Method for detecting a poor road surface, and motor vehicle

Abstract

A method 6 is provided for detecting a poor road surface for a motor vehicle (l, Figure l) with at least four wheels (2, Figure l). The method involves monitoring vibrations occurring on at least four

Description

The present invention relates to a method for detecting a poor road surface for a motor vehicle. The invention also relates to a motor vehicle. Modem motor vehicles can be equipped with an anti-jolt function that can be used to increase driving comfort when the drivetrain is stimulated to vibrate, so-called drivetrain vibrations, by high torque gradients or by passing through drivetrain backlashes, and a dual-mass flywheel. When driving on a poor road surface, wheel vibrations occur on the wheels of the vehicle that are misinterpreted as drivetrain vibrations by an anti-jolt function. These wheel vibrations correspond to alternating increases and decreases in wheel speed, i.e. accelerations and decelerations in wheel speed. When the anti-jolt function is activated, a drive of the vehicle used to drive at least one vehicle wheel is controlled to generate counter-torques counteracting the vibrations. Appropriately, the anti-jolt function on the vehicle is automatically activated as required. As a result, the anti-jolt function is deactivated when a corresponding sensor system detects a poor road surface, which prevents the corresponding interventions by the drive. As a result of the incorrect negative torque interventions of the anti-jolt function on a poor road surfaces due to wheel excitation, there is a high energy input into the exhaust system. This can be particularly disadvantageous in terms of fuel consumption, may additionally have a negative effect on the driving behaviour, in particular with regards to comfort, and can lead to a high load and increased wear of the exhaust system, in particular a catalytic converter. Accordingly, there is a need for a reliable detection of a poor road surface in order to avoid unnecessary activation of the anti-jolt function. However, reliable detection of a poor road surface may also be advantageous for other systems of the motor vehicle, e.g. an anti-blocking system or misfire detection. For off-road vehicles that feature an off-road operating mode, the configuration is typically such that the anti-jolt function is not activated when the off-road operating mode is switched on in order to avoid the disadvantages mentioned for the drivetrain and exhaust system. However, there can be a corresponding loss of comfort if the anti-jolt function is not activated on a smooth substrate or good road surface. Conversely, in an on-road operating mode, where the anti-jolt function is usually activated, the aforementioned disadvantages occur on poor road surfaces, which is 29 05 25 also optimised by a detection of a poor road surface. DE 10 2013 207 563A1 discloses a method for determining travel path conditions during unbraked or braked travel of a vehicle by means of a wheel-specific characteristic, which is derived from a change over time in wheel speeds detected on at least one vehicle wheel. The travel path conditions are intended to be taken into account by an anti-jolt system. The respective travel path condition is in this case determined by a jolt signal being formed by double differentiation of the wheel speed, by the difference between the absolute value of the jolt signal and a tolerance value being chronologically summed or integrated to form the characteristic variable, and by the travel path condition being determined by comparing the characteristic variables with a vibration signal threshold value. DE 10 2010 031 467 A1 discloses a method for improving the control behaviour of an anti-blocking braking system in which the rotational behaviour of the individual vehicle wheels is measured and evaluated to determine a vehicle reference speed, the wheel slip, the deceleration, and the acceleration of the individual vehicle wheels. DE 10 2020 205 588A1 discloses a sensor arrangement for an anti-blocking system, whereby the sensor arrangement for each vehicle wheel comprises a first sensor for determining a speed and a second sensor for detecting a further physical variable. DE 102 14 455A1 discloses a method for off-road detection that is used in connection with a method for monitoring a condition of the tire, in particular for detecting a tire pressure drop. The present invention seeks to provide an improved or at least different method for detecting a poor road surface, which is characterised in particular by a high level of reliability. This may be achieved according to an aspect of the invention by the subject matter of the independent claim. Advantageous embodiments are the subject matter of the dependent claims. In the method according to an aspect of the invention, at least four wheels of the 29 05 25 vehicle are monitored with regard to vibrations that occur at the respective wheel. According to an aspect of the invention, a vibration analysis is performed on each monitored wheel, during which an intensity and a frequency of vibrations are detected and compared to predetermined threshold values for the intensity and frequency. In the method according to an aspect of the invention, the current substrate is recognised as a poor road surface if the threshold values for intensity and frequency are exceeded simultaneously on all monitored wheels, i.e., within the same monitoring interval. By taking into account the vibration behaviour of four wheels of the vehicle, an incorrect interpretation of the substrate as a poor road surface can be prevented if the substrate only has isolated potholes or if the vehicle briefly departs