MODEL FOR PREDICTING WEAR AND THE END OF LIFE OF A TIRE

Abstract

A method for estimating the overall wear of a tyre having a crown, the crown comprising a tread having a mean thickness E, the tyre delimiting an internal cavity, comprises the following steps: acquiring a transfer function F of the tyre on a reference ground depending on influencing factors and the thickness E; acquiring a passage function β of the mounted assembly, said passage function being defined for a section of road;
in a measurement cycle determining a force F.sub.X and a rate of slip g % at the wheel centre of the tyre, when running in a straight line involving variations in acceleration on the dry section of road; determining a load Z1 experienced by the mounted assembly; determining a temperature T1 of the mounted assembly; determining an inflation pressure P1 of the internal cavity.

Claims

1.-15. (canceled)

16. A method for estimating a level of overall wear of a tire of an assembly mounted under running conditions on a vehicle, the tire having a crown which is extended by two sidewalls that end in two beads, exhibiting revolution about a natural axis of rotation, the crown comprising a tread situated radially on an outside of the tire with respect to the natural axis of rotation, the tread having a mean thickness E, and the mounted assembly comprising components including a wheel and the tire delimiting an internal cavity, the method comprising the following steps: acquiring a transfer function F of the mounted assembly between a longitudinal stiffness K.sub.XX.sup.ref on a reference ground and influencing factors, as a product of a first function F1 having as influencing factors at least inflation pressure P, temperature T and load Z experienced, and a second, bijective function F2 having at least as influencing factor the thickness E of the tread; and acquiring a passage function β of the mounted assembly, the passage function being defined for a section of road as a ratio of the longitudinal stiffnesses K.sub.XX of the mounted assembly for the same influencing factors, numerator stiffness being evaluated on ground equivalent to the section of road and denominator stiffness being evaluated on a reference ground; and, in one and measurement cycle, determining at least one force F.sub.X experienced by the mounted assembly and at least one rate of slip g % at a wheel center of the mounted assembly, or acquiring parameters Q1 of the vehicle allowing determinations thereof, when the vehicle is running in a straight line involving variations in acceleration on the section of road, the latter being dry; determining a load Z1, or acquiring parameters Q2 of the vehicle allowing the determination, experienced by the assembly mounted under running conditions; determining a temperature T1 of the assembly mounted under running conditions; and determining an inflation pressure P1 of the internal cavity of the assembly mounted under running conditions, wherein the method further comprises acquisition of a first longitudinal stiffness K.sub.XX.sup.act of the mounted assembly on actual ground with aid of a first relationship between the forces F.sub.X, the rates of slip g % or the parameters Q1, wherein the method further comprises acquisition of a second longitudinal stiffness on the reference ground K.sub.XX.sup.ref the second longitudinal stiffness being evaluated with aid of the transfer function F supplied with at least the influencing factors T1, P1, Z1 or the parameters Q2 and at least one characteristic thickness E0 of the tread, wherein the method further comprises acquisition of a scalar β1 defined with aid of the passage function β supplied with at least the influencing factors T1, P1, Z1, and wherein the thickness E of the tread is determined by a first relationship between the scalar β1, the first longitudinal stiffness K.sub.XX.sup.act and the second longitudinal stiffness K.sub.XX.sup.ref as follows: $EE=F_2^{-1}\left(\frac{F_2\left(E_0\right)*K_{\mathrm{xx}}^{\mathrm{act}}}{{\beta }_1*K_{\mathrm{xx}}^{\mathrm{ref}}}\right).$

17. The method according to claim 16, wherein, with the transfer function F of the mounted assembly depending on the ageing D of at least one of the components of the mounted assembly, the method further comprises acquisition of ageing D1 of the at least one component of the mounted assembly in a first state cycle of the mounted assembly comprising the measurement cycle, and acquisition of the second longitudinal stiffness K.sub.XX.sup.ref is effected using the ageing D1 of the at least one component of the mounted assembly.

18. The method according to claim 16, wherein the acquisition of the transfer function F of the mounted assembly is effected by numerical simulation or experimental measurements.

