GB2580381A

GB2580381A - Method and device for monitoring an instantaneous behaviour of a tire of a vehicle

Info

Publication number: GB2580381A
Application number: GB1900238.5A
Authority: GB
Inventors: Cimponeriu Andrei-Stefan; Kretschmann Matthias
Original assignee: Continental Automotive GmbH
Current assignee: Continental Automotive GmbH
Priority date: 2019-01-08
Filing date: 2019-01-08
Publication date: 2020-07-22
Anticipated expiration: 2039-01-08
Also published as: GB201900238D0; GB2580381B

Abstract

An aspect of the invention provides a method for monitoring an instantaneous behaviour of a tyre (2, figure 2) (road or tyre condition, aquaplaning risk) of a vehicle (1, figure 6), comprising: acquiring S1an acceleration signal (a) representative of an acceleration of a specified point of the tyre (2); bandpass filtering S2 of the acceleration signal (a); separating S3 the bandpass filtered acceleration signal (A) for one revolution of the tyre (2) into a plurality of signal intervals (11-110) and determining for each of the signal intervals (11-110) a volatility measure (VM1-VM10) representative of a volatility of the signal (A) within the respective signal interval (11-110); determining S4 a first parameter (P1) representative of a mean value of the volatility measures (VM1-VM10) and/or determining a second parameter (P2) representative of a maximum difference between the volatility measures (VM1-VM10); determining S5 an indication of the instantaneous behaviour of the tire (2) based on the first parameter (P1) and/or the second parameter (P2).

Description

Method and device for monitoring an instantaneous behaviour of a tire of a vehicle

Background of the Invention

Field of the Invention

The present invention relates to a method and a device for monitoring an instantaneous behaviour of a tire of a vehicle in a rolling condition of the tire.

Description of the Prior Art

The document DE 42 42 726 Al discloses a method and a system for aquaplaning detection for a tire of a vehicle. According to this prior art, a deformation of profile elements of the tire is detected in the circumferential direction during passage through a footprint region of the tire, and a thus obtained signal representative of the deformation is compared with a predetermined signal profile derived from previously achieved measurement results on a dry road.

The document EP 1 487 681 B1 discloses a method and a system for monitoring the instantaneous behaviour of a tire of a vehicle in a rolling condition of the tire, which allows e.g. aquaplaning detection. According to this prior art, a reference curve which represents the acceleration profile of a specified point of the tire as a function of the position of the point in a revolution of the tire is acquired and stored in advance. Then a signal representative of the acceleration of the specified point of a tire is acquired, a cyclic curve representing an actual acceleration profile is derived from the signal, and the derived cyclic curve is compared with the reference curve. Depending on the result of the comparison, a signal indicating the instantaneous behaviour of the tire (e.g. aquaplaning behaviour) is emitted.

A disadvantage of the above mentioned prior art is the necessary effort for acquiring suitable reference curves corresponding to a normal behaviour of the tire. Furthermore, a crucial point in practice is that such normal behaviour of a tire and thus a reference curve (of the signal) for a particular tire is subject to changes during the lifetime of the tire, e.g. due to changes of the mechanical properties of the tire material and/or the decrease of the tread depth of the tire. Therefore, a definition of criteria of signal analysis or definition of a reference curve, respectively, which is suitable for a new tire may become false during the lifetime of the tire.

Summary of the Invention

It is an object of the present invention to provide a method and a device for monitoring an instantaneous behaviour of a tire of a vehicle in a rolling condition of the tire, by which the above-mentioned problems can be avoided, wherein an indication of the behaviour can be provided in a simple and reliable manner.

A method for monitoring an instantaneous behaviour of a tire of a vehicle in a rolling condition of the tire according to a first aspect of the invention comprises: a) acquiring an acceleration signal representative of an acceleration of a specified point of the tire, b) bandpass filtering of the acceleration signal for providing a bandpass filtered acceleration signal, c) separating the bandpass filtered acceleration signal for one revolution of the tire into M signal intervals, wherein M is an integer between 4 and 20, and determining for each of the M signal intervals a volatility measure representative of a volatility of the bandpass filtered acceleration signal within the respective signal interval, d) determining a first parameter representative of a mean value of the volatility measures determined for the M signal intervals belonging to one revolution of the tire and/or determining a second parameter representative of a maximum difference between the volatility measures determined for the M signal intervals of the one revolution of the tire, e) determining an indication of the instantaneous behaviour of the tire based on the first parameter and/or the second parameter.

