WO2012045953A1 - Method and device for the detection of local transient overheating in a component of a braking system - Google Patents

Method and device for the detection of local transient overheating in a component of a braking system Download PDF

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Publication number
WO2012045953A1
WO2012045953A1 PCT/FR2011/052226 FR2011052226W WO2012045953A1 WO 2012045953 A1 WO2012045953 A1 WO 2012045953A1 FR 2011052226 W FR2011052226 W FR 2011052226W WO 2012045953 A1 WO2012045953 A1 WO 2012045953A1
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WO
WIPO (PCT)
Prior art keywords
component
temperature
braking
overheating
heat
Prior art date
Application number
PCT/FR2011/052226
Other languages
French (fr)
Inventor
Sébastien BOUDEVIN
Original Assignee
Peugeot Citroën Automobiles SA
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Publication date
Application filed by Peugeot Citroën Automobiles SA filed Critical Peugeot Citroën Automobiles SA
Publication of WO2012045953A1 publication Critical patent/WO2012045953A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T17/00—Component parts, details, or accessories of power brake systems not covered by groups B60T8/00, B60T13/00 or B60T15/00, or presenting other characteristic features
    • B60T17/18—Safety devices; Monitoring
    • B60T17/22—Devices for monitoring or checking brake systems; Signal devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
    • F16D66/00—Arrangements for monitoring working conditions, e.g. wear, temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
    • F16D66/00—Arrangements for monitoring working conditions, e.g. wear, temperature
    • F16D2066/001—Temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
    • F16D66/00—Arrangements for monitoring working conditions, e.g. wear, temperature
    • F16D2066/006—Arrangements for monitoring working conditions, e.g. wear, temperature without direct measurement of the quantity monitored, e.g. wear or temperature calculated form force and duration of braking

Definitions

  • the invention relates to a method and a device for the detection of local transient overheating in a component of a braking system.
  • This invention finds applications in vehicles, especially automobiles, to prevent, in real time, any deterioration of the braking capacity of such a vehicle and to limit the wear of critical components constituting this system. It is more particularly intended for friction braking systems, such as disc brakes, drum brakes or shoe brakes depending on the vehicles concerned, where brake linings are tightened on an element in relative displacement relative to these linings in order to convert by friction, the kinetic energy driving this mobile element into heat, which is dissipated in the surrounding environment.
  • the elements in contact are subjected to high temperatures which modify their physical properties, in particular the coefficient of friction at the interface between the liners and the movable element, and accelerate the degradation of both the linings and the mobile element.
  • high temperatures which modify their physical properties, in particular the coefficient of friction at the interface between the liners and the movable element, and accelerate the degradation of both the linings and the mobile element.
  • increasing the temperature at the interface between the movable member and the linings may lead to a drop in the coefficient of friction at the same interface, which reduces the braking efficiency.
  • This phenomenon is commonly referred to as "brake fade” or "fading” in English.
  • the overheated brake system components transmit their heat to the other components of the braking system, whose subsequent rise in temperature can also cause operating disorders.
  • the hydraulic fluid commonly referred to as "brake fluid”
  • actuating the jaws bringing the linings of the movable member may, in contact with said jaws, heated by these linings enter locally boiling and cause plugs of steam, or "vapor lock” in English, in the hydraulic brake system.
  • Supervisory devices by sensor or by calculation of the temperature during braking allow, according to the prior art, to at least partially limit these phenomena of overheating.
  • these devices of the prior art are based on the determination of a mean temperature, which is obtained by a braking energy balance, possibly adjusted using a temperature measurement.
  • International Patent Application WO9621145 relating to a disk-braking and liquid cooling system, describes the measurement of the temperature of the cooling liquid and the deduction, by a mathematical model, based on an energy balance, the average braking temperature and the amount of energy dissipated to heat by this system.
  • Such an overall measurement does not make it possible to detect in real time a risk of fading of the braking or of the steam plug in the hydraulic braking circuit.
  • the braking devices of the prior art are oversized in order to avoid these risks.
  • this oversizing is penalizing in terms of cost and mass of the braking system.
  • the invention aims to solve these disadvantages of the prior art by proposing a method for the detection of local transient overheating in a component of a braking system, which method comprises, for a time t1 and a time step ⁇ , the steps of:
  • a) acquire, with a suitable sensor, a measurand representative of the braking intensity
  • the method which is the subject of the invention by combining a macroscopic information relating to the braking conditions and calculation means, makes it possible to determine local overheating information in the monitored component and to anticipate this risk of overheating more reliably than could not the methods and devices of the prior art.
  • the temporal and spatial knowledge of the field and the temperature gradients within a braking system makes it possible to estimate local transient overheating peaks in order to prevent the risks of braking fading as well as the premature thermomechanical damage of this system. .
  • the invention can be implemented according to the advantageous embodiments described below, which can be considered individually or in any technically operative combination.
  • the method is not very demanding on computing resources and allows the calculation, in real time or in near real time, of the evolution of the spatial distribution of temperature in the component.
  • the calculation of step c °) comprises a step of solving the differential equation of heat by the numerical integration of a discrete formulation thereof.
  • the method that is the subject of the invention is not very resource-intensive for calculating the temporal distribution of the temperature in the targeted component.
  • the discrete formulation of the differential equation of heat comprises the expression of the nodal temperature at any point of a mesh of the component, for a time step ⁇ .
  • This formulation reduces the instantaneous dimension of the problem to be solved by substituting itself for an analytical resolution, very difficult to obtain from a mathematical point of view.
  • the resolution of the heat equation under this formulation instantaneously produces the spatio-temporal distribution of temperature in all the points of the mesh of the component.
  • This calculation step is further simplified, and its accelerated realization, if the spatial mesh of the component is a set mesh. Since the mesh pitch is constant, the resolution scheme is iterative both in time and spatially, basing each iteration on the previous solution in time and space.
  • the mesh of the component comprises the regulated mesh of two substructures of the component, and the formulation of the equation of heat comprises conditions of temperature continuity between the two meshes.
  • the resolution of the heat equation is based on a finite difference method with an explicit Euler formulation.
  • the method which is the subject of the invention comprises a step of acquiring a measurand representative of the heat exchange conditions of the component with its environment.
  • the braking process is carried out under quasi-adiabatic conditions.
  • the method comprises a step e) of transmitting a signal when the temperature of at least one point of the spatiotemporal distribution exceeds the overheating limit temperature.
  • the signal can be sent to the driver or a supervisory device capable of modifying the braking conditions to maintain it under optimum conditions depending on the circumstances.
  • the component is a brake lining and the overheating limit temperature is determined by the risk of braking fade. This feature secures emergency braking at high speed.
  • the component is a brake fluid and the limiting temperature of Overheating is determined by the risk of creating a vapor lock in the brake system. This feature secures repeated intense braking.
  • the invention also relates to a device for implementing a method according to any one of the preceding embodiments, for monitoring a braking system, which device comprises:
  • ⁇ means capable of measuring the heat exchange conditions between the braking system and the surrounding environment
  • ⁇ ⁇ a computer memory comprising:
  • This device can be advantageously integrated with a vehicle including automobile.
  • a vehicle advantageously comprises means for measuring the conditions of heat exchange with the environment comprising a vehicle speed sensor.
  • FIGS. 1 to 6 in which:
  • Figure 1 schematically illustrates in perspective a set of components of a braking system
  • FIG. 2 shows a sectional view in perspective and a detail of this braking system
  • FIG. 3 shows an example of a mesh set in one dimension of a brake pad, FIG. 3A, and FIG. 3B a schematic example of the calculation of the spatio-temporal distribution of the temperature in this brake pad;
  • FIG. 4 shows an example of a two-dimensional regulated mesh, FIG. 4B, of a complex-shaped component such as a brake disk, FIG. 4A, by decomposing it into substructures;
  • FIG. 5 shows an exemplary vehicle incorporating a device for implementing the method that is the subject of the invention
  • FIG. 6 represents a logic diagram of an exemplary embodiment of the method that is the subject of the invention.
  • Figure 1 in a schematic representation of an exemplary embodiment of a braking system 100, it comprises a movable member, here a brake disc 110, and brake linings 120, commonly referred to by the term “platelets” in this embodiment, which are mounted in a bracket 130, fixed relative to the disc 110.
  • This disc is fixed to the hub of the vehicle wheels (not shown) by a centering housing 140 and bolts housed in the fixing holes 141 provided for this purpose.
  • the disk is therefore rotated at the same speed as the wheels of the vehicle.
  • the stirrup 130 comprises means, generally hydraulic, for clamping the linings 120 on the sides of the disc 110 and thus convert the kinetic energy that it conveys into heat, which in turn is dissipated in the surrounding medium.
  • FIG. 2 represents this device only on a the faces of the disc 110 but the fittings 120 'act symmetrically on the other side thereof.
  • the friction of the linings 120 on the disc 110 produces heat at the interface between these two elements, which heat flows in a flow ⁇ + , defining a quantity of energy per unit area by conduction.
