EP1049612A1

EP1049612A1 - Method and device for determining the adhesion and adhesion limit for vehicle tyres

Info

Publication number: EP1049612A1
Application number: EP99958150A
Authority: EP
Inventors: Rolf Gnadler; Hans-Joachim Unrau
Original assignee: DaimlerChrysler AG
Current assignee: Mercedes Benz Group AG
Priority date: 1998-12-01
Filing date: 1999-12-01
Publication date: 2000-11-08
Also published as: WO2000032456A1; DE19855332A1

Abstract

The invention relates to a method and a device for determining the adhesion and/or the adhesion limit for a tyre of a vehicle. The data from the driving dynamics sensors are analysed with a driving dynamics simulation model and the analysis of the data from the roadway sensors takes the tyre characteristics into account, these being adapted to the current tyre behaviour during operation. The information from the roadway sensors is preferably analysed using a bound method in order to isolate the state of the roadway.

Description

Method and device for determining the adhesion and adhesion limit in vehicle tires

The invention relates to a method and a device for determining the adhesion and / or the adhesion limit of a tire of a moving vehicle. The driving state of the vehicle is measured by means of a plurality of driving dynamics sensors, and the state of the road is determined by means of at least one road sensor that detects the state of the road. Furthermore, a computer is provided for evaluating the data of the driving dynamics sensors and the roadway sensor, which uses a driving dynamics simulation model to determine the kinematic state of the wheel and the frictional engagement or, taking into account at least one stored tire map with tire characteristics, the traction limit.

If a vehicle equipped with tires is in a normal driving state with comparatively low longitudinal and lateral acceleration values, i.e. not in the area of the driving limit, no reliable statements can yet be made about the adhesion and the adhesion limit of tires or wheels, axles or the vehicle become. It is largely uncertain how large they are Traction reserves are, ie the "distance" between the current horizontal forces (circumferential forces and lateral forces) between the tire and the road (the traction) and the maximum transferable forces (the traction limit).

An estimate of the adhesion and the adhesion limit in a normal driving condition with comparatively low longitudinal and transverse acceleration values in series vehicles has so far only been possible qualitatively and only very roughly based on the experience of the driver. For this purpose, the driver can perceive, for example, that the roadway is wet and, based on his experience, emotionally assume a decrease in the adhesion limit compared to the dry roadway. However, this is only partially successful, which shows the increase in the frequency of accidents on wet roads. In a series production vehicle, there has so far been no possibility of quantitatively determining the adhesion and the adhesion limit at low longitudinal and lateral accelerations.

Also when approaching the driving limit, i.e. the adhesion limit, with comparatively higher longitudinal and lateral acceleration values, so far no reliable information about the adhesion and the adhesion limit can be given. In series vehicles, systems such as ABS, ASR or ESP are known that detect when the vehicle reaches a traction limit or a dynamic driving limit. However, the adhesion and the adhesion limit are neither determined while the vehicle is in a normal driving state, nor when it approaches the driving limit.

In the literature reference H.-J. Görich, system for determining the current adhesion potential of a car in the Driving operation, progress reports VDI series 12, no. 181, VDI-Verlag 1993, Düsseldorf, a system was proposed which in many cases enables an estimation of the adhesion and the adhesion limit. Driving dynamics sensors provide information about the driving condition. Furthermore, roadway sensors, each of which is exclusively responsible for a specific roadway, provide information about the roadway condition. In addition, extensive tire map measurements are required for different road conditions. With the help of a simple, not particularly fast vehicle computing model and a vehicle computer that does not allow operation in real time, the current driving condition, ie the adhesion of the axles and the vehicle, is compared with the determined adhesion limit of the vehicle. The results for the vehicle are graphically displayed on a screen in the vehicle.

Although the known system provides information on the adhesion and the adhesion limit of the vehicle, it has various disadvantages.

One disadvantage is that extensive tire maps with a large number of tire curves are required for all conceivable driving conditions and road conditions. These tire characteristics are assumed to be unchangeable. With a decreasing tread depth during the operating life of the vehicle, for example, this leads to the results being inaccurate.

In addition, the road conditions are only roughly divided into three groups, namely dry, wet and winter smooth. The tire maps are assumed to be constant within a group. This also leads to sometimes very inaccurate results, as is known is that in reality, for example, the water level on wet roads has a big impact. Another disadvantage is that the adhesion is determined only axially and the adhesion and the adhesion limit for the vehicle. This also leads to inaccuracies in the determination, especially if the wheels roll on different road surfaces. So there is no possibility to calculate the adhesion for each individual wheel separately.

In the literature reference Th. Dieckmann, a novel approach to determining the adhesion conditions in tire / road contact, tires, chassis, road, conference report of the VDI-Gesellschaft Fahrzeugtechnik, No. 916, VDI-Verlag, 1991, Düsseldorf, as well as in the document DE 3705983 AI ("Device for monitoring the degree of utilization of the existing road surface friction value when braking and / or accelerating a motor vehicle") proposes a method in which the initial slope of the circumferential force-slip curves of the wheels allows conclusions to be drawn about the maximum values of the transmissible ones Circumferential forces are drawn and from this the conclusion is drawn about the adhesion and the adhesion limit of the entire vehicle. This principle is relatively imprecise and has the following disadvantages.

