EP2512832A1

EP2512832A1 - Unambiguous detection of the wear threshold of a tyre

Info

Publication number: EP2512832A1
Application number: EP10809021A
Authority: EP
Inventors: Antoine Paturle
Original assignee: Michelin Recherche et Technique SA Switzerland; Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Current assignee: Michelin Recherche et Technique SA Switzerland; Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2009-12-18
Filing date: 2010-12-15
Publication date: 2012-10-24
Also published as: CN102741066A; JP2013514226A; JP5677458B2; WO2011077029A1; FR2954224A1; BR112012014995A2; FR2954224B1; US20120266650A1

Abstract

The invention relates to a method for detecting the wear of a tyre including a tread and having at least two predetermined radial wear thresholds S_i, during which: beyond each threshold S_i, the tread is shaped such as to include NE_i sets of audible cavities associated with the threshold S_i; and for each threshold S_i, k_min is the minimum value of the values of k_i, with: K_i=NE_i/NE_i-1 when for the value of i є [2, M], NE_i/NE_i-1 >1, or K_i=NE_i-1/NE_i when for the value of i є [2, M], NE_i-1/NE_i >1 for each threshold, a noise footprint emitted by the audible cavity or cavities associated with each threshold is detected at a speed V, and the value of the speed V is limited for detecting the noise footprint at an interval l=]V_min; V_max] verifying V_max ≤ k_min.V_min.

Description

UNIVERSAL DETECTION OF WEAR THRESHOLD OF A TIRE

The present invention relates to a method for detecting the wear of a tire. It applies in particular, to be restricted to tires for vehicles of any type, tourism or trucks.

As a tire rolls on a ground, its tread that is in contact with the ground wears by friction. To facilitate the control of the wear and to detect a too pronounced wear, the tires are provided with indicators of wear, in particular sound, allowing the user to detect several levels of wear.

For each threshold, the indicators of sound wear generate an acoustic or acoustic fingerprint noise with characteristics, including frequency, remarkable. These frequency characteristics are a function of parameters comprising, inter alia, the number of wear indicators, their implantation geometry, the speed of rotation of the tire or the dimensions of the tire. Thus, for some values of these parameters, the characteristics of the characteristic noise of the witnesses associated with several thresholds are identical, so that it is impossible to determine which threshold of wear is reached.

The object of the invention is to provide a method for unequivocally identifying the wear threshold reached.

For this purpose, the subject of the invention is a method for detecting wear of a tire comprising a tread and having at least two predetermined radial wear thresholds, characterized in that:

beyond each threshold S ,, the tread is shaped so that it comprises NE, set (s) of at least one cavity called "sound" associated with the threshold S ,; each cavity of each assembly being substantially axially aligned with each other cavity of the assembly; and for each threshold S ,, k _min is the minimum value of the values of k, for i 6 [2, M] where M is the total number of predetermined radial wear thresholds with:

ki = NE _i / NE _i-1 when for the value of i 6 [2, M], Ν Ε / Ν ΕΜ> 1, or - ki = NE _i-1 / NE _i when for the value of i 6 [2 , M], NE _M / NEi> 1 for each threshold, an acoustic fingerprint noise emitted by the sound cavity or cavities associated with this threshold is detected at a speed V, and the value of the speed V for the detection is limited. acoustic impression noise at an interval l =] V _min ; V _max ] checking V _max <k _min .V _min . The method according to the invention makes it possible to alert a user of the tire and to identify the wear threshold reached regardless of the values of the parameters stated above.

In the present application, the acoustic fingerprint noise of each set is the sound signature of each set. This noise can also be considered as the acoustic footprint of each set.

Indeed, the noise emitted by the sound cavities associated with each threshold is characteristic of this threshold, in particular because of the number of cavities associated with each threshold and the distribution of these cavities. In such a method, it is implicit that the number of set (s) of sound cavity (s) associated with each threshold is different from the number of set (s) of cavity (s) sound ( s) associated with each other threshold. In the interval I, the characteristics, in particular frequency, of the noise of two different thresholds can not be identical. Thus, a single wear threshold is associated with each value of the characteristics, especially frequency, noise. For example, once determined V _min and knowing k _min , it is possible to determine V _max and therefore I for a unique detection. Conversely, once V _max determined and knowing k _min , it is possible to determine V _min and therefore I for unambiguous detection. For any value of V included in the interval I, it is therefore possible to identify the wear threshold reached unequivocally. Thus, it is possible, by means of the processing unit to distinguish the achievement of each wear threshold.

The cavities associated with the different thresholds have a particular shape that gives them sound properties, that is to say that these cavities cause a characteristic noise during the rolling of the worn tire.

For each cavity associated with each threshold, this characteristic noise appears only when the tire is worn beyond the corresponding threshold. Each cavity associated with a threshold thus forms a sound wear indicator beyond said threshold.

Thus, even if the driver does not visually and regularly inspect the surface condition of his tires, he will be informed of the crossing of each threshold when, while driving, he will hear a characteristic hiss.

Preferably, a processing unit is used and one or more microphones for detecting rolling sounds, connected to the processing unit able to detect the hissing noise of the rolling noise and to inform the driver of the wear of his tires. .

By speed, it will be understood that this is the linear speed of rotation of the tire which is substantially equal to the speed of the vehicle shod with the tire.

