Method and sistem for detecting an aquaplane condition of a tyre mounted on a vehicle

Abstract

Method and apparats are provided for detecting an aquaplane condition of a tire (805) during the rolling of the tire on a rolling surface (515; 1205), wherein said tire comprises a tread band in which at least one circumferential groove (303-1 - 303-4; 1603-1 - 1603-4) is formed which is provided with at least one wear bar (305-1, 305-2; 1605-1, 1605-8), the method comprising: applying radially internally to the tire a tire monitoring device (810), the tire monitoring device comprising an electronic unit (900) comprising a sensor (930) configured for detecting physical quantities indicative of deformations experienced by the tire in the rolling on the rolling surface and for outputting measurements of said physical quantities, monitoring said measurements of said physical quantities during the rolling of the tire on the rolling surface and determining a passage of said monitoring device in correspondence of a contact zone (510) of the tire with said rolling surface.

Description

[0001] METHOD AND SISTEM FOR DETECTING AN AQUAPLANE CONDITION OF A TYRE MOUNTED ON A VEHICLE

[0002] DESCRIPTION

[0003] Background of the invention

[0004] Field of the invention

[0005] The present invention relates to a method and a system for detecting an aquaplane condition of a tyre mounted on a vehicle. The present invention also relates to a method of controlling a vehicle that exploits the detection of the aquaplane condition of one or more tyres mounted on the vehicle. The present invention further relates to a vehicle equipped with tyres and comprising a system for detecting an aquaplane condition experienced by one or more of the tyres mounted on the vehicle. Overview of the related art

[0006] In the context of this document, by “aquaplane” it is meant the condition in which a tyre, mounted on a moving vehicle, loses directionality due to the presence of a layer of water between the tyre and the ground (or, more generally, the rolling surface of the tyre, typically the road surface), so that even if the driver of the vehicle on which the tyre is mounted tries to modify the trajectory of the vehicle itself, the tyre continues according to the direction substantially imposed by the inertia without changing its trajectory.

[0007] The aquaplane condition occurs when the drainage and expulsion of water in the channels and / or in the grooves of the tread, in correspondence with the footprint region, becomes insufficient, so much so that the tyre loses contact, totally or partially, with the rolling surface.

[0008] The term "tread", or "tread surface", means the radially external surface of the tyre, intended for contact with the rolling surface of the tyre, which in use is represented by the road surface. The tread surface is defined on a "tread band" of the tyre on which a plurality of grooves with a circumferential and / or transverse pattern are typically defined, which define said channels and / or grooves and which delimit a corresponding plurality of blocks which, altogether, define the "tread pattern" of the tyre.

[0009] In this document the terms “radially internal”, “radially external”, “radial” are used with reference to the axis of rotation of the tyre. In particular, by "radial" it is meant a direction substantially perpendicular to the axis of rotation of the tyre.

[0010] The term "circumferential" is used with reference to the direction of the annular development of the tyre, i.e., the rolling direction of the tyre, which corresponds to a direction lying on a plane coinciding with or parallel to the "equatorial plane" of the tyre, i.e., the center plane perpendicular to the axis of rotation of the tyre. The term “transverse” is used to refer to the direction transverse to the equatorial plane of the tyre.

[0011] In the presence of aquaplaning, the tyre is therefore lifted from the road surface in correspondence with the contact region (footprint region) of the tyre with the road surface itself, with consequent loss of directionality and traction of the tyre itself.

[0012] More specifically, in the presence of significant layers of water on the road surface and / or at high rolling speeds of the tyre, the tyre tends to deform compared to a condition of normal interaction between the tyre and the rolling surface. This deformation causes in particular a reduction in the contact area in the contact region, and a consequent reduction in adherence between the tyre and the rolling surface.

[0013] The phenomenon of aquaplane can be extremely dangerous, because in such conditions the driver can essentially lose control of the vehicle, no longer being able to follow the road, avoid obstacles, etc.

[0014] Summary of the invention

[0015] It is known in the art to equip vehicle tyres (in particular for some types of tyres such as, but not only, those for high performance levels) with monitoring devices which, mounted on the tyres themselves, for example positioned inside the tyres and in particular, but not limited to, on the radially internal surface of the tyre opposite to the tread, are configured and operable to detect characteristic physical quantities of the tyre, in order to allow a substantially real-time control of the operation and conditions of the tyre itself. Among the characteristic physical quantities of the tyre that such monitoring devices are configured to detect, there are the deformations undergone by the tyre while rolling on a surface, such as the road surface.

[0016] Such monitoring devices are configured to periodically communicate with the instrumentation available on board the vehicle on which the tyres are mounted, so that all useful pieces of information can be provided to the driver and / or the vehicle control systems, for example to activate or better adjust alarm and / or control systems for vehicle dynamics, braking, etc.

[0017] The tyre monitoring devices typically include an electronic unit, in turn comprising at least one sensor capable of measuring / identifying the deformations undergone by the tyre during rolling, such as for example an accelerometer, a strain gauge, a piezoelectric sensor etc. (in the following, such a sensor will be also referred to as the "accelerometer", it being understood that similar considerations also apply when other sensors capable of measuring / identifying the deformations undergone by the tyre during rolling are used). This sensor is, for example, capable of measuring the radial acceleration or other physical quantity descriptive of the deformations of the tyre during rolling on the road surface (for example the tangential acceleration - also called circumferential acceleration -, and / or the lateral acceleration). From the time profile of the acceleration, for example the radial acceleration, measured by the sensor (hereinafter also called “sensor signal” or “signal”) it is possible for example to identify the width, and estimate the length, of the area of contact of the tyre with the rolling surface: in fact, when the monitoring device, mounted on the tyre and during the rolling of the tyre on the rolling surface, passes in correspondence with the contact area between the tyre and the rolling surface, the measured radial acceleration drops rather suddenly from a substantially high value (in absolute value) which depends on the angular rotation speed of the tyre, to a substantially zero value.

[0018] During tests conducted on various tyres of different brands and types, the Applicant observed that, in the tests conducted on wet surfaces (concisely, in the wet), characteristic trends of the signal were present in the radial acceleration profile obtained from the accelerometer measurements (similar considerations apply for the (tangential acceleration and, to a certain extent, also for the lateral acceleration), such as for example “peaks” (“spikes”) additional to the expected trend of the signal characteristic of the monitoring device approaching to, transit across and moving away from the contact area.

[0019] Fig. 1A shows a diagram showing the trend, or profile, of the radial acceleration measured by the accelerometer of a monitoring device mounted on a tyre during a test conducted by the Applicant. In the diagram of Fig. 1A, the abscissa axis represents the time axis t and the ordinate axis reports the values Ar of the radial acceleration measured by the accelerometer, in arbitrary units. The test was conducted in a bath filled with water forming a layer approximately 6 mm high on the bottom of the bath, to simulate wet road conditions, and the tyre was rotated at an angular speed corresponding to a linear speed of 105 km / h (a speed which, as known to the Applicant, with a similar layer of water, is such as to induce the phenomenon of aquaplaning on the tyre being tested). In particular, Fig. 1A shows two portions 100a and 100b of the measured radial acceleration profile, spaced in time, around two respective consecutive passages of the monitoring device in correspondence with the contact area of the tyre with the rolling surface. The two regions indicated with 105 of the two portions 100a and 100b of the acceleration profile, in which the measured radial acceleration has values (in arbitrary units) around a value Ar*, correspond to the two transits of the monitoring device in correspondence with the contact area of the tyre with the rolling surface. As can be observed, the measured radial acceleration has three spikes 110a, 110b and 110c in succession, preceding the regions 105. Fig. IB shows a diagram showing the profile of the radial acceleration measured by the accelerometer of the monitoring device mounted on the tyre, as a result of a test conducted on the same tyre as that of the test in Fig. 1A, equipped with the same monitoring device, rotated at an angular speed corresponding to a linear speed of approximately 100 km / h, but on a dry rolling surface: as it is possible to see, in the two portions 100c and lOOd, spaced in time, of the measured radial acceleration profile around the two respective consecutive passages of the monitoring device in correspondence with the contact area of the tyre with the rolling surface (regions 105 of the two portions 100c and lOOd of the acceleration profile, in which the measured radial acceleration has values, in arbitrary units, around a value Ar**), the presence of the spikes 110a, 110b and 110c is not detected.

[0020] It is possible to observe that the peaks or spikes 110a, 110b and 110c represent characteristic trends of the signal, additional to the expected trend of the signal characteristic of the approaching, transit and moving away of the monitoring device to / across / from the contact area of the tyre with the rolling surface. In particular, the spikes 110a, 110b and 110c are characterized by their brevity in time, compared to the time duration of the regions 105 of the profile corresponding to the transits of the monitoring device in correspondence with the contact area of the tyre with the rolling surface; the temporal brevity of the spikes 110a, 110b and 110c translates into their corresponding reduced angular amplitude (in a representation of the profile of the radial, or tangential, acceleration, measured as a function of an angle that describes one revolution of the tyre). The spikes 110a, 110b and 110c are also characterized by their repeatability, both for each revolution of a tyre and on different tyres. Furthermore, the spikes 110a, 110b and 110c are distinguished from oscillations 115 present in the accelerometer signal, which are due to tyre oscillations: these oscillations in the accelerometer signal are significantly smaller than the spikes 110a, 110b and 110c.