On the one hand, only the peripheral force properties of the tires are taken into account, so that only limited conclusions can be drawn about the lateral force properties.

Furthermore, it has been shown that a sufficiently significant change in the initial slope is not discernible in all practical cases. For example, when changing from dry to wet roads with small and medium water levels, there is a large one Difference between the adhesion limits possible, whereas the initial gradients differ only very slightly.

It is also known that the initial slope of the circumferential force-slip curves depends not only on the condition of the road surface, but also on the properties of the tires, which change, for example, as the tread depth decreases. Since the stored characteristic curves are fixed and do not take into account changes in the tire properties during the operating period, the current gradient cannot be reliably determined from the initial gradient.

Document DE 4338587 C2 ("Method for Estimating the Gripping Behavior of a Road Surface Compared to the Wheels of a Motor Vehicle Driving Over It") proposes to measure the torque of the drive wheels and the rotational speed of all wheels. The wheel load acting on the drive wheels is also estimated. When the drive wheels reach certain circumferential slip values and approach the adhesion limit, the current adhesion of the wheels is equated with the current adhesion limit of the wheels. This is stored in a memory as an instantaneous but temporary estimate. This stored estimated value is updated as soon as certain conditions are present, for example when a driving condition with high circumferential slip values is reached again in which the wheels have a different frictional connection. In this way, the adhesion and the adhesion limit of wheels are determined, and it can be concluded on the adhesion and the adhesion limit of the vehicle. However, this proposed principle has the disadvantage that a sufficiently precise estimate is only possible if the vehicle comes close to the driving limit. No determination can be made in normal driving conditions.

Furthermore, the stored adhesion limits can only be updated if certain criteria, for example high circumferential slip values, are met. Since this is only the case in rare driving conditions, the stored values cannot be updated permanently and therefore reliably despite the permanent operation of the system.

Furthermore, it is provided according to this document to measure the torque that is present at the drive wheels. This measurement is relatively complex and must work equally well when braking as well as accelerating. In addition, only the adhesion limit of the tires is estimated, without information about the course of the complete tire characteristic being provided.

Systems have also become known that have been investigated as part of research projects. They either only allow qualitative statements about the adhesion and the adhesion limit or require complex sensors to detect the condition of the road, which are unsuitable for practical use or would cause unacceptably high costs if used in series production.

Proceeding from this prior art, the object on which the invention is based is to create a method and a device with which in good Approximation of the current adhesion and / or the current adhesion limit of a tire or axles of a moving vehicle can be determined in as many driving conditions as possible, that is to say even with comparatively low longitudinal and lateral acceleration values. The current adhesion limit should therefore be able to be determined long before it is reached. Furthermore, it is desirable if the associated tire maps can be provided comparatively inexpensively.

The invention is thus intended to provide reliable and accurate information about the current adhesion or the current adhesion limit in the least possible manner. This information can then be made available to the driver, for example, or forwarded to a system that intervenes in a driving or braking process.

To achieve this object in a method or a device of the type described in the introduction, it is provided according to the invention that the tire characteristics (for different road conditions and for example for different wheel loads) are adapted to the current tire behavior starting from an initial set of basic tire characteristics in the course of the operating time become.

In the method according to the invention, the current frictional connection, in particular the circumferential and lateral forces, and the kinematic state of the wheel, in particular circumferential slip and slip angle, are continuously calculated with the aid of the computer, the driving dynamics simulation model and the signals from the driving dynamics sensors. Furthermore, the current adhesion limit is determined by first performing a lane recognition and then belonging to a tire map memory Tire characteristics (for example for different wheel loads) are selected and finally the current adhesion limit is determined after an adjustment of the tire characteristics.

With this method, the driving dynamics sensors provide measurement data about the kinematic state of the vehicle and possibly about the forces or moments acting on the vehicle. They serve as input variables for the calculation calculations of the computer by means of the driving dynamics simulation model. The simulation calculations provide the current adhesion and the kinematic state of the wheels as output variables. These values represent output data from the system and can also be used to determine the current adhesion limit.

The present road condition (for example dry, wet, snow, etc.) can in principle be determined in a manner known per se using one or more road sensors. However, a disadvantage here is that the decision as to which road condition is present depends in each case on the correct and reliable function of a specific, special sensor for the respective road condition or on a specific evaluation size. If a sensor malfunctions or the evaluation size is incorrect, the corresponding lane can no longer be identified.

In order to ensure the accuracy of the determination, the road condition should be recognized precisely and safely. For this purpose, according to a preferred additional feature, it is proposed that the roadway condition be determined by means of several different roadway sensors, the information derived from their signals being used by means of a barrier method to limit the roadway access. Stands are evaluated. In addition to the information about the condition of the roadway, which are determined by the roadway sensors, results of the driving dynamics simulation calculation can also be evaluated in the barrier method. For example, information that can be taken into account in the barrier method can be the initial slope of the actually present adhesion curve, which can be determined using the vehicle dynamics simulation calculation.

