EP2408630A1

EP2408630A1 - Method for monitoring the condition of a tire

Info

Publication number: EP2408630A1
Application number: EP10716556A
Authority: EP
Inventors: Antoine Paturle
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2009-03-19
Filing date: 2010-03-18
Publication date: 2012-01-25
Also published as: JP2012520793A; CN102427957A; FR2943276B1; US20120010776A1; BRPI1009582A2; CN102427957B; FR2943276A1; US8731767B2; WO2010106297A1

Abstract

The tire (14) includes a tread shaped such that, beyond a predetermined radial wear threshold, the tread includes an assembly of at least one wear indicator including a so-called "sound" cavity (120A, 120B, 121) arranged in a circumferential groove of the tread. During the monitoring process, an acoustic signal above a predetermined threshold is detected (100) by an acoustic sensor (20) onboard the vehicle (12), said signal being capable of including an acoustic fingerprint noise produced by the assembly of at least one wear indicator (120A, 120B, 121) while the tire (14) runs on the ground, and information relating to the acoustic signal is transmitted (308) to a remote server (30) that is not onboard the vehicle (12).

Description

Method for monitoring the state of a tire

The invention relates to the field of motor vehicle tires and the monitoring of their condition. For example, the invention relates to monitoring the state of wear or pressure of a tire.

For obvious safety reasons, it is important that the tire is properly inflated, is not overloaded and wear is not excessive. In fact, a pronounced wear of the tread, an overload or an under-inflation can cause a puncture, a burst, hydroplaning on wet road, a loss of endurance, a heating ...

To facilitate the control of the state of the tire, it is commonly provided with status indicators.

An example of a state indicator to control wear consists of a rib formed at the bottom of a groove of the tire tread and the height of which corresponds to the minimum depth of the grooves of the tire necessary for a correct and safe operation of the tire. . Thus, when the tread of the tire is worn and the top of the rib is flush with the outer surface of the tread, it means that the minimum depth tolerated for the grooves is reached or exceeded. It is therefore urgent to replace the tire for safety.

A disadvantage of this type of status 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, when during a technical inspection of the vehicle, a garage checks the state of wear of the tires or their pressure.

The object of the invention is in particular to provide a method for monitoring the condition of the tires of a motor vehicle that does not require permanent vigilance of the driver of the vehicle.

To this end, the subject of the invention is a method of monitoring at least one tire of at least one motor vehicle comprising a tread, characterized in that the tread is shaped so that, beyond a predetermined radial wear threshold, the tread comprises an assembly of at least one wear indicator comprising a cavity called "sound" arranged in a circumferential groove of the tread, each cavity opening radially towards the outside of the tire and being shaped so as to be closed by the ground of substantially sealed manner during its passage in the area of contact of the tire with the ground, the method comprising the following steps:

detection by an acoustic sensor embarked on the vehicle of an acoustic signal capable of including an acoustic impression noise produced by the assembly during the rolling of the tire on a ground beyond the predetermined radial wear threshold,

transmitting information relating to the acoustic signal to a remote server that is not on board the motor vehicle.

Because the cavity is shaped so as to be closed by the floor in a substantially watertight manner, the air is temporarily trapped during the passage of the cavity 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 relaxation of the air lasts about a few milliseconds and causes a specific acoustic noise noise, sometimes called hissing or pumping noise, a function in particular of the shape and volume of the cavity.

This characteristic noise, which only appears when the tire is worn beyond the threshold, thus forms a sound warning means. Thus, even if the driver does not visually and regularly inspect the surface condition of his tires, he will be informed of the excessive wear of his tires when, while driving, by the detection of this characteristic hissing.

The characteristic noise acoustic impression produced by the assembly can be detected by means of a system comprising an acoustic sensor, in particular by a microphone.

Following this detection, the invention proposes to transmit, to a remote non-embedded server on the vehicle, information relating to the detected acoustic signal.

Due to the fact that the status information is available remotely, it can be viewed or processed by someone other than the driver of the vehicle. Thus, it is no longer necessary for the driver to be regularly vigilant since a remote system or a third person can inform him of the condition of his tires at the appropriate time.

By being disposed in the grooves, the noise emitted by each cavity is amplified relative to a cavity that would be disposed elsewhere in the tread. This amplification allows the reliable detection of the acoustic print noise that can be difficult to distinguish from the surrounding noise forming, with the sound of the acoustic impression, the acoustic signal. The noise emitted by the assembly is also amplified by a horn formed by the tire and the ground once the cavity has passed the contact area. This amplification effect flag is maximum when the 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.

Since this phenomenon of hissing occurs only when air is compressed in the cavity and then expanded by escaping from it, it is important that the cavity is sealed substantially by the ground during its passage in the cavity. 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, do not could not form a sound cavity within the meaning of the invention. A method according to the invention may further include one or more of the following features.

Beyond the predetermined radial wear threshold, each indicator comprises at least one pair of first and second sound cavities and a so-called "sound" channel connecting each sound cavity of the pair to each other, each first and second sound cavity being respectively arranged in a first and second circumferential groove of the tread, the channel being formed in the tread, each cavity of the pair and the associated channel:

- opening radially outwardly of the tire,

- Being shaped so as to be closed by the ground substantially sealingly during their passage in the area of contact of the tire with the ground. The sound cavities 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. The channel connecting the cavities of each pair compensates for this loss of performance while allowing the detection of tire wear.

Optionally, each first and second groove having a predetermined depth when the tire is new, the tread comprises at least two ribs formed transversely to the bottom of each first and second groove, of predetermined height when the tire is new, substantially equal to the difference between the depth in which the distance separating the two ribs is less than a predetermined distance so that, beyond the predetermined radial wear threshold, each cavity formed by each first and second groove and delimited by the two ribs is sound.

