METHOD AND SYSTEM FOR MONITORING A PARAMETER RELATED TO A TIRE DURING THE RUNNING OF A VEHICLE

Abstract

A monitoring of a tire is performed by using a monitoring unit operated at low frequency and with low power needs, without the need of providing complex hardware and software adapted for reconstructing a signal descriptive of the tire deformations and/or for recognizing the start and the end of peaks or valleys or other significant points of such signal. The monitoring uses a statistical approach for the estimation of the length of the contact area, or of other parameters related to it, based on an estimation of a probability of finding the monitoring unit in correspondence of the contact area at a certain time during rolling.

Claims

1-28. (canceled)

29. A method for monitoring a tire of a vehicle, the method comprising: a) associating a monitoring unit with the tire, wherein the monitoring unit comprises at least one sensing element adapted to measure at least one quantity descriptive of deformations of the tire; b) fitting the tire to a wheel of the vehicle and operating the vehicle to cause rotation of the tire on a rolling surface, wherein, due to the fitting and operating, the tire is deformed to form a contact area between the tire and the rolling surface; c) during the rotation of the tire, measuring the quantity within an amount of time at a sampling frequency lower than about 1.5 kHz, wherein the sampling frequency is higher than about 50 Hz, or higher than about 150 Hz; d) for each measurement of the quantity performed in c), determining whether the measured quantity has a value representative of a passage of the monitoring unit in correspondence with the contact area, to obtain a first number of passages of the monitoring unit in correspondence with the contact area within the amount of time; e) estimating at least one parameter related to the tire based on the first number, the sampling frequency, and the amount of time; and f) performing the monitoring of the tire based on the at least one parameter estimated.

30. The method according to claim 29, wherein the sampling frequency is lower than about 750 Hz.

31. The method according to claim 29, wherein the sampling frequency ranges from about 150 Hz to about 600 Hz.

32. The method according to claim 29, wherein the sampling frequency is chosen in order to obtain, for a vehicle speed up to 100 km/h, an average number of measurements of the quantity having a value representative of a passage of the monitoring unit in correspondence with the contact area of at least 0.5 measurements per tire round trip, at least 0.75 measurements per tire round trip, or at least 1 measurement per tire round trip.

33. The method according to claim 29, wherein the measurement of the quantity is performed to obtain a sequence of measurements of the quantity, the method further comprising extracting from the sequence a set of measurements representative of passages of the monitoring unit in correspondence with the contact area to obtain the first number of passages.

34. The method according to claim 29, further comprising: g) interrupting the measurement of the quantity after at least one occurrence of a measurement of the quantity having a value representative of a passage of the monitoring unit in correspondence with the contact area; and h) starting again the measurement of the quantity after a switch off time; wherein the estimating at least one parameter comprises calculating a second number of virtual measurements based on the sampling frequency and the switch off time.

35. The method according to claim 29, further comprising determining an overall number of measurements based on the sampling frequency and the amount of time, wherein the estimating at least one parameter is performed based on the first number and the overall number.

36. The method according to claim 29, wherein the determination of whether the measured quantity has a value representative of a passage of the monitoring unit in correspondence with the contact area is performed by defining a threshold value and comparing the value of the measured quantity with the threshold value.

37. The method according to claim 36, wherein the measurement of the quantity is performed to obtain a sequence of measurements of the quantity, the method further comprising extracting from the sequence a set of measurements representative of passages of the monitoring unit in correspondence with the contact area to obtain the first number of passages, and wherein the extraction of the set of measurements from the sequence of measurements is performed by selecting measurements of the sequence based on a comparison with the threshold value.

38. The method according to claim 36, further comprising setting an initial value of the threshold before starting the measurement of the quantity, and adjusting the threshold value in response to variations of a rotation speed of the tire.

39. The method according to claim 29, wherein the monitoring unit is secured to a crown portion of the tire and comprises at least one sensing element adapted to measure at least a radial acceleration of the crown portion during rotation of the tire.

40. The method according to claim 29, wherein the at least one parameter related to the tire is a length of the contact area during rotation (PL).

41. The method according to claim 29, wherein the monitoring unit comprises at least one further sensing element adapted to measure a tire pressure and/or a tire temperature.

