METHOD FOR RECOVERING ENERGY DURING BRAKING OF A VEHICLE WITH AN ELECTRIC PROPULSION SYSTEM

Abstract

The invention relates to a method for determining the maximum deceleration potential P (1000) of a tire driven by an electric motor equipping a vehicle, comprising the following steps: - Determining a parameter vector V (1001) of the road surface condition, including a humidity parameter FP; - Determining the load Z (1002) applied to the tire; - Determining the load Zveh (1003) applied to the vehicle; - If the vector V is contained within the subspace delimited by a predefined surface S0, whose equation takes into account a value FP0 of the humidity parameter FP, the maximum deceleration potential P is defined by a state potential P0 (1004) by the following relation: where µsec is a real number between 0.8 and 2.0. Otherwise, it is defined by a state potential P1 (1005) by the following relation: where µhum is a real number between 0.4 and 0.6. Fig. 2

Description

Title of the invention: METHOD FOR RECOVERING ENERGY DURING BRAKING OF A VEHICLE COMPRISING AN ELECTRIC PROPULSION SYSTEM Scope of the invention

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

[0002] The development of motor vehicles partially powered by electric motors has been booming for two decades, whether the vehicle is a passenger car, a bus, or a goods vehicle. These vehicles can be fully electric, or hybrid, meaning that electric propulsion on one axle is combined with internal combustion propulsion on the other, for example. Finally, these electric motors are powered in propulsion mode by an electric battery that can be charged at a roadside or home charging station, or by an electricity generator such as an internal combustion engine or a fuel cell. The drawback of these electric propulsion systems lies in their limited range, due to the trade-off between the weight of the battery and the capacity it provides to power the electric motor.The advantage of electric motors is their reversibility, allowing them to switch from a propulsion mode during acceleration to a regenerative braking mode during deceleration. Naturally, the more optimized these deceleration and energy recovery phases are, the more efficient the battery charging and therefore the improved range of the transport vehicle.

[0003] However, it is possible to control the vehicle's braking, that is, to choose the axle(s) that will bear the braking load or to choose the type of braking to activate if several braking systems are available on the vehicle. Document DE 102019102244 first describes a device for recharging the battery of an electric vehicle during deceleration phases. This device includes a module for detecting a road moisture parameter, which feeds a module for comparing this parameter to 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. defined. This document also teaches a method for controlling electrical energy recovery during deceleration phases, comprising the following steps: detecting a moisture parameter of the road surface on which the vehicle is traveling, comparing this parameter to a predefined value, and if the moisture parameter is below this predefined value, increasing the electric vehicle's energy recovery up to a predefined threshold. However, this document remains silent on the choice of this threshold value, which corresponds to a maximum level of electrical energy recovery by the electric motor. Finally, the choice of these thresholds must also ensure safe vehicle deceleration, particularly in terms of vehicle stability, for example.

[0004] In order to enforce braking on the electrically driven axles to take advantage of the reversibility of the electric motors to recharge the batteries, it is important not to exceed the tire's grip threshold with the road in order to maintain the tire's guidance and, consequently, that of the vehicle. This grip threshold defines the maximum level of friction the tire can withstand before it slips relative to the ground. Naturally, this grip threshold depends on the characteristics of the road surface, the tire's intrinsic properties related to its material composition and thermomechanical structure, as well as the tire's operating conditions, such as inflation pressure and applied static load.

[0005] The objects of the invention which follow are intended to solve the problems related 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 influencing parameters V of the condition of the pavement where the vehicle is traveling, including a pavement moisture parameter FP; • Determine the Z load applied to the tire; • Determine the total load Zveh applied to the vehicle; • If the influencing parameter vector V is contained within the subspace bounded by at least one predefined surface S0 whose equation takes into account a value FP0 of the humidity parameter FP, such that the humidity parameter FP is less than the value PF0, the maximum deceleration potential P of the tire is defined by a state potential PO using the following relationship • „ z FO - -—- * ^SqSP • where psee being a real value between 0.8 and 2.0, preferably equal to 1.2, • Otherwise, the maximum deceleration potential P of the tire is defined by a state potential PI using the following second relation: Pi — + >( • where phum being a real value between 0.4 and 0.6, preferably p hum is equal to 0.5.

