EP3458317A1

EP3458317A1 - Method for determining the anticipated grip margin of a vehicle in a driving situation

Info

Publication number: EP3458317A1
Application number: EP17730866.5A
Authority: EP
Inventors: Jean-Louis Linda; Benjamin LEVRARD; Marc Duvernier
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2016-05-20
Filing date: 2017-05-22
Publication date: 2019-03-27
Also published as: WO2017198972A1; FR3051422A1

Abstract

The invention relates to a method for determining a tyre road grip margin, by estimating the potential grip available at a given moment between the vehicle tyre and the road on which the tyre is travelling, and determining an anticipated grip requirement according to the driving situation.

Description

Method of determining an anticipated margin of adhesion for a vehicle in a taxi situation

FIELD OF THE INVENTION

The present invention is in the field of motor vehicles, and in particular in the field of systems and devices for assisting the driving of such vehicles.

[0002] Motor vehicles are today equipped with numerous equipment to improve the safety of the driver and passengers of a vehicle. Thus known brake assist systems (ABS) to prevent wheel lock in case of severe braking. Also known electronic trajectory correctors (ESP), which allow, by a control of the trajectory, to avoid slippage of vehicles.

The development of these systems has been made possible by the installation of many electronic devices in vehicles, and the implementation of electronic computers increasingly powerful, for embedding large computing power in vehicles automobiles without additional bulk.

To avoid accidents, especially in difficult weather or driving conditions, it seems useful to estimate the risks relating to the loss of grip of a vehicle in a rolling situation. Such a loss of adhesion occurs when the efforts that the vehicle will require at the tire / road contact ie the need for adhesion are greater than the potential of the tire and the roadway to pass such efforts ie the maximum adhesion potential available .

Thus, it is useful for a driver to know what is the margin of adhesion available at a given time or a near time horizon, namely on the next minutes of taxiing. In fact, knowing this information, a driver will be able to know if his driving is safe, that is to say that it solicits the tires in reasonable proportions compared to the driving conditions, or if on the contrary he has a risky driving that it is necessary to adapt. It is specified here that the term "risky driving" should not be understood as an absolute judgment, but rather as an evaluation in view of driving conditions.

The adhesion margin information can also be transmitted to safety or steering systems present in the vehicle, such as a cruise control or braking devices. In the state of the art, various solutions for estimating the potential for adhesion available between a tire and the road on which rolls the tire. Some of these solutions are based on the solicitation of the adhesion potential up to a certain level, for example half of the maximum potential, and propose to extrapolate the maximum potential available. However these solutions require a maneuver close to the limit of adhesion, which does not allow to leave a sufficient safety margin for the driver of the vehicle, especially in conditions of low level of adhesion. However, none of these solutions offers an estimate of the potential available in real time.

In addition, concerning the need for adhesion, there are solutions for interrogating vehicle devices such as accelerometers or gyrometers to obtain a local estimate and in real time of the stresses exerted on the tires.

Also known from application EP 1932734A1, a method of estimating a risk of ground fault of a motor vehicle. However, it is noted that this method applies only in real time, and however does not allow to anticipate a need for adhesion on a trajectory to come.

The present invention aims to remedy these drawbacks by proposing a solution for determining a margin of adhesion, and its use to provide a driver and / or a vehicle with relevant driving assistance information. .

BRIEF DESCRIPTION OF THE INVENTION

Thus, the invention relates to a method for determining an anticipated adhesion margin of a tire on a roadway, the method comprising the following steps in which:

The potential for adhesion available at a given moment between a tire of the vehicle and the road surface on which the tire is rolled is estimated as a function of known and / or measured influencing parameters.

A future adhesion requirement is determined in anticipation, as a function of parameters included in the group comprising: a current or future rolling situation of the vehicle, meteorological data, cartographic data, data relating to the driver, - A comparison criterion is applied between the adhesion potential and the need for adhesion to come, to determine a margin of adhesion.

