Method for determining the wear condition of a tire sidewall for city buses

Description

[0001] The present invention relates to a tire for a heavy vehicle for urban use, more particularly an urban bus, and has as its object a method for determining the state of wear of a sidewall of such a tire.

[0002] Generally, a tire consists of two sidewalls, which are two lateral sections connecting a tread to two beads. The tread is positioned around the circumference of the tire and is designed to wear down as the tire is driven. The beads are designed to secure the tire to a rim.

[0003] More specifically, a sidewall usually comprises, from the outside to the inside of the tire, at least one outer layer of rubber material, in contact with atmospheric air and generally comprising, on an outer face, a set of recessed or raised markings, a carcass reinforcement comprising at least one layer of metallic or textile reinforcements coated in a rubber material, and at least one inner layer of rubber material, intended to be in contact with the inflation gas when the tire is mounted and inflated on its rim.

[0004] It is well known that urban bus tires are characterized by their thick sidewalls, meaning they have an outer layer of rubber material thick enough to allow for some abrasion before the carcass reinforcement is exposed to friction against curbs. Indeed, the sidewalls of an urban bus tire are regularly subjected to friction against curbs during the bus's stopping and starting maneuvers. This friction causes abrasion of the outer sidewall layer, and when this layer is completely worn, it leads to degradation of the carcass reinforcement, potentially resulting in a burst, which is detrimental to the safety of people near the urban bus.Therefore, it is essential to be able to estimate the remaining thickness of the outer sidewall layer during the use of the tire in order to decide either to turn the tire over on its rim, to expose the other sidewall, or to replace it.

[0005] Estimating the remaining thickness of the outer sidewall layer at a given date is most often done using a visual inspection of the sidewall to assess the presence or absence of at least one wear indicator formed within the sidewall. A wear indicator is generally a cavity worn into the outer sidewall layer from an outer face of the sidewall; this cavity can have a variable shape. Various embodiments of such a wear indicator have been described, by way of example, in documents KR 101981887B1, IT 2018 0000 3254 A1, US 2021 / 031569 A1, EP 3251958B1, JP 2014180904A, WO 2013118657A1, CN 201380726, JP 2003200717A and EP 0726173B1.

[0006] However, visually inspecting a wear indicator is not always easy due to insufficient contrast between the wear indicator and the surrounding sidewall, particularly in the case of direct visual inspection with the naked eye. Consequently, the presence or absence of a wear indicator often results from the observer's subjective assessment.

[0007] To reliably schedule tire rotations or replacements of worn sidewalls—essential for ensuring safety—every operator of urban bus tires needs precise monitoring of sidewall wear. This translates into an estimate of the remaining service life before the sidewall is completely worn. Poorly scheduled maintenance can also cause unexpected vehicle downtime, resulting in additional operating costs.

[0008] The inventors have therefore set themselves the objective, for a tire for heavy vehicles for urban use, in particular for urban buses, of proposing a method for determining the state of wear of a sidewall of such a tire, allowing to automate and make reliable the measurement of depth of the wear indicator at a given date, and therefore the estimation of the residual thickness of the outer layer of the sidewall, and to determine an estimate of the remaining operating time of the tire.

[0009] As defined in independent claim 1 in the appendix, the invention relates to a method for determining the wear condition of a tire sidewall for heavy vehicles used in urban environments: said sidewall comprising at least one wear indicator recessed relative to an outer sidewall face, in contact with atmospheric air, and visually contrasting with the outer sidewall face, said method for determining the wear state of the sidewall comprising: a step of capturing the state of the wear indicator, at a given date Ti, a step of determining the depth Pi of the wear indicator, at the given date Ti, a step of determining the average wear rate Vi of the wear indicator, at the given date Ti, a step of estimating the predicted maintenance date M of the tire, at which the depth of the wear indicator is zero, a step of providing at least one piece of information on the wear state of the sidewall and on the predicted maintenance date Mi of the tire.