19. The method according to claim 16, wherein the acquisition of the transfer function F is effected on macro-smooth ground.

20. The method according to claim 16, wherein the acquisition of the transfer function F is effected using a mathematical model of the type:
F=(Π.sup.j(G.sup.j/G.sub.0.sup.j).sup.α.sup.j)*(E/E.sub.ref).sup.α where: Gj.sub.0 and E.sub.ref are constants: α.sub.j, and α are real numbers; G.sup.j are influencing factors; and E is the thickness of the tread.

21. The method according to claim 19, wherein the acquisition of the passage function β comprises the following steps: carrying out a set of measurement cycles associated with various sections of road, the sections of road being dry, in one and the same state cycle of the mounted assembly; acquiring, for each measurement cycle, the first longitudinal stiffness k.sub.XX on actual ground and the second longitudinal stiffness k′.sub.XX.sup.ref on a reference ground; evaluating, for each measurement cycle, a difference X between the first and the second longitudinal stiffness; defining a target measurement cycle from the set of measurement cycles by identifying the one that has the smallest difference X; and assigning the identity function to the passage function β defined for the section of road associated with the target measurement cycle.

22. The method according to claim 16, wherein the acquisition of the passage function β comprises the following steps: acquiring a mean thickness E2 of the tread; carrying out a measurement cycle associated with a section of road, the section of road being dry, in one and the same state cycle of the mounted assembly; acquiring the first longitudinal stiffness k.sub.XX on actual ground; acquiring a third longitudinal stiffness k″.sub.XX.sup.ref on reference ground, the third longitudinal stiffness being evaluated with aid of the transfer function F supplied with the influencing factors comprising the influencing factors acquired during the measurement cycle and at least the thickness E2 of the tread; acquiring a coefficient λ as a ratio of the first longitudinal stiffness k.sub.XX on actual ground to the third longitudinal stiffness k″.sub.XX.sup.ref on reference ground; and determining the passage function β associated with the section of road passing through the point (λ, P1, Z1, T1) associated with the measurement cycle.

23. The method according to claim 16, wherein the acquisition of the passage function β comprises the following steps: acquiring a second passage function β2 of the mounted assembly, the second passage function being defined for a second section of road; acquiring, for the ground of the second section of road, a vector M2 characterizing the macro-roughness of the ground relative to the reference ground; acquiring, for the ground of the section of road, a vector M characterizing the macro-roughness of the ground relative to the reference ground; and determining the passage function β of the mounted assembly, the passage function being defined for the section of road e by a relationship between the passage function β2 and the relative position of the vector M2 with respect to the vector M.

24. The method according to claim 16 further comprising the following additional steps: determining a variation ΔU, between at least two acquisitions of the thickness E of the tread, of at least one parameter U associated with the use of the tire including rotation cycles effected, kilometers travelled, time, and use time of the tire; and determining at least one rate V of overall wear of the tire, the rate being defined by a ratio between a variation ΔE in the thickness E between the at least two acquisitions of the thickness E of the tread and the variation ΔU of the at least one parameter U associated with the use of the tire.

25. A method for predicting the end of life of a tire having a tread situated radially on an outside with respect to a natural axis of rotation of the tire, having a mean thickness E, a characteristic thickness E0 and an end-of-life thickness E.sup.end comprising the following steps: determining at least one thickness E1 of the tread of a tire during at least one first state cycle of the tire of a first mounted assembly comprising the tire using the method according to claim 16; determining a rate V1 of wear of the tire, the rate being associated with the at least one thickness E1, by determining a variation ΔU, between at least two acquisitions of the thickness E of the tread, of at least one parameter U associated with the use of the tire including rotation cycles effected, kilometers travelled, time, and use time of the tire and determining at least one rate V of overall wear of the tire, the rate being defined by a ratio between a variation ΔE in the thickness E between the at least two acquisitions of the thickness E of the tread and the variation ΔU of the at least one parameter U associated with the use of the tire; determining a value U1 of the parameter U, the value being associated with the at least one thickness E1; determining an end-of-life prediction of the tire with aid of a value U.sup.end of the at least one parameter U associated with the use of the tire, the value being defined by a second function linking the rate V1 of wear, the at least one thickness E1 associated with a value U1 of the parameter U and the end-of-life thickness E.sup.end.