I - Estimation of an available adhesion potential

The estimate of an adhesion potential can be carried out in real time, that is to say, it estimates the potential of the ground on which the vehicle is rolling, at the moment when we estimate. In a particular embodiment, the adhesion potential estimated at an instant n is considered to be identical at an instant n + 1 if the parameters having an influence on the adhesion have not changed between the instants n and n + 1 .

The estimate can also be made in advance on a known future path, either because the trip was recorded in a vehicle navigator, or because it is possible, from a GPS position of the vehicle , to know the road on which the vehicle moves.

I-1-Determination of influential parameters

In a particular embodiment, a method according to the invention comprises an initial step of determining influential parameters on the adhesion potential, these parameters being included in the group comprising the grip number of the roadway, the height at road sand or average texture depth called PMT, the height of the water on the road surface, the surrounding air temperature, the running speed, and all the characteristics of the tire having an influence on the adhesion, in particular but not exclusively the tire pressure, its tread height, its load, and the type of tire.

These influential parameters are provided directly by the vehicle, and / or provided by an external system, and / or measured in real time. Thus, for example, the grip number of the roadway can be provided by pre-existing maps. The temperature can be measured in real time, for example by sensors currently available on a vehicle.

The parameters of the tire, such as the pressure, the tread height, the load and the rolling speed can be determined by systems embedded in the vehicle or in the tires.

In a particular embodiment, the initial step of determining influential parameters comprises a step of measuring the sound power generated by the tire during taxiing, and a step of determining the height of water on the roadway. and the height of sculpture according to this sound power. In another particular embodiment, the macro-texture of the road is also determined according to this sound power. For this purpose, the vehicle in which a method according to the invention is implemented must be provided with a microphone installed in the tires or in the front or rear bumpers of the vehicle.

The number of parameters having a potential impact on the noise of the tire can be significant. However, it appears that certain parameters have a weak or second-order influence on the nature of the noise generated by the tire. This may be the case for example of the internal pressure of the tire or the load of the tire.

Thus, it appears that the weather condition of the road, characterized by a height of water on the roadway, seems to be a parameter of the first order. Its impact on the noise of the tire is very important and especially weakly dependent on all the other parameters such as the state of the road surface, the state of wear of the tire or the type of tire tread. These other parameters are also likely to a lesser extent to vary the rolling noise as far as it is known to discern their own acoustic signatures.

Regarding this water level, it differentiates a dry road from a wet road, characterized by a height of water flush with the natural roughness of the road surface, or a wet road for which the height of water exceeds the level of natural roughness of the pavement of the road.

In an exemplary embodiment, this height of water on the road is estimated using one of the means included in the group comprising:

fixed weather stations installed along the road, and including means of communicating to vehicles traveling on the road the water level during their passage, - optical sensors embedded on the vehicle,

analytical models to estimate a residual water level according to known meteorological data (amount of precipitation, sunshine ...) or data concerning the road (drainability, slope, traffic ...).

Regarding the average depth of texture, a coating is called a closed coating when it takes a smooth appearance and without macro-roughness, such as a bitumen having sown after having undergone high temperatures. A coating will be considered open, when macro-roughness is important like that of a coating used or that of a country road repaired quickly using a superficial coating made by projecting pebbles on bitumen. A medium coating describes all the coatings in an intermediate state between the two preceding states and more particularly qualifies the new coatings. The different macro-textures can thus be categorized as follows: a closed macro-texture coating has a PMT between 0 and 0.4 millimeters. A medium macro-texture coating has a PMT between 0.4 and 1.1 millimeters, and an open macro-texture coating has a PMT greater than 1.1 millimeters. It is known that the macro-roughness of a coating strongly influences the noise generated by the tire. In particular, the phenomenon of pumping air trapped between the ground and the sculpture of the tire is all the more pronounced that the road surface is closed. Real-time knowledge of the condition of a road can be useful if, for example, this information is returned by a large number of vehicles or a dedicated fleet of vehicles, to a centralized tracking and monitoring system. maintenance of the road network.

