Device for determining a friction coefficient parameter

Abstract

The invention relates to a device (1, 1a) for determining a coefficient of friction parameter for a tire of a vehicle (2), comprising an interface (3) for receiving microwave radio frequency waves emitted by a microwave radio mast (4) at a known transmission power located in a microwave radio frequency range, wherein an evaluation unit (5) is provided which is configured to determine a received power of the received microwave frequency waves, and wherein the evaluation unit (5) is configured to compare the transmitted power and the received power and to generate an attenuation value based on the comparison, and wherein the evaluation unit (5) is configured to determine, based on the attenuation value, whether precipitation is present and to estimate a road surface condition based on this, and wherein the evaluation unit (5) is configured to use the estimated road surface condition as a coefficient of friction parameter. The invention relates to a method and a driver assistance system.

Description

[0001] The invention relates to a device for determining a friction coefficient parameter for a tire of a vehicle, comprising an interface for receiving directional radio frequency waves emitted by a directional radio mast at a known transmission power, which is located in a directional radio frequency range.

[0002] The coefficient of friction between a road surface and a tire is one of the most important pieces of information for various driver assistance systems, such as an anti-lock braking system (ABS), an automatic stability control (ASC), an electronic stability program (ESP), an automatic distance control, an electronic passenger or the like.

[0003] The coefficient of friction is influenced by numerous factors such as the road surface condition (e.g. water on the road), temperature, the vehicle's center of gravity, the chassis design and the tire properties.

[0004] However, the direct friction conditions between road and tires cannot be recorded, which is a central component for the various driver assistance systems.

[0005] In a conventional vehicle driven by a human driver, the driver can determine, at least to some extent, whether the current coefficient of friction is rather high or rather low, for example through experience, short braking, visual perception or similar.

[0006] In particular, the road surface condition such as rain / snow or ice is one of the most important parameters for determining the friction coefficient.

[0007] For example, the current coefficient of friction is rather high on a well-maintained and clean road surface, as well as in dry conditions, thus achieving good static friction between the vehicle and the road. However, wet conditions, black ice, road surface dirt, and similar conditions adversely affect the coefficient of friction. Water / ice on the road surface, in particular, results in a very low coefficient of friction.

[0008] When a vehicle is partially or fully autonomous, estimating the current friction coefficient is difficult because the information from the human driver is at least lost.

[0009] Estimating the coefficient of friction usually attempts to define a coefficient of friction or a friction coefficient interval using existing technologies inside and outside the vehicle. Detecting the intermediate layer, the layer between the tire and the road surface, requires cost-intensive technologies that are not currently integrated into the vehicle. This sensor technology is usually used to validate the cost-effective approximate estimate of the coefficient of friction.

[0010] All currently known friction coefficient estimates have in common that their quality still has great potential with regard to highly automated driving.

[0011] There are therefore many ways to determine the coefficient of friction in the state of the art.

[0012] DE 10 2009 041 566 B4 discloses a method in which the road friction coefficient is determined, preferably according to friction coefficient classes, in a vehicle computer or vehicle control system, wherein a friction coefficient parameter that is constantly updated during the journey and is therefore constantly available is determined and at least one friction coefficient parameter that is only updated depending on the situation and is therefore not constantly available is determined and these parameters are linked to one another in an evaluated manner to form a common friction estimate, wherein a plausibility check of the common friction estimate is carried out with the driver behavior, in particular the friction coefficient derived therefrom, and / or at least one of the two initial friction coefficient parameters.

[0013] DE 10 2016 205 430 A1 discloses a method for determining the friction coefficient of a drivable surface using an ego vehicle with the following steps: Acquiring first data values ​​representing humidity in the environment of the ego vehicle; verifying the plausibility of the acquired first data values ​​by comparing them with at least one second data value; and determining third data values ​​representing the coefficient of friction of the drivable surface, wherein the determination is made depending on the plausibility check of the first data values ​​with the at least one second data value.