26. A system for implementing the method according to claim 16 comprising: a vehicle equipped with at least one mounted assembly comprising the tire that can be put under running conditions; at least one storage means; at least one calculation means; at least one analysis means; at least one first transmission means between the vehicle and the at least one storage means; at least one second transmission means between the at least one storage means and the at least one calculation means; at least one third transmission means between the at least one analysis means and the at least one storage means or the at least one calculation means; input data from the vehicle; intermediate data stored in the at least one storage means that can be transmitted by at least one external system; at least one output result from the at least one calculation means; and at least one decision from the at least one analysis means, wherein the input data include the load Z1, the temperature T1, the pressure P1, the force F.sub.X, the rate of slip g %, the parameters Q1 and Q2, the at least one parameter U associated with the use of the tire including rotation cycles effected, kilometers travelled, time, and use time of the tire and variations ΔU of the at least one parameter U, wherein the intermediate data are included in the group comprising mean thickness E2 of the tread, ageing D1 of at least one component of the mounted assembly, characteristic thickness E0 and end-of-life thickness E.sup.end of the tread of the tire, the transfer function F of the mounted assembly, the passage function β of the mounted assembly associated with the section of road, and vector M characterizing the macro-roughness of the ground of the section of road with respect to a reference ground, wherein the at least one output result includes the thickness E of the tread of the tire, the rate V of overall wear of the tire, the end-of-life prediction U.sup.end of the tire associated with the parameter U, the first longitudinal stiffness k.sub.XX.sup.act, the second longitudinal stiffness k′.sub.XX.sup.ref, and the third longitudinal stiffness k″.sub.XX.sup.ref, and wherein the at least one decision expressing the state of wear of the tire is transmitted to, stored in, or both transmitted to and stored in the at least one storage means with aid of at least one fourth transmission means.

27. The system according to claim 26, wherein, with the mounted assembly being equipped with a measurement device comprising a storage means and a means for transmitting to the vehicle or the at least one storage means, at least some of the input data comes from the mounted assembly.

28. The system according to claim 26, wherein the at least one fourth transmission means comprises a means for transmitting to the vehicle that effects the communication of the at least one decision.

29. The system according to claim 26, wherein the at least one fourth transmission means comprises a means for transmitting to a third party that effects the communication of the at least one decision.

30. The system according to claim 26, wherein a part of the at least one storage means, a part of the at least one calculation means, or a part of the at least one analysis means is located on the vehicle or on the mounted assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0110] The invention will be understood better from reading the following description. This application is given only by way of example and made with reference to the appended figures, in which:

[0111] The figures indexed 1 present characterization curves of the longitudinal stiffness K.sub.XX.sup.ref depending on the use parameters of a mounted assembly,

[0112] FIG. 2 presents characterizations of the longitudinal stiffness K.sub.XX.sup.ref depending on the thickness E of the tread of a mounted assembly and the effect of the ground;

[0113] FIG. 3 presents variations in the curves F.sub.X(g %) of an assembly mounted on a vehicle in two states of the tyre on one and the same actual ground,

[0114] FIG. 4 presents the end-of-life prediction of a tyre, evaluated with the aid of the method.

[0115] FIG. 5 is a flowchart of the processes of the invention.

[0116] FIG. 6 is a diagram of the system for implementing the processes of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0117] The figures indexed 1a to 1c present an illustration of the characterization curves of a mounted assembly made up of a Michelin brand tyre of size 235/35R19 from the PilotSport 4S range mounted on a sheet-metal machine wheel of the 8.5J19 ET0 type. The mounted assembly thus formed is inflated under nominal conditions to 2.6 bar under a nominal load of 450 kg. The characterizations are carried out on a test bed of the flat track type provided with bonded ground 120 of the 3M brand. The mounted assembly experiences a cycle of stresses made up of braking and acceleration operations in a straight line after pre-rolling of the mounted assembly for 20 minutes over a cycle of moderate stresses. This pre-rolling makes it possible to thermomechanically put the mounted assembly into a stabilized thermal condition.