Regarding the tire tread height, which characterizes its state of wear, one distinguishes the new state, the worn state, and an intermediate state considered here as the state of the tire with mid-wear. Information about the evolution of the wear characteristic over time is useful, especially if it is coupled with the information of the weather condition of the road. Indeed, it is known that a vehicle equipped with worn tires which rolls on a wet coating is more likely to lose its grip than if it had new tires.

In one embodiment, the estimate of a remaining sculpture height is given in real time by one of the means included in the group comprising:

Sensors embedded in the tire,

Optical sensors evaluating the evolution of the height of sculpture, these sensors being on board the vehicle or installed on the ground,

Magnetic sensors,

On-board wear models taking into account the mileage traveled, the use, the vehicle type, wear measurement points made by mechanical or optical means ... The type of sculpture of the tire is, for example, a summer type sculpture or a winter type sculpture. These two types of tires are essentially distinguished by treads with different, more directional, heavily cut and laminated tread patterns in the case of winter sculptures, less directional and less notched in the case of summer sculptures, as well as by the nature of the tread patterns. materials forming the tread, softer in the case of winter tires, and harder in the case of summer tires. These characteristics are not without influence on the behavior and handling of the vehicle, and therefore on its adherence.

1-2 -Method using a mathematical model

Knowing the influential parameters, several embodiments are possible for determining the available adhesion potential. In a first preferred embodiment, a mathematical formula is thus used that makes it possible to estimate this adhesion potential as a function of the speed. Thus, the potential can be calculated as follows:

f (soil micro-roughness, speed, sand height, water height, tread depth, inflation pressure, load) This function is specific to each pneumatic tire on the market and approved. All or part of the parameters indicated in this expression have previously been measured and / or determined beforehand, as previously described.

1-3 -Method using abacuses

In another embodiment, the step of determining an adhesion potential as a function of the speed is performed by the implementation of predetermined adhesion level abacuses. In this embodiment, several steps are implemented, will be subsequently described in detail using figures:

Adhesion level plots are constructed according to influential parameters. - The values of these parameters are measured in real time.

The abacus corresponding to the values of the parameters is selected, and

The estimated value of the adhesion potential is read on the chart for the actual speed of travel. 1-4 - Rolling radius method

In another embodiment of the present invention, the step of determining an available adhesion potential comprises the following steps:

the evolution of a rolling radius of the tire is evaluated as a function of the predetermined rolling conditions of said tire on soils of variable and known adhesions, to constitute an experimental database,

from the experimental database, a model for estimating the adhesion potential is established by determining a function connecting the rolling friction potential and the vehicle parameters,

during the rolling of the tire, the rolling radius is determined and, by applying said model, and depending on the vehicle parameters, the adhesion potential of said tire is evaluated.

Once the available adhesion potential is available, a method according to the invention provides for determining a need for anticipated adhesion, a function of one or more sets of parameters included in the group comprising: a running situation in progress or future vehicle, weather data, map data, driver data.

II - Estimation of a need for adhesion

We will first describe a means of real-time estimation of a need for adhesion, as known to those skilled in the art. This passage of the description will however make it possible to specify certain general definitions applicable both in real time and in anticipation.

We will then specify two ways of estimating a need for adhesion in anticipation.

II-l- Real time estimation

The estimate of a need for adhesion can be performed using accelerations determined in real time. In fact, in a first step which is often sufficient in view of the results sought, it is sufficient to consider the global acceleration γ experienced by the vehicle in relation to a need for adhesion which is also global, then there exists between the adhesion and the acceleration a simple mathematical relation g-μ = γ, where g is the gravitational constant. In the rest of the description, we will sometimes make shortcuts of language between the maximum available adhesion and the acceleration γ then expressed in g. In a more advanced embodiment, it is possible to pass, using a vehicle model, the adhesion available at the level of the vehicle to the local tire-by-tire stresses and then to calculate as many local adhesion requirements, to preferentially retain the most restrictive .

The vehicle accelerations are, in one embodiment, measured by accelerometer type devices embedded directly on the vehicle, or installed in external devices present inside the vehicle, such as a smartphone or tablet. . Acceleration can also be measured on the CAN bus of the vehicle.