Advantageously, with the method according to the first aspect of the invention it is possible to determine an indication of the instantaneous behaviour of the tire without the need of an acquisition and storing of a reference curve as in the above mentioned prior art. Rather, the invention relies on an evaluation of the acquired acceleration signal without the need for a reference curve.

With the method according to the first aspect of the invention, it is provided a first parameter and/or a second parameter in a manner as described above, so that an indication of the instantaneous behaviour of the tire (road and/or tire condition, in particular e.g. aquaplaning risk etc.) can be easily determined e.g. comprising a comparing of the first parameter with a predetermined threshold value assigned to the first parameter and/or comparing the second parameter with a predetermined threshold value assigned to the second parameter.

As an alternative for each such comparison with a threshold value, it is also possible to determine whether the first parameter lies in a predetermined range assigned to the first parameter and/or to determine whether the second parameter lies in a predetermined range assigned to the second parameter.

In this respect, in a more general implementation of the invention, for determining a particular indication of the instantaneous behaviour of the tire, it is also possible to apply any other suitably predetermined criterion assigned to this indication, the fulfilment of which criterion can be checked based on the determined value(s) of the first and/or second parameter(s).

In particular, the invention can be very advantageously used e.g. for detecting a danger of potential aquaplaning at an early stage before the grip of the tire on a road is actually lost.

In an embodiment, the step a) is realized by using an electronic tire unit which is arranged at the tire (preferably in the tire, e.g. at an inner side of a tire running surface).

The electronic tire unit can comprise an acceleration sensor for providing the acceleration signal representative of the acceleration, wherein the specified point of the tire is defined by the position of the electronic tire unit at the tire.

In a preferred embodiment, the acceleration signal acquired in step a) is representative of the radial acceleration. Alternatively or in addition, another acceleration, e.g. the tangential acceleration can be used for the acquiring in step a).

In an embodiment, in step a) the acceleration signal is acquired in (or converted into) the form of a time-discrete acceleration signal with a sampling frequency amounting to at least 1000 Hz, preferably at least 1500 Hz (wherein the latter reflects a relevant frequency content in the acceleration signal of up to a Nyquist frequency of 1500 Hz! 2 = 750 Hz).

In particular if step a) is realized by using an electronic tire unit, also step b) can be realized by using this electronic tire unit.

In this case, the electronic tire unit can comprise a bandpass filtering device performing the bandpass filtering.

In an embodiment, the bandpass filtering in step b) is realized by use of a bandpass filtering device designed as an analogue filter (e.g. in case of filtering a time-continuous analogue acceleration signal acquired in step a), which can be implemented by an analogue electronic circuit arrangement.

In another embodiment, however, the bandpass filtering in step b) is realized by use of a bandpass filtering device designed as a digital filter (e.g. in case of filtering a time-discrete acceleration signal provided in step a)).

Such a digital filter (for digital signal processing) can be implemented by suitable hardware, e.g. by an FPGA (Field Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). Alternatively or in addition, the digital filter can be implemented by a computing device, in particular using software running on a program-controlled digital computing device as e.g. a microcontroller, which includes or which is connected to a storing unit for storing software for operating the program-controlled computing device.

In an embodiment, a lower limiting frequency of the bandpass filtering in step b) amounts to 0 Hz. In another embodiment, the lower limiting frequency amounts to at least 100 Hz, in particular to at least 200 Hz.

In an embodiment, an upper limiting frequency of the bandpass filtering in step b) amounts at most to 1000 Hz, in particular at most to 800 Hz.

In the case of monitoring the instantaneous behaviour of the tire in terms of a road roughness, the lower limiting frequency of the bandpass filtering lies preferably in a range of 100 Hz to 300 Hz, and the upper limiting frequency of the bandpass filtering lies preferably in a range of 400 Hz to 600 Hz.