[0007] In order to enforce braking on the electrically driven axles to take advantage of the reversibility of the electric motors to recharge the batteries, it is important, however, not to exceed the tire's adhesion threshold with the road surface in order to maintain tire guidance and consequently ensure vehicle safety. This adhesion threshold, under deceleration stress, defines the maximum level of friction the tire can withstand before it slips relative to the ground. It is known that this tire adhesion threshold during braking is a zero-order function of the road surface moisture content on which the vehicle is traveling. The method, through a vector of influencing road surface parameters including a road surface moisture parameter, allows the soil moisture content to be determined between two distinct states corresponding to either a dry or a wet surface.This distinction is encountered in most cases of vehicle use.

[0008] Naturally, 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 affecting the tire's grip performance on the ground. This is governed by two parameters related to tire operation: inflation pressure and the static load applied to the tire. While the inflation pressure is generally constant across the vehicle's tires, the distribution of the static load on the vehicle can vary significantly between the different axles depending on the vehicle type. In order to evaluate the intrinsic deceleration potential of a tire, it is necessary to avoid making 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 soil and the tire, the dry p and the wet p, can be fixed values ​​taken from predefined intervals, these intervals being disjoint by definition. The choice between the two values ​​results from the positioning of the vector of influencing parameters of the pavement condition relative to a specific surface S0 that traces the boundary between the wet soil and the dry soil according to . a predefined moisture parameter PF in the space of influential parameters. The surface equation SO is defined such that the moisture parameter is equal to a PFO value of the moisture parameter that marks the transition of the soil from a dry to a wet state, regardless of the amount of water on the soil.

[0009] Thus, the proposed method makes it possible to define, for each tire driven by an electric motor, a maximum permissible level of deceleration P that guarantees a tire-ground friction condition regardless of the applied load and the condition of the road surface. 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 electric motor's energy recovery system is not the limiting factor in energy recovery capacity, the determination of the energy recovery threshold that ensures the tire remains in safe driving conditions. The presented method achieves this by guaranteeing that the tire-ground friction threshold does not cause it to slip relative to the ground.

[0010] Advantageously, the determination method comprises the following steps: • The step of determining the influential parameter vector V comprising an outside temperature parameter Text where the vehicle is traveling, • If the parameter vector V crosses the predefined surface S0 such that the humidity parameter FP is greater than the value PFO, and the influential parameter vector V is contained within a subspace delimited by the predefined surface SI, whose definition takes into account a value T0 of the outside temperature parameter, such that the outside 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 relation: ' — -— « '•'î.xA • where p_snow is a real value between 0.1 and 0.3, preferably p_snow is equal to 0.2.

[0011] In the specific case where the weather conditions on which the vehicle is traveling lead to the tire driving on a snowy or icy road, the tire's grip is affected due to the very low level of friction experienced by the road surface compared to an asphalt or bituminous surface. To distinguish this particular driving case, an outside temperature parameter should be added to the humidity parameter to determine the possible presence of such driving conditions. The maximum deceleration potential of the tire should then be adjusted to a threshold P2. Taking into account a snow factor (tire-snow factor) between 0.1 and 0.3, adjusting this new threshold allows for energy recovery for the electric motors powering the tires while ensuring a level of vehicle safety for steering and maneuvering in these weather conditions. Although the deceleration potential is low, it remains non-zero and ensures better vehicle range. This snow factor (tire-snow factor) is taken as a fixed value based on the positioning of the influencing parameter vector V relative to two surfaces in the influencing parameter space, defining the thresholds for crossing a road surface condition from a first state where the road is wet to a second state where the road is snow-covered or icy, and vice versa.

