Method for recovering braking energy of a vehicle comprising an electric propulsion system

Abstract

The invention relates to a method for determining the maximum deceleration potential P (1000) of a tyre driven by an electric motor of a vehicle, comprising the following steps: - determining a vector of parameters V (1001) of the state of the roadway comprising a moisture parameter FP; - determining the load Z (1002) applied to the tyre; - determining the load Zveh (1003) applied to the vehicle; - if the vector V is contained within the sub-space delimited by a predefined surface S0, the equation of which takes into account a value FP0 of the moisture parameter FP, the maximum deceleration potential P is defined by a state potential P0 (1004) by the following equation: (I) where µsec is a real number from 0.8 to 2.0; - otherwise, it is defined by a state potential P1 (1005) by the following equation: (II) where µhum is a real number from 0.4 to 0.6.

Description

DESCRIPTION TITLE: METHOD FOR RECOVERING ENERGY DURING BRAKING OF A VEHICLE COMPRISING ELECTRIC PROPULSION Field of invention

[0001] The present invention relates to the field of methods for recovering electrical energy for means of automobile transport whose propulsion is provided by an electric motor. Technological background

[0002] The development of motor vehicles whose propulsion is partly provided by an electric motor has been booming for two decades, whether this motor vehicle is a passenger car, a bus or a goods vehicle. These vehicles can be entirely electric, hybrid, i.e. electric propulsion on one axle is combined with internal combustion propulsion on the other axle for example. Finally, these electric motors are powered in propulsion mode by an electric battery that can be charged at a roadside or home power station, or by an electricity generator such as an internal combustion engine or a fuel cell. The disadvantage of these electric propulsions lies in their short autonomy compared to the compromise between the weight of the electric energy storage battery and their reserve to power the electric motor.The advantage of electric motorization is the reversibility of the engine, which allows it to switch from a propulsion mode during vehicle acceleration phases to an electrical energy recovery mode during vehicle deceleration phases. Of course, the more these phases, vehicle deceleration and electrical energy recovery are optimized, the more efficient the battery recharge is and therefore the autonomy of the transport vehicle is improved.

[0003] However, it is possible to control the vehicle's braking, i.e. choose the axle(s) that will support the braking or choose the type of braking to be applied if several brakes are available on the vehicle. In document DE102019102244, we firstly teaches a device for recharging the battery of an electrically powered vehicle during the deceleration phases of the vehicle comprising a module for detecting a humidity parameter of the roadway supplying a module for comparing this parameter with predefined values ​​and a module for controlling the vehicle's electrical energy recovery options depending on whether the parameter is below or above these predefined values. This document also teaches a method for controlling the recovery of electrical energy during the deceleration phases comprising the following steps; detecting a humidity parameter of the roadway on which the vehicle is traveling, comparing this parameter with a predefined value and if the humidity parameter is below this predefined value, increasing the recovery of the electric vehicle up to a predefined threshold.However, this document remains silent on the choice of the value of this threshold, which corresponds to a level of maximum electrical energy recovery by the electric motor. Finally, the choice of these thresholds must also ensure safe deceleration of the vehicle, particularly in terms of vehicle stability, for example.

[0004] In order to impose braking on electrically powered axles in order to take advantage of the reversibility of electric motors to recharge the batteries, it is important not to exceed the tire's grip threshold with the road in order to continue to maintain the notion of tire guidance and consequently that of the vehicle. This grip threshold defines the maximum friction level allowed by the tire before it slips relative to the ground. Of course, this grip threshold is a function of both the characteristics of the ground on which the tire is rolling, the intrinsic properties of the tire linked to its material composition and its thermomechanical structure, but also the conditions of use of the tire such as the inflation pressure and the static load applied.

[0005] The following objects of the invention aim to solve the problems linked to the identification of the maximum energy recovery threshold by the electric motor which propels the tires during the deceleration phases of the vehicle while ensuring the safety conditions of the vehicle on which the tires are mounted. Description of the invention

[0006] The invention relates to a method for determining the maximum deceleration potential P of a tire driven in rotation by an electric motor equipping a vehicle comprising the following steps: • Determine at least one vector of influential parameters V of the state of the roadway where the vehicle is driving, including a humidity parameter FP of the roadway; • Determine the Z load applied to the tire; • Determine the total load Z ve h applied to the vehicle; • If the vector of influential parameters V is contained in the subspace delimited by the at least one predefined surface S0 whose equation takes into account a value FPO of the humidity parameter FP, so that the humidity parameter FP is lower than the value PFO, the maximum deceleration potential P of the tire is defined by a state potential PO using the following relationship: • where gsec is a real value between 0.8 and 2.0, preferably JJ-sec is equal to 1.2, • Otherwise, the maximum deceleration potential P of the tire is defined by a state potential PI using the following second relationship: • WHERE phum being a real value between 0.4 and 0.6, preferably ghum is equal to 0.5.