[0014] Further possibilities are known from Francesco Beritelli and Francesco Scaglione: Poster: Real-time rainfall estimation based on LTE vehicular communications for road safety applications. 2017 IEEE Vehicular Networking Conference (VNC), 2017, 33-34. DOI: 10.1109 / VNC.2017.8275651 or DE 10 2008 014 104 A1. It is therefore a constant task to provide an improved device, especially with regard to autonomous or semi-autonomous vehicles.

[0015] The object is achieved by a device for determining a friction coefficient parameter having the features of claim 1.

[0016] Advantageous embodiments emerge from the dependent patent claims, the description and the figures.

[0017] The object is achieved by a device for determining a friction coefficient parameter for a tire of a vehicle, comprising an interface for receiving microwave radio frequency waves emitted by a microwave radio mast at a known transmission power, which is located in a microwave radio frequency range, wherein an evaluation unit is provided which is designed to determine a received power of the received radio frequency waves, and wherein the evaluation unit is designed to compare the transmitted power and the received power and to generate an attenuation value based on the comparison, and wherein the evaluation unit is designed to determine, based on the attenuation value, whether precipitation is present and to estimate a road surface condition based thereon, and wherein the evaluation unit is further designed to use the estimated road surface condition as a friction coefficient parameter.

[0018] In particular, the evaluation unit can also be designed to use the information as to whether precipitation is present.

[0019] In particular, the use can be in a forwarding to a driver assistance system, which determines a friction coefficient taking into account other vehicle parameters.

[0020] The invention recognizes that an improvement in quality, particularly with regard to speed, can be achieved by measuring the precipitation intensity by changing the mobile network. It is known that the amount of precipitation can be measured from power fluctuations of the mobile network on microwave links. Unlike radio and television transmitters, microwave systems use waves in the millimeter range, corresponding to frequencies from 15 GHz to 80 GHz. If the wavelength and scattering bodies are similar in size, as is the case with the microwaves and raindrops, Mie scattering can be assumed.

[0021] Raindrops therefore have a size that corresponds to the wavelength of this radiation. Resonance effects occur, and attenuation increases significantly. The contribution to attenuation increases disproportionately. The specific attenuation and average rain rate also exhibit an almost linear relationship. The reason for this almost linear relationship lies in the connection between both quantities and the droplet size distribution of rain in the atmosphere. The rain rate is determined by the number and volume of the different sized droplets and their falling speed. The specific attenuation is determined by the number and extinction coefficient of the different sized droplets. The extinction coefficient is a measure of the attenuation effect. Since the droplet circumference is approximately equal to the wavelength, raindrops attenuate the propagation of microwave radio waves.

[0022] It is known that rain (slippery conditions) is one of the most important friction parameters for determining the coefficient of friction.

[0023] According to the invention, the microwave frequency waves emitted by a microwave mast, for example, a cell phone mast, are received in the millimeter range. This emitted microwave radiation is transmitted at a known transmission power. The current transmission power can also be transmitted, for example, by the mast itself.

[0024] According to the invention, the transmitted microwave radiation is received as received power by the vehicle or the evaluation unit, which has an interface. At the typically used frequencies of 15 GHz to 80 GHz, the transmitted microwave radiation is strongly attenuated by raindrops. According to the invention, the transmitted power is compared with the received power. For this purpose, for example, a difference value is generated as an attenuation value.

[0025] From the measurement of this attenuation, the evaluation unit can now infer the presence of precipitation. For example, precipitation can only be considered detected if the attenuation value remains approximately constant over a time period, allowing individual measurement errors to be eliminated.

[0026] The road surface condition can now be estimated based on precipitation.

[0027] The information as to whether precipitation is present, as well as the estimate of the road surface condition, can now be transmitted to a driver assistance system, which here also includes control units, or the evaluation unit can determine the friction coefficient itself, taking into account other friction coefficient parameters.

[0028] In particular, snow can also be detected using suitable algorithms or a neural network, for example by calculating out any measurement errors that may occur.

