WO2008012312A1

WO2008012312A1 - Tire with a tread element for measuring its grip potential

Info

Publication number: WO2008012312A1
Application number: PCT/EP2007/057630
Authority: WO
Inventors: Frédéric SPETLER
Original assignee: Societe De Technologie Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2006-07-27
Filing date: 2007-07-24
Publication date: 2008-01-31
Also published as: FR2904260A1; FR2904260B1

Abstract

Tire (1) comprising among its tread pattern elements (4) one or more measuring elements (3) positioned in such a way that, in normal operation, these measuring elements (3) can slide for a moment on the ground (5). The tire (1) then allows, at the same moment, the determination of the maximum grip potential of the tread on the ground. The characteristics of the material of the measuring element (3) are defined with respect to those of the material of the tread pattern element (4) by means of an inequality, which makes it possible to monitor the difference between the speeds of wear of the measuring element (3) and the other elements (4), in such a way that, irrespective of the wear, the measuring element (3) remains in contact with the ground and can perform a reliable measurement.

Description

PNEUMATIC WITH A CALIBER ROLLER BEARING ELEMENT

FIELD OF THE INVENTION

The present invention relates to a tire with a calibrated tread element. The invention relates more particularly to the determination of ranges of correlation between physical parameters of materials constituting two different elements of the tire and forming part of the tread, one of which is said to be sacrificed.

STATE OF THE PRIOR ART

EP-I 076 235 B1 discloses a tire whose tread comprises a first and at least a second element having a ground contact surface positioned at a distance from the wheel axis respectively Rs and Ra wherein the constituent materials of the first and second members are different and such that Rs is less than Ra and the adhesion potential of the material of the first member is less than that of the material of the second member, or the wear resistance of the material of the first element is greater than that of the second element where the Young's modulus of the material of the first element is greater than that of the material of the second element.

These choices of materials are intended to maintain during the wear of the tire in normal service the difference between the distances Rs and Ra so that, in normal operation, the contact surface of the first element undergoes sliding by relative to the ground during its passage in the contact area while the contact surface of the second element does not slip on the ground.

The first element or measuring element comprises sensor means capable of measuring the deformations or stresses at least in the tangential direction in the contact surface of the first element during its passage through the contact area. These means make it possible, in particular, to measure the adhesion potential of the rolling tire.

In fact, it has been found that the above indications can be faulted: a first element may retain a sliding potential greater than that of the other elements of the tread, but, with time, this first element can lose contact with the roadway by wearing out too quickly. As a result, it can no longer slide and thus loses its primary function of measurement in contact with the roadway. Ultimately, the problem is that the measurements made by the measuring elements or first elements are not always reliable over time because the wear of the tire can disrupt the results obtained.

SUMMARY OF THE INVENTION

The invention relates to a tire whose tread comprises first and second elements having contact surfaces with the ground positioned at distances from the wheel axis respectively Rs and Ra, characterized in that , considering Abi, Ab ₂ , μi, μ ₂ , E ₁ , E ₂ and King, Ro ₂ , characteristic parameters respectively of the abradability, adhesion, rigidity and orthotropy of the constituent materials of the first and the second element, these parameters respect the following relation:

Ab ₂ μ ₂ with B and C having positive or negative values; and in that B = 1.2 and C = 0.25 for respective ratios Ei on E ₂ and Ro i on Ro ₂ equal to 1.

The tire according to the invention makes it possible to control the difference between the wear speeds of the measuring element and the other elements of the tread.

The tire according to the invention preferably has a distance Rs for the first element smaller than the distance Ra for the second element and preferably the difference between Ra and Rs is between 5 and 20% of the height. initial second elements; the initial height of an element being the distance between the surface of contact of the element and the bottom of adjacent lamellae (see Fig. 2). This difference in height between the two elements ensures that when passing through the contact area, the first element has a sliding distance greater than that of the second.

The decisive advantage of the tire according to the invention is that even if, in the new state, Ra and Rs have similar or identical values, the control of their respective wear allows the gap (Ra-Rs) to grow up to satisfactory values for the intended applications.

Similarly, throughout the life of the tire, the gap (Ra - Rs) remains compatible with the intended applications. The check is made during the entire service life of the tire.

