WO2015074744A1

WO2015074744A1 - Method and device for determining a coefficient of friction in a vehicle

Info

Publication number: WO2015074744A1
Application number: PCT/EP2014/003010
Authority: WO
Inventors: Stefan Jacobi; Karl-Ludwig Haken
Original assignee: Dr. Ing. H.C. F. Porsche Aktiengesellschaft
Priority date: 2013-11-19
Filing date: 2014-11-11
Publication date: 2015-05-28
Also published as: DE102014103843A1

Abstract

The invention relates to a method for determining a coefficient of friction between at least one tire on a vehicle and a roadway, wherein the coefficient of friction is obtained in accordance with at least one pre-classified driving condition of the vehicle and in accordance with pre-classified environmental conditions, the coefficient of friction being estimated using at least one estimation process to which at least one parameter of a confidence factor is allocated. The invention further relates to a corresponding device.

Description

Method and device for friction coefficient determination in a vehicle

The present invention relates to a method and a device for calculating a coefficient of friction between at least one tire of a vehicle and a roadway. The calculation is based on various estimation methods, each of which is assigned a confidence factor.

The driving behavior of a vehicle is highly dependent on a respective coefficient of friction between the tire and the road. If the coefficient of friction is high, it can be correspondingly accelerated or decelerated or driven accordingly fast around a curve. If the coefficient of friction is low, the vehicle can easily become unstable due to a loss of liability to the road surface and cause dangerous driving situations with correspondingly dangerous driving conditions. For a driver, it is very important to know how much traction or power is available to the roadway, i. What is the maximum available adhesion between the tire and the road? This information can also increase the control performance of all vehicle dynamics control systems, such as. An anti-lock braking system (ABS) with appropriate processing.

Individual methods for calculating a coefficient of friction between the tire and the road have already been described. Thus, the German document DE 10 2009 002 245 AI discloses a method for determining a coefficient of friction between the tire and the road in a vehicle, in which an actual tire return torque with a

Reference tire torque is adjusted, wherein a ratio of the

Moments on the current coefficient of friction is closed.

In the German publication DE 10 2010 036 638 AI, however, a method for determining the coefficient of friction in a vehicle is presented, in which a

Cornering force is determined on at least one steered wheel. In this case, a rack power is detected and a restoring moment on the steered wheel in dependence

CONFIRMATION COPY the rack force and the cornering force determined as a function of a caster and determined on the basis of the return torque of the coefficient of friction.

Also on the basis of a rack-and-pinion force, DE 10 2006 036 5 751 A1 determines a state variable of a vehicle according to a given kinematic relationship as a function of the respective rack force, which in turn is calculated as a function of the steering moments acting in the steering system.

In the document DE 195 23 354 AI, however, is a device for estimating0 of current friction coefficients of the road on the basis of data from a

Steering angle sensor, a vehicle speed sensor and a yaw rate sensor disclosed. Furthermore, this data is described in the calculation of

Include torque distribution on the front and rear wheels. In addition, a yawing-moment computing unit is provided for overcoming the oversteer / understeer 5 phenomenon of the vehicle by appropriately controlling the left and right wheels

prevent.

Against this background, a method for determining a coefficient of friction between at least one tire of a vehicle and a roadway with the features of claim 1 is presented. Further embodiments are the corresponding

Subclaims refer. Furthermore, a device having the features of independent claim 15 is provided.

In the method according to the invention, it is provided that the coefficient of friction is formed as a function of at least one respective driving state of the vehicle to be classified in advance, and of respective environmental conditions to be classified in advance, and the coefficient of friction is estimated by at least one estimation method

at least one estimation method with at least one characteristic value of a

Trust factor is occupied. The term "occupy" in the context of the presented invention, a mathematical assignment, preferably a weighting example. By multiplication by a factor to understand. In the context of the present invention, a coefficient of friction or adhesion is to be understood as meaning a coefficient of friction or coefficient of adhesion or a friction coefficient or a coefficient of friction. The coefficient of friction is a measure of the friction force in relation to the contact force between two bodies, in particular between the tire and the road. In a broader sense, the term friction also includes the more

Phenomenologically coined term Kraftübertragungsvermögen of the tire on the road, which may be very low in aquaplaning or road surface smoothness.

In addition to the quantitative calculation of the abovementioned physical parameters such as coefficient of friction, the method also includes the strongly qualitative ones

Determination or estimation, whether e.g. Aquaplaning or Fahrbahnglätte exists. This can be done by methods such as FuzzyLogic or Assotiative Saving or by direct route e.g. done by simple phenomenological considerations. The inventive method is based on several successive building up

Process steps. In a first step, a classification of a respective driving state takes place. In this case, the respective driving state of the vehicle is advantageously classified by means of a longitudinal, transverse and vertical dynamic state of the vehicle. A driving state in the context of the present invention is to be understood as movement of a vehicle relative to the roadway. The respective current driving state can be described by a temporally variable, vectorial direction of travel, consisting of longitudinal, transverse and vertical dynamic parts. The transverse dynamics are divided into potential driving states "straight ahead", "stationary cornering" and "unsteady cornering". Furthermore, a distinction between left and right curve is possible. The unsteady cornering can be further divided into or out of the curve.

In longitudinal dynamics, a distinction is made between "constant speed",

"accelerated" and "braked". In the driving state "braked" can be further differentiated between "braked with service brake" and "braked with engine brake". This distinction is necessary because there may be a significant difference in the adhesion of individual wheels to the respective brake types, i. For example, individual wheels can more easily block when braking with the service brake.

The longitudinal dynamics can thus be divided into driving states such as "accelerated", "constant", "motor-braked" or "braked". Another classification would be, for example.

"accelerated", "constant", "decelerated" and "driven" and "engine brake" and "service brake", the second example offers the advantage that even driving conditions of downhill with engine brake or service brake with constant or even increasing speed clearly described can be.