In the barrier method, a large number of different types of information are superimposed so that certain road conditions can be excluded on the basis of existing combinations of sensor signals or other information, so that the correct road condition is finally identified as a result of the logical combination of the information present. This should not be confused with a system of a redundant arrangement of roadway sensors, in which several different sensors are intended to sense the same roadway condition independently of one another. In the case of the barrier method which is advantageously used, various information is collected, the combination of this information being used to infer the state of the roadway.

If the road condition was determined, for example, using the barrier method, the associated tire map (with characteristic curves for, for example, different wheel loads) or the associated tire characteristic curve can be selected from a tire map memory. The selection can be supported by information from the vehicle dynamics sensors. When a device according to the invention is started up for the first time, a basic tire map that has an initial set of basic tire characteristics is used contains, which are stored in the computer for a few different tire-road combinations.

These basic tire characteristics are adapted to the current tire behavior in the course of the vehicle's operating time by correcting the individual characteristics. This is possible because the system is designed in such a way that it recognizes a change in the adhesion behavior due to a change in the tire properties, for example due to a change in the tread height, during the operating time in that in this case the current adhesion and the kinematic Condition of the wheels does not match the selected map or the selected characteristic curve. The correction can be repeated for each new deviation found.

The tire characteristic curves can therefore preferably be adapted if, on the basis of a comparison of the results of the driving dynamics simulation model and the determination of the roadway condition, a deviation of the current force closure in the present kinematic state of the wheel from the selected tire characteristic curve is recognized.

The basic tire maps or the tire maps preferably contain only a small total number of tire curves (for different road conditions and, for example, different wheel loads) to be taken into account in the driving dynamics simulation calculation, preferably less than 40, particularly preferably less than 20 tire curves. According to an additional advantageous feature, however, it can be provided that one or more tire maps are expanded in the course of the operating time by tire curves for other road conditions that were not included in the basic tire maps and are have proven to be appropriate. In this respect, the system can be capable of learning and can be designed adaptively.

If both the current road surface condition is identified and the associated tire characteristic is selected by the system and adapted to the current tire behavior, the adhesion limit can be determined before it is reached. With the aid of the method according to the invention, the adhesion and the adhesion limit can thus be determined more precisely than was previously possible. An advantage of the preferred barrier method is that the road condition can be recognized more reliably, with redundant detection being possible.

It is also advantageous in a preferred embodiment of the invention that a change in the adhesion behavior can be detected, which is caused by a change in the tire properties, for example by the changed profile height, in the course of the operating time. In addition, only a few basic tire maps or basic tire characteristics are required, which can be adapted and, if necessary, expanded over the course of the operating time.

According to a further advantageous feature, it is proposed that the driving dynamics simulation model is a real-time model, by means of which the computer calculates the current kinematic state of the wheel and / or the current adhesion and / or the current adhesion limit of the wheel in real time. Such a driving dynamics simulation model, which works in real time, can be created, for example, with fast, compact differential equations using knowledge of the dynamic behavior of the vehicle in question. If the driving dynamics simulation model used is specifically designed for real time, the current frictional connection calculated in real time with this model and the kinematic state of the wheels can be used in a favorable manner as an input variable for a mechatronic control system that intervenes in a regulating manner in driving behavior. If the current adhesion is calculated separately for each wheel, the results can be used, for example, for an optimized driving dynamics control, which can better guarantee the stability of the vehicle in critical driving situations.

This data can also be used advantageously by mechatronic control systems by determining the adhesion limit in real time. For example, in this case. a mechatronic brake system can react faster to changing road grip when braking hard. If the adhesion limit for each wheel is determined individually, a different grip for the wheels of an axle can be taken into account when initiating a braking operation.

The determination of the adhesion and / or the adhesion limit is therefore preferably carried out separately for the individual wheels of the vehicle or the wheels of an axle, since this enables the kinematic state and critical driving behavior to be recognized more precisely. This is a favorable prerequisite for a system that, for example, issues a warning to the driver or intervenes in driving behavior. By determining the adhesion limit separately for individual wheels, it can be more precisely estimated whether critical adhesion behavior of the vehicle can be expected due to different adhesion limits on the individual wheels if the vehicle is approaching the driving limit. In this case, the driver can be warned, for example, at a greater distance before the driving limit is reached. In the case of an individual calculation or evaluation of the wheels of an axle, it can also be recognized and taken into account if the wheels have different coefficients of friction, for example due to different road conditions.

In some embodiments, however, it can also be advantageous if the determination of the adhesion and / or the adhesion limit is carried out axially, the wheels of an axle being treated identically, or if the adhesion and / or adhesion limits of all wheels are used to determine the adhesion and / or the adhesion limit of the entire vehicle is determined. The calculation of the adhesion or the adhesion limit of the entire vehicle is suitable for describing the driving state or the driving limit of the vehicle in a simple and clear manner. With a suitable representation of the adhesion or the adhesion limit, for example, the driver can be informed while driving.