[0010] The invention essentially aims to estimate the wear level of a city bus tire sidewall at any point during the tire's life, as well as the anticipated maintenance date, whether by rotating the tire onto the rim or replacing it, and to communicate this information to the vehicle operator to enable them to plan their intervention. The given date Ti for determining the sidewall wear corresponds to a scheduled inspection date, a specific mileage, or a given tread wear level. This determination takes place on a tire mounted on the vehicle and therefore concerns the sidewall positioned on the outside of the vehicle.

[0011] Advantageously, the wear indicator state capture step is a wear indicator image capture step using an automatic optical means.

[0012] An automatic optical device includes, but is not limited to, a camera or video camera system. Using such a camera system, placed at ground level and photographing the entire sidewall of the tire when the vehicle is stationary, allows for: To see all areas of the sidewall, therefore all wear indicators possibly present on the sidewall, and to take into account circumferential irregularities of the raking levels, To perform real distance / image calibrations thanks to the wheel dimension, To have a reduced analysis time.

[0013] According to a first embodiment, the step of taking the image of the wear indicator is carried out using an automatic optical means positioned perpendicular to the sidewall, such that a sidewall lighting system emits light rays contained within an angle, centered on a normal to the sidewall passing through the center of rotation of the tire, of at most equal to 60°.

[0014] In this case the camera system is positioned substantially perpendicular to the side in an angular sector of no more than 60°.

[0015] According to a second embodiment, the step of taking the image of the wear indicator is carried out using an automatic optical means positioned tangentially to the side, such that a lighting system of the side emits light rays contained in an angle forming, with a tangent to the outer face of the side, at most equal to 30°.

[0016] In this case, the camera system is positioned approximately tangentially to the sidewall within an angular sector of no more than 30° relative to the tangent to the sidewall. The camera system can be placed either on the front or rear side of the tread, with the tire mounted on the vehicle.

[0017] Advantageously, the wear indicator comprising means for determining its depth at the given date Ti, the step of determining the depth of the wear indicator is a step of observation and / or measurement of the means of the wear indicator.

[0018] A preferred embodiment of a wear indicator, including means for determining its depth at a given date Ti, is a wear indicator having a through-section on the outer flank face containing an inscribed circle whose diameter decreases continuously with flank wear, and having a non-smooth inner wall comprising a distribution of raised or recessed features relative to the inner wall, and / or a texture raised relative to the inner wall, such that said inner wall visually contrasts with the outer flank face. An inscribed circle is understood to be a circle tangent internally to the contour of the through-section. The diameter of the circle, i.e., the portion of the through-section it delimits, decreases continuously as the outer flank layer is eroded.

[0019] The inner wall of the wear indicator provides an advantageous visual contrast thanks to: either raised or recessed elements relative to the inner wall, such as, for example and not limited to, striations, or a raised texture such as, for example and not limited to, a "velvet" type texture made up of strands and / or blades, as described for example in documents WO 2007045425 and WO 2011036061, or a combination of the two preceding means.

[0020] These two types of features, present on the inner wall, have a dual function: on the one hand, to allow the determination, at any level of sidewall wear, of the residual depth of the hollow cavity constituting the wear indicator, i.e. the residual thickness of the outer sidewall layer in rubbery material in which the wear indicator is hollowed out, and, on the other hand, to guarantee a good contrast between the wear indicator and the portion of sidewall that surrounds it, and, consequently, a better visibility of the wear indicator guaranteeing a better reliability of the determination of the residual thickness of the outer sidewall layer.

[0021] Furthermore, the open section of any wear indicator has a contour that can, for example, be circular or multilobed, meaning it comprises at least two lobes. The shape of this contour can change depending on the wear of the sidewall: for example, a multilobed contour when new can become circular after a certain level of wear.

[0022] For this particular embodiment of wear indicator, the determination of its depth at the given date Ti is therefore based on the measurement of the dimensions of its through section, characterized in particular by the diameter of the circle inscribed in said through section, and / or the analysis of the shape of its through section, said dimensions and / or said shape of the through section being correlated to a depth of the wear indicator.