In the state of the art, visual wear indicators are also formed by ribs formed at the bottom of circumferential grooves of the tire. However, these visual wear indicators are arranged so that the ribs are far apart from each other. Thus, the distance separating two adjacent ribs is much greater than the length of the contact area of the tire with the ground and at no time two neighboring ribs are simultaneously in contact with the ground. Thus, in the state of the art, the volume defined by the groove and delimited by two neighboring ribs certainly forms a cavity, but this cavity is not sound because it is not able to be closed substantially sealed by floor.

The acoustic sensor belongs to a telephone embedded in the cabin of the vehicle. This phone can be for example a phone mounted in a fixed manner in the passenger compartment of the vehicle or a mobile phone belonging to one of the occupants of the vehicle. This solution is particularly advantageous because it reduces the number of devices present in the vehicle by reusing embedded devices. In addition, a telephone includes means of communication to the outside which facilitates the transmission of data to the remote server. The acoustic sensor belongs to an electronic box embedded in the vehicle, for example a geolocation electronic box.

The method further comprises preprocessing the acoustic signal and for extracting the acoustic print noise therefrom. Since the acoustic signal can vary depending on the wear or the pressure of the tire, the pre-treatment allows to interpret this signal to estimate the level of wear of the tire and thus qualify its state by means of acoustic noise.

In one embodiment, the pre-treatment is implemented by an on-board system on the motor vehicle, before the transmission step. In another embodiment, the pre-processing is implemented by the remote server after the transmitting step.

Preferably, the acoustic fingerprint noise comprising several elementary frequency components of acoustic fingerprint and the acoustic signal comprising several elementary frequency components, during the pre-treatment: - we enumerate several series of elementary frequency components, each series listed being likely to forming at least a portion of the elementary frequency components of acoustic fingerprint;

one of the series listed is selected from a series, called a series of acoustic impressions; - A so-called local confidence index of the acoustic fingerprint series is determined.

The method according to the invention makes it possible to alert a user of the tire without necessarily knowing parameters such as the speed of the vehicle, the geometry of implantation of the sound wear indicators and their number. In fact, the elementary frequency components of the acoustic print noise are characteristic of the noise emitted by the witnesses. Thus, when the radial wear threshold of the tire is exceeded, the noise acoustic noise emitted by the witnesses comprises several elementary frequency components distributed in frequency according to the parameters. This frequency distribution is in accordance with a predetermined pattern. This pattern is defined by spacing ratios between the different elementary signals. Thus, by enumerating several series composed of elementary frequency components acquired and capable of forming at least a portion of the elementary frequency components of acoustic fingerprint, that is to say conforming to the predetermined pattern, we list series of elementary frequency components that are capable of each of them being characteristic of the noise emitted by the set of sound wear indicators. Since the acoustic print noise is unique and has outstanding and distinctive characteristics due to its predetermined pattern, the acoustic fingerprint series can be selected from the series listed by predetermined criteria.

The method further comprises a post-processing in which the remote server establishes a diagnosis of the state of the tire and its evolution during the course of the time depending on the result of the pre-treatment. For this, the server may include means for storing past states. The diagnosis makes it possible in particular to estimate the remaining life of the tire or the type of use thereof depending on the type of conduct of the driver. In one embodiment:

several acoustic signals are acquired which are successive in time and capable of understanding acoustic noise, each acoustic signal comprising several elementary frequency components,

for each acoustic signal, a series of acoustic fingerprint is selected and a local confidence index of the selected acoustic fingerprint series is determined, and during the post-treatment:

a global confidence index is determined from the local confidence indices of the acoustic fingerprint series; if the global confidence index is, in absolute value, greater or less than a predetermined threshold associated with this index; of global confidence, it emits an alert of the wear of the tire.

The amplitude of the noise emitted by the assembly in the frequency domain depends in particular on the coating on which the tire rolls. For example, relatively smooth soil is more conducive to the emission of control noise than porous soil. However, detection remains possible in both cases. There are therefore favorable coatings for detection and other less favorable, these two types of coatings can succeed one another randomly. Thus, a first local index may, for a first acoustic signal, be greater than the threshold associated with the local index, then a second local index, may, for a second acoustic signal, subsequent to the first, be lower than said threshold. In this case, it is not known whether the radial wear threshold has actually been crossed and whether the second index is below the threshold due to an unfavorable coating or if the radial wear threshold has not been crossed. and if the first index wrongly indicates it.

In order to reduce this risk of false alarms and to make the detection process more robust, several successive acoustic signals are processed temporally. If several series of acoustic fingerprints of successive acoustic signals have a local confidence index indicating an exceeding of the radial wear threshold, there is a high probability that the radial wear threshold has actually been crossed which is indicated by the global confidence index. In another embodiment:

several acoustic signals are acquired that are successive in time and capable of understanding the acoustic print noise, each acoustic signal comprising several elementary frequency components, for each acoustic signal a series of acoustic fingerprints are selected, and during the treatment:

a global index of confidence is determined from a continuity in time between the elementary frequency components of each series of selected acoustic fingerprint,

if the global confidence index is, in absolute value, greater or less than a predetermined threshold associated with this global confidence index, an alert is issued of tire wear.

In this embodiment, it also reduces the risk of alert twists. The global confidence index is determined from the graphical representation, independent of the local confidence indices, unlike the previous embodiment in which the global confidence index is a function of the local confidence indices. Thus, it ensures the correct detection of the wear of the tire by means of local and global confidence indexes not related to each other which makes the process more robust.

The method enables the monitoring of tires of a plurality of motor vehicles, and a diagnosis of all the tires of the plurality of vehicles is made. Indeed, this method can be implemented advantageously by a vehicle renter who can then monitor the condition of the tires of its entire fleet of vehicles. Thanks to the remote transmission of the condition of the tires, the renter does not need to consult each of the vehicles. The role of the remote server is to centralize all this information.