  • a fraction of this thermal flux is injected, in particular to the fittings 120, which also transmit this heat according to an outgoing flow ⁇ " to the piston 230 and then to the hydraulic fluid contained in the circuit 240 and in contact with the piston 230.
  • Another part of the heat is dissipated in the various components of the braking system and to the vehicle components such as the stirrups 130, or the hub of the wheels by the The disk and its centering housing 140. Finally some of the heat is dissipated by convection with ambient air and by radiation with the surrounding parts.
  • the amount of heat transmitted is a function of the friction power at the disk-to-lining interface, which is proportional to:
  • This heat transfer is accompanied by an increase in the temperature of the components concerned, which temperature may be sufficient to modify temporarily or permanently the physicochemical properties of the materials constituting them, or even to produce phase or state changes. .
  • an overheating at the interface between the lining 120 and the disc 110 may cause a decrease in the dynamic coefficient of friction so a fall in the braking efficiency, the temperature itself transiently reached, may also accelerate the wear of both the disk 110 and the linings 120, finally, it can bring the hydraulic fluid in contact with the piston 230 at its boiling point is introduced into the hydraulic circuit 240 a gaseous phase that can affect its operation.
  • the object of the invention is to determine and monitor in real time any risk of overheating of one or more components of the braking system to improve its operational safety and its lifetime.
  • the supervision is carried out by means of a calculation of the spatio-temporal distribution of the temperature in each of the monitored components.
  • a calculation uses as input the heat flux ⁇ + , which is evaluated from the three parameters defining the dissipation power during braking and mentioned above.
  • the coefficient of friction at the disk interface 110 lining 120 is known or measured experimentally and intervenes as a data possibly expressed according to an empirical function of various parameters such as the temperature, the degree of wear or the age of the linings 120 and disk 110;
  • the clamping force can be deduced from the measurement of the pressure of the hydraulic fluid in the braking circuit 240, which pressure can be measured in real time by appropriate means 250;
  • the relative speed between the linings 120 and the disk 110 can be determined by appropriate sensors (not shown) or more simply can be deduced from the speed of the vehicle.
  • MT dtofarad & of this equation reflects the spatial distribution of the temperature in the component.
  • Ask ⁇ ⁇ ⁇ ⁇ returns to consider that the temperature is homogeneous in the component and allows to easily solve the equation of the heat which integrates in:
  • T is the average temperature of the component
  • Q the quantity of heat
  • M the mass of the component
  • Cp the heat capacity of the constituent material.
  • this simplified calculation does not make it possible to detect local overheating.
  • overheating at the interface between the linings 1 20 and the disc 110 will only very slightly affect the average temperature of these linings, but will be sufficient to cause brake fading.
  • the fittings are made of a material that is slightly diffusive with respect to that of the brake disc 110, which is generally made of cast iron, very high spatial temperature distribution gradients appear in the thickness of the linings.
  • the geometry of the component must be taken into account, which geometry must be described in the form of mathematical functions.
  • the geometry of the components of the braking system is complex and the resolution of the equation, in particular by the finite element method, based on a variational approach of the Fourrier law by a Galerkin method, requires resources and a computation time incompatible with the targeted applications and the monitoring of the operation of the braking system.
  • the resolution of the equation of heat by a discrete numerical scheme both at the spatial and temporal scale is based, according to the invention on a simplified geometry of the studied system, which is thermally equivalent in term response to the actual global geometry. A heat transfer function is thus obtained for each constituent member of the braking system.
  • a lining 120 can be discretized by a one-dimensional mesh 221 which makes it possible to calculate using this discrete digital scheme the spatial distribution of temperature according to the thickness of the filling, the temperature being considered homogeneous according to the other directions.
  • a two-dimensional mesh 222 can be used to calculate the spatial distribution of the temperature according to the thickness of the lining 120 and its contact surface with the disk 110.
  • a three-dimensional mesh 223 makes it possible to calculate the spatial distribution of temperature in the entire volume of the liner 120 and allows, for example, to take into account a bias wear of the liner.
  • the choice of the discretization to use is a function of the component, the nature of the solicitations it undergoes and the expected information.
  • the discrete formulation is advantageously chosen of order 2 spatially, according to each of the directions in the case of a mesh with more than one dimension, and of order 1 in time, so that the nodal resolution of the corresponding differential equation can be performed by the finite difference method according to an implicit, explicit or semi-implicit resolution scheme.
  • a one-dimensional mesh adjusted to the thickness L of the liner 120 is used to calculate the spatio-temporal distribution of the temperature in this component.
  • the mesh is said to be set because the nodes are aligned and equidistant throughout the mesh.
  • the elementary heat flux ⁇ through the lining 120 is observed from an Eulerian point of view. That is to say, according to a point of view which observes the transport of heat in the spatial grid formed by the mesh 221.
  • TU, j ⁇ - 1) TU.f> + - ⁇ (TU---y- 2T3 ⁇ 4, ⁇ + T - 1, />)
  • FIG. 3B schematically illustrates the calculation principle giving the temperature at each node of the mesh 222 as a function of the time 302 and its position 301 according to the dimension x.
  • the principle consists in calculating for a time t + ⁇ the temperature reached at a point of coordinates x, from the waiting temperature at point ⁇ - ⁇ and point ⁇ + ⁇ at time t.
  • the use of a set mesh is however more delicate when the component studied is of more complex shape, such as in the case of a brake disc.
  • the component is then decomposed into sub-structures whose simpler geometry and if simplified, lends itself better to a set mesh.
  • the disk 110 is split into 3 sub-structures:
  • these substructures are represented in their thermal behavior by 3 meshs set 410 ', 420' and 440 'two-dimensional by taking advantage the rotation symmetry of the component.
  • Each of these meshes is bound by thermal boundary conditions 411, 421, 441 to the mesh of the contiguous substructure, conditions which express the thermal continuity between the substructures.
  • the spatiotemporal thermal response of the resolution of the differential heat equation from this simplified mesh-set model thus makes it possible to continuously estimate the temperature of a reference node 460, the evolution of which must comply with certain threshold criteria or continuously estimate thermal gradients between two nodes 460, 461, for example to prevent accelerated wear of the disk consecutive to a temperature gradient too high between these points.
  • a vehicle 500 including automotive may be equipped to implement the method object of the invention.
  • a vehicle 500 comprises brake disks 110 integral with the wheels.
  • the braking system comprises a hydraulic transmitter 540, the action on the brake pedal of the vehicle 541, communicates the stirrups 130 with a hydraulic fluid under pressure, contained in the transmitter 540 via a circuit
  • the vehicle advantageously comprises an onboard computer 510 which comprises memory means and digital calculation means as well as analog or digital signal acquisition ports. This calculator detects any braking event via a pressure sensor 250 on the hydraulic brake circuit 240. From this information the computer 510 determines the contact pressure between the disk 110 and the liners.
  • the computer 510 also realizes the acquisition of the instantaneous speed of the vehicle and is linked for this purpose to the speedometer 550 thereof. From the pressure in the hydraulic circuit and the speed, the computer determines, from constant stored in its memory means such as the coefficient of friction at the disc-brake interface, the amount of energy dissipated during braking which determines the heat flow in the components of the braking system.
  • the computer implements the method that is the subject of the invention for calculating the spatio-temporal distribution of temperature in the monitored components. In case of local exceeding of a critical temperature or a high local thermal gradient, the computer sends a signal 560. In this example, the signal 560 is used on a display 570 to warn the driver of too severe braking conditions. Alternatively, the signal 560 can be used to control the brake pressure.
  • the method of the invention proceeds according to this embodiment starting with a step 600 of scanning. If braking and detected in a step 610, the acquisition of the braking pressure 621 and the speed 631 allows in a step 620 to calculate the heat flow entering the component as explained previously.
  • the knowledge of the speed 631 makes it possible to calculate, in a step 632, the instantaneous heat flux leaving the component ⁇ ", in particular by exchange with the surrounding medium and the ventilation of the disk.From these data, a calculation step 630 makes it possible to calculate If the analysis of this distribution in a step 640 reveals an overheating critical temperature exceeded for the component considered, a signal is emitted during a step 650.

Abstract

The invention relates to a method and a device for the detection of local transient overheating in a component of a braking system. The invention is suitable for use in vehicles, particularly motor vehicles, in order to provide a real-time warning concerning any deterioration in the braking capability of such a vehicle and to limit the wear of the critical components of the system. The method comprises the following steps, for a time t1 and a time step Δt, consisting in: a) acquiring (621) a measurand representative of the braking intensity, using a suitable sensor; b) determining (620) the heat flow entering the component, based on the aforementioned measurand; c) calculating (630) the temperature space-time distribution in the component; d) comparing the temperature reached at at least one point of the space-time distribution with an overheating temperature threshold; and e) if said temperature is reached, emitting (650) a signal when the temperature of at least one point of the space-time distribution exceeds an overheating temperature threshold.