In the invention, it uses four material parameters that are: the adhesion μ, abradability Ab characterizing the wear resistance, stiffness E characterized in particular by Young's modulus E _γ and finally orthotropy Ro.

Then, ratios are formed between values of the same parameter: a value of a parameter for a measurement element taken as numerator,

- a value of the same parameter for a tread element taken as the denominator.

Thus four reports are formed for each of the four parameters that are studied.

According to the invention, the solution consists in proposing an inequation linking two ratios of two parameters. Each ratio is established between two identical parameters of a measuring element on one side and a tread element on the other.

In the invention, the inequation is experimentally established thanks to two of the four aforementioned parameters and this, in the form of two ratios, respectively an adhesion ratio μi / μ ₂ and a Abi / Ab abradability ratio. ₂ . This inequality then allows delimiting a design limit of the tire in general and the measuring element in particular, depending on the adhesion, wear resistance, rigidity and orthotropy that is desired confer on him. In the end, we then choose materials, or manufacturing process steps for which this inequality is respected.

This design limit then defines two areas of manufacture of the tire.

A first domain that reliably exploits the results delivered by the measurement elements. In this field, the results are reliable, regardless of the moment of measurement in the life of the tire and the type of driving. Of course, the driving conditions must remain reasonable.

A second domain that does not allow it.

On the other hand, the invention relates to the determination and variation of two other ratios: the rigidity ratio RRig of the two elements represented in particular by the module of

Young E _γ ,

the ratio of orthotropy Ro of the two elements, the orthotropy Ro measuring the differential stiffness between a tangential direction and a radial direction, directions perpendicular to each other.

The design choices leading to these two new ratios have an influence on the coefficients B and C of the inequality connecting the adhesion ratio μi / μ ₂ and abradability Abi / Ab ₂ . The design limit of the tire or the measuring element is thus modified or refined.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on reading the description which follows and the examination of the figures that accompany it. These are presented only as an indication and in no way limitative of the invention. The figures show: - Figure 1: a representation of a tire on a roadway;

- Figure 2: a radial section of a tire designating a measuring element and a tread element;

- Figure 3: the evolution as a function of the mileage traveled of the height of elements of the tread of a tire;

- Figure 4: the evolution as a function of the mileage of the difference in height between first and second elements of the tread of a tire;

FIG. 5: a curve representing the areas of functionality or non-functionality of a measuring element as a function of the ratio of the abradabilities of this element and of an element of the tread and according to the ratio of the adhesions of these elements. same elements and this, for elements having ratios of rigidity and orthotropy parameters equal to 1;

FIGS. 6a to 6d: curves representing the domains of functionality or non-functionality of a measuring element as a function of the ratio of the abradabilities of this element and of a tread element and according to the ratio of the adhesions of these same elements and for different ratios of rigidities of these same elements and for an orthotropic ratio equal to 1;

FIG. 7: a curve representing the evolution of the coefficients B and C of the separation curve of two domains rendering the measurements on the tire functional or non-functional, according to the respect or not of the inequation and this, according to the different stiffness ratio values;

FIGS. 8a to 8d: curves representing the changes in the abradability ratio between a measuring element and a tread element as a function of the ratio of the adhesions of these same elements and for different orthotropic ratios of these same elements. elements and for a stiffness ratio equal to 1; and

FIG. 9: a curve representing the evolution of the coefficients B and C of the separation curve of the two domains rendering the measurements on the tire functional or non-functional according to the respect or not of the inequality and this, as a function of the different values; of the orthotropic report. DETAILED DESCRIPTION OF THE DRAWINGS

In Figure 1 is shown a tire 1 whose tread 2 comprises a first element 3 and a second element 4 which will be called in the following developments respectively measuring element 3 and element 4 of the tread . These pairs of two elements are positioned along the tread 2 of the tire 1. They are positioned so that they can, during a measurement, both be in the area of contact with the roadway 5.

The measuring element of Figure 1 corresponds to a carving bread having in its central part a measurement zone separated from the rest of the bread by four slats placed in a rectangle. This type of measuring element is described in particular in document EP 1 231 120. The measuring elements can also be ribs or loaves as described in document 1 076 235.