It is also the vertical dynamic state of motion of the vehicle here

This term covers both the overall movement of the vehicle in the topography of a landscape (uphill or downhill travel or in-plane travel) or the states of motion of individual wheels with respect to the vehicle body over the road surface such as sprung and sprung and thus the connection to the effective Contact forces or normal forces in the

Include tire contact surfaces.

The lateral dynamics, on the other hand, are divided eg into "curve (left)", "transition (left)", "straight ahead", "transition (right)", "curve (right)". In order to stabilize or optimize a driving behavior of a vehicle, first of all an exact knowledge of the respective driving state of the vehicle is necessary. Therefore, in the inventive method first on a yaw rate or a

Yaw acceleration, the lateral dynamics and via an actual longitudinal acceleration and / or the brake pressure the longitudinal dynamics classified, i. assigned to one of the aforementioned driving conditions. Sensors necessary for the classification of the longitudinal acceleration as well as for the classification of the lateral acceleration are generally already present in vehicles with vehicle dynamics control.

Furthermore, in a second step, a classification of respective

Ambient conditions of the vehicle, as these also affect the coefficient of friction and thus the driving behavior of the vehicle. The classification of the ambient conditions takes place in at least three

Categories, namely "dryness", "slipperiness" and "wetness". A further division of the road surface smoothness is conceivable when using suitable sensors. A

Distinction between the different categories is made using at least one sensor from the following lists of sensors: rain sensor,

Humidity sensor, outside temperature sensor, tire temperature sensor,

Tire vibration sensor, Radträgerschwingungssensor, sound or

Structure-borne sound sensors, vehicle environment sensors, front-rear-view camera,

Driving dynamics sensors.

Is additionally an air humidity sensor available due to the

Outside temperature are estimated, whether dew precipitated on the road. If in this case the outside temperature is below approx. 3 ° C, the formation of ice slipperiness is to be expected.

In one possible embodiment of the method according to the invention, it is provided that, using at least one sensor, an energy which is present in a respective one Tire of the vehicle is converted into heat, is calculated and the calculated energy is used to estimate a height of any water film on the road surface depending on the driving speed. If a vehicle is additionally equipped with tire temperature sensors, the forces required to classify longitudinal and lateral dynamics are used to estimate respective forces acting between the tire and the road surface. Estimating these forces acting between tire and road surface calculates the energy that is converted into heat in the tire.

Further, using measurements provided by the tire interior temperature sensors, respective energies that the respective tires deliver to the environment are estimated. If more energy is emitted to the environment than is possible at the measured ambient temperature by air and road contact, it can be assumed that cooling is currently taking place through a film of water which absorbs the energy additionally emitted by the respective tire. The additional energy released can be calculated by a function of a driving speed and a height of the water film on the roadway, whereby the height of the water film can be inferred at a known given amount of energy and driving speed.

In one possible embodiment of the method according to the invention, it is provided that the at least one estimation method is selected as a function of a respective driving state to be classified beforehand.

Since the current coefficient of friction significantly influences a respective driving state, it is provided that the respective at least one estimation method, via which the current coefficient of friction is determined, is selected as a function of previously determined classification results of the driving state, wherein the selection of the at least one

Estimation preferably takes place automatically. By means of the previously classified driving conditions, it is possible to make a selection of friction coefficient estimation methods suitable at a particular time. Further, the results of the classification allow for weighting results of methods involved in friction coefficient estimation if more than one friction coefficient estimation method is used.

In a further possible embodiment of the method according to the invention, it is provided that the at least one estimation method is selected as a function of respective classified environmental conditions.

Since respective ambient conditions of the vehicle in addition to the driving condition also have or may have a significant influence on the current coefficient of friction between the vehicle or tire and road, it is provided that the respective at least one estimation method for estimating the current coefficient of friction as a function of the previously determined classification results of the environmental conditions and / or the

Driving state is selected, the selection is preferably done automatically.

In principle, all suitable methods for the possible description of influencing factors on the coefficient of friction between tire and roadway can be used, wherein preferably methods for estimating respective driving conditions via longitudinal and lateral acceleration sensors and methods for determining respective ones

Slippage between different wheels, a tire wake, a surge resistance, a rainfall or a water film on the road to be used for Reibwertermittlung.

The different estimation methods can enter into the calculation, ie the estimation of the coefficient of friction, equally or with a different weighting adapted to the respective classification results. In order to adapt the respective estimation methods to respective ambient conditions and / or driving conditions, according to the invention, the respective ones are provided

To weight estimation methods individually, i. with a confidence factor or a respective value of the confidence factor assigned to the respective estimation method to a respective ambient condition and / or driving condition.

In a further possible embodiment of the method according to the invention, it is provided that at least one possible interference variable is identified and identified with a

Weighting factor or a corresponding characteristic value of a confidence factor is weighted.

In such complex calculations as the Reibwertschätzung or the

Friction value determination is of great importance, such as crosswind, bank, longitudinal inclination, ruts, different traction in the left and right lane and an ABS or FDR control intervention. It is therefore provided to determine such disturbance variables, for example using a measurement of a steering torque and / or spring travel or a vertical acceleration of the vehicle, to identify and, if necessary, to include in a calculation of the coefficient of friction. In a further possible embodiment of the method according to the invention, it is provided that respective disturbance variables are also weighted by at least one confidence factor, i. that each disturbance with a respective

corresponding characteristic value of the at least one confidence factor is assigned or weighted.

By using a confidence factor for the estimation methods and, analogously, another confidence factor for the disturbances, corresponding influences can be weighted and thus assessed for their reliability. In the context of the present invention, a confidence factor is a factor which is used to weight a respective function or method, for example an estimation method, against other methods and thereby its specific relative proportion of one based on a plurality of methods determine the overall result. A confidence factor consists of characteristic values, the respective specific driving conditions and / or environmental conditions or

Assessed estimation methods are assigned and which are used to weight the respective estimation method with these. Since the method according to the invention comprises at least one estimation method and in particular a combination of a plurality of estimation methods for determining or

Calculating the coefficient of friction between the tire and the road surface seems to be one

Weighting of respective estimation methods from the majority of estimation methods, if applicable

meaningful. This weighting takes place, as explained above, for example on the basis of environmental conditions and / or driving conditions.