[0007] In order to impose braking on electrically powered axles in order to take advantage of the reversibility of electric motors to recharge the batteries, it is important, however, not to exceed the adhesion threshold of the tire with the road in order to continue to maintain the notion of tire guidance and consequently guarantee the safety of the vehicle. This adhesion threshold, under deceleration stress, defines the maximum friction level allowed by the front tire that it slips relative to the ground. However, it is known that this tire grip threshold during braking is a zero-order function of the humidity state of the road surface on which the vehicle is traveling. The method allows, through the vector of influential parameters of the road surface condition including a road surface humidity parameter, to judge the soil humidity state between two distinct states which correspond either to dry soil or to wet soil. This distinction is encountered in most vehicle use cases.

[0008] Of course, the tire's grip potential necessarily depends on the load applied to the tire. Indeed, the contact pressure between the ground and the tire is also a first-order parameter on the tire's grip performance on the ground. This is controlled by two tire usage variables, namely the inflation pressure and the static load applied to the tire. While the inflation pressure is generally constant across the various tires of the vehicle, the distribution of the static load on the vehicle can vary more significantly between the various axles depending on the type of vehicle. In order to evaluate the intrinsic deceleration potential of a tire, it is advisable not to make the tire's grip potential dependent on the static load, which justifies the formulation used. The values ​​that characterize the state of contact between the ground and the tire, the p secand ghum can be lumped values ​​taken from the predefined intervals, these intervals being disjoint by definition. The choice between the two values ​​results from the positioning of the vector of influential parameters of the state of the pavement with respect to a specific surface S0 which traces the boundary between wet and dry soil according to a predefined humidity parameter PF in the space of influential parameters. The equation of the surface S0 is defined so that the humidity parameter is equal to a value PFO of the humidity parameter which marks the transition of the soil from a dry state to a wet state, regardless of the quantity of water on the soil.

[0009] Thus, the proposed method makes it possible to define for each tire powered by an electric motor, a maximum admissible level of deceleration by the tire P which guarantees a condition of friction of the tire with the ground whatever the load applied and the state of the road where the tire rolls. However, the electrical energy recovery system of an electric motor itself presents an asymptote related to its sizing. The objective is to ensure, in cases where the energy recovery system of the electric motor is not the blocking point of the energy recovery capacity, to determine the energy recovery threshold which ensures that the tire remains in safe driving conditions. And the method presented allows this by guaranteeing that the friction threshold of the tire on the ground does not cause it to slip relative to the ground.

[0010] Advantageously, the determination method comprises the following steps: • The step of determining the vector of influential parameters V including an outside temperature parameter Text where the vehicle is driving, • If the parameter vector V crosses the predefined surface S0 so that the humidity parameter FP is greater than the value PFO, and the influential parameter vector V is contained in a subspace delimited by the predefined surface SI, the definition of which takes into account a value T0 of the external temperature parameter, so that the external temperature parameter T is less than the value T0, the maximum deceleration potential P of the tire is defined by a state potential P2 using the following third relationship: have a real value between 0.1 and 0.3, preferably p ne ige is equal to 0.2.

[0011] In the particular case in which the weather conditions in which the vehicle is driven lead to the tire rolling on a snowy or icy road, the tire's grip conditions are affected due to the very low level of friction that the said road surface supports in comparison with an asphalt or bitumen surface. To distinguish this particular case of rolling, it is appropriate to add to the humidity parameter an external temperature parameter which makes it possible to judge the possible presence of such a rolling condition. It is then appropriate to adjust the maximum deceleration potential of the tire up to a threshold P2 taking into account a snow factor p neige which is between 0.1 and 0.3. The adjustment of this new threshold allows to keep an energy recovery phase for the electric motors propelling the said tires while guaranteeing a level of safety of the vehicle to steer or maneuver in this type of weather conditions. Although the deceleration potential is low, it remains non-zero and ensures a better autonomy of the vehicle. This snow factor p ne be taken as a lump sum according to the positioning of the influential parameter vector V in relation to two surfaces, in the space of influential parameters, defining the thresholds for crossing a state of the roadway from a first state where the roadway is wet to a second state where the roadway is snowy or icy and vice versa.

[0012] According to a first embodiment, the determination method comprising a step of identifying said tire, the maximum deceleration potential P is weighted by an adhesion index I which quantifies the capacity of said identified tire to adhere to the ground during braking, this adhesion index I is associated with the identification of the tire.

[0013] Although standard values ​​can be taken for the value of the maximum deceleration potential P, whatever the condition of the road on which the tire is running and the type of tire, it is possible to give more dynamics to the energy recovery by weighting this standard value through a grip index I which is linked to the individual tire through a prior step of identification of the individual. This makes it possible to raise the maximum deceleration potential P or to reduce it compared to the standard value according to information associated with the identity of the tire. This information is linked to the relative performance of the tire in braking conditions on the ground which best reflects the capacity of the tire in the deceleration phase.It can be an index I intrinsically linked to the tire as technical data held by the manufacturer or the retailer of the tire product or an average value which is associated with a categorization of the tire, this value can then be public.