The remote server, according to the diagnosis, transmits to a user a recommendation of use of the tire. This recommendation of use may concern the speed or the remaining distance to be traveled before changing one or more of the tires. The system can also recommend the driver to immediately change his tires.

The recommendation is sent by SMS or email to the user. This is advantageous especially when the acoustic signal of the whole status is detected using the driver's mobile phone. This recommendation can also be transmitted by any other means of information such as a phone, a pocket organizer, a portable terminal or not ...

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

The invention also 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 follows, given solely by way of example and with reference to the appended figures in which: FIG. 1 is a diagram of an installation adapted to the implementation the monitoring method according to the invention; FIG. 2 is a diagram of the tread of a new tire, FIG. 3 is a diagram of the tread of the tire shown in FIG. 2, in a worn state, FIG. 4 is a diagram in a sectional view. radial of the tread of the tire shown in FIG. 3, FIGS. 5A-5E and 6A-6E illustrate theoretical signals of the acoustic print noise emitted by sound wear indicators of the tire of FIG. 3 and FIG. an acoustic signal comprising this acoustic print noise; Figure 7 is a diagram of the steps of the monitoring method according to first and second embodiments of the invention; Figures 8 to 12 illustrate acoustic signals of the acoustic signal detected inside a passenger compartment of a vehicle shod with tires of Figure 3; Figures 13 to 15 illustrate variations of relevance indices according to characteristics; FIG. 16 illustrates several acoustic signal frames measured successively, FIGS. 17 and 18 illustrate a further step of the method according to a third embodiment of the method. FIG. 1 shows a plant designated by the general reference

Adapted for carrying out a method according to the invention for monitoring motor vehicle tires 12.

In Figure 1, motor vehicles 12 are cars. The invention can also be implemented on any type of motor vehicle equipped with tires, in particular on trucks.

Each car 12 includes tires 14 whose state is to be monitored. The state of the tire characterizes, for example, its wear or its pressure.

For this, each tire 14 is provided with audible state indicators 16, ie witnesses 16 capable of emitting an acoustic impression noise which varies as a function of the state of the tire, in particular as a function of its wear.

The vehicle 12 further comprises, within its cabin, a system 18 for detecting an acoustic signal comprising the acoustic fingerprint noise produced by all or the witnesses 16 beyond a wear threshold. predetermined radial. The system 18 comprises an acoustic sensor such as a microphone 20, processing means 22 of the signal detected by the acoustic sensor 20, and means 24 for transmitting the results of the remote processing.

The system 18 can be a fixed system embedded in the vehicle

12, especially in its cabin. The system can thus be a fixed telephone whose acoustic sensor 20 is attached to a windshield pillar close to the driver's mouth and whose processing means 22 are integrated in the vehicle computer.

This system can also be in the form of an electronic box type GPS tracking device, personal digital assistant, emergency call system ... In this case, the acoustic sensor 20 can be integrated in the housing or external and connected to the processing means 22 of the housing.

The system 18 can also be a mobile system that is not permanently embedded in the passenger compartment of the vehicle 12, for example a mobile phone 26 of the driver 28. In this case, the acoustic sensor 20, the processing means 22 and the transmitting means 24 are integrated within the mobile telephone 26. In FIG. 1, the mobile telephone 26 of the driver 28 is shown separately from the system 18. As indicated above, these two systems can be combined.

The installation 10 further comprises a remote server 30 to which are connected means 32 for transmitting and receiving data remotely, a database 34 and a control and control terminal 36 able to be consulted by a user 38 . The server 30 is able to interact with the surveillance systems 18 integrated in the vehicles 12 through the cooperation of the transmission means 24 with the transmitting and receiving means 32.

There is shown in Figure 2 a portion of the tire 14 in the new state. The tire 14 comprises a tread 112 of substantially cylindrical shape, the outer surface of which is provided with sculptures 114. In particular, the tread 1 12 comprises first and second grooves 1 16A, 116B circumferential and parallel, hollowed out at the tire surface of predetermined depth when the tire 14 is new. For example, the depth of these furrows is of the order of 8 millimeters for a passenger vehicle.

Transversally to the grooves 1 16A, 1 16B, the tread 1 12 of the tire comprises a set of ribs 18 formed at the bottom of the grooves 1 16A, 116B, the height of the ribs 1 18 being predetermined when the tire is new. For example, the height of these ribs is of the order of 3 millimeters. In the example shown in Figure 2, the ribs 118 are evenly distributed along the circumference of the tire 14, the distance between two neighboring ribs being of the order of 20 to 30 millimeters.

The tread 1 12 also includes a pair of first and second cavities 120A, 120B respectively arranged in the first and second grooves 16A, 16B and a transverse channel 121 associated with the pair of cavities 120A, 120B. The channel 121 is formed in the band 1 12 and connects the cavities 120A, 120B together. The cavities 120A, 120B are aligned axially. In a variant, they are axially offset with respect to each other.

The volume defined by each groove 116A, 16B and two neighboring ribs 1 18 respectively form each cavity 120A, 120B emerging radially outwardly of the tire 14. The channel 121 also opens outwardly of the tire 14.

When the tire is new, as shown in FIG. 2, the height of the ribs 118 is smaller than the depth of the grooves 116 so that two neighboring cavities 120A, 120B comprise a fluidic communication passage located above the ribs. 1 18, that is to say at the top of the ribs 1 18. Thus, even when the tread is in contact with a floor 11 and smooth, the soil 11 1 does not completely close the cavities 120A, 120B because the top of the ribs is not in contact with the ground 111. In this case, the different cavities 120A, 120B neighbors are in fluid communication with each other by a throttling channel delimited by the top of the ribs and the soil 11 1 covering the cavities or by the channel 121. FIG. 3 shows the tire 14 of FIG. 2 in a worn state.

