Method and system for detecting an interaction condition of a tyre with a surface

Abstract

Method and system (99) for detecting an interaction condition (IC) of a tyre (3) with a surface (900), wherein the system (99) comprises a monitoring device (4) fixed to an inner surface (5) of the tyre (3) at a crown portion (6) and configured to acquire a radial acceleration signal (AS) from the crown portion (6), and a processing unit (8) in communication with the monitoring device (4) and programmed to receive from the monitoring device (4) the radial acceleration signal (AS) and to perform the following steps of the method: calculating an adjustment factor Af according to the formula Af = ASavg + w2R*, where ASavg is an average value of the radial acceleration signal (AS), w is the angular velocity of the tyre, and R* is a parameter representative of a radius of the tyre (3); obtaining an adjusted radial acceleration signal (ASa) by a difference between the radial acceleration signal (AS) and the adjustment factor (Af); detecting the interaction condition (IC) as a function of the adjusted radial acceleration signal (ASa).

Description

[0001] DESCRIPTION

[0002] Title: METHOD AND SYSTEM FOR DETECTING AN INTERACTION CONDITION OF A TYRE WITH A SURFACE

[0003] Technical Field of the Invention

[0004] The present invention relates to a method and a system for detecting an interaction condition of a tyre with a surface. The present invention also relates to a vehicle comprising the detection system.

[0005] State of the art

[0006] Typically a tyre has a structure that is substantially toroidal around an axis of rotation thereof during operation, and presents an equatorial plane orthogonal to the axis of rotation, said equatorial plane being typically a plane of (substantial) geometric symmetry (e.g., neglecting any minor asymmetries, such as the tread pattern and / or the markings on the sidewalls and / or the internal structure).

[0007] By "crown portion" it is meant a portion of tyre located at the tread band.

[0008] The term "radial" is used with reference to a perpendicular direction to the axis of rotation of the tyre. By "footprint" it is meant the portion of the outer surface of the tread band which, during the rolling of the mounted tyre subjected to a load (for example, due to mounting on a vehicle), is at any given moment in contact with the rolling surface. The footprint typically has substantially null curvature (or substantially infinite radius of curvature), or in any case, it substantially assumes the conformation of the rolling surface. By "footprint portion" it is meant a respective crown portion corresponding (instantaneously) to the footprint.

[0009] The expression "lying internally" or "externally to the footprint portion" referred to a crown portion means that, as a result of the rotation of the tyre, the respective crown portion comes to be located either inside or outside the footprint portion of the tyre at a given instant / time interval, or at a given (corresponding) angular position / angular interval.

[0010] By "passage internally to the footprint portion" referred to said crown portion, it is meant an interval, preferably whole, expressed for example in units of time or in degrees of rotation (e.g., relative to a full rotation), during which the crown portion continuously lies inside the footprint portion of the tyre as a result of the rotation of the tyre. The passage can also, for example, consist of a single moment in time or angular position wherein the crown portion coincides with the footprint portion in the case of identical surface extension of the two portions.

[0011] In the present context, the term "interaction condition of a tyre" refers globally to a condition to which the tyre is subjected due to, and / or as a consequence of, rolling on a given surface. A condition of interaction can be, for example, a condition of aquaplaning (partial or total) to which the tyre may be subjected, as well as one or more quantities related to the rolling tyre, such as the current radius of the tyre, the angular speed, etc.

[0012] Summary of the Invention

[0013] In the context of monitoring a vehicle in motion on a surface, the Applicant has found it particularly advantageous to detect a condition of interaction of a tyre of the vehicle, rolling on the surface, with the surface on which the vehicle is traveling.

[0014] The detection of the interaction condition can indeed provide useful control parameters related to the tyre, such as one or more physical quantities inherent to the tyre, for example, the angular speed of the tyre, the current radius, or operating conditions of the tyre with respect to the surface, such as the occurrence of an aquaplaning condition of the tyre.

[0015] Such detection of the interaction condition is thus part of the broader context of the vehicle's active safety controls, serving as a useful method for detecting parameters from which it is then possible to calibrate activation and / or adjustment routines for these active safety controls.

[0016] In the above context, the Applicant has realized that it is particularly advantageous to detect said interaction condition of a tyre from the detection of a radial acceleration signal of a crown portion of said tyre, for example, by means of a sensor fixed directly to the inner surface of the tyre (i.e., the surface facing the mounting rim when the tyre is mounted). For this reason, it is important that the detected signal is as free as possible from measurement errors, since, as previously mentioned, it is through the detection of said interaction condition that control parameters are identified, which are used to trigger vehicle control systems.

[0017] However, the Applicant has also found that, during the use of the tyre, the aforementioned radial acceleration detection sensors may be subject to progressive drift of their operating conditions relative to the factory settings. For example, the Applicant has found that one phenomenon that may potentially occur is the variation in the offset value of the acceleration sensor compared to the factory value measured during the calibration phase of the sensor. In summary, the offset value is the value returned by default by the acceleration sensor in the presence of zero acceleration, at least along the radial component, of the tyre (tyre not rotating). If this offset value is known, such as during the acceleration calibration phase of the sensor, its contribution to the reading provided by the sensor can be appropriately taken into account to obtain reliable measurements.

[0018] However, the Applicant has observed that the offset value can vary over time, for example due to particular operating temperatures and / or working conditions, aging, etc., in an unpredictable manner, both in terms of the timing of the variation and the extent of this variation, resulting in the introduction of errors in the radial acceleration values returned by the sensor. Following such a variation in the offset value, an acquired acceleration signal would be rigidly and entirely shifted towards higher or lower values (translation along the y-axis, for example, in an acceleration / time graph), without the acquired acceleration values actually corresponding to the real operating conditions of the tyre.