Description

PROCÉDÉ ET DISPOSITIF POUR LA DÉTECTION D'UNE SURCHAUFFE TRANSITOIRE LOCALE DANS UN COMPOSANT D'UN SYSTÈME DE  METHOD AND DEVICE FOR DETECTION OF LOCAL TRANSIENT OVERHEAT IN A COMPONENT OF A SYSTEM OF
FREINAGE  BRAKING
L'invention concerne un procédé et un dispositif pour la détection d'une surchauffe transitoire locale dans un composant d'un système de freinage. Cette invention trouve des applications dans les véhicules, notamment automobiles, pour prévenir, en temps réel, toute dégradation des capacités de freinage d'un tel véhicule et pour limiter l'usure des composants critiques constituant ce système. Elle est plus particulièrement destinée aux systèmes de freinage par friction, tels que les freins à disque, à tambour ou à patins selon les véhicules concernés, où des garnitures de freinage sont serrées sur un élément en déplacement relatif par rapport à ces garnitures afin de convertir, par friction, l'énergie cinétique entraînant cet élément mobile en chaleur, laquelle est dissipée dans le milieu environnant. Au cours de ce processus les éléments en contact sont soumis à des températures élevées qui modifient leurs propriétés physiques, notamment le coefficient de frottement à l'interface entre les garnitures et l'élément mobile, et accélèrent la dégradation tant des garnitures que de l'élément mobile. Par exemple, l'accroissement de la température à l'interface entre l'élément mobile et les garnitures peut conduire à une chute du coefficient de frottement à cette même interface, laquelle réduit l'efficacité du freinage. Ce phénomène est couramment désigné par le terme « d 'évanouissement du freinage » ou « fading » en anglais. Les composants du système de freinage ainsi surchauffés, transmettent leur chaleur aux autres composants du système de freinage, dont la montée en température consécutive, peut également entraîner des désordres de fonctionnement. Par exemple le fluide hydraulique, couramment désigné par « liquide de frein », actionnant les mâchoires rapprochant les garnitures de l'élément mobile, peut, au contact desdites mâchoires, chauffées par ces garnitures, entrer localement en ébullition et provoquer des bouchons de vapeur, ou « vapor lock » en anglais, dans le circuit hydraulique de freinage.  The invention relates to a method and a device for the detection of local transient overheating in a component of a braking system. This invention finds applications in vehicles, especially automobiles, to prevent, in real time, any deterioration of the braking capacity of such a vehicle and to limit the wear of critical components constituting this system. It is more particularly intended for friction braking systems, such as disc brakes, drum brakes or shoe brakes depending on the vehicles concerned, where brake linings are tightened on an element in relative displacement relative to these linings in order to convert by friction, the kinetic energy driving this mobile element into heat, which is dissipated in the surrounding environment. During this process the elements in contact are subjected to high temperatures which modify their physical properties, in particular the coefficient of friction at the interface between the liners and the movable element, and accelerate the degradation of both the linings and the mobile element. For example, increasing the temperature at the interface between the movable member and the linings may lead to a drop in the coefficient of friction at the same interface, which reduces the braking efficiency. This phenomenon is commonly referred to as "brake fade" or "fading" in English. The overheated brake system components transmit their heat to the other components of the braking system, whose subsequent rise in temperature can also cause operating disorders. For example the hydraulic fluid, commonly referred to as "brake fluid", actuating the jaws bringing the linings of the movable member, may, in contact with said jaws, heated by these linings enter locally boiling and cause plugs of steam, or "vapor lock" in English, in the hydraulic brake system.
Finalement la surchauffe répétée et brutale de la surface des garnitures ainsi que de la surface des pistes de freinage de l'élément mobile, crée des contraintes thermiques par la dilatation différentielle entre une couche en surface et le reste du volume des garnitures ou de l'élément mobile. Ces contraintes thermiques conduisent à des fissurations, couramment désignées sous le terme de « faïençage », lequel faïençage accélère la dégradation de ces garnitures ou de l'élément mobile. Finally, the repeated and sudden overheating of the surface of the linings as well as the surface of the braking tracks of the movable element, creates thermal stresses by the differential expansion between a surface layer and the rest of the volume of the gaskets or movable member. These thermal stresses lead to cracks, commonly referred to as "crazing", which crazing accelerates the degradation of these linings or the movable member.
Des dispositifs de supervision par capteur ou par calcul de la température en cours de freinage, permettent, selon l'art antérieur, de limiter au moins partiellement ces phénomènes de surchauffe. Toutefois ces dispositifs de l'art antérieur reposent sur la détermination d'une température moyenne, laquelle est obtenue par un bilan énergétique du freinage, éventuellement recalé à l'aide d'une mesure de température. A titre d'exemple, la demande de brevet internationale W09621145 relative à un système de freinage à disque et à refroidissement liquide, décrit la mesure de la température du liquide de refroidissement et la déduction, par un modèle mathématique, basé sur un bilan énergétique, de la température moyenne de freinage et la quantité d'énergie dissipée en chaleur par ce système. Une telle mesure globale ne permet pas de détecter en temps réel un risque d'évanouissement du freinage ou de bouchon de vapeur dans le circuit hydraulique de freinage. Par suite, les dispositifs de freinage de l'art antérieur sont surdimensionnés de sorte à écarter ces risques. Toutefois, ce surdimensionnement est pénalisant en termes de coût et de masse du système de freinage.  Supervisory devices by sensor or by calculation of the temperature during braking, allow, according to the prior art, to at least partially limit these phenomena of overheating. However, these devices of the prior art are based on the determination of a mean temperature, which is obtained by a braking energy balance, possibly adjusted using a temperature measurement. By way of example, International Patent Application WO9621145 relating to a disk-braking and liquid cooling system, describes the measurement of the temperature of the cooling liquid and the deduction, by a mathematical model, based on an energy balance, the average braking temperature and the amount of energy dissipated to heat by this system. Such an overall measurement does not make it possible to detect in real time a risk of fading of the braking or of the steam plug in the hydraulic braking circuit. As a result, the braking devices of the prior art are oversized in order to avoid these risks. However, this oversizing is penalizing in terms of cost and mass of the braking system.
L'invention vise à résoudre ces inconvénients de l'art antérieur en proposant un procédé pour la détection d'une surchauffe transitoire locale dans un composant d'un système de freinage, lequel procédé comprend, pour un instant t1 et un pas de temps Δΐ, les étapes consistant à :  The invention aims to solve these disadvantages of the prior art by proposing a method for the detection of local transient overheating in a component of a braking system, which method comprises, for a time t1 and a time step Δΐ , the steps of:
a°) acquérir, avec un capteur approprié, un mesurande représentatif de l'intensité de freinage ;  a) acquire, with a suitable sensor, a measurand representative of the braking intensity;
b°) déterminer à partir de ce mesurande le flux de chaleur entrant dans le composant ;  b) determine from this measurand the flow of heat entering the component;
c°) calculer la distribution spatio-temporelle de température dans le composant ;  c °) calculate the spatio-temporal distribution of temperature in the component;
d°) comparer la température atteinte en au moins un point de la distribution spatio-temporelle avec une température limite de surchauffe. Ainsi, le procédé objet de l'invention, en combinant une information macroscopique relative aux conditions de freinage et des moyens de calcul permet de déterminer des informations locales de surchauffe dans le composant surveillé et d'anticiper ce risque de surchauffe de manière plus fiable que ne le pouvaient les procédés et les dispositifs de l'art antérieur. La connaissance temporelle et spatiale du champ et des gradients de température au sein d'un système de freinage permet d'estimer les pics de surchauffes transitoires locales afin de prévenir les risques d'évanouissement du freinage ainsi que l'endommagement thermomécanique prématuré de ce système. d °) compare the reached temperature in at least one point of the spatio-temporal distribution with an overheating limit temperature. Thus, the method which is the subject of the invention, by combining a macroscopic information relating to the braking conditions and calculation means, makes it possible to determine local overheating information in the monitored component and to anticipate this risk of overheating more reliably than could not the methods and devices of the prior art. The temporal and spatial knowledge of the field and the temperature gradients within a braking system makes it possible to estimate local transient overheating peaks in order to prevent the risks of braking fading as well as the premature thermomechanical damage of this system. .
L'invention peut être mise en œuvre selon les modes de réalisation avantageux exposés ci-après, lesquels peuvent être considérés individuellement ou selon toute combinaison techniquement opérante.  The invention can be implemented according to the advantageous embodiments described below, which can be considered individually or in any technically operative combination.
Avantageusement, les étapes a°) à d°) sont répétées pour un instant t2=t1 +At, le calcul de la distribution spatio-temporelle de l 'étape c°) étant réalisé à partir de la solution déterminée lors de l'itération précédente. Ainsi le procédé est peu gourmand en ressources de calcul et permet le calcul, en temps réel ou en quasi-temps réel, de l'évolution de la répartition spatiale de température dans le composant.  Advantageously, the steps a °) to d °) are repeated for a time t2 = t1 + At, the computation of the spatio-temporal distribution of the step c °) being carried out starting from the solution determined during the iteration previous. Thus, the method is not very demanding on computing resources and allows the calculation, in real time or in near real time, of the evolution of the spatial distribution of temperature in the component.