In other words, it is a tire having traveled many kilometers and whose tread 112 has been progressively worn until losing a few millimeters, of the order of 5 mm. In this case, the wear of the tread 112 of the tire 14 shown in FIG. 3 is of the order of 6 millimeters, that is to say greater than the distance separating, when the tire is new, the top of the ribs 1 18 of the surface of the tread. Given this pronounced wear, the top of the ribs 118 is at the same level as the surface of the tread 112. Thus, the mouth of each cavity 120A, 120B and the channel 121 is defined by a substantially planar contour formed on the tread. Each pair of cavities 120A, 120B and associated channel 121 are separate and separate from one another.

Each cavity 120A, 120B has a length of the order of 20 to 30 millimeters corresponding to the circumferential gap between two adjacent ribs 1 18 and a depth of the order of 2 millimeters, less than or equal to the initial height of the rib 118.

Each pair of cavities 120A, 120B and the associated channel 121 form one of the sound wear indicators 16. The tire 14 comprises a set of eight indicators 16, that is to say a set of eight pairs of sound cavities 120A, 120B and eight transverse channels 121 associated regularly distributed along the circumference of the tire 14. Thus, the witnesses 16 are evenly distributed circumferentially in the tread 1 12. The pairs of cavities 120A, 120B and the channels 121 are of shapes identical.

Beyond the predetermined radial wear threshold, the total volume of pairs of sound cavities 120A, 120B and associated sound channels 121 is greater than or equal to 4 cm ³ , preferably 5 cm ³ .

Because the mouth of each cavity 120A, 120B and the channel 121 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 14 is worn, the cavities 120A, 120B and the channel 121 are shaped so as to be closed by the ground in a substantially watertight manner as they pass through the contact area of the tire 14 with floor.

Such cavities 120A, 120B and such an associated channel 121 formed on the surface of the tread 14 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 sealed during their passage in the contact area, are called "sound". Different cavity sizes or different orientations of these cavities 120A, 120B and associated channels 121 with respect to the tread can be envisaged. In the tire 14, such sound cavities only appear when the tire is worn beyond a predetermined radial wear threshold and are non-existent below this threshold, especially when the tire is new.

FIG. 4 shows a view in radial section of a tire similar to that of FIG. 4 while driving on a floor. The dimensions are changed arbitrarily for the sake of clarity. This tire 14 is in a worn state and therefore comprises a set of eight sound cavities 120A, 120B and eight associated channels 121.

There is shown by an arrow 122 the direction of rotation of the tire 14 during its rolling on the ground. At a given moment, a portion of the tread 112 of the tire 14 is in contact with the ground. This part in contact is called contact area 124. The cavities 120A, 120B of each pair are positioned axially in a central portion 132 of the contact area 124 of the tire formed by a portion of a circumferential tread of the tire 14 .

In the example shown in FIG. 4, the contact area 124 comprises three pairs of sound cavities 126 and three associated sound channels whose radially outer mouth is covered by the floor 11. Thus, these three pairs of sound cavities 126 and their associated sound channels are hermetically sealed.

The contact area 1 12 of the tire also comprises pairs of sound cavities 128 and their associated sound channels, located upstream of the pairs of closed cavities 126 and their associated channels, which are open because their mouth is not in the chamber. contact area and is therefore not covered by the ground. When rolling the tire in the direction indicated by the arrow 122, the pairs of open cavities

128 and their associated channels will progress to the contact area 124 until their mouth is closed by the ground 11 1. Finally, the tread 1 12 of the tire 14 also comprises pairs of cavities 130 and their channels associated downstream pairs of cavities 126 and closed associated channels, relative to the direction of rotation of the tire. In the example shown in Figure 5, the cavity pair 130 and the downstream associated channel shown are open because the ground 11 1 is not in contact with their mouth. Has a previous instant, this pair of cavities 130 and the associated channel were closed as located in the area of the contact area 124 of the tire with the ground 1 11.

Thus, during the rolling of the tire, a pair of sound cavities 120 and the associated sound channel successively occupies an upstream position 128 in which they are open, then a position 126 located in the contact area 124 in which they are closed. because covered by the ground, then finally an open position 130 again in which they are no longer covered by the ground.

In other words, the rotation of the tire causes, for a pair of cavities and a given associated channel, the admission of air inside the pair of cavities and the associated channel, the compression of the air contained in the pair of cavities and the associated channel when they are closed by the ground in the contact area 124, then the expansion of the air contained in the pair of cavities and the associated channel when opening those by separating the tread from the ground.

This succession of admission / compression / expansion steps is at the origin of the characteristic noise of acoustic impression, sometimes called hissing or pumping noise resulting from the expansion of the compressed air contained in the pair of cavities and the channel associated.

We will now explain the principle of detecting the pumping noise emitted by the sound wear indicators 16 with reference to FIGS. 5A-E and 6A-E. These figures illustrate the theoretical pumping noise of the used passenger vehicle tire of FIG. 3 traveling at a substantially constant speed of 90 km / h.

FIGS. 5A-5C illustrate theoretical signals in the time domain and FIGS. 6A-6C illustrate theoretical signals in the frequency domain respectively obtained from each signal 5A-5C by Fourier transform. FIG. 5A illustrates a temporal signal Sτ, u _> called the unitary tap of a control 16.

This draw represents the amplitude (in Pa) of the noise emitted by the indicator 16 and takes the form of a damped sinusoid having a natural frequency fo, a maximum amplitude ao and a damping characteristic time t ₀ . In this case, f _o = 1200 Hz, at _o = 0.044 Pa and t ₀ = 0.001 s. The unitary frequency signal S _F , u of FIG. 6A takes the form of a Gaussian centered on the natural frequency f ₀ . It should be noted that the shorter the unit tap, the less the sine wave oscillates and the wider the frequency spectrum. Conversely, the longer the unit tap, the more the sine wave oscillates and the frequency spectrum is narrow. Thus, for a perfect undamped sinusoid, the Fourier transform of FIG. 5A would have the form of a Dirac peak of frequency f ₀ . FIG. 5B illustrates a temporal signal S _{T, D} of the witnesses 16 of the tire of FIG. 3. As the tire comprises eight witnesses 16, the temporal scroll signal takes the form of a Dirac comb of period T _T = 0.019 s and amplitude 1 having several peaks corresponding to the passage of each control 16 in the contact area.