Advantageously, the acoustic impression noise comprises several elementary frequency components of acoustic fingerprint, preferably forming at least a portion of a Dirac comb. The elementary frequency components of the acoustic fingerprint noise are characteristic of the noise emitted by the cavities. Thus, when each wear threshold of the tire is reached, the noise acoustic noise emitted by the witnesses comprises several elementary frequency components distributed in frequency. In addition, such acoustic impression noise has a comb pattern of elementary frequency components remarkable, unique and therefore easy to detect.

According to other optional features of the method:

Each elementary frequency component of the acoustic fingerprint noise is at least one adjacent elementary frequency component of the acoustic fingerprint noise of a frequency difference included in a reference frequency interval associated with a single threshold. For each threshold, the reference frequency interval is characteristic of this threshold. Thus, when a wear threshold is reached, the acoustic impression noise emitted by the cavities associated with this threshold comprises several elementary frequency components distributed in frequency according to the predetermined pattern. The predetermined reference frequency interval corresponds to the set of frequency differences that can separate the elementary frequency components of the noise associated with each wear threshold. Thus, this frequency reference interval covers all the frequency differences that can separate two elementary frequency components of the noise associated with each different wear thresholds. In the interval I, the frequency difference separating two elementary frequency components of the noise is therefore associated with a single wear threshold.

The predetermined reference frequency interval is between 1 and 300 Hz. This frequency interval comprises the frequency difference that can separate the elementary frequency components of the noise emitted by the cavities. The reference frequency interval is determined by taking into account the extreme values of the parameters that one does not wish to have to enter or modify, for example the dimensions of the tire. Thus, for a passenger vehicle, for a speed varying between 10 and 130 km / h, a number of witnesses varying between 1 and 20 and a circumference varying between 1, 30 m and 3.0 m, the frequency difference of the elementary frequency components of the noise emitted by the cavities belongs to the interval between 1 Hz and approximately 300 Hz. We find a similar frequency range for heavy-duty vehicles operating at speeds of less than 90 km / h, equipped with tires with a maximum of 32 witnesses and a circumference of between 2.1 and 3.7 m.

In one embodiment, each set consists of a single sound cavity.

In another embodiment, each set comprises at least two cavities substantially axially aligned with each other.

In this embodiment, a cavity of a set associated with a threshold has substantially the same azimuth as that of another cavity of the set associated with the same threshold. Thus, these cavities are simultaneously sound.

In another embodiment, two axially aligned cavities are associated with two different thresholds. In this case, the two cavities are not part of the same set.

Optionally, the sets of sound cavity (s) associated with each threshold are arranged so that, beyond each threshold, the sets of sound cavity (s) associated with each threshold are equi-distributed circumferentially on the tire.

By "circumferentially equi-distributed" is meant that each set of cavity (s) associated with a given threshold is located substantially at the same spatial distance from the two sets of cavity (s) adjacent thereto. In the case where a single set is associated with a given threshold, this unique set is equally distributed circumferentially. Indeed, in this case, the adjacent sets are formed by this same set.

In addition, in all cases, as the cavity assemblies are circumferentially equispaced around the tread of the tire regardless of the threshold reached, the characteristics of the noise emitted beyond each threshold are unique and remarkable. Thus, the noise emitted by the tire is easily detectable among the rolling noise of the tire, the wind, the engine noise or the noise of the kinematic chain associated therewith. Indeed, the noise emitted beyond each threshold has, in the frequency domain, the shape of a Dirac comb. a feature that can be easily identified from all the noises mentioned above.

The cavities may be offset axially relative to each other while being equi-distributed circumferentially around the tread.

Optionally, beyond each threshold, each sound cavity emerges radially outwardly of the tire, and is shaped so as to be closed by the ground in a substantially watertight manner as it passes through the area of contact of the tire. with the ground.

Indeed, because each cavity is shaped so as to be closed by the ground substantially sealed, it temporarily traps air during its passage in the contact area of the tire with the ground. However, under the effect of the deformation of the tire in the contact area, the air trapped in the cavity compresses and then suddenly relaxes at the exit of the contact area when the tread leaves the contact with the ground at the rear of the tire and that consequently the cavity opens.

This expansion of the air lasts about a few milliseconds and causes a specific noise, sometimes called hissing or pumping noise, a function in particular of the shape and volume of the cavity.

Since this phenomenon of hissing occurs only when air is compressed in the cavity and then expanded by escaping from the cavity, it is important that this cavity is sealed substantially by the ground during its passage in the contact area. Indeed, a cavity whose top would be covered by the ground but which, moreover, would include transverse channels in fluid communication with the outside air, would not form a sound cavity because the air that it contains could not be compressed. This is particularly the case with regard to tread patterns of tires of the state of the art which are generally formed by a network of channels communicating the different cavities with each other and with the outside air.

Similarly, a cavity whose dimensions are too large to be completely covered by the ground during its passage in the contact area, for example a cavity whose length is greater than the length of the contact area, does not could not form a sound cavity within the meaning of the invention.

In one embodiment, k _min = 2.

According to optional features of the invention the interval I is chosen among the following speeds in km / h:] 50; 100],] 60; 120] and] 65; 130]. Optionally, the tire comprises:

at least one circumferential groove, of predetermined depth when the tire is new, and

at least two ribs formed transversely to the bottom of the groove, of predetermined height when the tire is new, substantially equal to the difference between the predetermined depth of the groove and one of the predetermined wear thresholds,

wherein the distance separating the two ribs is less than a predetermined distance so that, beyond one of the thresholds or each predetermined radial wear threshold, the cavity formed by the groove and delimited by the two ribs is sound.