[0021] The observation of the radial acceleration profiles obtained by conducting the aforementioned tests, as well as further and similar tests on tyres of different types and different brands, led the Applicant to hypothesize that the presence of such characteristic trends, i.e., of spikes similar to the spikes 110a, 110b and 110c in the radial acceleration profile of Fig. 1 A could be due to the rolling condition of the tyres on a wet surface.

[0022] Then, observing the diagram in Fig. 2 (time axis t reported in abscissae and radial acceleration Ar in ordinates, in arbitrary units), which corresponds to Fig. 1A both with regards to the tyre being tested and for the monitoring device that equipped it, and, again, for the conditions in which the test was carried out (bath filled with water forming a layer approximately 6 mm high, tyre rotated at an angular speed corresponding to a linear speed of approximately 120 km / h, speed which, as known to the Applicant, with a similar layer of water is such as to induce the phenomenon of aquaplaning on the tyre being tested), but in which the whole trend, or profile, of the radial acceleration measured by the sensor on a tyre in a relatively longer period of time is plotted, the Applicant has found that, between two consecutive regions 205 corresponding to two transits of the monitoring device in correspondence with the contact area of the tyre with the rolling surface, eight spikes 210a, 210b, 210c, 210d, 210e, 210f, 210g and 210h have been detected.

[0023] The observation that the characteristic trends in the accelerometer signal, in the form of spikes, appeared only in the tests on wet surfaces, and that the number of spikes, eight as it has been seen, was equal to the number of "wear indicators", also eight in number (more precisely, eight transverse rows, as explained below), which were provided on the tyre subjected to testing, led the Applicant to hypothesize that these characteristic trends or spikes in the profile of the radial acceleration measured by the accelerometer were in some way related to the interaction between the wear indicators and the wet bottom of the rolling surface (bottom of the bath or road surface).

[0024] As known to those skilled in the art, it is known to provide, for the purposes of monitoring the wear of tyres during their use, wear indicators or "wear bars" in tyres ("Tread Wear Indicator" or "TWI", in jargon) positioned in grooves in the tyre tread.

[0025] The wear bars provided in the grooves of the tyres are useful in providing a visual indication of the degree of tread wear.

[0026] The provision of wear indicators on tyres is regulated by Regulation N. 30 of the United Nations Economic Commission for Europe (UNECE), “Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers”, in which the «wear indicators» are defined as projections placed inside the tread grooves (in particular in the 'principal grooves', i.e., the wide grooves located in the central zone of the tread) intended to visually indicate the degree of wear of the tread. According to this Regulation, a tyre must have at least six transverse rows of wear indicators (except for tyres of dimensions suitable for mounting on rims with a nominal diameter less than or equal to 12, in which four rows of indicators are permitted), distributed in such a way as to be approximately equidistant in the principal tread grooves; these wear indicators must not be confused with the rubber reliefs existing between the grooves or tread blocks. The wear indicators must indicate, with a tolerance of +0.60 / -0.00 mm, that the residual depth of the tread grooves is no longer greater than 1.6 mm. The height of the wear indicators is determined by measuring the difference, starting from the tread surface, between the depth of the grooves measured at the top of the wear indicators and the depth of the grooves measured immediately after the junction at the base of the wear indicators.

[0027] Based on the intuition that the characteristic trends, in the form of spikes, in the profile of the radial acceleration measured by the accelerometer of the tyre monitoring device during the tests on wet surfaces could be correlated to the interaction between the wear indicators, provided on the tyres in compliance with the aforementioned Regulation, and the wet bottom of the rolling surface, the Applicant wanted to counter-prove this hypothesis. To this end, the Applicant manually removed initially some of the wear indicators, then all the wear indicators present on the tyre being tested, and repeated the test on wet surfaces described in relation to Fig. 1A and Fig. 2.

[0028] Fig. 3A schematically shows a portion of the tread surface 301 of the tyre 300 used to conduct the tests. Circumferential grooves are formed in the tread surface 301, in particular four grooves 303-1, 303-2, 303-3 and 303-4. As required by the aforementioned Regulation, wear bars were formed in the grooves 303-1, 303-2, 303- 3, 303-4. In particular, Fig. 3A shows two transverse rows of four wear bars, one wear bar in each groove 303-1, 303-2, 303-3, 303-4: a first row of four wear bars 305-1 and a second row of four wear bars 305-2. It is underlined that Fig. 3 A shows only an exemplary, preferred but not limiting, arrangement of the wear bars: the wear bars made in the different grooves of a tyre do not necessarily have to be aligned transversely to the circumference of the tread surface 301 of the tyre itself: the wear bars made in the different grooves can be unaligned. In particular, in the case where a tyre has three or more grooves, as in the example of Fig. 3A, the wear bars may comprise groups of wear bars that repeat in two or more circumferentially distant positions along the tread, such as for example the two groups of wear bars 305-1 and 305-2 in Fig. 3A. In each group, the wear bars can all be aligned with each other transversally to the circumference of the tread surface, or they can all be unaligned, slightly offset from each other, or some wear bars in the group can be aligned with each other and unaligned from the others wear bars of the group, in particular the wear bars of a group can be arranged alternately with respect to a line transverse to the tread.

[0029] Fig. 3B shows the tyre 300 in side view. The (positions of) the eight transversal rows 305-1, 305-2, 305-3, 305-4, 305-5, 305-6, 305-7 and 305-8 of wear bars provided on the tyre are schematically indicated, being for example angularly equispaced of angles of 45° along the circumference of the tread surface 301.

[0030] As mentioned above, to counter-check the hypothesis that the spikes in the radial acceleration profile measured during the tests on wet surfaces could be related to the interaction between the wear indicators and the wet surface, the Applicant manually removed some of the wear bars, and notably the (all four) wear bars of rows 305-2, 305-4, 305-6 and 305-8. In other words, the four wear bars of alternating rows of wear bars along the circumference of the tread surface 301 were manually removed.

[0031] Performing the tyre test before, Fig. 4A, and after, Fig. 4B, the removal of the four rows 305-2, 305-4, 305-6 and 305-8 of wear bars, in the same conditions (bath filled with water forming a layer about 1.5 mm high, tyre rotated at an angular speed corresponding to a linear speed of about 120 km / h, which, as known to the Applicant, with a similar layer of water, is such as to induce the aquaplaning phenomenon on the tyre being tested) and detecting the radial acceleration measurements provided by the accelerometer of the monitoring device that equipped the tyre, from the comparison between the portion of the radial acceleration profile measured by the accelerometer when all the (eight rows of) wear bars were present and the portion of the radial acceleration profile measured by the accelerometer after removal of the four alternating rows 305-2, 305-4, 305-6 and 305-8 of wear bars, it can be observed that one of the previously observable spikes, namely the spike 110b, is no longer visible.

[0032] The Applicant then manually removed the remaining four rows 305-1, 305-3, 305-5 and 305-7 of wear bars, thus eliminating all the wear bars of the tyre 300, and repeated the test: the result is shown in Fig. 4C, from which it can be seen that none of the previously observable spikes 110a, 110b and 110c is present any longer: the trend of the accelerometer signal returns to be substantially similar to that observable in the tests on dry surfaces.

[0033] This supports the hypothesis that the spikes in the radial acceleration profile measured by the accelerometer during the tests on wet surfaces are related to the interaction between the wear indicators and the wet surface of the rolling surface.

[0034] As a further proof of this hypothesis, the Applicant then carried out some tests with a tyre equipped with two different tyre monitoring devices, each equipped with a respective sensor (for example an accelerometer) capable of measuring / identifying the deformations experienced by the tyre during rolling. In the tyre tested, the two monitoring devices were placed in circumferentially different positions, spaced from each other by a certain angle a, in particular an angle of approximately 10°, as schematically shown in Fig. 5A and Fig. 5B. In these figures, reference 500 identifies the tyre being tested, references 505-1 and 505-2 identify the first and second tyre monitoring devices mounted on the tyre 500 and reference 510 identifies the contact area of the tyre 500 with a rolling surface 515. The two monitoring devices 505-1 and 505-2 were mounted to the tyre 500 at an angular distance a, of 10° from each other. The arrow R in Fig. 5B indicates the direction of rotation of the tyre.

