Patent Application
20120266650
The present invention relates to a method for detecting the wear of a tyre. It applies in particular, without being restricted thereto, to tyres for vehicles of any type, passenger vehicles or heavy goods vehicles.
As a tyre rolls on ground, its tread which is in contact with the ground wears by friction. To make it easier to monitor wear and detect overly pronounced wear, tyres are furnished with wear gauges, especially sonic gauges, allowing the user to detect several levels of wear.
For each threshold, the sonic wear gauges generate an acoustic footprint noise or acoustic footprint exhibiting notable characteristics, especially frequency characteristics. These frequency characteristics are dependent on parameters comprising, inter alia, the number of wear gauges, their geometry of installation, the speed of rotation of the tyre or else the dimensions of the tyre. Thus, for certain values of these parameters, the characteristics of the characteristic noise of the gauges associated with several thresholds are identical so that it is impossible to determine which wear threshold is attained.
The aim of the invention is to provide a method making it possible to identify in an unequivocal manner the wear threshold attained.
For this purpose, the subject of the invention is a method for detecting wear of a tyre comprising a tread and exhibiting at least two predetermined thresholds of radial wear, characterized in that:
beyond each threshold Si, the tread is devised so that it comprises NEi set(s) of at least one so-called “sonic” cavity associated with the threshold Si; each cavity of each set being substantially aligned axially with each other cavity of the set; and
for each threshold Si, Kmin is the minimum value of the values of ki for i ∈ [2, M] where M is the total number of predetermined thresholds of radial wear with:
ki=NEi/NEi-1 when for the value of i ∈ [2, M], NEi/NEi-1>1, or
ki=NEi-1/NEi when for the value of i ∈ [2, M], NEi-1/NEi>1
for each threshold, an acoustic footprint noise emitted by the sonic cavity or cavities associated with this threshold is detected at a speed V, and
the value of the speed V for detecting the acoustic footprint noise is limited to an interval I=]Vmin; Vmax] satisfying Vmax<kmin·Vmin.
The method according to the invention makes it possible to alert a user of the tyre and to identify the wear threshold attained whatever the values of the above-stated parameters.
In the present application, the acoustic footprint noise of each set is the sonic signature of each set. This noise can also be considered to be the acoustic footprint of each set.
Indeed, the noise emitted by the sonic cavity or cavities associated with each threshold is characteristic of this threshold, especially because of the number of cavities associated with each threshold as well as with the distribution of these cavities. In such a method, it is implicit that the number of set(s) of sonic cavity(cavities) associated with each threshold is different from the number of set(s) of sonic cavity(cavities) associated with each other threshold. In the interval I, the characteristics, especially frequency characteristics, of the noise of two different thresholds may not be identical. Thus, a single wear threshold is associated with each value of the characteristics, especially frequency characteristics, of the noise. For example, once Vmin has been determined and knowing kmin, it is possible to determine Vmax and therefore I for unequivocal detection. Conversely, once Vmax has been determined and knowing kmin, it is possible to determine Vmin and therefore I for unequivocal detection. For any value of V lying in the interval I, it is therefore possible to identify the wear threshold attained in an unequivocal manner. Thus, it is possible, by means of the processing unit to distinguish the attaining of each wear threshold.
The cavities associated with the various thresholds exhibit a particular shape which confers sonic properties on them, that is to say these cavities cause characteristic noise during the rolling of the worn tyre.
For each cavity associated with each threshold, this characteristic noise appears only when the tyre is worn beyond the corresponding threshold. Each cavity associated with a threshold thus forms a sonic gauge of wear beyond the said threshold.
Thus, even if the driver does not visually and regularly inspect the surface state of his tyres, he will be informed of the crossing of each threshold when, while rolling, he hears a characteristic hiss.
Preferably, a processing unit and one or more microphones are used for detecting the rolling noise, linked to the processing unit and able to detect the hiss amidst the rolling noise and to inform the driver of the wear of his tyres.