The CAN bus of the vehicle also provides information such as speed V and ω _ζ Thus, in the case where one rolls on a portion of the path having an established radius of curvature, but unknown, it is then possible to calculate it. Indeed, we know that this radius will be equal to R = V ² / y _y = V / ω _ζ . Knowing the radius of curvature, it is then possible to determine, in addition, a stall speed in the turn, and thus to determine a speed margin instead of the margin of adhesion, in the form (Vdécrhage - Vactuelle ).

II-2- Estimation in anticipation on a known path: simplifying hypothesis

In one embodiment, the need for adhesion is determined by estimating, according to a future rolling maneuver, the forces that will be transmitted to the ground.

Knowing the approximate trajectory taken by the driver on the next rolling maneuver, it is possible to estimate the need for grip during this maneuver. Indeed, it is known that a vehicle of mass M subjected to an event is the seat of an acceleration y (V) exerted in the plane of the vehicle. Using an analytical model of the complete vehicle, one can deduce among others of this acceleration y (V), the center wheel forces F _x , F _y and F _z for each tire of the vehicle, and calculate accordingly the need for adhesion μ _ρηβ ιι () at the level of each tire on this event of the path defined by:

^ F _X ² + Fy ²

V-tire p It is specified here that, in the reference of the tire, the axis OX will designate the axis representing the circumferential direction of the tire, OY the axis parallel to the axis of rotation of the tire or transverse axis, and OZ 1 axis normal to the axis of rotation of the tire, or radial axis.

In one embodiment, a first simplifying hypothesis will be used which makes it possible to obtain a need for adhesion with a precision of order 0. In the case where the next event is a curve, it is known that when a vehicle of mass M is inscribed at constant speed in a curve of radius of curvature R, the acceleration undergone by the vehicle, and whose substantial effort is taken up by the roadway, is defined by _y (V) = V ² / R, in the absence of slope and tilt.

According to a second simplifying assumption, considering the case where all the tires are identical and undergo the same conditions, it is known that the principle of balance of efforts between those produced by the vehicle on the ground and those that the tire contact / transmitting roadway makes it possible to establish the formula g ^ (V) = γ (V), g being the acceleration of the gravity (in m / s ² ), γ (V) being the acceleration in the plane of the vehicle (in m / s ² ).

However, it is not possible to know in advance the actions performed by the driver, so in this embodiment will neglect the longitudinal acceleration. This assumption is often verified at the apex of the turns where the curvature is the most accentuated and the acceleration is _there most marked at a given speed. It is specified here that the apex corresponds to the point of the curve of maximum curvature.

In addition, we do not always know the speed of the vehicle on the upcoming taxi operation, and in this case it is useful to use categories of driving, as explained below.

II-3 - Predictive estimation on a known path with conductive profiles

In another preferred embodiment, to determine the acceleration of the vehicle, predetermined driver categories are used.

To determine categories of conductors, we observe the speed and / or acceleration of a number of individuals on the same path, and we perform a hierarchical classification on all available observations. It is specified here that the variables are recorded with a frequency specific to the recording means. These variables are not statistically considered as continuous curves, but as a set of point observations. Thus, each individual is associated with a set of observations for each of these passages.

The principle of this classification is, using a concept of adequate distance, to group the users in classes, each as homogeneous as possible and, between them, as distinct as possible. In an exemplary embodiment, the classes are such that the intra-class variance is minimized, while the intergroup variance is maximized.

Advantageously, to perform the classification, we record the speed and / or acceleration of an individual during several passages on the same course, each passage giving rise to a set of observations. To define the distance between two users, the distance between the speeds and / or reference accelerations of each of these users is calculated.

Once the classes are determined, we determine the average speed of each class, also called profile speed.

In such a hierarchical classification, the number of classes used is chosen a posteriori, and is considered adequate if the interclass variance does not decrease significantly by adding a class.

Thus, in an exemplary embodiment of the present invention, it has been envisaged to use six classes, to minimize the interclass variance. However, it has been found that equally relevant results are obtained with four classes. This number of four classes is therefore preferentially chosen, for reasons of parsimony. This makes it possible to reduce the computing power and the necessary computing times.

