentially corresponds to the vehicle parameters of the tread depth estimation method with regard to at least one, preferably with regard to the majority, particularly preferably with regard to all, vehicle parameters.

[0087] In addition, the estimation of the final tread depth in the indirect tread depth estimation method can be carried out using machine learning, whereby the person skilled in the art can, for example, train corresponding commercially available programs within the framework of supervised learning with known abrasion severity numbers and associated abrasion values ​​as well as, if necessary, other influencing parameters from reference experiments. In this case, an indirect tread depth estimation method is preferred, wherein the estimation of the final tread depth at the end of the driving section is carried out using a machine learning-based estimation module stored in the memory unit of an electronic data processing device, wherein the electronic data processing device is configured to determine the driving distance in the driving section,the determined wear severity index of the vehicle tire in the driving section and the initial tread depth at the beginning of the driving section, as well as optionally further influencing parameters, as input to the estimation module and to estimate the final tread depth based on the input, wherein the estimation module is trained to estimate the final tread depth at the end of the driving section from the driving distance in the driving section, the determined wear severity index of the vehicle tire in the driving section and the initial tread depth at the beginning of the driving section, as well as optionally further influencing parameters, wherein the training is carried out with a set of training data comprising a plurality of known tread depths obtained from known initial tread depths as a result of known wear severity indexes after known driving distances. An indirect tread depth estimation method is preferred, wherein the training is carried out with a set of training data,which correspond to the influencing parameters of the indirect profile depth estimation method with regard to at least one, preferably with regard to the majority, particularly preferably with regard to all, influencing parameters.

[0088] The invention also relates to a vehicle system which is specifically designed for carrying out the method according to the invention, namely a vehicle system, in particular for carrying out the method according to the invention, comprising: i) a vehicle having at least one vehicle tire, ii) an electronic data processing device having a memory unit, and iii) an alignment sensor for detecting the time-dependent alignment of the vehicle, wherein the electronic data processing device is configured to correct tread depth information stored for the vehicle tire of the vehicle on the memory unit of the electronic data processing device as a function of the change in the alignment of the vehicle detected by the alignment sensor in a time interval.

[0089] The invention and preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figure. It shows: Fig. 1 a schematic representation of a vehicle system according to the invention, which is specifically designed for carrying out the method according to the invention, in a preferred embodiment.

[0090] Fig. 1 shows a schematic representation of a vehicle system according to the invention, which is specifically designed for carrying out the method according to the invention, in a preferred embodiment.

[0091] The exemplary vehicle 12 of the vehicle system may be, for example, a truck and includes a vehicle tire 10 whose tread depth is to be estimated.

[0092] The vehicle 12 includes an orientation sensor 14, which in the example shown is embodied as an electronic magnetic compass. The orientation sensor 14 is designed as a component of the vehicle 12 and allows the detection of the vehicle's orientation and thus, in particular, the registration of maneuvers at low speeds or minor changes in the position of the vehicle's center of gravity.

[0093] The data collected by the alignment sensor 14 are, in the example shown, Fig. 1by the electronic data processing device 18, which includes a storage unit 16. The electronic data processing device 18 and the storage unit 16 are part of a device separate from the vehicle, which in the example shown is designed as a mobile phone, which can be arranged, for example, in the driver's cab. The data collected by the alignment sensor 14 is transmitted to the mobile terminal by means of an electronic communication arrangement 20 using a short-range wireless communication method, for example, via Bluetooth.

[0094] In the example shown, tread depth information is stored on the storage unit 16 for all vehicle tires 10 of the vehicle 12, which tread depth information includes in particular the mean absolute tread depth of the central circumferential tread groove of the vehicle tires 10.

[0095] If the vehicle 12 is now moved translationally only along the longitudinal direction in an observed time interval, the alignment sensor 14 detects no change in alignment, at least on the practically relevant distance scales, and in the method according to the invention, no correction of the stored profile depth information needs to be carried out, so that any updating of the profile depth information may be carried out exclusively by an indirect profile depth estimation method used.

[0096] However, if a change in the alignment of the vehicle 12 is registered with the alignment sensor 14 in an observed time interval, the tread depth information stored on the storage unit 16 is corrected, wherein in particular a tire-specific correction can also be carried out depending on the position of the respective vehicle tire 10 in the chassis of the vehicle 12, for example in order to correct the left and right vehicle tires 10 to different degrees during a registered right-hand bend in order to take into account the different load situations in this scenario.

[0097] In an exemplary correction method, only those movements of the vehicle 12 can be considered within a time interval that are associated with a minimum degree of orientation change that occurs without the speed of the vehicle 12 or its position change exceeding a certain limit. Such movements can be classified, for example, into movement classes of a classification, taking into account the characteristic courses of the orientation change in combination with information about the respective speed or position change during the orientation change.