The term speed will be understood to mean the linear speed of rotation of the tyre which is substantially equal to the speed of the vehicle fitted with the tyre.
Advantageously, the acoustic footprint noise comprises several elementary frequency components of acoustic footprint, preferably forming at least part of a Dirac comb. The elementary frequency components of the acoustic footprint noise are characteristic of the noise emitted by the cavities. Thus, when each wear threshold of the tyre is attained, the acoustic footprint noise emitted by the gauges comprises several elementary frequency components distributed frequency-wise. Furthermore, such acoustic footprint noise exhibits a notable comb pattern of elementary frequency components that is unique and therefore easy to detect.
According to other optional characteristics of the method:
Each elementary frequency component of the acoustic footprint noise is distant from at least one adjacent elementary frequency component of the acoustic footprint noise by a frequency gap lying in a reference frequency interval associated with a unique threshold. For each threshold, the reference frequency interval is characteristic of this threshold. Thus, when a wear threshold is attained, the acoustic footprint noise emitted by the cavities associated with this threshold comprises several elementary frequency components distributed frequency-wise according to the predetermined pattern. The predetermined reference frequency interval corresponds to the set of the frequency gaps which may separate the elementary frequency components of the noise associated with each wear threshold. Thus, this reference frequency interval covers all the frequency gaps that may separate two elementary frequency components of the noise associated with each different wear threshold. In the interval I, the frequency gap separating two elementary frequency components of the noise is therefore associated with a single wear threshold.
The predetermined reference frequency interval lies between 1 and 300 Hz. This frequency interval comprises the frequency gap liable to separate the elementary frequency components of the noise emitted by the cavities. The reference frequency interval is determined by taking account of the extreme values of the parameters that it is desired not to have to enter or modify, for example the dimensions of the tyre. Thus, for a passenger vehicle, for a speed varying between 10 and 130 km/h, a number of gauges varying between 1 and 20 and a circumference varying between 1.30 m and 3.0 m, the frequency gap of the elementary frequency components of the noise emitted by the cavities belongs to the interval lying between 1 Hz and about 300 Hz. A similar range of frequencies holds for heavy goods vehicles travelling at speeds of less than 90 km/h, equipped with tyres with a maximum of 32 gauges and with a circumference varying between 2.1 and 3.7 m.
In one embodiment, each set consists of a single sonic cavity.
In another embodiment, each set comprises at least two cavities aligned substantially axially with one another.
In this embodiment, a cavity of a set associated with a threshold exhibits substantially the same azimuth as that of another cavity of the set associated with the same threshold. Thus, these cavities are simultaneously sonic.
In another embodiment, two axially aligned cavities are associated with two different thresholds. In this case, the two cavities do not form part of the same set.
Optionally, the sets of sonic cavity(cavities) associated with each threshold are arranged so that, beyond each threshold, the sets of sonic cavity(cavities) associated with each threshold are equi-distributed circumferentially over the tyre.
The expression “equi-distributed circumferentially” is understood to mean that each set of cavity(cavities) associated with a given threshold is situated substantially the same spatial distance from the two sets of cavity(cavities) which are adjacent to it. In the case where a single set is associated with a given threshold, this single set is also equi-distributed circumferentially. Indeed, in this case, the adjacent sets are formed by this same set.
Furthermore, in all cases, as the sets of cavity(cavities) are equi-distributed circumferentially around the tread of the tyre whatever threshold is attained, the characteristics of the noise emitted beyond each threshold are unique and notable. Thus, the noise emitted by the tyre is easily detectable amidst the rolling noise of the tyre, the wind, the noise of the engine or the noise of the drivetrain associated therewith. Indeed, the noise emitted beyond each threshold exhibits, in the frequency domain, the shape of a characteristic Dirac comb that can easily be identified amidst all the above-stated spurious noises.
The cavities will be able to be offset axially with respect to one another while being equi-distributed circumferentially around the tread.
In an optional manner, beyond each threshold, each sonic cavity emerges radially to the exterior of the tyre, and is devised so as to be closed by the ground in a substantially leaktight manner as it passes across the area of contact of the tyre with the ground.