By placing the cavities in the grooves, the noise emitted by the cavities is amplified compared to sound wear indicators which would be disposed elsewhere in the tread. The noise emitted is also amplified by a flag formed by the tire and the ground once each cavity having passed the contact area. This amplification effect flag is maximum when each sound cavity is preferably arranged axially in a central portion of the contact area of the tire.

Central part of the contact area means the area of the contact area extending axially over substantially half the width of this contact area under the nominal load and pressure conditions and centered relative to the median plane. central of the tire.

In a so-called "descending" sound pattern embodiment, > 1 for any value of i C [2, M].

In other words, the number NE of sets of sound cavities increases with tire wear.

In this embodiment, by increasing the number of sets and therefore the number of cavities, the total volume of the cavities may increase at each threshold. It is found that the detection of the noise emitted by the cavities is then easier as and when the wear of the tire.

In a variant of this embodiment, each cavity associated with a given threshold is also associated with the threshold greater than the given threshold. This makes it possible to minimize the number of cavities appearing at each threshold. Thus, we minimize the effect cavities on the performance of the tire, in particular the hydro-dynamic performances. Thus, each cavity associated with a given threshold is also associated with all the thresholds greater than the given threshold. This characteristic obviously does not apply to the cavities of the highest threshold.

In another variant of this embodiment, the sound cavity or cavities associated with a given threshold do not include any sound cavity associated with the threshold below the given threshold. Thus, when the given threshold is reached, the cavity or cavities associated with the threshold below the given threshold cease to be audible. In other words, each set of cavities is strictly associated with a single wear threshold.

In another variant, the sound cavity or cavities associated with a given threshold comprise a portion of the sound cavities associated with the threshold below the given threshold and sound cavities that have appeared beyond the given threshold. Thus, only a few sound cavities associated with the lower threshold are also sound cavities associated with the given threshold.

In another embodiment said sound pattern "amount",

for any value of i 6 [2, M].

In other words, the number NE of sets of sound cavities decreases with tire wear.

The sound cavities, when arranged in the grooves, can degrade the performance of the tire with respect to a tire without such sound cavities, especially in terms of evacuation of water through the grooves. This degradation of the water evacuation performance is even greater than the wear of the tire is advanced. Thus, by reducing the number of sets of sound cavities and therefore the number of sound cavities with the advance of the wear of the tire, it limits the potential loss of performance generated by the sound cavities. In return, it is preferable to provide a sufficient number of cavities so that the total volume of the cavities is sufficiently large, especially so that it is greater than the predetermined minimum volume.

In a variant of this embodiment, the sound cavity or cavities associated with a given threshold are no longer sound or disappear beyond the threshold greater than the given threshold. The sound cavities associated with the threshold greater than the given threshold are therefore only cavities appearing beyond the threshold greater than the given threshold. In other words, each cavity is strictly associated with a single wear threshold. In another variant of this embodiment, the sound cavity or cavities associated with a given threshold comprise a portion of the sound cavity or cavities associated with a threshold below the given threshold.

The invention also relates to a computer program, characterized in that it comprises code instructions for controlling the execution of the steps of the method as defined above when it is executed on a computer.

The invention further relates to a data recording medium comprising, in registered form, a program as defined above.

Another object of the invention is to provide a program as defined above over a telecommunication network with a view to downloading it.

The invention will be better understood on reading the description which will follow, given solely by way of nonlimiting example and with reference to the drawings in which:

Figure 1 is a diagram of the tread of a new tire with "descending" sound pattern according to a first embodiment;

Figures 2 and 3 are diagrams of the tread of the tire shown in Figure 1, worn beyond first and second wear thresholds respectively;

Figure 4 is a diagram in a radial section of the tread of the tire shown in Figure 3;

FIG. 5 illustrates a frequency spectrum of the acoustic cavity noise of the cavities of the tire of FIG. 3;

Figures 6A and 6B schematically illustrate the distribution of sound cavity assemblies of the tire of Figures 1 to 3;

Figures 7 and 8 show frequency bands of the noise emitted by the different cavities associated with the different thresholds of the tire of Figures 1 to 3 and 6A and 6B;

FIGS. 9A to 9F schematically illustrate the distribution of sets of sound cavities of a "descending" sound pattern tire according to a second embodiment;

Figures 10 and 11 show frequency bands of the noise emitted by the different cavities associated with the different thresholds of the tire of Figures 9A to 9F;

Figures 12A and 12B schematically illustrate the distribution of sets of sound cavities of a tire with sound patterns "amount" according to a third embodiment;

Figures 13 and 14 show frequency bands of the noise emitted by the different cavities associated with the different thresholds of the tire of Figures 12A and 12B.

FIG. 1 shows a portion of a tire according to a first embodiment of the invention, designated by the general reference 10. The tire 10 is intended for a passenger vehicle. The tire 10 is substantially of revolution about an axis.

The tire 10 comprises a tread 12 of substantially cylindrical shape, the outer surface of which is provided with sculptures 14. In particular, the tread 12 comprises two circumferential and parallel grooves 16, hollowed on the surface of the tire, of depth H predetermined when the tire 10 is new. The depth H of these grooves 16 is of the order of 8 mm and their width is of the order of 10 mm.