[0019] On the other hand, estimating the offset value of the acceleration sensor is complex, especially in real-world conditions with tyres equipped with sensors and placed on the market for various types of vehicles.

[0020] A theoretical solution to this issue could be provided by performing a new sensor calibration routine to estimate the new offset value. However, from a practical point of view, the Applicant has found that such a sensor calibration routine is not feasible, as it would require, for each tyre equipped with a sensor placed on the market, a periodic recall of the tyre to a laboratory, followed by the execution of the new calibration routine.

[0021] Furthermore, even in the context of performing such a new calibration routine, it would not be entirely effective, as the phenomenon of offset drift could reoccur shortly after calibration, making it of limited practical use.

[0022] The Applicant has therefore addressed the problem of detecting an interaction condition of a tyre with a surface in a simple, precise, reliable, and robust manner over time, in light of the aforementioned phenomenon of offset value variation.

[0023] According to the Applicant, the aforementioned problem is solved by a method and a system for detecting an interaction condition of a tyre with a surface, wherein a raw radial acceleration signal of a crown portion of the tyre is acquired, and this raw signal is processed to obtain an adequate radial acceleration signal of the crown portion in which the contribution from the offset value present in the raw signal is eliminated, and wherein the interaction condition is detected based on this adequate signal.

[0024] According to one aspect, the invention relates to a method for detecting an interaction condition of a tyre with a surface.

[0025] The method preferably comprises providing a monitoring device fixed on an inner surface of said tyre at a crown portion of said tyre.

[0026] The method preferably comprises acquiring, during rolling of said tyre on said surface with an angular speed, a radial acceleration signal of said crown portion of said tyre, more preferably by means of said monitoring device. The method preferably comprises calculating an adjustment factor Af according to the following formula:

[0027] Af = ASavg + w2R*

[0028] - wherein ASavg is an average value of said radial acceleration signal,

[0029] - wherein w is said angular speed of said tyre,

[0030] - wherein R* is a parameter representative of a radius of said tyre;

[0031] In a first embodiment, the method preferably comprises obtaining an adjusted radial acceleration signal by a difference between said radial acceleration signal and said adjustment factor Af.

[0032] The method preferably comprises detecting said interaction condition of said tyre with said surface as a function of said adjusted radial acceleration signal (or at least a portion thereof, as further described below).

[0033] According to another aspect, the invention relates to a system for detecting an interaction condition of a tyre with a surface.

[0034] Preferably, the system comprises a monitoring device fixed on an inner surface of said tyre at a crown portion of said tyre and configured for acquiring, during a rolling of said tyre on said surface with an angular speed, a radial acceleration signal of said crown portion of said tyre.

[0035] Preferably, the system comprises a processing unit in communication with said monitoring device.

[0036] Preferably, said processing unit is programmed for receiving said radial acceleration signal from said monitoring device.

[0037] Preferably, said processing unit is programmed for calculating an adjustment factor Af according to the following formula:

[0038] Af = ASavg + w2R* wherein ASavg is an average value of said radial acceleration signal, wherein w is said angular speed of said tyre, wherein R* is a parameter representative of a radius of said tyre. In a first embodiment, preferably said processing unit is programmed for obtaining an adjusted radial acceleration signal by a difference between said radial acceleration signal and said adjustment factor Af.

[0039] Preferably, said processing unit is programmed for detecting said interaction condition of said tyre with said surface as a function of said adjusted radial acceleration signal (or at least a portion of it, as further described below).

[0040] According to a further aspect, the invention relates to a vehicle equipped with tyres comprising the system for detecting according to the present invention.

[0041] According to the Applicant, the calculation of the aforementioned adjustment factor according to the formula described above allows for obtaining, during the normal operation of the tyre and potentially every time desired (even at each complete rotation of the tyre), an accurate, reliable, and always updated estimate of the contribution made by the offset value to the acquired radial acceleration signal, i.e., the raw signal, through easily obtainable quantities and without necessarily having to directly calculate the offset value.

[0042] The obtaining of the adjusted radial acceleration signal by taking the difference between the acquired radial acceleration signal and the adjustment factor allows for eliminating, from the acquired radial acceleration signal, the contribution provided by the offset value, whatever it may be, and thus making the adjusted signal independent of the offset value and any respective variation.

[0043] In this way, the aforementioned issues of sensor reading unreliability due to the unpredictable variation of the offset value are eliminated, as well as those related to potential solutions aimed at estimating the offset value itself, such as new calibration routines. This results in the direct acquisition, by the processing unit, typically onboard the vehicle, of the adjusted radial acceleration signal immune from the unpredictable measurement errors related to the variation of the offset value. Thus, it is possible to detect the interaction condition of the tyre in a simple, precise, reliable, and robust manner over time.

[0044] The term "average value" referred to the acquired radial acceleration signal means the average of the radial acceleration values of the crown portion acquired by the sensor within a given acquisition interval. The average may, for example, be an arithmetic mean.

[0045] The present invention in one or more of the above aspects may feature one or more of the following preferred characteristics.

[0046] Preferably said processing unit is programmed to perform one or more of the following operations preferably provided for the method according to the present invention.

[0047] Preferably providing said monitoring device comprises arranging at least one sensor suitable for detecting at least one radial component of an overall acceleration of said crown portion of said tyre.

[0048] Preferably said monitoring device comprises said sensor. For example, the sensor is encapsulated in a containment body of the monitoring device, wherein said containment body is fixed to said internal surface of the tyre. The sensor, typically following encapsulation in the containment body, may be arranged at a certain distance (e.g. around one centimetre) from the inner surface of the tyre.