Indeed, because each cavity is devised so as to be closed by the ground in a substantially leaktight manner, it temporarily traps air as it passes across the area of contact of the tyre with the ground. Now, under the effect of the deformation of the tyre in the contact area, this air trapped in the cavity compresses and then expands fiercely on exiting the contact area when the tread loses contact with the ground at the rear of the tyre and when consequently the cavity opens.
This expansion of the air lasts of the order of a few milliseconds and causes a specific noise, sometimes called hiss or pumping noise, dependent especially on the shape and volume of the cavity.
Given that this hiss phenomenon appears only when air is compressed in the cavity and then expanded by escaping from the cavity, it is important that this cavity be closed in a substantially leaktight manner by the ground as it passes across the contact area. Indeed, a cavity whose top were covered by the ground but which, moreover, comprised transverse channels in fluidic communication with the exterior air, would not form a sonic cavity since the air that it contains could not be compressed. This is especially the case as regards the sculptures of the treads of the tyres of the prior art which are generally formed by a network of channels through which the various cavities communicate with one another and with the exterior air.
Likewise, a cavity whose dimensions were too large to be able to be totally covered by the ground as it passes across the contact area, for example a cavity whose length were greater than the length of the contact area, could not form a sonic cavity within the meaning of the invention.
In one embodiment, kmin=2.
According to optional characteristics of the invention the interval I is chosen from among the following speed intervals in km/h: ]50; 100], ]60; 120] and ]65; 130].
Optionally, the tyre comprises:
at least one circumferential groove, of predetermined depth when the tyre is brand new, and
at least two ribs made transversely at the bottom of the groove, of predetermined height when the tyre is brand new, substantially equal to the difference between the predetermined depth of the groove and one of the predetermined wear thresholds,
in which the distance separating the two ribs is less than a predetermined distance so that, beyond one or each of the predetermined thresholds of radial wear, the cavity formed by the groove and delimited by the two ribs is sonic.
By disposing the cavities in the grooves, the noise emitted by the cavities is amplified with respect to sonic wear gauges which would be disposed elsewhere in the tread. The noise emitted is also amplified by a pavilion formed by the tyre and the ground once each cavity has passed the contact area. This amplification by pavilion effect is a maximum when each sonic cavity is preferably disposed axially in a central part of the contact area of the tyre.
The expression central part of the contact area is intended to mean the zone of the contact area extending axially over substantially half the width of this contact area under the nominal conditions of loading and pressure and centred in relation to the central median plane of the tyre. In one embodiment with so-called “descending” sonic pattern, ki=NEi/NEi-1>1 for any value of i ∈ [2, M].
Stated otherwise, the number NEi of sets of sonic cavities increases with the wear of the tyre.
In this embodiment, by increasing the number of sets and therefore the number of cavities, the total volume of the cavities can increase at each threshold. It is noted that detection of the noise emitted by the cavities is then easier as the tyre wears.
In a variant of this embodiment, each cavity associated with a given threshold is also associated with the threshold above the given threshold. This makes it possible to minimize the number of cavities appearing at each threshold. Thus, the effect of the cavities on the performance of the tyre, especially the hydro-dynamic performance, is minimized. Thus, each cavity associated with a given threshold is also associated with all the thresholds above the given threshold. This characteristic obviously does not apply to the cavities of the highest threshold.
In another variant of this embodiment, the sonic cavity or cavities associated with a given threshold do not comprise any sonic cavity associated with the threshold below the given threshold. Thus, when the given threshold is attained, the cavity or cavities associated with the threshold below the given threshold cease to be sonic. Stated otherwise, each set of cavities is strictly associated with a single wear threshold.
In another variant, the sonic cavity or cavities associated with a given threshold comprise part of the sonic cavities associated with the threshold below the given threshold and sonic cavities that have appeared beyond the given threshold. Thus, only a few sonic cavities associated with the lower threshold are also sonic cavities associated with the given threshold.