42. The method according to claim 29, wherein the at least one parameter related to the tire is a load exerted on the tire by the vehicle.

43. The method according to claim 40, wherein the monitoring unit comprises at least one further sensing element adapted to measure a tire pressure, and a load exerted on the tire by the vehicle is estimated based on the length (PL) and the tire pressure.

44. The method according to claim 29, further comprising starting the measurement of the quantity when at least one of the following access conditions is met: a speed of the vehicle is comprised within a predetermined speed range, or an absolute value of longitudinal acceleration of the vehicle is lower than a predetermined amount.

45. The method according to claim 29, further comprising stopping the measurement of the quantity when at least one of the following stopping conditions is met: an absolute value of longitudinal acceleration of the vehicle exceeds a predetermined acceleration threshold, a speed of the vehicle is outside a predetermined speed range, or the amount of time exceeds a predetermined maximum amount of time.

46. The method according to claim 45, wherein the predetermined maximum amount of time is about 10 seconds.

47. A system for monitoring a tire of a vehicle, comprising: a monitoring unit adapted to be associated with the tire, wherein the monitoring unit comprises at least one sensing element adapted to measure at least one quantity descriptive of deformations of the tire; and at least one processing unit comprising software modules adapted to estimate at least one parameter related to the tire when the tire is fitted to a wheel of the vehicle and the vehicle is operated to cause rotation of the tire on a rolling surface, and due to the fitting and operating, the tire is deformed to form a contact area between the tire and the rolling surface; wherein the at least one sensing element is adapted to: a) measure the quantity within an amount of time at a sampling frequency lower than about 1.5 kHz during the rotation of the tire, wherein the sampling frequency is higher than about 50 Hz, or higher than about 150 Hz; and wherein the software modules are adapted to: b) for each measurement of the quantity performed in a), determine whether the measured quantity has a value representative of a passage of the monitoring unit in correspondence with the contact area, to obtain a first number of passages of the monitoring unit in correspondence with the contact area within the amount of time, c) estimate the at least one parameter related to the tire based on the first number, the sampling frequency, and the amount of time, and d) provide the at least one parameter estimated related to the tire to at least one interface towards a control system configured to perform the monitoring of the tire based on the at least one parameter estimated.

48. A monitoring unit adapted to be associated with a tire, the monitoring unit comprising: at least one sensing element adapted to: a) measure at least one quantity descriptive of deformations of the tire within an amount of time at a sampling frequency lower than about 1.5 kHz during the rotation of the tire, wherein the sampling frequency is higher than about 50 Hz, or higher than about 150 Hz; at least one processing unit comprising software modules adapted—when the tire is fitted to a wheel of a vehicle and the vehicle is operated to cause rotation of the tire on a rolling surface, and due to the fitting and operating the tire is deformed to form a contact area between the tire and the rolling surface—to: b) for each measurement of the quantity performed in a), determine whether the measured quantity has a value representative of a passage of the monitoring unit in correspondence with the contact area, to obtain a first number of passages of the monitoring unit in correspondence with the contact area within the amount of time; and a transmitting unit; wherein the software modules are adapted to communicate to a controlling unit external to the tire the first number or at least one parameter related to the tire estimated based on the first number, the sampling frequency, and the amount of time, via the transmitting unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0145] The above, as well as 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:

[0146] FIG. 1 shows a radial acceleration profile versus time for three consecutive tire round trips measured at 5 kHz sampling frequency.

[0147] FIG. 2 shows a magnification of a detail of FIG. 1 around one peak in the acceleration profile of FIG. 1.

[0148] FIG. 3 shows radial acceleration versus time for three consecutive tire round trips measured at 250 Hz sampling frequency.

[0149] FIG. 4 shows radial acceleration versus time for a high number of consecutive tire round trips measured at 250 Hz sampling frequency.

[0150] FIG. 5 shows a monitoring unit fitted into a tire.

[0151] FIG. 6 shows a scheme of a monitoring unit according to an embodiment of the invention.

[0152] FIG. 7 shows a scheme of a vehicle comprising a tire monitoring system and a vehicle control system according to an embodiment of the invention.

[0153] FIG. 8 shows a scheme of a controlling unit according to an embodiment of the invention.