In order to enable a weighting of the estimation methods with one another when calculating the coefficient of friction, it is provided that each result obtained by applying an estimation method for the coefficient of friction with a respective one of the estimation methods

multiplied by the associated characteristic value of the respective confidence factor, ie, weighted, and all the results thus weighted from the individual estimation methods are added up. The weighting also includes other mathematical methods which, for example, can also take account of the mutual influence of a plurality of factors of trust. For reasons of normalization, in a calculation using weighted procedures, it is necessary to include a total of the respective weightings in the calculation. Such an inclusion can take place, for example, in the form of a division of the total result obtained from the summation by a sum of the respective characteristic values of the confidence factor. The influence of the disturbance variables is taken into account by calculating the coefficient of friction as a function of disturbance variables which correspond to a respective characteristic value of a variable associated with the respective ambient conditions and / or a respective driving condition

Weighting factor are weighted. For this purpose, the respective weighted disturbance variables are offset against each other and compared with a predetermined minimum value. If the result of the calculation of the weighted disturbances lies below the specified value

Minimum value, so currently no reliable friction coefficient estimation is possible.

The use of confidence factors enables a reliable determination or estimation of the coefficient of friction and offers the driver as well as a respective one

Vehicle control system thereby a trustworthy way to assess respective driving maneuvers.

Are fixed to the respective estimation method for determining the coefficient of friction

Assigned to trust factors or characteristic values, for example, by a technician before commissioning the vehicle, the corresponding characteristic values, i. E. Values of the confidence factor for a specific driving condition and / or concrete

Outdoor conditions. These characteristics require a fixed hierarchy of respective estimation methods with one another, in which, for example, a method based on the tire temperature as well as a method based on a wheel speed is included in the calculation of the coefficient of friction. It is due to the respective

For example, a contribution of a tire temperature-based estimation method to only one fourth of a contribution of a wheel speed-based estimation method is taken into account in the calculation or estimation of the coefficient of friction.

The described relative influence of respective estimation methods is determined by the respective confidence factors or their characteristic values, for example, those to be provided

Control unit of the vehicle are deposited described. The characteristics of the

Confidence factors can take on any value and possibly also on respective previously classified driving situations or environmental conditions are dynamically adjusted, whereby a relative influence of respective estimation method on the coefficient of friction changes accordingly. By weighting with subsequent standardization, respective methods can contribute more or less to a respective overall result.

In a further possible embodiment of the method according to the invention, it is provided that the at least one estimation method is weighted with a respective characteristic value of a corresponding confidence factor, and a value which results in an estimated maximum adhesion is calculated from all weighted estimated values of respective methods or estimation methods.

By using multiple weighted, i. With respective characteristic values of respective confidence factors of calculated estimation methods, a reliable estimation of a currently available maximum adhesion or friction value between tire and roadway can be achieved. In this case, the currently available maximum frictional connection can be converted into the current coefficient of friction, wherein a transfer from the current coefficient of friction to the currently available maximum frictional connection is also possible. In the context of the invention, a maximum available adhesion is to be understood as a value which indicates how much traction a respective tire or the whole

Vehicle currently available. Therefore, the respective tire can be loaded up to this value before the contact with the road is lost and, for example, the respective tire is blocked or twisted and produces high slip.

In a further possible embodiment of the method according to the invention, provision is made for respective characteristic values of respective confidence factors to be more specific

Estimated method or disturbance variables are calculated and a value calculated thereby is compared with a previously provided minimum value and falls below the minimum value by the calculated value, a message is generated, which states that currently no reliable estimate of the maximum available adhesion is possible.

Since the respective confidence factors or the corresponding characteristic values are in

Depending on the classified driving condition and / or environmental conditions change, it is provided to consider a quality criterion in the form of a minimum value. For this purpose, all relevant characteristic values are offset against each other, i. For example, summed up and compared with the previously provided minimum value. If the value calculated thereby, for example an average value of the confidence factor, is below the minimum value, no reliable estimation of the maximum available frictional connection or the coefficient of friction is currently possible. It can be envisaged in such a case, in which the result of the calculation of the characteristic values of the respective confidence factor is smaller than the minimum value, to provide the driver of the vehicle with a warning or control units that currently no reliable estimate of the maximum adhesion or the coefficient of friction is possible.

In a further possible embodiment of the method according to the invention, it is provided that the respective disturbance variables are weighted and a value, for example an average, is calculated from respective weighted disturbance variables.

As already explained for the confidence factors of the at least one estimation method for estimating the coefficient of friction or maximum frictional connection, this is also provided for the determined disturbances, these with respective characteristic values of

Confidence factors that can be assigned fixed or dynamic, to be offset and compared with a previously provided minimum value. If the calculated value is below the minimum value, it may be provided to provide the driver of the vehicle with a warning or control devices information that currently no reliable estimate of the maximum traction or the coefficient of friction is possible. In a further possible embodiment of the method according to the invention, it is provided that the respective characteristic value of the further confidence factor is compared with the minimum value to be provided in advance, and falls below the value

value to be provided by the further confidence factor a last estimated coefficient of friction is assumed to be still valid.