Avantageusement également, le calcul de l'étape c°) comprend une étape consistant à résoudre l'équation différentielle de la chaleur par l'intégration numérique d'une formulation discrète de celle-ci. Ainsi, le procédé objet de l'invention est peu gourmand en ressources pour le calcul de la distribution temporelle de la température dans le composant visé.  Advantageously also, the calculation of step c °) comprises a step of solving the differential equation of heat by the numerical integration of a discrete formulation thereof. Thus, the method that is the subject of the invention is not very resource-intensive for calculating the temporal distribution of the temperature in the targeted component.
Selon un mode de réalisation particulièrement avantageux, la formulation discrète de l'équation différentielle de la chaleur comprend l'expression de la température nodale en tout point d'un maillage du composant, pour un pas de temps Δΐ. Cette formulation réduit la dimension instantanée du problème à résoudre, en se substituant à une résolution analytique, très délicate à obtenir d'un point de vue mathématique. Ainsi la résolution de l'équation de la chaleur sous cette formulation produit instantanément la distribution spatio-temporelle de température dans tous les points du maillage du composant. Cette étape de calcul est encore simplifiée, et sa réalisation accélérée, si le maillage spatial du composant est un maillage réglé. Le pas du maillage étant constant, le schéma de résolution est itératif à la fois en temps et spatialement, en basant chaque itération sur la solution précédente en temps comme en espace. According to a particularly advantageous embodiment, the discrete formulation of the differential equation of heat comprises the expression of the nodal temperature at any point of a mesh of the component, for a time step Δΐ. This formulation reduces the instantaneous dimension of the problem to be solved by substituting itself for an analytical resolution, very difficult to obtain from a mathematical point of view. Thus the resolution of the heat equation under this formulation instantaneously produces the spatio-temporal distribution of temperature in all the points of the mesh of the component. This calculation step is further simplified, and its accelerated realization, if the spatial mesh of the component is a set mesh. Since the mesh pitch is constant, the resolution scheme is iterative both in time and spatially, basing each iteration on the previous solution in time and space.
Avantageusement le maillage du composant comprend le maillage réglé de deux sous-structures du composant, et la formulation de l'équation de la chaleur comprend des conditions de continuité de température entre les deux maillages. Cette caractéristique permet de profiter des facultés de calcul accéléré, par la formulation discrète et la résolution itérative, sur des composants de géométrie complexe qui ne peuvent être entièrement maillés par un maillage réglé.  Advantageously, the mesh of the component comprises the regulated mesh of two substructures of the component, and the formulation of the equation of heat comprises conditions of temperature continuity between the two meshes. This feature makes it possible to take advantage of the accelerated calculation capabilities, by the discrete formulation and the iterative resolution, on components of complex geometry that can not be fully meshed by a set mesh.
Avantageusement, la résolution de l'équation de la chaleur est basée sur une méthode de différences finies avec une formulation d'Euler explicite.  Advantageously, the resolution of the heat equation is based on a finite difference method with an explicit Euler formulation.
Avantageusement, le procédé objet de l'invention comprend une étape d'acquisition d'un mesurande représentatif des conditions d'échange thermique du composant avec son environnement. Dans des véhicules modernes, notamment automobiles, le processus de freinage est réalisé dans des conditions quasi- adiabatiques. Cependant, dans des circonstances telles que des freinages répétés, il est avantageux d'affiner le calcul en tenant compte de ces conditions d'échange, qu'elles soient convectives ou radiatives. Advantageously, the method which is the subject of the invention comprises a step of acquiring a measurand representative of the heat exchange conditions of the component with its environment. In modern vehicles, especially automobiles, the braking process is carried out under quasi-adiabatic conditions. However, in circumstances such as repeated braking, it is advantageous to refine the calculation taking into account these exchange conditions, whether convective or radiative.
Avantageusement, le procédé comprend une étape e°) consistant à émettre un signal lorsque la température d'au moins un point de la distribution spatiotemporelle dépasse la température limite de surchauffe. Ainsi le procédé participe à la sécurité active du véhicule dans les phases de freinage. Le signal peut être adressé au conducteur ou à un dispositif de supervision apte à modifier les conditions de freinage pour maintenir celui-ci dans des conditions optimales fonctions des circonstances.  Advantageously, the method comprises a step e) of transmitting a signal when the temperature of at least one point of the spatiotemporal distribution exceeds the overheating limit temperature. Thus the process contributes to the active safety of the vehicle in the braking phases. The signal can be sent to the driver or a supervisory device capable of modifying the braking conditions to maintain it under optimum conditions depending on the circumstances.
Selon un exemple de réalisation, le composant est une garniture de freinage et la température limite de surchauffe est déterminée par le risque d'évanouissement du freinage. Cette caractéristique sécurise le freinage d'urgence à grande vitesse.  According to an exemplary embodiment, the component is a brake lining and the overheating limit temperature is determined by the risk of braking fade. This feature secures emergency braking at high speed.
Selon un autre exemple de réalisation, qui peut être combiné avec le précédent, le composant est un liquide de frein et la température limite de surchauffe est déterminée par le risque de création d'un bouchon de vapeur dans le circuit de freinage. Cette caractéristique sécurise les freinages intenses répétés. According to another embodiment, which can be combined with the previous one, the component is a brake fluid and the limiting temperature of Overheating is determined by the risk of creating a vapor lock in the brake system. This feature secures repeated intense braking.
L'invention concerne également un dispositif pour la mise en œuvre d'un procédé selon l'un quelconque des modes de réalisation précédents, pour la surveillance d'un système de freinage, lequel dispositif comprend :  The invention also relates to a device for implementing a method according to any one of the preceding embodiments, for monitoring a braking system, which device comprises:
■ un capteur apte à mesurer la pression effective de freinage ; ■ a adapted to measure the actual brake pressure sensor;
■ des moyens aptes à mesurer les conditions d'échange thermique entre le système de freinage et le milieu environnant ; ■ means capable of measuring the heat exchange conditions between the braking system and the surrounding environment;
■ un calculateur comprenant en mémoire : ■ a computer memory comprising:
• un maillage d'un composant du système de freinage • a mesh of a component of the braking system
• un programme de calcul itératif selon un schéma numérique discret pour calculer la température en tout point du maillageAn iterative calculation program according to a discrete numerical scheme for calculating the temperature at any point of the mesh
• un dispositif de communication apte à indiquer la survenue d'une surchauffe du composant dans le système de freinage. • a communication device capable of indicating the occurrence of overheating of the component in the braking system.
Ce dispositif peut être avantageusement intégré à un véhicule notamment automobile. Un tel véhicule comprend avantageusement des moyens pour mesurer les conditions d'échange thermique avec l'environnement comprenant un capteur de vitesse du véhicule.  This device can be advantageously integrated with a vehicle including automobile. Such a vehicle advantageously comprises means for measuring the conditions of heat exchange with the environment comprising a vehicle speed sensor.
L'invention sera maintenant plus précisément décrite dans le cadre de ses modes de réalisation préférés, nullement limitatifs, et des figures 1 à 6, dans lesquelles :  The invention will now be more specifically described in the context of its preferred embodiments, in no way limiting, and FIGS. 1 to 6, in which:
la figure 1 illustre schématiquement en perspective un ensemble de composants d'un système de freinage ;  Figure 1 schematically illustrates in perspective a set of components of a braking system;
- la figure 2 représente selon une vue de profil en coupe et en perspective un détail de ce système de freinage  - Figure 2 shows a sectional view in perspective and a detail of this braking system
la figure 3 montre un exemple de maillage réglé en une dimension d'une plaquette de frein, figure 3A, et, figure 3B un exemple schématique du calcul de la distribution spatio-temporelle de la température dans cette plaquette de frein ; la figure 4 présente un exemple de maillage réglé bidimensionnel, figure 4B, d'un composant de forme complexe tel qu'un disque de frein, figure 4A, en décomposant celui-ci en sous-structures ; FIG. 3 shows an example of a mesh set in one dimension of a brake pad, FIG. 3A, and FIG. 3B a schematic example of the calculation of the spatio-temporal distribution of the temperature in this brake pad; FIG. 4 shows an example of a two-dimensional regulated mesh, FIG. 4B, of a complex-shaped component such as a brake disk, FIG. 4A, by decomposing it into substructures;
la figure 5 montre un exemple de véhicule intégrant un dispositif pour la mise en œuvre du procédé objet de l'invention ;  FIG. 5 shows an exemplary vehicle incorporating a device for implementing the method that is the subject of the invention;
la figure 6 représente un logigramme d'un exemple de réalisation du procédé objet de l'invention.  FIG. 6 represents a logic diagram of an exemplary embodiment of the method that is the subject of the invention.