[0154] FIG. 9 shows a comparison between the measurement of the length of the contact area length obtained using a 5 kHz sensor (PLMeas) and a length of the contact area length obtained with a 250 Hz sensor (PLRaw) with the method according to an aspect of the present invention.

[0155] FIG. 10A shows a comparison of the load estimated by the method according to an aspect of the present invention and the direct reference measurement carried out with dynamometric hubs for the right wheel of the front axle (FR) of a vehicle.

[0156] FIG. 10B shows a comparison of the load estimated by the method according to an aspect of the present invention and the direct reference measurement carried out with dynamometric hubs for the right wheel of the rear axle (RR) of a vehicle.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0157] Reference is made to FIG. 5 showing a portion of a tire (1) comprising a monitoring unit (2) adapted, configured to work at low sampling frequency, e.g. lower than 1-1.5 kHz.

[0158] 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.

[0159] With reference to FIG. 6, 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).

[0160] The monitoring unit (2) can be a relatively cheap (“tire-rotation triggered monitoring unit” as defined in the foregoing), currently available on the market (e.g., tire pressure monitoring sensing unit model FXTH87, produced by NXP Semiconductors), generally comprising temperature and/or pressure sensors and an accelerometer or other inertial sensor, whose output signal is only used for “waking up” the tire temperature and/or tire pressure measurements (where “waking up” also includes making the tire temperature and/or tire pressure measurements relatively more frequent than a basic, stand-by measurement rate), that is, an accelerometer which is operated at low sampling frequency in order to save power so as to save power when the vehicle is at rest (e.g. during parking). According to an embodiment of the present invention, the acceleration sensor or other inertial device available on such low frequency operated monitoring unit is 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.

[0161] 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.

[0162] 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).

[0163] The accelerometer (3) is configured to operate at low sampling frequency and to output a trigger signal for triggering the tire pressure and temperature measurements by the pressure sensor (4) and the temperature sensor (5). According to an embodiment of the present invention, the measurement at low sampling 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).

[0164] 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). 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 (such as the length of the tire contact area with the tire rolling surface and/or the load exerted on a tire). 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, via the transceiver (7) and the antenna (9), to complete the processing up to obtain said tire related parameters. 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. 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.

[0165] The transceiver section (7) is configured for bidirectional communication via the RF antenna (9) with an external controlling unit 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.

[0166] 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.

[0167] FIG. 7 schematically shows an embodiment of a system for monitoring tires. 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 scoters, 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.

[0168] The monitoring units (2) are in communication with a controlling unit (11). The controlling unit (11) is in communication with a vehicle control system (12) configured for adjusting vehicle control parameters based on tire related parameters 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).

[0169] 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 a hardware of software module implemented in the vehicle control system (12).

[0170] The controlling unit (11) is external with respect to the tires (1) wherein the monitoring (2) unit 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).

[0171] For example, the external controlling unit (11) can be a box attached to the vehicle windshield. 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).

[0172] FIG. 8 schematically shows an embodiment of a controlling unit (11) suitable for the system for monitoring tires of FIG. 7. 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.

[0173] In the preferred embodiment shown in FIG. 8, 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.

[0174] 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.

[0175] The interface (16) can be a CAN BUS interface adapted for bidirectional communication with the vehicle control system (12).

[0176] 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).

[0177] 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), or measurements performed by the monitoring units (2), or results of partial processing performed on said measurements by the monitoring units (2). The CPU (18) is also configured, via suitable software/firmware modules, to process such data in order to estimate at least one tire related parameter. 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), and/or possibly discarding those measurements performed during acquisitions occurred within time intervals in which those access conditions were not met.

[0178] 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. In the preferred embodiment shown in FIG. 8, the tire related parameter or parameters 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).

[0179] In an exemplary operation mode, each tire (1) fitted to a wheel of the vehicle (100) is caused to rotate on a rolling surface. 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, i.e. identifying information of the tire (e.g. tire identifier, tire size, tire model, tire radius etc.) is stored within the memory associated with the CPU (6) of the respective monitoring unit (2).

[0180] Pressure and temperature measurements can be 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).

[0181] The controlling unit (11) monitors the vehicle status based on GPS data.

[0182] 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 0.3 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.