In the context of the present invention, it has surprisingly been found that the extraordinarily difficult requirements can be solved with a sufficiently precise determination of the adhesion or the adhesion limit of a tire with relatively little effort without, as previously thought necessary, a high technical effort to provide a large number of tire maps or lines or to determine the condition of the road is required. The invention thus achieves goals which the professional community has long sought. In order to achieve particularly good results, the features explained above and the features of the following exemplary embodiments are advantageously used individually or in combination with one another, whereby the advantageous effects of the interaction of the features of the invention can result.

The invention is explained in more detail below on the basis of exemplary embodiments schematically illustrated in the figures, which reveal further features and special features.

Show it:

1 is a process diagram for the detection of adhesion and adhesion limit,

2 shows a barrier method for determining the state of the road,

Fig. 3 shows a tire map with five tire characteristics and

Fig. 4 is a highly accurate adjustment of a tire characteristic.

With regard to the meaning of the terms used in this application text, reference is also made to the following literature: DIN 70000; DIN 44300; J. Reimpell- K. Hoseus, chassis technology: vehicle mechanics, Vogel Buchverlag 1992; A. Zo otor, chassis technology: driving behavior, Vogel Buchverlag 1991. The terms mentioned in these literature references may differ slightly from each other, but can easily be assigned by a person skilled in the art.

1 shows a flow chart for a more detailed explanation of the mode of operation of a system according to the invention for agree the adhesion and the adhesion limit for each individual wheel of a vehicle. "Force engagement" is understood to mean the resultant from circumferential and lateral force that acts on the wheel, ie the force engagement is described by two forces or their resultants. The "adhesion limit" is understood to mean the maximum possible circumferential and lateral force that can be transmitted in the current driving condition and on the current road surface. The adhesion limit is thus described by two forces.

The circumferential force is the component of the ground reaction force in the direction of the X _w ~ axis (DIN 70000), ie clearly the force (driving or braking force) in the longitudinal direction of the wheel, in the center plane of the rim and in the level of the road surface. The lateral force is the component of the ground reaction force in the direction of the Y _w axis (DIN 70000), that is to say the force transverse to the wheel, perpendicular to the longitudinal direction of the wheel in the roadway plane.

The system shown schematically in Fig. 1 performs the processing of two main tasks. In the left area of the flow diagram, system components are shown that are used to calculate the current adhesion. The system components on the right are used to determine the current adhesion limit before this limit is reached. However, the determination of the adhesion limit is not independent of the determination of the adhesion. There is a data exchange from the left area to the right.

The system comprises two groups of sensors. One group comprises driving dynamics sensors 1, which provide data on the driving dynamics of the vehicle. The other Group comprises roadway sensors 2, which provide data about the roadway condition.

The driving dynamics sensors 1, some of which may already be standard in the motor vehicle, provide, for example, measurement data about the longitudinal acceleration of the vehicle, the lateral acceleration, the roll angle, the pitch angle, the yaw angle, the rotational speeds of the individual wheels and the wheel loads of the individual wheels.

It is also possible not to measure individual quantities directly, but to determine them indirectly. In general, vehicle dynamics variables derived from data measured by means of the vehicle dynamics sensors can also be taken into account in the method. For example, the yaw angle can be determined by integrating the measured yaw angular velocity or the wheel load cannot be measured, but can be determined indirectly by measuring the deflection of the wheels with respect to the body. For example, the measurement of the wheel loads of the wheels of an axle can also be replaced by a measurement of the axle load, which is distributed to the individual wheels with the aid of data from the driving dynamics sensors 1, in particular the roll angle.

The measurement of the wheel loads can also be replaced, for example, by determining the total weight. The total weight can be determined, for example, by measuring the drive torques and using the measurement signals of the acceleration sensor in the longitudinal direction. In this case, the distribution of the axle loads and, in particular of the roll angle, the distribution of the individual wheel loads can be carried out using data from the vehicle dynamics sensors 1, in particular the pitch angle. The data from the vehicle dynamics sensors 1 and any variables derived indirectly therefrom are forwarded to the vehicle dynamics simulation model 3, which is advantageously operated in real time. Real-time systems are characterized in that they can process external events within a specified time and thus fulfill the external time conditions (DIN 44300). This means that in real-time simulation the calculated dynamic phenomenon corresponds to the phenomenon that occurred in reality at all times. There is no significant time delay between the behavior of the real-time system and the behavior of the real system.

With the help of the driving dynamics simulation model 3, the circumferential forces currently acting on the individual wheels, the circumferential slip values, the lateral forces and the slip angle are calculated. "Circumferential slip" is understood to mean the size S _{χ w} according to DIN 70000, which clearly describes the slip between the tire and the road surface that occurs when braking or driving, since the wheel rotates slower when braking at the same driving speed and faster when driving than in free rolling condition. According to DIN 70000, the slip angle is the angle from the X _w ~ axis to the tangent of the trajectory of the wheel contact point and clearly describes the angle between the longitudinal direction of the wheel and the direction of the wheel center speed.