In a further possible embodiment of the method according to the invention, it is provided that the at least one estimation method is selected from the following list of estimation methods:

a) calculation of a global adhesion between at least one tire and the road surface by means of a measured longitudinal and lateral acceleration, b) calculation of respective wheel loads by the currently occurring longitudinal and

C) estimating respective longitudinal and lateral forces through knowledge of the use of a calculation according to a) and b) and knowledge of a drive and control system of the respective vehicle, d) determining a tire longitudinal stiffness or determining an equivalent quantity by forming a quotient of tire longitudinal force and longitudinal tire slip, e) determining a tire lateral stiffness or an equivalent quantity by forming a quotient of tire lateral force and tire lateral slip, f) determining a total tire stiffness or an equivalent size by formation a quotient of tire force and tire slip by means of

Combination of claim dl and d2 or by means of a holistic vectorial approach, g) determining the maximum available frictional connection between at least one tire and the roadway by a ratio between actual longitudinal, lateral or total tire stiffness and longitudinal, lateral or

Total Tire Stiffness on Proven Roads h) Calculating a return torque of a front axle of the respective vehicle by converting an EPS tie rod force using knowledge of axle and steering kinematics i) Calculating a lateral force on the front axle from a respective one

Vehicle movement, j) calculating a trailing distance from a quotient of restoring torque and lateral force when the wheel is rolling free, and k) calculating the maximum available frictional connection between the respective tire and the roadway by comparing the actual restoring torque with one

Preset torque to be specified in grip-free, dry carriageway,

I) determining a water film thickness on the roadway by determining various patterns of a longitudinal acceleration signal and a steering wheel angle in relation to a steering torque and a wheel speed, m) determining the friction coefficient by using distance-related data stored in an on-board database and comprising descriptive sizes of the roadway , and o) determining the coefficient of friction by using data from communication with off-board sources or external data servers. The distance-related data can be stored, for example, in a navigation device as an in-vehicle database. By means of vehicle position determination, the data in the vehicle can be used with foresight. These are, for example.

geographical position of the carriageway, geometric course and roadway height above sea level, roadway longitudinal and lateral inclination, type of surfacing, micro and macrotexture, others

Characteristics that permanently influence the road friction coefficient, dome and drop, ruts, exposure to bridges or shading. From the vehicle external sources such as From other vehicles or from external data servers, track-related, time-variable data in the vehicle can be updated on a timely basis and / or locally and / or on the location and route of the vehicle

be provided in a forward-looking manner. This includes the entire field for the

Road friction value relevant information. Contained are predicted and / or current and / or past information that can be measured or observed. These may have been collected by other road users or stationary observers or weather stations. These are, for example, the current road condition incl. Degree of coverage with media such. Water, snow, ice, frost, oil, leaves; as well as place, time, prognosis and course of the comprehensively characterized weather situation incl. temperature and in particular also the place and time course of kind and amount of precipitation and the ruling ones

Visibility conditions that, in conjunction with the coefficient of friction, influence the driving style of the driver and the activation of vehicle systems. Important information on the driving condition, the environmental conditions or potential risks by approaching limit states can also be derived from other sensors located in the vehicle and with appropriate weighting in one

Use the overall system approach.

These include, for example, the following sensors: The rain sensor for controlling the windshield wiper provides information about the current amount of rainfall on the windshield and thus by correction of various factors such as driving speed, road inclination approximately the water level on the road.

Acceleration or structure-borne noise sensors in the vehicle are capable of

Vehicle overall system to contribute to the determination of water level, micro and macrotexture of the road surface, snow and ice and to provide aquaplaning conditions. The water height determination works e.g. by measuring sound or structure-borne noise intensities in characteristic for road spray water

Frequency bands. Roadway micro- and macrotexture, snow, ice can be obtained by similar methods from the analysis of the vibration behavior in the tire, in the suspension or in the whole vehicle.

Other informative sources of information on the subject of friction coefficient estimation are the sensors for monitoring the vehicle environment, such as ACC radars and cameras. Certain weather conditions and operating conditions are determined by

Self-diagnosis (e.g., ACC radar blindness due to icing) detected

Recognize and avoid functional restrictions. This can be done in one

Be used throughout the system. About cameras can provide information about the

Road conditions can be determined dry, wet, ice, snow or the spray behind the vehicle as a result of water on the road.

By using respective estimation methods for determining the coefficient of friction or the maximum available frictional connection of the respective tire of the vehicle with the roadway, it is possible to reliably determine the values of the coefficient of friction or the maximum available frictional connection and continuously to respective conditions, ie to respective ambient conditions and / or to adapt to driving situations or driving conditions. According to the invention, it is provided to weight respective estimation methods with a confidence factor and to use them as a function of respective disturbance variables, which may also be weighted, for example, via another confidence factor. Because different vehicles have a different sensor configuration The method according to the invention is based on a multiplicity of potentially usable estimation methods, it being possible to optionally increase a scope of the estimation method used to determine the coefficient of friction or of the maximum available frictional connection with a corresponding availability of respectively necessary sensors.

In a further possible embodiment of the method according to the invention it is provided that the determined coefficient of friction or the determined maximum available

Tangle combined with data of a navigation system and can be used to calculate respective braking distances, braking intervention times and / or cornering speeds.

By prior knowledge of a respective current coefficient of friction, it is possible to regulate a brake pressure so that a blocking of the respective wheel or tire can be prevented even before the onset of a first wheel standstill. Such

Pilot control or regulation reduces a necessary stopping distance compared to a conventional anti-lock braking system, which only intervenes when a respective tire or a respective wheel has already run into the locked state. Especially on a slippery road, such a late intervention has an unfavorable effect on a necessary braking distance.

Furthermore, the present invention relates to a corresponding device for controlling a driving stability of a vehicle having at least one arithmetic unit, wherein at least one previously provided characteristic value of a confidence factor is to be included in respective calculations of a coefficient of friction or a maximum available adhesion and a respective driver of the vehicle and / or others

Vehicle dynamics control systems are informed about a current coefficient of friction between at least one tire of the vehicle and a roadway. The control of the driving stability of the vehicle takes place as a function of the at least one Calculated unit calculated friction coefficient or the calculated maximum available frictional connection.

Among other things, the device according to the invention can be used to control the driving stability of the vehicle. Furthermore, specific to the driver

Information about available traction or lateral acceleration reserves are presented. Necessary calculations are performed by a control unit of the vehicle or by a computing unit that may be included in the device. By an estimate of a current coefficient of friction, for example.