Still for the sake of parsimony, in an exemplary embodiment, the categories are determined using not all the available observations, but only part of these observations. For example, observations on relevant driving areas, such as turns or areas of high acceleration, will be chosen.

The relevant driving zones are for example determined by mapping the driving area, or by a vehicle behavior during a passage on these areas, the behavior being for example analyzed in view of a speed and / or a vehicle acceleration on these areas. It is then possible to store in the vehicle the different driver categories and their associated speed profiles. Thus, in this embodiment, knowing the category in which the vehicle is located, and knowing the path taken by the vehicle, it is possible to determine the acceleration that will undergo the vehicle, and therefore the need for adhesion .

II-4 - Prediction estimation in two dimensions

In the foregoing paragraphs, a simplifying assumption has been used according to which longitudinal acceleration was neglected in order to estimate an anticipated adhesion requirement. However, in some embodiments of the invention, it may be advantageous to focus on the need for adhesion in both dimensions and transverse. Thus, the total acceleration experienced by the vehicle is then γ =

And we can estimate a need for adhesion in each of the directions in the form g ^ _x (V) = _Tx (V) and g ^ _y (V) = _Ty (V)

Thus, the margin of adhesion estimates that will be made later to be globally, or differentially in both directions.

The estimation of a margin of adhesion in both directions allows the driver and driver assistance systems (ABS, ESP, etc.) to implement and visualize both the type of maneuvers required (acceleration, braking, yawing of the vehicle, etc.) and the associated intensity not to exceed the limits of adhesion in both longitudinal and transverse directions

III- Estimation of a margin of adhesion

III-1 - Comparison between the anticipated need and the potential

The comparison of an adhesion potential and an anticipated adhesion requirement, determined according to previously described methods, makes it possible to estimate a margin of adhesion. This comparison can be done in different ways, depending on the intended uses and / or applications.

Thus, in one embodiment, a division is made between the necessary acceleration, determined in the context of the estimate of the anticipated adhesion requirement, and the determined adhesion potential, possibly multiplied by the constant g . This gives a value that corresponds to a percentage of consumed margin. A percentage of the remaining or available margin could also be determined by subtracting the margin percentage consumed from 100. In another embodiment, a subtraction is performed between the same two values as above, and a residual acceleration potential is thus obtained.

III-2 - Determination of an alert threshold

Advantageously, the adhesion margin thus determined can be used to create alerts, for example to the driver, so that he can adapt his driving in the case where the margin of adhesion would become too low. For this purpose, it is useful to determine one or more alert thresholds, expressed in the margin of adhesion consumed or available, and expressed in percentage or point.

In an advantageous embodiment, the determination of an alert threshold takes into account a reserve of margin or acceleration which incorporates a consumption of adhesion necessary for the efforts to be transmitted to the ground, even at constant speed. . Indeed, elements such as the resistance to the progress, the aerodynamic forces, the slope, induce a consumption of adhesion which is not taken into account by the preceding computations. However, it is useful to permanently maintain a sufficient margin of adhesion, for example, to allow to pass a braking force.

Thus, in one embodiment, an alert threshold is set at 25% margin reserve and / or 0.2 acceleration reserve points. In another embodiment, alert thresholds are set which change according to the speed.

By way of example, it is specified here that a passenger vehicle of 1950 kg at a steady speed of 100 km / h consumes an adhesion of the order of 0.03 in resistance to advance and aerodynamic forces and a share of adhesion directly related to the slope (0.1 for a slope of 10%, ...).

III-3 - Driver warning or information system

In one embodiment, a method according to the invention further comprises a step of informing the driver of the adhesion margin consumed and / or available.

This display can take different forms which will be further detailed with the aid of the figures. One can thus consider displaying a percentage of adhesion consumed or available in real time. One can also consider using colors corresponding to different alert thresholds as explained above.