The roadway 5 is represented by a plane defined along two axes X and Y. The axis X of the plane of the roadway 5, rolling direction, represents all the longitudinal tangential stresses imposed on the tire 1 during its rolling. The Y axis of the plane of the roadway 5, bearing axis, represents the direction of all the transverse tangential stresses imposed on the tire 1. The tire 1 is also subjected to normal stresses in the plane of the roadway 5 represented by the axis Z. The XYZ axes are orthogonal to each other.

The two types of elements 3 and 4, in contact simultaneously on a portion of the roadway 5, namely the measuring element 3 and at least one element of the tread 4, are located on two distinct parts of the tire 1.

The material constituting an element 4 of the tread 2 must have characteristics different from those of the material of a measuring element 3, the main criterion being that the measuring element 3 must imperatively slide earlier the element 4 of the tread 2 while keeping a relative wear relative to that of the element of the tread controlled. As a result, this allows to warn the driver of any loss or loss of adhesion of the tire 1.

Thus, the two materials must have properties determined by different parameters that are: adhesion, wear resistance, rigidity and orthotropy.

The adhesion μ qualifying, in a simplified way, the adhesion potential of an element 3 or an element 4, is the ratio, as seen above, between the maximum or global tangential forces that this element 3 or 4 in its totality can undergo during a contact with the ground in a given place and the vertical force applied to the surface of this same element.

[0030] The wear resistance of a material of an element is represented by its abradability Ab, thus a high abradability index Ab indicates a low wear resistance and a low abradability indicates resistance to abrasion. better wear.

The rigidity E of an element, in turn, is represented in particular by its Young Ey module. In the same way, depending on whether the value of the Young Ey modulus is higher or lower, the rigidity E of the element will be respectively more or less important.

The orthotropy Ro of a material is a parameter defining the quality of a material of which one or more of its properties vary according to the direction in which they are evaluated. Mainly, in the case of orthotropy, along two perpendicular directional axes in-between.

For this we define:

- Exz which represents the shear stiffness of an element along an axis X, this axis X being perpendicular to the Y axis of rolling of the tire, the Y axis being the axis of rotation of a wheel which carries the tire and the Z axis being perpendicular to the two preceding ones, as a function of a constraint oriented along the X axis collinear with the rolling direction, - Eyz which represents the shear stiffness of the same element along the Y axis according to a stress oriented along the Y axis,

- Ezz which represents the compression stiffness of the same element along the Z axis, according to a stress oriented along the same axis Z.

In this way, the Rox and Roy orthotropies of an element along the X axis and the Y axis respectively correspond to the ratio of Exz on Ezz and Eyz on Ezz.

Thus according to a value of a parameter of the material of the measuring element 3 with respect to that of the same parameter of the material of the element 4 of the tread, we will initiate a higher sliding of the element. 3 relative to that of a member 4 of the tread.

In Figure 2 is shown a measuring element 3 and an element 4 of the tread in contact on the roadway 5. It is found that the distance Rs of the contact surface of a measuring element 3 up to the wheel axis is smaller than the distance Ra from the contact surface of an element 4 of the tread to the wheel axle. This manufacture of the structure of the elements of a tire 1 and more precisely of its tread 2 allows a measuring element 3 compared to an element 4 of the tread to undergo a particularly normal pressure along the Z axis, less than that of an element 4 of the tread and thereby to slip earlier.

In the invention is more particularly interested tangential forces present on the surface of a measuring element 3 in contact with the roadway 5.

In the manufacture of a tire 1 is the material of the tread 2 which imposes its requirements and constraints for reasons of adhesion, wear resistance over time, etc..

Then, depending on the material chosen, it is the material used for the measuring elements 3 which is developed. The design of the tire to allow the smooth operation of the measuring elements, according to the invention, must therefore respond to the inequality posed. Figure 3 shows the evolution as a function of the mileage traveled of the height of tread elements or rolls of the tread of a tire and Figure 4 the evolution of the deviation Ra - Rs depending mileage.

The curve corresponds to the evolution of any element of the tread. The height changes from 8 mm in new condition to almost 2 mm after 15,000 kilometers.