[0023] Advantageously, the step of determining the average wear rate Vi of the wear indicator is a step of calculating a ratio Vi=(Pi-Pr) / (Ti-Tr), Pi and Pr being the respective depths of the wear indicator (6) at the given date Ti and at a reference date Tr prior to Ti.

[0024] Knowing the average wear rate Vi of the tread wear indicator at a given date Ti allows us to determine the sidewall wear kinetics within the tire's usage context. This average rate is calculated between date Ti and a reference date Tr prior to Ti. The reference date Tr can be taken to be the initial date T0 of tire mounting on the vehicle, the tire being then in new condition, with an initial tread depth of P0.

[0025] Advantageously the step of estimating the expected maintenance date Mi of the tire, at which the depth of the wear indicator Pi is zero, is a step of determining the time ti, counted from the date Ti, at the end of which the depth of the wear indicator Pi is zero under the assumption of an average wear rate Vi of the wear indicator.

[0026] Knowing the average wear rate Vi of the wear indicator at the given date Ti allows, by extrapolation assuming this rate is constant, to determine the time required to reach zero depth of the wear indicator, i.e. complete abrasion of the outer layer of the sidewall, with generally a residual thickness of material between the bottom of the wear indicator and the carcass reinforcement for the protection of the latter.

[0027] Most often, the reporting stage includes a display step on a user interface. This display step provides a direct visual feedback to the user monitoring the tire, thus saving time.

[0028] Preferably the restitution step includes information relating to a depth Pi of the wear indicator at the given date Ti.

[0029] The restitution step advantageously includes information relating to a wear rate U=(P0-Pi) / P0 of the sidewall, at the given date Ti, P0 being the initial depth of the wear indicator, measured on the sidewall in the new condition and Pi being the depth of the wear indicator, measured on the sidewall at the given date Ti.

[0030] The feedback stage preferably includes information relating to an estimate of the expected maintenance date at which the depth of the wear indicator is zero.

[0031] Most often, the process of determining the wear level of a tire sidewall includes a step of tire identification. It is indeed necessary to correctly identify each tire individually in order to monitor the evolution of its sidewall wear and decide whether to rotate it onto the rim or replace it altogether. In fact, due to their respective manufacturing characteristics and their different positions on the vehicle, two tires generally have different sidewall wear patterns.

[0032] Preferably the process of determining the wear condition of a tire sidewall including a step of identifying the tire by recognizing an individualized marking or by reading an RFID (Radio Frequency Identification Data) identifier of the tire.

[0033] In one identification method, the tire's unique marking, consisting of a series of numbers, is typically captured. This marking can be highlighted, for example, by chalk markings that provide contrast with the rest of the tire. In a second identification method, an RFID (Radio Frequency Identification) tag, embedded in the tire, for example via an affixed label, contains tire identification data that can be read by a suitable device.

[0034] Advantageously, the method for determining the wear condition of a tire sidewall includes a step of identifying the wear indicator on the tire in question. Sidewall wear is not necessarily uniform around its entire circumference. Therefore, it can be useful to have several wear indicators on the same sidewall, distributed around its circumference, to determine an average sidewall wear: hence the importance of being able to identify each wear indicator and associate it with the measured wear characteristics.

[0035] Another advantage of the process for determining the wear condition of a tire sidewall is that it includes a step of transmitting captured information to a database. Having a remote database is indeed beneficial, avoiding the need to store too much information locally.

[0036] The invention also relates to a system for implementing the method of determining the wear state of a tire sidewall according to any one of the embodiments of the method previously described.

[0037] The system for implementing a method for determining the wear condition of a tire sidewall includes: means of capture, means of data transmission, means of analysis, a database.

[0038] Advantageously, the system for implementing a method for determining the wear condition of a tire sidewall includes means for displaying the wear condition of the sidewall.

[0039] Even more advantageously, in the system for implementing a process for determining the wear state of a tire sidewall, the means for capturing and / or displaying and / or transmitting data and / or analyzing data are implemented by an optoelectronic device.