[0029] The presence and utilization of over 100,000 cell phone towers results in a comprehensive coverage. Rain can thus be precisely located and detected more quickly than with a rain sensor.

[0030] In particular, this rain detection device for determining the friction coefficient parameter represents a reliable, fail-safe method that reliably detects precipitation even in the event of malfunctions or failure of the rain sensor.

[0031] Furthermore, this device requires no additional sensors; the evaluation unit can be implemented as a pure software module, while an interface is usually already present in the vehicles. This results in a cost-effective method for detecting the very important friction coefficient parameter, which can also be easily retrofitted.

[0032] In a further embodiment, a storage unit is provided which has a base value which defines an attenuation without precipitation, wherein the evaluation unit is designed to carry out an estimation of an amount of precipitation based on the base value and the attenuation value.

[0033] In particular, the evaluation unit can subtract the base value from the attenuation value to estimate the amount of precipitation.

[0034] The base value can be a constant that varies depending on the area. The base value indicates the attenuation without rain influence, which is subtracted during the rainy period from, for example, the difference between transmitted power and received power. The base value can be assumed to be constant and derived from the value during the dry period. This can be used to define the amount of precipitation. If an amount of precipitation is located in this way, a resulting amount of water on the road surface can be deduced. This amount of water on the road surface is defined as the intermediate layer between the tire and the road and is used to identify the road surface condition, which can be used to determine a friction coefficient parameter.

[0035] Furthermore, the evaluation unit can be configured to create the baseline value during a route during a dry period and link it to the route. This allows a precise baseline value to be created on busy routes, such as the commute, and the amount of precipitation to be determined more accurately. For example, reception is less good in forests or rural areas than in cities. Furthermore, the baseline value can also be linked to the time of day / temperature and the route. This results in an even more precise baseline value.

[0036] Furthermore, a further development provides a control unit for manually generating the base value during a route. This means that such a base value can be generated manually, for example, by the driver in dry weather. For example, the base value can be generated / recorded while driving by operating the control unit.

[0037] Alternatively or additionally, the evaluation unit can be configured to automatically generate a baseline value during a route based on a detected dry period, i.e., dry weather, and link this value to the route. This allows a new or current baseline value to be generated regularly without manual assistance.

[0038] In further development, the evaluation unit is designed to use the amount of precipitation as a friction coefficient parameter and to transmit it to a driver assistance system for further processing.

[0039] Furthermore, the evaluation unit can be designed to estimate the amount of water on the road surface from the detected amount of precipitation and, based on this, to estimate the road surface condition.

[0040] In particular, the amount of precipitation is used to estimate the road surface condition. In heavy rain, for example, the amount of water forms a floating intermediate layer, which significantly reduces the coefficient of friction. Thus, such information contributes to increased driving safety, especially in autonomous vehicles.

[0041] In a further embodiment, the device has a temperature sensor for measuring the outside temperature, wherein the evaluation unit is designed to estimate the road surface condition as a friction coefficient parameter from the detected amount of water on the road surface, taking into account the outside temperature.

[0042] If a precipitation amount can be located, a corresponding amount of water on the road surface can be determined. This amount of water on the road surface is defined as the intermediate layer between the tires and the road surface. By taking the local temperature into account, a corresponding friction coefficient can be determined based on the current road surface condition (e.g., ice / slippery).

[0043] Thus, by detecting the amount of precipitation in conjunction with the corresponding temperature, it is possible to determine, for example, whether the road surface is icy or wet, which significantly reduces the coefficient of friction, especially on an icy road surface.

[0044] In a further embodiment, the device has a rain sensor designed to detect rain, with the evaluation unit further configured to validate the rain detected by the rain sensor based on the detected precipitation. Thus, malfunctions or defects in the rain sensor can be easily and cost-effectively detected. This contributes significantly to driving safety, since a slippery road surface caused by water or ice significantly reduces the coefficient of friction.