In another embodiment with so-called “ascending” sonic pattern, ki=NEi-1NEi>1 for any value of i ∈ [2, M].
Stated otherwise, the number NEi of sets of sonic cavities decreases with the wear of the tyre.
The sonic cavities, when they are arranged in the grooves, may degrade the performance of the tyre with respect to a tyre devoid of such sonic cavities, especially in terms of dispersal of water by the grooves. This degradation of the water dispersal performance is all the greater the more advanced the wear of the tyre. Thus, by decreasing the number of sets of sonic cavities and therefore the number of sonic cavities with the advancing of the wear of the tyre, the potential loss of performance generated by the sonic cavities is limited. On the other hand, it is preferable to provide a sufficient number of cavities so that the total volume of the cavities may be sufficiently large, especially so that it is greater than the predetermined minimum volume.
In a variant of this embodiment, the sonic cavity or cavities associated with a given threshold are no longer sonic or disappear beyond the threshold above the given threshold. The sonic cavities associated with the threshold above the given threshold are therefore solely cavities appearing beyond the threshold above the given threshold. Stated otherwise, each cavity is strictly associated with a single wear threshold.
In another variant of this embodiment, the sonic cavity or cavities associated with a given threshold comprise part of the sonic cavity or cavities associated with a threshold below the given threshold.
The subject of the invention is also a computer program, characterized in that it comprises code instructions for controlling the execution of the steps of the method such as is defined hereinabove when it is executed on a computer.
The subject of the invention is furthermore a medium for recording data comprising, in recorded form, a program such as defined hereinabove.
Another subject of the invention is making available of a program such as defined hereinabove on a telecommunication network with a view to its downloading.
The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and while referring to the drawings in which:
Represented in
The tyre 10 comprises a tread 12 of substantially cylindrical shape, whose external surface is furnished with sculptures 14. In particular, the tread 12 comprises two circumferential and parallel grooves 16, cut out in the surface of the tyre, of predetermined depth H when the tyre 10 is brand 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 tyre 10 comprises visual wear gauges (not illustrated) indicating a legal wear threshold SL for the tyre. The depth of each groove corresponding to the threshold SL is fixed at 1.6 mm, thus corresponding to a threshold SL=6.4 mm.
Transversely to the grooves 16, the tread 12 of the tyre comprises a set of ribs 18 made at the bottom of the grooves 16. The set of ribs comprises two types of ribs 18A, 18B each corresponding to at least one predetermined wear threshold S1, S2 for the tyre. Each rib 18A, 18B exhibits respectively a first and second predetermined height h1, h2 when the tyre is brand new. h1>h2 and S2>S1 so that each rib of type 18A is associated with the thresholds S1 and S2 and each rib of type 18B is associated with the unique threshold S2. The first threshold S1 corresponds substantially to 90% of the threshold SL, that is to say h1=2.5 mm and S1=5.5 mm. The second threshold S2 corresponds substantially to 100% of the threshold SL, that is to say h2=1.6 mm and S2=6.4 mm. The thresholds S1, S2 are represented schematically in
Thus, in this embodiment, the first threshold S1 corresponds to wear beyond which the tyre exhibits performance that may possibly be degraded on a wet pavement. The second threshold S2 corresponds, on the other hand, to wear beyond which the tyre no longer complies with the legal requirements.
The distance separating two ribs of the same type is of the order of 20 to 30 millimetres. The volume defined by a groove 16 and two neighbouring ribs 18A, 18B forms respectively a cell 19A, 19B arranged in each circumferential groove 16. Each cell 19A, 19B of each pair of cells 19A, 19B is linked to the other cell of the pair by a transverse channel 21A, 21B. Each pair of cells 19A and the channel 21A form a set consisting of a cavity 20A emerging radially to the exterior of the tyre 10. Likewise, each pair of cells 19B and the channel 21B form a set consisting of a cavity 20B emerging radially to the exterior of the tyre 10. In
When the tyre is brand new, as is represented in
Represented in
In this instance, the wear of the tread 12, represented in
The wear of the tyre is less than the threshold S2, stated otherwise less than the distance separating, when the tyre 10 is brand new, the top of the ribs 18B from the surface of the tread 12. The top of the ribs 18B is at a lower level that that of the tread at this juncture of the wear.