Figure 1 , selon une représentation schématisée d'un exemple de réalisation d'un système de freinage 100, celui-ci comprend un élément mobile, ici un disque de frein 110, et des garnitures de freinage 120, couramment désignées par le terme « plaquettes de frein » dans cet exemple de réalisation, lesquelles sont montées dans un étrier 130, fixe par rapport au disque 110. Ce disque est fixé au moyeu des roues du véhicule (non représentées) par un logement de centrage 140 et des boulons se logeant dans les trous de fixation 141 prévus à cet effet. Le disque est par conséquent entraîné en rotation à la même vitesse que les roues du véhicule. L'étrier 130 comprend des moyens, généralement hydrauliques, pour serrer les garnitures 120 sur les flancs du disque 110 et ainsi transformer l'énergie cinétique qu'il convoie en chaleur, laquelle est à son tour dissipée dans le milieu environnant.  Figure 1, in a schematic representation of an exemplary embodiment of a braking system 100, it comprises a movable member, here a brake disc 110, and brake linings 120, commonly referred to by the term "platelets" in this embodiment, which are mounted in a bracket 130, fixed relative to the disc 110. This disc is fixed to the hub of the vehicle wheels (not shown) by a centering housing 140 and bolts housed in the fixing holes 141 provided for this purpose. The disk is therefore rotated at the same speed as the wheels of the vehicle. The stirrup 130 comprises means, generally hydraulic, for clamping the linings 120 on the sides of the disc 110 and thus convert the kinetic energy that it conveys into heat, which in turn is dissipated in the surrounding medium.
Figure 2, les garnitures 120 sont serrées sur les flancs du disque 110 par des pistons 230 pilotées par un circuit hydraulique 240 convoyant un fluide sous pression. Le freinage est réalisé en mettant en communication la chambre de pressurisation 231 avec ce fluide sous pression ce qui a pour effet de pousser le piston 230, agissant sur les garnitures 120, vers le disque 110. La figure 2 ne représente ce dispositif que sur une des faces du disque 110 mais des garnitures 120' agissent symétriquement sur l'autre face de celui-ci.  2, the gaskets 120 are tightened on the flanks of the disc 110 by pistons 230 driven by a hydraulic circuit 240 conveying a fluid under pressure. The braking is carried out by placing the pressurization chamber 231 in communication with this pressurized fluid, which has the effect of pushing the piston 230, acting on the packings 120, towards the disc 110. FIG. 2 represents this device only on a the faces of the disc 110 but the fittings 120 'act symmetrically on the other side thereof.
Le frottement des garnitures 120 sur le disque 110 produit de la chaleur à l'interface entre ces deux éléments laquelle chaleur s'écoule selon un flux φ+, définissant une quantité d'énergie par unité de surface par conduction. Une fraction de ce flux thermique est injectée, notamment vers les garnitures 120, qui transmettent également cette chaleur selon un flux sortant φ" au piston 230 puis au fluide hydraulique contenu dans le circuit 240 et en contact avec le piston 230. Une autre partie de la chaleur est dissipée dans les divers composants du système de freinage et vers les organes du véhicule tels que les étriers 130, ou le moyeu des roues par le disque et son logement de centrage 140. Finalement une partie de la chaleur est dissipée par convection avec l'air ambiant et par rayonnement avec les pièces environnantes. The friction of the linings 120 on the disc 110 produces heat at the interface between these two elements, which heat flows in a flow φ + , defining a quantity of energy per unit area by conduction. A fraction of this thermal flux is injected, in particular to the fittings 120, which also transmit this heat according to an outgoing flow φ " to the piston 230 and then to the hydraulic fluid contained in the circuit 240 and in contact with the piston 230. Another part of the heat is dissipated in the various components of the braking system and to the vehicle components such as the stirrups 130, or the hub of the wheels by the The disk and its centering housing 140. Finally some of the heat is dissipated by convection with ambient air and by radiation with the surrounding parts.
La quantité de chaleur transmise est fonction de la puissance de frottement à l'interface disque-garniture, laquelle est proportionnelle à :  The amount of heat transmitted is a function of the friction power at the disk-to-lining interface, which is proportional to:
l'intensité du serrage de la garniture 120 sur le disque 110 - le coefficient de frottement de la garniture sur le disque ;  the intensity of the tightening of the lining 120 on the disc 110 - the coefficient of friction of the lining on the disc;
la vitesse relative entre le disque et la garniture.  the relative speed between the disc and the pad.
Ce transfert de chaleur s'accompagne d'une hausse de la température des composants concernés, température qui peut être suffisante pour modifier provisoirement ou définitivement des propriétés physico-chimiques des matériaux les constituant, voir même y produire des changements de phase ou d'état. Ainsi il existe des seuils critiques de température pouvant conduire à ces modifications. A titre d'exemple non limitatif, une surchauffe à l'interface entre la garniture 120 et le disque 110 peut entraîner une baisse du coefficient de frottement dynamique donc une chute de l'efficacité du freinage, la température même atteinte de manière transitoire, peut également accélérer l'usure tant du disque 110 que des garnitures 120, finalement, elle peut porter le fluide hydraulique en contact avec le piston 230 à son point d'ébullition est introduire dans le circuit hydraulique 240 une phase gazeuse pouvant nuire à son fonctionnement. L'objectif de l'invention est de déterminer et surveiller en temps réel tout risque de surchauffe d'un ou plusieurs composants du système de freinage afin d'améliorer sa sécurité de fonctionnement et sa durée de vie.  This heat transfer is accompanied by an increase in the temperature of the components concerned, which temperature may be sufficient to modify temporarily or permanently the physicochemical properties of the materials constituting them, or even to produce phase or state changes. . Thus, there are critical temperature thresholds that can lead to these modifications. By way of non-limiting example, an overheating at the interface between the lining 120 and the disc 110 may cause a decrease in the dynamic coefficient of friction so a fall in the braking efficiency, the temperature itself transiently reached, may also accelerate the wear of both the disk 110 and the linings 120, finally, it can bring the hydraulic fluid in contact with the piston 230 at its boiling point is introduced into the hydraulic circuit 240 a gaseous phase that can affect its operation. The object of the invention is to determine and monitor in real time any risk of overheating of one or more components of the braking system to improve its operational safety and its lifetime.
Pour réaliser une telle supervision, il est nécessaire d'avoir accès à tout instant à la température en tout point du composant surveillé. Cette supervision ne peut être réalisée de manière économique par des capteurs d'autant plus que plusieurs de ces composants, tels que les garnitures 120, sont des pièces d'usure dans lesquelles il est difficile d'intégrer de tels capteurs de manière économique et fiable. Selon l'invention la supervision est réalisée par l'intermédiaire d'un calcul de la distribution spatio-temporelle de la température dans chacun des composants surveillés. Un tel calcul utilise comme entrée le flux de chaleur φ+, lequel est évalué à partir des trois paramètres définissant la puissance de dissipation au cours du freinage et évoqués supra. To achieve such supervision, it is necessary to have access at any time to the temperature at any point of the monitored component. This supervision can not be achieved economically by sensors, especially since several of these components, such as gaskets 120, are wearing parts in which it is difficult to integrate such sensors in an economical and reliable manner. . According to the invention the supervision is carried out by means of a calculation of the spatio-temporal distribution of the temperature in each of the monitored components. Such a calculation uses as input the heat flux φ + , which is evaluated from the three parameters defining the dissipation power during braking and mentioned above.
- le coefficient de frottement à l'interface disque 110 garniture 120 est connu ou mesuré expérimentalement et intervient comme une donnée éventuellement exprimée selon une fonction empirique de divers paramètres tels que la température, le degré d'usure ou l'âge des garnitures 120 et du disque 110 ;  the coefficient of friction at the disk interface 110 lining 120 is known or measured experimentally and intervenes as a data possibly expressed according to an empirical function of various parameters such as the temperature, the degree of wear or the age of the linings 120 and disk 110;
l'effort de serrage peut être déduit de la mesure de la pression du fluide hydraulique dans le circuit 240 de freinage, laquelle pression peut être mesurée en temps réel par des moyens appropriés 250 ;  the clamping force can be deduced from the measurement of the pressure of the hydraulic fluid in the braking circuit 240, which pressure can be measured in real time by appropriate means 250;
la vitesse relative entre les garnitures 120 et le disque 110 peut être déterminée par des capteurs appropriés (non représentés) ou plus simplement peut être déduite de la vitesse du véhicule.  the relative speed between the linings 120 and the disk 110 can be determined by appropriate sensors (not shown) or more simply can be deduced from the speed of the vehicle.
La connaissance de ce flux, permet, en résolvant l'équation de la chaleur de connaître la température dans chaque composant.  The knowledge of this flow, by solving the equation of heat, allows to know the temperature in each component.