One can also consider a display that takes into account the longitudinal and transverse components of the adhesion, or on the contrary a simplified display that only displays the standard. Finally, in another embodiment, one can consider the use of a specific visual or audible alert when the previously defined alert thresholds are exceeded.

According to the embodiments, the margin of adhesion that will be communicated to the driver of a vehicle, or to a system installed in the vehicle, will be the margin directly resulting from the comparison between the need for adhesion and the potential. adherence, or a corrected margin, taking into account the uncertainties of determination, and a reserve braking or acceleration, previously mentioned.

In anticipation, the margin of adhesion can be displayed as a color on the map of a browser

BRIEF DESCRIPTION OF THE FIGURES

Other objects and advantages of the invention will become apparent from the following description of a preferred but nonlimiting embodiment, illustrated by the following figures in which:

FIG. 1 shows an example of abacuses that can be used in a method according to the invention, for determining an adhesion potential,

FIG. 2 shows graphs representing a need for anticipated adhesion as a function of a rolling speed and an available grip potential as a function of a rolling speed,

FIG. 3 shows predetermined curves of adhesion potential as a function of a weather condition of the road and a state of the tire associated with anticipated adhesion requirements for different types of drivers on a given turn of the path,

FIGS. 4a and 4b show examples of conductive alert display implemented in a method according to the invention.

FIGS. 5a and 5b show examples of implementation of a method according to the invention in a vehicle. DESCRIPTION OF THE BEST MODE OF CARRYING OUT THE INVENTION

FIG. 1 shows an example of abacuses that can be used in a method according to the invention, for determining an adhesion potential.

Preferably, the charts are parameterized according to the influential parameters that are available during an implementation of the invention, for example the water height and the sculpture height, and are plotted as a function of the running speed.

The number of charts to be created is therefore a function of the number of values of these quantities that we will measure. Typically if it is known to measure 2 levels of wear (new / worn) and 2 levels of humidity (dry / wet), we will create 4 charts corresponding to the possible combinations of these two states. If certain combinations lead to very close adhesion results, the number of abacus can be reduced.

The charts are constructed in several stages:

First, a statistical distribution of each of the inputs of the model is determined. As many abacuses are computed as there will be a combination of these parameters but each is calculated with a very small standard deviation around the value of the parameter measured. Typically, the identification of a worn tire reduces the distribution to 2mm ± 1.5mm instead of 5mm ± 4mm in the absence of this information. The accuracy of the adhesion estimation is greatly improved.

N draws are selected from these input parameter distributions (typically N = 1000 or 10000).

N variants of μ are calculated with these N combinations for P speed cases (typically 11 cases of speeds ranging from 30 to 130 km / h in steps of 10 km / h)

N curves μ (ν) are thus drawn, each corresponding to a draw among N combinations of input parameters.

Finally, we extract from this curve the percentile that interests us according to the risk of estimation, such as the limit of 10% or 1% of the lowest.

In ² output of this step, so we have a curve μ (ν) for each possible combination of influential parameters. Thus, FIG. 1 shows four curves on which:

51 is the available grip for a new tire, on a wet road,

52 is the available grip for a worn tire, on a wet road,

53 is the available grip for a new tire on a wet road, and

- S4 is the grip available for a worn tire, on a wet road.

It is clear in the example below that this information creates 3 classes of adhesion potential significantly different.

This approach reduces the number of information to be stored without losing prediction quality since accurate calculations are made upstream of the operation.

Once one has the need for adhesion and available adhesion potential, it is then possible to determine a rolling speed limit. FIG. 2 shows the preferential mode of determining this speed. Curve 20 represents the need for adhesion of a vehicle as a function of the rolling speed. This need is for example determined in real time according to a running maneuver in progress, or even in advance depending on a future driving maneuver, or predetermined information depending on the category of the driver and the driver. journey to come.

Curve 21 represents the available adhesion potential as a function of the rolling speed. This adhesion potential being determined by one of the methods described in the present application. The rolling limit speed corresponds to the speed 22 at the intersection of curves 20 and 21. When a vehicle is traveling at speed 23, the grip potential μ is available _{February 3} ΐ, and adhesion is consumed μ ₂ 3ο · Therefore, the adhesion margin at this speed 23 is the difference between μ¾ι and μ ₂ 3ο · It is also possible to express to the driver, or to the regulation system, the speed margin (speed 22 - speed 23) still available before matching the consumed and available adhesions.