The frequency of scroll signal S _{F, D} also takes the form of a Dirac comb characterized by elementary frequency components equidistributed, spaced a pitch F _T us = 1 / Tτus and amplitude F _T us = 1 / Tτus = 52.2. Note that the amplitude of the frequency signal S _F , _D is much greater than the amplitude of the time signal S _{T, D} - Figure 5C illustrates a total time signal Sτ, τ of the witnesses 16 corresponding to the convolution product of the temporal signal unit S _τ , u of Figure 5A and the scrolling time signal S _{T, D} of Figure 5B. The total time signal Sτ, τ thus takes the form of a succession of damped sinusoids of maximum amplitude substantially equal to 0.044 Pa. The total frequency signal S _F, τ corresponds to the product of the unit frequency signal

S _F, u of FIG. 6A and the scrolling frequency signal S _{F, D} of FIG. 6B. The total frequency signal S _F , τ thus takes the form of the unit frequency signal S _F , u sampled at the frequency F _T us and amplified by a factor F _T us with respect to the time unit signal S _τ , u- This amplification comes from of the frequency conversion of the temporal scroll signal S _{T, D} - In this case, the amplitude of the total frequency signal S _FT is substantially equal to 2.28 Pa.

In fact, the total signal S _τ , τ, S _FT of the indicators 16 is covered by a spurious signal B corresponding to the surrounding noise. Noise B was recorded in the passenger compartment of a BMW 318d vehicle traveling at 90 km / h equipped with standard tires. FIG. 5D illustrates a temporal signal B _τ corresponding to the noise measured inside the passenger compartment. The maximum amplitude of such a noise B _τ is substantially equal to 0.034 Pa. The maximum amplitude of the corresponding frequency signal B _F as represented in FIG. 6D is substantially equal to 0.348 Pa.

FIG. 5E illustrates a total time signal STT corresponding to the superposition of the total theoretical time signal S _τ , τ of FIG. 5C and of the time signal corresponding to the noise B ₁ - of FIG. 5D. The signal-to-noise ratio in the time domain is substantially equal to 1.04. FIG. 6E illustrates a total frequency signal SFT corresponding to the superposition of the total theoretical frequency signal S _FT of FIG. 6C and the frequency signal B _F of FIG. 6D corresponding to the measured noise. The signal-to-noise ratio in the frequency domain is substantially equal to 13.4. The analysis of these signals shows in particular the interest of working with signals in the frequency domain because they have a signal-to-noise ratio higher than the signals in the time domain. The detection of wear and the reliability of this detection are thus greatly improved. The total frequency signal SFT of FIG. 6E has several characteristics including in particular the predetermined distribution pattern, the pitch between each peak equal to F _T us, the maximum amplitude A of the signal and the number of elementary frequency components N of the signal.

F _T us is a function of the speed V of the tire 14, the number N _T us of equi-distributed witnesses 16 and the circumference C of the tire 14.

The maximum amplitude A is a function of the damping characteristic time t ₀ , the total volume V _T us of the cavities 120A, 120B and the associated channels 121 and the speed V of the tire 14. The maximum amplitude A is also a function temporal signal acquisition parameters comprising a sampling frequency Fe and an acquisition time T of the time signal.

The number of elementary frequency components N is a function of the bandwidth of the elementary tap of each witness 16 which itself depends on the damping characteristic duration t ₀ . N also depends on the frequency F _T us, the interaction of the total signal of the witnesses 16 and the signal corresponding to the noise and the frequency resolution Δf defined as the ratio of the sampling frequency Fe over the acquisition duration T .

FIGS. 7 to 16 show the various steps of a method for monitoring the condition of the tires 14 of the vehicles 12, according to first and second embodiments of the invention. FIG. 8 shows a total gross time signal S _{T, B} of an acoustic noise measured in the passenger compartment of a BMW 318d vehicle equipped with a used right front tire according to FIG. 3. The acquisition parameters are T = 1s, Fe = 8000 Hz. However, the characteristics of the tire 14 such as the number N _T us of controls 16, the circumference C of the tire 14, the total volume V _T us of the cavities 120A, 120B and associated channels 121, nor the speed V of the vehicle.

During a first step 90, the vehicle 12 is running on a floor. The rolling of the tires 14 of the vehicle 12 on the ground causes the emission of a raw temporal acoustic signal S _{T, B} likely to include the SF.T. During a next step 100, the acoustic signal comprising the surrounding noise and capable of understanding the sound pattern noise S _{F, T} is detected by the acoustic sensor 20 of the surveillance system 18 on board the motor vehicle. Then, during a pre-treatment comprising steps 101 to 306, the acoustic signal detected by the acoustic sensor 20 is processed to isolate the acoustic impression noise produced by all the witnesses 16 and to extract an acoustic impression therefrom feature. These pre-processing steps can be implemented permanently, periodically or on demand. The pre-treatment is carried out by the means 22 of the system 18.

In a step 101, a Fourier transform is applied to the total gross time signal S _{T, B} of FIG. 8 in order to obtain a total gross frequency spectrum S _{F, B} represented with a logarithmic frequency scale in FIG. 9.

During a step 102, a frequency domain Df of the raw spectrum S _{F, B} between 500 and 2500 Hz is then isolated, here between 1000 and 2000 Hz represented with a linear frequency scale in FIG.