The driving dynamics simulation model 3 supplies the current adhesion 4 of the individual wheels as the output variable. The output data of the driving dynamics simulation model 3 including the variables longitudinal acceleration, lateral acceleration, roll angle, pitch angle, yaw angle, wheel speeds and wheel loads also become components Lane detection 5 and characteristic curve adjustment 6 forwarded.

The roadway sensors 2, for example, provide data about the roadway temperature and / or about the roadway state, for example by means of optical or acoustic methods. Sensors can also be used which only make a yes / no statement, for example whether the roadway is dry or not.

The data from the roadway sensors 2 are processed by the roadway recognition 5, which also receives results of the calculations of the driving dynamics simulation model 3. These calculation results are used for road surface recognition if the current operating points in the tire characteristic curve are in the linear range of the circumferential force slip and lateral force slip angle curves, i.e. when the vehicle is traveling with comparatively low longitudinal and lateral accelerations. In this case, the initial slope of the circumferential force slip and / or the lateral force slip angle characteristic curve can be determined with the current operating points. In DIN 70000, the gradient of the circumferential force-slip curve is referred to as the circumferential force / circumferential slip gradient. The initial slope of the circumferential force-slip curve is equivalent to the circumferential force / circumferential slip gradient at the circumferential force 0.

These initial gradients as well as data about the road temperature and the road condition are thus available for determining the road condition by means of optical or acoustic methods. With the help of a barrier method, the road condition can now be recognized. Since there is at least partial redundancy when the roadway condition is recognized, in some cases perform a plausibility check. If, for example, a high water level is detected due to the optical or acoustic methods, very low road surface temperatures must not be present at the same time. If this should nevertheless be the case, it can be concluded that the lane recognition is incorrect and the system is switched off. Alternatively, there is also the option of giving priority to certain signals so that the system remains active and only outputs an error message.

If the lane recognition 5 works correctly, the determined road condition, preferably separated for the individual wheels, is forwarded to a map memory 7. The map memory 7 also receives information from the vehicle dynamics sensors 1, in particular about the wheel load of the wheel for the selection of the appropriate tire characteristic.

In order to increase the accuracy, further parameters can be taken into account, such as the influence of the camber angle. Since this is generally not measured in vehicles, a substitute dependency on a measured variable or on a combination of measured variables, for example wheel load and lateral acceleration, can be used. Finally, with the information from the lane recognition 5 and the driving dynamics sensors 1, a suitable tire map (for example for different wheel loads) and a suitable tire map, preferably for each individual wheel, are selected.

The selected tire characteristic curve (or a tire characteristic diagram) is forwarded to the characteristic curve adaptation 6. Since the characteristic curve adaptation 6 also the output data of the driving nik simulation model 3, it can be checked whether the current adhesion 4 and the kinematic state of the individual wheels match the selected tire characteristic. If this is not the case, the tire characteristic curve or the tire characteristic diagram is corrected by adapting individual characteristic curves that are stored in the characteristic diagram memory 7.

However, the adaptation does not have to be limited to the selected tire characteristic curve 10, but when adapting a tire characteristic curve one or more further tire characteristic curves of one or more tire characteristic diagrams 9 can also be adapted accordingly. The adaptation of further, so to speak "adjacent" tire characteristics can be carried out, for example, on the basis of theoretical or empirical knowledge of tire characteristics.

The reason for this correction or adaptation can include that the tire properties have changed over the course of the operating time, for example due to a decreasing tread depth. A change in tire properties due to a tire change is also recognized and corrected by the simulation calculation. In this case, if the current frictional connection 4 deviates from the selected tire characteristic curve, the characteristic curve can be performed approximately precisely and in the vicinity of the driving limit in normal driving conditions, which is explained in connection with FIG. 4.

The characteristic curve adaptation 6 outputs corrected or adapted tire characteristic curves for the wheels, which are also returned to the map memory 7 for storage. Since the adhesion limit 8 is described by the maximum values of the individual tire characteristics, it is approximately known when the driving is in a normal driving state. If the accuracy of the characteristic curve adaptation is increased when the vehicle approaches the driving limit, the adhesion limit in the border area is known more precisely.

2 shows a table for a more detailed explanation of the procedure for lane detection 5 with the aid of a barrier method. In a barrier method, the state of the road is not measured precisely, but is limited using various information. For this purpose, information is collected that allows conclusions to be drawn about the condition of the road. The more information is available, the more precisely the road condition can be determined. With the evaluation of a single piece of information, the road condition can initially only be narrowed very roughly. If additional information is also evaluated, the narrowing down becomes more and more precise, even if the individual pieces of information, taken alone, only allow a rough narrowing down.