[0014] Preferably, the maximum deceleration potential P being defined by the state potential PO, the adhesion index I corresponds to an adhesion index value on dry ground which is deduced from a standardized grip class which is associated with the identification of the tire.

[0015] Of course, it is possible to adjust the tire's deceleration potential when the road surface is in a condition described as dry. To do this, a standardized grip class is used. The class information can be public and gives an indication of the tire's braking capacity relative to a reference. This reference to a reference allows tires to be standardized relative to each other. Thus, a numerical value can be extracted that allows the tire's maximum deceleration potential to be adjusted both positively and negatively. This ensures better electrical energy recovery than the general method for tires that publicly present increased braking capacity on dry ground. But it also allows less efficient tires to be constrained in terms of braking capacity, which guarantees vehicle safety during these phases of energy recovery by the electric motor.

[0016] Most preferably, the standard grip class is a standard grip class on dry ground or a standard grip class on wet ground.

[0017] In the case of a dry road surface, the grip index I can ideally be deduced from a standard grip class on dry ground which best corresponds to the deceleration capacity of the tire on this type of road surface. However, it is also possible to use a standard grip class on wet ground because, at iso tire and for standard tires in particular, the relative classification of tires in the braking phase between a wet road surface and a dry road surface is not modified by the humidity of the road surface, in particular in the absence of water above the support plane on the highest points of the road surface on the scale of the contact zone of the tire with the ground. A possible adaptation of the numerical value of the grip index I deduced from the standard grip class is to be carried out in the case of use of the standard grip class on wet ground.

[0018] According to another preferred embodiment, the maximum deceleration potential P being defined by the state potential PI, the adhesion index I corresponds to a wet grip index value that is deduced from a standardized wet grip class that is associated with the tire identification.

[0019] It is possible to weight the maximum deceleration potential of the tire P and in particular the potential state PI on wet ground using a grip index I which is a function of a standardized wet grip class. This grip class is associated with the tire identification and can be public data or proprietary data from the tire manufacturer. An increase or decrease value of the potential state PI is then associated which is linked to the tire's grip class. This grip class is defined for wet ground.

[0020] For example, the wet grip class may be one of the classes defined by European Regulation EC-228 / 2011 if the target vehicle is a passenger vehicle or by the ISO-15222 standard (ISO 5222:2011) if the target vehicle is a truck or van. The wet braking performance of a vehicle equipped with the said tire is then compared to the performance of the same vehicle equipped with a reference tire, called SRTT (Standard Reference Truck Tire). The wet braking performance of the SRTT tire is conventionally equal to 1.00.

[0021] The conditions of these standardized tests are preferably specified either by the ISO-15222 standard for trucks and buses that fall under a tire class called C3 and vans that fall under a tire class called C2, or by the European regulation EC-229 / 2011 for passenger vehicles that fall under the class called CL Of course, one can refer to any equivalent standard applicable in the country concerned, without departing from the invention. In practice, these tests make it possible to assign a grip class to the tire, symbolized by a letter ranging from A to F. The correspondence table below illustrates the link between the numerical value of the class on wet ground, noted G, and the letter of the class for tires of class C3.

[0022] In the context of the invention, the adhesion index I will be taken as a reference to the numerical value G of the chosen adhesion class, taking, as an illustrative example, the numerical barycenter of each class knowing that the numerical interval of each class is 0.14. Thus, the first class A will be defined at a value of I of 1.32 and the last class G has a value of I of 0.57.

[0023] According to another preferred embodiment, the maximum deceleration potential P being defined by the state potential P2, the grip index I corresponds to a grip index value on winter ground which is deduced from a standardized grip class which is associated with the identification of the tire.

[0024] Preferably, the standard grip class is a standard grip class on winter ground or a standard grip class on wet ground.

[0025] Of course, it is possible to adjust the deceleration potential of the tire P when the road surface is in a condition described as winter. To do this, a standardized grip class is used. The class information can be public and gives an indication of the tire's braking capacity relative to a reference. This reference to a reference allows tires to be standardized relative to each other. Thus, a numerical value can be extracted that allows the maximum deceleration potential P of the tire to be adjusted both in terms of potential gain and potential loss. This ensures better electrical energy recovery than the general method for tires. publicly presenting an increased braking capacity on winter ground, such as snow or ice. But this also makes it possible to constrain the worst tires in terms of braking capacity on this type of road surface, which guarantees vehicle safety during these phases of energy recovery by the electric motor.

[0026] In the case of a wet and cold road surface, the grip index I can ideally be deduced from a standard grip class on winter surfaces which best corresponds to the deceleration capacity of the tyre on this type of road surface. However, it is also possible to use a standard grip class on wet surfaces because, at iso tyre and for standard tyres in particular, the relative classification of tyres in the braking phase between a wet road surface and a winter road surface can easily be deduced from one another, the classification is generally reversed'.