[0118] The measurements of the temperature and of the pressure of the mounted assembly are effected via a TMS positioned on the inner liner of the tyre in line with the crown such that the sensor is substantially in the mid-plane of the tyre. The load experienced by the mounted assembly is applied with the aid of the cylinder of the test bed or a dynamometric hub measures the vertical force F.sub.Z applied and also the longitudinal component F.sub.X and axial component F.sub.Y. The measurement is effected with an imposed force by controlling the vertical force F.sub.Z applied. A variation in torque about the axis of rotation of the mounted assembly is applied at the wheel centre of the mounted assembly via the test bed. The torque applied is measured with the aid of the dynamometric hub. In addition, the position of the axis of rotation of the mounted assembly with respect to the ground on which it runs is measured, as is the rotational speed of the wheel centre of the mounted assembly by way of an encoder mounted between the stator and the rotor of the axis of rotation of the test bed. Finally, the running of the ground is also controlled by the machine. In addition, a motion sensor measures the speed at which the ground runs. The presence of the bonded coating makes it possible to avoid slipping of the tyre on the ground while complying with the optional condition of running on a macro-smooth ground.

[0119] FIG. 1A presents, for this mounted assembly, the experimental characterizations, represented by dots, obtained on a reference ground referred to as macro-smooth for the abovementioned mounted assembly by varying the inflation pressure P of the mounted assembly between three possible inflation pressures according to the ETRTO (European Tyre and Rim Technical Organisation) standard for this mounted assembly for several controlled loading and temperature conditions. The continuous curve is a transfer function F (1005) model of the independent influencing parameters type which minimizes the error between the experimental points and the mathematical model. Dependence of the second longitudinal stiffness K.sub.XX.sup.ref at the inflation pressure P is clearly apparent. The measurement points obtained under controlled metrological conditions make it possible to identify the various parameters of the transfer function F (1005) associated with the parameter of the inflation pressure.

[0120] FIG. 1B and FIG. 1C show the characteristics of the same mounted assembly that are effected on the test bed of the flat track type by varying the temperature and the applied load, respectively. The temperature variations in FIG. 1b correspond to temperature variations of the mounted assembly that can be encountered conventionally under various use conditions. They are acquired by varying the regulated temperature of the cell accommodating the test bed and by applying a greater or lesser variation in the stress applied to the tyre. For temperatures that are difficult to control on the test bed, the use of a numerical simulation model of the mounted assembly was used. In a first phase, the numerical model, in particular that of the tyre, was validated using experimental measurements. In a second phase, numerical simulations were effected for thermal stresses that are difficult to reproduce experimentally. For the numerical model, the ground is grippy smooth ground representative of the bonded ground on the test bed.

[0121] The variations in load for FIG. 1C are acquired by modifying the controlled load of the test bed, complying with the loads permissible for the mounted assembly according to the ETRTO standard.

[0122] The continuous curves are the mathematical model of the transfer function F (1005) identified for this mounted assembly, considering, in the set of influencing parameters, that the parameters are independent of one another. The readjustment of the mathematical model to the various experimental curves allows the unique identification of the various coefficients of the transfer function F (1005) of the mounted assembly on a reference ground of the macro-smooth type.

[0123] Of course, the characterizations for the influencing parameters of the first group G are effected on at least three different levels of each influencing parameter of the second group H such as the ageing and the level of overall wear of the tyre and of the first group G other than the one intended to be characterized.

[0124] Finally, with the numerical model having previously been validated using experimental measurements of a particular mounted assembly, it is preferable to reuse this numerical model of the tyre in order to form a numerical simulation campaign by modifying the other components of the mounted assembly, the thermomechanical stresses applied and the various states of the mounted assembly. The numerical simulations are less time-consuming and consume fewer resources than the experimental campaigns after the validation phase of the numerical model of the tyre.