Vehicle control systems such as an anti-lock braking system (ABS) or a

Stability program or a traction program of the powertrain or the spring damper system or a steering system can be regulated efficiently. This means that respective control or regulation operations of the respective

Vehicle control system can be adapted to the current coefficient of friction, whereby, for example, reduces a brake pressure to be applied and a blocking of the tire even before a detection of blocking, as provided, for example, in an ABS is prevented. It is understood that the above-mentioned features can be used not only in the respectively specified combination, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail with reference to the drawing.

FIG. 1 shows a schematic course of a classification of a respective one

Driving state in a possible embodiment of the method according to the invention. FIG. 2 shows a schematic course of a classification of respective ones

Ambient conditions of a vehicle in a possible embodiment of the method according to the invention. FIG. 3 shows a schematic course of a determination of the respective disturbance in a calculation of a coefficient of friction between the tire and the roadway in a possible one

Embodiment of the method according to the invention.

FIG. 4 shows a schematic overview of the calculation of the coefficient of friction

used method in a possible embodiment of the method according to the invention.

FIG. 5 shows a possible embodiment according to the invention of a table with characteristic values of confidence factors which are used for the weighting for calculating the

Friction value used method.

FIG. 6 shows a diagram of a possible estimation according to the invention of a maximum adhesion between respective tires and a roadway. FIG. 7 shows a further possible embodiment according to the invention of a table with confidence factors of respective disturbance variables used to calculate the coefficient of friction.

The sequence shown in FIG. 1 of a classification of a respective driving state 1 of a vehicle serves for the assignment or division of the respective driving situation 1 into one of nine current driving states 2, 4, 6, 8, 10, 12, 14, 16, 18 by means of

Measurements of a current direction of travel (lateral dynamics) 20, a current one

Velocity profile (longitudinal dynamics) 22 and an applied brake pressure 27. The velocity profile is thereby measured by a tachometer, the

Direction of travel by measured values of a yaw rate sensor and the brake pressure determined by a brake pressure sensor. The respective values of the speedometer and the Yaw rate sensors are calculated, interpreted and finally assigned to a specific, predefined driving state.

Based on the measured values of the yaw rate sensor, the lateral dynamics 20 are pre-classified by means of a yaw rate ψ 21, i. If the yaw rate ψ 21 corresponds approximately to the value zero, the driving situation 1 is assigned to a current driving state "straight ahead" 6. If the yaw rate 21 is greater or less than the value zero, then another calculation of a respective yaw acceleration ψ 23, 25 takes place. If the yaw rate 21 has assumed a value less than zero and the corresponding yaw acceleration 25 has assumed approximately zero, then the driving situation 1 is assigned to the driving state "curve right" 10. If the yaw acceleration 25 is not equal to zero, then the vehicle is in a "transition state" 8.

If the yaw rate 21 has assumed a value greater than zero and the corresponding yaw acceleration 23 is approximately zero, then the current driving state is assigned to a "left turn" 2, whereas if the yaw acceleration 23 is not equal to zero, the vehicle is in a "transitional state". 4 is located.

For the classification of the longitudinal dynamics 22, an interpretation of a current actual longitudinal acceleration v, 26 takes place, which is derived from the current one

Driving speed is calculated. If the current longitudinal acceleration 26 is approximately zero, then the longitudinal acceleration is assigned to the driving state "constant" 14, if the longitudinal acceleration 26 is greater than zero, then the current driving state is classified as "accelerated" 12 and in the case of a value of the longitudinal acceleration being less than zero the driving state classified as "braked" 18. Since a vehicle both by means of a

Brake motor braked as can be braked by a service brake, is further differentiated in the case of a value of the longitudinal acceleration less than zero on an applied brake pressure 27. If the brake pressure 27 is greater than zero, then the current driving state is "braked" 18, whereas in the case of a value of the brake pressure 27 equal to zero, a driving state "motor-braked" 16 is classified. By including the brake pressure 27 in the classification, it is possible to clearly describe even driving situations of a downhill with engine or service brake with constant or even increasing speed.

If, in addition, the vertical acceleration is measured, a further classification with regard to the vertical dynamics is conceivable. Impacts regarding the friction coefficient estimation are to be considered especially with longer lasting vertical accelerations eg in depressions and on dome.

By merging the classification results of longitudinal and lateral acceleration, respective driving conditions can be assigned to respective environmental conditions, such as, for example, "braked wet" or "accelerated dry". Since, during the respective driving situation 1, respective ambient conditions are also relevant for a driving behavior or a coefficient of friction between the tire and the roadway, these are interpreted in a further classification method illustrated in FIG. The classification method for interpreting the current environmental conditions is based on measured values of sensors 201, 203, 205 and 207, the measured values of the various sensors 201, 203, 205 and 207 being determined with one another

be adjusted to ensure a reliable classification result. Initially, the measured values of a rain sensor 201 are interpreted in an intermediate step 211. If actual precipitation is to be measured, then an adjustment step 213 follows, as indicated by the arrow 214 or an adjustment step 215, as indicated by the arrow 212. Provide an outside temperature sensor 203 or a

Tire temperature sensor 205 in the respective adjustment steps 215 and 213, respectively

matching, ie leading to the same classification result measurements, the environment is classified as "wet" 233. However, if the outside temperature sensor 203 measures a value below 3 ° C, the environment is classified as "potentially smooth" 232. The rain sensor 201 currently measures no precipitation and provides a comparison step 216, that even using data of the tire temperature sensor 205 currently no cooling water film 220 is present, the current environmental conditions are classified as "dry" 231. An estimation of the presence of the water film 220 on the tire of the vehicle is made using both the outside temperature sensor 203, the

Tire temperature sensor 205 as well as driving dynamics sensors 207, wherein the driving dynamics sensors 207 in particular for the calculation of a respective

Energy input into the tires 218 are used with the measurements of the outside temperature sensor 203 and the tire temperature sensor 205 in a

Adjustment step 219 is adjusted.