In the case of monitoring the instantaneous behaviour of the tire in terms of an aquaplaning condition, the lower limiting frequency of the bandpass filtering lies preferably in a range of 300 Hz to 500 Hz, and the upper limiting frequency of the bandpass filtering lies preferably in a range of 650 Hz to 850 Hz.

In particular if step b) is realized by using an electronic tire unit, also step c) can be realized by using this electronic tire unit. The computing device of the electronic tire unit can be designed as a program-controlled computing device as e.g. a microcontroller, which includes or which is connected to a storing unit for storing software for operating this computing device.

In this case, the electronic tire unit can comprise a program-controlled computing device performing calculations on a digital representation of the bandpass filtered acceleration signal. The computing device may be the same as a computing device already used to perform step b).

In a preferred embodiment, in step c) the bandpass filtered acceleration signal for one revolution of the tire is separated into equally long signal intervals.

If in step c) the signal intervals are not equally long, it is preferred to choose signal intervals, such that the lengths of any two intervals differ not more than by a factor of 2 from one another.

In a preferred embodiment, in step c) the number M of signal intervals lies in a range of 6 to 10.

In a preferred embodiment, in step c) the volatility is defined as a sum of absolute values of differences between values of the bandpass filtered acceleration signal at equidistantly consecutive points in time within the respective signal interval.

In an embodiment of step c), the bandpass filtered acceleration signal is smoothed before said differences are determined. Such smoothing can be accomplished e.g. by using an analogue smoothing filter in case of a time-continuous signal, or e.g. by applying a moving average calculation on at least two consecutive data points in case of a time-discrete signal. Alternatively or in addition, such a smoothing may be applied to a signal or data, respectively, provided in a later stage of the method, as e.g. to the volatility measures determined in step c).

If the signal intervals are not equally long, said sum can be defined e.g. as a weighted sum, e.g. as the arithmetic sum of the absolute values of differences between values of the bandpass filtered acceleration signal at equidistantly consecutive points in time within the respective signal interval divided by the length of the respective signal interval.

In this context, the length of a particular signal interval can be defined e.g. as the temporal length, i.e. the duration of this signal interval. Alternatively, this length can be defined e.g. as the number of the equidistantly consecutive points in time (e.g. of acquired data points) within the respective signal interval.

In particular if step c) is realized by using an electronic tire unit, also step d) can be realized by using this electronic tire unit.

In this case, the electronic tire unit can comprise a computing device performing calculations on the volatility measures for determining the first parameter and/or the second parameter. The computing device may be the same as a computing device already used to perform step b) and/or step c).

In an embodiment, in step d) the first parameter is defined as the arithmetic mean value of the volatility measures determined for the M signal intervals belonging to the one revolution of the tire.

In an embodiment, in step d) the second parameter is defined as the arithmetic difference between the maximal volatility measure determined for the M signal intervals and the minimal volatility measure determined for the M signal intervals.

In particular if step d) is realized by using an electronic tire unit, also step e) can be realized by using this electronic tire unit.

In this case, the electronic tire unit can comprise a computing device performing calculations on the first parameter and/or the second parameter, for determining the indication of the instantaneous behaviour of the tire. The computing device may be the same as a computing device already used to perform step b) and/or step c) and/or step d).

Furthermore, in this case, the electronic tire unit can be designed to wirelessly transfer the result of the step e), i.e. said indication(s), from the electronic tire unit by means of an RF communication to an RF receiver, which is installed at the vehicle.

As an alternative to the performing of all the steps a) to e) by use of an electronic tire unit arranged at the respective tire, it may be provided that a result of any of the steps a) to d) is wirelessly transferred from the electronic tire unit by means of an RF communication to an RF receiver, which is installed at the vehicle and which is coupled with an electronic control unit of the vehicle, and that the performing of the respective further steps, i.e. from step b) or c) or d) onwards, or the step e), is accomplished by means of this electronic control unit of the vehicle The electronic control unit of the vehicle can be designed as a program-controlled computing device as e.g. a microcontroller, which includes or which is connected to a storing unit for storing software for operating this program-controlled computing device.