[0125] FIG. 2 presents the change in the second longitudinal stiffness K.sub.XX.sup.ref on a reference ground acquired for a mounted assembly comprising a tyre of the Energy Saver type of size 195/65R15 mounted on an alloy wheel 6.5J15 ET23. The measurements were taken on an analytic trailer while running on test tracks of which the macro-roughness is monitored by profilometry. In this case, the variable parameter is the mean thickness E of the tread, with the various other influencing parameters of the longitudinal stiffness such as the load applied, the inflation pressure and the temperature of the mounted assembly also being monitored. The mobile test bed subjects the mounted assembly to varying acceleration phases involving both acceleration and deceleration by applying a torque to the mounted assembly about the natural axis of rotation of the tyre. The variation in the mean thickness of the tread was acquired by the automatic planing of the tyres in one and the same tyre preparation cycle. Thus, the ageing of the various tyres is similar. The altitude of the natural axis of rotation of the mounted assembly was adapted so that the load applied to each mounted assembly was identical. The speed of the tyre corresponds to the linear speed of the mobile test bed via the information relating to the speed of the mobile test bed retrieved on the CAN bus. A wheel marker and a position means for measuring the height of the wheel centre with respect to the ground of the mounted assembly complete the equipment.

[0126] In general for tyres equipping passenger vehicles and vans, the torque applied at the wheel centre is around 30 daN.Math.m in order to ensure that the tyre does not slip on the ground, this amounting to saying that the coefficient of slip of the material of the tread under use conditions with respect to the ground is not achieved. Of course, this torque applied should be adapted depending on the category of tyre to be measured.

[0127] Discrete measurements, represented by the dots, correspond to the experimental characterizations of the longitudinal stiffness estimated during tests on the reference ground of the test track. The solid curve corresponds to the second longitudinal stiffness evaluated with the aid of the transfer function F (1005) of the mounted assembly corrected by a passage function β (1004) associated with the reference grounds. The two other, dotted or dashed-line, curves correspond to the second longitudinal stiffness evaluated with the aid of the transfer function F (1005) of the mounted assembly each corrected by a passage function β (1004) associated with the actual grounds 1 or 2. In this case, the transfer function F (1005) used is also the product of power functions of the various independent parameters. The passage functions (1004) make it possible to estimate the longitudinal stiffnesses on actual ground with only the transfer function F (1005) of the mounted assembly being known. The passage function β (1004), regardless of the ground, is more or less constant or depends on the thickness E of the tread for a given ground. The various grounds are grounds that are controlled in terms of roughness and make it possible, for one and the same tyre, to acquire a passage function β (1004) variety making it possible to take the nature of the ground into account.

[0128] Of course, it is possible to acquire an estimation of the influence of the ageing D of the mounted assembly and in particular of the tyre by preparing tyres that have experienced different kinds of ageing by way of an identical method. For example, by accelerating the ageing by way of specific storage conditions, in an oven for example at various temperatures, or by performing running sessions with greater or lesser thermomechanical stresses, different kinds of ageing will be obtained among the tyres. Planing of the various tyres may also be effected in this case in order to obtain one and the same thickness E of the tread before the characterization campaign for the identification of the transfer function F (1005).

[0129] FIG. 3 presents curves of forces F.sub.X in the longitudinal direction of the mounted assembly as a function of the rate of slip g % of a mounted assembly made up of a Michelin brand tyre of size 235/35ZR19 from the range PilotSport 4S mounted on an alloy wheel of type 8.5J19 ET20. This mounted assembly is mounted on the front axle of a traction-type Focus ST vehicle of the Ford brand.

[0130] The measurements were taken on one and the same section of road for two different states of the tyre with the same use conditions. The grey measurement points represent a state of the tyre having a thickness E1 and ageing D1 close to the slightly worn and young state of the tyre. The black measurement points represent a second state of the tyre corresponding to a thickness E2 and a level of ageing D2 corresponding to a state close to the end of life of the tyre and ageing equivalent to one year of average use in a temperate country. Only the acceleration phases on the course up to driving torques not exceeding 35 daN.Math.m are shown here in order to consider that the tyre does not slip on the road surface.