Beyond the threshold S1, each cavity 20A exhibits a depth that is less than the height h1. Here, the depth is less than 2.5 mm and equals 2 mm for 6 mm of wear. 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 tyre 10.
Because the mouth of each cavity 20A is defined by a substantially plane contour, it is able to be plugged perfectly and hermetically by smooth and plane ground during rolling. Stated otherwise, when the tyre 10 is worn beyond the threshold S1, each cavity 20A is devised so as to be closed by the ground in a substantially leaktight manner as it passes across the area of contact of the tyre 10 with the ground. Between the thresholds S1 and S2, each cavity 20B is not closed by the ground in a leaktight manner on account of the constriction channel delimited by the top of each rib 18B and the ground 11.
Represented in
In this instance, the wear of the tread 12, represented in
Beyond the threshold S2, each cavity 20B exhibits a depth that is less than the height h2. Here, the depth is less than 1.6 mm and equals 1 mm for 7 mm of wear. 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 tyre 10.
Because the mouth of each cavity 20A, 20B is defined by a substantially plane contour, it is able to be plugged perfectly and hermetically by smooth and plane ground during rolling. Stated otherwise, when the tyre 10 is worn beyond the threshold S2, each cavity 20A, 20B is devised so as to be closed by the ground in a substantially leaktight manner as it passes across the area of contact of the tyre 10 with the ground.
Each cavity 20A, 20B exhibits, beyond the corresponding threshold S1, S2, a length of the order of 20 to 30 millimetres corresponding to the circumferential gap between two adjacent ribs 18A, 18B of one and the same cavity.
Such cavities 20A, 20B formed on the surface of the tread 10 of a tyre which, on the one hand, emerge radially to the exterior of the tyre and, on the other hand, are devised so as to be closed hermetically as they pass across the contact area, are termed “sonic”. In this embodiment, each cavity 20A is sonic beyond each threshold S1, S2 whereas each cavity 20B is sonic only beyond the threshold S2. In the example illustrated, the numbers NEi, NEi-1 of sets of cavities associated respectively with two consecutive thresholds Si, Si-1 satisfy NEi-1<NEi for i ∈ [2, M] where M is the total number of predetermined thresholds of radial wear and the threshold Si being greater than the threshold Si-1. Therefore for each value of i ∈ [2, M], we have ki=NEi/NEi-1 since NEi/NE1-1>1. A tyre in which NE2>NE1 is thus termed a tyre with “descending” sonic pattern. In this embodiment, k1=NE2/NE1=N2/N1=2.
The cavities 20A, 20B are arranged so that, beyond each threshold S1, S2, the sets of sonic cavities 20A, 20B are equi-distributed circumferentially over the tyre 10. As each set consists of a single cavity, the sonic cavities 20A, 20B are therefore equi-distributed circumferentially over the tyre 10. Furthermore, the tread is devised so that, beyond each threshold S1, S2, all the sonic cavities 20A, 20B are identical as is illustrated in
Furthermore, each cavity 20A associated with the threshold S1 is also associated with the threshold S2. In the tyre 10, such sonic cavities are nonexistent below the threshold S1, especially when the tyre is brand new.
Represented in
The direction of rotation of the tyre 10 while rolling on the ground has been represented by an arrow 22. At a given instant, a part of the tread 12 of the tyre 10 is in contact with the ground. This part in contact is called the contact area 24. The tread 12 is devised so that each sonic cavity 20A, 20B exhibits, as it passes across the area of the contact 24 of the tyre 10 with the ground 11, a contact cross-section which is constant as a function of the wear of the tyre 10.
