METHOD AND SYSTEM FOR ESTIMATING A VEHICLE BODY MOTION DURING THE RUNNING OF A VEHICLE ALONG A ROAD SEGMENT

Abstract

A method and system are disclosed for estimating a relative motion of vehicle body portions with respect to each other along a road segment having a length (L); the method and system allow to estimate road unevenness induced vehicle body motions and are based on the estimation of the deformation, over multiple tire rotations, of at least two tires of a vehicle.

Claims

1-10. (canceled)

11. A method for estimating a relative motion of vehicle body portions with respect to each other along a road segment having a length, wherein the length corresponds at least to a plurality of tire rotations, the method comprising: a) associating a respective monitoring unit to at least two tires of a vehicle, wherein the monitoring units each comprise at least one respective sensing element adapted to measure at least one quantity descriptive of a respective deformation of the tires; b) fitting the at least two tires to a respective wheel of the vehicle and operating the vehicle to cause rotation of the at least two tires on a rolling surface along the road segment wherein, due to the fitting and operating, the at least two tires are deformed to form a respective contact area between each of the at least two tires and the rolling surface; c) for each of the at least two tires, measuring the quantity at least during respective passages of the respective monitoring units in correspondence of respective contact areas of the at least two tires, d) for each of the respective passages, processing the measured quantity to obtain a value of a respective tire deformation undergone by each of the at least two tires in each of the respective passages, and to obtain, for each of the at least two tires, a respective plurality of values of the respective tire deformation over multiple tire rotations, e) assembling the respective pluralities of values of the respective tire deformations to obtain, for each of the at least two tires, a respective curve representative of a deformation of the tires over multiple rotations along the road segment, resulting in at least two curves, f) comparing relative trends of the at least two curves to identify the relative motion of the respective vehicle body portions with respect to each other along the road segment.

12. The method according to claim 11, wherein the at least two tires are fitted to different axles of the vehicle.

13. The method according to claim 11, wherein the at least two tires are fitted to the same axle of the vehicle.

14. The method according to any of claim 11, wherein comparing relative trends of the at least two curves further comprises: calculating a respective Fourier transform of the at least two curves, to obtain at least a first and a second Fourier transforms, and identifying the relative motion based on a processing of the first and second Fourier transforms.

15. The method according to claim 14, further comprising the steps of: multiplying the first Fourier transform to the complex conjugate of the second Fourier transform to obtain a Fourier product curve, extracting a phase information related to at least one spatial wavelength from the Fourier product curve, and identifying the relative motion based on a processing of the phase information related to the at least one spatial wavelength.

16. The method according to claim 11, wherein the measuring of the quantity is carried out at a measuring frequency higher than or equal to 0.5 KHz.

17. The method according to claim 11, further comprising starting the measurement of the quantity when at least one following access condition is met: a speed of the vehicle is comprised within a predetermined speed range; and an absolute value of longitudinal acceleration of the vehicle is lower than a predetermined amount.

18. The method according to claim 17, wherein the speed of the vehicle within the predetermine speed range ranges from 40 km/hour to 100 km/hour; and wherein the absolute value of longitudinal acceleration of the vehicle is lower than 1 m/s.sup.2.

19. The method according to claim 11, wherein the monitoring unit is secured to a crown portion of the respective tire, and comprises at least one sensing element to measure at least a radial acceleration, a tangential acceleration, or a combination thereof of the crown portion during rotation of the tire.

20. A system for estimating a relative motion of vehicle body portions with respect to each other, wherein the system comprises at least two monitoring units to be respectively associated with at least two tires of the vehicle, the monitoring units respectively comprising at least one sensing element to measure at least one quantity descriptive of a deformation of the respective associated tire, wherein, when the at least two tires are fitted to respective wheels of the vehicle and the vehicle is operated to cause rotation of the tires on a rolling surface, due to the fitting and operating the tires, are deformed to form a respective contact area between the at least two tires and the rolling surface; wherein the system further comprises at least one processing unit comprising software modules adapted to estimate a relative motion of the vehicle body portions with respect to each other along a road segment, wherein the software modules are adapted: for each of the at least two tires, measuring the quantity at least during respective passages of the respective monitoring units in correspondence of the respective contact areas, for each of the respective passages, processing the measured quantity to obtain a value of a respective tire deformation undergone by each of the at least two tires in each of the respective passages, and obtaining, for each of the at least two tires, the respective plurality of values of the respective tire deformation over multiple tire rotations, assembling the respective pluralities of values of the respective tire deformations to obtain, for each of the at least two tires, a respective curve representative of a deformation of the tires over multiple rotations along the road segment, resulting in at least two curves, comparing relative trends of the at least two curves to identify the relative motion of the respective vehicle body portions with respect to each other along the road segment.