The tire 10 includes visual wear indicators (not shown) indicating a threshold SL of legal wear of the tire. The depth of each groove corresponding to the threshold SL is set at 1.6 mm, which corresponds to a threshold SL = 6.4 mm.

Transversally to the grooves 16, the tread 12 of the tire comprises a set of ribs 18 formed at the bottom of the grooves 16. The set of ribs comprises two types of ribs 18A, 18B each corresponding to at least one threshold Si, S ₂ d predetermined wear of the tire. Each rib 18A, 18B has respectively a first and second height h-ι, h ₂ predetermined when the tire is new. hi> h ₂ and S _2> If so that each type of rib 18A is associated with the thresholds Si and S ₂ and 18B each type of rib is associated with the single threshold S _2. The first threshold Si corresponds substantially to 90% of the threshold SL, that is to say that mm. The second threshold S ₂ corresponds substantially to 100% of the threshold SL, that is to say that h ₂ = 1, 6 mm and S ₂ = 6.4 mm. The thresholds Si, S ₂ are shown schematically in FIGS. 6A-6B. FIG. 6A represents the tire 10 having reached the first wear threshold Si but having not yet reached the second wear threshold S ₂ . FIG. 6B shows the tire 10 having reached the second wear threshold S ₂ .

Thus, in this embodiment, the first threshold Si corresponds to wear beyond which the tire has performance that can be degraded on a wet coating. The second threshold S ₂ corresponds to a wear beyond which the tire no longer complies with the legal requirements.

The distance separating two ribs of the same type is of the order of 20 to 30 millimeters. The volume defined by a groove 16 and two neighboring ribs 18A, 18B respectively form a cell 19A, 19B arranged in each circumferential groove 16. Each cell 19A, 19B of each pair of cells 19A, 19B is connected to the other cell of the pair by a channel 21 A, 21 B transversal. Each pair of cells 19A and the channel 21A form an assembly consisting of a cavity 20A opening radially outwardly of the tire 10. Similarly, each pair of cells 19B and the channel 21B form an assembly consisting of a cavity 20B opening radially outwardly of the tire 10. In Figures 6A-6B, the cavities 20A, 20B are shown schematically in lines. These lines extend radially over a radial portion schematically between which thresholds the corresponding cavities are sound.

When the tire is new, as shown in FIG. 1, the height of the ribs 18A, 18B is smaller than the depth of the grooves 16 so that each cavity 20A, 20B comprises a fluidic communication passage situated above ribs 18A, 18B, that is to say at the top of the ribs 18A, 18B. Thus, even when the tread is in contact with a flat and smooth ground 11, the ground 11 does not completely close the cavities 20A, 20B because the top of the ribs is not in contact with the ground 11. In this case, case, the different cavities 20A, 20B are in fluid communication by a throttling channel delimited by the top of the ribs and the soil 11 covering the cavities.

FIG. 2 shows the tire 10 of FIG. 1 worn beyond the threshold Si. In other words, it is a tire which has traveled many kilometers and whose tread 12 has been gradually worn until losing a few millimeters. This tire 10 is also shown diagrammatically in FIG. 6A where it can be seen that, beyond the threshold S 1, the tire 10 comprises assemblies each consisting of a cavity 20A. So we have

During the rotation of the tire, the cavities 20A are, from the point of view of the rolling tire, equi-distributed circumferentially on the tread 12 so that each cavity 20A periodically comes into contact with the ground when the tire is traveling at a speed substantially constant. In this case, the wear of the tread 12 of the tire 10 shown in Figure 2 is 6 mm, that is to say greater than the threshold Si, ie greater than the distance between, when the tire 10 is new, the top of the ribs 18A of the surface of the tread 12. In view of the wear greater than Si, the top of the ribs 18A is at the same level as the surface of the tread 12. Thus, the mouth of each cavity 20A is defined by a substantially plane contour formed on the tread 12 and the cavities 20A are distinct and separated from the other cavities.

The wear of the tire is less than the threshold S ₂ , ie less than the distance separating, when the tire 10 is new, the top of the ribs 18B of the surface of the tread 12. The top of the ribs 18B is at a minimum lower level than that of the tread at this stage of wear.

Beyond the threshold Si, each cavity 20A has a depth less than the height h-ι. Here, the depth is less than 2.5 mm and is 2 mm for a wear of 6 mm. The height of each rib 18A is then equal to the depth of each cavity 18A. This height or depth is equal to the difference between the depth of each groove 16 and the wear of the tire 10.

Because the mouth of each cavity 20A is defined by a substantially plane contour, it is able to be closed perfectly and hermetically by a smooth and flat floor during rolling. In other words, when the tire 10 is worn beyond the threshold Si, each cavity 20A is shaped so as to be closed by the ground in a substantially watertight manner as it passes through the contact area of the tire 10 with floor. Between the thresholds S ₁ and S ₂ , each cavity 20B is not closed by the ground in a sealed manner because of the throat channel delimited by the top of each rib 18B and the ground 11.

FIG. 3 shows the tire 10 of FIGS. 1 and 2 used beyond the threshold S ₂ . This tire 10 is also shown diagrammatically in FIG. 6B where it can be seen that, beyond the threshold S ₂ , the tire 10 comprises NE ₂ = 10 assemblies each consisting of a cavity 20B. We therefore have NE ₂ = N ₂ = 10.