Curve b corresponds to a bread or measuring element offset by 0.8 mm in new condition. This measuring element has the same material properties as the elements of the tread. It can be seen that the gap, initially functional, tends to decrease gradually until it cancels out. This measurement element is not functional.

The curve c corresponds to a bread or measuring element also shifted from 0, 8 mm in new condition. This measuring element 3 has material properties relative to those of the elements of the tread 4 satisfying the inequality

log ₁₀ - -> - (1,4 - B - -) ² + C. It can be seen that the gap is decreasing but remains significant. Ab ₂ μ ₂ This measuring element is functional.

[0044] Figure 4 shows the evolution of the deviations Ra - Rs according to the mileage.

The curve corresponds to the case of non-functional bread. We see that the gap satisfying the new state gradually decreases to zero. Under these conditions, it is no longer possible to use this measuring element to perform adhesion measurements.

The curve b corresponds to the case of functional bread. In this case, the gap gradually decreases but remains greater than 0.2 mm throughout the life of the tire.

In what follows, we agree that a bread is functional if its properties allow it to slip in all or part of the contact area between the tread and the pavement in free running condition (that is to say without engine force or braking applied to the tire) for at least two thirds of the life of the tire.

For the usual elements of the tread and for the tires tested, the deviations between Ra and Rs, or "sacrificed heights" allowing a measuring element to be functional are in a range of 0.2 to 1.4 mm.

A well-adjusted measuring element in wear need not necessarily keep a sacrificed height constant throughout the life of the tire. It is simply necessary that the evolution of this sacrificed height allows the measuring element to slip in free rolling condition for at least two thirds of the life of the tire (thus avoiding the heights sacrificed too much). weak), while continuing to come into contact with the ground (avoid too high heights sacrificed). Of course all measurements are performed under normal load and inflation pressure conditions.

All of the following figures were obtained using a model of the contact area of a tire based on the Koutny model and was validated by tire tests equipped with measuring elements made of materials. of varied characteristics.

In FIG. 5 is represented: on the abscissa, the value of the ratio Rmu = μl / μ2 of the adhesion μl of the material of a measuring element on the adhesion μ2 of the material of an element of the strip rolling,

in the ordinate, the value of the logarithm base 10 of the Ab / Ab2 ratio of the abradability (AbI) of the material of a measuring element on the abradability (Ab2) of the material of a tread element.

It is thus found experimentally that for a given value of an adhesion ratio, it is associated with several possible values of abradability ratios for which the measuring element of the tire remains functional. The measuring element is described as functional if it can slide correctly on the road, which allows reliable adhesion measurements.

In addition, all the measurements are carried out for rigidities of the measuring element El and for rigidities of the element of the tread E2 identical; the rigidity ratio RRig = El / E2 is then equal to 1, as is the RRorth orthotropy ratio

Thus, two zones 12 and 13 are highlighted on the graph according to that depending on the combinations between the adhesion ratio μi / μ ₂ and abradability Abi / Ab ₂ ratios, the measuring element is functional or not.

It is then found that the two zones 12 and 13 thus obtained are on either side of a boundary 14 delimited according to a curve of the type Y = - (1.4-BX) ² + C, with in this case , B = I.2 and C = O.25.

In addition, it can be seen in the graph that the zone 12 for which a measuring element 3 remains functional corresponds to an empirico-theoretical relationship between the adhesion and abradability ratios of the materials of the two elements 3 and 4. to inequality:

i ^og ₁₀ ^ AbΓ ₂ ≥ -O- ^{4 "5} - μ ₂ ) ^{2 + C}

In FIGS. 6a to 6d, are represented:

on the abscissa, the value of the ratio Rmu = μi / μ ₂ of the adhesion of the material of a measuring element μi to the adhesion of the material of a tread element μ ₂ ,

- In ordinate, the value of the base logarithm of the Abi / Ab ₂ ratio of the abradability Ab i of the material of a measuring element on the abradability Ab ₂ of the material of a tread element.

For all these FIGS. 6a to 6d, the ranges of adhesion and abradability ratios for which it is desired to establish whether a measuring element is functional or not according to the criterion described previously, remain identical to that of FIG. 5. On the other hand, these measurements are made for different RRig rigidity ratios. respectively: 0.2, 0.5, 2 and 5, and still for an orthorthotropy ratio RRorth equal to 1.