21. A vehicle having at least two tires fitted thereon, comprising a system for estimating the relative motion of the vehicle body portions with respect to each other according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0121] Additional features and advantages of the invention will be better apparent from the following description of some preferred embodiments thereof, made hereinafter for exemplifying and non limiting purposes, to be read with reference to the attached figures, in which:

[0122] FIG. 1 shows a road texture profile classification dividing the road texture/profile in short term and long term irregularities.

[0123] FIG. 2A qualitatively shows the respective movements of rear (solid line) and front (dashed line) vehicle body portions during vehicle pitching or heaving, while FIG. 2B shows the effect of road unevenness on a vehicle in the framework of the quarter car model.

[0124] FIG. 3 shows the relative dynamic of the relatively fast tire rolling (≈10 Hz) and the relatively slow vehicle body motion (≈1 Hz) in the case of vehicle pitching.

[0125] FIG. 4 shows the relative dynamic of the relatively fast tire rolling (≈10 Hz) and the relatively slow vehicle body motion (≈1 Hz) in the case of vehicle heaving.

[0126] FIG. 5A shows a deformed tire wherein R.sub.Und (dashed) is the tire radius in the tire portion which is not deformed while R.sub.Def (solid) is the tire radius in the contact area, a portion where the tire is deformed on a rolling surface. FIG. 5B shows a deformed tire, and the passage of said monitoring unit associated to it in correspondence of a tire contact area. A monitoring unit associated to a tire is considered to be in correspondence of a tire contact area when is within a 120° angle comprising (but not necessarily centered around) a tire contact area.

[0127] FIG. 6 shows a monitoring unit fitted into a tire.

[0128] FIG. 7 shows a scheme of a monitoring unit according to an embodiment of the invention.

[0129] FIG. 8 shows a scheme of a vehicle comprising a tire monitoring system and a vehicle control system according to an embodiment of the invention.

[0130] FIG. 9 shows a scheme of a controlling unit according to an embodiment of the invention.

[0131] FIG. 10 shows the respective deformations curves of the four tires of a vehicle over multiple tire rotations along a 260 meters long road segment.

[0132] FIG. 11 shows the absolute values and phases of the Fourier transforms of the deformation curves of FIG. 10.

[0133] FIG. 12 shows the Fourier product curves of tire pairs according to the embodiment of FIG. 10 and FIG. 11.

[0134] FIG. 13 shows the respective deformations curves of the four tires of a vehicle over multiple tire rotations along a 20 meters long road segment.

[0135] FIG. 14 shows the absolute values and phases of the Fourier transforms of the deformation curves of FIG. 13.

[0136] FIG. 15 shows the Fourier product curves of tire pairs according to the embodiment of FIG. 12 and FIG. 13.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0137] Reference is made to FIG. 6 showing a portion of a tire (1) comprising a monitoring unit (2) adapted to measure a quantity descriptive of the deformation of a tire at a measuring frequency.

[0138] Said monitoring unit (2) is secured to a crown portion of said tire (1), preferably substantially in correspondence of the equatorial plane of the tire. In particular, the monitoring unit (2) may be glued or connected via an adhesive tape to the inner liner of the tire.

[0139] With reference to FIG. 7, the monitoring unit (2) comprises a sensing section (10), a battery (8), a processing unit (or CPU) (6) associated with a memory, a transceiver (7), an antenna (9).

[0140] The monitoring unit (2) can be of the type currently available on the market generally comprising temperature and/or pressure sensors and an accelerometer, or other inertial sensors, used for detecting the tire deformation, i.e., the output signal of the acceleration sensor (or other inertial device) is analysed, or processed, to derive information about tire deformations.

[0141] Particularly, the sensing section (10) of the monitoring unit (2) comprises an accelerometer (3), particularly a radial accelerometer, oriented within the monitoring unit (2) so as to have an axis substantially orthogonal to the inner surface of the tire. The accelerometer (3) is configured to output an acceleration measurement descriptive of deformations in radial direction which said tire (1) undergoes during rolling. Other sensing elements adapted for measuring physical quantities descriptive of tire deformations could be used, such as tangential accelerometers, lateral accelerometers, strain gauges, etc.