[0045] In particular, the evaluation unit can be configured to generate appropriate measures in the event of non-validation. This could, for example, involve instructing other evaluation systems / sensor systems to explicitly search for rain in existing camera images / sensor images, or the evaluation unit can generate warnings.

[0046] In a further development, an interface is provided for receiving current regional weather data, and the evaluation unit is configured to determine whether precipitation is present based on the attenuation value, taking the current regional weather data into account. The current regional weather can be used, for example, to validate a detected precipitation, or, in the event of deviating forecasts, the evaluation unit can perform a further check.

[0047] A method for determining a friction coefficient parameter for a tire of a vehicle comprises the steps: - receiving microwave radio frequency waves transmitted by a microwave mast with a known transmission power, which is located in a microwave radio frequency range, - determining a received power of the radio frequency waves by an evaluation unit, - comparing the transmitted power and the received power to generate an attenuation value, - determine whether precipitation is present based on the attenuation value and estimate a road surface condition based on whether precipitation is present, - using the estimated road surface condition as a friction coefficient parameter.

[0048] In particular, the information whether precipitation is present or not can also be used.

[0049] The method is particularly designed to run on the device according to the invention. In particular, advantages and advantageous configurations of the device can be transferred to the method.

[0050] In a further development, the attenuation value is calculated as the difference between the transmitted power and the received power. In particular, to estimate the amount of precipitation, a base value can be subtracted from the attenuation value, with the base value defining attenuation without precipitation.

[0051] The baseline value is preferably created during a route over a dry period and linked to the route.

[0052] A driver assistance system for determining a friction coefficient, the driver assistance system comprises an interface for receiving a friction coefficient parameter sent by a device as described above and / or by a method carried out as described above.

[0053] The friction coefficient parameter can be used to determine a maximum friction coefficient based on other specific friction coefficient parameters, such as road surface / tire tread depth / speed, etc.

[0054] A driver assistance system can also be designed as a control unit, etc.

[0055] Further features and advantages of the present invention will become apparent from the following description with reference to the accompanying figures, which schematically show: Fig. 1: a device in a first embodiment Fig. 2: a device in a further embodiment.

[0056] Fig. 1 shows a device 1 for determining a friction coefficient parameter of a vehicle 2.

[0057] This comprises an interface 3. The interface 3 is designed to receive microwave radio waves transmitted by a microwave mast 4. Furthermore, the microwave radio waves are transmitted with a known transmission power in a microwave frequency range, which is either transmitted in an updated form by the microwave mast 4 or is otherwise known.

[0058] The device 1 has an evaluation unit 5 which is designed to determine a reception power of the received radio frequency waves.

[0059] The evaluation unit 5 then compares the transmitted power with the received power and generates an attenuation value.

[0060] This can be expressed in particular as the difference between transmit power and receive power: Attenuation value = transmit power − receive power

[0061] At the typically used frequencies of 15 GHz to 80 GHz, the emitted microwave radiation is strongly attenuated by raindrops. Measuring this attenuation allows us to determine the amount of precipitation. The attenuation value is therefore a measure of precipitation.

[0062] To estimate the amount of precipitation, evaluation unit 5 subtracts a base value from the attenuation value. The base value is defined as the attenuation without precipitation, essentially a local base attenuation in the area. Attenuation occurs, for example, when driving through a forest or in very sparsely populated areas, etc.

[0063] This gives the estimated amount of precipitation roughly as follows: Precipitation amount = damping value − base value The base value can be a constant which varies depending on an area.

[0064] The base value indicates the damping without rain influence, which is subtracted from the difference value during the rainy period. The base value can be assumed to be constant, resulting from the value during the dry period. This allows the amount of precipitation to be defined. If a precipitation amount can be located in this way, the resulting amount of water on the road surface can be determined. This amount of water on the road surface is defined as the intermediate layer between the tire and the road surface and serves to identify the road surface condition, which can be used to determine a friction coefficient parameter.