In the example represented in
The contact area 12 of the tyre also comprises a sonic cavity 28, situated upstream of the closed cavity 26, which is open since its mouth is not in the contact area and is consequently not covered by the ground. During the rolling of the tyre in the direction designated by the arrow 22, the open cavity 28 will progress towards the contact area 24 until its mouth is plugged by the ground 11.
Finally, the tread 12 of the tyre 10 also comprises a cavity 30 situated downstream of the closed cavity 26, with respect to the direction of rotation of the tyre 10. In the example represented in
Thus, in the course of the rolling of the tyre, a given sonic cavity successively occupies an upstream position 28 in which it is open, and then a position 26 located in the contact area 24 in which it is closed since it is covered by the ground, and then finally an open position 30 again in which it is no longer covered by the ground.
Stated otherwise, the rotation of the tyre causes, for a given cavity, the admission of air into the cavity, the compression of the air contained in the cavity when the latter is closed by the ground in the contact area 24, and then the expansion of the air contained in the cavity during the opening of the latter by separation of the tread from the ground.
This succession of admission/compression/expansion steps gives rise to a characteristic noise, sometimes called hiss 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 especially on the shape, on the volume and on the number of sonic cavities used. Preferably, the cavities are devised so that this noise is detectable by a user of the motor vehicle or by an electronic device.
Represented in
The parameters such as the number of wear gauges, their geometry of installation, the speed of rotation of the tyre or else the dimensions of the tyre, define a reference frequency interval IR to which the frequency FTUS is liable to belong. For a range of passenger vehicle tyres, whose circumference may vary between 1.3 m and 3 m, whose number of gauges may vary between 1 and 10 and, for which the speed of the vehicle may vary between 10 km/h and 130 km/h, the frequency FTUS may vary in the interval IR lying between 1 and 278 Hz. For tyres of heavy goods vehicle type, the interval IR is similar.
Illustrated in
Two bands B1=[36 Hz; 94 Hz] and B2=[72 Hz; 187 Hz] have been illustrated in
A tyre according to a second embodiment has been represented in
In contradistinction to the first embodiment, the tyre 10 according to the second embodiment comprises six predetermined thresholds of radial wear S1-S6 with NE1=N1=2, NE2=N2=1, NE3=N3=4, NE4=N4=8, NE5=N5=16 and NE6=N6=32 and therefore the following ratios ki: k1=k2=k3=k4=k5=k6=NE2/NE1=N2/N1=NE3/NE2=N3/N2=NE4/NE3=N4/N3=NE5/NE4=N5/N4=NE6/NE5=N6/N5=2. As in the first embodiment, the tyre 10 is “descending” sonic pattern tyre.
The depth of the grooves 16 is of the order of 14 millimetres, here 14.3 mm. The depth of each groove corresponding to the threshold SL is fixed at 2 mm, thereby corresponding to a threshold SL=12.3 mm. The set of ribs comprises third, fourth, fifth and sixth types of ribs 18C-18F, in addition to the ribs 18A, 18B. Each rib 18C-18F exhibits respectively a third, fourth, fifth and sixth height h3, h4, h5 and h6, predetermined when the tyre is brand new. h1>h2>h3>h4>h5>h6 and S6>S5>S4>S3>S2>S1 so that each rib of type 18A is associated with the thresholds S1-S6, each rib of type 18B is associated with the thresholds S2-S6, each rib of type 18C is associated with the thresholds S3-S6, each rib 18D is associated with the thresholds S4-S6, each rib 18E is associated with the thresholds S5 and S6 and each rib 18F is associated with the threshold S6 alone. The first threshold S1 corresponds substantially to 19% of the threshold SL, that is to say h1=12 mm and S1=2.3 mm. The second threshold S2 corresponds substantially to 35% of the threshold SL, that is to say h2=10 mm and S2=4.3 mm. The third threshold S3 corresponds substantially to 51% of the threshold SL, that is to say h3=8 mm and S3=6.3 mm. The fourth threshold S4 corresponds substantially to 67% of the threshold SL, that is to say h4=6 mm and S4=8.3 mm. The fifth threshold S5 corresponds substantially to 84% of the threshold SL, that is to say h5=4 mm and S5=10.3 mm. The sixth threshold S6 corresponds substantially to 100% of the threshold SL, that is to say h6=2 mm and S6=12.3 mm.