[0142] The sensing section (10) of said monitoring unit (2) further comprises a pressure sensor (4) configured to output a measurement of the pressure internal to said tire (1). The sensing section (10) of the monitoring unit (2) further comprises a temperature sensor (5) configured to output a measurement of the temperature of said tire (1). The accelerometer (3) is configured to operate at a measuring frequency and preferably said measuring frequency is higher than 0.5 KHz, more preferably higher than or equal to 1 KHz, even more preferably higher than or equal to 5 KHz.

[0143] According to an embodiment of the present invention, the measurement, at a measuring frequency, of the acceleration descriptive of deformations in radial direction which said tire (1) undergoes during rolling outputted by the accelerometer (3) is provided to the central processing unit, CPU, (6).

[0144] The central processing unit, CPU, (6) is configured, via suitable software/firmware modules, to receive, from the sensing section (10), data related to the measurements performed by the radial accelerometer (3) and the temperature and pressure sensors (4,5).

[0145] The CPU (6) is also configured, via suitable software/firmware modules, to process the data received from said sensors and accelerometer (3,4,5) in order to obtain, from said data, tire related parameters, in particular the deformation undergone by a tire associated with a certain monitoring unit over a tire rotation or multiple rotations of said tire.

[0146] Alternatively, the CPU (6) can be configured, via suitable software/firmware modules, to process said data up to a certain extent, i.e. to perform only part of the processing, and then to send the processing results to an external controlling unit (11), via the transceiver (7) and the antenna (9), to complete the processing up to obtain said tire related parameters, in particular to obtain the deformation undergone by a tire associated with a certain monitoring unit over a tire rotation or multiple rotations of said tire.

[0147] Ultimately the choice of whether distributing the processing between the monitoring units (2) and the external controlling unit (11) for the tire related parameter estimation is a tradeoff between several constraints to be balanced, such as: hardware complexity, battery consumption, cost, processing power available to the CPU of the monitoring units, etc.

[0148] The CPU (6) may be also configured, via suitable software/firmware modules, to receive access and/or stopping conditions from the external controlling unit. The access conditions may be used by the CPU (6) as a trigger to command the sensing section (10) to start the measurements needed for the estimation of the tire related parameters, and/or to start the processing needed for the estimation of the tire related parameters.

[0149] The stopping conditions may be used by the CPU (6) as a trigger to stop or suspend the measurements performed by the sensing section (10), and/or to stop or suspend the processing needed for the estimation of the tire related parameters.

[0150] The transceiver section (7) is configured for bidirectional communication via the RF antenna (9) with an external controlling unit (11) specifically configured for communication with the monitoring units (2) comprised within the tires of a vehicle. Alternatively, the transceiver section (7) can directly communicate, via the RF antenna (9), with a vehicle control system, such as the vehicle board computer. In preferred embodiments, the transceiver (7) comprises a Bluetooth Low Energy (BLE) module.

[0151] The battery (8) directly or indirectly feeds electrical power to the various components of the monitoring unit (2). In preferred embodiments, it can be a battery rechargeable with power scavenged from mechanical energy caused by tire rotation.

[0152] FIG. 8 schematically shows an embodiment of a system for estimating a relative motion of vehicle body portions with respect to each other along a road segment.

[0153] The system is implemented in a vehicle (100) fitted with four tires (1), each of which comprising a respective monitoring unit (2). The vehicle (100) may be for example a car. However, the present invention also applies to other kinds of vehicles, such as two or three wheeler scooters, motorbikes, tractors, buses, trucks or light trucks, i.e. to vehicles with two, three, four, six or more wheels distributed on two or more axles. The vehicle (100) can be driven by electrical power, or relying on thermal propulsion or it can be a hybrid vehicle.

[0154] The monitoring units (2) are in communication with a controlling unit (11).

[0155] In one embodiment the controlling unit (11) is in communication with a vehicle control system (12) configured for adjusting vehicle control parameters based on the relative motion of vehicle body portions with respect to each other along a road segment estimated by the monitoring units (2) and/or by the controlling unit (11). The vehicle control system (12) can be the control board computer of the vehicle (100), and/or a subsystem configured for adjusting at least one of said vehicle control parameters (e.g. a suspension control subsystem, a brake control subsystem, a steering control subsystem, a module configured for estimating a residual mileage of the vehicle).

[0156] In another embodiment data related to: the results of the measuring of said quantity representative of the deformations of said tires, and/or said plurality of values of said tire deformations and/or said respective curve representative of a motion of said respective vehicle body portions over multiple rotations of said tire along said road segment, are transmitted to a remote processing unit external to said vehicle as for example a cloud server.

