EP2720885A1

EP2720885A1 - Tire having multilevel sonic wear indicators

Info

Publication number: EP2720885A1
Application number: EP12738493.1A
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: 2011-06-15
Filing date: 2012-06-15
Publication date: 2014-04-23
Also published as: WO2012172260A1; CN103608194A; BR112013028182A2; FR2976522B1; FR2976522A1; US20140124108A1; JP2014516867A

Abstract

The invention relates to a tire (10) including two sets (E₁E₂) of sonic wear indicators (TUS₁-TUS₂) corresponding to two wear thresholds so as to generate noise when each threshold is exceeded. Each indicator (TUS₁-TUS₂) of each set (E₁E₂) is axially aligned with each of the other indicators (TUS₁TUS₂) of the set (E₁E₂). The number of set(s) (E₁E₂) of indicator(s) associated with each threshold is different from the number of set(s) of indicator(s) associated with each of the other thresholds. The sets (E₁E₂) of threshold(s) (TUS₁TUS₂) associated with each threshold are equidistantly circumferentially distributed over the tire (10). Each indicator is made of a rubber projection extending from the bottom of a circumferential groove.

Description

Pneumatic tires with multilevel sound wear indicators

[01] The invention relates to the field of vehicle tires and the detection of their level of wear.

[02] As a tire rolls on a ground, its tread that is in contact with the ground wears by friction. This wear in particular causes a decrease in the depth of tread formed in the tread.

[03] For obvious reasons of safety, it is important to check the tread wear of the tire before it is too great and does not degrade tire performance too much, especially on snowy roads. or wet road.

[04] To facilitate the control of wear and to detect excessive wear, tires are commonly equipped with visual wear indicators allowing the user to differentiate several levels of wear.

[05] An example of commonly used multi-level wear indicators consists of three letters "DWS" (Dry-Wet-Snow for Dry-Snow-Drained) formed in the tread of the tire and whose depth corresponds to the threshold of wear beyond which the tire no longer has a functioning as correct and safe under conditions corresponding to the letter. Thus, when the three letters "DWS" are visible, the depth of the sculptures is sufficient for all conditions of use. When the letter "S" disappears, the remaining letters "DW" indicate that the carvings have sufficient depth for most wet and dry road conditions. Finally, when the letter "W" disappears, the remaining letter "D" indicates that the sculptures have a depth suitable for dry road conditions.

[06] A disadvantage of this type of wear indicator is that it requires the vigilance of the driver of the motor vehicle and a regular visual check of the condition of his tires. However, many drivers fail to perform such checks and change their tires too late, for example when during a technical inspection of the vehicle, a garage checks the state of wear of the tires.

[07] In addition, this type of wear indicator does not warn the driver of the vehicle once one of the wear thresholds reached which does not allow to anticipate the achievement of the upper threshold. Thus, although they are attentive to the tire wear of their vehicles, many drivers ride in traffic conditions with tires having reached one of the wear thresholds. not to ensure correct and safe operation of the tires under the conditions corresponding to this threshold.

[08] The invention aims in particular to provide a tire with a type of wear indicator more effective and safer.

[09] For this purpose, the subject of the invention is a tire comprising:

- at least two wear thresholds,

for each wear threshold, at least one set of at least one sound wear indicator associated with at least this wear threshold so as to generate an acoustic impression noise at least above this threshold, each witness of each set being substantially axially aligned with each other witness in the set;

- the number of set (s) of witness (s) associated with each threshold being different from the number of set (s) of witness (s) associated with each other threshold;

the sets of witness (s) associated with each threshold being equi-distributed circumferentially on the tire; and

each control being constituted by a protrusion of rubber extending radially from the bottom of a circumferential groove of the tire, the projection being arranged so as to come into contact with the ground during its passage through the contact area; tire with the ground beyond the threshold associated with the witness.

[010] Due to the different number of set (s) of witnesses associated with each threshold, the characteristics of the noise emitted by the witnesses beyond each threshold are different. Thus, for a given speed, beyond a given threshold, the noise emitted by the witnesses associated with this given threshold has certain characteristics whereas, beyond another threshold, the noise emitted by the witnesses associated with this other threshold has other characteristics.