[0035] Fig. 6A and Fig. 6B are two diagrams showing the profile of the radial acceleration Ar measured by the accelerometers of the two tyre monitoring devices, plotted in ordinate in arbitrary units, as a function of an angle, plotted in abscissa (in degrees, indicated with “°” in the figures) ranging from 0° to 180° and which corresponds to half a revolution of the wheel (i.e., of the tyre), centered (at 90°) on the center of the contact area 510 of the tyre 500 with the rolling surface.

[0036] In the diagram of Fig. 6A, a local system is assumed as a reference system, centered on (the center of) the contact area 510 of the tyre 500 with the rolling surface; the regions 105' and 105" in the two profiles, which correspond to the transit of one and the other tyre monitoring devices in correspondence of the contact area of the tyre with the rolling surface, are consequently substantially overlapped. It can be observed how the characteristic trends in the accelerometer signal, represented by the spikes 110b', 110c' observable in the acceleration profile measured by the sensor of the first monitoring device 505-1, are spaced 10° apart from the spikes 110b", 110c" observable in the acceleration profile measured by the sensor of the second monitoring device 505-2. This is consistent with the mutual distance between the two monitoring devices, from which it follows that they are placed at different distances from the wear bars formed on the tyre.

[0037] In Fig. 6B, a global system is instead assumed as the reference system. The contact area of the tyre with the rolling surface is no longer forced to be centered on 90°. It is observed that in this case the regions 105' and 105" of the two radial acceleration profiles measured by the two sensors, which correspond to the transit of the two monitoring devices in correspondence with the contact area 510 of the tyre 500 with the rolling surface 515, are out of phase by approximately 10°, i.e., by the angular distance between the two monitoring devices 505-1 and 505-2, while the spikes 110b', 110c' are substantially overlapped.

[0038] Furthermore, the Applicant repeated the tests on two identical tyres, of the same brand and of the same model / type, mounting a different monitoring device on each, in the same position. For example, the two tyre monitoring devices are two different devices chosen from those described in the following documents in the name of the same Applicant: WO 2013 / 098711 Al, WO 2015 / 144770 Al, WO 2018 / 065846 Al, WO 2019 / 123118 Al, WO 2020 / 026281 Al, WO 2020 / 026282 Al. The tests were conducted by rotating the tyres at an angular speed corresponding to a linear speed of approximately 110 km / h on a surface of approximately 6 mm of water (a speed which, as known to the Applicant, with a similar layer of water, is such as to induce the phenomenon of aquaplaning on the tyres being tested). The result of the tests is shown in the diagram of Fig. 7, which, like the diagrams of Fig. 6A and Fig. 6B, reports in ordinate the radial acceleration Ar measured by the accelerometer (or other tyre deformation sensor), in arbitrary units, as a function of an angle, reported in abscissa (in degrees, indicated with “°” in the figures) ranging from 0° to 180°. The solid line 705 refers to the acquisition of a first tyre monitoring device, the dotted line 710 refers to the acquisition of a second tyre monitoring device. It is possible to see that, beyond the differences in absolute value of the measured radial accelerations, the radial acceleration profiles measured by the two different monitoring devices are substantially superimposable.

[0039] The observation of the results of all the tests conducted confirmed to the Applicant that the presence of the wear bars on the tyres is responsible, and determines, when the tyre is rolling on a wet surface, the appearance of characteristic trends, represented by spikes in the profiles of radial acceleration measured by the accelerometer of the monitoring device mounted on the tyre.

[0040] The Applicant has therefore surprisingly found that, from the analysis of the radial acceleration signal (similar considerations also apply to the tangential acceleration and, to a certain extent, to the lateral acceleration) provided by an accelerometer (or other sensor) capable of measuring / identifying the deformations undergone by the tyre during the rolling of a tyre monitoring device applied to a tyre, it is possible to derive useful information to detect, and therefore to establish, whether the tyre is experiencing an aquaplane condition.

[0041] The characteristic trends, in the form of spikes, in the measured radial acceleration profiles, which are generated by the presence of the wear bars when the tyre experiences an aquaplane condition, cannot be confused with the regions of the acceleration profiles corresponding to the transits of the monitoring device in correspondence with the contact area of the tyre with the rolling surface, since, as can be seen from the diagrams commented above, the spikes, even at relatively high speeds, are substantially narrower, therefore shorter, than the regions corresponding to the transits in correspondence with the contact area with the rolling surface. The spikes generated by the wear bars in aquaplane conditions are therefore discernible, even from the oscillations in the accelerometer signal caused by tyre oscillations, which are significantly smaller than the aforementioned spikes.

[0042] According to an aspect of the present invention, a method is provided for detecting an aquaplane condition of a tyre mounted on a vehicle during the rolling of the tyre on a rolling surface, wherein said tyre comprises a tread band in which at least one circumferential groove is formed which is provided with at least one wear bar.

[0043] The method comprises applying radially internally to the tyre, in a position opposite to said tread band, a tyre monitoring device. The tyre monitoring device comprises an electronic unit comprising a sensor configured for detecting physical quantities indicative of deformations experienced by the tyre in the rolling on the rolling surface and for outputting measurements of said physical quantities.

[0044] The method comprises monitoring said measurements of said physical quantities during the rolling of the tyre on the rolling surface.

[0045] The method comprises determining, based on said monitoring said measurements of said physical quantities, a passage of said tyre monitoring device in correspondence of a contact region of the tyre with said rolling surface.

[0046] The method comprises determining an aquaplane condition experienced by the tyre from the detection, in said measurements of physical quantities, of a characteristic trend in a region preceding and / or following the passage of said tyre monitoring device in correspondence of the contact region of the tyre with the rolling surface; said characteristic trend is correlated with an interaction of said at least one wear bar with a water layer present on said rolling surface.

[0047] According to another aspect of the present invention, a system is provided which is configured for detecting an aquaplane condition of a tyre during the rolling of the tyre on a rolling surface, wherein said tyre comprises a tread band in which at least one circumferential groove is formed which is provided with at least one wear bar.

[0048] The system comprises a tyre monitoring device applied radially internally to the tyre, in a position opposite to said tread band. The tyre monitoring device comprises an electronic unit comprising a sensor configured for detecting physical quantities indicative of deformations experienced by the tyre in the rolling on the rolling surface and for outputting measurements of said physical quantities. The system comprises at least one processing unit comprising software modules configured for:

[0049] - monitoring said measurements of said physical quantities during the rolling of the tyre on the rolling surface, and

[0050] - determining, based on said monitoring said measurements of said physical quantities, a passage of said tyre monitoring device in correspondence of a contact region of the tyre with said rolling surface.

[0051] The processing unit comprises software modules configured for determining an aquaplane condition experienced by the tyre from the detection, in said measurements of physical quantities, of a characteristic trend in a region preceding and / or following the passage of said tyre monitoring device in correspondence of the contact region of the tyre with the rolling surface, said characteristic trend being correlated with an interaction of said at least one wear bar with a water layer present on said rolling surface.

[0052] The present invention further relates to a vehicle provided with tyres and comprising a system according to the previous aspect of the invention, for detecting an aquaplane condition experienced by one or more of the tyres mounted on the vehicle.

[0053] The present invention, in one or more of the aspects thereof previously set forth, may comprise one or more of the following optional features.

[0054] Preferably, said characteristic trend which is detected from said measurements of physical quantities comprises at least one spike in a region that precedes and / or follows the passage of said tyre monitoring device in correspondence of the contact region of the tyre with the rolling surface, said at least one spike being correlated with said interaction of said at least one wear bar with the water layer present on said rolling surface.

[0055] Advantageously, as discussed in the foregoing, the Applicant has found that when a tyre experiences an aquaplane condition, peaks or spikes can be observed in the measurements of the detected physical quantities, said peaks or spikes being well distinguishable from the other trends normally detectable in the measurements, when no aquaplane condition is experienced.

[0056] Preferably, the tyre monitoring device is applied to the tyre in a position immediately preceding said at least one wear bar in a sense of rotation of the tyre.

[0057] Advantageously, the Applicant has found that, with such an arrangement of the monitoring device, the characteristic trend correlated with an interaction of said at least one wear bar with the water layer present on said rolling surface, particularly said at least one spike, does not interfere with the determination of the passage of the tyre monitoring device in correspondence of the contact region of the tyre with the rolling surface, and results more easily detectable.

[0058] In particular, in embodiments of the present invention, said at least one circumferential groove is provided with at least a first wear bar and a second wear bar which are circumferentially consecutive, the second wear bar following, in the sense of rotation of the tyre, the first wear bar. The tyre monitoring device is preferably applied to the tyre in a position within a semi-region, between the first and the second wear bars, which is contiguous to the second wear bar and which extends circumferentially substantially from a half of a distance from the first wear bar to the second wear bar.

[0059] Preferably, the tyre monitoring device is applied to the tyre in a position within a sub-semiregion, between the first and the second wear bars, which is contiguous to said second wear bar and which extends circumferentially substantially 1 / 6 of said distance from the first wear bar to said second wear bar.