On the left-hand side in FIG. 2, line-by-line information about the state of the roadway is listed, which can originate from roadway sensors 2 or from the evaluation of the calculation with the driving dynamics simulation model 3. They preferably include at least three of the following types: air temperature, road temperature, optical or acoustic detection of snow, optical or acoustic detection of ice, optical or acoustic detection of water or optical or acoustic detection of a dry road. The respective information can be present, for example, as an analog measured variable, digital information (yes / no) or as qualitative information (high, medium, low). Various columns of roadway states are given in the columns, which are assumed to be unknown and are to be determined by roadway recognition 5. These road conditions can preferably include three or more of the following road conditions: dry, damp, wet, low water level, high water level, snow, ice, loose ground.

If, for example, the roadway temperature measurement provides the information "very low temperature" and the roadway sensor for detecting snow and ice supplies a positive signal and the evaluation of the initial gradient of the circumferential force-slip curve shows that there is a flat initial gradient, only one snow-covered lane. This result is achieved even though no lane sensor 2 is used that specifically only recognizes the snow-covered lane. Furthermore, this barrier system is redundant to a certain extent, since at least some of the results can be checked easily. If, for example, the sensor for determining the road temperature fails in the example described, the snow-covered road can still be identified using the two remaining pieces of information.

3 shows an example of a tire map 9 which contains a plurality of tire curves 10 for different road conditions. A tire characteristic curve 10 is a curve in the tire characteristic diagram 9, in which the peripheral force U as a function of the slip s or the lateral force as a function of the slip angle can be represented. A tire map 9 is generally a diagram in which a plurality of tire curves 10 are shown for different parameters. For example, circumferential force slip or lateral force slip angle Curves for different wheel loads can be shown, all other parameters being kept constant. A further possibility is, for example, as in FIG. 3, circumferential force slip curves for different road surfaces.

In the context of the invention, the road condition and / or the wheel load are preferably taken into account as parameters of the tire characteristic 10 or the tire characteristic 9. Further or other advantageous parameters can be, for example, the lateral acceleration, the longitudinal acceleration, the wheel speed or the camber angle.

When the system is started up for the first time or, for example, after a desired reset to initial values, the tire maps 9 advantageously contain a basic set of characteristic curves 10 which does not yet cover all conceivable parameter combinations. The basic tire characteristic curves form a basic tire characteristic map, in which tire characteristic curves, for example for a few road conditions and / or wheel loads, are stored in a simplified, general manner. When commissioning for the first time, only a few basic tire characteristics can be saved for a few different tire-road combinations. These characteristics apply to an average tire and do not exactly reflect the behavior of the tire that is actually installed. The exact behavior depends, among other things. tire type, tread condition, tire pressure and other parameters.

The basic characteristic curve fields are sufficient, since in the system according to the invention the stored characteristic curves 10 are corrected or adapted. The road condition is taken into account. Furthermore, the tire characteristics 9 can advantageously also be extended by more Tire characteristics 10 are expanded. In this case, missing parameter combinations can initially be covered by interpolation, which are replaced by own tire characteristics 10 during the operating life of the vehicle.

It can advantageously be provided that the tire characteristics 9 comprise at least three basic tire characteristics or tire characteristics 10 for the following road conditions: dry, damp, wet, low water level, high water level, snow, ice, loose ground. The influence of the wheel load and the interaction between circumferential and lateral forces can be taken into account, for example, based on experience.

Since the actual behavior of a tire does not exactly match the behavior described by the basic characteristic curves, the tire characteristic curves 10 and thus also the tire characteristic diagrams 9 are adapted during driving operation, a change in the tire behavior, for example due to wear, also being taken into account. As long as normal operating conditions with comparatively low longitudinal and lateral accelerations with comparatively small circumferential force slip and slip angle values are present, an approximate adaptation of the tire characteristics 10 can take place as soon as a deviation of the current frictional connection (in the case of a present kinematic state of the wheel) from that selected tire characteristic curve is determined, and thus an approximate determination of the adhesion limit 8 can be carried out. This is possible, although the exact course of the actual tire characteristic curve 10 is not yet known in the area of large circumferential force slip and slip angle values, ie with comparatively high circumferential and / or lateral forces. FIG. 4 shows how, according to a particularly advantageous feature of the invention, the adaptation of the tire characteristic curves 10 or the determination of the adhesion limit 8, 8a is carried out precisely in the area of the driving limit of the vehicle. This highly precise adjustment takes place as soon as the vehicle approaches the driving limit and the current adhesion 4 and the kinematic state of the wheels may no longer match the selected tire characteristic curve 10. As a result, the calculation of the adhesion limit 8 becomes more precise the closer the vehicle approaches the driving limit.

The tire characteristic curve 10 can generally be adapted as soon as there are deviations between the calculated, current operating point 11 and the tire characteristic curve 10 originally selected from the map memory 7. The operating point 11 describes the driving state of a vehicle or a tire, to which a specific circumferential force U, a specific circumferential slip s, a specific lateral force and a specific slip angle can be assigned. The position of the operating point in a tire map 9 or on a tire curve 10 is not necessarily determined in the context of the invention by direct, direct measurement of the circumferential force U and slip s or lateral force and slip angle, but the variables mentioned are derived from the driving dynamics simulation model 3 calculated back, the selection of the tire characteristic curve 10 including the road surface recognition 5.