[0049] In one embodiment, said method comprises calculating said parameter representative of the radius of said tyre as a function of a geometric radius of said tyre and of said distance between said inner surface of said tyre and said sensor. In this way, the calculation of the representative parameter requires reduced computational effort, as it involves quantities considered constant.

[0050] Preferably said parameter representative of the radius is calculated by the difference between said geometric radius (internal, i.e., between a center of rotation of the tyre and said inner surface) and said distance between the inner surface of the tyre and the sensor. In this way, the calculation is simple and direct.

[0051] In one embodiment, said method comprises estimating said parameter representative of the radius of said tyre as a function of one or more of the following operative parameters: vertical load acting on said tyre, inner pressure of said tyre, said angular speed of said tyre. In this way, an estimate of the parameter representative of the radius can be obtained with high precision.

[0052] Preferably said radial acceleration signal comprises one or more, more preferably a plurality of, acquired values of radial acceleration of said crown portion of said tyre. For example, the radial acceleration signal is a digital signal. Preferably obtaining said adjusted radial acceleration signal comprises subtracting said adjustment factor directly from each of said one or more acquired values of radial acceleration. Preferably said adjusted radial acceleration signal comprises one or more, more preferably a plurality of, adjusted values of radial acceleration. Preferably each adjusted value of radial acceleration is calculated by subtracting said adjustment factor from a respective acquired value of radial acceleration. In this way, the adjusted signal is obtained in a simple and direct manner. For example, the adjusted radial acceleration signal is also a digital signal.

[0053] Preferably, acquiring said radial acceleration signal is performed within an acquisition window comprising at least a first portion of a complete rotation of said crown portion around an axis of rotation of said tyre for which said crown portion lies externally to a footprint portion of said tyre. In other words, the radial acceleration signal is preferably acquired at least in a time interval, or an angular interval as a fraction of the full rotation, in which the crown portion lies externally to the footprint portion of the tyre. In this way, the accuracy of the acquired signal is improved, as the radial acceleration of the crown portion is acquired when it is in free rotation, i.e., not subject to potential disturbance phenomena related to passing through the footprint portion.

[0054] In one embodiment, the acquisition window may coincide with a single time instant or a single angular position (i.e., a radial acceleration signal corresponding to a single value of radial acceleration is acquired).

[0055] Preferably said acquisition window further comprises a second portion of said complete rotation of said crown portion around said axis of rotation of said tyre for which said crown portion lies internally to said footprint portion of said tyre. In this way, the acquisition is simplified as it is not necessary to discriminate whether the crown portion lies within the footprint portion. The Applicant has indeed realized that the aforementioned potential disturbance phenomena related to the passage of the crown portion through the footprint portion can be mitigated by acquisitions made outside the footprint portion.

[0056] Preferably, said acquisition window corresponds to at least half of said complete rotation of said crown portion, more preferably it corresponds to an entire full rotation of the crown portion. In this way, the acquisition is extremely simple and does not require any additional interventions (for example, to discriminate whether the crown portion is inside or outside the footprint portion). Preferably, said acquisition window is centered on a passage of said crown portion internally the footprint portion of said tyre. In this way, the accuracy of the adjusted signal is further improved.

[0057] Preferably, said first portion of said complete rotation is contiguous to said second portion of said complete rotation. In this way, the acquisition is further simplified.

[0058] Preferably, said method comprises calculating said average value of the radial acceleration signal over the entire extent of said acquisition window. In this way, the calculation is simple and does not require particular precautions. Preferably, detecting said interaction condition of said tyre comprises identifying, in said adjusted radial acceleration signal, a sub-portion of said adjusted radial acceleration signal corresponding to a passage of said crown portion internally to a footprint portion of said tyre. The Applicant has indeed observed that the sub-portion of the adjusted signal corresponding to the passage of the crown portion in the footprint is particularly advantageous for detecting the interaction condition, especially when the interaction condition represents a condition of aquaplaning of the tyre on the surface, as further described below.

[0059] Preferably, detecting said interaction condition of said tyre comprises calculating a comparison parameter as a function of a respective average value of said adjusted radial acceleration signal in said sub-portion. The Applicant has found that calculating the respective average value of the adjusted radial acceleration signal in the sub-portion is particularly advantageous for calculating the comparison parameter (on the basis of which the interaction condition is detected, as described below). In fact, since the respective average value of the adjusted radial acceleration signal in the sub-portion, under normal rolling conditions of the tyre on a dry surface, should be substantially equal to zero (because the radial acceleration of the footprint portion is zero as the footprint portion has no curvature), it is advantageous, for example in terms of ease of detection and / or calculation, to check for any deviation of this respective average value from zero (deviation from zero, which the Applicant has advantageously observed to allow detection of the interaction condition, as will be described below).

[0060] In this context the Applicant observes that obtaining the adjusted radial acceleration signal free from the contribution of the offset value of the acceleration sensor, i.e., free from the aforementioned rigid translation of the entire signal to values different from the real ones, is particularly advantageous in order to reduce, or even eliminate, the risk of false positives in detecting the interaction condition. In the presence of the offset value contribution, it could indeed result in a respective average value of the adjusted radial acceleration signal in the sub-portion that is different from zero (offset shift), without this corresponding to an actual and real interaction condition of the tyre with the surface. Preferably, detecting said interaction condition of said tyre comprises detecting said interaction condition of said tyre as a function of a comparison between said comparison parameter and at least one threshold value. In this way, the detection is quick and straightforward.