[0131] With the aid of the continuous curves defined as being the linear regression line of the measurement points of each state of the tyre, the first longitudinal stiffnesses (1009) on actual ground of the two mounted assemblies are estimated here. It can be seen that the level of longitudinal stiffness on actual ground is influenced by the state of the tyre, the other parameters being considered to be equivalent between the two states of the tyre.

[0132] FIG. 4 shows the estimated progress of the overall wear of a tyre with respect to the change in a tyre U associated with the use of said tyre. This parameter U may be for example the distance travelled or the number of rotation cycles effected by the tyre. The estimation is carried out via the acquisition of the longitudinal stiffnesses (1009, 1010) done regularly throughout the use of the tyre, which are represented by the solid circles. Depending on the nature of the tread of the tyre and on an estimation of the macro-roughness of the ground, a first passage function β (1004) is identified over a section of road in which the measurement of the parameters (1007, 1008) is regularly carried out, making it possible to acquire the first longitudinal stiffness on actual ground (1009) and the second longitudinal stiffness on reference ground (1010). Thus, the method (1000) according to the invention makes it possible to estimate the variation in the mean thickness of the tread during the use of the tyre with respect to a characteristic thickness E0 (1002). It is thus possible to estimate a rate of wear V (1013) by taking into account at least a variation in the mean thickness ΔE of the tread between two acquisitions of the mean thickness (1011), for example the new state and a measurement during the use of the tyre, while knowing the variation ΔU (1012) of the parameter U between the two mean thicknesses taken as reference. Knowing the end-of-life thickness E.sup.end (1003) of the tread, beneath which the safety risks are greatly accentuated, makes it possible to identify an end-of-life prediction according to the parameter U called U.sup.end (1015) with the aid of the method (1100) for predicting end of life.

[0133] Of course, the prediction is based on a hypothesis relating to the passage function β (1004). If, during the use of the tyre, a measurement E2 of the mean thickness of the tyre is taken, during a check of the tyres at a transport vehicle professional for example or when passing over a drive-over scanner at a highway toll booth or traffic lights, a new evaluation of the passage function β (1004) of the section of road can be effected. This manifests itself on the curve in FIG. 4 by a discontinuity which illustrates just the taking into account of the actual measurement E2 of the mean thickness of the tread. A new point, represented by a square in FIG. 4, illustrates this measurement point characterized by the thickness E2 of the tread. Next, the change in slope that may occur results from an adjustment of the passage function β (1004) associated with a section of road. This adjustment is made by identifying a point of the passage function β (1004) associated with the level of overall wear E2. Next, the new curve acquired with a readapted slope, reproducing the rate V of wear of the tyre, can be projected onto the straight line defined by the end-of-life thickness E.sup.end (1003) of the tread in order to estimate the end-of-life wear U.sup.end (1015) of the tyre. Here, it is assumed that the estimation of the overall wear of the tyre (1011) is realized regularly on one and the same section of road located by a geographic position. The change in ground can thus result for example from the change in the section of road taken as reference to obtain the first longitudinal stiffness (1009). The change in ground may also result from an adjustment of the passage function β (1004) during the use of the tyre. Thus, in the new state, an inclusive function is attributed to the passage function β (1004) as the identity function through unfamiliarity with the nature of the ground where the measurement cycle is carried out. During the use of the tyre, using a characterization method for the passage function β (1004), for example a true measurement of the mean thickness E2 of the tread, makes it possible to identify a passage function β (1004) that is more representative of the nature of the ground.

[0134] FIG. 5 shows a flowchart incorporating the method (1000) for estimating overall wear and the method (1100) for predicting the end of life of a tyre under running conditions on a vehicle.

[0135] Step 1001 is the identification of the mounted assembly and very particularly of the tyre. This step can be carried out via the assignment of the identifier of the components of the mounted assembly that are associated with the vehicle in a database.

[0136] The identification 1001 makes it possible first of all to define a characteristic thickness E0, corresponding to the step 1002, as, for example, the thickness in the new state and the end-of-life thickness E.sup.end of the tyre, corresponding to step 1003. Next, the identification 1001 of the mounted assembly also makes it possible to know the stiffness of the tread of the tyre, thereby making it possible to estimate one or more passage functions β (1004) that are each associated with a section of road characterized by macro-roughness from a plurality of possible passage functions. Failing that, the user chooses a function passage β (1004) from the list of potential passage functions β that is representative of the median nature of the sections of road that the vehicle will encounter. The choice of the passage function β corresponds to step 1004. Finally, the identification 1001 also makes it possible to choose the transfer function F of the mounted assembly corresponding to step 1005. This transfer function F is indispensable for the method for estimating overall wear.