The initial region 12 of the tire characteristic curve 10 can be regarded approximately as linear to a large extent. Especially in the initial area, the adjustment of the Tire characteristic 10 or the determination of the adhesion limit approximate.

At higher slip values, i.e. on the other hand, in the vicinity of the approximately applicable adhesion limit 8a, which is determined by the maximum value of the selected tire characteristic curve 10, the selected characteristic curve 10 leaves the linear range. A deviation of the selected characteristic curve 10 from the actually valid characteristic curve 14, from which the actual adhesion limit 8 can be determined, can also be determined in this area by the fact that the operating point 11 is not on the selected tire characteristic curve 10, but differs therefrom. In the non-linear case, this is the case for operating points 11 which lie above the deviation point 13.

The deviation point 13 is the point on the selected tire characteristic 10, from which the actually valid tire characteristic deviates from the selected tire characteristic 10 or from a linear course in the direction of increasing slip or slip angle values. The area from which the operating point 11 deviates from the tire characteristic curve 10 or from a linear course is shown in FIG. 4 by an arrow pointing upwards.

As soon as the operating point 11 is no longer on the selected tire characteristic curve 10, the selected tire characteristic curve 10 is corrected, so that a new corrected tire characteristic curve 14 results. This adapted tire characteristic curve 14 then deviates, for example, from the originally selected characteristic curve 10 likewise from the deviation point 13. The adjustment can be made approximately in the linear starting area. The detection of a deviation combined with an exact Adaptation of the tire characteristic curve or determination of the adhesion limit is preferably possible if the linear initial range 12 is exceeded. The exact adaptation of the tire characteristic curve or determination of the adhesion limit are not only possible in the immediate vicinity of the adhesion limit, but also relatively early in the wider area of the adhesion limit.

A deviation of the operating point 11 from the selected tire characteristic curve 10 or a deviation of the tire characteristic curve 10 from the linear starting area can be used for a sliding correction of the characteristic curve, any deviation being used for a correction. In some embodiments, however, it can also be expedient if a correction is only carried out when the deviation exceeds a certain threshold value.

The selected tire characteristic curve 10 can be adapted to a corrected tire characteristic curve 14 upon detection of a deviation, which can be carried out, for example, by means of the theoretical or empirical knowledge of adjacent tire characteristic curves or the basic behavior of vehicle tires. Since the adaptation of the tire characteristic curve 10 to a corrected tire characteristic curve 14 can take place more precisely, in particular when the vehicle approaches the driving limit, the accuracy of the determination of the adhesion limit 8 in the area of the adhesion limit 8 or the driving limit is increased.

In this way, an approximate adjustment of the tire characteristics in operating situations with comparatively low longitudinal and lateral accelerations and an exact adjustment of the tire characteristics is possible with every approach to the driving limit, regardless of whether the driving situation is critical or not. With normal driving operation, there is a permanent, approximate estimate of the current adhesion limit. If the vehicle approaches the limit area, the determination of the current adhesion limit becomes more precise. This means that precise data is available as soon as an exact intervention in driving behavior is required.

With the invention, reliable and accurate information about the current adhesion and the current adhesion limit is given before the adhesion limit is reached. It is particularly advantageous that not only the current adhesion limit, but also the course of the valid tire characteristic curve is present in order to enable extrapolations of the vehicle behavior as well as optimal control quality in the event of a vehicle control.

Reference list

1 driving dynamics sensor

2 lane sensor

3 Driving dynamics simulation model

4 adhesion

5 lane recognition

6 characteristic curve adjustment

7 map memory

8 adhesion limit

8a adhesion limit of the uncorrected tire characteristic

9 Tire map

10 tire characteristic

11 operating point

12 initial area

13 deviation point

14 corrected tire characteristic

U circumferential force s slip

Claims

claims

Method for determining the adhesion (4) and / or the adhesion limit (8) of a tire of a moving vehicle, comprising measuring the driving state of the vehicle by means of several driving dynamics sensors (1), determining the state of the road by means of at least one road sensor that detects the state of the road ( 2) and evaluating the data from the driving dynamics sensors (1) and the roadway sensor (2), a computer using a driving dynamics simulation model (3) to determine the kinematic state of the wheel and the frictional connection (4) or taking into account at least one stored tire map ( be adapted to the current tire behavior 9) determined by the tire characteristics (10), the adhesion limit (8), characterized in _/ that the tire characteristic curves (10) operating time, starting from an initial set of base tire characteristic curves in the course of loading.

Method according to Claim 1, characterized in that the tire characteristic curves (10) are adjusted when a deviation from a tire characteristic curve (10) is detected on the basis of a comparison of the results of the driving dynamics simulation model (3) and the determination of the road condition.