[0012] According to a first embodiment, the determination process includes a step of identifying said tire, the maximum deceleration potential P is weighted by an adhesion index I which quantifies the ability 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 fixed values ​​can be used for the maximum deceleration potential P, regardless of the road surface and tire type, energy recovery can be made more dynamic by weighting this fixed value with a friction index I, which is linked to the individual tire through a preliminary tire identification step. This allows the maximum deceleration potential P to be increased or decreased relative to the fixed value based on information associated with the tire's identity. This information relates to the tire's relative braking performance on the road surface, which best reflects the tire's deceleration capacity.This can be an index intrinsically linked to the tire as technical data held by the manufacturer or trader of the tire product, or an average value that 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 friction index I corresponds to a value of friction index on dry ground which is deduced from a standardized friction 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 dry condition. This is done using a standardized grip class. The class information can be publicly available and provides an indication of the tire's braking capacity relative to a benchmark. This benchmark allows tires to be standardized against each other. Thus, a numerical value can be extracted that allows the tire to be adjusted. The maximum deceleration potential of the tire is measured in both positive and negative directions. This ensures better electrical energy recovery than the general method for tires publicly advertised as having increased braking capacity on dry surfaces. Furthermore, it limits the use of less efficient tires in terms of braking capacity, thus guaranteeing vehicle safety during these energy recovery phases by the electric motor.

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

[0017] In the case of a dry road surface, the friction index I can ideally be derived from a standardized dry grip class that best corresponds to the tire's deceleration capacity on this type of road surface. However, it is also possible to use a standardized wet grip class because, with identical tires and for standard tires in particular, the relative ranking of tires during braking between a wet and a dry road surface is not affected by the road surface moisture level, especially in the absence of water above the contact patch at the highest points of the road surface at the scale of the tire's contact patch. A possible adjustment of the numerical value of the friction index I derived from the standardized grip class must be made when using the standardized wet grip class.

[0018] According to another preferred embodiment, the maximum deceleration potential P being defined by the state potential PI, the friction 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 state potential PI on wet surfaces, using a friction 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. A value is then associated with an increase or decrease in the state potential PI, which is linked to the tire's grip class. This grip class is defined for wet surfaces.

[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 car, or by standard ISO-15222 (ISO 5222:2011) if the target vehicle is a truck or van. The wet braking performance of a vehicle equipped with said tire is then compared to the performance of the same vehicle equipped with a reference tire, known as an SRTT (Standard Reference Truck Tyre). The wet braking performance of the SRTT tire worth 1.00 by convention.

[0021] The conditions for these standardized tests are preferably specified either by ISO 15222 for trucks and buses belonging to tire class C3 and vans belonging to tire class C2, or by European Regulation EC 229 / 2011 for passenger vehicles belonging to class Cl. Of course, reference may be made to any equivalent standard applicable in the country concerned, without departing from the scope of the invention. In practice, these tests allow the tire to be assigned a grip class, symbolized by a letter from A to F. The table below illustrates the relationship between the numerical value of the wet grip class, denoted G, and the class letter for C3 tires. C3 Tires Wet Grip Index Wet Grip Class G > 1.25 A 1.10 <G< 1.24 B 0.95 < G< 1.09 C 0.80 < G< 0.94 D 0.65 < G<0.79 E G<0.64 F

[0022] Within the framework 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 with 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 friction index I corresponds to a value of friction index on winter ground which is deduced from a standardized friction class which is associated with the identification of the tire.

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

[0025] Of course, it is possible to adjust the deceleration potential of tire P when the road surface is in a condition described as wintery. For this purpose, 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 This reference to a benchmark allows for the standardization of tires relative to one another. A numerical value can then be extracted, enabling adjustment of the tire's maximum deceleration potential (P) in terms of both potential gain and potential loss. This ensures better electrical energy recovery than the general method for tires publicly advertised as having increased braking capacity on winter surfaces, such as snow or ice. Furthermore, it limits the performance of tires with the lowest braking capacity on these types of surfaces, thus guaranteeing vehicle safety during energy recovery phases by the electric motor.