[0065] During heavy rain, for example, the amount of water forms a floating intermediate layer, which causes a significant reduction in the coefficient of friction.

[0066] The base value can, for example, be generated manually during the journey, or automatically during a journey, or it can be set in advance.

[0067] For example, the driver can operate a control unit during a dry period on a route to establish a baseline value. This baseline value can then be linked to the route. Furthermore, the baseline value can also be linked to the time of day / temperature and linked to the route. This results in an even more accurate baseline value.

[0068] Such routes could be, for example, the daily commute to work. This results in a more accurate baseline value.

[0069] Alternatively, the evaluation unit 5 can be configured to generally generate baseline values ​​during dry periods and link them to the route. Based on the amount of precipitation, the evaluation unit 5 can then estimate the amount of water on the road surface.

[0070] Furthermore, a temperature sensor 6 can be provided for measuring the outside temperature.

[0071] Based on the outside temperature, the evaluation unit 5 can estimate the amount of water on the road surface as the road surface condition. This could be, for example, ice / black ice in low temperatures, or slush or a lot of water in cold weather, etc.

[0072] If a precipitation amount is located, the resulting amount of water on the road surface can be determined. This amount of water on the road surface is defined as the intermediate layer between the tire and the road surface and serves to identify the road surface condition, which can be used to determine the friction coefficient parameter.

[0073] During heavy rain, for example, the amount of water forms a floating intermediate layer, which causes a significant reduction in the coefficient of friction.

[0074] Thus, by detecting precipitation in conjunction with the corresponding temperature, it can be concluded that the road surface is icy or wet, for example.

[0075] The evaluation unit 5 can transmit the water quantity as well as its condition as road surface condition as a friction coefficient parameter for information to a driver assistance system 7 for generating the friction coefficient.

[0076] This allows the amount of precipitation to be measured from power fluctuations in the mobile network over microwave links. The amount of precipitation can be derived from the radiation fluctuations between the transmitter masts and the vehicle as the receiver. Raindrops dampen the propagation of electromagnetic waves.

[0077] A fine-mesh network of cell towers allows for high coverage and fine-resolution precipitation detection. This high coverage and the device according to the invention allow for localized rainfall to be detected with minimal time delay.

[0078] Thus, the influence of rain / ice etc. can be immediately included as a friction coefficient parameter in the friction coefficient calculation.

[0079] Fig. 2 shows a further device 1a according to the invention.

[0080] This includes interface 3.

[0081] The device 1a also has the evaluation unit 5, which is designed to determine a received power of the received radio frequency waves and to compare the transmitted power with the received power to generate the attenuation value: Attenuation value = transmit power − receive power

[0082] To estimate the amount of precipitation, the evaluation unit 5 subtracts the base value from the attenuation value.

[0083] This results in the estimated amount of precipitation as: Precipitation amount=attenuation value−basic value.

[0084] The base value can be a constant that varies depending on the area. This can be generated manually during the trip, automatically during the trip, or predefined.

[0085] The base value indicates the damping without rain influence, which is subtracted from the difference value during the rainy period. The base value can be assumed to be constant, resulting from the value during the dry period. This allows the amount of precipitation to be defined. If an amount of precipitation is located in this way, the resulting amount of water on the road surface can be determined. This amount of water on the road surface is defined as the intermediate layer between the tire and the road and is used to identify the road surface condition, which can be used to determine a friction coefficient parameter. In heavy rain, for example, the amount of water forms a floating intermediate layer, which causes a significant reduction in the friction coefficient.

[0086] Based on the amount of precipitation, the evaluation unit 5 can now estimate the amount of water on the road surface.

[0087] Furthermore, a rain sensor 8 can be provided, which is designed to detect rain. Upon detection of rain, this sensor transmits the information to the corresponding driver assistance system 7.