The various thresholds correspond to various stages of the life of the tyre during which diverse actions must be undertaken so as to distribute the wear over the whole of the tread and thus increase the lifetime of the tyre.
Thus, the threshold S2 corresponds to wear for which it is possible to swap the tyre on one and the same axle. The threshold S4 corresponds to wear for which it is possible to return the tyre. The threshold S5 corresponds to wear for which it is possible to regroove the tyre so as to restore its performance, especially as regards water dispersal.
Just as in the first embodiment, the sets of cavities 20A-20F, here the sonic cavities 20A-20F, are arranged so that, beyond each threshold S1-S6, the set(s) of sonic cavities 20A-20F, here the sonic cavities 20A-20F, are equi-distributed circumferentially over the tyre 10.
Furthermore, each cavity 20A associated with the threshold S1 is also associated with the threshold S2-S6, each cavity 20B is associated with the thresholds S2-S6, each cavity 20C is associated with the thresholds S3-S6, each cavity 20D is associated with the thresholds S4-S6, each cavity 20E is associated with the thresholds S5 and S6 and each cavity 20F is associated with the threshold S6 alone.
Illustrated in
Six frequency bands B1=[3 Hz; 8 Hz], B2=[5 Hz; 16 Hz], B3=[11 Hz; 33 Hz], B4=[22 Hz; 66 Hz], B5=[44 Hz; 132 Hz] and B6=[88 Hz; 264 Hz] have been illustrated in
Represented in
In contradistinction to the previous embodiments, the number of sets of sonic cavities 20A, 20B decreases with the wear of the tyre 10. The numbers NEi, NEi-1 of sets of cavities associated respectively with two consecutive thresholds Si, Si-1 satisfy NEi-1>NEi for i ∈ [2, M] where M is the total number of predetermined thresholds of radial wear and the threshold Si being greater than the threshold Si-1. Therefore for each value of i ∈ [2, M], we have we have ki=NEi-1/NEi since NEi-1/NEi>1. Such a tyre is termed a tyre with “ascending” sonic pattern. In this embodiment, k1=NE1/NE2=N1/N2=2.
In contradistinction to the first embodiment, each sonic cavity 20B associated with the second threshold S2 is also associated with the first threshold S1. Only part of the sonic cavities 20A associated with the first threshold S1 is also associated with the second threshold S2.
Illustrated in
Two bands B1=[72 Hz; 187 Hz] and B2=[36 Hz; 94 Hz] have been illustrated in
The invention is not limited to the embodiments described above.
Furthermore, the tread will be able to comprise more than two grooves and therefore sets of cavities comprising more than two substantially axially aligned cavities, that is to say exhibiting the same azimuth.
The tread will also be able to comprise a single groove. Each cavity will therefore be formed by a cell.
The tread will be able to comprise several grooves and each cavity to comprise a single sonic cell so that two circumferentially successive cavities are situated in two different grooves.
The tread will be able to comprise cavities arranged in each groove, the cavities being substantially aligned axially pairwise without however being linked to one another by a channel. Such cavities will be able to be associated with the same wear threshold or else with two different wear thresholds.
In all these cases, the cavities may have variable or constant contact cross-section and be used equally well with tyres having “ascending” or “descending” sonic patterns.
By way of additional examples of a tyre with descending sonic pattern, it will be possible to utilize tyres with three or four thresholds exhibiting the following characteristics:
By way of additional examples of a tyre with ascending sonic pattern, it will be possible to utilize tyres with three or four thresholds exhibiting the following characteristics:
| Number | Date | Country | Kind |
|---|---|---|---|
| 0959241 | Dec 2009 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR10/52739 | 12/15/2010 | WO | 00 | 7/10/2012 |