FIG. 3 shows an optimal use in terms of resources of a method according to the invention for determining the curve 20 described in FIG. 2. In this case of use, it is supposed that four categories of driver have been determined. beforehand, the graph shows four groups of points, called K1, K2, K3 and K4, corresponding to the need for adhesion called by different drivers in the different driving categories, and observed, in the graph shown, at a given position d a driving maneuver. The points VK1, VK2, VK3 and VK4 represent the speeds obtained by statistical processing, stored in the vehicle for this position on the path, and synthesize respectively the four categories of predetermined driver. These four points VK1, VK2, VK3 and VK4 then make it possible to draw the curve 30 which shows an anticipated need for adhesion, as a function of a running speed of a planned vehicle, in particular as a function of known cartographic data on a path to come up. This curve is therefore based on the users observed in this real situation of driving maneuver.

In this FIG. 3, four curves SI, S2, S3 and S4 are also shown showing the available adhesion as a function of the speed for four influential parameter combinations:

SI is the available grip for a new tire, on a wet road,

- S2 is the adhesion available for a worn tire, on a wet road,

53 is the available grip for a new tire on a wet road, and

54 is the grip available for a worn tire on a wet road.

In this mode of use, knowing the behavior of the conductors (curve 30) and knowing the state of the influencing parameters, one will choose wisely the adhesion curve available to apply the method described in FIG. 2, and thus determine the margin of adhesion and / or speed margin. If the tire is new and the vehicle is maneuvering on a wet road, we must consider curve S3 and the intersection with curve 30 gives a limit speed of 45 km / h which corresponds to a coefficient of adhesion of 0.6. . If the vehicle is then traveling at 36 km / h, the anticipated adhesion requirement is 0.4 (curve 30) while the available adhesion is 0.62 (curve S3). A possible expression of the margin of adhesion is then 0.22 (0.62 less 0.4) and the speed margin is 9 km / h (ie 45 minus 36).

Figures 4a and 4b show examples of display, for a driver of the vehicle, information concerning a margin of adhesion.

In Figure 4a, there is provided a display in the form of a target, having three concentric circles. The central circle, for example displayed with a green color, represents indicates that the adhesion consumed is between 0 and 60% of the available adhesion. The intermediate circle, for example displayed with an orange color, indicates that the adhesion consumed is between 60%> and 80%> of the available adhesion, and the outer circle, for example displayed with a red color, indicates that the adhesion consumed is between 80%) and 100%) of the available adhesion. A color gradation will preferably be chosen to alert the driver to the risk gradation of his driving. On the target of Figure 4a, the adhesion is shown in two dimensions, respectively corresponding to the transverse and longitudinal components of the stresses. In another example, illustrated in FIG. 4b, it is chosen to display the information only in one dimension, and therefore the standard of adhesion is used rather than the two components. On the display of Figure 4b, there are three areas, displayed with three different colors, and has thresholds similar to those of Figure 4b.

In Figure 4a, we also see that displays a history close adhesions consumed (of the order of 0.5 to ls before the present moment). This history allows the driver to be aware of the evolution of his driving, or at least the consequences of his behavior on the evolution of grip.

The same type of display could be obtained to show not a history of adhesions consumed, but instead an anticipated margin of adhesion on a path to come. Indeed, as previously described, the invention makes it possible to determine a need for adhesion in anticipation, as a function of map data, and thus to deduce an anticipated margin of adhesion at different points of a future path.

This display could be performed according to the two transverse and longitudinal dimensions, according to the estimate as previously described in Part II-4.

Figures 5a and 5b show examples of implementation of a method according to the invention in a vehicle. Figure 5a shows more particularly an implementation using a connected device not integrated in the vehicle, type Smartphone or tablet. Thus, in this embodiment, the device 100 includes GSM communications means for receiving external data such as maps or traffic information or the like. In addition, the device 100 comprises means for receiving information enabling the GPS location of the vehicle or a determination of the vehicle speed.