[01 1] By "circumferentially equi-distributed sets" is meant that each set of control (s) associated with a given threshold is situated substantially at the same angular distance of the two sets of associated control (s) (s). ) at this threshold and which are adjacent to it. In other words, the equi-distributed sets of control (s) associated with a given threshold present, two by two, the same angular difference. 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.

[012] In addition, since the control assemblies (s) are equi-distributed circumferentially around the tread of the tire regardless of the threshold reached, the noise emitted beyond each threshold have unique and remarkable frequency characteristics. . Indeed, the spectral analysis of the noise emitted Beyond each threshold, a Dirac comb is visible in the frequency domain, which can easily be identified among all the parasitic noises, such as the rolling noise of the tire, the wind, the engine noise or the noise of the chain. kinematics associated with it. For this purpose, a wear detection method described in application PCT / FR2010 / 052584 may be used. Alternatively, other methods may be used.

[013] The witnesses may be axially offset from each other while being equi-distributed circumferentially around the tread.

[014] For each witness associated with each threshold, the acoustic print noise appears only when the tire is worn beyond the corresponding threshold. Each witness associated with a threshold thus forms a sound wear indicator beyond said threshold.

[015] In the present application, the noise noise generated by the witnesses is the sound signature of the witnesses. This noise can also be considered as the acoustic footprint of the witnesses.

[016] 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, the noise of acoustic impression will be detected.

[017] Preferably, a processing unit and one or more microphones for detecting rolling sounds are used, connected to the processing unit able to detect the acoustic impression noise among the rolling noise and to inform the driver. tire wear.

[018] The witnesses may be axially offset from each other while being equi-distributed circumferentially around the tread.

[019] It will be noted that in all the embodiments and the variants associated therewith, the characteristics of the controls associated with each threshold make it possible to ensure the circumferential equi-distribution of the controls beyond each threshold whatever the number of witnesses associated with each threshold and their axial disposition.

[020] Each sound wear indicator consisting of a gum projection is different from a sound cavity comprising two transverse ribs, in particular a sound cavity of this type such that, beyond each threshold, each sound cavity opens radially outwardly of the tire, and is shaped so as to be closed by the ground in a substantially watertight manner during of its passage in the area of contact of the tire with the ground. Such sound cavities are described in the publication FR 2 937 902.

[021] Apart from the above-mentioned gum projections, the tire may optionally comprise sound cavity wear indicators comprising two transverse ribs delimiting the cavity, for example for another wear threshold.

[022] However, in another embodiment, the tire comprises no cavity delimited by two ribs formed transversely to the bottom of a groove, of predetermined height when the tire is new, substantially equal to the difference between the predetermined depth of the tire. groove and one of the predetermined wear thresholds, the distance separating the two ribs being less than a predetermined distance so that, beyond one of the thresholds or each wear threshold, the cavity formed by the groove and the two ribs be sound.

[023] In one embodiment, each set comprises a single control.

[024] In another embodiment, each set comprises at least two controls.

[025] In this embodiment, a control of a set associated with a threshold has substantially the same azimuth as that of another control of the set associated with the same threshold. Thus, these witnesses are simultaneously sound.

[026] In another embodiment, two axially aligned indicators are associated with two different thresholds. In this case, the two witnesses are not part of the same set.

[027] Surprisingly, the inventors at the origin of the invention have discovered that the projections are sufficient to cause a characteristic noise during the rolling of the tire beyond the wear threshold. The inventors advance the hypothesis according to which this noise is generated by at least two distinct physical phenomena having a synergistic effect. On the one hand, once the wear threshold is reached, the noise is generated by the impact of the protrusion on the ground. On the other hand, once the wear threshold is reached, when the tire rolls on the ground, an air plug is likely to form in the groove upstream of the projection because of the significant relative speed between the tire. tire and the air into which the tire enters. Air is thus trapped temporarily in a space between this cap and the projection during the passage of this space in the contact area of the tire with the ground. Under the effect of the deformation of the tire in the contact area, this air trapped in this space compresses and then slackens abruptly at the exit of the contact area when the tread leaves the contact with the ground at the same time. rear of the tire.