The RF receiver of the vehicle may be used to receive RF signals from a plurality of electronic tire units arranged at different tires of the same vehicle.

In an embodiment, at least the step e) is realized by using an electronic control unit of the vehicle, wherein preferably all the preceding steps a) to d) are realized by using an electronic tire unit of the respective tire.

In an embodiment, the method further comprises a step of outputting an information to a driver of the vehicle and/or outputting an information to at least one electronic system of the vehicle.

Such an information may represent the result of step e), e.g. a measure of a road roughness and/or a measure of an aquaplaning risk and/or an information derived from such result (e.g. an aquaplaning warning).

In an embodiment, the outputting of the information (e.g. a warning information) is carried out when the determined indication of the behaviour of the tire fulfils a predetermined information criterion (e.g. warning criterion).

In an embodiment, for monitoring the instantaneous behaviour of the tire in terms of a road roughness, in step d) at least the first parameter is determined and in step e) an indication regarding the road roughness is determined based on at least the first parameter.

In an embodiment, the indication regarding the road roughness is provided as a level of road roughness, wherein this level may be represented (or measured, respectively) e.g. by the first parameter itself. In an alternative embodiment, in step e) such a level of road roughness is determined based on the first parameter and at least the instantaneous vehicle speed.

The vehicle speed may be determined by use of the electronic tire unit of the respective tire, which is also used for performing at least the step a).

In an embodiment, for monitoring the instantaneous behaviour of the tire in terms of an aquaplaning condition, in step d) at least the second parameter is determined and in step e) an indication regarding the aquaplaning condition is determined based on at least the second parameter.

In particular, there may be provided that in step d) the first parameter and the second parameter are determined and that in step e) the indication regarding the aquaplaning condition (and/or another indication) is determined based on the first parameter and the second parameter.

In an embodiment, in step e) the indication regarding the aquaplaning condition is provided as a level of aquaplaning risk, wherein this level may be represented (or measured, respectively) e.g. by the second parameter itself.

In an embodiment, in step e) such a level of aquaplaning risk is determined based on the second parameter and at least one of the first parameter and the vehicle speed.

For example, in step e) the level of aquaplaning risk may be represented by a (mathematical) combination of the first and second parameters, e.g. the second parameter divided by the first parameter, or e.g. depending on the second parameter in case of the first parameter lying in a predetermined range, e.g. below a predetermined threshold value.

In such embodiments, the vehicle speed may be used for determining said range and/or determining said threshold value.

When the instantaneous behaviour of the tire is determined dependent on the vehicle speed, according to an embodiment, the vehicle speed is determined by means of the electronic tire unit, which is used to perform at least the step a). To this end, the electronic tire unit may acquire the acceleration signal, on the basis of which a determination of the rotational speed of the tire is realized (The rotational speed of the tire can be used as a measure for the vehicle speed).

Alternatively or in addition, the vehicle speed can be determined by means of suitable sensor means arranged at the vehicle (e.g. wheel speed sensors and/or a GPS device etc.). Such sensor means can provide at least one sensor signal representative of the vehicle speed to an electronic control unit of the vehicle that also performs at least step e).

In an embodiment, step e) further comprises a classifying of the determined indication of the instantaneous behaviour of the tire, for example a classifying regarding an amount (e.g. resulting in a classification as low, medium, high), and/or a classifying regarding a quality (e.g. resulting in a classification as good, medium, bad/danger) etc. In an embodiment, if the first parameter as well as the second parameter are relatively low (e.g. both lying below respectively predetermined threshold values), step e) may determine an indication corresponding to a normal road (clean, dry and even road) However, if the first parameter is relatively high (e.g. lying above a respectively predetermined threshold value), step e) may determine an indication corresponding to a rough road, e.g. an off-road condition. In this case, higher values of the first parameter may be interpreted as belonging to rougher roads or a higher level of road roughness, respectively. Alternatively or in addition, the determined value of the second parameter may be used for an even more accurate characterisation of the indication.

If the first parameter is relatively low (e.g. lying below a respectively predetermined threshold value) and the second parameter is relatively high (e.g. lying above a respectively predetermined threshold value), this may be interpreted as an indication corresponding to an aquaplaning risk.