[0026] In the case of a wet and cold road surface, the friction index I can ideally be deduced from a standardized winter road surface friction class that best corresponds to the tire's deceleration capacity on this type of road surface. However, it is also possible to use a standardized wet road surface friction class because, for identical tires and standard tires in particular, the relative ranking of tires during braking between a wet road surface and a winter road surface is easily deduced from one another; the ranking is generally reversed.

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

[0028] The wear level of a tire can affect its grip performance on the road surface by altering the amount of rubber in direct contact with the surface. This, in turn, modifies the contact pressure between the tire and the road, which in turn increases the rubber's temperature by intensifying friction. This heating, or conversely, cooling, alters the adhesion between the tire and the road surface. This principle is observed on dry pavement: an increase in the rubber / road contact area due to a change in the tread pattern during wear leads to improved grip and, consequently, a greater maximum deceleration potential for the tire. Conversely, on wet and winter surfaces, the tread pattern allows for the evacuation of the third component: water, snow, or ice.Therefore, an increase in the rubber / road contact rate due to a change in the tread groove pattern during wear can lead to a degradation of the adhesion potential and therefore of the maximum deceleration potential of the tire. Of course, the nature of the rubber compounds of the... The tire, particularly that of the components in contact with the ground, influences the grip capacity; therefore, the wear index U should be linked to the tire's identity to take this dependence into account if one wishes to be more precise.

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

[0030] The term "void" 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 ways. It can be a surface void, measured by looking at the void level at the tire's contact patch on the ground; it is then expressed as a percentage of the surface area associated with the outer edge of the tire's contact patch on the ground. It can also be expressed as the average void area in a radial section of the tire, the tread of which is then homogenized. It is then expressed as a percentage of the surface area delimited by the lines furthest radially from the tire relative to the natural axis of rotation. Finally, it can be expressed as the void volume in a section of the homogenized tire tread, per unit angular area of ​​the tire.Finally, it can also correspond to the tread groove volume limited to the sector of the tread delimiting the tire's contact patch. Depending on the groove characterization considered, the wear evolution law must be adapted for each of the different maximum deceleration potentials. Naturally, a tire's groove pattern is linked to its specific characteristics.

[0031] Very advantageously also, the process includes 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 amount of water on the road surface. Indeed, when moving forward, the front axle of a vehicle is confronted with the water accumulated on the road. Whereas the tires of the rear axle, at typical driving speeds of around 50 km / h, will encounter less water on the road. The front tires will have displaced the water before it returns to the road surface when the rear axle passes. Furthermore, in heavy rainfall, the action of the front axle can induce a local increase in water just in front of the front tire due to the saturation of its tread pattern. This accumulation can cause partial separation of the tire from the road surface on the part of the tire exposed to this accumulated water.This leads to a deterioration in tire grip and therefore its impact must be addressed with a specific evolution law compared to dry ground conditions.

[0033] According to another advantageous embodiment, the process comprises a step of determination of 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 temperature of the tire Tpneu, the temperature index T is associated with the identification of the tire.