[028] Each wear indicator consisting of a single projection and not of two projections forming a cavity closed in air during its passage in the contact area of the tire with the ground, with an equal number of wear indicators, the number of projections disposed in the groove or grooves is divided by two. This limits the potential loss of performance generated by the projections. The adhesion performance of the tire is therefore relatively little impacted.

[029] The projections being arranged in the grooves, the noise emitted through the projections is amplified compared to sound wear indicators that would be arranged elsewhere in the tread. The noise emitted is amplified by a horn formed by the tire and the ground once the sound wear indicator has passed the contact area. This amplification effect flag is maximum when the projections are preferably arranged axially in a central portion of the tread. The central portion of the tread means the region of the tread extending axially, that is to say parallel to the axis of rotation of the tire, over substantially half the width of this tread. rolling under the nominal conditions of load and pressure and centered relative to the central median plane of the tire.

[030] The gum protrusions may extend transversely over only a portion of the width of a circumferential groove. In this case, the evacuation of water contained in a circumferential groove is favored in case of rain.

[031] However, it has been found that the sound effect generated by a gum protrusion is significantly greater when this gum protrusion extends transversely over the entire width of a circumferential groove. When this rubber projection comes into contact with the ground (the tire being worn at least to the level of the corresponding wear threshold), the circumferential groove is then closed by the ground at the level of the gum protrusion, which defines an upstream space and a downstream space of this groove, without communication between them at the level of the gum projection. It can be seen that this advantageously increases the sound effect advantageously.

[032] The circumferential width of a gum protrusion is generally between 2 and 15 mm (millimeters), and preferably between 3 and 10 mm. These values are suitable for the generation of adequate rolling noise. The circumferential position of a protrusion can be considered from the median circumferential position of the protrusion in contact with the ground, from the threshold considered.

[033] Preferably, the projections are arranged so that, irrespective of the wear of the tire, two circumferentially successive protrusions of the same groove and the groove delimit an open space to the air during the passage of the two projections in the contact area of the tire with the ground. [034] Optionally, when the tire is new, each circumferential groove has a predetermined depth and the height of each projection of each control is substantially equal to the difference between the predetermined depth of the groove and the threshold associated with the control.

[035] A protrusion of gum can be full, that is to say without cavity.

[036] Optionally, each projection comprises at least one cavity formed in the projection, the cavity being shaped so, beyond the threshold associated with the control comprising the projection:

- to open radially towards the outside of the tire, and

- Be closed by the ground substantially sealed during its passage in the area of contact of the tire with the ground.

[037] Such a cavity typically does not extend to the bottom of the circumferential groove. Its volume is typically substantially less than 250 mm ³ (cubic millimeters), for example less than 150 mm ³ .

[038] Such a cavity is however sound. The noise it generates, although limited, is added to the noise generated by the projections and gives an amplified noise compared to a projection without a cavity.

[039] In addition, the cavity makes it possible to visually distinguish the first threshold projection from the legal wear indicator.

[040] Finally, such a cavity does not penalize the performance of the tire or complicate its design.

[041] In one embodiment, each projection of each witness associated with a threshold is circumferentially separated from each projection of each witness associated with each other threshold.

[042] In another embodiment, each projection of each control associated with a threshold is contiguous to a projection of a control associated with another threshold, which has the advantage that these two projections do not define between them closed cavity likely to disturb the expected noise detection.

[043] In addition, the number of locations of the first and second threshold projections is reduced. The adhesion performance of the tire is therefore relatively little or not impacted by the wear indicators.

[044] In one embodiment, at least one projection has a variable ground contact section as a function of tire wear.

[045] Thus, it is possible to vary the contact surface of the projection with the ground and thus to vary the volume of the noise produced by the protrusion.

[046] Preferably, the contact section increases with tire wear. [047] In another embodiment, at least one protrusion has a constant contact section with the ground as a function of tire wear.

[048] In a so-called "downward" sound pattern embodiment, the numbers NE ,, NE _{i + 1} of set of controls respectively associated with two consecutive thresholds S ,, S _{i +} i satisfy NEi <NE _{i + 1} , the threshold S _{i +} i being greater than the threshold S, ..