Alternatively or in addition, an indication aquaplaning risk or a level of aquaplaning risk (as also any other indication) may also be determined based on a suitably predetermined (mathematical) combination of the first parameter and the second parameter, e.g. identical to or at least dependent on the value of first parameter normalized by (e.g. divided by) the value of the second parameter.

In an embodiment providing that in step d) the first parameter and the second parameter are determined and in step e) an indication regarding an aquaplaning condition is determined based on the first parameter and the second parameter, a warning criterion for outputting a warning can be provided, which is fulfilled when a value of the second parameter normalized by the first parameter exceeds a predetermined threshold value. This threshold value may be fixedly predetermined or predetermined e.g. dependent on the vehicle speed and/or another operational parameter of the tire (e.g. tire pressure, tire temperature, etc.) or the vehicle (e.g. outside temperature, longitudinal acceleration of the vehicle, etc.).

The indication(s) of the instantaneous behaviour of the tire may be calculated by use of a program-controlled computing device (as already mentioned). In this respect, the indication(s) can e.g. be retrieved from a look-up table implemented by software running on such computing device(s), based on the results of the previously conducted determination (and/or a classification) of the first parameter and/or the second parameter, and as the case may be, further based on one or more further parameters as e.g. vehicle speed, tire pressure, tire temperature etc. The invention can be advantageously used in particular e.g. for providing an aquaplaning warning information. Advantageously, it is possible to detect a danger of aquaplaning before it actually takes place (and the grip of the tire is lost).

Generally, in this situation there is a relatively great difference (asymmetry) between a leading side and a trailing side of the tire's footprint. At the leading side, a film or wedge of water forms between the tire and the ground (e.g. road surface), whereas at the trailing side fewer water is present between the tire and the ground. In this situation, the second parameter determined in step e) will be relatively high. In contrast, when aquaplaning already takes place, water is more evenly distributed in the area of the footprint. In this situation, the second parameter determined in step e) will be somewhat decreased in comparison with the case of the situation just before the start of aquaplaning.

In the invention, an information as e.g. a warning information can be outputted to a driver of the vehicle e.g. as an optical signal and/or an acoustic signal.

Alternatively or in addition, an information can be outputted to at least one electronic system of the vehicle, e.g. an antilock braking system (ABS) or an electronic stability program (ESP).

Alternatively or in addition to outputting of a warning, an information representing and/or characterizing the instantaneous behaviour determined in step e) can be outputted to the at least one electronic system of the vehicle, which then can e.g. evaluate the received information (e.g. data), e.g. for generating a warning.

Further, the invention can be advantageously used e.g. for outputting an indication related to the condition of the ground on which the tire rolls or the vehicle is driving, respectively (road condition).

For example, the invention may be used for detection of an off-road condition, or e.g. for detection of different types of roads (e.g. dry road, wet road, dirty road, soft ground, cobble stone pavement etc.).

According to another aspect of the present invention, there is provided a device for monitoring an instantaneous behaviour of a tire of a vehicle in a rolling condition of the tire, wherein the device comprises: an acceleration sensor arranged at, e.g. in the tire, for acquiring an acceleration signal representative of an acceleration of a specified point of the tire, bandpass filtering means for bandpass filtering of the acceleration signal for providing a bandpass filtered acceleration signal, first determining means for separating the bandpass filtered acceleration signal for one revolution of the tire into M signal intervals, wherein M is an integer between 4 and 20, and for determining for each of the M signal intervals a volatility measure representative of a volatility of the bandpass filtered acceleration signal within the respective signal interval, second determining means for determining a first parameter representative of a mean value of the volatility measures determined for the M signal intervals belonging to one revolution of the tire and/or for determining a second parameter representative of a maximum difference between the volatility measures determined for the M signal intervals of the one revolution of the tire, third determining means for determining an indication of the instantaneous behaviour of the tire based on the first parameter and/or the second parameter.

The embodiments and specific details described here for the method according to the first aspect of the invention can be provided, in a corresponding manner, individually or in any combination, as embodiments or specific details of the device according to the further aspect of the invention.