In this case, the wear of the tread 12 of the tire 10 shown in FIG. 3 is 7 mm, that is to say greater than the threshold S ₂ , but also the threshold Si, ie greater than the distance separating, when the tire 10 is new, the top of the ribs 18B of the surface of the tread 12. Given the wear greater than S ₂ , the top of the ribs 18B, but also that of the ribs 18A, is at the same level as the surface of the tread 12. Thus, the mouth of each cavity 20B is defined by a substantially planar contour formed on the tread 12 and the cavities 20B are distinct and separated from other cavities. The mouth of each cavity 20A remains unchanged with respect to the mouth obtained beyond the threshold Si and before the threshold S ₂ .

Beyond the threshold S ₂ , each cavity 20B has a depth less than the height h ₂ . Here, the depth is less than 1, 6 mm and is 1 mm for a wear of 7 mm. The height of each rib 18A, 18B is then equal to the depth of each cavity 18A, 18B. This height or depth is equal to the difference between the depth of each groove 16 and the wear of the tire 10.

Because the mouth of each cavity 20A, 20B is defined by a substantially planar contour, it is able to be closed perfectly and hermetically by a smooth and flat floor during rolling. In other words, when the tire 10 is worn beyond the threshold S ₂ , each cavity 20A, 20B is shaped so as to be closed by the ground in a substantially watertight manner when it passes through the contact area of the body. pneumatic 10 with the ground.

Each cavity 20A, 20B has, beyond the corresponding threshold Si, S _2, a length of the order of 20 to 30 millimeters corresponding to the circumferential gap between two adjacent ribs 18A, 18B of the same cavity.

Such cavities 20A, 20B formed on the surface of the tread 10 of a tire which, on the one hand, open radially towards the outside of the tire and, on the other hand, are shaped to be hermetically closed during their passage in the contact area, are called "sound". In this embodiment, each cavity 20A is sound beyond each threshold Si, S ₂ while each cavity 20B is sound only beyond the threshold S ₂ . In the example illustrated, the numbers NE ,, ΝΕ -ι of set of cavities respectively associated with two consecutive thresholds S ,, SM satisfy NEj.i <NEj for i 6 [2, M] where M is the total number of predetermined radial wear thresholds and the threshold S, being greater than the threshold SM- So for each value of i 6 [2, M], we have ki = NE _i / NE _i-1 because Ν Ε, / Ν ΕΜ> 1 - A tire in which NE ₂ > NEi, tire with "descending" sound pattern is thus qualified. In this embodiment, = 2.

The cavities 20A, 20B are arranged so that, beyond each threshold Si, S ₂ , the sets of sound cavities 20A, 20B are evenly distributed. circumferentially on the tire 10. As each set consists of a single cavity, the sound cavities 20A, 20B are equi-distributed circumferentially on the tire 10. In addition, the tread is shaped so that, beyond of each threshold Si, S ₂ , all the sound cavities 20A, 20B are identical as shown in FIGS. 6A-6B.

In addition, each cavity 20A associated with the threshold Si is also associated with the threshold S ₂ . In the tire 10, such sound cavities are non-existent below the threshold Si, especially when the tire is new.

FIG. 4 shows a view in radial section of a tire similar to that of FIGS. 1 to 3 while taxiing on a ground. The dimensions are changed arbitrarily for the sake of clarity. This tire 10 is in a worn state beyond the threshold S ₂ and therefore comprises a set of sound cavities 20A, 20B.

There is shown by an arrow 22 the direction of rotation of the tire 10 during its rolling on the ground. At a given moment, a portion of the tread 12 of the tire 10 is in contact with the ground. This part in contact is called contact area 24. The tread 12 is shaped so that each sound cavity 20A, 20B has, during its passage through the contact area 24 of the tire 10 with the ground 11, a section constant contact according to the wear of the tire 10.

In the example shown in Figure 4, the contact area 24 comprises a sound cavity 26, the radially outer mouth is covered by the ground 1 1. Thus, this sound cavity 26 is hermetically sealed.

The contact area 12 of the tire also comprises a sound cavity 28 located upstream of the closed cavity 26, which is open because its mouth is not in the contact area and is therefore not covered by the ground. When rolling the tire in the direction designated by the arrow 22, the open cavity 28 will progress to the contact area 24 until its mouth is closed by the ground 11.

Finally, the tread 12 of the tire 10 also comprises a cavity 30 situated downstream of the closed cavity 26, with respect to the direction of rotation of the tire 10. In the example shown in FIG. 4, the downstream cavity 30 shown is open because the ground 11 is not in contact with its mouth. At a previous instant, this cavity 30 was closed because located in the area of the contact 24 of the tire with the ground 11.

Thus, during the rolling of the tire, a given sound cavity successively occupies an upstream position 28 in which it is open, then a position 26 located in the contact area 24 in which it is closed because covered by the ground, and finally an open position 30 again in which it is no longer covered by the ground.

In other words, the rotation of the tire causes, for a given cavity, the admission of air inside the cavity, the compression of the air contained in the cavity when it is closed by the ground in the contact area 24, then the expansion of the air contained in the cavity during opening thereof by separating the tread from the ground.