[0183] The controlling unit (11) further communicates to each of the monitoring units (2) the speed V of the vehicle so that said monitoring units (2) can set an initial absolute threshold value for the acceleration, e.g. as V.sup.2/(2R), wherein R is a tire radius. Alternatively the controlling unit (11) can communicate to said monitoring units (2) the initial value of said threshold.

[0184] The controlling unit (11) may also communicate the amount of time to be allocated for the measurements, or the overall number of measurements to be performed. The amount of time or the overall number of measurements can also be directly stored in the software/firmware of each monitoring unit (2). In particular, the amount of time should be long enough to encompass several complete tire roundtrips at the vehicle speeds of interest. For example, the amount of time can be of several seconds (e.g. 10 seconds).

[0185] When the measurement is started, the radial acceleration is measured at a low sampling frequency below 1-1.5 kHz, for example 250 Hz. Preferably, an overall number of at least one thousand of measurements is performed within the allocated amount of time. For example, a monitoring unit working at 250 Hz will perform an overall number of 2500 measurements in 10 seconds.

[0186] During the radial acceleration measurements, the value of each measurement is compared with said threshold value in order to determine whether each sample value can be considered as representative of a passage of the monitoring unit in correspondence of the contact area between the tire and the rolling surface.

[0187] In this particular case, having set the initial threshold value as 0.5*V.sup.2/R, radial acceleration samples whose absolute value is lower than said threshold will be considered as representative of passages of said monitoring unit in correspondence of the contact area. In fact, as long as the monitoring unit remains in correspondence of the contact area, the radial acceleration is substantially zero since the monitoring unit is locally moving on a substantial rectilinear path.

[0188] The threshold value, initially set as V.sup.2/(2R), can be changed in response to variation of the rotation speed of said tire (1). The updated threshold value can be communicated by said external controlling unit (9) to each of said monitoring units (2) or can be calculated by each monitoring unit (2) itself.

[0189] In the latter case, an estimation of the rotation speed of the tire (1) can be carried out internally in each monitoring unit (2) by estimating the round trip time based on the time interval between consecutive values or groups of values lower than the set threshold. The estimated round trip time is used for obtaining the tire rotation speed and/or an updated speed of the vehicle, which can be used to update the threshold value.

[0190] The determination of whether a sample can be considered as representative of a passage of the monitoring unit (2) in correspondence of the contact area can be carried out sample by sample. Alternatively, a sequence of measurements can be obtained, followed by an extraction from said sequence of a set of measurements having values representative of passages of said monitoring unit (2) in correspondence of said contact area.

[0191] In both the aforementioned cases, the occurrences of the values representatives of passages of the monitoring unit (2) in correspondence of the contact area are counted by CPU of the monitoring unit (2), so as to obtain a first number of passages of said monitoring unit (2) in correspondence of said contact area. Preferably, the overall number of measurements is also determined by counting the measurements carried out. Alternatively the overall number of measurements can be directly obtained as the product of said sampling frequency and said amount of time, or the ratio between the amount of time and the sampling period (i.e. the inverse of the sampling frequency).

[0192] Said first number of passages can be used by the monitoring unit (2) to estimate at least one tire related parameter or can be communicated to said external controlling unit (11) or directly to the vehicle control system (12).

[0193] In particular, this first number can be used for determining the probability of said monitoring unit (2) to be in correspondence of the contact area at a certain time, which can be calculated for example as the ratio between said first number and said overall number of measurements (2500 measurements in this example).

[0194] Alternatively, said probability can be calculated as the ratio between the time spent by the monitoring unit (2) in correspondence with the contact area (i.e. the ratio between the first number of measurements and the sampling frequency, or the product of the first number of measurement and the sampling period) and said amount of time in which the measurement is carried out (10 seconds in this example).

[0195] To determine the overall number of measurements, it is not really necessary to actually carry out and/or count the radial acceleration measurements at each sampling period. Measurements within tire round trips to be performed when the monitoring unit (2) is certainly not in correspondence of the contact area can be skipped and substituted by “virtual measurements” which are not actually carried out. In such case, the overall number of measurements is determined as the sum of the number of actual measurements carried out and the number of virtual measurements. Advantageously, this can result in a significant saving of the energy used by the battery (8) of the monitoring unit (2) for the estimation of the at least one tire related parameter, ultimately increasing the lifespan of its battery (8).