[0040] The features of the invention will be better understood with the help of the figures 1 à 5C , not shown to scale: Figure 1 Schematic representation of the device for determining the wear condition of a tire sidewall mounted on an urban bus. Figure 2 Positioning of the automatic optical device (or imaging system) relative to the tire mounted on an urban bus axle, Figure 3 Perspective view of a tire for an urban bus, including a wear indicator. Figure 4 Cross-sectional view of a tire for an urban bus, including a wear indicator. Figure 5A Front view of a wear indicator having a circular open cross-section with concentric circular grooves raised relative to the inner wall, Figure 5B Front view of a wear indicator having a circular open cross-section with concentric circular grooves raised relative to the inner wall and a texture between the grooves, Figure 5C : Front view of a wear indicator having a through section with a multilobed contour (4 lobes).

[0041] There figure 1 This is a schematic representation of the device used to determine the wear condition of a tire sidewall mounted on a city bus. figure 1 This document describes in particular the step of capturing an image of a wear indicator 6, formed in the sidewall 2 of the tire 1, by an automatic optical means 9. The automatic optical means 9 is positioned near the sidewall 2, on the outer side of the vehicle, to capture the image of the wear indicator 6. The automatic optical means 9 is placed at ground level so as to photograph the entire sidewall of the tire when the vehicle is stationary. This positioning makes it possible, in particular, to see all areas of the sidewall, and therefore all wear indicators that may be present, and to take into account circumferential irregularities in the level of wear on the sidewall. Furthermore, calibrations of the actual distance to the image are possible with respect to the wheel size.In addition, the automatic optical means 9 allows the transmission of captured information (tire identifier, wear indicator identifier, wear indicator depth, predicted tire maintenance date) to a database.

[0042] There figure 2 The diagram illustrates the positioning of the automatic optical means (or imaging system) relative to the tire mounted on an urban bus axle. In a first embodiment, the automatic optical means 9 is positioned perpendicular to the sidewall 2, such that a lighting system for the sidewall 2 emits light rays within an angle N, centered on a normal to the sidewall 2 passing through the center of rotation of the tire 1, of at most 60°. In a second embodiment, the automatic optical means 9 is positioned tangentially to the sidewall 2, such that a lighting system for the sidewall 2 emits light rays within an angle R forming, with a tangent to the outer face of the sidewall 2, of at most 30°.In the latter case, the camera system can be placed either on the front side of the tread or on the rear side of the tread, the front and rear parts being defined in relation to the direction of travel V of the vehicle.

[0043] There figure 3 is a perspective view of a tire 1 for an urban bus including a wear indicator 6. The tire 1 includes two sidewalls 2 connecting a tread 3 intended to come into contact with a ground, respectively to two beads 4, intended to come into contact with a rim 5.

[0044] There figure 4 is a meridional cross-sectional view of a tire 1 for an urban bus including a wear indicator 6. This view represents half of a meridional section of the tire. The sidewall 2 includes, on an outer sidewall face 21 in contact with atmospheric air, a wear indicator 6 recessed in a layer of rubber material axially external to a carcass reinforcement 8 wrapped around each bead 4 mounted on the rim 5.

[0045] There figure 5A is a front view of a wear indicator 6 having a through section 61 with a circular contour with concentric circular striations 63 raised relative to the inner wall 62.

[0046] There figure 5B is a front view of a wear indicator 6 having a through section 61 with a circular contour combining concentric circular striations 63 raised relative to the inner wall 62 and a texture 64 between the striations.

[0047] There figure 5C is a front view of a wear indicator 6 having a through section 61 with a multilobed contour (4 lobes) and an inner wall 62.

[0048] The invention was studied more specifically in the case of a 275 / 70R22.5 X Michelin Incity tire, intended for use on an urban bus. For such a tire, the recommended inflation pressure is 9 bar, the recommended static load is 3550 kg, and the recommended maximum speed is 100 km / h.