[049] In other words, the number NE, set of witnesses increases with the wear of the tire.

[050] In this embodiment, increasing the number of sets and therefore the number of witnesses, it is found that the detection of the noise emitted by the witnesses is then easier as and when the wear of the tire.

[051] In a variant of this embodiment, for any value of i 6 [1, M] with M the total number of thresholds and k, natural number. This minimizes the number of witnesses appearing at each threshold. Thus, the effect of the witnesses on the performance of the tire, in particular the hydro-dynamic performances, is minimized. Thus, each control associated with a given threshold is also associated with all the thresholds above the given threshold. This characteristic obviously does not apply to witnesses associated only with the highest threshold.

[052] In another variant, the witness or witnesses associated with a given threshold comprise a portion of the witnesses associated with the threshold below the given threshold and witnesses that have appeared beyond the given threshold. Thus, only some witnesses associated with the lower threshold are also witnesses associated with the given threshold. This can especially correspond to the case of contiguous projections:

[053] When a projection corresponding to a determined wear threshold is not contiguous to another projection, it typically also constitutes a wear indicator associated with any higher wear threshold. By cons, in the case where a projection is contiguous to another projection corresponding to a higher wear threshold, when the latter wear threshold is reached the two contiguous projections form a single projection, forming a single wear indicator corresponding to this threshold (and not two juxtaposed witnesses).

[054] Therefore, the number of wear indicators associated with a threshold must be analyzed as a function of the number of distinct projections in contact with the ground from this threshold.

[055] The number of sets of sound wear indicators corresponding to a determined wear threshold is generally between 2 and 30.

[056] It is preferably at most 10 and very preferably 8 to 10 sets for a passenger vehicle. It's usually at most 22 and so preferred from 12 to 20 sets for a heavy duty van.

[057] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example and with reference to the drawings in which:

Figure 1 is a perspective view of a tread of a new pneumatic sound pattern "down" according to a first embodiment;

Figure 2A schematically illustrates a developed tread of the tire of Figure 1;

Figure 2B is a view similar to that of Figure 2A of a variant of the tire of Figure 1;

Figure 3 is a perspective view of the tread of the tire shown in Figure 1, worn beyond a first wear threshold;

Figure 4A is an axial sectional view in a plane passing through a groove of the tread of the tire of Figure 3;

Figure 4B is a view similar to that of Figure 4A of a variant of the tire of Figure 3;

Figure 5 is a perspective view of the tread of the tire shown in Figure 1, worn beyond a second wear threshold;

FIGS. 6A and 6B schematically illustrate the distribution of sets of sound cavities of the tire of FIG. 1;

FIG. 7 schematically illustrates a developed tread of a "descending" sound pattern tire according to a second embodiment;

FIGS. 8A to 8F schematically illustrate the distribution of the sets of sound cavities of the tire of FIG. 7;

Figure 9 is a view similar to that of Figure 1 of a new tire according to a third embodiment of the invention;

Figure 10 is an axial sectional view in a plane passing through a groove of a tread of the tire of Figure 9 worn to a first wear threshold;

Figure 11 is a view similar to that of Figure 1 of a new tire according to a fourth embodiment of the invention;

FIG. 12 is an axial sectional view in a plane passing through a groove of a tread of the tire of FIG. 11 worn to a point first wear threshold.

[058] There is shown in Figure 1 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.

[059] The tire 10 comprises a tread 12 of substantially toroidal shape, whose outer surface is provided with sculptures 14. In particular, the tread 12 comprises two grooves 16 circumferential and parallel, hollowed on the surface of the tire, of predetermined depth H 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. The tire 10 comprises sets E1, E2 audible wear warning lamps TUS. Each TUS control consists of a protrusion 18 of rubber extending radially from the bottom of one of the grooves 16.

[060] The tire 10 comprises two types of TUS lamps, designated TUS1, TUS2 each respectively associated with at least one predetermined radial wear threshold S1, S2 of the tire so as to generate an acoustic impression noise at least beyond one of the thresholds S1, S2. In this case, each witness TUS1 associated with the threshold S1 is also associated with the threshold S2 so as to generate acoustic noise noise beyond the two thresholds S1, S2. Each witness TUS2 is only associated with the threshold S2 so as to generate acoustic noise noise beyond the single threshold S2.