La formulation générale de l'équation de chaleur, dite également loi de Fourrier, est donnée par l'équation différentielle suivante : βΰΐ. CpÎ l— f ÂtTXâwigredm} = YPÎÙ Où p(T) est la masse volumique du matériau constituant le composant exprimée en fonction de la température, Cp(T) est la capacité calorifique de ce même matériau, et λ(Τ) sa conductivité thermique, T la température et t le temps, ∑P(t) la somme des puissances thermique des différentes sources de chauffage, qui dans le cas du freinage correspond à la puissance mécanique de freinage, ainsi que les pertes convectives/radiatives.  The general formulation of the heat equation, also called Fourrier's law, is given by the following differential equation: βΰΐ. Where p (T) is the density of the material constituting the component expressed as a function of temperature, Cp (T) is the heat capacity of the same material, and λ (Τ) its thermal conductivity. , T the temperature and t the time, ΣP (t) the sum of the thermal powers of the different heating sources, which in the case of braking corresponds to the mechanical power of braking, as well as the convective / radiative losses.
. . dT  . . dT
MT} .'"£ · T }—  MT}. '"£ · T} -
Le terme ' ' ' dt de cette équation reflète la distribution temporelle de la température. The term ' '' dt of this equation reflects the temporal distribution of temperature.
Le terme MT dtofarad& de cette équation reflète la distribution spatiale de la température dans le composant. Poser ΐΓΧάίν βτ άΐΓί = β revient à considérer que la température est homogène dans le composant et permet de résoudre facilement l'équation de la chaleur qui s'intègre en :
Figure imgf000011_0001
The term MT dtofarad & of this equation reflects the spatial distribution of the temperature in the component. Ask ΐΓΧάίν βτ άΐΓί = β returns to consider that the temperature is homogeneous in the component and allows to easily solve the equation of the heat which integrates in:
Figure imgf000011_0001
Où T est la température moyenne du composant, To sa température initiale, Q la quantité de chaleur, M la masse du composant et Cp la capacité calorifique du matériau le constituant. Cependant, ce calcul simplifié, équivalent à un bilan énergétique, ne permet pas de détecter une surchauffe locale. À titre d'exemple une surchauffe à l'interface entre les garnitures 1 20 et le disque 110 n'affectera que très modérément la température moyenne de ces garnitures mais sera suffisante pour provoquer un évanouissement du freinage. En effet, les garnitures étant constituées d'un matériau faiblement diffusif par rapport à celui du disque de frein 110 qui est généralement constitué de fonte, de très forts gradients spatiaux de distribution de la température apparaissent dans l'épaisseur des garnitures.  Where T is the average temperature of the component, To its initial temperature, Q the quantity of heat, M the mass of the component and Cp the heat capacity of the constituent material. However, this simplified calculation, equivalent to an energy balance, does not make it possible to detect local overheating. By way of example, overheating at the interface between the linings 1 20 and the disc 110 will only very slightly affect the average temperature of these linings, but will be sufficient to cause brake fading. Indeed, since the fittings are made of a material that is slightly diffusive with respect to that of the brake disc 110, which is generally made of cast iron, very high spatial temperature distribution gradients appear in the thickness of the linings.
Afin de détecter par calcul un tel risque de surchauffe il est indispensable de résoudre l'équation de la chaleur sans négliger le terme div gra tri) .  In order to detect by calculation such a risk of overheating it is essential to solve the equation of heat without neglecting the term div gra tri).
Cependant, pour résoudre une telle équation, la géométrie du composant doit être prise en compte, laquelle géométrie doit être décrite sous la forme de fonctions mathématiques. Or, la géométrie des composants du système de freinage est complexe et la résolution de l'équation, notamment par la méthode des éléments finis, en s'appuyant sur une approche variationnelle de la loi de Fourrier par une méthode de Galerkin, nécessite des ressources et un temps de calcul incompatibles avec les applications visées et la surveillance du fonctionnement du système de freinage. Pour accélérer ce temps de calcul, la résolution de l'équation de la chaleur par un schéma numérique discret tant à l'échelle spatiale que temporelle, repose, selon l'invention sur une géométrie simplifiée du système étudié, qui soit thermiquement équivalente en terme de réponse par rapport à la géométrie globale réelle. Une fonction de transfert thermique est ainsi obtenue pour chaque organe constitutif du système de freinage. Figure 2, selon trois exemples de discrétisation spatiale, une garniture 120 peut être discrétisée par un maillage unidimensionnel 221 qui permet de calculer à l'aide de ce schéma numérique discret la distribution spatiale de température selon l'épaisseur de la garniture la température étant considérée homogène selon les autres directions. Alternativement, un maillage bidimensionnel 222 peut être utilisé pour calculer la distribution spatiale de la température selon l'épaisseur de la garniture 120 et sa surface de contact avec le disque 110. Finalement, un maillage tridimensionnel 223 permet de calculer la répartition spatiale de température dans tout le volume de la garniture 120 et permet, par exemple, de prendre en compte une usure biaise de la garniture. Le choix de la discrétisation à utiliser est fonction du composant, de la nature des sollicitations qu'il subit et des informations attendues. However, to solve such an equation, the geometry of the component must be taken into account, which geometry must be described in the form of mathematical functions. However, the geometry of the components of the braking system is complex and the resolution of the equation, in particular by the finite element method, based on a variational approach of the Fourrier law by a Galerkin method, requires resources and a computation time incompatible with the targeted applications and the monitoring of the operation of the braking system. To accelerate this computation time, the resolution of the equation of heat by a discrete numerical scheme both at the spatial and temporal scale, is based, according to the invention on a simplified geometry of the studied system, which is thermally equivalent in term response to the actual global geometry. A heat transfer function is thus obtained for each constituent member of the braking system. FIG. 2, according to three examples of spatial discretization, a lining 120 can be discretized by a one-dimensional mesh 221 which makes it possible to calculate using this discrete digital scheme the spatial distribution of temperature according to the thickness of the filling, the temperature being considered homogeneous according to the other directions. Alternatively, a two-dimensional mesh 222 can be used to calculate the spatial distribution of the temperature according to the thickness of the lining 120 and its contact surface with the disk 110. Finally, a three-dimensional mesh 223 makes it possible to calculate the spatial distribution of temperature in the entire volume of the liner 120 and allows, for example, to take into account a bias wear of the liner. The choice of the discretization to use is a function of the component, the nature of the solicitations it undergoes and the expected information.
Selon la méthode des différences finies, une formulation discrète de l'équation de la chaleur est obtenue par une approximation polynomiale de l'équation de la chaleur au voisinage de chaque nœud du maillage à partir de la formule de Taylor. Le fondement théorique d'une telle méthode est connu de l'art antérieur et n'est pas présenté plus en détail.  According to the finite difference method, a discrete formulation of the heat equation is obtained by a polynomial approximation of the equation of heat in the vicinity of each mesh node from the Taylor formula. The theoretical basis of such a method is known from the prior art and is not presented in more detail.
La formulation discrète est avantageusement choisie d'ordre 2 spatialement, selon chacune des directions dans le cas d'un maillage à plus d'une dimension, et d'ordre 1 en temps, de sorte que la résolution nodale de l'équation différentielle correspondante peut être réalisée par la méthode des différences finies selon un schéma de résolution implicite, explicite ou semi-implicite.  The discrete formulation is advantageously chosen of order 2 spatially, according to each of the directions in the case of a mesh with more than one dimension, and of order 1 in time, so that the nodal resolution of the corresponding differential equation can be performed by the finite difference method according to an implicit, explicit or semi-implicit resolution scheme.
Figure 3A, selon un exemple de réalisation de l'invention, un maillage unidimensionnel réglé s'étendant selon l'épaisseur L de la garniture 120 est utilisé pour calculer la répartition spatio-temporelle de la température dans ce composant. Le maillage est dit réglé car les nœuds sont alignés et équidistants sur tout le maillage. Le flux élémentaire de chaleur φ au travers de la garniture 120 est observé d'un point de vue eulérien. C'est-à-dire, selon un point de vue qui observe le transport de chaleur dans la grille spatiale constituée par le maillage 221 .  3A, according to an exemplary embodiment of the invention, a one-dimensional mesh adjusted to the thickness L of the liner 120 is used to calculate the spatio-temporal distribution of the temperature in this component. The mesh is said to be set because the nodes are aligned and equidistant throughout the mesh. The elementary heat flux φ through the lining 120 is observed from an Eulerian point of view. That is to say, according to a point of view which observes the transport of heat in the spatial grid formed by the mesh 221.
La formulation nodale discrète de l'équation de la chaleur, selon un exemple de formulation explicite en différence finie, est donnée par l'équation suivante :  The discrete nodal formulation of the heat equation, according to an explicit finite difference formulation example, is given by the following equation:
TU,j→- 1) = TU.f>+ -^ (TU -§- î y- 2T¾, } + T - 1,/>) Pour chaque nœud situé à une distance ί*Δχ depuis le bord 320 de la garniture 120 en contact avec le disque et pour chaque instant t=j*At à partir d'un état antérieur 'a' est la diffusivité thermique exprimée en unité SI en m. s"2 tel TU, j → - 1) = TU.f> + - ^ (TU---y- 2T¾,} + T - 1, />) For each node located at a distance ί * Δχ from the edge 320 of the liner 120 in contact with the disk and for each instant t = j * At from an earlier state 'a' is the thermal diffusivity expressed in SI unit in m. s "2 such
A  AT
a =  a =
que PCP où À est la conductivité thermique et Cp la capacité thermique du matériau constituant la garniture 120. that P C P where A is the thermal conductivity and Cp the heat capacity of the material constituting the lining 120.