[0157] Typically, the communication between the monitoring units (2) and the controlling unit (11) is a wireless communication (e.g. Bluetooth communication). The communication between the controlling unit (11) and the vehicle control system (12) can be wireless and/or wired (e.g. on a CAN BUS). In other preferred embodiments, the controlling unit (11) can be hardware of software module implemented in the vehicle control system (12).

[0158] The controlling unit (11) is external with respect to the tires (1) wherein the monitoring (2) units are secured. Said controlling unit (11) can be placed anywhere in the vehicle which can be reached by the wireless (e.g. Bluetooth) signal transmitted by the monitoring units (2).

[0159] For example, the external controlling unit (11) can be a box integrated in the vehicle. In another embodiment, the external controlling unit (11) can be a mobile personal device of the vehicle driver (e.g. a smartphone or a tablet), provided with suitable software applications/modules configured at least for communication with the monitoring units (2), as well as for processing data received from the monitoring units (2).

[0160] FIG. 9 schematically shows an embodiment of a controlling unit (11) suitable for a system for estimating a relative motion of vehicle body portions with respect to each other along a road segment of FIG. 8.

[0161] The controlling unit (11) comprises a GPS unit (13), a transceiver section (14), a RF antenna (15), an interface (16) to the vehicle control system (12), a battery (17), a processing unit (18) associating with a memory.

[0162] In the preferred embodiment shown in FIG. 11, the controlling unit (11) comprises a GPS unit (13). Alternatively, the controlling unit (11) may use data provided by an external GPS unit, for example a GPS unit on the vehicle or on a mobile personal device of the vehicle driver, such as a smartphone or a tablet.

[0163] In a preferred embodiment, said GPS unit (11) (either comprised within said controlling unit (11) or not) it is used to track the position of said road segment having a length (L) so as said road segment can be associated with a geographical map.

[0164] The transceiver section (14) of the controlling unit (11) is configured for bidirectional communication via a RF antenna (15) with the monitoring units (2). In preferred embodiments, the transceiver section (14) comprises a Bluetooth Low Energy (BLE) module.

[0165] The interface (16) can be a CAN BUS interface adapted for bidirectional communication with the vehicle control system (12).

[0166] The battery (17) directly or indirectly feeds electrical power to the various components of the controlling unit (11). In other embodiments, the controlling unit (11) can be powered by the vehicle battery, via the interface (16).

[0167] The processing unit, CPU, (18) of the controlling unit (11) is configured, via suitable software/firmware modules, to receive data from the monitoring units (2) comprised within the tires. Such data may comprise tire parameters estimated by the monitoring units (2), for example a tire deformation, or measurements performed by the monitoring units (2), or results of partial processing performed on said measurements by the monitoring units (2).

[0168] For example the monitoring unit (2) can transmit to the controlling unit (11) data regarding the results of the measuring of said quantity representative of the deformations of said tires, and/or said plurality of values of said tire deformations and/or said respective curve representative of a motion of said respective vehicle body portions over multiple rotations of said tire along said road segment.

[0169] The CPU (18) is also configured, via suitable software/firmware modules, to process such data in order to estimate the a relative motion of vehicle body portions with respect to each other or to communicate said estimated relative motion already provided by the monitoring unit (2) to the vehicle control system (12).

[0170] The CPU (18) may be also configured, via suitable software/firmware modules to monitor access and/or stopping conditions to be applied for triggering starting and/or stopping/suspending the estimation of the tire related parameter(s), like the tire deformation, and/or possibly discarding those measurements performed during acquisitions occurred within time intervals in which those access conditions were not met, or measurements not respecting predetermined quality standards.

[0171] Ultimately the choice of whether distributing the processing between the monitoring units (2) and the external controlling unit (11) for said at least two tires deformations estimation (and obtaining of the related deformation curves over multiple tire rotations) is a tradeoff between several constraints to be balanced, such as: hardware complexity, battery consumption, cost, processing power available to the CPU of the monitoring units, etc.

[0172] In the preferred embodiment shown in FIG. 9 and, a relative motion of vehicle body portions with respect to each other estimated by the CPU of the monitoring units (2) and/or by the CPU of the controlling unit (11) is/are eventually made available to the vehicle control system (12) via the interface (16).

[0173] In an exemplary operation mode, each of said at least two tires (1) fitted to a wheel of the vehicle (100) is caused to rotate on a rolling surface.