This succession of admission / compression / expansion steps is at the origin of a characteristic noise, sometimes called hissing or pumping noise resulting from the expansion of the compressed air contained in the cavity. The amplitude and the frequency signature of this noise depend in particular on the shape, the volume and the number of sound cavities used. Preferably, the cavities are shaped so that this noise is detectable by a user of the motor vehicle or by an electronic device.

FIG. 5 shows a frequency spectrum SFT of the noise generated by the cavities associated with the second threshold S ₂ visible in FIG. 3. For example, by means of a microphone, a signal of the acoustic fingerprint noise generated is acquired. by the cavities 20B. A Fourier transform is applied to the signal to obtain a raw frequency spectrum. Then, after processing steps of this raw frequency spectrum, in particular filtering, a filtered frequency spectrum is obtained. The frequency spectrum SFT of the noise represented in FIG. 5 comprising several elementary frequency components P1-P8 is thus obtained. The spectrum takes the form of a Dirac comb characterized by the elementary frequency components equidistributed. Each elementary frequency component is distant from the adjacent frequency component of a substantially constant frequency difference F _T us. In this case F _TU s = 120 Hz.

The parameters such as the number of wear indicators, their implantation geometry, the rotational speed of the tire or the dimensions of the tire define an IR reference frequency interval at which the frequency F _T us is likely to belong. For a range of passenger tires, whose circumference can vary between 1, 3 m and 3 m, the number of witnesses can vary between 1 and 10 and whose vehicle speed can vary between 10 km / h and 130 km / h, the frequency F _T us can vary in the IR range between 1 and 278 Hz. For heavy type tires, the IR interval is similar.

FIG. 7 illustrates two frequency bands B1 = [50 Hz; 79 Hz] and

B2 = [101 Hz; 159 Hz] in which is located F _T us for the noise generated by the cavities respectively associated with each threshold Si, S ₂ for the tire 10 of Figures 1 to 3 which has a rolling circumference of 1, 93 m in the state new. As calculated above, k ₁ = NE ₂ / NE ₁ = N ₂ / N ₁ = 2 so that the minimum value k _min of the values of k, for i 6 [2, M] is equal to 2. For each threshold S ₂ , S ₂ , SFT acoustic noise noise emitted by the cavities 20A and 20B is detected. In order to uniquely identify the threshold S, associated with the noise generated by the tire 10, the speed V for the detection of noise is limited to an interval l =] V _min ; V _max ] =] 70 km / h; 110 km / h] checking V _max <k _min .V _min . In this case, the bands B1, B2 are disjoint so that for a value of F _T us determined from the acoustic print noise, it is unequivocally identified by which cavities 20A or 20B the corresponding noise is generated.

FIG. 8 illustrates two bands B1 = [36 Hz; 94 Hz] and B2 = [72 Hz; 187 Hz]. In this case, the velocity interval V in which the noise is detected is l =] V _min ; V _max ] =] 50 km / h; 130 km / h] and do not check V _max <k _min .V _min . The bands B1, B2 have a recovery interval [72 Hz; 94 Hz] so that for values F _T us of this overlap interval, the corresponding noise is generated by the cavities 20A or 20B without it being possible to identify which ones generate the noise.

FIGS. 9A-9F show a tire according to a second embodiment. The tire 10 is intended for a vehicle of the heavy vehicle type. Elements similar to those designated in the preceding figures are designated by identical references.

In contrast to the first embodiment, the tire 10 according to the second embodiment comprises six predetermined radial wear thresholds SrS ₆ with, NE ₂ = N ₂ = 2, NE ₃ = N ₃ = 4, NE ₄ = N ₄ = 8, NE ₅ = N ₅ = 16 and NE ₆ = N ₆ = 32 and therefore the following ratios k: NE ₃ / NE ₂ = N ₃ / N ₂ = NE ₄ / NE ₃ = N ₄ / N ₃ = NE ₅ / NE ₄ = N ₅ / N ₄ = NE ₆ / NE ₅ = N ₆ / N ₅ = 2. As in the first embodiment, the tire 10 has a "downward" sound pattern.

The depth of the grooves 16 is of the order of 14 millimeters, here 14.3 mm. The depth of each groove corresponding to the threshold SL is set at 2 mm, which corresponds to a threshold SL = 12.3 mm.

The rib assembly includes third, fourth, fifth and sixth ribs 18C-18F, in addition to the ribs 18A, 18B. Each rib 18C-18F has respectively a third, fourth, fifth and sixth height h ₃ , h ₄ , h ₅ and h ₆ predetermined when the tire is new. h ₁ > h ₂ > h ₃ > h ₄ > h ₅ > h ₆ and S ₆ > S ₅ > S ₄ > S ₃ > S ₂ > If each type of rib 18A is associated with the thresholds SrS ₆ , each rib 18B is associated with thresholds S ₂ - S ₆ , each rib 18C is associated with the thresholds S ₃ -S ₆ , each rib 18D is associated with the thresholds S ₄ -S ₆ , each rib 18E is associated with the thresholds S ₅ and S ₆ and each rib 18F is associated with the only threshold S ₆ . The first threshold Si corresponds substantially to 19% of the threshold SL, that is to say that mm. The second threshold S ₂ corresponds substantially to 35% of the threshold SL, that is to say that h ₂ = 10 mm and S ₂ = 4.3 mm. The third threshold S ₃ corresponds substantially to 51% of the threshold SL, that is to say that h ₃ = 8 mm and S ₃ = 6.3 mm. The fourth threshold S ₄ corresponds substantially to 67% of the threshold SL, that is to say that h ₄ = 6 mm and S ₄ = 8.3 mm. The fifth threshold S ₅ corresponds substantially to 84% of the threshold SL, that is to say that h ₅ = 4 mm and S ₅ = 10.3 mm. The sixth threshold S ₆ corresponds substantially to 100% of the threshold SL, that is to say that h ₆ = 2 mm and S ₆ = 12.3 mm.