[0027] Advantageously, the method comprising a step of determining a state of wear of the tire, the deceleration potential P is weighted by a wear index U which quantifies the capacity of said tire to adhere to the ground according to the state of wear of the tire, this wear index U is associated with the identification of the tire.

[0028] The state of wear of the tire can influence the grip performance of the tire on the ground by modifying the quantity of rubber in direct contact with the ground. This then modifies the contact pressure between the tire and the ground which has the effect of increasing the heating of the rubber by the intensification of friction. This heating or its opposite, the cooling modifies the adhesion power between the tire and the ground. This reasoning is observed on dry roads, an increase in the rubber / ground contact rate due to a modification of the tread groove pattern during wear, leads to an improvement in the grip potential and therefore the maximum deceleration potential of the tire. On the other hand, on wet and winter ground, the tread groove of the tire allows the third component, water, snow or ice, to be evacuated.Therefore, an increase in the rubber / ground contact rate due to a change in the tread pattern during wear can lead to a deterioration in the adhesion potential and therefore the maximum deceleration potential of the tire. Of course, the nature of the tire's rubber, in particular that. components in contact with the ground influence the grip capacity, it is therefore appropriate to link the wear index U to the identity of the tire to take this dependence into account if we wish to be more precise.

[0029] Very advantageously, the wear index U is a function of the available hollow of the tire tread.

[0030] The term "hollow" here refers to the absence of material, i.e. the void, at the level of the tire tread. This void can be characterized in several forms. It can be surface by looking at the void level at the tire's footprint on the ground, it is then expressed as a percentage relative to the surface associated with the outer delimitation of the tire's footprint on the ground. It can also be expressed as the average void surface in a radial section of the tire whose tread is then homogenized. It is then expressed as a percentage relative to the surface delimited by the lines most radially distant from the tire compared to the natural rotation tax. It can also be expressed by the void volume in a section of the homogenized tread of the tire, per angular unit of the tire.Finally, it can also correspond to the volume of the tread hollow limited to the sector of the tread delimiting the contact area of ​​the tire. Depending on the characterization of the hollow taken into account, the wear evolution law must be adapted for each of the different potentials of maximum deceleration state. Naturally, the pattern of hollow of a tire is linked to its identity.

[0031] Very advantageously also, the method comprises a step of determining a rolling speed v of the tire, the wear index U is a function of the rolling speed v of the tire.

[0032] The various tires of a vehicle, depending on their position on the vehicle, do not necessarily encounter the same height of water on the road. Indeed, when moving forward, the front axle of a vehicle is confronted with the water accumulated on the road. Whereas the tires of a rear axle will have, for normal driving speeds of around 50 km / h, reduced quantities of water present on the road. The tires of the front axle will have expelled the water before it returns to the road when the rear axle passes over. In addition, for large quantities of water, the action of the rear axle front can induce a local increase in water just in front of the front tire by saturating the hollow network of the latter. This accumulation can cause a partial separation of the tire from the road on the part of the tire subjected to this accumulation of water. This generates a deterioration in the grip of the tire and therefore its consideration must be made with a specific evolution law in relation to dry ground.

[0033] According to another advantageous embodiment, the method comprising a step of determining a tire temperature Tpneu, the maximum deceleration potential P is weighted by a temperature index T taking into account the outside temperature Text and the tire temperature Tpneu, the temperature index T is associated with the identification of the tire.

[0034] It is known that the adhesion performance of the rubbers of a tire is a function of the temperature of the rubbers and in particular of the difference between this and the ambient environment in which the tire is traveling. Taking into account the heat exchange between the tire rubbers and the external environment makes it possible to monitor the evolution of the temperature of the tire rubbers and in particular to control the runaway temperature due to insufficient heat exchange with the external environment. Of course, these behaviors are differentiated according to the nature of the rubbers used but also the structure of the tire to reduce or accentuate these heat exchanges with the external environment. Therefore, this temperature index T is preferentially linked to the identification of the tire to be more precise, at least according to the range of the tire, the so-called summer, all-season or winter tires.

[0035] The invention also relates to a method for controlling the recovery of electrical energy from an electric motor propelling at least one tire of a vehicle comprising the following steps: • Determine at least one vector of influential parameters V of the state of the roadway where the vehicle is driving, including a humidity parameter FP of the roadway, preferably at least one external temperature parameter Text where the vehicle is driving; • From at least one vector of influential parameters V, determine a maximum deceleration potential P (1000) of the at least one tire; • Adjust the energy recovery of the electric motor associated with the at least one tire up to a threshold R; in which the threshold R is a function of the maximum deceleration potential P of the at least one tire and the load Z applied to the at least one tire according to the following relationship: = Z * P

[0036] The purpose of the maximum deceleration potential P of the tire is to evaluate, according to the load Z applied to the tire by the vehicle, the energy recovery threshold R admissible by the tire per unit of time. Thus, by controlling the braking force of the energy recovery system of the electric motor up to the threshold R, it is ensured that the recovery per unit of time is maximum and that this guarantees the safety of the vehicle occupants by ensuring that the tire will maintain friction with the ground.If a flat-rate estimate of this threshold R is possible by taking into account the condition of the ground, dry or wet, and the braking capacity of the tire which best corresponds to the maximum deceleration load of the vehicle, in more precise determinations of the threshold R, it is possible to take into consideration the state of wear of the tire, new, half-worn or worn, but also its state of heating, the design of its tread according to the state of wear in particular by means of access to more or less sophisticated data linked to the identity of the tire.