[0174] As a consequence of the fitting, the tire is deformed so as to form a contact area between the tire (1) and the rolling surface. Each monitoring unit (2) comprised within a tire (1) is preferably paired with said tire, e.g. by storing identifying information of the tire (e.g. tire identifier, tire size, tire model, tire radius etc.) within the memory associated with the CPU (6) of the respective monitoring unit (2).

[0175] Pressure and temperature measurements can be optionally performed by the monitoring unit (2) comprised within the tire (1) at discrete time intervals, for example every 30 seconds or upon request of said controlling unit (11) at any time during tire rolling. The start of pressure and temperature measurement can be triggered based on a signal sent by the accelerometer (3) when the tire starts to rotate, or upon request from the external controlling unit (11) or the vehicle control system (12).

[0176] The controlling unit (11) monitors the vehicle status based on GPS data and/or based on data read from the CAN BUS.

[0177] In one preferred embodiment when the speed of the vehicle (100) is between 40 km/h and 100 km/h (or more preferably within 60 km/h and 80 km/h) and/or when the absolute value of the longitudinal acceleration is lower than 1 m/s.sup.2, the controlling unit (11) determines that the access conditions are met and communicates to each of the monitoring units (2) to start the measurement of the selected physical quantity representative of the tire deformation, e.g. the radial acceleration, in order to start the estimation of at least one tire related parameter. A further access condition may be based on the check that the absolute value lateral acceleration of the vehicle is lower than 0.3 m/s.sup.2.

[0178] When the measurement of the quantity representative of a tire deformation is started, the radial accelerations (or another quantity representative of the deformation of a tire) of each of said at least two tires are measured at a measuring frequency at least during respective passages (or rotations) of said respective monitoring units in correspondence of said respective contact areas over multiple tire rotations along said road segment.

[0179] For example, a passage of a monitoring unit associated to a tire in correspondence of a tire contact area may correspond to the spanning, by the monitoring unit during tire rotation, of an angle (e.g. of about 120) degrees comprising (but not necessarily centered around) a tire contact area as shown in FIG. 5B.

[0180] In another embodiment, the measuring frequency can be changed in response to variation of the rotation frequency of said tire (1), so as to maintain a proper accuracy of the measurements of said quantity. The updated measuring frequency value can be communicated by said external controlling unit (11) to each of said monitoring units (2) of said at least two tires or, in another embodiment, an updated frequency can be calculated by each of said monitoring units (2).

[0181] In both the aforementioned embodiments, said measuring frequency is higher than or equal to 0.5 KHz, preferably higher than or equal to 1 KHz, even more preferably higher than or equal to 5 KHz.

[0182] By measuring at least during passages in the respective contact areas, an optimal trade-off can be achieved among several constraints: duration of the measurement, power consumption during measuring and power consumption during data transmission from the monitoring unit to the control unit and vice versa.

[0183] As previously discussed, the measuring of the radial acceleration (or of another quantity representative of the deformation of a tire) is carried out for each of said at least two tires over multiple tire rotations along a road segment having a length (L).

[0184] Provided that said length (L) corresponds at least to some tires rotations (preferably at least 5 tire rotations, even more preferably 10 tire rotations), said length (L) can be selected to any predetermined value of interest.

[0185] For example said length (L) can be 20 meters which corresponds at least to about 10 rotations of said at least two tires (assuming an average circumferential length of a tire of about 2 meters) and which is generally the “granularity” preferred to properly describe an unevenness parameter of a road segment.

[0186] The measuring of the radial acceleration can be iterated over many road segments having the same length (L) or even different lengths.

[0187] In FIG. 10 for example it is shown an example of a run lasting for 260 meters, i.e. for 13 road segments of identical length of 20 meters.

[0188] Alternatively the measurement of the radial acceleration can be stopped during one or more road segments and started again or the length (L) can be varied during the measurement of the radial acceleration.

[0189] Said length (L) can be set before the starting of the measurement in a predetermined mode operation or, alternatively, can be also selected in post processing fashion, after having acquired the measured radial acceleration for a sufficiently long amount of time or distance.

[0190] Generally speaking, the longer said length (L), the higher the resolution in terms of spatial frequencies accessible and, ultimately, the more accurate estimation of a vehicle body motion.

[0191] It is recalled here that a spatial frequency is the inverse of a spatial distance between periodically repeated portions of the road profile and has the dimension of an inverse of a length, generally it is expressed as 1/meters as in this description and related figures.

[0192] For example, if said length (L) is selected to be about 20 meters, the shortest accessible spatial frequency is 1/(20 meters).