[0049] Two types of wear indicators, formed in the sidewall of the tire under study, were analyzed using the method for determining the wear state of a sidewall according to the invention: a first type of wear indicator having a through-section with a circular contour, and a second type of wear indicator having a through-section with a four-lobed contour. In both cases, when the sidewall is new, the diameter of the circle inscribed in the through-section is 22 mm, and the depth of the wear indicator is 5 mm. The first type comprises circular grooves, spaced at a 2 mm pitch, with a height of 0.5 mm and a thickness of 5 mm, and / or includes a texture. The second type may or may not include a texture. An analysis of these wear indicators, at various levels of sidewall wear, according to the method according to the invention, has demonstrated the reliability of the determination of the depth of the wear indicator.

Claims

1. Method for determining the state of wear of a sidewall (2) of a tyre (1) for a heavy-duty vehicle for urban use: - said sidewall (2) comprising at least one wear indicator (6) which is recessed in relation to an outer face of the sidewall, is in contact with the atmospheric air, and visually contrasts with the outer face of the sidewall, - said method for determining the state of wear of the sidewall (2) being characterized by: - a step of sensing the state of the wear indicator (6) on a given date Ti, - a step of determining the depth Pi of the wear indicator (6) on the given date Ti, - a step of determining the mean rate of wear Vi of the wear indicator (6) on the given date Ti, - a step of estimating the provisional date of maintenance Mi for the tyre (1) when the depth of the wear indicator (6) will be zero, - a step of outputting at least one item of information about the state of wear of the sidewall (2) and about the provisional date of maintenance Mi for the tyre (1).

2. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to Claim 1, wherein the step of sensing the state of the wear indicator (6) is a step of acquiring an image of the wear indicator (6) via an automatic optical means (9).

3. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to Claim 2, wherein the step of acquiring an image of the wear indicator (6) is carried out using an automatic optical means (9) positioned perpendicularly to the sidewall (2) such that a system for illuminating the sidewall (2) emits light rays comprised within an angle (N) at most equal to 60° centred on a normal to the sidewall (2) that passes through the centre of rotation of the tyre (1).

4. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to Claim 2, wherein the step of acquiring an image of the wear indicator (6) is carried out using an automatic optical means (9) positioned tangentially to the sidewall (2) such that a system for illuminating the sidewall (2) emits light rays comprised within an angle (R) that forms at most equal to 30° with a tangent to the outer face of the sidewall (2).

5. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 4, said wear indicator (6) comprising means for determining its depth on the given date Ti, wherein the step of determining the depth of the wear indicator (6) is a step of observing and / or measuring the means of the wear indicator (6).

6. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to Claim 5, wherein the step of determining the mean rate of wear Vi of the wear indicator (6) is a step of calculating a ratio Vi=(Pi-Pr) / (Ti-Tr), with Pi and Pr being the depths of the wear indicator (6) on the given date Ti and on a reference date Tr prior to Ti, respectively.

7. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to Claim 6, wherein the step of estimating the provisional date of maintenance for the tyre (1), when the depth of the wear indicator (6) will be zero, is a step of determining the time ti, starting from the date Ti, after which the depth of the wear indicator (6) will be zero assuming a mean rate of wear Vi of the wear indicator (6).

8. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 7, wherein the outputting step comprises a step of displaying on an interface for a user.

9. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 8, wherein the outputting step comprises information relating to a depth Pi of the wear indicator (6) on the given date Ti.

10. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 9, wherein the outputting step comprises information relating to an amount of wear U=(P0-Pi) / P0 of the sidewall (2) on the given date Ti, with P0 being the initial depth of the wear indicator (6) measured on the sidewall (2) when it is new, and Pi being the depth of the wear indicator (6) measured on the sidewall (2) on the given date Ti.

11. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 10, wherein the outputting step comprises information relating to an estimation of the provisional date of maintenance when the depth of the wear indicator (6) will be zero.

12. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 11, comprising a step of identifying the tyre.

13. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 12, comprising a step of identifying the tyre by recognizing an individual marking or by reading an RFID (Radio Frequency Identification Data) identifier of the tyre.

14. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to either of Claims 1 and 13, comprising a step of identifying the wear indicator (6) on the identified tyre.

15. Method for determining the state of wear of a sidewall (2) of a tyre (1) according to any one of Claims 1 to 14, comprising a step of sending information that has been recorded to a database.