[0088] In addition, the evaluation unit 5 is configured to validate the rain detected by the rain sensor 8 based on the detected precipitation. This allows for the simple and cost-effective detection of malfunctions or a defect in the rain sensor 8. If the evaluation unit 5 detects precipitation and the rain sensor 8 does not detect rain, the evaluation unit 5 can, for example, trigger other systems to explicitly search for rain in other sensor data, such as existing camera images / sensor images. A warning can also be generated for the driver assistance system 7.

[0089] Furthermore, the temperature sensor 6 can be provided for measuring the outside temperature.

[0090] Based on the outside temperature, the evaluation unit 5 can estimate the amount of water on the road surface as the road surface condition. This could be, for example, ice / black ice at low temperatures, or slush or a lot of water in cold weather, etc. Taking the local temperature into account, the corresponding friction coefficient can then be determined.

[0091] Thus, by detecting precipitation in conjunction with the corresponding temperature, it can be concluded that the road surface is icy or wet, for example.

[0092] The evaluation unit 5 can transmit the water quantity as well as its condition as a road surface condition as a friction coefficient parameter and, if applicable, also the warning for information to a driver assistance system 7 for generating the friction coefficient. List of reference symbols 1.1a device 2 vehicles 3 Interface 4 microwave masts 5 Evaluation unit 6 Temperature sensor 7 Driver assistance system 8 Rain sensor

Claims

[1] Device (1, 1a) for determining a friction coefficient parameter for a tire of a vehicle (2), comprising an interface (3) for receiving microwave radio frequency waves emitted by a microwave radio mast (4) at a known transmission power, which is located in a microwave radio frequency range, where an evaluation unit (5) is provided which is designed to determine a received power of the received radio frequency waves, and wherein the evaluation unit (5) is designed to compare the transmitted power and the received power and to generate an attenuation value based on the comparison, and wherein the evaluation unit (5) is designed to determine whether precipitation is present based on the attenuation value and to estimate a road surface condition based on this, and wherein the evaluation unit (5) is designed to use the estimated road surface condition as a friction coefficient parameter, characterized by that an interface (3) is provided for receiving current regional weather data and wherein the evaluation unit (5) is designed to determine whether precipitation is present on the basis of the attenuation value, taking into account the current regional weather data. [2] Device (1, 1a) according to claim 1, characterized by that a storage unit is provided which has a basic value which defines an attenuation without precipitation, wherein the evaluation unit (5) is designed to carry out an estimation of an amount of precipitation on the basis of the basic value and the attenuation value. [3] Device (1, 1a) according to claim 2, characterized by that the evaluation unit (5) is designed to subtract the base value from the attenuation value in order to estimate the amount of precipitation. [4] Device (1, 1a) according to claim 2 or 3, characterized by that the evaluation unit (5) is designed to create the base value during a route over a dry period and to couple it to the route. [5] Device (1, 1a) according to claim 4, characterized by that a control unit is provided to generate the base value manually during a route. [6] Device (1, 1a) according to claim 4 or 5, characterized bythat the evaluation unit (5) is designed to automatically generate a base value during a route on the basis of a determined dry period and to link this to the route. [7] Device (1, 1a) according to one of the preceding claims 2 to 6, characterized by that the evaluation unit (5) is designed to estimate a quantity of water on the road surface from the detected amount of precipitation and, on the basis of this, the road surface condition. [8] Device (1, 1a) according to claim 7, characterized by that the device (1, 1a) has a temperature sensor (6) for measuring the outside temperature, and wherein the evaluation unit (5) is designed to estimate the road surface condition as a friction coefficient parameter from the detected amount of water on the road surface, taking into account the outside temperature. [9] Device (1, 1a) according to one of the preceding claims, characterized bythat the device (1, 1a) has a rain sensor (8) which is designed to detect rain, wherein the evaluation unit (5) is designed to validate the rain detected by the rain sensor (8) on the basis of a detected precipitation. [10] Device (1, 1a) according to claim 9, characterized by that the evaluation unit (5) is designed to generate appropriate measures in the event of non-validation.

Images