[0193] Summarizing, the longer the length of said length (L) the shorter the spatial frequency accessible and the higher the resolution of the measurement for the estimation of a vehicle body motion starting from said at least two tires deformations.

[0194] The shortest accessible spatial frequencies can be increased, if necessary, by increasing the length (L) of the road segment under investigation, which, it is here recalled, can be selected also in post processing fashion.

[0195] On the other hand, the longest accessible spatial frequency is set by the circumferential length of a tire which has an average value of about 2 meters, hence the the longest accessible spatial frequency is 1/(2 meters).

[0196] Generally speaking the longest accessible spatial frequency is proportional to the inverse of a tire circumferential length.

[0197] The longest accessible spatial frequencies can be varied by increasing the number of monitoring units associated to each of said at least two tires, for example using two monitoring units in different position of a tire, in particular placed along a diameter of a tire, in this way the effective circumferential length of a tire can be considered as half, so that the the longest accessible spatial frequency increases accordingly.

[0198] In some other embodiments, the length (L) of the road segment can be selected upon requirement given by regulators.

[0199] During the measurement of the quantity representative of a tire deformation, such as the radial accelerations the measured radial acceleration data can be directly sent by the monitoring units (2) to the controlling unit (11) or can be partly processed by the monitoring units (2).

[0200] Alternatively the measured radial acceleration data can be directly sent by the monitoring units (2) to the controlling unit (11) when the measurement of the radial acceleration is over, in a post processing fashion.

[0201] In another embodiment part of the processing of the radial acceleration data is carried out within said monitoring units (2) while the rest of the processing is carried out by the controlling unit (11) or, in a further embodiment, the radial acceleration data (or a preprocessed version of said radial acceleration data) are sent to a processing unit (not shown) external to said vehicle, for example a cloud server.

[0202] As previously discussed the radial acceleration measuring by the monitoring units (2) of said at least two tires (1), is carried out at least during respective passages of said respective monitoring units (2) in correspondence of said respective contact areas over multiple tire rotations along said road segment.

[0203] It is worthy to recall here that to the purpose of the present invention, it is not necessary to estimate the deformation of a tire every rotation of said tire (1), but, depending on the vehicle speed, a deformation estimation every other tire rotation, or at some other slower rate, could be enough: the higher vehicle speed, the higher the tire rotation, and the lower the need of estimating the tire deformation every tire rotation in order to properly sample the relatively slowly varying (≈1 Hz) vehicle body motions, as previously extensively discussed.

[0204] In any case for each of said passages wherein the radial acceleration is measured for said at least two tires, the measured radial acceleration in each passage (or in each complete rotation) is processed to obtain, for each of said at least two tires, a respective deformation value associable to each of said passages.

[0205] In other words, as a result of the processing of the radial acceleration data of each of said passages, a respective plurality of values of a respective tire deformation for each of said two tires (1) are obtained.

[0206] A tire deformation of each passage, or rotation, is obtained in one embodiment by performing a double integration of the radial acceleration measured in each of said passages, or rotations, of said tires (1), and by tracking the maximum value of the obtained double integrated function; alternatively a tire deformation value can be obtained, for example, based on an estimation of the size/dimension/length of the contact area during each of said passages.

[0207] As previously discussed, said respective plurality of values of a respective tire deformation for each of said two tires can be further assembled, in one embodiment, within each monitoring unit (2) so as to obtain, for each of said at least two tires, a respective curve representative of the deformation of a tire over multiple rotations of said tire along said road segment; or, alternatively, said respective plurality of values can be sent to the controlling unit (11) external to said tire to be therein assembled or to be further sent to a processing unit (not shown) external to said vehicle (100), for example a cloud server.

[0208] At the expiring of a maximum amount of time allocated for the radial acceleration measurement, or when a distance equal to about said length (L), or greater, has been run by the vehicle, the external controlling unit (11) communicates each monitoring unit (2) to stop the acceleration measurements and to communicate their outcome, for example the results of said measuring and/or said pluralities of values of said at least two tires deformations and/or said respective deformation curves. Alternatively each monitoring unit (2) can independently stop the acceleration measurements.

[0209] As previously underlined, the choice of whether distributing the processing to eventually obtain said respective deformation curves, between the monitoring units (2) and the external controlling unit (11) is a tradeoff between several constraints to be balanced, such as: hardware complexity, battery consumption, cost, processing power available to the CPU of the monitoring units, etc.