[061] Each witness TUS1, TUS2 consists respectively of a protrusion

18A, 18B also associated with at least one predetermined wear threshold S1, S2 of the tire. Each projection 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 projection 18A is associated with the thresholds Si and S ₂ and each projection 18B is associated with the single threshold S _2.

[062] The tire 10 comprises no cavity delimited by two ribs formed transversely to the bottom of a 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 wear thresholds. predetermined, the distance separating the two ribs being less than a predetermined distance so that, beyond one of the thresholds or each wear threshold, the cavity formed by the groove and the two ribs is sound. [063] The threshold S ₂ is reached after the threshold Si. In other words, the threshold S ₂ is more advanced than the threshold Si. The threshold S ₂ is reached when the wear of the tire is greater than the wear. for which the threshold Si is reached. 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.

[064] 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.

[065] In FIGS. 6A-6B, the TUSi, TUS ₂ controls are schematized by lines. These lines extend radially over a radial portion schematizing between which thresholds the TUSi, TUS ₂ corresponding witnesses are sound.

[066] 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 .

[067] When the tire is new, as shown in FIG. 1, the height of the projections 18A, 18B is smaller than the depth of the grooves 16 so that each TUSi, TUS _{2 control} comprises a space situated above it protrusions 18A, 18B, that is to say at the top of the projections 18A, 18B. Thus, even when the tread is in contact with a flat and smooth ground, the ground does not come into contact with the projections 18A, 18B.

[068] There is shown in Figure 2A a developed diagram of the tread of the tire of Figure 1.

[069] Each E-ι set of TUSi controls comprises two protrusions 18A and each set E ₂ TUS ₂ controls comprises two protrusions 18B. Each projection 18A, 18B respectively of each set Ei, E ₂ is substantially axially aligned with respectively each other projection 18A, 18B respectively of the same set Ei, E ₂ .

[070] Sets EE ₂ respectively witnesses TUSrTUS ₂ respectively associated with each threshold Si, S ₂ , here the projections 18A-18B, are distributed circumferentially on the tire 10. Thus, on the one hand, the sets of projections 18A are equi-distributed circumferentially on the tire 10 and, on the other hand, the set of projections 18B are equi-distributed circumferentially on the tire 10.

[071] Moreover, all the sets of projections 18 are evenly distributed circumferentially on the tire 10. Thus, beyond each threshold Si, S ₂ corresponding, during the rotation of the tire, the projections 18A, 18B enter a constant time interval in contact with the ground when the tire is traveling at a substantially speed constant.

[072] The tire 10 comprises sets E-ι of two witnesses

TUSi and NE ₂ = 10 sets E ₂ of two witnesses TUSi, TUS ₂ . Thus, the number of sets of witnesses associated with each threshold is different from the number of sets of witnesses associated with each other threshold.

[073] There is shown in Figure 2B a developed diagram of a variant of the tread of Figure 2A.

[074] Unlike the tread of FIG. 2A, the tire 10 comprises sets E-ι of a single control TUSi and NE ₂ = 10 sets E ₂ of a single control TUSi, TUS ₂ . In addition, all the TUSi, TUS ₂ indicators are arranged in the same groove 16.

[075] There is shown in Figure 3 the tire 10 of Figure 1 worn beyond the threshold Si. In other words, it is a tire having traveled many kilometers and whose tread 12 was 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 sets of two TUSi indicators.

[076] 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 projections 18A of the surface of the tread 12. Considering the wear greater than Si, the top of the projections 18A is at the same level as the surface of the tread 12 .

[077] The wear of the tire is less than the threshold S ₂ , in other words less than the distance separating, when the tire 10 is new, the top of the projections 18B of the surface of the tread 12. The top of the projections 18B is at a lower level than that of the tread at this stage of wear.

[078] Beyond the threshold Si, each projection 18A 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 projection 18A is then equal to its depth. This height or depth is equal to the difference between the depth of each groove 16 and the wear of the tire 10.