[0060] In embodiments of the present invention, the tyre comprises at least two circumferential grooves each comprising at least one respective wear bar, the wear bars of the at least two circumferential grooves being aligned in a direction transversal to the circumferential grooves.

[0061] In embodiments of the present invention, the tyre comprises a plurality of circumferential grooves, each comprising a respective plurality of wear bars, the plurality of wear bars of said circumferential grooves being arranged in groups of wear bars in corresponding circumferential positions, the wear bars of each of said groups being transversally aligned or unaligned or transversally alternated.

[0062] Brief description of the figures

[0063] Features and advantages of the present invention, both those discussed in the previous section and other, further advantages and features, will appear more clearly by reading the following detailed description of exemplary and non-limitative embodiments of the present invention; for a better intelligibility, the following description should be read making reference to the annexed figures, wherein:

[0064] Fig. 1A shows, in the form of a diagram, the trend, or profile, of the radial acceleration measured by a sensor of a monitoring device mounted on a tyre during a test conducted by the Applicant on a wet surface, in the zones of approaching, transit and moving away to / across / from the contact area between the tyre and the rolling surface of the portion of the tyre to which the monitoring device is attached;

[0065] Fig. IB shows, in diagram form, the profile of the radial acceleration measured during a test conducted by the Applicant on a dry surface on the same tyre with the same monitoring device as in Fig. 1A;

[0066] Fig- 2 shows, in diagram form, the radial acceleration profile measured by the sensor of the tyre referred to in Fig. 1A during a test on a wet surface, in a wider time interval than the diagram in Fig. 1A;

[0067] Fig. 3A schematically shows two rows of wear bars provided on a tyre;

[0068] Fig. 3B schematically shows an arrangement of eight rows of wear bars provided on a tyre;

[0069] Fig. 4A is a diagram similar to that of Fig. 1A, referring to a test on a wet surface of the tyre of Fig. 3B, with all the eight rows of wear bars;

[0070] Fig. 4B shows the effect of manually removing alternate rows of wear bars from the tyre in Fig. 3B, when subjected to the same test;

[0071] Fig. 4C shows the effect of manually removing all the wear bars from the tyre in Fig- 3B, when subjected to the same test;

[0072] Fig. 5A schematically shows a portion of a tyre equipped with two monitoring devices spaced apart along the circumference of the tyre;

[0073] Fig. 5B shows the tyre of Fig. 5A in elevation, with the two monitoring devices shown schematically;

[0074] Fig. 6A and Fig. 6B show, in diagram form, radial acceleration profiles measured by two sensors of two tyre monitoring devices mounted on a same tyre at different angular positions along the circumference of the tyre, during a test carried out by the Applicant on a wet surface;

[0075] Fig- 7 shows, in diagram form, the radial acceleration profile measured during a test on a wet surface of two identical tyres equipped with different monitoring devices;

[0076] Fig. 8 schematically shows a portion of a tyre equipped with a tyre monitoring device provided with a sensor capable of detecting deformations undergone by the tyre during rolling on a surface, in particular a sensor capable of measuring the radial acceleration or tangential acceleration;

[0077] Fig- 9 shows a diagram of a tyre monitoring device according to an embodiment of the present invention;

[0078] Fig. 10 shows a schematic of a vehicle including a tyre monitoring system and a vehicle control system in accordance with an embodiment of the present invention;

[0079] Fig- 11 shows a diagram of a vehicle control unit according to one embodiment of the present invention;

[0080] Fig. 12A - Fig. 12D schematically show a possible physical explanation of the effect of the wear bars on the radial acceleration measured by the sensor;

[0081] Fig. 13A - Fig. 13C schematically show three possible positionings of a tyre monitoring device with respect to the wear bars on a same tyre, tested by the Applicant;

[0082] Fig. 14A and Fig. 14B again show, in different schematic views, the three possible positionings of the monitoring device of Fig. 13A - Fig. 13C;

[0083] Fig. 15 shows in diagram form the radial acceleration profiles measured during a test on a wet surface on the three tyres of Fig. 14A - Fig. 14C;

[0084] Fig. 16 schematically shows preferred placements of the monitoring device, in accordance with the present invention, and

[0085] Fig. 17 schematically shows suitable application positions of the monitoring device in an exemplary tyre equipped with eight rows of wear bars arranged circumferentially.

[0086] Detailed description of exemplary embodiments

[0087] With reference to the accompanying figures, Fig. 8 schematically shows a portion of a tyre 805 equipped with a tyre monitoring device 810 provided with a sensor (contained in the monitoring device 810 and therefore not visible in the figure) capable of measuring one or more physical quantities descriptive of the deformations undergone by the tyre 805 during rolling on a rolling surface, for example the road surface. In embodiments of the present invention, the sensor is capable of measuring radial acceleration. Alternatively or additionally, the sensor may be able to measure tangential acceleration, and / or lateral acceleration; below, for conciseness, reference will be made to a sensor capable of measuring radial acceleration, without this having to be understood as a limitation of the present invention: considerations similar to those that will be carried out also apply to sensors capable of measuring (only, or also) the tangential acceleration, and / or the lateral acceleration. In embodiments of the present invention, the sensor may be or comprise an accelerometer (particularly a uniaxial accelerometer or a biaxial accelerometer or a triaxial accelerometer), and / or a strain gauge, and / or a piezoelectric sensor and similar sensors.

[0088] By way of example, the tyre monitoring device 810 is conveniently attached to the radially internal surface 815 of the tyre 805, opposite the tread 820 of the tyre 805.

[0089] By way of example only, but not by way of limitation, the tyre monitoring device 810 can be conveniently fixed on a portion of the radially internal surface 815 of the tyre 805 located in correspondence with the equatorial plane 825 of the tyre 805, for example transversely to the equatorial plane 825. The term "equatorial plane" means the centerline plane perpendicular to the axis of rotation of the tyre 805.

[0090] For example, the tyre monitoring device 810 may be of the type described in one of the following documents in the name of the same Applicant: WO 2013 / 098711 Al, WO 2015 / 144770 Al, WO 2018 / 065846 Al, WO 2019 / 123118 Al, WO 2020 / 026281 Al, WO 2020 / 026282 Al.

[0091] Fig. 9 shows a diagram of the tyre monitoring device 810 in accordance with an exemplary and non-limiting embodiment of the present invention.

[0092] The tyre monitoring device 810 comprises an electronic unit 900 which comprises a detection section 905, a processing unit (or Central Processing Unit, CPU) 915 associated with a memory, a transceiver 920, an antenna 925. The electronic unit 900 is powered by a battery 910.

[0093] In embodiments of the present invention, the detection section 905 of the tyre monitoring device 810 comprises an accelerometer 930, particularly a radial accelerometer, oriented within the tyre monitor device 810 so as to have an axis substantially orthogonal to the radially internal surface 815 of the tyre 805. The accelerometer 930 is configured to provide in output a measurement of acceleration descriptive of the deformations in the radial direction that the tyre 805 undergoes while rolling on the rolling surface, for example on the road surface. Alternatively, or in addition, according to the present invention, other sensors or sensing elements suitable for measuring physical quantities descriptive of the tyre deformations could be used, such as tangential accelerometers, lateral accelerometers, strain gauges, etc.

[0094] The tyre monitoring device 810 can include, in addition to the accelerometer (or other device capable of measuring one or more physical quantities descriptive of the deformations undergone by the tyre 805 during rolling on a rolling surface), other sensors, for example temperature and / or pressure sensors.

[0095] In the non-limiting exemplary embodiment of the present invention shown, the detection section 905 of the tyre monitoring device 810 further comprises a pressure sensor 935 configured to output a measurement of the pressure inside the tyre 805. The detection section 905 of the tyre monitoring device 810 may further comprise a temperature sensor 940 configured to output a measurement of temperature of the tyre 805.

[0096] The accelerometer 930 is configured to measure and output measurements of the acceleration descriptive of the deformations in the radial direction that the tyre 805 undergoes while rolling on a rolling surface such as the road surface. The acceleration measurements output by the accelerometer 930 are provided to the central processing unit, CPU, 915.

[0097] The central processing unit, CPU, 915 is configured, via appropriate software / firmware modules, to receive, from the detection section 905, the data relating to the measurements carried out by the radial accelerometer 930 and, if provided, by the pressure sensor 935 and temperature sensor 940. The CPU 915 is also configured, via appropriate software / firmware modules, to process the data (measurements) received from the accelerometer 930 and, if provided, from the pressure sensor 935 and temperature sensor 940 in order to obtain, from such data, parameters relating to the tyre (such as the length of the contact area of the tyre with the rolling surface of the tyre and / or the load exerted on a tyre).