[0098] If, in the method according to the invention, a change in the alignment of the vehicle 12 is registered, which, for example, falls into the movement class of a lateral parking maneuver, the tread depth information stored for the vehicle tires 10 of the vehicle 12 can be corrected, for example, by a predetermined value specific to lateral parking maneuvers. In this theoretical example, the parking maneuver following a stationary phase can also be detected via the alignment sensor 14, optionally in conjunction with other sensors, in particular speed and / or position sensors. This, in turn, can cause a corresponding further correction of the stored tread depth information.

[0099] The tread depth information of the vehicle tires 10 thus obtained, which has been corrected at least twice in the method according to the invention, can then be used, for example, as an initial value for an indirect tread depth estimation method, in particular a parameter-based indirect tread depth estimation method taking into account abrasion severity indicators, by using in particular the distance traveled during the subsequent journey to derive new tread depth information from the previously corrected tread depth information, which includes information about the tread condition at the end of the journey and which in turn can be stored on the memory unit 16.

[0100] Continuing the procedure described above, the new tread depth information thus obtained can be corrected in the method according to the invention, for example, to take into account a maneuver performed at the end of the route. In this way, the interaction of the indirect tread depth estimation method with the method according to the invention for correcting stored tread depth information yields particularly accurate estimates of the tread depths of the vehicle tires 10, without the need for manual measurement of the vehicle tires 10. List of reference symbols

[0101] 10Vehicle tire 12Vehicle 14Alignment sensor 16Storage unit 18Electronic data processing device 20Electronic communication unit

Claims

1. Method for estimating the tread depth of vehicle tyres (10) on a vehicle (12), comprising the method steps of: a) moving the vehicle (12) in a time interval, b) detecting the time-dependent orientation of the vehicle (12) in the time interval using an orientation sensor (14) that can be used to detect the orientation of the vehicle (12) relative to the earth's magnetic field or the earth's rotation axis, and c) correcting tread depth information stored for a vehicle tyre (10) of the vehicle (12) in a storage unit (16) of an electronic data processing device (18) on the basis of the detected change in the orientation of the vehicle (12) in the time interval, wherein the movement of the vehicle (12) in the time interval comprises a change in the orientation of the vehicle (12) by 15° or more, preferably 30° or more, particularly preferably 45° or more, based on the longitudinal axis of the vehicle (12), wherein the change in the orientation takes place at an average vehicle speed of 10 km / h or less, preferably 5 km / h or less, particularly preferably 2.5 km / h or less, and wherein the change in the orientation takes place for a maximum change in the position of the vehicle centre of gravity of 20 m or less, preferably 10 m or less, particularly preferably 5 m or less.

2. Method according to Claim 1, wherein the movement of the vehicle (12) in the time interval comprises a manoeuvring movement or parking movement.

3. Method according to either of Claims 1 and 2, wherein the time-dependent orientation of the vehicle (12) is detected at a measurement frequency of 0.1 Hz or more.

4. Method according to one of Claims 1 to 3, wherein the time-dependent orientation of the vehicle (12) is detected at a measurement frequency of 5 Hz or less.

5. Method according to one of Claims 1 to 4, wherein the orientation sensor (14) detects the orientation of the vehicle (12) relative to the earth's magnetic field.

6. Method according to one of Claims 1 to 5, wherein the orientation sensor (14) detects the orientation of the vehicle (12) relative to the earth's rotation axis.

7. Method according to one of Claims 1 to 6, wherein the electronic data processing device (18) is part of an apparatus separate from the vehicle (12), wherein, in the case of an orientation sensor (14) implemented as part of the vehicle (12), the vehicle (12) comprises an electronic communication unit (20) for wirelessly communicating with the electronic data processing device (18) in the separate apparatus.

8. Method according to one of Claims 1 to 7, wherein the orientation sensor (14) is part of an apparatus that is separate from the vehicle (12) and is arranged in the vehicle (12).

9. Method according to one of Claims 1 to 8, wherein the tread depth information stored in the storage unit (16) is calculated with an indirect tread depth estimation method carried out by the electronic data processing device (18).

10. Vehicle system, in particular for carrying out the method according to one of Claims 1 to 9, comprising: i) a vehicle (12) having at least one vehicle tyre (10), ii) an electronic data processing device (18) having a storage unit (16), and iii) an orientation sensor (14) for detecting the time-dependent orientation of the vehicle (12) relative to the earth's magnetic field or the earth's rotation axis, wherein the electronic data processing device (18) is configured to correct tread depth information stored for the vehicle tyre (10) of the vehicle (12) in the storage unit (16) of the electronic data processing device (18) on the basis of the change in the orientation of the vehicle (12), as detected by the orientation sensor (14) in a time interval, wherein the movement of the vehicle (12) in the time interval comprises a change in the orientation of the vehicle (12) by 15° or more, preferably 30° or more, particularly preferably 45° or more, based on the longitudinal axis of the vehicle (12), wherein the change in the orientation takes place at an average vehicle speed of 10 km / h or less, preferably 5 km / h or less, particularly preferably 2.5 km / h or less, and wherein the change in the orientation takes place for a maximum change in the position of the vehicle centre of gravity of 20 m or less, preferably 10 m or less, particularly preferably 5 m or less.