Then, in a step 104, the noise is eliminated and optionally normalizes the raw spectrum S _{F, B} in the frequency domain Df. In this case, we define a filter curve passing through the minima of the raw spectrum S _{F, B} , then subtract the filter curve to the raw spectrum S _FB We obtain then the filtered spectrum shown in Figure 11. On this spectrum If filtered, a normalization can be carried out.

Finally, in a step 106, the elementary frequency components of the filtered spectrum of FIG. 11 having an intensity greater than a predetermined intensity threshold are isolated. As shown in FIG. 12, a net spectrum S _A is thus obtained comprising several elementary frequency components. The net spectrum or processed acoustic signal S _A is thus obtained from the total raw time signal S _{T, B} which has been processed. As a variant, the processing steps may not take place or else other additional filtering steps are implemented.

In this case, the processed acoustic signal S _A comprises 30 elementary frequency components, numbered from 1 to 30 in FIG. 12. If the tire is worn, the sound cavities emit a signal similar to the theoretical signal illustrated in FIG. 6C. In order to determine whether the tire is worn, that is to say if the lamps 16 emit the pumping noise, it is therefore necessary to determine whether the signal S _A comprises a signal similar to the theoretical signal S _FT emitted by the witnesses 16 . It has been seen that the unavailable characteristics define a reference frequency interval I at which the frequency F _T us is likely to belong. For a range of passenger tires, the circumference of which may vary between 1.3 m and 3 m, the number of witnesses may vary between 1 and 10 and the speed of the vehicle may vary between 10 km / h and 130 km / h, the frequency F _T us may vary in the range I between 1 and 278 Hz. For heavy type tires, the interval I is similar.

With reference to FIG. 12, during a step 200, all the pairs of elementary frequency components of the processed acoustic signal S _A are enumerated and a frequency difference separating the signals of each pair is determined from one another. For 30 elementary frequency components, we obtain 435 possible pairs. Only the couples for which the frequency difference separating them belongs to the interval I are retained. Thus, only 317 pairs have a frequency difference lying in the range 1-278 Hz. For example, there is shown in FIG. Table 1 below 40 pairs of elementary frequency components among the 317 and the corresponding frequency differences.

Table 1: Example of pairs of elementary frequency components and corresponding frequency differences Then, in a step 202, each frequency difference of each pair of elementary frequency components is classified in a family, referred to as a frequency difference family, defined by a family frequency difference interval σ _F. Each interval of family frequency difference is included in the interval I and is determined according to the interval I and a frequency resolution Δf of the acoustic signal S _A. In this case, we define 26 frequency difference families whose frequency difference intervals are given in Table 2 below and all less than or equal to 4 Hz. As a variant, all the intervals σ _F are less than or equal to 2 Hz.

Table 2: Families of frequency differentials

In what follows, we will only describe the family treatment No. 17 in a step 204, the treatment of the other families deducing mutatis mutandis. Among the 317 couples, the pairs whose frequency separation between them belongs to the family frequency difference interval No. 17, here at the interval 102-106 Hz, are determined as shown in Table 3.

Table 3: Couples of elementary frequency components of family # 17

Then, in a step 206, we list all the series of elementary frequency components comprising at least two consecutive elementary frequency components separated by a frequency difference Es, said serial, included in the range of family frequency difference σ _F. Each enumerated series is capable of forming at least a portion of the elementary frequency components of acoustic fingerprint. It is indeed a question of reconstituting the Dirac comb characteristic of the total signal of the witnesses 16. For the family n ° 17, one thus lists 3 series grouped in table 4 below. Each enumerated series comprises at least two elementary frequency components spaced two by two by a frequency difference included in the reference frequency interval I and more precisely in the family frequency difference interval O _F. Thus, each series of acoustic fingerprint is likely to represent a theoretical signal generated by the witnesses 16 with different values of the unknown characteristics that are the number N _T of witnesses 16, the circumference C of the tire 14, the total volume V _T us cavities 120A, 120B and associated channels 121, and the speed V of the vehicle.

Table 4: Series Listed in Family 1

Then, in a step 300, for each family, a serial reliability index Is of each enumerated series is determined according to predetermined first characteristics. These first predetermined characteristics comprise a dispersion D _E of the frequency difference between the elementary frequency components of the series, a ratio R between the acoustic signal and the noise, the number N _s of elementary frequency components in the series and the density D of the series, that is to say the ratio of the total number of elementary frequency components on the maximum number of elementary frequency components possible. In this case, for series 2, D _E = 0.5, R = 13.4, Ns = 8, D = 100%

Then, in a step 302, the index Is is calculated as a barycenter of R, D, N _s and D _E. The Is index of each series of each family is calculated. Then, we compare the indices Is of each enumerated series of each family. Here, the higher the index Is, the more likely the corresponding series is to represent the theoretical signal sought. The acoustic fingerprint series having the highest index Is is then selected. In this case, series No. 2 of family No. 17 has the index Is = 0.994 the highest of the three series identified.

Alternatively, after calculating the index Is of each enumerated series of each family, a series is selected in each of the 26 families according to the first predetermined characteristics. We thus obtain 26 selected series. Then, for each series selected in each family, a family index If is determined according to second predetermined characteristics of each selected series. The first and second characteristics may be identical or different. Finally, we select the series of acoustic fingerprint by comparing each family index If of the 26 selected series.