The different thresholds correspond to different stages of the life of the tire during which various actions must be taken to distribute the wear on the entire tread and thus increase the life of the tire. Thus, the threshold S ₂ corresponds to wear for which the tire can be rotated on the same axle. The threshold S ₄ corresponds to a wear for which the tire can be turned over. The threshold S ₅ corresponds to a wear for which we can regroove the tire to restore its performance, including water evacuation.

As in the first mode, the sets of cavities 20A-20F, here the sound cavities 20A-20F, are arranged so that, beyond each threshold Si.S ₆ , the set of sound cavities 20A-20F, here the sound cavities 20A-20F are equi-circumferentially distributed on the tire 10.

In addition, each cavity 20A associated with the threshold Si is also associated with the threshold S ₂ -S ₆ , each cavity 20B is associated with the thresholds S ₂ -S ₆ , each cavity 20C is associated with the thresholds S ₃ -S ₆ , each cavity 20D is associated with thresholds S ₄ -S ₆ , each cavity 20E is associated with the thresholds S ₅ and S ₆ and each cavity 20F is associated with the single threshold S ₆ .

Six frequency bands B1 = [5 Hz; 8 Hz], B2 = [11 Hz; 16 Hz], B3 = [22 Hz; 33 Hz], B4 = [44 Hz; 66 Hz], B5 = [88 Hz; 132 Hz] and B6 = [176 Hz; 264 Hz] in which is located F _T us for the noise generated by the cavities respectively associated with each threshold SrS ₆ for the tire 10 of the second embodiment which has a running circumference of 3.03 m in new condition. As calculated above, so that the minimum value k _min is equal to 2. For each threshold SrS ₆ , the soundproofing noise SFT emitted by the cavities 20A-20F is detected. In order to uniquely identify the threshold S, associated with the noise generated by the tire 10, the speed V for the detection of noise is limited to an interval l =] V _min ; V _max ] =] 60 km / h; 90 km / h] checking V _max <k _min .V _min . In this case, the bands B1-B6 are disjoint so that for a value of F _T us determined from the acoustic print noise, it is unequivocally identified by which cavities 20A-20F the corresponding noise is generated.

FIG. 11 shows two bands with six frequency bands B1 = [3 Hz; 8 Hz], B2 = [5 Hz; 16 Hz], B3 = [1 1 Hz; 33 Hz], B4 = [22 Hz; 66 Hz], B5 = [44 Hz; 132 Hz] and B6 = [88 Hz; 264 Hz]. In this case, the velocity interval V in which the noise is detected is l =] V _min ; V _max ] =] 50 km / h; 130 km / h] and do not check V _max <k _min .V _min . The B1-B6 bands have two-by-two overlap intervals [5 Hz; 8 Hz], [11 Hz; 16 Hz], [22 Hz; 33 Hz], [44 Hz; 66 Hz] and [88 Hz; 132 Hz] so that for values F _T us of these overlapping intervals the corresponding noise is generated by cavities without it being possible to identify which ones generate the noise.

FIGS. 12A-12B show a third embodiment of a tire according to the invention comprising two wear thresholds. Elements similar to those designated in the preceding figures are designated by identical references.

Unlike previous embodiments, the number of sets of sound cavities 20A, 20B decreases with the wear of the tire 10. The numbers _NE, ΝΕ, ι .- cavities sets associated with two consecutive thresholds respectively _S, Si-i verify NEj.i> NEJ for 6 i [2, M] where M is the total number of predetermined radial wear thresholds and the threshold S, being greater than the threshold MS. So for every value of i 6 [2, M], we have because NEn / NE,> 1. Such a pneumatic tire is referred to as an "upright" sound tire. In this embodiment, k ₁ = NE ₁ / NE ₂ = N ₁ / N ₂ = 2.

Unlike the first embodiment, each sound cavity 20B associated with the second threshold S ₂ is also associated with the first threshold Si. Only a portion of the sound cavities 20A associated with the first threshold Si is also associated with the second threshold S _2.

FIG. 13 illustrates two frequency bands B1 = [101 Hz; 159 Hz] and B2 = [50 Hz; 79 Hz] in which is located F _T us for the noise generated by the cavities respectively associated with each threshold Si _, S ₂ for the tire 10 of the third embodiment which has a rolling circumference of 1, 93 m in the state new. As calculated above, k ₁ = NE ₁ / NE ₂ = N ₁ / N ₂ = 2 so that the minimum value k _min of the values of k, for i 6 [2, M] is equal to 2. The interval l =] V _min ; V _max ] =] 70 km / h; 1 10 km / h] therefore verifies V _max <k _min .V _min . The bands B1, B2 are disjoint so that for a value of F _T us determined from the acoustic impression noise, it is unambiguously identified by which cavities 20A or 20B the corresponding noise is generated.