[0061] In one embodiment, said respective avarage value of the adjusted radial acceleration signal in the sub-portion is calculated by weighted averaging with weights defined according to a Gaussian or Normal distribution. In this way, the accuracy of detecting the interaction condition is improved. For example, by assigning greater weight to the adjusted radial acceleration values located centrally in the sub-portion compared to the extreme values, any signal disturbances due to the passage of the crown portion in the edge regions of the footprint portion are eliminated. In a preferred embodiment, said interaction condition is representative of at least one aquaplane condition of said tyre on said surface. The term "aquaplaning condition" refers to the condition in which a tyre, rolling on a surface, loses its grip with the surface, even to the point of completely losing it, due to the presence of a layer of water between the tyre and the surface. The Applicant has found that the present detection method is particularly advantageous for detecting one or more aquaplaning conditions of the tyre on the surface.

[0062] Preferably (particularly when said interaction condition is representative of at least one aquaplaning condition of said tyre on said surface), said comparison parameter is calculated as a function of a ratio between said respective average value of the adjusted radial acceleration signal in said sub-portion and said angular speed squared of said tyre. In this way, the comparison parameter is normalized with respect to the angular speed of the tyre and thus independent of the tyre's rotational speed. This simplifies the detection of the condition, as, for example, it is possible to maintain a constant threshold value despite variations in the tyre's angular speed.

[0063] Preferably (particularly when said interaction condition is representative of at least one aquaplane condition of said tyre on said surface), detecting said interaction condition comprises detecting a first or a second interaction condition if said comparison parameter is less than or greater than respectively a second threshold value or a first threshold value. The first and second interaction conditions, when the interaction condition is representative of at least one aquaplaning condition, each represent a respective aquaplaning condition of the tyre. According to the Applicant, it is thus advantageously possible to detect two distinct aquaplaning conditions using a single comparison parameter.

[0064] In one embodiment, said first threshold value is greater than said second threshold value. Preferably, said first threshold value is greater than zero. Preferably, said second threshold value is less than zero. Such characteristics related to the threshold values have proven particularly suitable for detecting the first and the second interaction condition, in particular when the interaction condition is representative of at least one aquaplaning condition of the tyre (as described below).

[0065] Preferably, said method comprises regulating, as a function of said detected interaction condition, a control apparatus of said vehicle, for example an ABS system of the vehicle or a traction control system. In this way, it is possible to control the vehicle in a feedback manner, with significant advantages for safety.

[0066] Preferably, said acquisition window is repeated in each complete rotation of said tyre. Preferably, for each complete rotation of said tyre, said method comprises repeating:

[0067] - acquiring a radial acceleration signal of the crown portion;

[0068] - calculating an adjustment factor Af according to the following formula:

[0069] Af = ASavg + w2R* where ASavg is the average value of the radial acceleration signal and w is the respective angular speed of the tyre referring to the current rotation (and where R* can be estimated at each rotation or kept constant);

[0070] - obtaining an adjusted radial acceleration signal by the difference between said radial acceleration signal and said adjustment factor;

[0071] - detecting an interaction condition of said tyre with said surface as a function of said adjusted radial acceleration signal. In this way, the method is dynamically updated, proving to be highly versatile.

[0072] Brief description of the drawings

[0073] Figure 1 schematically shows a vehicle according to the present invention;

[0074] Figure 2 schematically shows a detail of the vehicle of Figure 1 ;

[0075] Figure 3 schematically shows a section of Figure 2;

[0076] Figure 4 shows a block diagram of the phases of a first embodiment of a detection method according to the present invention;

[0077] Figure 5 shows in detail a respective logical block of the diagram of Figure 4;

[0078] Figure 6 shows an application of the method according to the present invention;

[0079] Figure 6b shows a diagram of a tyre rolling on a surface;

[0080] Figures 7 and 8 show some exemplary applications of the method according to the present invention.

[0081] Detailed description of some embodiments of the invention

[0082] The features and advantages of the present invention will be further clarified by the following detailed description of some embodiments, presented by way of example and not as a limitation of the present invention, with reference to the attached figures.

[0083] Figure 1 schematically shows a vehicle 1 according to the present invention. Vehicle 1 can be a vehicle with an internal combustion engine and / or electric motor, with two or more driven wheels.

[0084] Exemplarily the vehicle 1 comprises four wheels 7 (distributed over two axles), each equipped with a respective tyre 3 (partially shown also in Figure 2) rolling on a surface 900 (shown in Figures 6b, 7, and 8). In one embodiment (not shown), the vehicle may have three or more axles.

[0085] The vehicle 1 exemplarily comprises a system for detecting 99 an interaction condition of a tyre 3 with surface 900. Exemplarily the system for detecting 99 is capable of detecting a respective interaction condition of each tyre 3 of vehicle 1 with surface 900.

[0086] The system 99 exemplarily comprises a monitoring device 4 for each tyre 3 (Figures 1 , 2, and 3). For example, the detection device 4 may be of the type described in one of the following documents in the name of the same Applicant: WO 2018 / 065846 A1 , WO 2019 / 123118 A1 , WO 2020 / 026281 A1 , WO 2020 / 026282 A1.

[0087] Exemplarily each monitoring device 4 is fixed to an inner surface 5 of the respective tyre 3, at a crown portion 6 of the respective tyre 3 (Figures 2 and 3). In particular, the monitoring device 4 can be fixed to a liner of tyre 3, typically by gluing (for example by means of a structural adhesive or by means of a pressure-sensitive adhesive - PSA). Preferably, the monitoring device 4 can be fixed substantially at an equatorial plane 100 of tyre 3. Further monitoring devices (not shown) can be arranged in more lateral position on the inner surface of tyre 3, and / or at different angular positions along the inner circumference of tyre 3.