[0196] The CPU (6) of the monitoring unit (2) can thus be configured, via suitable software/firmware modules, to switch off the measurement of the radial acceleration value during a switch off time comprised between two consecutive passages of said monitoring unit in correspondence of said contact area, i.e. within a round trip outside said contact area. Such software/firmware modules are also configured for determining the number of virtual measurements (i.e. the number of measurement not actually carried out) based on the sampling frequency and said switch off time.

[0197] This is particularly convenient in the embodiment wherein the monitoring unit (2) calculates the time occurring between two consecutive round trips. In this case, said switch off time can be preferably set in the range between one third and three quarters of the round trip time.

[0198] At the expiring of a maximum amount time allocated for the radial acceleration measurement, the external controlling unit (11) communicates each monitoring unit (2) to stop the acceleration measurements and to communicate their outcome, for example said first number of measurements.

[0199] Alternatively said external controlling unit (9) can communicate each monitoring unit (2) to stop the measurements when some stopping conditions are met, for example if the vehicle speed is outside a predetermined speed range or if an absolute value of the longitudinal acceleration exceeds a predetermined acceleration threshold.

[0200] Alternatively the monitoring unit (2) itself can stop the acceleration measurement at the expiring of the maximum amount of time, or, in the embodiment previously described wherein said monitoring unit (2) can estimate the vehicle speed, when at least one of the rotation/vehicle speed or the longitudinal acceleration is outside a predetermined range.

[0201] Once the acceleration measurement is over, the following quantities are available to the tire monitoring system for the estimation of a tire related parameter: a first number of passages of said monitoring unit in correspondence of the contact area during the amount of time allocated for the measurements; an overall number of (actual and possibly virtual) measurements, or its corresponding value calculated based on the sampling frequency and the amount of time allocated; tire pressure and/or temperature.

[0202] Based on such data, at least one tire related parameter can be estimated.

[0203] In preferred embodiments, the length of the contact area and/or the load exerted on the tire (1) can be estimated.

[0204] As previously discussed, the tire related parameter can be estimated by said monitoring units (2), or by the external controlling unit (11), or by the vehicle control system (12).

[0205] For example, the CPU (6) of the monitoring units (2) can process the acceleration data and send to the external control unit (11) the first number N1 of measurements representative of passages of each monitoring unit in correspondence of the contact area, the overall number N2 of (actual and possibly virtual) measurements, the tire pressure and the temperature values. The CPU (18) of the controlling unit (11) can then estimate the length of the contact area and/or the load exerted on the tires based on such data.

[0206] In particular, based on the fact that the set of measurements performed in the amount of time at the sampling frequency is a statistic set, the ratio N1/N2 corresponds to a probability p of finding each monitoring unit in correspondence of the contact area of the respective tire at a certain time during tire rolling.

[0207] A length of the contact area PL could be then estimated based on the tire circumference and such probability p, by using the formula

PL=2 πR p=2 πR N1/N2

wherein R is a radius (e.g. a rolling radius) of the tire.

[0208] The tire pressure and the length of the contact area PL can be then used to estimate the load exerted on the tire.

[0209] For example, the load Fz exerted by the vehicle on the tire can be calculated from the estimated length of the contact area PL based on a polynomial fitting function of the contact area length, e.g. by using the above mentioned formulas:

Fz=A(P)+B(P)*PL

Fz=A(P)+B(P)*PL+C(P)*PL.sup.2

wherein P is the tire pressure, PL is the length of the contact area and A, B, C are calibration parameters depending on the tire pressure P, whose values can be obtained by a calibration performed for the tire model to which the monitoring unit is associated. The calibration can be performed by using conventional testing machines on which a tire inflated at a controlled pressure and temperature is rotated over a conveyor belt under controlled conditions of exerted load and rotation peed. Such calibration coefficient A, B, C could be stored in the memory of the monitoring unit, the controlling unit and/or communicated to the vehicle control system.