Although the No. 17 acoustic fingerprint series of family No. 17 is the most likely to be that corresponding to the noise emitted by the witnesses of all the series listed, it is not excluded that the first characteristics of this series remain insufficient to issue an alert for tire wear. Thus, in a step 304, an index of relevance Ip of each first characteristic, in this case the ratio R (FIG. 13), of the dispersion D _E of the frequency difference (FIG. 14) of the number N _s of elementary frequency components in the series (Figure 15) and the density D of the series. In these figures, each relevance index is defined by a sigmoid variable function of each first characteristic. For example, for a soundprint series having a ratio R = 7, the relevance index Ip associated with N is equal to 0.98. For a series of acoustic fingerprint having a dispersion D _E = 1, 5, the relevance index Ip associated with D _E is equal to 0.9. For a series of acoustic fingerprint comprising N _s = 4 elementary frequency components, the relevance index Ip associated with N ₃ is equal to 0.5. Then, during a step 306, a local confidence index is calculated from the indices Ip. The index Here is equal to the product of the indices Ip. As a variant, Here is equal to an arithmetic or weighted average of the indices Ip.

Then, during a step 308, information relating to the acoustic signal produced by the set of cookies 16 including the here local confidence index are transmitted to the remote server 30 by the transmission means 24 and the means of transmission. The server 30 is able to collect information relating to the condition of the tires of a whole fleet of vehicles, in particular of the two vehicles shown in FIG. 1. Then, a post-processing operation is carried out comprising a step 310 in which the server 30 proceeds with the processing of the received information, including here local confidence indices. This post-processing includes for example a storage in the database 34 information relating to the same vehicle over time.

The post-processing also includes a step 312 for analyzing the various information stored over time to establish a diagnosis of the state of the tire according to its past evolution. In fact, several successive acoustic signals are isolated in the frequency domain. For each acoustic signal, a series of acoustic fingerprints is selected. The signals of the acoustic fingerprint series S1-S11 selected from the successive acoustic signals as a function of time are graphically represented, as in FIG. It will be noted that the series S3, S8 and S9 do not appear. This may be due to noise, for example. The small frequency offsets from one series to another are due to small changes in the rate that changes the frequency F _T us between two adjacent elementary frequency components of each acoustic fingerprint series. A global confidence index Icg is determined from a continuity in time of the signals of the acoustic fingerprint series. Here, the position of the signals of one series is compared with the signals of the next series. The graphical representation of the signals is used, for example by means of image recognition algorithms to determine an index Icg of global confidence Icg. In another variant, the global confidence index Icg is determined from these local indices Here, for example by a sliding average of the last 5 local indices.

The diagnosis makes it possible, in particular, to identify recommendations for the future use of the tires of the vehicle. These recommendations may, for example, be a function of the driver's type of driving (sporty or regular driving, etc.) Thus, in the course of step 314, the remote server 30 sends a recommendation or recommendation to use the tires of the motor vehicle determined previously, for example a limit speed not to be exceeded, an instruction to inflate the tires or a recommendation of change of one or more tires. This recommendation may also include a tire model adapted to driving the driver. In the two variants set out above, if the index Icg is greater, in absolute value, than a predetermined overall threshold Sg associated with this overall index Icg, the server 30 issues a tire wear warning 14. This recommendation of use can be for example sent to the driver 28 of the motor vehicle on his mobile phone 26 via the transmission means 32 connected to the server 30. Thus, the driver 28 does not have to worry about the state its tires since it can be automatically warned actions to be taken on its tires in due time. The recommendation of use may also be accessible on a terminal 36 connected to the server 30 and searchable by a user 38 who is not necessarily the driver of the vehicle. The link of the terminal 36 to the server 30 may be a wired link but may also be a remote link, for example via the Internet network. The user 38 can access, via his terminal 36, the information concerning the condition of the tires of one or more motor vehicles 12 and the recommendations for use of these tires. Thus, the terminal 36 can centralize the information of a fleet of motor vehicles, which can be particularly useful in the case of a rental car company. The rental company may use this information to charge the driver of the vehicle according to the type of driving he has had. In fact, the mileage information available to date is incomplete since it does not allow the rental company to distinguish a driver from the sporty driving of a driver with a smooth ride. In a second embodiment of the method of the invention, the acoustic signal detected during step 100 is transmitted directly to the remote server 30 which itself proceeds to the pre-processing steps 101 to 306 and the post-processing 310-212. This second embodiment is interesting if the processing means 22 of the onboard system 18 have a limited computing capacity. FIGS. 17 and 18 show additional steps of the monitoring method according to a third embodiment. In this third embodiment, a step of reconstituting the series is carried out before the step of determining the index Is and after the step of enumerating the series in each family. These reconstitution steps can be implemented during the pre-treatment indifferently with the first and second embodiments. Indeed, it is possible that signals of an unlisted series have been altered, for example due to abnormal measurement conditions. Thus, a series, which would have been, under normal measurement conditions, enumerated and understood eight elementary frequency components P1-P8 as represented in FIG. 18 has been split into two series respectively comprising the elementary frequency components P1-P2 and the components elementary frequency P5-P8 as shown in FIG. 17. The elementary frequency components P3 and P4 were not detected. In order to reconstitute the entire series, after the enumeration step of the series in each family, at least one remote signal of one of the signals of the series is searched for a multiple frequency deviation of the family frequency difference interval. σ _F. It is found that the peak P5 is distant from P1 and P2 by a difference substantially equal to respectively four and three times the family frequency difference interval σ _F. Thus, the enumerated series consisting of the elementary frequency components P1-P2 is completed by the signals of the series consisting of the elementary frequency components P5-P8 which are distant from one of the signals P1-P2 of a frequency deviation multiple of the difference family frequency O _F.

The invention is not limited to the embodiments described above. Indeed, the method can also be implemented by knowing all or part of the parameters of the tire determining the frequency F _T- Thus, knowing the number N _T us of controls 16, especially because all the tires comprising this type of witnesses 16 has an identical number, the circumference C of the tire 14 and the speed V of the tire 14, for example from a GPS (Global Positioning System), it reduces the frequency reference interval and improves the robustness of detection. For example, knowing the speed V = 90 km / h with an accuracy of ± 5 km / h of a tire of circumference C = 1, 927 m including Nτus ⁼ 4, the reference frequency interval is between 49 Hz and 55 Hz. The comb is therefore all the more unique and easy to detect as the parameters of the tire are known precisely.