The rigidity E of a material can be characterized according to different methods. In the context of the invention, the measurement of the Young's modulus that is used is a secant modulus in extension measured for a deformation of 10% after three cycles of accommodation of the specimens.

Thus, the stiffness ratios RRig between the Young's (Ey) secant modulus at 10% of a measuring element 3 (EyI) and that (Ey2) of an element 4 of the tread are respectively for Figures 6a, 6b, 6c and 6d of 0.2, 0.5, 2 and 5.

It is noted in all these figures that the two zones 12 and 13 thus obtained for which a measuring element 3 remains functional or not, are on either side of a boundary 14 delimited still according to a curve of the type. Y = - (1.4- BX) ² + C.

On the other hand, it is found that this same curve undergoes a translation along the Y axis while substantially modifying its curvature as a function of the variation of the rigidity ratio RRig = E1 / E2.

Indeed, the higher the stiffness ratio RRig increases and the zone 12 corresponding to a functional measuring element 3 is important. The quantities B and C for FIGS. 6a, 6b, 6c and 6d then respectively have values of 1.15, 1.18.1.22 and 1.25 for B and 1.25, 0.7, 0.25, 0.2 and -0.7 for C.

It is thus established experimentally that the quantities B and C vary according to the relative values given to the stiffness E1 of the material of a measuring element 3 with respect to that E2 given to the material of an element 4 of the tread. We therefore have magnitudes B and C functions, of the ratio of E1 and E2: B = f (E1 / E2) and C = g (E1 / E2).

This appears in more detail in FIG. 7. This shows that the combination of both the adhesion parameters, abradability (wear resistance) and rigidity, allows to open more widely the ranges of elaboration of the material of the measuring element 3 with respect to the material of the element 4 of the tread CE, while maintaining a functional measuring element 3 with a well-locked wear.

In FIG. 7 is shown:

on the abscissa, the value of the logarithm base 10 of the ratio of the rigidities evaluated according to the Young's modules,

- on the ordinate, the values of the constants B and C.

In an empirico-theoretical manner, represented in this FIG. 7, two equations for the quantities B and C are established for the two straight lines 19 and 20 respectively corresponding to B and C such that:

β = 0.07 log ₁₀ - ^ - + 1.2 and C = -1.411og ₁₀ - ^ - + 0.26 E ₂ E ₂

We can then see that the zone 12 answering the inequality

log _w ^ ≥ - (lΛ - B * -y ₊ C

Ab ₂ μ ₂ and corresponding to a functional measuring element of the tire, extends proportionally according to that the stiffness E1 of the measuring element 3 becomes more and more important relative to that E2 of an element 4 of the tire strip. rolling.

As for the rigidity parameter, the modification of the relative orthotropy RoI of a measuring element 3 with respect to the Ro2 orthotropy of a tread element 4 involves a modification of the domain for which the measuring element 3 remains functional.

For this we define in the same way a ratio of RoI orthotropies of a measuring element 3 of the Ro2 of an element 4 of the tread. This ratio is studied according to the axes tangent to the tread X or Y depending on the radial axis Z is Exz / Ezz or Eyz / Ezz or more generally established according to the formula: , _Λ,. . . ,, element of the band

rolling.

In FIGS. 8a to 8d, are represented:

in abscissa X, the value Rmu = μl / μ2 of the ratio of the adhesion μl of a measuring element 3 on the adhesion μ2 of a component 4 of the tread;

on the ordinate Y, the value of the logarithm base 10 of the abradability ratio AbI of a measuring element 3 on the abradability Ab2 of an element 4 of the tread.

These FIGS. 8a to 8d show experimentally an area 21 for which a measuring element 3 remains functional while varying, in this case, the ratio of the respective orthotropies of the two elements 3 and 4.

In FIGS. 8a, 8b, 8c and 8d, these orthotropic ratios correspond respectively to the values 0.2, 0.5, 2 and 5.