[0210] In a more preferred embodiment, the load Fz exerted by the vehicle on the tire can be more precisely calculated from the contact area length PL based on a polynomial function of the contact length PL wherein the coefficients of said polynomial function further depend on tire pressure and rotation speed, e.g. according to above mentioned formulas:

Fz=A(P,ω,T)+B(P,ω,T)*PL

Fz=A(P,ω,T)+B(P,ω,T)*PL+C(P,ω,T)*PL.sup.2

wherein P is the tire pressure, PL is the estimated length of the contact area, ω is the tire rotational speed and A(P,ω,T), B(P,ω,T), C(P,ω,T) are calibration parameters depending on the tire pressure, tire rotation speed and tire temperature

[0211] Once the at least one tire related parameter has been estimated, it can be passed to the vehicle control system (12).

[0212] The vehicle control system (12) can perform the vehicle control by adjusting at least one vehicle control parameter based on an estimated tire parameter received by the external controlling unit (11) or from said monitoring units (2). For example, the vehicle control system can activate or adjust to the best alarm systems and/or vehicle dynamics control, braking, steering etc. In addition information about the vehicle status or tire related parameters (pressure, temperature, length of the contact area, load) can be communicated to the driver or can be used remotely, i.e. transmitted outside the vehicle, e.g. to one or more driver's personal devices or cloud servers.

[0213] In preferred embodiments, the vehicle control system (12) may comprise a brake controller (for example, an anti-lock brake unit), and/or a steering controller, and/or a suspension controller, and/or an engine controller, and/or a transmission controller.

[0214] For example, a vehicle brake control system may adjust the braking force on each tire according to the load on the tire.

[0215] As another example, the loads on each tire may be used to determine the vehicle stability envelope and to select the maximum variation allowed from steering commands. This information may be applicable to a steering control system (Electrically Assisted Steering Systems) to limit the yaw rate.

[0216] As another example, a vehicle suspension control system may adjust the stiffness of the suspension springs for each tire according to the load on the tire. Furthermore, a sensed unequal load distribution between left fitted tires and right fitted tires could be compensated by an Active Roll Control system, that currently use sensed lateral acceleration to increase the hydraulic pressure to move stabilizer bars, in order to remove a vehicle lean when cornering.

[0217] The conditions of the vehicle may indicate that the performance of the vehicle is reduced and that the driver should restrict his driving maneuvers. The vehicle control system itself can take action, for example in order to limit the maximum vehicle speed to maintain stability and not exceed the tire specifications, or to limit steering yaw rate in order to keep rollovers from occurring. The driver may be alerted to the current vehicle control system condition and of the actions that the vehicle control system has taken on his behalf to safe the vehicle (reducing the maximum attainable speed, steering rate, engine power), as needed on a display device. On the same display device it may also be shown whether he should take further action on his own (inflate the tires in case of excessive load not compliant with the current inflation pressure of the tires, change the distribution of mass, restrict driving maneuvers and speed). The display device may comprise a visual and/or an audible unit, for example located in the dashboard of the vehicle.

[0218] Alternatively or in combination, the vehicle control system may comprise an evaluator of a vehicle range, i.e. a residual mileage available to the vehicle (e.g. based on an available fuel and/or on an available battery power in an electrically driven vehicle), so that the vehicle control system may perform an adjustment of the residual mileage, e.g. based on the estimated load.

EXAMPLES

[0219] The tire monitoring method and system of the present invention have been tested with different vehicles and tires models.

[0220] In a first example, a FIAT DAILY 35C15 light truck has been used, equipped with Pirelli tires model CARRIER 195175R16. All the six tires of said light truck have been fitted with monitoring units (2) according to the scheme illustrated in FIG. 5 and FIG. 6. The monitoring units included a tire pressure monitoring sensing unit model FXTH87, produced by NXP Semiconductors, operating at a sampling frequency of 250 Hz and comprising a two axis accelerometer. The monitoring units were installed into the tires so as to align one of the two axes with the radial direction.

[0221] A controlling unit communicating via Bluetooth with the monitoring units has been installed within the car. The controlling unit estimated the length of the contact area based on the measurements performed by the monitoring units.

[0222] At the same time each tire (1) has been fitted also with a high frequency operated radial acceleration sensor to have precise measurement of the length of each tire contact area during rolling.

[0223] This further sensor was a high frequency accelerometer operated at 5 KHz being able to reconstruct a precise acceleration signal as the one shown in FIG. 1, from which it is possible to determine the length of the contact area, to be used as a comparison with the outcome of the estimation performed via the low frequency operated monitoring units.