[0098] According to the present invention, the CPU 915 is configured, via appropriate software / firmware modules, to process the measurements received from the accelerometer 930 in order to obtain indications relating to an aquaplane condition experienced by the tyre 805. These indications relating to the possible aquaplaning condition experienced by the tyre 805 are obtained from the analysis of the measurements received from the accelerometer 930. In particular, if the analysis of the measurements received from the accelerometer highlights the presence of one or more spikes in the profile of the radial acceleration measured by the accelerometer 930, then it is possible to determine that the tyre 805 is experiencing an aquaplane condition. As previously observed, the spikes generated by the wear bars in aquaplane conditions are discernible with respect to the trend of the radial acceleration profile measured by the accelerometer 930 when the tyre monitoring device 810 passes in correspondence with the contact area of the tyre with the rolling surface, since, as can be seen from the diagrams commented above, the spikes, even at relatively high speeds, are substantially narrower than the regions corresponding to the transits in correspondence with the contact area with the rolling surface.

[0099] Alternatively, the CPU 915 can be configured, via appropriate software / firmware modules, to process such data received from the accelerometer 930 up to a certain extent, i.e., to perform only a part of the processing (for example a preprocessing, or preparation of the raw data received from the accelerometer 930 for their subsequent processing), and then to send the processing results to a control unit external to the tyre monitoring device 810, via the transceiver section 920 and the antenna 925, to complete the processing up to obtaining said parameters relating to the tyre and said indications relating to an aquaplane condition experienced by the tyre 805.

[0100] The transceiver section 920 is configured for one-way or, preferably, bidirectional communication, via the RF antenna 925, with a control unit, external to the tyre monitoring device 810, specifically configured for communication with the tyre monitoring devices 810 mounted inside the tyres of a vehicle. Alternatively, the transceiver section 920 may communicate directly, via the RF antenna 925, with a vehicle control system, such as a vehicle's on-board computer. In preferred embodiments, the transceiver section 920 includes a Bluetooth Low Energy (BLE) module.

[0101] The battery 910 directly or indirectly supplies electrical power to the various electrical and electronic components of the tyre monitoring device 810, in particular to the electronic unit 900. In preferred embodiments, the battery 910 may be a rechargeable battery with power recovered from the mechanical energy caused by the rotation of the tyre 805.

[0102] Fig. 10 schematically shows an example of the implementation of a system for monitoring the tyres of a vehicle. The system is implemented in a vehicle 1000 equipped with four tyres 805, each of which comprises a respective tyre monitoring device 810. The vehicle 1000 can be, for example, a passenger car. However, the present invention also applies to other types of vehicles, such as two or three-wheeled scooters, motorcycles, tractors, buses, trucks or light trucks, or to vehicles with two, three, four, six or more wheels distributed over two or more axles. The vehicle 1000 may be powered by electric power, or rely on thermal propulsion, or may be a hybrid vehicle.

[0103] The tyre monitoring devices 810 are in communication with a control unit 1005. The control unit 1005 is in communication with a vehicle control system 1010 configured to adjust the vehicle control parameters based on the parameters related to the tyre estimated by the monitoring units 810 and / or the control unit 1005. The vehicle control system 1010 can be the vehicle on-board computer 1000, and / or a subsystem configured to adjust at least one of said vehicle control parameters (e.g., a suspension control subsystem, a brake control subsystem, a steering control subsystem).

[0104] Typically, the communication between the tyre monitoring devices 810 and the control unit 1005 is a wireless communication (e.g., a Bluetooth communication). The communication between the control unit 1005 and the vehicle control system 1010 can be wireless and / or wired (e.g., on CAN BUS). In other preferred embodiments, the control unit 1005 may be a hardware or software module implemented in the vehicle control system 1010.

[0105] The control unit 1005 is external to the tyres 805 in which the tyre monitoring devices 810 are fixed. The control unit 1005 can be positioned in any point of the vehicle reachable by the wireless (e.g. Bluetooth) signal transmitted by the tyre monitoring devices 810.

[0106] For example, the control unit 1005 may be attached to the windshield of the vehicle 1000. In another embodiment, the control unit 1005 may be a personal mobile device of the driver of the vehicle (e.g., a smartphone or tablet), equipped with suitable software applications / modules configured at least for communication with the tyre monitoring devices 810, as well as for processing the data received from the tyre monitoring devices 810.

[0107] Fig. 11 schematically shows an exemplary embodiment of a control unit 1005 suitable for the tyre monitoring system of Fig. 10. The control unit 1005 includes a transceiver section 1105, an RF antenna 1110, an interface 1115 with the vehicle control system 1010, a battery 1120, a processing unit 1125 with associated memory.

[0108] The transceiver section 1105 of the control unit 1005 is configured for one-way or, preferably, bi-directional communication, via the RF antenna 1110, with the tyre monitoring devices 810. In preferred embodiments, the transceiver section 1105 includes a Bluetooth Low Energy (BLE) module.

[0109] The interface 1115 may be a CAN BUS interface adapted for bidirectional communication with the vehicle control system 1010.

[0110] The battery 1120 directly or indirectly supplies electrical power to the various electrical and electronic components of the control unit 1005. In other embodiments, the control unit 1005 may be powered by the vehicle battery, via the interface 1115.

[0111] The processing unit, CPU, 1125 of the control unit 1005 is configured, via appropriate software / firmware modules, to receive data from the tyre monitoring devices 810 mounted inside the tyres 805. Such data may include tyre parameters estimated by the tyre monitoring devices 810, or measurements carried out by the tyre monitoring devices 810, or results of partial processing carried out on said measurements by the tyre monitoring devices 810. The CPU 1125 is also configured, via appropriate software / firmware modules, to process such data in order to estimate at least one parameter relating to the tyre, in particular to estimate an aquaplane condition experienced by the tyre 805.

[0112] Ultimately, the choice whether to distribute between the tyre monitoring devices 810 and the external control unit 1005 the processing for the estimation of the parameters relating to the tyre(s) 805, and in particular for the determination of a aquaplane condition experienced by the tyre(s) 805, is a tradeoff between several constraints that have to balanced, such as: hardware complexity, battery consumption, cost, processing power available for the CPU of the tyre monitoring devices 810, etc. In the exemplary embodiment shown in Fig. 11, the tyre-related parameter(s) estimated by the CPU of the tyre monitoring devices 810 and / or by the CPU 1125 of the control unit 1005 is / are optionally made available to the control system 1010 of the vehicle via the interface 1115.

[0113] In embodiments of the present invention, part of the processing may also be performed by a cloud server with which the control unit 1005 (or the vehicle control system 1010) is in communication via a communications network, e.g. a cellular network.

[0114] In an exemplary mode of operation, each tyre 805 mounted on a wheel of the vehicle 1000, when the vehicle 1000 is in motion, rotates on a rolling surface, for example the road surface of a road traveled by the vehicle 1000. As a result of the mounting on the vehicle, the tyre 805 deforms, forming a contact region between the tyre 805 and the rolling surface.

[0115] The CPU 915 (or the CPU 1125, if the monitoring device 810 does not perform processing on the signal received from the accelerometer) monitors the radial acceleration profile.

[0116] By monitoring the radial acceleration profile, the CPU is able to extract information from the signals about the operating conditions of the tyre such as the width (length) of the contact area of the tyre with the rolling surface. This is useful for example to estimate the weight of the vehicle.

[0117] In accordance with the present invention, by monitoring the radial acceleration profile, the CPU 915 (or the CPU 1125, if the tyre monitoring device 810 does not carry out processing on the signal received from the accelerometer) is able to identify the presence of a (one or more) spikes (such as the spikes 110a, 110b, 110c; 210a - 210g), which originate in the radial acceleration profile measured by the accelerometer as a result of the tyre experiencing an aquaplane condition.

[0118] Spike detection can for example include comparisons of the values of the measured radial (and / or tangential) acceleration with radial (and / or tangential) acceleration threshold values and time duration or angular amplitude threshold values (as can be seen from the diagrams shown in the figures and discussed previously, the time duration and angular amplitude of the spikes that are generated by the interaction between the layer of water on the rolling surface and the wear bars are less than the time duration and angular amplitude of the regions of the radial acceleration profile that correspond to the transit of the monitoring device in correspondence with the contact area of the tyre with the rolling surface).

[0119] Alternatively, or in addition, spike detection can for example be carried out by conducting a time-frequency analysis of the measured radial (and / or tangential) acceleration profile (to evaluate its energy content).

[0120] By way of example and not exhaustively, the time-frequency analysis can be a so-called “wavelet” analysis, a methodology known in the field of signal analysis. Through this analysis, it is possible to highlight a high energy content of the radial (and / or tangential) acceleration signal, for a certain frequency range, in correspondence with the angular position coinciding with that of the spikes. This energy content relating to a specific angular portion can be compared with a reference value, to identify the presence of characteristic trends (spikes) attributable to the aquaplane condition.