[0088] Exemplarily the crown portion 6 coincides with a portion of the tyre located at the tread area and, substantially, underlies a base surface of the monitoring device (that is, the surface through which the device is fixed to the inner surface 5, Figure 3).

[0089] Optionally, the crown portion can be identified as a portion of the tyre with a greater extension than the base surface of the monitoring device.

[0090] Exemplarily each monitoring device 4 is configured to acquire, during a rolling of the respective tyre 3 on the surface with angular speed w, a radial acceleration signal AS of the crown portion 6 of tyre 3. In detail, each monitoring device 4 exemplarily comprises a respective sensor 41 (schematically shown in Figure 3) suitable for detecting at least one radial component of an overall acceleration of the crown portion 6 of tyre 3.

[0091] The system for detecting 99 also exemplarily comprises a processing unit 8 (shown only schematically in Figure 1) in communication with each monitoring device 4, for example via a radio signal and / or wired connection. The processing unit may be installed on board the vehicle or directly integrated into one or more of the monitoring devices 4, or even within sensor 41. Hybrid hardware and / or software solutions may also be provided, comprising one or more of the alternatives just mentioned.

[0092] In use, the system for detecting 99 allows for performing a method of detecting an interaction condition of a tyre 3 with surface 900 according to the present invention, typically using one or more hardware devices programmed via one or more software modules residing and / or loaded onto suitable memories.

[0093] A first embodiment of the detection method according to the present invention will be described below with reference to Figures 4-6. The following will be described with reference to a given tyre 3 equipped with its respective monitoring device 4, but it can be conceptually extended to each of the tyres 3 of vehicle 1 .

[0094] First, the method exemplarily comprises acquiring, during the rolling of tyre 3 on surface 900 with the angular speed w, the radial acceleration signal AS of the crown portion 6 of tyre 3, using the monitoring device 4 associated with the given tyre. Exemplarily the processing unit 8 is programmed to receive the radial acceleration signal AS from the monitoring device 4.

[0095] Exemplarily the radial acceleration signal AS comprises a plurality of acquired values of radial acceleration of the crown portion of the tyre. For example, the radial acceleration signal AS is a digital signal. A graphical example of the radial acceleration signal AS is shown in Figure 6, where the radial acceleration in m / s2is represented on the vertical axis, and the progressive number of sampling values is represented on the horizontal axis. Alternatively (not shown), the radial acceleration signal AS may be plotted as a function of time or rotation degrees relative to the full rotation (e.g., an angular range between 0°-360°, or the entire full rotation).

[0096] Exemplarily, not shown, the radial acceleration signal AS may be obtained after analog-to-digital conversion of a corresponding analog signal produced by sensor 41 , optionally suitably processed (e.g., using a calibration curve) to obtain a vector of acquired radial acceleration values expressed in m / s2. Alternatively, the acquired signal AS may be expressed in a pure integer scale.

[0097] Exemplarily acquiring the radial acceleration signal AS is performed in an acquisition window corresponding to a full complete rotation of the crown portion 6 around the rotation axis 200 of the tyre (i.e., in one full revolution of monitoring device 4 around the rotation axis 200 of tyre 3).

[0098] Exemplarily the shape of the radial acceleration signal AS obtained and shown in Figure 6 includes a peak P where the radial acceleration values approach zero, and two tails Z, positioned on opposite sides of peak P.

[0099] The tails Z of the radial acceleration signal AS correspond, each or globally, to a first portion of a full rotation of the crown portion 6 around the rotation axis 200 of tyre 3, in which the crown portion 6 lies externally to the footprint portion of tyre 3. Exemplarily the footprint portion corresponds to the segment C-D in Figure 6b (the corresponding letters also shown in Figure 6), and the tails Z correspond exemplarily to the segments A-B and E-A in Figures 6 and 6b, respectively.

[0100] Exemplarily, with reference to Figures 6 and 6b, the peak P of the radial acceleration signal AS corresponds to a passage of the crown portion 6 inside the footprint portion C-D of tyre 3. Exemplarily, the peak P thus corresponds to a second portion of the full rotation of crown portion 6 around the rotation axis 200 of tyre 3, in which the crown portion 6 lies inside the footprint portion C-D of tyre 3.

[0101] The remaining portions of the radial acceleration signal AS, exemplarily corresponding respectively to the segments B-C and D-E in Figures 6 and 6b, correspond to transition regions that can be defined as the entry and exit regions from the footprint portion C-D. Conceptually, these transition regions can be considered part of the aforementioned first portion of the full rotation of crown portion 6. Exemplarily the first and second portions of the full rotation of crown portion 6 are thus contiguous to each other.

[0102] Exemplarily the acquisition window is centered on the passage of crown portion 6 inside the footprint portion C-D of tyre 3.

[0103] Exemplarily the processing unit 8 is programmed to perform the following operations foreseen for the detection method, symbolically depicted in Figure 4 and, in detail, in Figure 5.

[0104] Exemplarily the method therefore comprises calculating an adjustment factor Af according to the following formula:

[0105] Af = ASavg + w2R*

[0106] - wherein ASavg is the average value of the radial acceleration signal AS,

[0107] - wherein w is the angular speed of tyre 3,

[0108] - wherein R* is a parameter representative of a radius of tyre 3.

[0109] Exemplarily the average value ASavg of the radial acceleration signal AS is calculated as the arithmetic mean of the acquired values of radial acceleration. Exemplarily, the average value ASavg is calculated over the entire acquisition window.