In an adjustment step 219, the vehicle dynamics sensor 207 provided by the outside temperature sensor 203, the tire temperature sensor 205, is provided

Measured values as well as a energy 218, which is converted into heat in a respective tire, according to the arrow directions, for the presence of a water film 220 closed. By measuring respective tire internal temperatures, the energies that the respective tires deliver to the environment are estimated. Is more energy delivered to the environment than that by means of the

Outside temperature sensor 203 measured ambient temperature by air and road contact of the respective tire is possible, it can be assumed that a cooling of the respective tire by a water film 220, whereby also the environment is classified as "wet" 233 accordingly. An amount of heat emitted in this case can be calculated, for example, as a function of a current driving speed and a height of the water film 220. If respective adjustment steps 216, 215, 213 or 219 have to reconcile contradictory measurements or partial results, then a new measurement is carried out and a classification of the contradictory values is omitted. The classification methods illustrated in FIGS. 1 and 2 permit a selection of friction coefficient estimation methods suitable at a given time and a weighting of results of friction coefficient estimation if more than one estimation method is used.

The method illustrated in FIG. 3 is based on an estimation of a steering torque. In this case, starting from a start state 301, a current state of a

Vehicle control system 303 detected. If the vehicle control system is active, there is a disturbance in a state of active control 305. If the vehicle control system 303 is not active, it is assessed by a comparison of a determined longitudinal acceleration in the vehicle-fixed coordinate system with a current actual longitudinal acceleration 26, if the vehicle is currently a slope 309 has overcome, which is the case when the longitudinal acceleration in the vehicle-fixed coordinate system is not equal to the actual actual longitudinal acceleration. If the longitudinal acceleration in the vehicle-fixed coordinate system corresponds approximately to the actual actual longitudinal acceleration 26, then a further adjustment step 313 of FIG

Transverse acceleration in the vehicle-fixed coordinate system with a product of actual yaw rate and current vehicle speed a current

Bank 315 of the carriageway classified. The vehicle is on one

Bank 315, when the lateral acceleration in the vehicle-fixed coordinate system with a product of actual yaw rate and current

Driving speed does not match. If the vehicle has a 3-axis acceleration and yaw rate sensor, the vehicle movement in space can be determined much more accurately. From the vehicle movement and the spring paths so the topography of the roadway with longitudinal and transverse inclination also

be calculated approximately.

A possible influence of crosswind 317 is classified via calculations 320, 322, and 324 and the matching steps 321, 323, and 325.

Further, depending on a result of the matching step 325 and a subsequent further matching step 327, a current occurrence of ruts 318 is made or different adhesion in left and right lane 319 closed. If the respective adjustment steps 321 and 323 together with the calculations 320 and 322 result in a unique result, the method ends in an end state 330. If the respective disturbance variables 305, 309, 315, 317, 318 or 319 are currently present, these become another one Calculation of the coefficient of friction provided and possibly charged with a confidence factor. Now or after a fixed time grid, the procedure is run again from starting point 301.

The method shown in Figure 4 for estimating a currently used

Friction 440 and a maximum available traction 450 between tire and roadway is based on various sub-methods 401, 402, 403, 404, 405, 406 and 407. In sub-method 401, a currently measured longitudinal acceleration 411 and a currently measured lateral acceleration 412 becomes a global one

Adhesion coefficient determined. In order to increase the accuracy of this determination, the measured values of the longitudinal acceleration 411 and the

Transverse acceleration 412 can be converted into rolling stock parallel values via roll and pitch angles. If a 3-axial acceleration sensor is used, a consideration of the currently acting vertical acceleration can increase the accuracy of the calculation of the lateral and longitudinal acceleration acting parallel to the road surface. The necessary knowledge of roll and pitch angles can either under

Use of knowledge of the vehicle can be estimated from respective accelerations or approximately calculated with the help of possibly provided spring travel sensors.

If a 3-axis rotation rate sensor is also available, the movement of the vehicle in space can be determined even more precisely. The conversion of

Accelerations in parallel to the road and longitudinal acceleration is thus possible in more detail.

A merger of longitudinal 411 a _x and lateral acceleration a _y 412 is given over the

V 2 2

a + a

i UM nci _{μ lobal} «- calculated. In subprocedure 402, wheel loads 413 are used to view a wheel-individual adhesion utilization from the currently occurring longitudinal and lateral accelerations 411, 412 as well as knowledge of a chassis and suspension system of the respective vehicle. By additional knowledge of a drive and brake system of the respective vehicle can be estimated in each footprint transmitted longitudinal and lateral forces and thus also appreciate a currently exploited at each wheel traction 414. An evaluation of respective wheel speeds 415 provided in sub-method 403 offers diverse potential for the calculation of parameters relevant to frictional engagement. at

Vehicles with single-axis drive can be determined by a comparison of driven to non-driven wheels, a respective slip on the driven wheels. With known driving force and axle load on a rear axle of the vehicle, by forming a quotient of driving force to slip, a longitudinal force stiffness 435 can be determined. If the longitudinal stiffness 435 is lower than in the case of a grippy, dry road surface and the same wheel load, then the respective tire in question will already slip partially. From a currently used traction 440 and a ratio of current longitudinal stiffness 435 to a longitudinal stiffness in handy

Lane can be closed to a maximum available traction 450. Since respective side forces also affect the longitudinal force stiffness 435, this calculation provides reliable values only if the longitudinal acceleration 411 is significantly greater than the lateral acceleration 412. Strong water film thicknesses can also lead to wheel speed fluctuations, which is why these are processed in corresponding process steps, i. Estimation method will be considered.

An EPS tie-rod force 416 can convert at knowledge of a ^¬ axle and steering kinematics in a restoring moment of the front axle of the vehicle in part methods 404th The restoring moment initially increases with increasing lateral force. At a Force utilization of approx. 60% already achieves the restoring moment, however, its maximum.