[079] Each projection 18A is arranged to come into contact with the ground as it passes through the contact area of the tire with the ground beyond the threshold Si.

[080] FIG. 4A is an axial sectional view in a plane passing through a groove of the tread of the tire of FIG. 3.

[081] In Figure 4A, there is shown two projections 18A, 18B having a ground contact section SC. The section SC is the section of the projection in a plane perpendicular to the radial direction of the tire 10. In this case, the sections SC of the projections 18A, 18B are equal and constant as a function of the wear of the tire 10, that is to say, whatever the wear of the tire 10.

[082] There is shown in Figure 4B a variant of the projections of Figure 4A.

[083] Unlike the protrusions of FIG. 4A, the projections 18A, 18B have a variable ground contact section SC depending on the wear of the tire 10. In this case, the contact section SC increases with tire wear 10.

[084] There is shown in Figure 5 the tire 10 of Figures 1 and 2 worn beyond the threshold S ₂ . This tire 10 is also shown diagrammatically in FIG. 6B where it can be seen that the tire 10 has NE ₂ = 10 sets of two TUSi, TUS ₂ controls.

[085] In the present case, the wear of the tread 12 of the tire 10 shown in FIG. 5 is 7 mm, that is to say greater than the threshold S ₂ , but also at the threshold Si, otherwise said greater than the distance separating, when the tire 10 is new, the top of the projections 18B of the surface of the tread 12. Taking into account the wear greater than S ₂ , the top of the projections 18B, but also that of the protrusions 18A, is at the same level as the surface of the tread 12.

[086] Beyond the threshold S ₂ , each projection 18B 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 projection 18A, 18B is then equal to its depth. This height or depth is equal to the difference between the depth of each groove 16 and the wear of the tire 10.

[087] Each projection 18A, 18B is arranged to come into contact with the ground during its passage in the contact area of the tire with the ground beyond the threshold S2.

[088] The TUSI witnesses, TUS ₂ are arranged to generate acoustic footprint noises beyond thresholds respectively Si, S ₂ and are referred to as "sound". In the example illustrated, the numbers NE ,, ΝΕμ-ι of set of witnesses respectively associated with two consecutive thresholds S ,, SM satisfy NEj.i <NEj for i 6 [2, M] where M is the total number of 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 > NE ₁ , tire with a "descending" sound pattern is thus described. In this embodiment, k ₁ = NE ₂ / NE ₁ = 2.

[089] There is shown in Figures 7 and 8A-8F, 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.

[090] There is shown in Figure 7 a developed diagram of the tread 12 of the tire 10 according to the second embodiment of the invention.

[091] Each set EE ₆ comprises a single wear indicator TUSi-TUS ₆ consisting of a projection 18A-18F.

[092] Unlike the first embodiment, the tire 10 according to the second embodiment comprises six wear thresholds SrS _6a, NE ₂ = 2, NE ₃ = 4 ₄ = 8 NE, NE ₅ = 16 and NE ₆ = 32 and therefore the following ratios kj: k ₄ = k ₅ = k ₆ = NE ₂ / NE ₁ = NE ₃ / NE ₂ = NE ₄ / NE ₃ = NE ₅ / NE ₄ = NE ₆ / NE ₅ = 2. As in the first embodiment, the tire 10 has a "downward" sound pattern. Thus, the number of sets of witnesses associated with each threshold is different from the number of sets of witnesses associated with each other threshold.

[093] 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.

[094] The tire 10 comprises sets E ₃ , E ₄ , E ₅ , E ₆ of four other types of TUS indicators, designated TUS ₃ , TUS ₄ , TUS ₅ , TUS ₆ each corresponding respectively to a threshold Si, S ₂ , S _3, S ₄ predetermined wear of the tire 10. Each TUS indicator _3, ₄ TUS, TUS _5, TUS ₆ is respectively constituted by a projection 18C-18F.