[0110] The Applicant has indeed observed that the presence of peak P in the acquired radial acceleration signal does not significantly affect the calculation of the average value (as also shown in Figure 6), which can therefore be performed over the entire acquisition window, advantageously avoiding a routine for identifying, in the acquired signal AS, at least the peak region P (for example, in order to exclude it, preferably along with the aforementioned transition regions, from the calculation of the average value ASavg). Alternatively, such a routine for identifying the peak region P can be provided, and the average value ASavg can be calculated over part of the acquisition window comprising (or corresponding to) the first portion (i.e., the tails Z of the AS signal).

[0111] Exemplarily the method further comprises calculating the parameter R* representing the radius of tyre 3 as a function of a geometric (internal) radius r (not shown) of tyre 3 and a distance d between the inner surface 5 of the tyre and sensor 41 (Figure 3), more specifically by the difference between the geometric radius r and the distance d (i.e., R* = r - d). Exemplarily, in fact, sensor 41 is encapsulated in a containment body 42 of the monitoring device 4, where the containment body 42 is fixed to the inner surface 5 of tyre 3. The sensor 41 , following encapsulation in the containment body, is exemplarily arranged at the aforementioned distance d from the inner surface 5.

[0112] In one embodiment (not shown), the method comprises estimating the parameter representing the radius of the tyre as a function of one or more of the following operational parameters: vertical load acting on the tyre, internal tyre pressure, angular velocity of the tyre. For example, the estimation of the parameter representing the radius may include performing a plurality of tests on one or more tyres of the same type as the tyre mounted on the vehicle, where each test is performed on a respective tyre having a predetermined value of one or more of the aforementioned operational parameters. Preferably, it is also provided to determine the value of the parameter representing the radius of the tyre based on the results of the aforementioned plurality of tests, for example using linear regression methodologies.

[0113] The method exemplarily comprises obtaining an adjusted radial acceleration signal ASa by the difference between the radial acceleration signal AS and the adjustment factor Af. In detail, it is exemplarily provided to obtain the adjusted radial acceleration signal ASa as a digital signal comprising a vector, the individual values of which, referred to as the adjusted radial acceleration values, are each calculated by the difference between a respective acquired value of radial acceleration from the acquired radial acceleration signal AS and the adjustment factor Af. An example of an adjusted radial acceleration signal ASa is exemplarily shown on the right side of figure 6 (the radial acceleration values in m / s2are shown on the y-axis, and the sampling values are shown on the x-axis). As can be observed, the adjusted radial acceleration signal ASa is identical to the acquired radial acceleration signal AS, except for a rigid translation towards higher radial acceleration values. The amplitude of this translation corresponds to the contribution made to the signal by the offset value of sensor 41. The Applicant has in fact realized that the adjustment factor Af, as calculated above, is representative of this contribution made by the offset value, without introducing the need to directly calculate such a contribution (which is generally unknown due to the random and unpredictable phenomena of variation of such an offset value).

[0114] The adjusted radial acceleration signal ASa obtained by subtracting the adjustment factor Af from each acquired value of radial acceleration is therefore cleansed of this offset contribution, and thus independent of the offset value and any corresponding variation over time. It is observed that the adjusted radial acceleration signal ASa reaches values close to zero at the respective peak, as correctly expected (since the radial acceleration of the contact patch is zero).

[0115] Exemplarily the method therefore comprises detecting the interaction condition IC of the tyre 3 with the surface 900 as a function of the adjusted radial acceleration signal ASa.

[0116] The detection of the interaction condition IC is exemplarily entrusted to the ICdet routine, shown in Figure 4 and, in detail, in Figure 5.

[0117] Exemplarily detecting the interaction condition IC of the tyre 3 comprises identifying, in the adjusted radial acceleration signal ASa, a sub-portion ASaP of the adjusted radial acceleration signal ASa corresponding to the passage of the crown portion 6 internally to the footprint portion C-D of the tyre 3. Exemplarily, the sub-portion ASaP corresponds to the peak of the adjusted radial acceleration signal ASa (which in turn corresponds to the peak P of the acquired radial acceleration signal AS, except for the aforementioned rigid translation).

[0118] In a second embodiment (not shown), the method may comprise, instead of obtaining the adjusted radial acceleration signal ASa and identifying the sub-portion in the adjusted signal ASa as described above, identifying, in the radial acceleration signal AS, a respective sub-portion of the radial acceleration signal AS corresponding to a passage of the crown portion 6 internally to the footprint portion of the tyre 3.

[0119] Indeed, as described above, the radial acceleration signal AS also comprises this respective sub-portion (it is noted that the acquired signal AS and the adjusted signal ASa are identical except for the aforementioned rigid translation along the ordinate axis). The method may therefore comprise obtaining the sub-portion ASaP of the adjusted radial acceleration signal ASa by a difference between the radial acceleration signal AS in the respective sub-portion and the adjustment factor Af. In other words, it may be provided to correct only the respective sub-portion (after it has been appropriately identified) of the acquired radial acceleration signal AS using the adjustment factor (i.e., eliminating the offset value contribution only from the values of the acquired signal AS included in the respective sub-portion). From the perspective of signal processing, these operations are entirely equivalent to obtaining the entire adjusted signal ASa and identifying the sub-portion ASaP within the adjusted signal ASa.

[0120] In a third embodiment (not shown), the method, instead of obtaining the adjusted radial acceleration signal ASa and identifying the sub-portion in the adjusted signal ASa as described above, and alternatively to the aforementioned second embodiment, may include the following steps:

[0121] - identify, in the radial acceleration signal AS, the respective sub-portion of the radial acceleration signal AS corresponding to the passage of the crown portion 6 inside the tread portion of the tyre 3;

[0122] - calculate a further average value of the radial acceleration signal AS (only) in the respective sub-portion;

[0123] - obtain the average value mASa of the adjusted radial acceleration signal ASa in the sub-portion by subtracting the further average value of the radial acceleration signal AS in the respective sub-portion from the adjustment factor (Af).