[0121] Once the aquaplane condition experienced by one or more of the tyres mounted on the vehicle has been determined, the vehicle control system 1010 may be configured to take the necessary actions to safeguard the safety of the vehicle occupants and other road users, in particular, by way of example, warning (visually and / or acoustically) the driver of the vehicle.

[0122] With reference to Fig. 12A - Fig. 12D, a heuristic justification for the appearance of spikes in the accelerometer signal in aquaplane conditions can be the following. In the figures, the reference 1205 indicates a rolling surface 1205 on which the tyre 805 rolls (for example the road surface of a road that is travelled by the vehicle on which the tyre 805 is mounted). The arrow 1210 indicates the direction of rotation (sense of rotation) of the tyre 805.

[0123] Fig. 12A refers to a rolling situation of the tyre 805 on a dry or substantially dry rolling surface 1205. Fig. 12B refers to a rolling situation of the tyre 805 on a rolling surface 1205 covered by a relatively shallow layer of water and / or with the tyre rotating at a relatively low speed. Fig. 12C and Fig. 12D refer to a rolling situation of the tyre 805 on a rolling surface 1205 covered by a relatively deep layer of water and / or with the tyre rotating at a relatively high speed.

[0124] When, as a result of the rolling of the tyre 805, one of the (eight, in the considered example) rows of wear bars, such as the row of wear bars 305-1 or the row of wear bars 305-2 shown in Fig. 3A, enters the contact area between the tyre 805 and the rolling surface (for example the road surface of the road travelled by the vehicle on which the tyre 805 is mounted), a sharp reduction in the section of the grooves 303- 1 - 303-4 in which the wear bars are provided, used for the evacuation of any water present on the rolling surface, occurs. Considering a realistic example of a thickness of the tread grooves 303-1 - 303-4 equal to approximately 8 mm and a height of the wear bars of approximately 1.6 mm, the reduction in the section of the grooves useful for the evacuation of water is approximately 20%.

[0125] If, due to the relatively high thickness of the water layer on the rolling surface of the tyre and / or as a result of the relatively high rotational speed of the wheel on which the tyre is mounted, the flow of water entering the tread grooves is relatively high and the residual section of the tread grooves 303-1 - 303-4 when the wear bars enter the contact area is no longer sufficient for the evacuation of the water. The excess water, which cannot be evacuated, generates a localized increase in pressure around the wear bars, which causes the generation of a characteristic pattern or oscillation of the acceleration signal inside the tyre; this oscillation propagates in the direction opposite to the direction of rotation of the tyre and is detected by the accelerometer of the tyre monitoring device.

[0126] The tests performed by the Applicant have highlighted that the spikes in the radial acceleration profile measured by the accelerometer, generated by the presence of the wear bars provided on the tyres and in rolling conditions of the tyres on wet surfaces, particularly in conditions such as to trigger the phenomenon of aquaplaning, can occur in regions (indicated with 105 in Fig. 1A and Fig. IB, and with 205 in Fig. 2) of the measured radial acceleration profile such as to interfere and make it difficult or unreliable to extract from the signals information about the operating conditions of the tyre, such as for example the identification of the width, and the estimate of the length, of the contact area of the tyre with the rolling surface, for the purposes mentioned above. For example, this is the case of a spike that occurs close to, or even partially overlapping with, one of the regions of the acceleration profile, corresponding to the transit of the monitoring device in correspondence with the contact area of the tyre with the rolling surface.

[0127] Tests conducted by the Applicant have highlighted that the position of the spikes in the radial acceleration profile measured by the accelerometer depends on the position, circumferentially along the radially internal surface of the tyre, in which the tyre monitoring device is mounted, and in particular on its position with respect to the wear bars provided on the tyre with reference to the direction of rotation of the tyre when using the latter and on the distance of the tyre monitoring device from the wear bars.

[0128] With reference to Fig. 13A - Fig. 13C and to Fig. 14A and Fig. 14B, in Fig. 13A - Fig. 13C there is shown a same portion of tread 1300a, 1300b, 1300c of a same tyre, equipped with an identical tyre monitoring device, applied to the radially internal surface of the tyre (and therefore not visible in the figures) in different positions, corresponding to the points indicated, respectively, with 1301a, 1301b and 1301c. The arrows 1305 indicate the direction of rotation of the tyre. The three positions 1301a, 1301b and 1301c differ from each other in terms of position, with respect to the direction of rotation 1305 of the tyre, from a pair of consecutive rows of wear bars between which the tyre monitoring devices are positioned, and in terms of distance, dl, d2, d3, from a row of wear bars (305-8, 305-4, 305-6) preceding the application position (1301a, 1301b, 1301c) of the tyre monitoring device, in the direction of rotation of the tyre 1305.

[0129] In particular, in the tyre of Fig. 13A the tyre monitoring device is applied (to the radially internal surface of the tyre) in a position 1301a located at a distance dl from the row 305-8 of wear bars preceding it in the direction of rotation 1305 of the tyre; in the tyre of Fig. 13B the tyre monitoring device is applied in a position 1301b located at a distance d2 < dl from the row 305-4 of wear bars preceding it in the direction of rotation 1305 of the tyre; in the tyre of Fig. 13C the tyre monitoring device is applied in a position 1301c located at a distance d3 < d2 from the row 305-6 of wear bars preceding it in the direction of rotation 1305 of the tyre.

[0130] It can be observed that in the tyre of Fig. 13A the position 1301a in which the tyre monitoring device is applied is relatively very distant from the row 305-8 of wear bars that precedes it in the direction of rotation 1305 of the tyre, being therefore located at a relatively small distance dl' from the row 305-1 of wear bars that follows the position 1301a of the tyre monitoring device in the direction of rotation 1305 of the tyre; in other words, the tyre monitoring device is mounted on the tyre substantially near, very close to the row 305-1 of wear bars that follows it in the direction of rotation of the tyre; the distance dl’ is for example the minimum distance allowed taking into account the dimensions of the tyre monitoring device. Furthermore, with reference to Fig. 14A and Fig. 14B, the position 1301a of the tyre monitoring device is in the part of the tread that goes from the external side 0 of the tyre to the equatorial plane of the tyre itself.

[0131] In the tyre of Fig. 13B, the position 901b in which the tyre monitoring device is applied is generally midway between the preceding row 305-4 of wear bars and the following row 305-3 of wear bars in the direction of rotation 1305 of the tyre. Furthermore, with reference to Fig. 14A and Fig. 14B, the position 1301b of the tyre monitoring device is substantially in the central part of the tyre, generally in correspondence with the equatorial plane of the tyre itself.

[0132] In the tyre of Fig. 13C, the position 1301c in which the tyre monitoring device is applied is relatively very close to the row 305-6 of wear bars that precedes it in the direction of rotation 1305 of the tyre, substantially very close to the row 305-6 of wear bars that precedes it in the direction of rotation of the tyre; the distance d3 between the row 305-6 of wear bars and (the position of) the tyre monitoring device 1301c is for example the minimum distance allowed taking into account the overall dimensions of the tyre monitoring device. Furthermore, with reference to Fig. 14A and Fig. 14B, the position 1301c of the tyre monitoring device is in the part of the tread that goes from the external side I of the tyre to the equatorial plane of the tyre itself.

[0133] The diagram in Fig. 15, which, like the diagrams in the previous Fig. 6A - Fig. 6C reports in ordinate the values of the radial acceleration Ar measured by the accelerometer, in arbitrary units as a function of an angle, reported in abscissa (in degrees, indicated with “°” in the figures) which goes from 0° to 180° and which corresponds to half a turn of the wheel (i.e., of the tyre), centered (at 90°) on the centre of the contact area of the tyre with the rolling surface, shows the results of tests conducted by the Applicant on the tyre in Fig. 13A - Fig. 13C in a bath filled with water forming a layer approximately 6 mm high on the bottom of the pool, to simulate wet road conditions, and with the tyre rotated at an angular speed corresponding to a linear speed of 95 km / h (a speed which, as known to the Applicant, with such a layer of water, is such as to induce the phenomenon of aquaplaning on the tyres being tested). The dashed curve indicated as 1505-1 corresponds to tyre 900a in Fig. 9A, the solid curve indicated as 1505-2 corresponds to tyre 900b in Fig. 9B, and the dotted curve indicated as 1505-3 corresponds to tyre 900c in Fig. 9C.

[0134] In curve 1505-2, a spike 1510 is observed immediately preceding, substantially very close to region 1515 of curve 1505-2 which corresponds to the transit of the tyre monitoring device across the contact area of the tyre 1300b with the rolling surface. This spike 1510 can interfere with, and make difficult or unreliable, the identification of the width, and the estimation of the length, of the contact area of the tyre with the rolling surface.

[0135] In curve 1505-3, a spike 1520 is observed immediately preceding, close to region 1515 of curve 1505-3 which corresponds to the transit of the monitoring device across the contact area of the tyre with the rolling surface. This spike 1520 can also interfere with, and make difficult or unreliable, the identification of the width and the estimation of the length, of the contact area of the tyre with the rolling surface.