[0037] Preferably, the electric motor propelling several tires of a vehicle, the threshold R of the energy recovery of the electric motor is defined by the following relation: R = (Xi Zi) * mm(Pj) where Pi is the maximum deceleration potential P of each tire i and Zi is the load applied to each tire i.

[0038] This makes it possible to recover more energy from the electric motor while ensuring that each tire powered by the engine does not exceed the maximum deceleration threshold P, ensuring that you do not slip and that you are at maximum speed. Of course, the deceleration potential of each tire depends on the condition of the road surface, but also on the tire through its composition and architecture and its life history. Brief description of the drawings

[0039] The invention will be better understood on reading the following description, given solely as a non-limiting example and with reference to the appended figures in which the same reference numbers designate identical parts throughout and in which: • Fig. 1 presents a three-dimensional view of the influential parameter space V of the road surface condition, highlighting the surface S0 and the surface SI for several influential parameter vectors V; • Fig. 2 shows a block diagram of the method for determining the maximum deceleration potential P of a tire according to the invention; • Fig. 3 shows a block diagram of the method for controlling energy recovery from an electric motor propelling tires of a vehicle according to the invention. Detailed description of the embodiments

[0040] Fig. 1 illustrates a three-dimensional view of the influential parameter space V of the road surface condition. Of course, this space is not necessarily 3-dimensional; it is an illustrative case.

[0041] Among the influential parameters of the roadway, the invention highlights the humidity parameter FP of the roadway and the external temperature Text, this can be for example the temperature of the ambient air where the vehicle is moving or the surface temperature of the roadway in contact with this air. The third dimension of the space of influential parameters of the roadway is noted GPi, it could be, for example, a millimeter-scale soil roughness parameter such as PMT (acronym for Mean Texture Depth)

[0042] This space of influential parameters allows to visualize the vector V of influential parameters for each tire rolling configuration. In this figure are illustrated three distinct vectors referenced from VI to V3. Each vector Vi corresponds to a specific state of the influential parameters of the roadway such as IThumidity of the roadway which allows to distinguish a dry ground from a wet ground. But also a wet ground from a wet ground where the water will accumulate above a plane resting on the vertical ends of the ground at the dimensional scale of the surface of the tire in contact with the ground, i.e. approximately an area of ​​100 cm 2 at 200 cm 2of equivalent surface. Thus, the nature of the soil, which is characterized for example by its roughness at the millimeter scale, appears to be a determining factor in the soil humidity parameter. In the case of this representation, the soil considered is a macrosmooth soil of the polished concrete type, which in fact limits the possible interactions between the nature of the soil and its humidity parameter. Thus, the surface S0, which symbolizes the transition from a so-called dry soil to a so-called wet soil, is similar to a locally flat surface in the space of the influential parameters of this macrosmooth soil of the polished concrete type.

[0043] Another influential parameter of the soil is represented, it is the external temperature at the level of the soil surface. The temperature T0 is the threshold temperature from which pure water will pass from its fluid state to a solid state of ice type, that is to say the zero temperature. However, this must be adapted according to the climatic specificities where the soil is located, both in terms of chemical species present in the air or water and in terms of climatic conditions (external temperature, wind)

[0044] The set of influential soil parameters defines in the chosen influential parameter space a vector starting from the origin whose components on each axis of the influential parameter space represent a value according to this space. Here, the space is defined at least through a humidity parameter FP and an external temperature which are not linked to each other due to the soil. This is not necessarily the case.

[0045] Here we denote three vectors of influential parameters denoted VI to V3, each representing the conditions of a polished concrete type floor. Vectors VI and V3 cross the surface S0 while vector V2 does not cross it. And vectors VI and V2 do not cross the surface SI while vector V3 crosses it.

[0046] In conclusion, vector VI crosses S0 without crossing SI, therefore the grip potential of any tire on this wet ground will be defined by PO which represents a grip potential on wet ground. Vector V2 does not cross S0, it corresponds to a so-called dry ground. The grip potential of any tire traveling on this ground will be defined by PL Finally, vector V3 crosses the surface S0 but also the surface SI, it therefore corresponds to a wet and wintry ground. Any tire traveling on this ground will have a grip potential of type P2.