From a recent vehicle movement can calculate a lateral force on the front axle. From the quotient of restoring moment and lateral force can be calculated with freely rolling wheel a tire trailing distance 417, which consists of a

geometric lag of a respective axle kinetics and the tire return torque composed. Analogous to the evaluation of the slip already described, the current restoring moment is compared with a restoring moment which is achieved on a grip, dry roadway with the same lateral force. Is the current

Return torque under the return torque, which can be achieved on dry, non-skid road with the same lateral force, can be concluded from the currently used traction and a ratio of current restoring torque to restoring torque at grip road to the maximum available traction 450. These calculations are reliable if there are no significant longitudinal forces on the steered front wheels, as when cornering, tire deformation occurs in the tire

In general, a decentral attack resulting longitudinal forces result, creating an additional share of the restoring torque is caused by the longitudinal forces.

When using a 3-axial acceleration and rotation rate sensor, the slip angle and with knowledge of the axle kinematics and elastokinematics and the slip angle can be determined. Analogously to the evaluation of the slip already described, the slip angle can additionally be evaluated.

Sub-method 405 relates to driving through individual road sections with a large water film thickness, wherein a significant increase in a current driving resistance is caused by a surge 420. By increasing the current

Travel resistance slightly decreases the driving speed and a current one

Longitudinal acceleration signal 411 changes abruptly. If at the same time the steering wheel angle changes and "inappropriate" the steering torque, then there is a unilaterally increased water film thickness, which in this context means "unsuitable" Steering torque is not caused by a respective driver of the vehicle but by the roadway, which can be assessed by evaluating the yaw rate 419 and other driving dynamics variables. If, in addition to individual wheels, the wheel speed abruptly decreases or the wheel speed becomes restless, there is already a floating up or short-term rising at the respective wheel. By detecting specific patterns, it is thus possible to be critical to the current water film height

Driving speed are closed. One challenge here is to identify other confounding factors, such as potholes or gusts of wind, which can also lead to wheel speed fluctuations or sudden vehicle deceleration.

The partial methods 406 and 407 have already been described in FIG. 2 and relate to a rain sensor, by means of which, taking into account a travel speed 421, a current amount of precipitation 422 is concluded. Whereas in partial method 407 the tire temperature sensor is used to deduce the energy input into the tires 218 and thereby the presence of a water film 220 in method step 431.

By combining respective partial methods 401 to 407, it is possible to ascertain additional knowledge about, for example, present ambient conditions. Thus, in the presence of the water film 220 by the method step 431 and an inappropriate change of the steering wheel angle, a presence of aquaplaning 430 can be inferred.

Is there an activity state of a vehicle control system, it is in a

Adjustment step 423 uses a determined from the partial methods 401 and 402 adhesion for determining the maximum available adhesion 450. If, on the other hand, no vehicle control system is active, the results from the partial methods 401 and 402 are used to determine the currently used force closure 440. Furthermore, a respective tread depth 433 of the tires of the vehicle has a significant influence on the corresponding measurements necessary for the respective partial methods 402, 403 and 404 and is therefore included in these calculations.

The same applies to a transverse and longitudinal inclination 434, which is taken into account in sub-methods 404 and 406.

Since the various sub-methods 401 to 407 can only provide reliable results in certain driving situations, a confidence factor or characteristic values of the confidence factor is determined for each estimation method as a function of the driving state, as illustrated in FIG.

In this case, respective sub-processes 401 to 407 are assigned corresponding characteristic values 555 to the classified driving situations "straight ahead" 6, "turn" 2, 10 or "transition" 4,8 as shown in FIG. 1, as shown by way of example in tables 520, 530 and 540 , For this purpose, the tables predefined by the described components of the lateral dynamics 20 are further divided according to the driving states of the longitudinal dynamics 22 likewise reported in FIG. 1 into "accelerated" 12, "constant" 14, "motor-braked" 16 and "operationally braked" 18.

The "control active" sub-processes 501, which consist of a merger of the sub-processes 401 and 402, "wheel speeds" 403, "tie rod force" 404, "sound resistance" 405, "rain sensor" 406 and "tire temperature" 407, are assigned a corresponding to the respective driving conditions Characteristic 555 is occupied and for further calculations to

Provided. Correspondingly, for example, the confidence factor or the characteristic value 555 of the sound resistance 405 changes as a function of the driving states "straight ahead" 6, "turn" 2, 10 or "transition" 4, 8, since as a rule already during cornering, due to differences Routes to be covered, which rotate individual wheels at different speeds. Accordingly, detection of aquaplaning 430 during cornering is more difficult than straight ahead driving. According to the driving conditions "Curve" 2, 10 or "transition" 4, 8 assigned lower characteristic values 555. The characteristic values 555 of the respective driving states can be changed dynamically, for example in

Dependence of respective classification results and / or sensor measurements, or by a technician in a programming step, for example, a control unit, be fixed.

The respective confidence factors may, for example, to a very precise and reliable estimate of the maximum available power circuit _max 660 are used with confidence factor of Formula 630, as shown in Figure 6.