[0224] Reference is now made to FIG. 9 wherein it is shown a plot of the measurements of the contact area length obtained using the 5 KHz sensor (PLMeas) and the contact area length measured with the 250 Hz sensor (PLRaw).

[0225] The plot shows different values of the contact area length obtained by carrying out tests with different loads exerted on the tires, different inflation pressures of the tires, different vehicle speeds.

[0226] For each measured point, PLRaw has been calculated as the product of the tire circumference and the probability (p) of finding the monitoring unit (2) in correspondence of the contact area at a certain time during tire rolling. Said probability (p) has been estimated as the ratio of the first number of measurements and an overall number of measurements performed in an amount of time encompassing a high number of round trips, as explained above.

[0227] A clear, almost linear correlation between PLMeas and PLRaw is shown in FIG. 9. This means that the method of the invention is able to precisely estimate a quantity (PLraw) substantially proportional to the actual length of the contact area. Should the length of the contact area be the tire related parameter to be estimated, the quantity PLraw could be calculated and then used in a calibration formula stored, e.g. in the memory of the monitoring unit or the controlling unit, for obtaining the actual length of the contact area.

[0228] The tire monitoring method and system of the invention have been further tested in a second example by using a Porsche Macan equipped with a Pirelli tire model PZERO 265145R20 for the front axle and a PZERO 295140R20 for the rear axle.

[0229] All the four tires of said car have been fitted with monitoring units (2) according to the scheme illustrated in FIG. 5 and FIG. 6. The monitoring units included a tire pressure monitoring sensing unit model FXTH87, produced by NXP Semiconductors, operating at a sampling frequency of 250 Hz and comprising a two axis accelerometer. The monitoring units were installed into the tires so as to align one of the two axis with the radial direction.

[0230] A controlling unit communicating via Bluetooth with the monitoring units has been installed within the car. The controlling unit estimated the length of the contact area and the load exerted on the tires based on the measurements performed by the monitoring units. The car has also been equipped with dynamometric hubs in the right wheel of both front and rear axle, so as to have a reference comparison for the load estimation.

[0231] In this case the quantity PLraw has also been used in the estimation of the load exerted on the tire, by using PLraw in place of PL in the formulas 1, 2, 3 or 4) previously discussed, wherein the coefficients of the polynomial function have been suitably calibrated for the tire models used in the test.

[0232] Reference is made to FIG. 10A and FIG. 10B, showing a comparison of the load estimated by the method of the present invention and the direct reference measurement carried out with the dynamometric hubs.

[0233] In particular, FIG. 10 A reports the comparison for the right wheel of the front axle (FR), while FIG. 10 B reports the comparison for the right wheel of the rear axle (RR).

[0234] Each circle in FIGS. 10A and 10B represents the load estimation based on the method of this invention using a respective measurement carried out in 10 seconds at a frequency of 250 Hz, i.e using an overall number of 2500 sampling points.

[0235] Each measurement is compared with a measurement carried out by using the dynamometric hub in the same 10 seconds time frame: these measurements are represented by triangles in FIG. 10 A and FIG. 10 B.

[0236] Load measurements have been repeated fifteen times with both methods.

[0237] A general agreement is found between the outcome of the method of the present invention and the reference one based on the dynamometric hubs.

[0238] In order to further increase the accuracy of the method of the present invention an average load value over the 15 measurements has been calculated. This is shown in FIGS. 10A and 10B respectively by the continuous horizontal line for the method of the present invention and by the dashed horizontal line for the dynamometric hub reference method.

[0239] For the right wheel of front axle an average value of 627 kg is estimated by the method of the present invention to be compared with an average value of 620 kg obtained with the reference method exploiting the dynamometric hubs.

[0240] For the right wheel of rear axle an average value of 540 kg is estimated by the method of the present invention to be compared with an average value of 513 kg obtained with the reference method exploiting the dynamometric hubs.

[0241] In both cases a very good agreement is found between the load values obtained by the method of the present invention with the one obtained by using the dynamometric hubs, the discrepancy being of the order of (1.5-5) % of the measured load value.

[0242] It is believed that the good agreement obtained between the load values could depend on the fact that the statistic approach explained above leads to an estimation of a length of the contact area PLraw exhibiting a consistent link to the actual length of the contact area PLmeas, which could be approximated, for example, by a linear relation.