The vehicle also comprises a computer 101a installed in the vehicle, and connected to different sensors such as microphones 102 and 103. This computer 101a comprises signal processing means from the sensors 102 and 103 to obtain information. concerning a height of water on the road, a texture depth of the road, a state of wear or pressure of the tire. In another embodiment, not shown in the figure, the vehicle further comprises other sensors, such as temperature sensors, wear sensors, pressure sensors installed directly on the vehicle and / or on the tires. In this case, the computer 101a comprises signal processing means from all the sensors.

After processing, the information is sent from the computer 101a to the device 100, which implements a method according to the invention to determine a margin of adhesion, and display it on a screen integrated in the device 100.

In the example shown in Figure 5b, a method according to the invention is implemented directly in the computer 101b of the vehicle. As before, this computer is connected to sensors 102 and 103 which have the same functions as in the example of FIG. 3a. On the other hand, in this example, the computer 101b is connected to the CAN bus of the vehicle, in order to read information such as the speeds and / or accelerations of the vehicle.

The display and control module 200 integrated in the vehicle comprises GSM communication means for receiving external data such as maps or traffic information or other information and means for receiving GPS geolocation information. of the vehicle. It can make this information available to the computer 101b on the CAN communication bus.

This module 200 is also provided with display means for displaying the adhesion margin, to inform the driver.

In an exemplary embodiment, the characteristics of the tire are taken into account for the implementation of the method. For this purpose, these characteristics are stored in a vehicle memory, and / or an identifier of the tire is read by an RFID type reading, and associated with characteristics stored in a database, and / or the adhesion model. implemented in the computer 101b or in the device 100, is chosen from a set of adhesion models as a function of an identifier of the tire.

Claims

A method of determining an anticipated adhesion margin of a tire on a roadway, the method comprising the following steps in which

A future adhesion requirement is determined in anticipation, according to parameters included in the group comprising: a current or future taxiing situation of the vehicle, driving conditions, meteorological data, cartographic data, data concerning the driver,

A comparison criterion is applied between the adhesion potential and the need for future adhesion, in order to determine an adhesion margin consumed and / or available.

The method of claim 1, wherein the adhesion requirement is determined as a function of speed using map data.

Method according to one of the preceding claims, wherein the need for adherence as a function of speed is determined using categories of conductor.

Determination method according to one of the preceding claims, wherein the determination of a need for anticipated adhesion is performed distinctly transversely and longitudinally.

The method of claim 1 to 3, wherein the comparison criterion implements subtraction and / or division.

The method of claim 1 to 4, further comprising a step of correcting the determined margin of adhesion, allowing to take into account a braking or acceleration reserve.

7. A method of determining an adhesion margin according to one of the preceding claims, further comprising a step of informing the driver of the adhesion margin consumed and / or available.

8. Determination method according to one of the preceding claims, comprising an initial step of determining influential parameters on the adhesion potential, these parameters being included in the group comprising the grip number of the roadway, the height to the sand of the road, the height of water on the road, the temperature, the pressure of the tire, its height of sculpture its load and the running speed

9. Determination method according to claim 7 wherein the initial step of determining influential parameters comprises a step of measuring the sound power generated by the tire during taxiing, and a step of determining the height of water on the tire. pavement and sculpture height according to this sound power.

The method of one of claims 1 to 4, wherein the step of determining an available bond potential comprises the following steps:

from the experimental data base, a model for estimating the adhesion potential is established by determining a function connecting the adhesion potential to the rolling radius and to vehicle parameters,

11. Method according to one of claims 1 to 4, wherein the step of determining an adhesion potential as a function of speed is performed by applying a mathematical formula implemented by an electronic calculator. present on the vehicle.

12. Method according to one of claims 1 to 4 wherein the step of determining an adhesion potential as a function of the speed is performed by the implementation of predetermined adhesion level abacuses.