[095] Each TUSi indicator associated with the threshold S1 is also associated with the thresholds S ₂ -S ₆ so as to generate an acoustic impression noise beyond the thresholds S ₂ -S ₆ , each control TUS ₂ is associated with the thresholds S ₂ -S ₆ so as to generate an acoustic impression noise beyond the thresholds S ₂ -S ₆ , each indicator TUS ₃ is associated with the thresholds S ₃ -S ₆ so as to generate an acoustic impression noise beyond the thresholds S ₃ - S ₆ , each TUS _{4 control} is associated with the thresholds S ₄ -S ₆ so as to generate an acoustic impression noise beyond the thresholds S ₄ -S ₆ , each control TUS ₅ is associated with S ₅ and S ₆ thresholds so as to generate acoustic noise noise beyond the thresholds S ₅ and S ₆ and each TUS ₆ indicator is associated with the only threshold S ₆ so as to generate acoustic noise only above threshold S ₆ .

[096] Each projection 18C-18F has respectively a 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 projection 18A is associated with the thresholds SrS ₆ , each projection 18B is associated with the thresholds S ₂ -S ₆ , each projection of the type 18C is associated with the thresholds S ₃ -S ₆ , each projection 18D is associated with the thresholds S ₄ -S ₆ , each projection 18E is associated with the thresholds S ₅ and S ₆ and each projection 18F is associated with the single 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

[097] The various 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.

[098] As in the first mode, the EE ₆ sets of witnesses

TUSi-TUS ₆ associated respectively with each threshold SrS ₆ , here the projections 18A-18F, are equi-distributed circumferentially on the tire 10. In addition, all sets EE ₆ are equi-distributed.

[099] There is shown in Figures 9 and 10 a tire according to a third embodiment of the invention. Elements similar to those shown in the preceding figures are designated by identical references.

Unlike the tires according to the previous embodiments, each projection 18A of each TUSi control is contiguous to a projection 18B of a TUS _{2 control} .

Referring to Figure 10 which shows the tire according to the third embodiment with a wear corresponding to the threshold Si, the two controls TUSi and TUS ₂ thus form a single wear indicator TUS constituted a gum protrusion 28 arranged at the bottom of the groove 16. The gum protrusion 28 has a general staircase shape and comprises first and second gum portions 30, 32 respectively forming the projections 18A, 18B. Each first and second portion 30, 32 respectively has a radially outer surface 34, 36 intended to come into contact with the ground during the passage of the corresponding projection 18A, 18B in the contact area of the tire 10 with the ground. The radial dimension of the surface 34 is greater than the radial dimension of the surface 36. In other words, the height h-ι of the first part 30 is greater than the height h ₂ of the second part 32.

FIGS. 11 and 12 show a tire according to a fourth embodiment of the invention. Elements similar to those shown in the preceding figures are designated by identical references.

Unlike the tire according to the third embodiment, each projection 18A comprises a small sound cavity 38 formed in the projection 18A. In this case, the cavity 38 is formed in the second portion 32 of the wear indicator TUS.

Beyond the threshold Si and, preferably also beyond the threshold S ₂ , the sound cavity 38 is shaped so as to open radially outwardly of the tire 10 and so as to be closed by the ground of substantially sealed manner during its passage in the area of contact of the tire 10 with the ground.

The invention is not limited to the embodiments described above.

The tread may comprise more than two grooves and therefore sets of witnesses comprising more than two substantially axially aligned indicators, that is to say having the same azimuth.

The tread may include a plurality of grooves and each witness comprise a single projection so that two successive witnesses circumferentially are located in two different grooves.

The tread may comprise witnesses arranged in each groove. Thus, two witnesses substantially aligned axially two by two may have a single threshold in common or more.

In all these cases, the projections may be variable or constant contact section.

[01 10] It will also be possible to provide a cavity in the projections other than those of the TUSi controls associated with the threshold Si.

[01 1 1] It is possible to combine the characteristics of the various embodiments described above once they are compatible with each other. other.

[01 12] 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.