La figure 3B illustre de manière schématique le principe de calcul donnant la température en chaque nœud du maillage 222 en fonction du temps 302 et de sa position 301 selon la dimension x. Le principe consiste à calculer pour un temps t+Δΐ la température atteinte en un point de coordonnées x, à partir de la température attente au point χ-Δχ et au point χ+Δχ à l'instant t. Ainsi, en partant d'une situation initiale à l'instant t0 où la distribution 310 nodale de la température est connue, en imposant en conditions aux limites aux nœuds d'extrémité 321 , 322 un flux de chaleur entrant ό<>+ et un flux de chaleur sortant ό<>~, l'évolution spatio-temporelle de la température aux nœuds est très facilement calculée et ne nécessite que des ressources très faibles en termes de puissance de calcul. Pour assurer la stabilité de l'algorithme le pas de temps Δΐ doit être choisi suffisamment àx - petit. En pratique la vérification de la condition " - permet d'assurer la stabilité de l'algorithme. Alternativement il est possible d'utiliser un schéma de résolution semi-implicite dit de Crank-Nicholson inconditionnellement stable. FIG. 3B schematically illustrates the calculation principle giving the temperature at each node of the mesh 222 as a function of the time 302 and its position 301 according to the dimension x. The principle consists in calculating for a time t + Δΐ the temperature reached at a point of coordinates x, from the waiting temperature at point χ-Δχ and point χ + Δχ at time t. Thus, starting from an initial situation at the instant t 0 where the nodal distribution 310 of the temperature is known, by imposing under the boundary conditions at the end nodes 321, 322 an incoming heat flux ό <> + and an outgoing heat flux ό <> ~ , the spatio-temporal evolution of the temperature at the nodes is very easily calculated and requires only very small resources in terms of computing power. To ensure the stability of the algorithm the time step Δΐ must be chosen sufficiently at x - small. In practice the verification of the condition " - makes it possible to ensure the stability of the algorithm Alternatively, it is possible to use a semi-implicit resolution scheme called Crank-Nicholson unconditionally stable.
Figure 4, l'utilisation d'un maillage réglé est cependant plus délicate lorsque le composant étudié est de forme plus complexe, tel que dans le cas d'un disque de frein. Avantageusement, selon un mode de réalisation de l'invention, le composant est alors décomposé en sous structures dont la géométrie plus simple et au besoin simplifiée, se prête mieux à un maillage réglé. Ainsi, selon cet exemple, le disque 110 est scindé en 3 sous structures:  4, the use of a set mesh is however more delicate when the component studied is of more complex shape, such as in the case of a brake disc. Advantageously, according to one embodiment of the invention, the component is then decomposed into sub-structures whose simpler geometry and if simplified, lends itself better to a set mesh. Thus, according to this example, the disk 110 is split into 3 sub-structures:
- la piste de freinage 410 sur laquelle frottent les garnitures ;  the braking track 410 on which the trimmings rub;
- le logement de centrage 140 qui lie le disque au moyeu de la roue ; et the centering housing 140 which links the disc to the hub of the wheel; and
- la zone de liaison 420 entre ces deux sous structures. the link zone 420 between these two substructures.
Figure 4B, ces sous-structures sont représentées dans leur comportement thermique par 3 maillages réglés 410', 420' et 440' bidimensionnels en tirant partie de la symétrie de rotation du composant. Chacun de ces maillages est lié par des conditions aux limites thermiques 411 , 421 , 441 au maillage de la sous-structure contiguë, conditions qui expriment la continuité thermique entre les sous- structures. 4B, these substructures are represented in their thermal behavior by 3 meshs set 410 ', 420' and 440 'two-dimensional by taking advantage the rotation symmetry of the component. Each of these meshes is bound by thermal boundary conditions 411, 421, 441 to the mesh of the contiguous substructure, conditions which express the thermal continuity between the substructures.
La réponse thermique spatio-temporelle du La résolution de l'équation différentielle de la chaleur à partir de ce modèle simplifié en maillage réglé, permet ainsi d'estimer en continu la température d'un nœud référence 460, dont l'évolution doit respecter certains critères seuils ou d'estimer en continu des gradients thermiques entre deux nœuds 460, 461 , par exemple pour prévenir une usure accélérée du disque consécutive à un gradient de température trop élevé entre ces points.  The spatiotemporal thermal response of the resolution of the differential heat equation from this simplified mesh-set model thus makes it possible to continuously estimate the temperature of a reference node 460, the evolution of which must comply with certain threshold criteria or continuously estimate thermal gradients between two nodes 460, 461, for example to prevent accelerated wear of the disk consecutive to a temperature gradient too high between these points.
Figure 5, un véhicule 500 notamment automobile, peut être équipé de manière à mettre en œuvre le procédé objet de l'invention. Selon un exemple de réalisation, un tel véhicule 500 comprend des disques de freinage 110 solidaires des roues. Le système de freinage comprend un émetteur hydraulique 540, l'action sur la pédale de frein du 541 du véhicule, met en communication les étriers 130 avec un fluide hydraulique sous pression, contenu dans l'émetteur 540 par l'intermédiaire d'un circuit hydraulique de freinage 240. Le véhicule comprend avantageusement un calculateur embarqué 510 lequel comprend des moyens de mémoires et des moyens de calcul numériques ainsi que des ports d'acquisition de signaux analogiques ou numériques. Ce calculateur détecte tout événement de freinage par l'intermédiaire d'un capteur de pression 250 sur le circuit hydraulique de freinage 240. À partir de cette information le calculateur 510 détermine la pression de contact entre le disque 110 et les garnitures. Le calculateur 510 réalise également l'acquisition de la vitesse instantanée du véhicule et est lié à cette fin au compteur de vitesse 550 de celui-ci. À partir de la pression dans le circuit hydraulique et de la vitesse, le calculateur détermine, à partir de constante stockées dans ses moyens de mémoire telles que le coefficient de frottement à l'interface disque-garnitures, la quantité d'énergie dissipée au freinage ce qui détermine le flux de chaleur dans les composants du système de freinage. Le calculateur met en œuvre le procédé objet de l'invention pour calculer la distribution spatio-temporelle de température dans les composants surveillés. En cas de dépassement local d'une température critique ou d'un gradient thermique local élevé, le calculateur émet un signal 560. Dans cet exemple, le signal 560 est utilisé sur un afficheur 570 pour prévenir le conducteur de conditions de freinage trop sévères. Alternativement, le signal 560 peut être utilisé pour piloter la pression de freinage. Figure 5, a vehicle 500 including automotive, may be equipped to implement the method object of the invention. According to an exemplary embodiment, such a vehicle 500 comprises brake disks 110 integral with the wheels. The braking system comprises a hydraulic transmitter 540, the action on the brake pedal of the vehicle 541, communicates the stirrups 130 with a hydraulic fluid under pressure, contained in the transmitter 540 via a circuit The vehicle advantageously comprises an onboard computer 510 which comprises memory means and digital calculation means as well as analog or digital signal acquisition ports. This calculator detects any braking event via a pressure sensor 250 on the hydraulic brake circuit 240. From this information the computer 510 determines the contact pressure between the disk 110 and the liners. The computer 510 also realizes the acquisition of the instantaneous speed of the vehicle and is linked for this purpose to the speedometer 550 thereof. From the pressure in the hydraulic circuit and the speed, the computer determines, from constant stored in its memory means such as the coefficient of friction at the disc-brake interface, the amount of energy dissipated during braking which determines the heat flow in the components of the braking system. The computer implements the method that is the subject of the invention for calculating the spatio-temporal distribution of temperature in the monitored components. In case of local exceeding of a critical temperature or a high local thermal gradient, the computer sends a signal 560. In this example, the signal 560 is used on a display 570 to warn the driver of too severe braking conditions. Alternatively, the signal 560 can be used to control the brake pressure.
Figure 6, le procédé objet de l'invention se déroule selon ce mode de réalisation en débutant par une étape 600 de scrutation. Si un freinage et détecté dans une étape 610, l'acquisition de la pression de freinage 621 et de la vitesse 631 permet dans une étape 620 de calculer le flux de chaleur entrant dans le composant tel qu'explicité précédemment. La connaissance de la vitesse 631 permet de calculer dans une étape 632 le flux de chaleur instantané sortant du composant φ" notamment par échange avec le milieu environnant et la ventilation du disque. À partir de ces données, une étape de calcul 630 permet de calculer la répartition spatio-temporelle. Si l'analyse de cette distribution dans une étape 640 révèle un dépassement d'une température critique de surchauffe pour le composant considéré, un signal est émis au cours d'une étape 650. Figure 6, the method of the invention proceeds according to this embodiment starting with a step 600 of scanning. If braking and detected in a step 610, the acquisition of the braking pressure 621 and the speed 631 allows in a step 620 to calculate the heat flow entering the component as explained previously. The knowledge of the speed 631 makes it possible to calculate, in a step 632, the instantaneous heat flux leaving the component φ ", in particular by exchange with the surrounding medium and the ventilation of the disk.From these data, a calculation step 630 makes it possible to calculate If the analysis of this distribution in a step 640 reveals an overheating critical temperature exceeded for the component considered, a signal is emitted during a step 650.