[0034] It is known that the adhesion performance of a tire's rubber compounds depends on the temperature of the compounds and, more specifically, on the difference between this temperature and the ambient environment in which the tire is driven. Taking into account the heat exchange between the tire compounds and the external environment makes it possible to monitor the evolution of the tire compounds' temperature and, in particular, to control temperature overheating due to insufficient heat exchange with the external environment. Of course, these behaviors vary depending on the type of rubber compounds used and also on the tire's structure, which either reduces or increases this heat exchange with the external environment. Therefore, this temperature index T is preferentially linked to the tire's identification, to be more precise, at least according to the tire range: 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 influencing parameters V of the condition of the pavement where the vehicle is traveling, including a humidity parameter FP of the pavement, preferably at least one outside temperature parameter Text where the vehicle is traveling; • From at least one influential parameter vector V, determine a maximum deceleration potential P (1000) of at least one tire; • Adjust the energy recovery of the electric motor associated with at least one tire up to a threshold R; in which the threshold R is a function of the maximum deceleration potential P of at least one tire and the load Z applied to at least one tire according to the following relationship: R - 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 permissible for the tire per unit of time. Thus, by controlling the braking force of the electric motor's energy recovery system up to the threshold R, it is ensured that the recovery per unit of time is maximized and that this guarantees the safety of the vehicle's 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 state of the ground, dry or wet, and the braking capacity of the tire which best corresponds to the maximum deceleration demand 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 related 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 = Œt ^î) * ™in(^i) • where Pi is the maximum deceleration potential P of each tire i and Zi is the load applied to each tire i.

[0038] Thus, it is possible to recover more energy at the electric motor level while ensuring that each tire driven by the motor does not exceed the maximum deceleration threshold P, thereby preventing slippage and ensuring maximum deceleration. Of course, the deceleration potential of each tire depends on the road surface condition, but also on the tire itself, its composition, design, and history. Brief description of the drawings

[0039] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the accompanying figures in which the same reference numbers designate identical parts throughout and in which: • Fig. 1 presents a three-dimensional view of the space of influential parameters V of the pavement condition, highlighting the surface S0 and the surface S1 for several influential parameter vectors V; • Fig. 2 presents a synoptic diagram of the method for determining the maximum deceleration potential P of a tire according to the invention; • Fig. 3 presents a synoptic 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 implementation methods

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

[0041] Among the influencing parameters of the pavement, the invention highlights the pavement moisture parameter FP and the outside temperature Text. This could be, for example, the ambient air temperature where the vehicle is moving or the surface temperature of the pavement in contact with this air. The third dimension of the space of influencing pavement parameters is denoted GPi; it could be, for example, a soil roughness parameter on the millimeter scale such as PMT (acronym for Mean Texture Depth).

[0042] This space of influential parameters allows visualization of the vector V of influential parameters for each tire rolling configuration. Three distinct vectors, referenced from VI to V3, are illustrated in this figure. Each vector Vi corresponds to a specific state of the influential pavement parameters, such as pavement moisture, which distinguishes between dry and wet soil. It also distinguishes between wet and damp soil, where water accumulates above a plane resting on the vertical edges of the soil at the dimensional scale of the tire surface in contact with the ground, representing an area of ​​approximately 100 cm² to 200 cm² of equivalent surface area. Thus, the nature of the soil, characterized, for example, by its roughness at the millimeter scale, appears as a determining factor in the soil moisture parameter.In this representation, the soil considered is a macrosmooth polished concrete type soil, which effectively limits the possible interactions between the soil type and its moisture content. Thus, the surface S0, which symbolizes the transition from a so-called dry soil to a so-called wet soil, resembles a local plane surface in the space of the influential parameters of this macrosmooth polished concrete type soil.

[0043] Another influential soil parameter is represented: the outside temperature at the soil surface. Temperature T0 is the threshold temperature at which pure water will change from its fluid state to a solid, ice-like state, i.e., zero. However, this temperature must be adjusted according to the specific climatic conditions where the soil is located, both in terms of the chemical species present in the air or water and in terms of climatic conditions (outside temperature, wind).

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

[0045] Three influential parameter vectors, denoted V1 and V3, are here denoted, each representing the conditions of a polished concrete type floor. Vectors V1 and V3 cross the surface S0, while vector V2 does not. And vectors V1 and V2 do not do not cross the SI surface while the vector V3 crosses it.