[0124] In other words, in the third embodiment, it may be provided to calculate the further average value of the radial acceleration signal AS in the respective sub-portion and correct this further average value by subtracting the adjustment factor from the further average value to directly obtain the average value mASa of the adjusted radial acceleration signal ASa in the sub-portion.

[0125] From a signal processing point of view, the third embodiment is entirely equivalent to the second embodiment described above and the first embodiment, which involves obtaining the adjusted radial acceleration signal ASa and identifying the sub-portion in the adjusted signal ASa.

[0126] Returning now to the first embodiment, exemplary detecting the interaction condition IC of the tyre 3 comprises calculating a comparison parameter RV as a function of a respective average value mASa of the adjusted radial acceleration signal ASa in the sub-portion ASaP. It is further observed that, even in the second and third embodiments, it is always possible to obtain the average value mASa of the adjusted radial acceleration signal ASa in the sub-portion ASaP from which the comparison parameter RV can be calculated.

[0127] In one embodiment, the respective average value mASa of the adjusted radial acceleration signal ASa in the sub- portion ASaP may be calculated by a weighted average of the adjusted radial acceleration values of the adjusted radial acceleration signal ASa in the sub-portion ASaP, with weights distributed according to a Gaussian or Normal distribution.

[0128] Alternatively the average value mASa may be calculated by a weighted average with weights distributed in a manner other than a Gaussian distribution, or by an arithmetic mean.

[0129] Exemplarily detecting the interaction condition IC of the tyre thus comprises detecting the interaction condition IC of the tyre based on a comparison between the comparison parameter RV and at least one threshold value.

[0130] The above, exemplarily described with reference to figure 5 and the ICdet routine, will now be further detailed with reference to a specific application case of the detection method according to the present invention, with reference to figures 7 and 8, where the interaction condition IC to be detected represents at least one condition of aquaplaning of the tyre on the surface.

[0131] In this specific application case, the comparison parameter RV is exemplarily calculated as a ratio between the respective mean value mASa of the adjusted radial acceleration signal ASa in the sub-portion ASaP and the square of the angular velocity w of the tyre 3.

[0132] Advantageously, the comparison parameter RV is zero if mASa is zero, positive if mASa is positive, and negative if mASa is negative (since w2in the denominator is always a positive value).

[0133] Detecting the interaction condition IC exemplarily includes detecting a first or second interaction condition if the comparison parameter RV is less than or greater than a second threshold value T2 or a first threshold value T1 , respectively. In detail, the first threshold value T1 is greater than zero, and the second threshold value T2 is less than zero. For example, the first threshold value T1 and the second threshold value T2 are respectively equal to +0.05 and -0.05.

[0134] Exemplarily, detecting the first interaction condition occurs when the comparison parameter RV is less than the second threshold value T2, i.e., RV < T2 (in this example, RV < -0.05). This first interaction condition corresponds physically to the situation shown in figure 7, i.e., a total aquaplaning condition of the tyre where the tyre is completely lifted off the surface 900 by a layer of water 901 placed between the surface 900 and tyre 3. However, the combination of the tyre's rolling motion and the characteristics of the water layer is such that it does not compress the tyre in the same way as a dry surface would. Therefore, the tyre is deformed in the contact area, but with a deformation different from that on a dry surface (for simplicity, in figure 7 the tyre is shown as essentially circular, although in reality, some deformation in the contact area is still present). In this situation, the Applicant has observed that the adjusted radial acceleration signal ASa still exhibits a peak, as shown in figure 7, but it settles around values less than zero (with the difference from zero denoted as AAccr in figure 7), resulting in a respective average value mASa less than zero (and thus RV less than zero). The second threshold value of -0.05 is useful for distinguishing any background noise present in the acquired signal AS (and thus in the adjusted signal ASa).

[0135] Exemplarily detecting the second interaction condition occurs when the comparison parameter RV is greater than T1 , i.e., RV > T1 (in this example, RV > +0.05). This second condition corresponds physically to the situation shown in figure 8, i.e., a respective total aquaplaning condition of tyre 3, where the tyre is completely lifted off the surface 900 by the water layer 901 placed between surface 900 and tyre 3. In this condition, the combination of the tyre's rolling motion and the characteristics of the water layer causes a compression of the tyre greater than that from the surface, such that the lower portion of the tyre becomes significantly deformed (even inwardly bent) and thus is no longer flat as it would be on a dry surface. In this situation, the Applicant has observed that the adjusted radial acceleration signal ASa shows a peak pattern as shown in figure 8, i.e., with a peak that reaches radial acceleration values greater than zero (with the difference from zero denoted as AAccr in figure 8), resulting in a respective average value mASa greater than zero (and thus RV greater than zero). The first threshold value, exemplarily set at +0.05, is useful for distinguishing any background noise present in the acquired signal AS (and thus in the adjusted signal ASa). It is observed that the removal of the contribution from the offset value achieved by the method according to the present invention is particularly advantageous in the context of detecting the first and second interaction conditions as aquaplaning conditions. This is because, once the contribution from the offset value and any corresponding variations are eliminated, it is possible to conclude with the desired precision and reliability that a deviation in the respective average value mASa of the adjusted radial acceleration signal ASa in the sub-portion ASaP (figures 7 and 8) is due to a given aquaplaning condition of the tyre (and not to measurement errors introduced by the offset value).

[0136] Optionally, it may finally be provided to adjust a vehicle control system (not shown), such as an ABS system and / or a traction control system, based on the detected interaction condition IC (for example, based on the first and / or second interaction condition).