[0210] In any case at the end of the radial acceleration measurements and their processing, a respective deformations curve for each of said at least two tires will be available for the comparison of their relative trends in order to identify a relative motion of vehicle body portions with respect to each other.

[0211] For example in FIG. 10 four deformation curves for each of the four tires of a vehicle are shown, respectively identified as Front Left (FL), Front Right (FR), Rear Left (RL), and Rear Right (RR), in this example the radial acceleration has been measured for about 260 meters, i.e. for 13 road segments of identical length (L) of 20 meters, at a vehicle speed of about 80 km/h; the radial acceleration measurements have been further processed to obtain a value of each tire deformation for each tire rotation which are indicated by circles in FIG. 10.

[0212] It is recalled here that each tire deformation curve is also descriptive of the motions of the vehicle body portion associated to a respective tire as previously discussed.

[0213] Hence based on the comparison of relative trends of said curves the relative motion of vehicle body portions with respect to each other is estimated.

[0214] In this embodiment the comparison of relative trends is carried out in the spatial frequency domain, by using a Fourier analysis.

[0215] First of all a respective Fourier transform of the four deformation curves is performed, the relative outcome is shown in FIG. 11 wherein the absolute values and the phase of each Fourier transform are respectively shown and they are respectively identified as Front Left (FL), Front Right (FR), Rear Left (RL), and Rear Right (RR) referring to a respective tire.

[0216] Depending on which vehicle body motion is under analysis a respective Fourier product curve is obtained by multiplying a first Fourier transform relative to a first tire for the complex conjugate of a second one relative to a second tire as it is shown in FIG. 12.

[0217] In FIG. 12 four respective Fourier product curves are sketched, both their absolute value and their phase, namely: [0218] FIG. 12A shows the absolute value and the phase of Fourier product curve relative to the Front Left (FL), Front Right (FR) tires. [0219] FIG. 12B shows the absolute value and the phase of Fourier product curve relative to the Front Right (FR), Rear Right (RR) tires. [0220] FIG. 12C shows the absolute value and the phase of Fourier product curve relative to the Front Left (FL), Rear Left (RL) tires. [0221] FIG. 12D shows the absolute value and the phase of Fourier product curve relative to the Rear Left (RL), Rear Right (RR) tires.

[0222] By analysing the Fourier product curves, the relative motion, with respect to each other, of vehicle body portions associated with the respective tires can be identified, for each spatial frequency, based on phase information related to each spatial frequency.

[0223] For example from FIG. 12C the relative motion of the front left side of the vehicle with respect to the rear left side can be identified for each spatial frequency: similar considerations hold for the other cases of FIG. 12.

[0224] In the case of FIG. 12C, said at least two tires belong to different axles of the vehicle so that vehicle pitching and/or heaving of the left part of the vehicle can be identified; as a matter of fact, spatial frequencies having a phase value close to π or to −π will contribute to pitching of the left side of the vehicle since this phase information, at those frequencies, is descriptive of antiphase behaviour and consequently of the left side of the vehicle portions moving in opposite directions (i.e. one downward and the other one upward).

[0225] On the other hand, spatial frequencies having a phase value close to zero will contribute to vehicle heaving since this phase information at those frequencies is descriptive of an in phase behaviour and, consequently, of the left side of the vehicle portions moving in the same directions (i.e. both downward and/or both upward).

[0226] Spatial frequencies having phase values not close to zero or not close to π or to −π, will contribute in this case to both pitching and heaving of the left side of the vehicle.

[0227] In the example of FIG. 12A, both tires belong to the front axle of the vehicle so that vehicle rolling of the front part of the vehicle can be identified; as a matter of fact, spatial frequencies having a phase value close to π or to −π will contribute to rolling of the front part of the vehicle since this phase information, at those frequencies, is descriptive of antiphase behaviour and consequently of the front portions of the vehicle moving in opposite directions (i.e. one downward and the other one upward).

[0228] On the other hand, spatial frequencies having a phase value close to zero will contribute to the vehicle front part heaving since this phase information at those frequencies is descriptive of a in phase behaviour and, consequently, of the front portions of the vehicle moving in the same directions (i.e. both downward and/or both upward).

[0229] Spatial frequencies having phase values not close to zero or not close to π or to −π, will contribute in this case to both rolling and heaving of the front part of the vehicle.

[0230] Analogous considerations apply to the examples of FIG. 12B and FIG. 12D.

[0231] Summarising by the analysis of the phases of the Fourier product curve of FIG. 12, it is possible , for each spatial frequency, to identify a relative motion of vehicle body portions with respect to each other induced by a road perturbation having said spatial frequency.