The respective characteristic values 555 are calculated, i. E. is added to a respective current total value of the driving characteristics of the

Confidence _factor V _Mges according to formula 630:

⁼ Λ · ν _μΑ + Αη · ν _μΔη + AF ^■ ν _μΑΡ + RS · ν _μΚ8 + RT ^■ ν _μΚΤ . By dividing a result of a sum of multiplications of the partial methods 501, 403, 404, 405, 406, 407 by the characteristic value 555 corresponding to the respective driving state 2, 4, 6, 8, 10, 12, 14, 16 or 18, by the current total value of the confidence factor V tot, the maximum available adhesion 660 _max according to formula 620:

_R _ ^Α · A - ^V VA + μ ^ _μ ^ + AF ■ Ύ _μ ^ + RS ■ - V ^ + RT ■ μ _κτ · ν _μΚΤ . If the current total confidence factor is below a critical value V _Mm i _n , then currently no reliable estimate of the maximum

available adhesion p _max 660 possible and it can be a warning 610 to the driver or corresponding information to ECUs are transmitted. A last estimated maximum available traction will still be considered valid

accepted. If the current total value of the confidence factor V _g to 630 above the critical value V _{\ n} or is identical to this, the maximum available traction M _max 660 valid can be calculated. For a further improvement of the estimate of the maximum available frictional connection max 660 is provided, possibly disturbances according to Figure 3, in the estimation of the maximum available frictional connection

660 record. For this purpose, it is provided that the disturbance variables 309, 315, 317, 318 and 319 are also assigned with driving state-specific 5 characteristic values 555 of a further confidence factor, in accordance with the system described in FIG.

By offsetting the respective characteristic values 555 of the disturbance variables 309, 315, 317, 318, and 319 shown in FIG. 7 with the determined values of the disturbance variables 309, 315,

10 317, 318, and 319, another total value of another confidence factor Vs _ge s can be calculated. If the further total value of the further confidence factor Vs _{ges is} below a critical value Vsmin to be provided previously, then no reliable coefficient of friction or adhesion can be estimated at this point or this driving state due to a lack of information about disturbances and it will be a last one

15 estimated coefficient of friction or maximum available adhesion is still valid

accepted. In this case too, corresponding information can be forwarded to the driver or to control units which indicate that at present no reliable estimation of a current maximum available frictional connection is possible. 0

Claims

claims

A method for determining a coefficient of friction between at least one tire of a vehicle and a roadway, wherein the coefficient of friction is formed as a function of at least one respective, to be classified in advance driving condition of the vehicle and respective environmental conditions to be classified in advance, wherein the coefficient of friction estimated by at least one estimation method is at least one

Estimation method is assigned with at least one characteristic value of a confidence factor.

2. The method of claim 1, wherein the respective driving state of the vehicle is classified by means of a longitudinal, transverse and vertical dynamic state of the vehicle.

3. The method of claim 1 or 2, wherein the respective environmental conditions of the vehicle using at least one sensor from the following list

Sensors are determined: rain sensor, humidity sensor,

Outside temperature sensor, tire temperature sensor, tire vibration sensor,

Radträgerschwingungssensor, sound or structure-borne sound sensors,

Vehicle environment sensors, front-rear camera, driving dynamics sensors.

4. The method of claim 3, wherein, using the at least one sensor, energy dissipating in a respective tire of the vehicle

is converted, and the calculated energy for estimating a height of a possibly present water film on the road in dependence of

Driving speed, is used.

5. The method according to any one of the preceding claims, wherein the at least one estimation method is selected depending on a respective classified driving state.

6. The method according to any one of the preceding claims, wherein the at least one estimation method is selected in dependence of respective classified environmental conditions.

5. The method according to any one of the preceding claims, wherein the coefficient of friction is calculated in dependence on a respective characteristic value of a confidence factor weighted disturbances.

8. The method of claim 7, wherein the disturbance variables are selected from the lo following list of disturbances: longitudinal inclination, bank, crosswind, ruts, different adhesion in left and right lane, control intervention of one

Anti-lock braking system, control intervention of a vehicle dynamics control system.

9. Method according to one of the preceding claims, in which the at least one estimation method is weighted with a respective characteristic value of a confidence factor and a value which results in an estimated maximum adhesion between tire and roadway is calculated from all weighted estimates of respective estimation methods.

10. The method of claim 9, wherein the respective confidence factors respective

Estimation method are calculated and the value thus calculated is compared with a previously provided minimum value and falls below the minimum value by the calculated value generates a message that says that currently no reliable estimate of the maximum available adhesion is possible.

25

11. The method according to claim 10, in which the further confidence factor is compared with the value to be provided in advance, and when the value to be provided by the confidence factor falls below the last estimated maximum available value

Adhesion is assumed to be still valid.

30

12. The method according to any one of the preceding claims, wherein the respective characteristic values of the at least one confidence factor are defined by a fixed size.

13. The method according to any one of the preceding claims, wherein the respective characteristic values of the at least one confidence factor are formed as a function of a respective driving state.

14. The method of claim 1, wherein the at least one estimation method is selected from the following list of estimation methods: a) calculation of a global adhesion between at least one tire and the roadway by means of a measured longitudinal and lateral acceleration, b) calculation of respective wheel loads by the currently occurring longitudinal and

C) estimating respective longitudinal and lateral forces through knowledge of the use of a calculation according to a) and b) and knowledge of a drive and control system of the respective vehicle, d) determining a tire longitudinal stiffness or an equivalent quantity by forming a quotient of tire longitudinal force and longitudinal tire slip,

e) Determining a tire transverse stiffness or an equivalent size by forming a quotient of tire lateral force and transverse tire slip, f) determining a total tire stiffness or an equivalent size by forming a quotient of tire force and tire slip by means of

Preset torque to be specified in grip-free, dry carriageway,

I) determining a water film thickness on the roadway by determining various patterns of a longitudinal acceleration signal and a steering wheel angle in relation to a steering torque and a wheel speed, m) determining the friction coefficient by using distance-related data stored in an on-board database and comprising descriptive sizes of the roadway , and o) determining the coefficient of friction by using data from communication with off-board sources or external data servers.

15. A device for controlling a driving stability of a vehicle having at least one arithmetic unit which is adapted to receive at least one previously provided characteristic value of a confidence factor in respective calculations of a friction coefficient for controlling the driving stability and a respective driver of the vehicle and / or other vehicle dynamics control systems on the current Friction value between at least one tire of the vehicle and a roadway are to inform and by means of communication device other vehicles and or data server on the coefficient of friction or power transmission or to determine the same required parameters in order to control the behavior of the other vehicle and / or information make the driver there.