[0047] Fig. 2 is a complete block diagram of the method for determining the maximum deceleration potential P of a tire according to the invention. To provide clarity to this block diagram. The various steps claimed are in actions represented by rectangular-shaped boxes possibly associated with a numerical reference. The arrows between the boxes translate the various possible interactions between the actions. The arrows in solid black line represent the essential actions claimed. The arrow in solid gray line corresponds to a specific alternative relating to the essential actions. The arrows in black dashes correspond to an alternative described in the description. The arrows in black dotted lines correspond to the alternatives of the method involving only the identification of the tire. The arrows in small light gray dashes correspond to the alternatives involving in addition to the state of wear of the tire.Finally, the gray dotted arrows correspond to the alternatives taking into account the tire thermal properties.

[0048] The heart of the process is found in the step referenced 1001 where a vector of parameters of the ground where the vehicle is traveling is constructed, including a humidity parameter PF and preferably an ambient temperature parameter Text. Of course, depending on the ground where the vehicle is traveling, it is also possible to take into account certain parameters of the nature of the ground to go even further in the precision of the diagnosis, such as, for example, example, PMT (acronym for Average Depth of Texture) to take into account the roughness of the ground at the millimeter scale.

[0049] From this step of determining the vector V, it is compared in a space of influential parameters of the soil with a first reference surface S0. This reference surface S0 is defined by a humidity parameter PFO which determines the passage of the roadway from a dry state to a wet state regardless of the height of water on the roadway. Depending on the space of influential parameters of the soil chosen, the vector V is compared with this surface S0. Implicitly, this surface S0 divides the space of influential parameters of the soil into two sub-spaces each representing a specific state of the soil, the first sub-space defines a so-called dry state while the second sub-space defines the wet state of the same soil. The comparison carried out consists of knowing whether the vector V crosses the surface S0 or not and therefore of distinguishing in which sub-space the arrival point of the vector V is located.

[0050] In the first case, if the first subspace is the target of the vector V, the method goes to the step referenced 1004. At this time, the maximum deceleration potential P of the tire is governed by a state potential PO which corresponds to a so-called dry road surface. Otherwise, the maximum deceleration potential P of the tire is controlled by the state potential PI which corresponds to a so-called wet road surface, which corresponds to the step referenced 1005. To identify these state potentials PO or PI, the method needs on the one hand to identify the load Z applied to the tire, which corresponds to step 1002. And on the other hand, the method also needs to identify the overall load Zveh applied to the vehicle, which corresponds to step 1003. These determinations can be fixed or obtained through a direct or indirect measurement of the load sought. This measurement can be made on the vehicle through dedicated devices or outside the vehicle.In this second case, the measurement information is sent back to the vehicle by means of communication. The last useful coefficient for each state potential is a fixed value.

[0051] Then, it is possible to define the wet state of the soil more precisely by dissociating a sub-space corresponding to a wet state called winter from a sub-space corresponding to a wet space that will be described as spring. To do this distinction it is appropriate that the external temperature parameter Text is present in the vector of the influential parameters V of the soil. At this time, the two sub-spaces are delimited by a surface SI which is defined by a specific external temperature T0. The positioning of the vector V of the influential parameters of the soil V in relation to this surface SI determines the membership of the soil to one or the other of the sub-spaces. If the sub-space of arrival of the vector V corresponds to that of a so-called spring state, we remain on step 1005 for the identification of the state potential PI. But, if the vector V arrives in the so-called winter sub-space, we move on to step 1006 and the maximum deceleration potential P is governed by the state potential P2. Necessarily these potentials need the results of steps 1002 and 1003.

[0052] By taking standard values ​​to determine the tire condition potentials while being safe, it is advisable to take the most penalizing reference values ​​to avoid the risk of making the tire slip on the road regardless of the tire. In order to improve the prediction of the maximum deceleration potential P of the tire and this regardless of the condition of the road, it is preferable to introduce a grip index I through step 1008. This index makes it possible to refine the maximum declaration potential P of the tire on the scale of T individuals through step 1007. Thus, obtaining the identity of the tire through step 1007 makes it possible to have access to specific information on the tire allowing to refine its grip potential according to the state of the ground, i.e. dry, wet or winter wet.This information makes it possible to weight the potential states PO, Pl, P2 at the individual scale. Of course, the weighting can vary depending on the state of the ground, which is reflected by the differentiated functions f, f and f ' at the respective stages 1004, 1005 and 1006. Thus, the energy recovery of the electric motor can be optimized in the long term depending on the individual tire and the climatic conditions in which the vehicle is traveling.

[0053] And in order to optimize the prediction of the maximum deceleration potential P of the tire, regardless of the condition of the road, it is preferable to introduce a wear index U through step 1010. This wear index U makes it possible to refine the maximum deceleration potential P of the tire according to the tire's usage history. This history is necessarily associated with the individual tire through of step 1007. This wear index U therefore requires a determination of the level of wear of the tire which can be done on a flat-rate basis or carried out through a specific measurement on the tire. This wear of the tire potentially modifies the geometry of the external surface of the tire in contact with the ground which modifies its adhesion potential. Here, the term wear will be understood to mean both the reduction in the thickness of the tire tread generated mainly by the interaction forces between the tire and the ground but also the aging of the thermomechanical properties of the tire materials due to the physicochemical attacks undergone during use.Thus, obtaining the identity of the tire through step 1007 allows access to specific information on the tire to refine its adhesion potential according to the state of the ground, i.e. dry, wet or winter wet. This information makes it possible to weight the potential states PO, Pl, P2 at the individual scale. Of course, the weighting can vary according to the state of the ground, which is reflected by the differentiated functions f, f and f ' in the respective steps 1004, 1005 and 1006. Thus, it is possible to optimize in the long term the energy recovery of the electric motor according to the individual of the tire and the climatic conditions in which the vehicle is traveling.