It can be seen that the two zones 21 and 22 respectively corresponding to a functional measuring element 3 and to a non-functional measuring element 3 are on either side of a boundary 23 delimited according to a Y-type curve. = - (1.4-BX) ² + C with B = h (Rol / Ro2) and C = k (Rol / Ro2), with always in the case, ratios of orthotropy and rigidity equal to let values of constants B and C such that: B = 1.2 and C = 0.25.

It can be seen that the extent of the domain of the zone 21 corresponding to the inequality:

logio Ab ₂ -o- ⁴ - * - μ ₂ r + c

and corresponding to a functional measuring element of the tire, extends proportionally as the orthotropy RoI of the measuring element 3 becomes more important relative to that Ro2 of a member 4 of the tread. It is observed in particular in Figures 8c and 8d for which the orthotropic ratios are respectively 2 and 5.

Thus, the design and manufacture of the tire 1 with an orthotropy of a measuring element 3 greater than that of an element 4 of the tread makes it possible to extend the range of adjustment between the adhesion and the abradability of these same elements for which the element or elements of measurements 3 remain functional.

It should be noted that in the inequation Y> - (1.4-BX) ² + C, the coefficients B and C also depend on the value of the orthotropy of the measuring element 3 and that of the element 4 of the tread knowing that the measurements are made for a rigidity ratio equal to 1.

In addition, the evolution of the quantities B and C as a function of RoI and Ro2 orthotropies and therefore the extension of the area 21 of the functional area of a measuring element 3 will be more or less important depending on the tire used in know: its dimensions, its pressure of use, its characteristics of use (classic, snow, any ground ...) ...

In FIG. 9 is shown:

on the abscissa, the value of the logarithm base 10 of the ratio Rorth = Rol / Ro2 of the orthotropies,

- on the ordinate, the values of the constants B and C.

Experimentally and shown in this figure 9, two empirical equations for the quantities B and C are established for the curve 23 and the straight line 24, such that:

B = -0.6i (bg _u ^ L) - 0.4 log ₁₀ ^ - + 1.13 and C = -1.8 log ₁₀ ^ - + 0.05 \ Ro2J Ro2 Ro2

Thus during an industrial application, depending on the type of material used for the casing of a tire and more particularly for its tread 2 imposing in particular its adhesion and its resistance to wear, it will be possible to then define, in proportion and thanks to the respect of the inequality of the invention, the material to constitute the measuring elements 3.

The properties of the materials namely, their adhesion, their resistance to wear, their rigidity or their orthotropy must therefore comply with the equations previously studied. For this purpose it will be possible to choose the proportions of quantities to be given to the basic elements involving this or that property before the mixing of these different components.

By way of example, by choosing an orthotropy ratio equal to one (Rol / Ro2 = 1), it is possible to obtain highly variable stiffness ratios (E1 / E2) for loaves or elements of the same geometrical shape. , isotropic, by modifying the composition of the rubbery materials, in particular by varying the levels of carbon black and vulcanizing agents used.

It is possible to obtain variable orthotropic ratios while keeping a stiffness ratio equal to 1 (E1 / E2 = 1) for loaves of the same geometrical shape, while taking as tread material an isotropic rubbery material and for the material of the measuring element a rubbery material reinforced with short reinforcing fibers with a matrix similar to that of the material of the tread. The presence of the short reinforcing fibers has little influence on the extension Young's modulus selected as a rigidity characteristic, but it has a great influence on the shear stiffness of the measuring bread (Exz and Eyz such as defined in [0033]), and thus on the value of the RoI orthotropy of the measuring element in the two directions x and y. This variation of RoI is particularly strong if the short fibers are arranged at 45 ° in the longitudinal direction relative to the normal to the tread: the bread or measuring element becomes proportionally more rigid in shear than it is in compression. By varying the concentration, the orientation and / or the size of the fibers in the rubbery material (which the skilled person knows how to achieve), various values of RoI are obtained. The determination of the adhesion and abradability characteristics is carried out according to known methods. With regard to the characterization of adhesion, there is a standardized device: the SRT ("Skid Resistance Tester"); the method of the test piece also makes it possible to crush a block of rubber at a pressure σz close to that experienced by a tread element (between 3 and 5 bars for example) and by sliding it on a given floor to a surface given speed (chosen, for example, between 1 and 300 cm / s) over a fixed sliding length Ig, for example 2 m, of

calculate the adhesion of the tire according to the formula μ = Vx ² + Y ² with X and Y

representing the tangential reaction forces on the element and Z representing the normal force, which depends on the size of the specimen crushed under 3 to 5 bars. The maximum adhesion is then calculated in order to know the high limit tolerated for an element of the tread.