In an embodiment, the acceleration sensor is provided to measure the radial acceleration at the location where it is arranged at the tire. Alternatively or in addition, it can be provided that the acceleration sensor measures e.g. the tangential acceleration.

In an embodiment, the bandpass filtering means are designed as an analogue filter. In another embodiment, the bandpass filtering means are designed as a digital filter. The digital filter can be implemented by an integrated circuit arrangement, e.g. an FPGA (Field Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). Alternatively or in addition, the digital filter can be implemented by a program-controlled computing device as e.g. a microcontroller, which includes or which is connected to a storing unit for storing software for operating the computing device.

Each of the first, second and third determining means can be designed as a respective computing device, in particular a program-controlled computing device as e.g. a microcontroller device, which is dedicated for performing the respective determination of step c), step d) and step e), respectively.

In an embodiment, the first and second determining means are implemented by a program-controlled computing device arranged in an electronic tire unit comprising also the acceleration sensor, whereas the third determining means are implemented by a program-controlled computing device arranged in the vehicle, e.g. by an electronic control unit (ECU) of the vehicle (e.g. controlling also other functionalities of the vehicle).

The electronic tire unit preferably comprises an RF (radio frequency) transmitter for sending RF signals including information about the indication of the instantaneous behaviour of the tire (or information enabling this determination) to an RF receiver installed at the vehicle.

The RF receiver of the vehicle may be designed for receiving RF signals from a plurality of electronic tire units arranged at different tires of the same vehicle.

The RF receiver can be coupled with an electronic control unit (ECU) of the vehicle (e.g. connected via a digital data bus system), so that the electronic control unit can e.g. implement the step e) (or e.g. the steps d) and e)) and/or can e.g. generate the already mentioned warning information (e.g. aquaplaning warning) for a driver of the vehicle (and/or for particular electronic systems of the vehicle).

If the electronic control unit receives or determines the indication(s) of the behaviour of a plurality of tires, the outputting of an information (e.g. warning) may depend on the result of an evaluation of the received information as a whole (e.g. taking into account a result of step e) for more than one tire, in particular all tires, of the vehicle).

According to another aspect of the present invention, there is provided a computer program product comprising software code for performing the monitoring method described therein.

Such software code can be used for controlling the operation of the above-mentioned computing device of the electronic tire unit and/or computing device (e.g. electronic control unit) of the vehicle.

Brief Description of the Drawings

The invention will now be described in more detail by way of example embodiments 35 with reference to the accompanying drawings, in which Fig. 1 is a flowchart of a monitoring method according to an embodiment of the invention, Fig. 2 illustrates a tire in a rolling condition, which is equipped with an electronic tire unit used for implementing the method of Fig. 1, Fig. 3 illustrates an example of a signal acquired by means of an acceleration sensor of the electronic tire unit in Fig. 2, and an illustration of a frequency spectrum of this signal, Fig. 4 illustrates another example of a signal acquired by means of the acceleration sensor in Fig. 2, and an illustration of the corresponding frequency spectrum, Fig. 5 illustrates a block diagram of the electronic tire unit according to an embodiment, and Fig. 6 illustrates a vehicle comprising a plurality of tires each equipped with an electronic tire unit, according to an embodiment.

Description of the Preferred Embodiments

Fig. 1 illustrates steps Si to S6 of a method for monitoring the instantaneous behaviour of a tire of a vehicle: Step Si: Acquiring an acceleration signal representative of a radial acceleration of a specified point at the tire, by using an electronic acceleration sensor of an electronic tire unit arranged in the tire.

Step S2: Bandpass filtering of the acceleration signal for providing at least one bandpass filtered acceleration signal, by using at least one digital filter implemented by a digital computing device arranged in the electronic tire unit.

Step S3: Separating the bandpass filtered acceleration signal for one revolution of the tire into a plurality of (e.g. ten) equally long signal intervals and determining for each of these signal intervals a volatility measure representative of a volatility of the bandpass filtered acceleration signal within the respective signal interval, by using the digital computing device arranged in the electronic tire unit. In this example, the result thereof is communicated from the electronic tire unit to an electronic control unit (ECU) of the vehicle (using RF communication).