[0137] Next, where required, the user finds out the state of ageing of the tyre, corresponding to step 1006. This passes through the identification (1001) of the tyre in order to know the history of the use of the tyre. This history can be found out by interrogating a database. This database may be external to the mounted assembly, present on the vehicle or on a server. If the state of ageing D1 (1006) of the tyre concerns only the age of the product or the total number of cycles effected or kilometres travelled, the information can be present on the mounted assembly by way of an electronic device of the TMS or TPMS type. Necessarily, this step 1006 takes place during a state cycle comprising the measurement cycle for evaluating the mean thickness of the tyre.

[0138] The next steps 1007 and 1008 are effected during a measurement cycle. The first step 1007 consists in acquiring, when running in a straight line on a dry road comprising phases of acceleration and deceleration, the associated forces F.sub.X measured at the wheel centre of the mounted assembly and the associated rate of slip g %. In the absence of direct forces F.sub.X at the wheel centre, access to parameters Q1 of the vehicle allows an estimation of the forces F.sub.X at the wheel centre, for example the torque applied to the wheel centre about the natural axis of rotation of the mounted assembly during acceleration or deceleration phases. Step 1008 corresponds to the acquisition of the use parameters of the mounted assembly such as the inflation pressure P1, the temperature T1 of the mounted assembly and the load Z1 applied, or the parameters Q2 of the vehicle that make it possible to acquire the load Z1. These parameters Q2 may be, for example, the static mass of the vehicle, the filling state of the fuel tank, and the indication of the number of buckled seat belts. This step 1008 should be effected just before, during or after the running in a straight line that is effected in step 1007.

[0139] Step 1009 chronologically follows step 1007, although it can be done between two measurement cycles. On the basis of the forces F.sub.X measured or evaluated and the associated rates of slip g % when running on the dry section of road, a point cloud associated with the pair of values (F.sub.X, g %) is plotted. Of this point cloud, only the set of points for which the tyre does not slip on the section of road is retained. Finally, the linear regression line of the set of points retained is identified. The slope of this regression line corresponds to the estimation of the first longitudinal stiffness K.sub.XX.sup.act on actual ground corresponding the dry section of road.

[0140] Step 1010 chronologically follows step 1008 coupled with steps 1002 and 1005. Thus, on the basis of the transfer function F (1005) chosen by virtue of the identification (1001) of the mounted assembly, a second longitudinal stiffness on reference ground K.sub.XX.sup.ref is estimated by supplying the transfer function F (1005) with the use parameters P1, T1 and Z1 measured in step 1008 and the thickness characteristic E0 chosen in step 1002. Depending on the sensitivity of the characteristics of the mounted assembly to ageing, this step 1010 can also be coupled with step 1006, in which an evaluation of the ageing D1 of the mounted assembly is effected.

[0141] The following step 1011 corresponds to the evaluation of the mean thickness of the tread and, consequently, to the overall wear of the tyre, by comparing this evaluated mean thickness with the specific thicknesses of the tyre, such as E.sup.end and E0. For this purpose, a relationship between the results of steps 1004, 1007 and 1008 is applied, the result of which is the mean thickness E associated with the state cycle of the tyre. When the second longitudinal stiffness on reference ground K.sub.XX.sup.ref (1010) is defined with the aid of a transfer function F (1005) which is the product of power functions of independent influencing factors as claimed in the claim, the thickness E can then be isolated from this transfer function F (1005) as the product of the constant E.sub.ref and the alpha root of the ratio of the first longitudinal stiffness on actual ground (1009) to the product of the passage function β (1004) and the second longitudinal stiffness on reference ground (1010). It will be assumed here that the passage function β (1004) is constant with the mean thickness of the tread. In the case of mutually dependent influencing parameters, the relationship identifying the mean thickness E is more complex.