the paved roadway, e.g. at the edge of the roadway. As a result, the method presented herein is highly reliable. According to another embodiment, the intensity of the vibrations can be formed by the amplitude of the vibrations. Advantageously, the frequency of vibrations can be formed by the number of vibrations whose intensity exceeds the threshold value for the intensity within a predetermined time window or monitoring interval. For example, a time window of several seconds is permanently observed in order to count the vibrations occurring therein, whereby preferably only the vibrations whose intensity exceeds the threshold value for the intensity are counted. The method is therefore very reliable. In this respect, the frequency of vibrations corresponds to a vibration frequency. According to another advantageous embodiment, the threshold value for the frequency can be variable and can be specified as a function of the current vehicle speed. In other words, the threshold value for the frequency is a function of the current vehicle speed, so it is a speed-dependent threshold value. This embodiment is based on the consideration that the distance travelled within a specified time window is a function of the current vehicle speed. Accordingly, given a poor road surface, the frequency of vibrations occurring in the time window is also a function of the current vehicle speed. By taking into account the current vehicle speed, the impact of the vehicle speed on determining the road condition can be eliminated, which improves the reliability of detecting a poor road surface. In one preferred embodiment, the vibration analysis is constantly updated. As a result, 29 05 25 the detection of a poor road surface is able to react quickly to a changing vibration behaviour. In the present context, an "embodiment" is synonymous with a "design" and / or "programming", so the expression "configured such that" is equivalent to the expression "designed and / or programmed such that". Additionally or alternatively, at least the threshold value for the frequency can comprise a hysteresis. Optionally, the threshold value for the intensity can also comprise a hysteresis. The hysteresis ensures that the detection of a poor road surface does not constantly switch between a positive and a negative evaluation for a substrate whose quality is in the range of a poor surface. According to this aspect of the invention, the motor vehicle is equipped with an antijolt function to increase comfort in the event of drivetrain vibrations. Advantageously, this anti-jolt function can then be manually or automatically deactivated as soon as, and in particular only when, a poor road surface is recognised. In one advantageous embodiment, the motor vehicle can feature at least one on-road operating mode and one off-road operating mode. In the present context, all operating modes of the vehicle that are not off-road operating modes are considered to be onroad operating modes, e.g. a comfort mode or a sports mode. Advantageously, it can then be useful for the anti-jolt function to be manually or automatically deactivated in the on-road operating mode and off-road operating mode as soon as, and in particular only when, a poor road surface is recognised. As a result, comfort can also be increased in the off-road operating mode by the active anti-jolt function. A motor vehicle according to an aspect of the present invention, which can in particular be an off-road capable passenger motor vehicle, is equipped with at least four wheels, by means of which the motor vehicle rests or drives on a substrate. The motor vehicle is also equipped with a drive engine for driving at least one of the wheels. In an offroad capable vehicle, the drive is conventionally configured to drive the four wheels. The motor vehicle is also equipped with wheel sensors for monitoring at least four wheels with regard to vibrations occurring thereon and an evaluation device which is coupled to the wheel sensors and which is configured to perform the aforementioned 29 05 25 method for the detection of a poor road surface. In one particularly advantageous embodiment, the motor vehicle features an anti-jolt function coupled to the drive for increasing comfort, which is configured such that, if no poor road surface is recognised, it controls the drive to generate a counter-torque that counteracts the vibrations. Further important features and advantages of the invention arise from the dependent claims, from the drawings, and from the accompanying figure description with reference to the drawings. It is understood that the features specified hereinabove and those yet to be explained hereinafter are usable not only in the respectively specified combination, but also in other combinations, or on their own, without departing the scope of the invention as defined by the claims. The components described hereinabove and referred to hereinafter of a higher-level unit, e.g., a device, an apparatus, or an assembly, which are designated separately, can constitute separate components of this unit, or integral regions or sections of this unit, even if shown differently in the drawings. Preferred exemplary embodiments of the invention are illustrated in the drawings and will be explained in further detail in the description hereinafter, whereby identical reference characters refer to identical, similar, or functionally identical components. Schematically shown are: Fig. 1 a highly simplified schematic diagram of a motor vehicle, Fig. 2 a block diagram for simplified representation of a method for the detection of a poor road surface. According to Fig. 1, a motor vehicle 1 comprises at least four wheels 2, by means of which the motor vehicle 