La description ci-avant illustre clairement que par ses différentes caractéristiques et leurs avantages, la présente invention atteint les objectifs qu'elle visait. En particulier, en permettant une surveillance spatio-temporelle de la température des composants d'un système de freinage elle permet de limiter le surdimensionnement de celui-ci sans perte sur la sécurité.  The above description clearly illustrates that by its different features and advantages, the present invention achieves the objectives it intended. In particular, by allowing spatio-temporal monitoring of the temperature of the components of a braking system, it makes it possible to limit oversizing of the latter without loss of safety.

Claims

REVENDICATIONS
1 . Procédé pour la détection d'une surchauffe transitoire locale dans un composant (120, 110) d'un système de freinage (100) caractérisé en ce qu'il comprend, pour un instant t1 et un pas de temps Δΐ, les étapes consistant à :  1. Method for the detection of local transient superheating in a component (120, 110) of a braking system (100), characterized in that it comprises, for a time t1 and a time step Δΐ, the steps of :
a°) acquérir (621 ), avec un capteur approprié (250), un mesurande représentatif de l'intensité de freinage ;  a) acquiring (621), with a suitable sensor (250), a measurand representative of the braking intensity;
b°) déterminer (620) à partir de ce mesurande le flux de chaleur entrant dans le composant (120, 110) ;  b) determining (620) from this measurand the flow of heat entering the component (120, 110);
c°) calculer (630) la distribution spatio-temporelle de température dans le composant (110, 120) ;  c) calculating (630) the spatio-temporal distribution of temperature in the component (110, 120);
d°) comparer (640) la température atteinte en au moins un point de la distribution spatio-temporelle avec une température limite de surchauffe.  d °) comparing (640) the temperature reached in at least one point of the spatio-temporal distribution with an overheating limit temperature.
2. Procédé selon la revendication 1 , caractérisé en ce que les étapes a°) à d°) sont répétées pour un instant t2=t1 +At, le calcul de la distribution spatiotemporelle de l'étape c°) étant réalisé à partir de la solution déterminée lors de l'itération précédente.  2. Method according to claim 1, characterized in that the steps a °) to d °) are repeated for a time t2 = t1 + At, the calculation of the spatiotemporal distribution of the step c °) being made from the solution determined during the previous iteration.
3. Procédé selon la revendication 1 , caractérisé en ce que le calcul de l'étape c°) comprend une étape consistant à résoudre l'équation différentielle de la chaleur par l'intégration numérique d'une formulation discrète de celle-ci.  3. Method according to claim 1, characterized in that the calculation of step c °) comprises a step of solving the differential equation of heat by the digital integration of a discrete formulation thereof.
4. Procédé selon la revendication 3, caractérisé en ce que la formulation discrète de l'équation de la chaleur comprend l'expression de la température nodale en tout point d'un maillage (221 , 22, 223, 440', 420', 410') du composant (110, 120) pour un pas de temps Δΐ.  4. Method according to claim 3, characterized in that the discrete formulation of the heat equation comprises the expression of the nodal temperature at any point of a mesh (221, 22, 223, 440 ', 420', 410 ') of the component (110, 120) for a time step Δΐ.
5. Procédé selon la revendication 4, caractérisé ce que le maillage spatial (221 , 22, 223, 440', 420', 410') du composant (110, 120) est un maillage réglé.  5. Method according to claim 4, characterized in that the spatial mesh (221, 22, 223, 440 ', 420', 410 ') of the component (110, 120) is a set mesh.
6. Procédé selon la revendication 4, caractérisé en ce que le maillage du composant comprend le maillage réglé (440', 410', 420') de deux sous- structures (140, 410, 420) du composant et que la formulation de l'équation de la chaleur comprend des conditions (411 , 421 , 441 ) de continuité de température entre les deux maillages (440', 410', 420'). 6. Method according to claim 4, characterized in that the mesh of the component comprises the set mesh (440 ', 410', 420 ') of two substructures (140, 410, 420) of the component and that the formulation of the equation of heat comprises conditions (411, 421, 441) of temperature continuity between the two meshes (440 ', 410', 420 ').
7. Procédé selon la revendication 3, caractérisé en ce que la résolution de l'équation de la chaleur est basée sur une méthode de différences finies dans une formulation d'Euler explicite. The method of claim 3, characterized in that the resolution of the heat equation is based on a finite difference method in an explicit Euler formulation.
8. Procédé selon la revendication 1 , caractérisé en ce qu'il comprend l'acquisition d'un mesurande (550) représentatif des conditions d'échange thermique du composant avec son environnement.  8. Method according to claim 1, characterized in that it comprises the acquisition of a measurand (550) representative of the heat exchange conditions of the component with its environment.
9. Procédé selon la revendication 1 , caractérisé en ce qu'il comprend une étape e°) consistant à émettre (650) un signal (560) lorsque la température d'au moins un point de la distribution spatio-temporelle dépasse une température limite de surchauffe.  9. The method of claim 1, characterized in that it comprises a step e)) of emitting (650) a signal (560) when the temperature of at least one point of the spatio-temporal distribution exceeds a temperature limit overheating.
10. Procédé selon la revendication 1 , caractérisé en ce que le composant est une garniture (120) ou un disque (110) de freinage et que la température limite de surchauffe est déterminée par le risque d'évanouissement du freinage.  10. The method of claim 1, characterized in that the component is a lining (120) or a disc (110) of braking and that the limit temperature of overheating is determined by the risk of fading braking.
1 1 . Procédé selon la revendication 1 , caractérisé en ce que le composant est un liquide de frein et que la température limite de surchauffe est déterminée par le risque de création d'un bouchon de vapeur dans le circuit de freinage (240).  1 1. Method according to claim 1, characterized in that the component is a brake fluid and that the overheating limit temperature is determined by the risk of creating a vapor plug in the braking circuit (240).
12. Dispositif pour la mise en œuvre d'un procédé selon l'une quelconque des revendications précédentes, pour la surveillance d'un système de freinage (100), caractérisé en ce qu'il comprend :  12. Device for implementing a method according to any one of the preceding claims, for monitoring a braking system (100), characterized in that it comprises:
■ un capteur (250) apte à mesurer la pression effective de freinage ; ■ a sensor (250) adapted to measure the actual braking pressure;
■ des moyens (550) aptes à mesurer les conditions d'échange thermique entre le système de freinage et le milieu environnant ; ■ un calculateur (510) comprenant en mémoire : ■ means (550) adapted to measure the heat exchange conditions between the braking system and the surrounding environment; A computer (510) comprising in memory:
• un maillage (221 , 222, 223, 440', 410', 420') d'un composant du système de freinage (100) ;  A mesh (221, 222, 223, 440 ', 410', 420 ') of a component of the braking system (100);
• un programme de calcul itératif selon un schéma numérique discret pour calculer la température en tout point du maillage ■ un dispositif de communication (570) apte à indiquer la survenue d'une surchauffe du composant (120, 110) dans le système de freinage (100). An iterative calculation program according to a discrete numerical scheme for calculating the temperature at any point of the mesh; a communication device (570) able to indicate the occurrence of an overheating of the component (120, 110) in the braking system ( 100).
13. Véhicule (500), notamment automobile, caractérisé en ce qu'il comprend un dispositif selon la revendication 12. 13. Vehicle (500), particularly automobile, characterized in that it comprises a device according to claim 12.
14. Véhicule (500) selon la revendication 13, caractérisé en ce que les moyens pour mesurer les conditions d'échange thermique avec l'environnement comprennent un capteur de vitesse (550) du véhicule (500).  14. Vehicle (500) according to claim 13, characterized in that the means for measuring the conditions of heat exchange with the environment comprise a speed sensor (550) of the vehicle (500).
PCT/FR2011/052226 2010-10-06 2011-09-26 Method and device for the detection of local transient overheating in a component of a braking system WO2012045953A1 (en)

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CN112431876A (en) * 2019-08-26 2021-03-02 上海汽车集团股份有限公司 Temperature estimation method and device for dry clutch
CN112431876B (en) * 2019-08-26 2022-05-27 上海汽车集团股份有限公司 Temperature estimation method and device for dry clutch
CN110728087A (en) * 2019-09-26 2020-01-24 内蒙古科技大学 Sandwich type multilayer composite material thermal performance numerical analysis method
CN110728087B (en) * 2019-09-26 2022-08-02 内蒙古科技大学 Sandwich type multilayer composite material thermal performance numerical analysis method

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