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

[0047] Figure 2 is a complete diagram of the method for determining the maximum deceleration potential P of a tire according to the invention. To clarify this diagram, the various claimed steps are represented by rectangular boxes, possibly associated with a numerical reference. The arrows between the boxes illustrate the various possible interactions between the actions. The solid black arrows represent the essential claimed actions. The solid gray arrow corresponds to a specific alternative concerning the essential actions. The dashed black arrows correspond to an alternative described in the description. The dotted black arrows correspond to the method alternatives involving only tire identification. The small light gray dashed arrows correspond to the alternatives involving, in addition to the tire's wear level.Finally, the grey dotted arrows correspond to alternatives that take into account the tire's thermal performance.

[0048] The core of the process is found in step 1001, where a vector of soil parameters for the vehicle's travel is constructed, including a humidity parameter PF and preferably an ambient temperature parameter Text. Of course, depending on the soil on which the vehicle travels, it is also possible to take into account certain soil type parameters to further refine the diagnosis, such as, for example, the PMT (Mean Texture Depth) to account for soil roughness at the millimeter scale.

[0049] From this step of determining the vector V, it is compared in a space of influencing soil parameters with a first reference surface S0. This reference surface S0 is defined by a moisture parameter PF0 which determines the transition of the pavement from a dry to a wet state regardless of the water level on the pavement. Depending on the chosen space of influencing soil parameters, the vector V is compared with respect to this surface S0. Implicitly, this surface S0 divides the space of influencing soil parameters into two subspaces, each representing a specific soil state. The first subspace defines a so-called dry state, while the second subspace defines the wet state of the same soil. The comparison performed consists of determining whether the vector V crosses the surface S0 or not, and thus distinguishing in which subspace is the arrival point of the vector V located?

[0050] In the first case, if the first subspace is the target of the vector V, the process proceeds to step 1004. At this point, 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, corresponding to step 1005. To identify these state potentials PO or PI, the process 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 process also needs to identify the overall load Zveh applied to the vehicle, which corresponds to step 1003. These determinations can be made using a fixed formula or obtained through a direct or indirect measurement of the load in question. This measurement can be taken on the vehicle through dedicated devices or outside the vehicle.In this second case, the measurement information is transmitted back to the vehicle via communication channels. The final coefficient used for each state potential is a fixed value.

[0051] Next, it is possible to define the soil moisture state more precisely by distinguishing a subspace corresponding to a so-called winter moisture state from a subspace corresponding to a spring moisture state. To make this distinction, the outside temperature parameter Text must be present in the soil influencing parameter vector V. At this point, the two subspaces are delimited by a surface S1, which is defined by a specific outside temperature T0. The positioning of the soil influencing parameter vector V relative to this surface SI determines whether the soil belongs to one or the other subspace.If the arrival subspace of the vector V corresponds to that of a so-called spring state, we remain at step 1005 for the identification of the state potential PL. However, if the vector V arrives in the so-called winter subspace, we move to step 1006 and the maximum deceleration potential P is governed by the state potential P2. These potentials necessarily require the results of steps 1002 and 1003.

[0052] When using standard values ​​to determine tire condition potentials while ensuring safety, it is advisable to use the most restrictive reference values ​​to avoid the risk of the tire slipping on the road surface, regardless of the tire. To improve the prediction of the maximum deceleration potential P of the tire, regardless of the road surface condition, it is preferable to introduce a grip index I through step 1008. This index allows for refining the maximum declared potential P of the tire at the individual level through step 1007. Thus, obtaining the tire's identity through step 1007 provides access to specific information about the tire, allowing for refining its grip potential according to the road surface condition. that is, dry, wet, or wet winter conditions. This information allows for the weighting of fixed PO, PI, and P2 state potentials at the individual tire level. Naturally, the weighting can vary depending on the soil condition, resulting in the differentiated functions f, f', and f” at steps 1004, 1005, and 1006, respectively. Thus, the energy recovery of the electric motor can ultimately be optimized according to the individual tire and the climatic conditions in which the vehicle operates.