[0054] For wet conditions in particular, the wear index can vary depending on the vehicle's rolling speed v. In fact, the saturation of the tread groove network of a tire is a function of the open volume of the tread linked to the wear of the tire but also to the flow of water to be evacuated by the groove network which is a function of the tire's rolling speed v since generally the water is rather stagnant in front of the tire when moving.

[0055] Finally, in order to also optimize the prediction of the maximum deceleration potential P of the tire, regardless of the condition of the road surface, it is preferable to introduce a temperature index T through step 1012. This temperature index T makes it possible to refine the maximum deceleration potential P of the tire according to the thermal stresses of the tire. These thermal stresses potentially vary from one individual tire to another, which justifies associating it with the individual tire through step 1007. This temperature index T therefore requires a determination of the temperature of the tire level, step 1011, which can be done on a lump sum basis or carried out through a specific measurement on the tire. The thermal of the tire potentially modifies the adhesion properties of the external surface of the tire in contact with the ground, which modifies its adhesion potential. Here, the term thermal will be understood to mean both the core temperature of the tire tread generated mainly by the deformations undergone by the materials but also the thermal exchanges with the environment external to the tire both by convection and radiation with the air and conduction with the ground. Thus, obtaining thermal information from the tire through step 1011 and from the external environment allows access to specific information on the tire allowing its adhesion potential to be refined according to the state of the ground, i.e. dry, wet or winter wet.This information makes it possible to weight the potential states PO, Pl, P2 at the individual scale. Of course, the weighting can vary depending on the state of the ground, which is reflected by the differentiated functions f, f and f ' at the respective stages 1004, 1005 and 1006. Thus, the energy recovery of the electric motor can be optimized in the long term depending on the individual tire and the climatic conditions in which the vehicle is traveling.

[0056] Fig. 3 is a block diagram of the method for controlling the recovery of electrical energy 2000 from an electric motor powering at least one tire of a vehicle according to the invention. This control is executed when the vehicle brakes.

[0057] This method begins with the step referenced 2001 of determining a vector of influential parameters V of the roadway on which the vehicle is traveling. This vector includes a humidity parameter PF of the roadway.

[0058] From the determination of this vector V, it is possible to identify the state of the ground by comparing this vector V to a surface S in the space of the influential parameters of the roadway. This surface S is at least defined by a specific value PF0 of the humidity parameter PF reflecting the passage of the state of the ground between a first state called dry and a second state called wet. Preferably, the surface S is also defined with a specific value T0 of the temperature parameter of the environment where the vehicle is traveling. This second specific value T0 reflects the passage of the ground from a state called spring to a so-called winter state. Thus, the surface S delimits three sub-spaces in the space of the parameters of the roadway leading to the determination of a specific state potential PO, PI or P2 for each sub-space. The maximum deceleration potential of the tire P is then governed at zero order by one of these state potentials. The determination of the maximum deceleration potential P of the tire can also preferentially take into account the individual grip capacity of the tire which is called grip index I. It can also take into account the history of the tire which is synthesized through a wear index U of the tire. This second index takes into account the geometric modifications of the tire due to the erosion of the rubbers but also the aging of the rubbers over time.Finally, it can also take into account the thermal properties of the tire through a temperature index T which integrates on the one hand the temperature of the environment where the tire is located but also the internal temperature of the tire generated by the thermomechanical stresses of the tire and its thermal exchange capacities with the environment external to the tire.

[0059] Finally, when the maximum deceleration potential P of the tire is established, it is possible to determine the recovery threshold of the electric motor R at the step referenced 2006. The threshold R takes into account the maximum declaration potential P of the tire obtained according to the state of the ground at one of the steps referenced 2002 to 2004 and the load Z applied to the tire which is the result of step 2005.

[0060] Preferably, if the electric motor powers several tires of the vehicle, the electrical energy recovery threshold R of the electric motor is then obtained by the sum of the loads applied to the various tires Pi powered by the electric motor multiplied by the smallest value of maximum deceleration potential of these same tires Pi. This ensures that none of the tires powered by the electric motor will be in a slipping situation.