3. The method according to claim 1 or 2, characterized in that the road condition is determined by means of several, different road sensors (2), the information derived from their signals being evaluated by means of a barrier method to limit the road condition.

4. The method according to any one of the preceding claims, characterized in that the roadway sensors (2) comprise at least three of the following types: air temperature, roadway temperature, optical or acoustic detection of snow or ice or water or dry roadway.

5. The method according to any one of the preceding claims, characterized in that the tire map (9) tire characteristics (10) in the form of peripheral force, slip and / or lateral force slip angle curves for certain road conditions and / or for different wheel loads.

6. The method according to any one of the preceding claims, characterized in that the tire map (9) comprises at least three basic tire characteristics or tire characteristics (10) for the following road conditions: dry, damp, wet, low water level, high water level, snow, ice, loose underground.

7. The method according to any one of the preceding claims, characterized in that the tire characteristics (9) only a small total number of tire characteristics (10), preferably less than 40, particularly preferably less than 20 tire characteristics for determining the Include adhesion (4) or the adhesion limit (8).

8. The method according to any one of the preceding claims, characterized in that a tire map (9) is expanded in the course of the operating time by tire characteristics (10) for further road conditions.

9. The method according to any one of the preceding claims, characterized in that when adjusting a tire characteristic (10) one or more further tire characteristics of one or more tire characteristics (9) are adjusted accordingly.

10. The method according to any one of the preceding claims, characterized in that the barrier method takes into account information from the vehicle dynamics simulation calculation.

11. The method according to any one of the preceding claims, characterized in that the barrier method takes into account the initial slope of the adhesion curve.

12. The method according to any one of the preceding claims, characterized in that the adaptation of the tire characteristics (10) in the area of normal operating conditions of the vehicle is carried out approximately and in the area of the driving limit exactly.

13. The method according to any one of the preceding claims, characterized in that the determination of the adhesion limit (8) in the area of normal operating conditions of the vehicle is carried out approximately and precisely in the area of the driving limit.

14. The method according to claim 12 or 13, characterized in that the exact adjustment or determination is carried out when the linear initial range (12) of the selected tire characteristic (10) is exceeded.

15. The method according to claim 12, 13 or 14, characterized in that the adaptation or determination is carried out when a calculated operating point (11) deviates from a selected tire characteristic curve (10).

16. The method according to any one of the preceding claims, characterized in that the driving dynamics simulation model (3) is a real-time model, by means of which the current kinematic state of the wheel and / or the current frictional connection (4) and / or the computer current adhesion limit (8) of the wheel is calculated in real time.

17. The method according to any one of the preceding claims, characterized in that the determination of the adhesion (4) and / or the adhesion limit (8) takes into account driving dynamics parameters which are derived from data measured by means of the driving dynamics sensors (1).

18. The method according to any one of the preceding claims, characterized in that the determination of the adhesion (4) and / or the adhesion limit (8) is carried out axially.

19. The method according to any one of the preceding claims, characterized in that by means of the determined Non-positive connections (4) and / or non-positive limits (8) of all wheels, the non-positive and / or the non-positive limit of the entire vehicle is determined.

20. Device for carrying out a method for determining the adhesion (4) and / or the adhesion limit (8) of a tire of a moving vehicle according to one of the preceding claims, comprising a plurality of driving dynamics sensors (1) for measuring the driving condition of the vehicle, at least one of the road condition Detecting road surface sensor (2) for determining the road surface condition and a computer for evaluating the data from the driving dynamics sensors (1) and the road surface sensor (2), which uses a driving dynamics simulation model (3) to determine the kinematic state of the wheel and the frictional connection (4) or taking into account at least one stored tire map (9) with tire curves (10), the adhesion limit (8) is determined, characterized in that the device for adapting the tire curves (10) based on an initial set of basic tire curves in the course of the operating time to the current tire behavior is formed.

21. The apparatus according to claim 20, characterized in that a plurality of different roadway sensors (2) are provided for determining the roadway state and the computer for limiting the roadway state taking into account the signals from the road web sensors and information is trained using a barrier method.

22. The method according to any one of claims 1-3, characterized in that the roadway sensors in addition to typical roadway wet conditions such as ice, snow and water also record properties of the subsurface, in particular roughness, mateno texture and / or an intermediate medium such as in particular 01, leaves, sand .

23. The method according to Ansprucn 22, characterized in that the tire map (9) comprises basic characteristics or tire characteristics (10) for different road wet conditions and / or properties of the ground.

24. The method according to any one of claims 1-5, characterized in that the tire map (9) tire characteristics (10) in the form of peripheral force-slip and / or lateral force-slip angle curves for different wheel speeds.

25. The method according to any one of claims 1-17, characterized in that the determination of the adhesion (4) and / or the adhesion limit (8) is carried out in lane or wheel-specific.

26. The method or device according to any one of the preceding claims, characterized in that instead of or m supplementing a stored tire map, a mathematical tire model is used to generate the tire characteristics in order to determine the adhesion and / or the adhesion limit, the transition from a tire characteristic to another is done by changing one or more parameters of the tire model.