[0142] The next step 1012 consists in acquiring the variation ΔU of a parameter U associated with the use of the tyre between two acquisitions of the mean thickness of the tread. The parameter U may be for example the number of rotation cycles about the natural axis of rotation or the number of kilometres travelled by the tread or the use time of the tyre. The two acquisitions (E1, E2) of the mean thickness of the tread may be for example two evaluations carried out by the method corresponding to two states of wear of the tyre or an evaluation of the mean thickness of the tread combined with the new state of the tyre or a measurement of the mean thickness of the tyre using an external measurement means.

[0143] The following step 1013 is the evaluation of the rate V of wear of the tyre and more specifically of the tread at a point of acquisition of the mean thickness of the tread of the tyre. To this end, it is necessary to have both the variation ΔU of the parameter U associated with the use of the tyre, acquired in the preceding step, and the corresponding variation of the mean thickness ΔE. The variation ΔE is the difference between the two acquisitions (E1, E2) that served as reference points for the variation ΔU effected in the preceding step. The ratio of the variation of the mean thickness ΔE to the variation of the parameter associated with the use of the tyre AU defines the rate V of wear of the mean thickness of the tread according to the parameter U.

[0144] Of course, the variation ΔU of the parameter U associated with the use of the tyre can also result from the difference between the acquisitions (U1, U2) of the parameter U that are effected in step 1014.

[0145] Finally, the last step 1015 consists in evaluating the end-of-life prediction U.sup.end according to the parameter U associated with the use of the tyre. This is obtained by combining the results of steps 1003, 1011, 1013 and 1014.

[0146] FIG. 6 is a flowchart of the system for implementing the processes for estimating the level of overall wear and for predicting the end of life of a tyre. The flowchart comprises structural elements represented by bubbles and transmission means between the structural elements represented by a line between the structural elements. The line may comprise, at its end, a solid circle indicating an end point of the transmission means or a solid rhombus indicating a starting point of the transmission means. Even so, the direction of communication indicated may also be bilateral, for example if the process incorporates a phase of interrogating a structural element with respect to another structural element. Finally, the flowchart also comprises the data contained in and exchanged between the various structural elements in the form of rectangles.

[0147] The input data are present at the vehicle 2001. These can also be present at least in part at the mounted assembly 2006 comprising the tyre, which is the area of interest of the methods that are the subjects of the present invention. These input data pass to a storage means 2002 via transmission means 2101. When some of the input data come from the mounted assembly 2006, these are transmitted to the storage means 2002 directly or via the vehicle 2001. The transmission means from the mounted assembly, denoted 2015, are represented by black dots.

[0148] The intermediate data contained in the storage means 2002 come in part from the input data from the vehicle 2001. However, they can also come from an external system 2005 via transmission means 2106. These intermediate data coming from the external system may be, for example, the transfer function F associated with the mounted assembly or the passage function β forming the link between the stiffness of the tread of the tyre and the nature of the section of road.

[0149] Next, the system comprises a calculation means 2003 for acquiring the various results by way of operations between the intermediate data. As a result, a transmission means 2102 allows the communication of the intermediate data to the calculation means 2003 in order to generate results.

[0150] These results can then pass via transmission means 2103 in the form of a dotted line to the analysis means 2004, either directly or via the storage means 2002. The analysis means 2004 then delivers a decision, which, via a transmission means 2107 in the form of a grey dot-dash line, will be transmitted directly to the vehicle 2001 or to a third party 2007 or stored in the storage means 2002 depending on how urgent the decision is.

[0151] This decision may be an item of information about the state of wear E of the tyre with respect to the end-of-life thickness E.sup.end of the tyre. The decision may also, depending on the end-of-life prediction E.sup.end of the tyre, be actions involving changing the tyre to be planned or to be effected rapidly. In the first case, the information will be transmitted to a fleet manager in order to arrange the planning. In the second case, the decision returns to the vehicle so that the driver can adapt the conditions of use of the tyre to the state of wear thereof and so that they can expect to change the tyre as soon as possible.