[0053] To optimize the prediction of the maximum deceleration potential P of the tire, regardless of the road surface condition, it is preferable to introduce a wear index U in step 1010. This wear index U allows for refining the maximum deceleration potential P of the tire based on its usage history. This history is necessarily associated with the individual tire through step 1007. Therefore, this wear index U requires determining the tire's wear level, which can be done using a standard method or through a specific measurement on the tire. This tire wear potentially alters the geometry of the tire's external surface in contact with the ground, thus modifying its adhesion potential.Here, the term "wear" refers both to the reduction in tread thickness of the tire, primarily caused by the interaction forces between the tire and the ground, and to the aging of the thermomechanical properties of the tire materials due to the physicochemical stresses they undergo during use. Thus, obtaining the tire's identity through step 1007 provides access to specific information about the tire, allowing its adhesion potential to be refined according to the ground conditions, i.e., dry, wet, or wet winter conditions. This information allows for the weighting of fixed state potentials PO, PI, and P2 at the individual tire level. Naturally, the weighting can vary depending on the ground conditions, which is reflected in the differentiated functions f, f', and f” in steps 1004, 1005, and 1006, respectively.Thus, the energy recovery of the electric motor can ultimately be optimized according to the individual tire and the climatic conditions in which the vehicle is traveling.

[0054] In wet conditions in particular, the wear index can vary depending on the vehicle's speed v. Indeed, the saturation of the tread grooves of a tire depends on the open volume of the tread due to tire wear, but also on the water flow rate to be evacuated by the grooves, which is a function of the tire's speed v, since water is generally rather stagnant in front of the moving tire.

[0055] Finally, in order to optimize the prediction of the maximum deceleration potential P of the tire regardless of the road surface condition, it is preferable to introduce a temperature index T through step 1012. This temperature index The temperature T allows for refining the maximum deceleration potential P of the tire based on its thermal stresses. These thermal stresses can vary from one individual tire to another, justifying its association with the individual tire through step 1007. This temperature index T therefore requires determining the temperature of the tire's surface, step 1011, which can be done using a standard method or through a specific measurement on the tire. The tire's temperature can potentially modify the adhesion properties of the tire's outer surface in contact with the ground, thus altering its adhesion potential.Here, the term "thermal" refers to both the core temperature of the tire tread, generated primarily by the deformations undergone by the material, and the heat exchange with the environment outside the tire, both through convection and radiation with the air, and conduction with the ground. Thus, obtaining thermal information about the tire through step 1011 and the external environment provides access to specific information about the tire, allowing its adhesion potential to be refined according to the ground conditions, i.e., dry, wet, or wet winter conditions. This information allows for the weighting of fixed state potentials PO, PI, and P2 at the individual tire level. Of course, the weighting can vary depending on the ground conditions, which is reflected in the differentiated functions f, f', and f” in steps 1004, 1005, and 1006, respectively.Thus, the energy recovery of the electric motor can ultimately be optimized according to the individual tire and the climatic conditions in which the vehicle is traveling.

[0056] Figure 3 is a schematic diagram of the method for controlling the recovery of electrical energy from an electric motor propelling at least one tire of a vehicle according to the invention. This control is executed during vehicle braking.

[0057] This process begins with the step referenced 2001 of determining a vector of influential parameters V of the pavement on which the vehicle travels. This vector includes a moisture parameter PF of the pavement.

[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 influencing parameters of the pavement. This surface S is at least defined by a specific value PF0 of the moisture parameter PF, reflecting the transition of the ground state 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 in which the vehicle travels. This second specific value T0 reflects the transition of the ground from a so-called spring state to a so-called winter state. Thus, the surface S delimits three subspaces in the space of pavement parameters, leading to the determination of a specific state potential PO, PI, or P2 for each subspace. The deceleration potential The maximum deceleration potential (P) of the tire is then governed to the zeroth 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, known as the grip index (I). It can also take into account the tire's history, summarized by a wear index (U). This second index considers the geometric changes in the tire due to rubber erosion, as well as the aging of the rubber over time. Finally, it can also consider the tire's thermal behavior through a temperature index (T), which incorporates both the temperature of the environment in which the tire is located and the internal temperature of the tire itself, generated by the thermomechanical stresses and its heat exchange capacity with the external environment.