1 rests or drives on a substrate. The vehicle 1 further comprises a drive 3 for driving at least one of the wheels 2. In the example in Fig. 1, the drive 3 is configured to drive all four wheels 2. The drive 3 can comprise an internal combustion engine and / or at least one electric motor. The vehicle 1 is also equipped 29 05 25 with wheel sensors 4, by means of which the wheels 2 can be monitored with regard to vibrations occurring thereon. The sensor system 4 is in this case represented by four individual sensor devices, each of which is associated with one of the wheels 2 and which are, e.g., configured to determine the current wheel rotational speed, i.e., to determine the wheel speed. The vehicle 1 is also equipped with an evaluation device 5, which is coupled to the wheel sensor system 4 and which is configured to perform a method 6 for detecting a poor road surface, which is explained in more detail hereinafter with reference to Fig. 2. In the example in Fig. 1, the vehicle 1 is also equipped with an anti-jolt function 7 which is, e.g., stored in or integrated into a vehicle controller 8. The anti-jolt function 7 is used to increase the comfort of the vehicle 1 in the event of drivetrain vibrations and is configured for this purpose such that, in the event that no poor road surface has been recognised, it controls the drive 3 to generate counter-torques to counteract the vibrations. For this purpose, the anti-jolt function 7 is coupled to the evaluation device 5 on the one hand, and to the drive 3 on the other hand, in particular via the vehicle controller 8. According to Fig. 2, at least four wheels 2 of the vehicle 1 are monitored with regard to vibrations occurring on the respective wheel 2 in the method 6 presented herein for the detection of a poor road surface. The individual method steps are indicated herein by rectangular fields or blocks. This wheel-specific vibration monitoring is represented by four blocks 9 in Fig. 2. In a further block 10, the results of the individual wheel vibration monitoring 9 converge, whereby a vibration analysis is performed individually on each wheel 4. This vibration analysis takes into account an intensity and a frequency of the vibrations detected at each wheel 2 and compares these to predetermined threshold values for the intensity and frequency. The vibration analysis with regard intensity and frequency is performed during a predetermined monitoring interval or time window. For example, the comparison with the predetermined threshold value for the intensity is performed in block 11. The threshold value for the intensity can in this case be stored in a memory and queried in that location. Consideration of the threshold value for the intensity is represented in Fig. 2 by block 12. 29 05 25 If the intensity of one of the monitored wheels 2 is below the associated threshold value 12 within the monitored time window, then a normal road surface or good road surface is still assumed and monitoring in the form of vibration analysis is continued according to a path 13 that leads back to block 10. If, on the other hand, the intensity exceeds the associated threshold value 12 for all monitored wheels 2 within the monitored time window, then the frequency of the vibrations is compared to a predetermined threshold value for the frequency in a next block 15 according to a path 14. The threshold value for the frequency can in this case be stored in a memory and queried in that location. Consideration of the threshold value for the frequency is represented in Fig. 2 by block 16. If the detected frequency of one of the monitored wheels 2 is below the predetermined threshold value 16 within the monitored time window, then the method follows a path 17 and monitoring in the form of vibration analysis is continued according to a path 17 that leads back to block 10. If, on the other hand, the frequency of all monitored wheels 2 within the monitored time window is greater than the associated threshold value 16, then it is determined in block 18 that the current substrate is a poor road surface. According to path 19, monitoring in the form of vibration analysis is then continued, which leads back to block 10. According to path 20, the presence of a poor road surface is provided to other systems of the vehicle 1 or at least supplied to another vehicle system, which is indicated by block 21. This further system 21 can, e.g., be the anti-jolt function 7 and / or an antiblocking system. In principle, the frequency of vibrations can be given by the current vibration frequency. However, in one preferable embodiment, the frequency of vibrations is formed by the number of vibrations whose intensity exceeds the threshold value for the intensity, whereby the number of vibrations is determined within a predetermined time window. Furthermore, the threshold value 16 for the frequency can be variable and a function of the current vehicle speed. Accordingly, the transmission of the current vehicle speed, which affects the current threshold value 16 for the frequency, is indicated by an arrow 22 in Fig. 2. For example, a map or table or algorithm can be stored in the respective memory in order to define the speed-dependent threshold value 16 for the frequency. The vibration analysis 9 on the monitored wheels 2 is performed constantly, so the detection of a poor road surface is constantly updated. The threshold values 12, 16 for intensity and frequency can be provided with a hysteresis so that the detection of a poor road surface is comparatively robust and reliable. A corresponding feedback for this hysteresis function is indicated in Fig. 2 regarding the threshold value 16 for the frequency by an additional path 23. 29 05 25 29 05 25