[0136] A better situation is observed in curve 1505-1, referring as mentioned to tyre 1300a, in which the spike 1125 closest to the region 1515 of curve 1505-1 which corresponds to the transit of the monitoring device across the contact area of the tyre with the rolling surface, is sufficiently advanced in time so as not to interfere and make it difficult to identify the width, and estimate the length, of the contact area of the tyre with the rolling surface.

[0137] In the three tests just discussed, the Applicant tested three different positions of the tyre monitoring device transversely to the tread: towards the external side O, substantially in the centre (on the equatorial plane) and more towards the internal side 1. the Applicant found that the position of the tyre monitoring device transversely to the tread is not decisive; a preferred positioning may be substantially in the centre, around the equatorial plane of the tyre.

[0138] The Applicant, based on the intuition, confirmed experimentally, that in conditions of rolling of the tyre on a wet rolling surface (with a thickness of the water layer and rotation speed of the tyre such as to generate an aquaplane condition), the presence of the wear bars on the tyre generates disturbances in the radial acceleration profile measured by an accelerometer (or other sensor capable of detecting the deformations undergone by the tyre in its rolling on a surface) of a tyre monitoring device with which the tyre is equipped, has therefore addressed the problem of where to position the tyre monitoring device so that, even in conditions of rolling on a wet surface, in particular in aquaplane conditions, the disturbances in the radial acceleration profile measured by the accelerometer generated by the interaction of the water with the wear bars do not interfere with the identification of the width, and the estimation of the length, of the contact area of the tyre with the rolling surface.

[0139] In particular, the improvement of the positioning of the tyre monitoring device, in addition to being important for the correct identification of the width, and the estimation of the length, of the contact area of the tyre with the rolling surface, is important not only for the detection of the total aquaplane condition (in which the tyre completely loses directionality) but also for the correct detection of the partial aquaplane condition (a condition in which the tyre remains at least partially in contact with the rolling surface and therefore maintains at least partially the ability to interact with the rolling surface) which is read in the area preceding the contact region of the tyre with the rolling surface, in the rolling direction (portion of the entry extrados), as described in the international application WO 2019 / 123501 in the name of the same present Applicant, of the radial acceleration signal. In fact, the disturbance in the radial acceleration profile measured by the accelerometer generated by the interaction of the water with the wear bars mainly interferes in this area of the signal, interfering with the detection of this particular aquaplane condition.

[0140] The Applicant has found that, in order to prevent the effects on the radial acceleration measurements of an accelerometer, or similar sensor, determined by the interaction of the wear bars with a layer of water covering the rolling surface of the tyre from interfering with the identification and monitoring of the contact area of the tyre with the rolling surface, the tyre monitoring device comprising the accelerometer should be positioned as far as possible, in the direction of rotation of the tyre, from a wear bar (or a row of wear bars) that precedes the monitoring device in the direction of rotation of the tyre (and which therefore comes into contact with the rolling surface of the tyre before the tyre monitoring device). In particular, the tyre monitoring device comprising the accelerometer should be positioned as close as possible, substantially very close (compatibly with physical constraints such as the dimensions of the tyre monitoring device) to a wear bar (or a row of wear bars) that follows the tyre monitoring device in the direction of rotation of the tyre. More generally, the Applicant has found that it is appropriate to apply the tyre monitoring device in a position immediately preceding, in the direction of rotation of the tyre, a wear bar or row of wear bars, i.e., in a position as close as possible to a wear bar that follows the position of application of the tyre monitoring device in the direction of rotation of the tyre.

[0141] In a tyre having at least two wear bars (or at least two rows of wear bars) circumferentially spaced apart, it is appropriate to apply the tyre monitoring device to a region of the radially internal surface of the tyre extending from substantially half the distance from the preceding wear bar (or row of wear bars), in the direction of rotation of the tyre (i.e., which, as the tyre rolls over the rolling surface, first contacts the latter), to the immediately following wear bar (or row of wear bars) in the direction of rotation of the tyre. In other words, by ideally dividing the region of the radially internal surface of the tyre that is located between two consecutive wear bars (or two rows of wear bars) into two consecutive semi-regions (in the direction of rotation of the tyre), each of length equal to half the distance between the two consecutive wear bars (or rows of wear bars), an appropriate positioning of the tyre monitoring device is in the semi-region closest to that wear bar (or row of wear bars) which, in the direction of rotation of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars).

[0142] The Applicant has also found that, by ideally dividing such semi-region closest to that wear bar (or row of wear bars) which, in the direction of rotation of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars) into two consecutive sub-semi-regions (in the direction of rotation of the tyre) each of length equal to half the length of such semi -region (i.e., one quarter of the distance between the two consecutive wear bars, or rows of wear bars), a preferable positioning of the tyre monitoring device is in that sub-semi -region closest to that wear bar (or row of wear bars) which, in the direction of rotation of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars).

[0143] The Applicant has further found that, by ideally dividing such semi-region closest to that wear bar (or row of wear bars) which, in the direction of rotation of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars) into three consecutive sub-semi-regions (in the direction of rotation of the tyre) each of length equal to one third of the length of such semi-region (i.e., one sixth of the distance between the two consecutive wear bars, or rows of wear bars), a preferable positioning of the tyre monitoring device is in that sub-semi-region closest to that wear bar (or row of wear bars) which, in the direction of rotation of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars).

[0144] Fig. 16 schematically shows suitable positionings of the tyre monitoring device in a respective tyre, for example the tyre 805 of Fig. 8.

[0145] The figure shows a portion of tread 1601 of the tyre 805. As in Fig. 3A, circumferential grooves or recesses are made in the tread surface 1601 of the tyre 805, in particular four recesses 1603-1, 1603-2, 1603-3 and 1603-4. Wear indicators in the form of wear bars are provided in the recesses 1603-1, 1603-2, 1603-3, 1603-4, which are useful for providing a visual indication of the degree of wear of the tread 1601 of the tyre 805. In particular, Fig. 16 shows two transverse rows of four wear bars, one wear bar in each recess 1603-1, 1603-2, 1603-3, 1603-4: a first row of four wear bars 1605-1 and a second row of four wear bars 1605-2; the two rows of wear bars 1605-1 and 1605-2 are consecutive to each other and the row of wear bars 1605-1 precedes the row of wear bars 1605-2 in the direction of rotation 1610 of the tyre 805 when, in use, the tyre 805 is mounted on a vehicle and the vehicle is in motion. The row of wear bars 1605-1 precedes the row of wear bars 1605-2 in the sense that when the tyre rotates in the direction of rotation 1610 the row of wear bars 1605-1 comes into contact with the rolling surface of the tyre 805, typically the road surface, before the row of wear bars 1605-2. It should be emphasized that Fig. 16 shows only an exemplary, preferred but not limiting arrangement of the wear bars: the wear bars made in the different grooves or recesses of a tyre do not necessarily have to be aligned transversely to the circumference of the tread surface 1601 of the tyre itself: the wear bars made in the different grooves or recesses may be unaligned.

[0146] Reference 1615 indicates the position in which the tyre monitoring device 810 is mounted, on the radially internal surface of the tyre 805.

[0147] According to the present invention, on the basis of the tests carried out by the Applicant and discussed above, in order to avoid that the effects on the radial acceleration measurements of the accelerometer (or similar sensor capable of detecting the deformations undergone by the tyre during its rolling on a surface, for example the road surface) of the tyre monitoring device 810, determined by the interaction of the wear bars, present on the tyre 805, with a layer of water covering the rolling surface of the tyre interfere with the identification and monitoring of the contact area of the tyre 805 with the rolling surface, the tyre monitoring device 810 comprising the accelerometer is positioned as far as possible, in the direction of rotation 1610 of the tyre 805, from a wear bar, or, in the example considered here, from a row of wear bars which, like the row of wear bars 1605-1, precedes (the position 1615 of) the tyre monitoring device 810 in the direction of rotation 1610 of the tyre 805.

[0148] In particular, according to an embodiment of the present invention, the tyre monitoring device 810 comprising the accelerometer is positioned as close as possible, substantially very close (compatibly with physical constraints such as the size of the tyre monitoring device 810 itself) to a wear bar (or, in the example considered here, to a row of wear bars) which (like the row of wear bars 1605-2) follows (the position of) the tyre monitoring device 810 in the direction of rotation 1610 of the tyre 805.