Step S4: Determining a first parameter representative of a mean value of the volatility measures determined for the signal intervals belonging to one revolution of the tire and/or determining a second parameter representative of a maximum difference between the volatility measures determined for the signal intervals of the one revolution of the tire, by using the electronic control unit (ECU) of the vehicle.

Step S5: Determining at least one indication of the instantaneous behaviour of the tire (e.g. an aquaplaning risk) based on the first parameter and/or the second parameter, by using the electronic control unit (ECU) of the vehicle.

Fig. 2 illustrates a wheel W of a vehicle, e.g. one of four wheels W1 to W4 of a vehicle 1 shown in Fig. 6. The wheel W comprises a rim and an air-filled tire 2 mounted on the rim. The tire 2 is equipped with an electronic tire unit 10 used for implementing the above described method (Fig. 1) In Fig. 2, an arrow 3 indicates a rotation of the wheel W and thus a rotation of the tire 2 in a rolling condition during a drive of the respective vehicle.

In this condition of the tire 2, a wheel load acting on the tire 2 causes a deformation of the tire 2 at the lower portion thereof, resulting in the formation of a footprint, i.e. an area at which the circumference of the tire 2 is flattened and is in contact with a road surface. Fig. 2 illustrates a length L of the footprint.

In the shown example, the electronic tire unit 10 is arranged at an inner side of a running surface of the tire 2.

Electronic tire units as such are known from the prior art of so-called tire pressure monitoring systems (TPMS) used in modern motor vehicles for monitoring the air pressure in the respective tires. In fact, also the shown electronic tire unit 10 is used as such component for realizing a TPMS in the respective vehicle.

Fig. 5 illustrates a block diagram of the electronic tire unit 10 of Fig. 2 according to an embodiment thereof.

The electronic tire unit 10 comprises a pressure sensor 12 providing a pressure signal "p" representative of the air pressure in the tire 2, and a radial acceleration sensor 14 providing an acceleration signal "a" representative of the radial acceleration of the point of the tire 2, which is specified by the location at which the electronic tire unit 10 and thus the acceleration sensor 14 is arranged at the tire 2.

Both sensor signals "p" and "a" are inputted to a program-controlled computing device of the electronic tire unit 10, comprising a processing unit 16 and a storing unit 18 coupled with the processing unit 16 and storing a software for operating the processing unit 16.

Further, the electronic tire unit 10 comprises an RF transmitter 20 for sending RF signals R including information about the measured tire pressure to an RF receiver arranged at the vehicle. From time to time, the processing unit 16 creates a data telegram including operational parameters regarding the operation of the tire 2 (e.g. tire pressure as represented by the pressure signal "p") and causes the RF transmitter 20 to send the data telegram in the form of an RF signal R. The electronic tire unit 10 may also comprise further sensor devices (e.g. temperature sensor) not shown in Fig. 5 for incorporating further information (e.g. temperature) into the RF signals R. Furthermore, in contrast to known electronic tire units, the electronic tire unit 10 performs the above described steps Si to 53 (Fig. 1) and incorporates the result of step S3 into RF signals R sent to the vehicle, so that the remaining steps S4 and S5 can be performed on the side of the vehicle.

Thus, the electronic tire unit 10 shown in Fig. 5 is a component, which is (also) used for monitoring the instantaneous behaviour of the tire 2 of the respective vehicle by conducting a monitoring method comprising the steps Si to S5 as described with reference to Fig. 1.

Fig. 3 shows in the lower part an example of an acceleration signal "a" provided by the acceleration sensor 14 (acquired in step Si) versus time t when the vehicle drives on a "wet road".

Most of the time, the signal "a" takes a value "av" corresponding to a centrifugal acceleration of approximately 50 g (1 g = 9,81 m/s2) in the present example, caused by the rotation 3 of the tire 2.

However, when the electronic tire unit 10 with the acceleration sensor 14 passes the footprint, the signal "a" shows a characteristic deviation from the value "av".