Claims

1. A method for detecting a poor road surface for a motor vehicle comprising at least four wheels, by means of which the motor vehicle drives on a substrate, and a drive for driving at least one of the wheels,- in which at least four wheels are monitored with regard to vibrations occurring at the respective wheel,- in which a vibration analysis is performed on each monitored wheel, during which analysis an intensity and a frequency of vibrations are detected and compared to predetermined threshold values for the intensity and frequency, - in which the current substrate is recognised as a poor road surface when the threshold values for intensity and frequency are simultaneously exceeded on all monitored wheels, wherein:- the motor vehicle is equipped with an anti-jolt function for increasing comfort when driving on a good road surface.

2. The method according to claim 1, wherein:- the intensity of the vibrations is formed by the amplitude of the vibrations.

3. The method according to any one of the preceding claims, wherein:- the frequency of vibrations can be formed by the number of vibrations whose intensity exceeds the threshold value for the intensity within a predetermined time window.

4. The method according to any one of the preceding claims, wherein:- the threshold value for the frequency is variable and is specified as a function of the current vehicle speed.

5. The method according to any one of the preceding claims, wherein:- the vibration analysis is constantly updated.29 05 256. The method according to any one of the preceding claims, wherein:- at least the threshold value for the frequency comprises a hysteresis.

7. The method according to any one of the preceding claims, wherein:- the anti-jolt function is automatically deactivated as soon as a poor road surface is recognised.

8. A motor vehicle,- comprising at least four wheels, by means of which the motor vehicle rests or drives on a substrate,- comprising a drive for driving at least one of the wheels,- comprising a wheel sensor system for monitoring at least four wheels with regard to vibrations occurring thereon,- comprising an evaluation device, which is coupled to the wheel sensor system and is configured to perform the method according to any one of the preceding claims.

9. The motor vehicle according to claim 8, wherein:- the motor vehicle features an anti-jolt function, which is coupled to the drive for increasing comfort when driving on a good road surface and which is configured such that, if no poor road surface is recognised, it controls the drive to generate counter-torques that counteract the vibrations.

10. The motor vehicle according to claim 8 or 9, the motor vehicle being a passenger motor vehicle.

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