Claims

CLAIMS1. Method for detecting an interaction condition (IC) of a tyre (3) with a surface (900), the method comprising:- providing a monitoring device (4) fixed on an inner surface (5) of said tyre (3) at a crown portion (6) of said tyre (3);- acquiring, during a rolling of said tyre (3) on said surface (900) with an angular speed (w), a radial acceleration signal (AS) of said crown portion (6) of said tyre (3) by means of said monitoring device (4);- calculating an adjustment factor Af according to the following formula:Af = ASavg + w2R*- wherein ASavg is an average value of said radial acceleration signal (AS),- wherein w is said angular speed of said tyre (3),- wherein R* is a parameter representative of a radius of said tyre (3);- obtaining an adjusted radial acceleration signal (ASa) by a difference between said radial acceleration signal (AS) and said adjustment factor (Af);- detecting said interaction condition (IC) of said tyre (3) with said surface (900) as a function of said adjusted radial acceleration signal (ASa).

2. Method according to claim 1 , wherein providing said monitoring device (4) comprises arranging at least one sensor (41) suitable for detecting at least one radial component of an overall acceleration of said crown portion (6) of said tyre (3).

3. Method according to claim 2, comprising calculating said parameter (R*) representative of the radius of said tyre (3) as a function of a geometric radius (r) of said tyre and of a distance (d) between said inner surface (5) of said tyre (3) and said sensor (41).

4. Method according to claim 1 or 2, comprising estimating said parameter (R*) representative of the radius of said tyre (3) as a function of one or more of the following operative parameters: vertical load acting on said tyre (3), inner pressure of said tyre (3), said angular speed (w) of said tyre (3).

5. Method according to anyone of the previous claims, wherein said radial acceleration signal (AS) comprises one or more acquired values of radial acceleration of said crown portion (6) of said tyre (3), and wherein obtaining said adjusted radial acceleration signal (ASa) comprises subtracting said adjustment factor (Af) directly from each of said one or more acquired values of radial acceleration.

6. Method according to anyone of the previous claims, wherein acquiring said radial acceleration signal (AS) is performed within an acquisition window comprising at least a first portion of a complete rotation of said crown portion (6) around an axis of rotation (200) of said tyre (3) for which said crown portion (6) lies externally to a footprint portion of said tyre (3).

7. Method according to claim 6, wherein said acquisition window further comprises a second portion of said complete rotation of said crown portion (6) around said axis of rotation (200) of said tyre (3) for which said crown portion (6) lies internally to said footprint portion of said tyre (3).

8. Method according to claim 7, wherein said acquisition window corresponds to at least half of said completerotation of said crown portion (6), and wherein said first portion of said complete rotation is contiguous to said second portion of said complete rotation.

9. Method according to claim 6 or 7 or 8, comprising calculating said average value (ASavg) of the radial acceleration signal (AS) over the entire extent of said acquisition window.

10. Method according to anyone of the previous claims, wherein detecting said interaction condition (IC) of said tyre (3) comprises:- identifying, in said adjusted radial acceleration signal (ASa), a sub-portion (ASaP) of said adjusted radial acceleration signal (ASa) corresponding to a passage of said crown portion (6) internally to a footprint portion of said tyre (3);- calculating a comparison parameter (RV) as a function of a respective average value (mASa) of said adjusted radial acceleration signal (ASa) in said sub-portion (ASaP);- detecting said interaction condition (IC) of said tyre (3) as a function of a comparison between said comparison parameter (RV) and at least one threshold value.

11. Method according to claim 10, wherein said interaction condition (IC) is representative of at least one aquaplane condition of said tyre (3) on said surface (900), and wherein said comparison parameter (RV) is calculated as a function of a ratio between said respective average value (mASa) of the adjusted radial acceleration signal (ASa) in said sub-portion (ASaP) and said angular speed (w) squared of said tyre (3).

12. Method according to claim 10 or 11 , wherein detecting said interaction condition (IC) comprises detecting a first or a second interaction condition if said comparison parameter (RV) is less than or greater than respectively a second threshold value (T2) or a first threshold value (T1), wherein said first threshold value (T1) is greater than said second threshold value (T2).

13. System (99) for detecting an interaction condition (IC) of a tyre (3) with a surface (900), the system (99) comprising:- a monitoring device (4) fixed on an inner surface (5) of said tyre (3) at a crown portion (6) of said tyre (3) and configured for acquiring, during a rolling of said tyre (3) on said surface (900) with an angular speed (w), a radial acceleration signal (AS) of said crown portion (6) of said tyre (3);- a processing unit (8) in communication with said monitoring device (4), wherein said processing unit (8) is programmed for:- receiving said radial acceleration signal (AS) from said monitoring device (4);- calculating an adjustment factor Af according to the following formula:Af = ASavg + w2R*- wherein ASavg is an average value of said radial acceleration signal (AS),- wherein w is said angular speed of said tyre (3),- wherein R* is a parameter representative of a radius of said tyre (3);- obtaining an adjusted radial acceleration signal (ASa) by a difference between said radial acceleration signal (AS) and said adjustment factor (Af);- detecting said interaction condition (IC) of said tyre (3) with said surface (900) as a function of said adjusted radial acceleration signal (ASa).

14. System (99) according to claim 13, wherein said monitoring device (4) comprises at least one sensor (41) suitable for detecting at least one radial component of an overall acceleration of said crown portion (6) of said tyre (3), and wherein said processing unit (8) is further programmed for performing said method for detecting according to anyone of claims from 2 to 12.

15. Vehicle (1) equipped with tyres (3) comprising the system (99) for detecting according to claim 13 or 14.

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