Claims

CLAIMS 1. Method for determining the maximum deceleration potential P (1000) of a tire driven in rotation by an electric motor equipping a vehicle comprising the following steps: - Determine at least one vector of influential parameters V (1001) of the state of the roadway where the vehicle is driving including a humidity parameter FP of the roadway; - Determine the load Z (1002) applied to the tire; - Determine the total load Z ve h (1003) applied to the vehicle; If the influential parameter vector V is contained in the subspace delimited by at least one predefined surface S0, the equation of which takes into account a value FP0 of the humidity parameter FP, so that the humidity parameter FP is less than the value FP0, the maximum deceleration potential P of the tire is defined by a state potential PO (1004) using the following relationship: where gsec being a real value between 0.8 and 2.0, preferably p sec is equal to 1.2, Otherwise, the maximum deceleration potential P of the tire is defined by a state potential PI (1005) using the following second relationship: where ghum being a real value between 0.4 and 0.6, preferably ghum is equal to 0.

5.

2. Method for determining the maximum deceleration potential P (1000) of a tire according to claim 1 in which the determination method comprises the following steps: - The step of determining the influential parameter vector V (1001) includes an outside temperature parameter Text where the vehicle is driving, - If the parameter vector V crosses the predefined surface S0 so that the humidity parameter FP is greater than the value PFO, and the influential parameter vector V is contained in a subspace delimited by a predefined surface SI, the definition of which takes into account a value T0 of the external temperature parameter, so that the external temperature parameter T is less than a value T0, the maximum deceleration potential P of the tire is defined by a state potential P2 (1006) using the following third relationship: where pneige being a real value between 0.1 and 0.3, preferably p ne ige is equal to 0.

2.

3. Method for determining the maximum deceleration potential P (1000) of a tire according to any one of claims 1 to 2 wherein, the determination method comprising a step of identifying (1007) said tire, the maximum deceleration potential P is weighted by an adhesion index I (1008) which quantifies the capacity of said identified tire to adhere to the ground during braking, the adhesion index I (1008) is associated with the identification of the tire (1007).

4. Method for determining the maximum deceleration potential P (1000) of a tire according to claim 3 wherein, the maximum deceleration potential P being defined by the state potential PO, the grip index I (1008) corresponds to a grip index value on dry ground which is deduced from a standardized grip class which is associated with the identification of the tire.

5. Method for determining the maximum deceleration potential P (1000) of a tire according to claim 4 in which the standardized grip class is a standardized grip class on dry ground or a standardized grip class on wet ground.

6. Method for determining the maximum deceleration potential P (1000) of a tire according to claim 3, in which the maximum deceleration potential P being defined by the state potential PI, the grip index I (1008) corresponds to a wet grip index value which is deduced from a standardized wet grip class which is associated with the identification of the tire.

7. Method for determining the maximum deceleration potential P (1000) of a tire according to claim 3, in which the maximum deceleration potential P being defined by the state potential P2, the grip index I (1008) corresponds to a grip index value on winter ground which is deduced from a standardized grip class which is associated with the identification of the tire.

8. Method for determining the maximum deceleration potential P (1000) of a tire according to claim 7 in which the standardized grip class is a standardized grip class on wet ground or a standardized grip class on winter ground.

9. Method for determining the maximum deceleration potential P (1000) of a tire according to any one of claims 1 to 8, wherein, the method comprises a step of determining a state of wear of the tire, the deceleration potential P is weighted by a wear index U (1010) which quantifies the road grip capacity of said tire according to the state of wear of the tire, the wear index U (1010) is associated with the identification of the tire (1007).

10. Method for determining the maximum deceleration potential P (1000) of a tire according to claim 9 in which the wear index U (1010) is a function of the available hollow of the tread of the tire.

11. Method for determining the maximum deceleration potential P (1000) of a tire according to any one of claims 9 to 10 in which the method includes a step of determining a rolling speed v (1009) of the tire, the wear index U (1010) is a function of the rolling speed v of the tire.

12. Method for determining the maximum deceleration potential P (1000) of a tire according to any one of claims 2 to 11 wherein, the method comprising a step of determining a tire temperature Tpneu (1011), the maximum deceleration potential P is weighted by a temperature index T (1012) taking into account the outside temperature Text and the tire temperature Tpneu, the temperature index T (1012) is associated with the identification of the tire (1007).

13. Method for controlling the recovery of electrical energy (2000) from an electric motor propelling at least one tire of a vehicle comprising the following steps: - Determine at least one vector of influential parameters V (1001) of the state of the roadway where the vehicle is driving including a humidity parameter FP of the roadway, preferably at least one external temperature parameter Text where the vehicle is driving; From the at least one vector of influential parameters V (1001), determine a maximum deceleration potential P (1000) of the at least one tire according to any one of claims 2 to 12; Adjusting the energy recovery of the electric motor associated with the at least one tire up to a threshold R; in which the threshold R is a function of the maximum deceleration potential P of the at least one tire and the load Z (1002) applied to the at least one tire according to the following relationship: R = Z * P 14. Method for controlling the recovery of electrical energy from an electric motor propelling at least one tire of a vehicle according to claim 13, in which, the electric motor propelling at least two tires i of the vehicle, the threshold R of the energy recovery of the electric motor is defined by the following relation: where Pi is the maximum deceleration potential P of each tire i and Zi is the load applied to each tire i.

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