In addition, the method can be implemented with a tire comprising wear indicators having no pairs of cavities interconnected by a channel. transverse. Each wear indicator may therefore comprise a sound wear cavity arranged in a circumferential groove of the tread, each cavity opening radially outwardly of the tire and being shaped so as to be closed by the ground in a substantially watertight manner. during its passage in the area of contact of the tire with the ground.

Claims

A method of monitoring at least one tire (14) of at least one motor vehicle (12) comprising a tread, characterized in that the tread is shaped so that, beyond a predetermined radial wear threshold, the tread comprises an assembly of at least one wear indicator comprising a cavity called "sound" arranged in a circumferential groove of the tread, each cavity (120A, 120B, 121 ) opening radially outwardly of the tire (14) and being shaped so as to be closed by the ground (11 1) substantially sealingly as it passes through the contact area (124) of the tire (14) with the sol (111), the method comprising the following steps:

detection (100) by an acoustic sensor (20) embarked on the vehicle (12) with an acoustic signal (S _{F, B} ) capable of including an acoustic impression noise (S _F, τ) produced by the assembly during the rolling of the tire (14) on a ground beyond the predetermined radial wear threshold,

- Transmitting (308) to a remote server (30) not on board the vehicle (12) automobile, information relating to the acoustic signal (S _{F, B} ).

2. The method of claim 1, wherein, beyond the predetermined radial wear threshold, each indicator comprises at least a pair of first and second sound cavities (120A, 120B) and a channel (121) said "sound" connecting each sound cavity of the pair to each other, each first and second sound cavity (120A, 120B) being respectively arranged in a first and second circumferential groove (116A, 116B) of the tread (12 ), the channel (121) being formed in the tread (112), each cavity (120A, 120B) of the pair and the associated channel (121): opening radially outwardly of the tire (14),

- Being shaped so as to be closed by the ground (11 1) in a substantially sealed manner during their passage through the contact area (124) of the tire (14) with the ground (11 1).

The method of claim 2, wherein each first and second grooves (116A, 116B) having a predetermined depth when the tire

(14) is new, the tread (112) comprises at least two ribs (118) formed transversely to the bottom of each first and second groove (116A, 116B), of predetermined height when the tire (14) is new, substantially equal to the difference between the depth in which the distance separating the two ribs (1 18) is less than a predetermined distance so that, beyond the radial wear threshold predetermined, each cavity (120A, 120B) formed by each first and second groove

(116A, 1 16B) and delimited by the two ribs (1 18) is sound.

4. Method according to any one of claims 1 to 3, wherein the acoustic sensor (20) belongs to a phone embedded in the passenger compartment of the vehicle (12).

5. Method according to any one of claims 1 to 3, wherein the acoustic sensor (20) belongs to an electronic box embedded in the vehicle, for example a geolocation electronic box.

6. Method according to any one of the preceding claims, further comprising a pre-treatment (100-306) of the acoustic signal and for extracting the acoustic print noise.

7. The method of claim 6, wherein the pre-treatment (100-306) is implemented by a system (18) on board the motor vehicle, before the transmission step (308).

The method of claim 6, wherein the pre-processing (100-306) is implemented by the remote server (30) after the transmitting step (308).

9. Method according to any one of claims 6 to 8, the acoustic pattern noise (S _F , τ) comprising several elementary frequency components of acoustic fingerprint and the acoustic signal (S _{F, B} ) comprising several elementary frequency components in which, during the pre-treatment (100-306):

several series of elementary frequency components are enumerated, each enumerated series being capable of forming at least a part of the elementary frequency components of acoustic fingerprint;

one of the series listed is selected from a series, called a series of acoustic impressions; a so-called local confidence index (Here) of the acoustic fingerprint series is determined.

The method of any of claims 6 to 9, further comprising a post-processing (310-312) in which the remote server (30) diagnostics the condition of the tire (14) and its past evolution over time based on pre-treatment outcome (100-306).

The method of claim 10, wherein:

several acoustic signals (S _{F, B} ) are acquired which are successive in time and capable of understanding the acoustic impression noise (S _F , τ), each acoustic signal (S _FB ) comprising several elementary frequency components, for each acoustic signal (S _{F, B} ), selecting a soundprint series (S1-S11) and determining a local confidence index (Here) of the selected acoustic fingerprint series (S1-S11), and during the post-processing (310-312): a global confidence index (Icg) is determined from the local confidence indices (Here) of the acoustic fingerprint series (S1-S11),

if the index (Icg) of overall confidence is, in absolute value, greater or less than a predetermined threshold (Sg) associated with this index (Icg) of global confidence, an alert is issued of tire wear (14 ).

The method of claim 10, wherein:

several acoustic signals (S _{F, B} ) are acquired which are successive in time and capable of including the acoustic fingerprint noise (S _F , τ), each acoustic signal (S _{F, B} ) comprising several elementary frequency components,

for each acoustic signal (S _FB ), a series of acoustic fingerprint (S1-S11) is selected, and during the post-processing (310-312):

a global confidence index (Icg) is determined from a continuity in time between the elementary frequency components of each series (SI-S1 1) of selected acoustic fingerprint, if the index (Icg) ) of global confidence is, in absolute value, greater or less than a predetermined threshold (Sg) associated with this index (Icg) global confidence, it emits a tire wear warning (14).

The method according to any one of claims 10 to 12, for monitoring the tires (14) of a plurality of motor vehicles (12), in which a diagnosis of all the tires (14) of the plurality of vehicles (12).

14. A method according to any one of claims 10 to 13, wherein the remote server (30), according to the diagnosis, transmits to a user (28, 38) a recommendation of use of the tire.

15. Method according to the preceding claim, wherein the recommendation is transmitted by SMS or electronic message to the user (28).

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

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

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