[0149] More generally, according to embodiments of the present invention, it is appropriate to apply the tyre monitoring device 810 in a position 1615 substantially half the distance D from the preceding wear bar (or from a preceding row of wear bars 1605-1), in the direction of rotation 1610 of the tyre, up to the immediately subsequent wear bar (or row of wear bars 1605-2), in the direction of rotation 1610 of the tyre. In other words, by ideally dividing the region of the radially internal surface 815 of the tyre 805 that is located between two consecutive wear bars (or two consecutive rows of wear bars) 1605-1 and 1605-2 into two consecutive semi-regions (in the direction of rotation 1610 of the tyre) each of length equal to half the distance D / 2 between the two consecutive wear bars (or rows of wear bars) 1605-1 and 1605-2, an appropriate positioning of the tyre monitoring device is in the semi-region 1620 closest to that wear bar (or row of wear bars) 1605-2 that, in the direction of rotation 1610 of the tyre, contacts the rolling surface after the other wear bar (or row of wear bars) 1605-1.

[0150] In preferred embodiments of the present invention, a suitable position for the application of the tyre monitoring device can be identified by ideally dividing such semi-region 1620 closest to that wear bar (or row of wear bars) which, in the direction of rotation of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars) into two consecutive sub-semi-regions (in the direction of rotation of the tyre) each of length equal to half the length of such semi-region (i.e., one quarter of the distance between the two consecutive wear bars, or rows of wear bars): a preferable positioning of the tyre monitoring device is in that sub-semi-region closest to that wear bar (or row of wear bars) which, in the direction of rotation of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars).

[0151] Even more preferably, by ideally dividing such semi-region 1620 closest to that wear bar (or row of wear bars) 1605-2 which, in the direction of rotation 1610 of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars) 1605-1 into three consecutive sub-semi-regions (in the direction of rotation 1610 of the tyre) each with a length equal to one third of the length of such semiregion, and therefore with a length D / 6 equal to 1 / 6 of the length Z), a preferable positioning of the tyre monitoring device 810 is in that sub-semi-region 1625 closest to that wear bar (or row of wear bars) 1605-2 which, in the direction of rotation 1610 of the tyre, comes into contact with the rolling surface after the other wear bar (or row of wear bars) 1605-1.

[0152] Fig. 17 schematically shows suitable application positions 1705 of the tyre monitoring device in an exemplary tyre equipped with eight rows of circumferentially arranged wear bars 1605-1 - 1605-8.

[0153] Thanks to the positioning of the tyre monitoring device in accordance with the present invention, the radial acceleration profile Ar measured by the accelerometer of the tyre monitoring device is of the type indicated by the curve 1505-1 of Fig. 15: when the tyre rolls on a wet surface, the effect of the interaction of the wear bars with the water layer gives rise to peaks or spikes that are sufficiently spaced apart from the regions of the profile corresponding to the transit of the tyre monitoring device in correspondence of the contact area of the tyre with the rolling surface. Thanks to this, the determination of the contact area is not disturbed by the presence of water on the rolling surface.

[0154] Furthermore, thanks to the positioning of the tyre monitoring device according to the present invention, it is possible to determine, from the profile of the radial acceleration measured by the accelerometer, whether the tyre is experiencing an aquaplane condition: this can be done by identifying the peaks or spikes in the profile of the measured radial acceleration.

[0155] Fig. 17 schematically shows suitable application positions 1705 of the tyre monitoring device in an exemplary tyre equipped with eight rows of circumferentially arranged wear bars 1605-1 - 1605-8.

Claims

CLAIMS1. Method for detecting an aquaplane condition of a tyre (805) during the rolling of the tyre on a rolling surface (515; 1205), wherein said tyre comprises a tread band (820) in which at least one circumferential groove (303-1 - 303-4; 1603-1 - 1603-4) is formed which is provided with at least one wear bar (305-1, 305-2; 1605-1 - 1605-8), the method comprising:- applying radially internally (815) to the tyre (805), in a position opposite to said tread band (820), a tyre monitoring device (810), the tyre monitoring device (810) comprising an electronic unit (900) comprising a sensor (930) configured for detecting physical quantities (Ar) indicative of deformations experienced by the tyre (805) in the rolling on the rolling surface (515; 1205) and for outputting measurements of said physical quantities (Ar);- monitoring said measurements of said physical quantities (Ar) during the rolling of the tyre (805) on the rolling surface (515; 1205);- determining, based on said monitoring said measurements of said physical quantities (Ar), a passage of said tyre monitoring device (810) in correspondence of a contact zone (510) of the tyre (805) with said rolling surface (515; 1205), characterized by comprising:- determining an aquaplane condition experienced by the tyre (805) from the detection, in said measurements of physical quantities (Ar), of a characteristic trend (110a - 110c; 210a - 210h) preceding and / or following the passage of said tyre monitoring device (810) in correspondence of the contact zone (510) of the tyre (805) with the rolling surface (515; 1205), said characteristic trend (110a - 110c; 210a - 210h) being correlated with an interaction of said at least one wear bar (305-1, 305-2) with a water layer (1220) present on said rolling surface (1205).

2. The method according to claim 1, wherein said characteristic trend comprises at least one spike (110a - 110c; 210a - 210h) in a zone that precedes and / or follows the passage of said tyre monitoring device (810) in correspondence of the contact zone (510) of the tyre (805) with the rolling surface (515; 1205), said at leastone spike (110a - 110c; 210a - 210h) being correlated with said interaction of said at least one wear bar (305-1, 305-2) with the water layer (1220) present on said rolling surface (1205).

3. The method according to claim 1 or 2, wherein said applying radially internally (815) to the tyre (805) a tyre monitoring device (810) comprises: applying the tyre monitoring device (810) in a position immediately preceding said at least one wear bar (1605-2) in a sense of rotation (1610) of the tyre (1205).

4. The method according to claim 3, wherein said at least one circumferential groove (1603-1 - 1603-4) is provided with at least a first wear bar (1605-1) and a second wear bar (1605-2) circumferentially consecutive and located at a mutual distance ( / )), the second wear bar (1605-2) following, in the sense of rotation (1610) of the tyre, the first wear bar (1605-1), and wherein said applying radially internally (815) to the tyre (805) the tyre monitoring device (810) comprises: applying the tyre monitoring device (810) in a position within a semi-region (1620), between the first (1605-1) and the second (1605-2) wear bar, which is contiguous to the second wear bar (1605-2) and which extends circumferentially substantially from a half of said distance ( / )) from the first wear bar (1605-1) to the second wear bar (1605-2).

5. The method according to claim 4, wherein said applying radially internally (815) to the tyre (805) the tyre monitoring device (810) comprises: applying the tyre monitoring device (810) in a position within a sub-semiregion (1625), between the first (1605-1) and the second (1605-2) wear bar, which is contiguous to said second wear bar (1605-2) and which extends circumferentially substantially 1 / 6 of said distance (D) from the first wear bar (1605-1) to said second wear bar (1605-2).

6. The method according to any one of the preceding claims, comprising at least two circumferential grooves each comprising a respective wear bar, the wear barsof the at least two circumferential grooves being aligned in a direction transversal to the circumferential grooves.

7. The method according to any one of the preceding claims, comprising a plurality of circumferential grooves each comprising a respective plurality of wear bars, the plurality of wear bars of said circumferential grooves being arranged in groups of wear bars in corresponding circumferential positions, the wear bars of each of said groups being transversally aligned or unaligned or transversally alternated.

8. A system (810, 1005, 1010) for detecting an aquaplane condition of a tyre (805) during the rolling of the tyre on a rolling surface (515; 1205), wherein said tyre comprises a tread band (820) in which at least one circumferential groove (303-1 - 303-4; 1603-1 - 1603-4) is formed which is provided with at least one wear bar (305- 1, 305-2; 1605-1 - 1605-8), the system comprising:- a tyre monitoring device (810) applied radially internally (815) to the tyre (805), in a position opposite to said tread band (820), the tyre monitoring device (810) comprising an electronic unit (900) comprising a sensor (930) configured for detecting physical quantities (Ar) indicative of deformations experienced by the tyre (805) in the rolling on the rolling surface and for outputting measurements of said physical quantities (Ar);- at least a processing unit (915, 1125) comprising software modules configured for:- monitoring said measurements of said physical quantities (Ar) during the rolling of the tyre (805) on the rolling surface;- determining, based on said monitoring said measurements of said physical quantities (Ar), a passage of said tyre monitoring device (810) in correspondence of a contact zone (510) of the tyre with said rolling surface (515; 1205), characterized in that: said processing unit (915, 1125) comprises software modules configured for:- determining an aquaplane condition experienced by the tyre (805) from the detection, in said measurements of physical quantities (Ar), of a characteristic trend (110a - 110c; 210a - 210h) in a zone preceding and / or following the passage of said tyre monitoring device (810) in correspondence of the contact zone (510) of the tyre (805) with the rolling surface (515; 1205), said characteristic trend (110a - 110c; 210a- 210h) being correlated with an interaction of said at least one wear bar (305-1, 305- 2) with a water layer (1220) present on said rolling surface (1205).

9. Vehicle (1000) provided with tyres and comprising a system according to claim 8 for detecting an aquaplane condition experienced by one or more of the tyres mounted on the vehicle.

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