FIG. 14 illustrates two bands B1 = [72 Hz; 187 Hz] and B2 = [36 Hz; 94 Hz]. In this case, the velocity interval V in which the noise is detected is l =] V _min ; V _max ] =] 50 km / h; 130 km / h] and do not check V _max <k _min .V _min . The bands B1, B2 have a recovery interval defined by [72 Hz; 94 Hz] so that for values F _T us of this overlap interval, the corresponding noise is generated by the cavities 20A or 20B without it being possible to identify which ones generate the noise.

The invention is not limited to the embodiments described above.

In addition, the tread may comprise more than two grooves and thus sets of cavities comprising more than two cavities substantially axially aligned, that is to say having the same azimuth.

The tread may also include a single groove. Each cavity will be formed by a cell.

The tread may include several grooves and each cavity comprise a single sound cell so that two successive cavities circumferentially are located in two different grooves.

The tread may comprise cavities arranged in each groove, the cavities being substantially axially aligned in pairs without being connected to one another by a channel. Such cavities may be associated with the same wear threshold or two different wear thresholds. In all these cases, the cavities may be variable or constant contact section and indifferently used with tires with sound patterns "up" or "down".

As additional examples of a tire with descending sound pattern, it will be possible to exploit tires with three or four thresholds having the following characteristics:

NEi = 1, NE ₂ = 2, NE ₃ = 4, NE ₄ = 8.

As additional examples of a tire with a rising sound pattern, it will be possible to exploit tires with three or four thresholds having the following characteristics:

NEi = 12, NE ₂ = 6, NE ₃ = 2.

Claims

REVEN DICATIONS

1. A method of detecting wear of a tire (10) comprising a tread (12) and having at least two predetermined radial wear thresholds (SrS ₆ ), characterized in that:

- Beyond each threshold S ,, the tread is shaped so that it comprises NE set (s) of at least one cavity (20A-20F) called "sound" associated with the threshold S ,; each cavity (20A-20F) of each assembly being substantially axially aligned with each other cavity of the assembly; and

for each threshold S ,, k _min is the minimum value of the values of k, for i 6 [2,

M] where M is the total number of predetermined radial wear thresholds with:

ki = NE _i / NE _i-1 when for the value of i 6 [2, M], Ν Ε, / Ν ΕΜ> 1, or ki = NE _i-1 / NE _i when for the value of i 6 [2 , M], NE _M / NEi> 1 for each threshold, an acoustic impression noise emitted by the sound cavity or cavities associated with this threshold is detected at a speed V, and

the value of the speed V for the detection of the acoustic print noise is limited to an interval l =] V _min ; V _max ] checking V _max <k _min .V _min .

2. The method of claim 1, wherein the acoustic fingerprint noise comprises several elementary frequency components acoustic fingerprint, preferably forming at least a portion of a Dirac comb.

3. Method according to the preceding claim, wherein each elementary frequency component of the acoustic fingerprint noise is distant from at least one adjacent elementary frequency component of the acoustic noise of a frequency difference (F _T us) included in a reference frequency interval (I) associated with a single threshold (SrS ₆ ).

4. Method according to the preceding claim, wherein the predetermined reference frequency interval (I) is between 1 and 300 Hz.

The method of any of the preceding claims, wherein each set consists of a single sound cavity (20A-20F).

6. A method according to any one of claims 1 to 4, wherein each set comprises at least two cavities (20A-20F) substantially axially aligned with each other.

The method of any one of the preceding claims, wherein the sets of sound cavity (s) associated with each threshold (SrS ₆ ) are arranged so that, beyond each threshold (SrS ₆ ), the sets of sound cavity (s) associated with each threshold (SrS ₆ ) are equi-distributed circumferentially on the tire (10).

8. Method according to any one of the preceding claims, wherein, beyond each threshold (SrS ₆ ), each sound cavity (20A-20F) opens radially outwardly of the tire (10), and is shaped from in such a way as to be closed by the ground (11) in a substantially watertight manner as it passes through the area of contact (24) of the tire (10) with the ground (11).

The method of any one of the preceding claims, wherein the tire comprises:

at least one circumferential groove (16) of predetermined depth when the tire (10) is new, and

at least two ribs (18A-18F) formed transversely to the bottom of the groove (16), of predetermined height when the tire (10) is new, substantially equal to the difference between the predetermined depth of the groove (16) and one of the thresholds d predetermined wear (SrS ₆ ),

wherein the distance separating the two ribs (18A-18F) is less than a predetermined distance so that, beyond one of the thresholds or each predetermined radial wear threshold, the cavity (20A-20F) formed by the groove (16) and delimited by the two ribs (18A-18F) is sound

10. A method according to any one of the preceding claims, wherein ki = NE _i / NE _i-1 > 1 for any value of i 6 [2, M].

A method according to any one of the preceding claims, wherein each cavity associated with a given threshold is also associated with the threshold greater than the given threshold.

12. A method according to any one of claims 1 to 11, wherein ki = NE _i-1 / NE _i > 1 for any value of i 6 [2, M].

Computer program, characterized in that it comprises code instructions for controlling the execution of the steps of the method according to any one of the preceding claims when executed on a computer.

14. A data recording medium comprising, in recorded form, a program according to the preceding claim.

15. Provision of a program according to claim 13 on a telecommunication network for download.