For the characterization of the abradability the principle of the test-piece also works, on the other hand one determines, in this case, the loss of mass, the loss of height, the loss of volume or any other magnitude representative of a associated U wear on the total mass of the gum test piece. The Archard law known in tribology is U = Ab-Oz ⁰ Ug * ³ with here α = 1.5 and β = 1 allows to deduce Ab.

Ultimately, the approach involves the creation of the characteristics of the tread material of the tire thus imposing a value of one or more parameters and thus imposing the manufacturing conditions corresponding to the tread material.

Then one or more ratios are chosen in their corresponding ranges involving new proportions for the components and the manufacture of the material of the measuring elements.

Therefore, the relative wear of a material relative to the other is controlled and stabilized and the measuring elements as well as the tread elements fill, throughout the service life of the tire. , their respective functions. The invention is not limited to the examples described and shown and various modifications can be made without departing from the scope defined by the appended claims.

Claims

A tire (1) whose tread (2) comprises a first element (3) having a ground contacting surface positioned at a distance from the axis of rotation of the tire Rs and at least a second element (4). ) having a ground contacting surface positioned at a distance from the axis of rotation of the tire Ra, characterized in that, considering Abi, Ab ₂ , μi, μ ₂ , E ₁ , E ₂ and King, Ro ₂ , characteristic parameters respectively of the abradability, the adhesion, the rigidity and the orthotropy of the materials constituting the first and the second element, these parameters respect the following relation:

2. A tire according to claim 1, wherein, when the ratio Ro i on Ro ₂ is equal to 1, the values B and C are functions of the rigidities E ₁ and E ₂ respectively of the first and the second element and are equal to:

E E

B = f and C = g

3. The tire according to claim 2, wherein, the stiffness being the Young Ey modulus secant in extension measured at an extension strain of 10%, we have:

B = 0.07 log ₁₀ ^ - + 1.2 and

C = -1.1411Og ₁₀ - ^ + 0.25 E ₂

4. A tire according to claim 1, wherein, when the ratio Ei on E ₂ is equal to 1, the values B and C are functions of the orthotropies Ro i and Ro ₂ respectively of the first and second elements and are worth: B = h Ro

'Ro and C = k Ro,

'Ro ₇

The tire according to claim 4, wherein the orthotropy Ro is represented by the formula:

E _xz which represents the shear stiffness of an element along an axis X, this axis X being the rolling axis of the tire, the axis Y being the axis of rotation of a wheel which carries the tire and the Z axis being perpendicular to the two preceding, as a function of a stress oriented along the axis X co linear to the rolling direction, - E _yz which represents the shear stiffness of the same element along the Y axis as a function of a constraint oriented along the Y axis, and

- E _zz which represents the compression stiffness of the same element along the Z axis, as a function of a stress oriented along this same axis Z; we have :.

B = -0.69 1Og ₁₀ + 1.13 and

C = -l, 81og ₁₀ - + 0.05 Ro _n

6. Pneumatic tire according to one of claims 4 and 5 wherein the orthotropy King of the first element is greater than the orthotropy Ro ₂ of the second element.

7. A tire according to one of claims 1 to 6, wherein the first member (3) is located on a central portion (6) of a tread (2), located between shoulders (7) of the tire.

8. A tire according to one of claims 1 to 7, wherein the distance Rs is smaller than the distance Ra.

9. A tire according to claim 8, wherein, the second elements being carving rolls having a given initial height, the difference between Ra and Rs is between 5 and 20% of said initial height of the second elements.

10. Tire according to one of claims 1 to 9, such that, the tread of said tire having a given contact area in rolling, said tire comprises sensor means inside the first element, the sensor means. being sensitive at least a tangential force in said contact surface of said first element during its passage in the contact area.