[0232] On the other hand, a quantitative analysis can be also carried out by using the absolute values (or modulus) of the Fourier product curves shown in FIG. 12, it is in fact clear that only the spatial frequencies having an absolute value different from zero (i.e. not close to zero) will actually contribute to a relative motion of vehicle body portions with respect to each other. Those frequencies are comprised within the dashed rectangles in FIG. 15A,B,C,D).

[0233] It is hence possible to estimate an unevenness parameter of a road segment based on the absolute values of each of the Fourier product curves of FIG. 12, for example by integrating the absolute value of the product curve over a certain range of spatial frequencies, for instance over the spectrum of spatial frequencies different from zero previously identified and comprised within the dashed rectangles in FIG. 12A,B,C,D).

[0234] In one embodiment, for example with reference again FIG. 12C, wherein pitching and/or heaving of the left side of a vehicle are identified based on the phase information of FIG. 12C, by integrating the absolute value of the relative Fourier product curve, an unevenness parameter (i.e. a numerical value) can be obtained which is descriptive of the global motion of said left side of a vehicle due to both pitching and/or heaving or a combination thereof along said road segment, in this case having a length of 260 meters.

[0235] As previously discussed, the information about the estimations about a relative motion of vehicle body portions with respect to each other, can be provided to a vehicle control system (12) and/or transmitted to a processing unit external to said vehicle, for a further processing or storage, for example a cloud server.

EXAMPLE

[0236] In all the following described experiment, tires manufactured and commercialized by the Applicant (Pirelli 205/65 R 16C-107 T Carrier) have been equipped with a monitoring unit, secured to the inner surface of the tread and adapted to measure the radial acceleration.

[0237] The monitoring unit could be driven to frequency high enough (i.e. higher or equal to 500 kHz) to properly resolve the dynamic of the radial acceleration in a single tire rotation for a vehicle speed exceeding 50 km/h so as to generate a radial acceleration signal over many tire rotations, or at least during passages of said monitoring units over a respective contact area of each tire.

[0238] Said tires have been fitted to the wheels of a light truck which has been driven along an Italian road dividing the route into many road segments having a length (L) of about 20 meters with the goal of estimating a relative motion of vehicle body portions with respect to each other in each of said 20 meters long road segments.

[0239] It will be shown the outcome of said relative motion estimations for a single 20 meters long road segment as an example, while the same procedure can be followed for any road segment.

[0240] In FIG. 13 are reported the deformation values of the four tires of said light truck along a 20 meters long road segment, namely Front Left (FL), Front Right (FR), Rear Left (RL), and Rear Right (RR).

[0241] Starting from said deformation curves of FIG. 13, a respective Fourier transform of the four deformation curves is performed; the relative outcome is shown in FIG. 14 wherein the absolute values and the phase of each Fourier transform are respectively shown and they are respectively identified as Front Left (FL), Front Right (FR), Rear Left (RL), and Rear Right (RR) referring to a respective tire.

[0242] Depending on which vehicle body motion is under analysis a respective Fourier product curve is obtained by multiplying a first Fourier transform relative to a first tire for the complex conjugate of a second one relative to a second tire as it is shown in FIG. 15.

[0243] In FIG. 15 four respective Fourier product curves are sketched, both their absolute value and their phase, namely: [0244] FIG. 15A shows the absolute value and the phase of Fourier product curve relative to the Front Left (FL) and Rear Left (RL) tires. [0245] FIG. 15B shows the absolute value and the phase of Fourier product curve relative to the Rear Left (RL) tire and Rear Right (RR) tires. [0246] FIG. 15C shows the absolute value and the phase of Fourier product curve relative to the Front Right (FR) and Rear Right (RR) tires. [0247] FIG. 15D shows the absolute value and the phase of Fourier product curve relative to the Front Left (FL) and Front Right (FR) tires.

[0248] By analysing the phases of each Fourier product curves the relative motion, with respect to each other, of vehicle body portions associated with the respective tires can be identified by using the same method described with reference to FIGS. 10 to 13.

[0249] For example by analysing the phase curve of FIG. 15B referring to of Fourier product curve of the Front Right (FR) and Rear Right (RR) tires, it can be easily identified that the rear part of the light truck underwent almost no rolling motion since the phase value of all the spatial frequencies of FIG. 15B are close to zero, while in the case of rolling of the rear portion of the light truck, their phase valued should be close to π or −π as previously discussed.

[0250] Analogous considerations hold for the other vehicle body motions.