[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 referenced step 2006. The threshold R takes into account the maximum declaration potential P of the tire obtained according to the soil condition at one of the referenced steps 2002 to 2004 and the load Z applied to the tire which is the result of step 2005.

[0060] Preferably, if the electric motor drives 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 driven by the electric motor multiplied by the smallest value of the maximum deceleration potential of these same tires Pi. Thus, it is ensured that none of the tires driven by the electric motor will be in a slipping situation.

Claims

Demands

1. A 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 condition of the road surface where the vehicle is traveling, including a road surface moisture parameter FP; - Determine the load Z (1002) applied to the tire; - Determine the total load Zveh (1003) applied to the vehicle; - If the influential parameter vector V is contained in the subspace delimited by at least one predefined surface S0, whose equation takes into account a value FP0 of the humidity parameter FP, such 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 relation: where psec is a real value between 0.8 and 2.0, preferably pseCest 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 relation: PI = — * where phum being a real value between 0.4 and 0.6, preferably phum is equal to 0.

5.

2. A method for determining the maximum deceleration potential P (1000) of a tire according to claim 1, wherein 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 traveling, - If the parameter vector V crosses the predefined surface S0 so that the humidity parameter FP is greater than the value PFO, and that 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 TO of the outside temperature parameter, so that the outside temperature parameter T is less than a value TO, the maximum deceleration potential P of the tire is defined by a state potential P2 (1006) using the following third relation: P2 = TT * where Pneige being a real value between 0.1 and 0.3, preferably pneige 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 an identification step (1007) of said tire, the maximum deceleration potential P is weighted by an adhesion index I (1008) which quantifies the ground adhesion capacity of said identified tire 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 friction index I (1008) corresponds to a value of friction index on dry ground which is deduced from a standardized friction 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 wherein the standardized grip class is a standardized grip class on dry ground or a standardized grip class on wet ground.

6. A method for determining the maximum deceleration potential P(1000) of a tire according to claim 3, wherein the maximum deceleration potential P is defined by the state potential PI, and the friction index I(1008) corresponds to a wet grip index value derived from a standardized wet grip class associated with the identification of the pneumatic.

7. 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 P2, the friction index I (1008) corresponds to a winter surface friction index value which is deduced from a standardized friction 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 wherein the standardized grip class is a standardized wet grip class or a standardized winter grip class.

9. Method of determining the maximum deceleration potential P (1000) of a tire according to any one of claims 1 to 8 wherein the method includes 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 ground adhesion 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 wherein the wear index U (1010) is a function of the available tread depth 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 wherein, the method comprises 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 temperature of the tire Tpneu (1011), the maximum deceleration potential P is weighted by a temperature index T (1012) taking into account the outside temperature Text and the temperature of the tire Tpneu, the temperature index T (1012) is associated with the identification of the tire (1007).

13. A 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 condition of the road surface where the vehicle is traveling, including a humidity parameter FP of the road surface, preferably at least one outside temperature parameter Text where the vehicle is traveling; - From at least one influential parameter vector V (1001), determine a maximum deceleration potential P (1000) of at least one tire according to any one of claims 2 to 12; - Adjust the energy recovery of the electric motor associated with at least one tire up to a threshold R; in which the threshold R is a function of the maximum deceleration potential P of at least one tire and the load Z (1002) applied to at least one tire according to the following relationship: R = Z * P

14. A method for controlling the recovery of electrical energy from an electric motor driving at least one tire of a vehicle according to claim 13, wherein, the electric motor driving 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: R = Qh Zj) » minfPi) 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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