Claims

1. Pneumatic tire (10), characterized in that it comprises:

at least two wear thresholds (SrS ₆ ),

for each wear threshold, at least one assembly (EE ₆ ) of at least one sound wear indicator (TUSi-TUS ₆ ) associated with at least this wear threshold (SrS ₆ ) so as to generate a acoustic impression noise at least above this threshold (SrS ₆ ), each indicator (TUSi-TUS ₆ ) of each set (EE ₆ ) being substantially axially aligned with each other control (TUSi-TUS ₆ ) of the together (EE ₆ );

the number (NE NE ₆ ) of set (s) (EE ₆ ) of witness (s) associated with each threshold (SrS ₆ ) being different from the number (NE NE ₆ ) of set (s) of witness (s) associated with each other threshold (SrS ₆ );

- the sets (EE ₆ ) of control (s) (TUSi-TUS ₆ ) associated (s) each threshold (SrS ₆ ) being equi-distributed circumferentially on the tire (10); and

- each indicator (TUS-TUS ₆ ) consisting of a projection (18A-18F) of rubber extending radially from the bottom of a groove (16) circumferential tire (10), the projection (18A-18F) ) being arranged to come into contact with the ground during its passage in the contact area of the tire (10) with the ground beyond the threshold (SrS ₆ ) associated with the control (TUSi-TUS ₆ ).

The tire (10) of claim 1, wherein each set comprises a single control (TUS-TUS ₆ ).

3. A tire (10) according to claim 1, wherein each set comprises at least two controls (TUSi-TUS ₆ ).

4. A tire according to any one of the preceding claims, comprising no cavity delimited by two ribs formed transversely to the bottom of a 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, the distance separating the two ribs being less than a predetermined distance so that, beyond one of the thresholds or each threshold, the cavity formed by the groove and the two ribs is sound.

A tire according to claim 4, wherein the projections (18A-18F) are arranged such that, irrespective of the wear of the tire (10), two circumferentially successive protrusions (18A-18F) of the same groove and the groove (16) delimits a space open to air during the passage of the two projections (18A-18F) in the contact area of the tire (10) with the ground.

A tire according to claim 4 or 5, wherein when the tire (10) is new, each circumferential groove (16) has a depth predetermined amount (H) and the height (hh ₆ ) of each projection (18A-18F) of each indicator (TUSi-TUS ₆ ) is substantially equal to the difference between the predetermined depth (H) of the groove (16) and the threshold ( SrS ₆ ) associated with the control (TUSi-TUS ₆ ).

7. A tire according to any one of claims 4 to 6, wherein each projection comprises at least one cavity formed in the projection (18A-18F), the cavity being shaped beyond the threshold associated with the control ( TUSI-TUS ₆ ) including the projection (SrS ₆ ):

to emerge radially towards the outside of the tire, and

- Be closed by the soil substantially tight during its passage in the area of contact of the tire (10) with the ground.

8. A tire (10) according to any one of claims 4 to 7, wherein each projection (18A-18F) of each control (TUSi-TUS ₆ ) associated with a threshold (SrS ₆ ) is circumferentially separated from each projection ( 18A-18F) of each control (TUSi-TUS ₆ ) associated with each other threshold (SrS ₆ ).

9. A tire (10) according to any one of claims 4 to 7, wherein each projection (18A-18F) of each control (TUSi-TUS ₆ ) associated with a threshold (SS ₆ ) is contiguous to a projection (18A -18F) of a witness (TUSi-TUS ₆ ) associated with another threshold (SS ₆ ).

A tire (10) according to any one of claims 4 to 9, wherein at least one protrusion (18A-18F) has a variable ground contact section (SC) as a function of tire wear (10). ).

1 1. Tire (10) according to the preceding claim, wherein the contact section (SC) increases with the wear of the tire (10).

The tire (10) according to any of claims 4 to 9, wherein at least one protrusion (18A-18F) has a contact section (SC) with the ground constant as a function of tire wear (10). ).

13. A tire (10) according to any one of the preceding claims, wherein the numbers NE ,, NE _{i + 1} of set of controls (TUSi-TUS ₆ ) respectively associated with two consecutive thresholds S ,, S _{i +} i verify NEi <NE _{i + 1} , the threshold S _{i +} i being greater than the threshold S ,.

14. Pneumatic tire (10) according to the preceding claim, wherein for any value of i 6 [1, M] with M the total number of thresholds and k, natural number.

The tire (10) according to any one of the preceding claims, wherein each witness associated with a given threshold (SrS ₆ ) is also associated with the threshold above the given threshold (SrS ₆ ).