In the shown example of Fig. 3 the deviation can be found in a time span approximately from 0,02 s to 0,05 s. In this time span, the signal value firstly increases to a first maximum, then decreases to a minimum (where "a" approximately is zero), then increases again to a second maximum, and finally decreases again to the value "av".

Fig. 3 illustrates in the upper part an illustration of the frequency spectrum of the acceleration signal "a" versus time t. In this illustration, dark areas represent low intensities of the corresponding frequency components at the corresponding times, whereas bright areas represent high intensities thereof Hereinafter, the steps Si to S5 (Fig. 1) are explained again with reference to the examples of the wheel arrangement of Fig. 2, the acceleration signal (spectrum) of Fig. 3 (and Fig. 4) and the electronic tire unit of Fig. 5.

In step Si, the acceleration sensor 14 of the electronic tire unit 10 continuously acquires a signal representative of the radial acceleration of the point of the tire 2, at which the electronic tire unit 10 is arranged (e.g. fixed at the inner side of the running surface of the tire 2). With each revolution of the tire 2, a course of the signal "a" as a function of the time t is acquired as depicted by way of example in Fig. 3. In this step, the acceleration signal "a" is acquired as (or converted into) a time-discrete data signal with a number of "N" data points per one revolution (3600) of the tire 2.

Preferably, and also in this example, a sampling rate amounts to at least 1500 Hz.

In step S2, the processing unit 16 of the electronic tire unit 10 can for example eliminate (or correct) "outliers" (obviously false acquired values of "a") from the signal "a" and/or can perform a smoothing of the signal "a".

At any rate, the processing unit 16 performs a bandpass filtering of the acceleration signal "a" and thus provides a bandpass filtered acceleration signal "A". The filtering is realized by a digital filter implemented by use of software, which is stored in the storing unit 18 and which controls the operation of the processing unit 16.

In this example, the processing unit 16 even performs two bandpass filtering processes on the signal "a", namely a first bandpass filtering with a lower limiting frequency of 400 Hz and an upper limiting frequency of 750 Hz, and a second bandpass filtering with a lower limiting frequency of 200 Hz and an upper limiting frequency of 500 Hz.

In step S3, the processing unit 16, for each of the two bandpass filtered acceleration signals "A", separates this signal for one revolution of the tire 2 into "M" equally long signal intervals 11, 12, 13, . . , IM.

Assuming in this example M = 10, the signal "A" is separated into 10 signal intervals 11, 12, 13, ... IM, i.e. 11, 12, 13, ... , 110.

Further, the processing unit 16 then determines for each of the signal intervals 11 to 110 a "volatility measure" VM1, VM2, VM3, ... and VM10, respectively, representative of a volatility of the signal within the respective signal interval M, 12, 13, ... and 110, respectively.

In this example, each of the volatility measures VMm, with m in [1 10] is calculated as follows: VMm = SUM (ABS (A(n)-A(n-1)) for n in [(m-1)*N/10 m*N/10] wherein "N" designates the number of data points per one revolution (360°) of the tire 2 (and the divisions by "10" (and the maximum value "10" for the index m) correspond to the choice of M = 10 in this example).

In this example, the result of step S3, i.e. the volatility measures VM1 to VM10 (for both bandpass filtered acceleration signals "A") is communicated from the electronic tire unit 10 using RE communication implemented by the RE transmitter 20 to an electronic control unit (ECU) of the vehicle. In this example, the electronic control unit of the vehicle performs the remaining steps 54 and 55.

In step S4, the electronic control unit, for each of the two bandpass filtered acceleration signals "A", determines a "first parameter" P1 representative of a mean value of the volatility measures VM1 to VM10 determined for the signal intervals 11 to 110 belonging to one revolution of the tire and determines a second parameter P2 representative of a maximum difference between the volatility measures VM1 to VM10 determined for the signal intervals 11 to 110 of the one revolution of the tire, in this example as follows: P1 = (VM1 + VM2 + VM3 + + VM8 + VM9 + VM10) / 10 P2 = MAX (ABS (VMk-VMI)) for k in [1... 10], I in [1... 10] In step S5, the control unit determines two indications of the instantaneous behaviour of the tire, namely in terms of an aquaplaning risk and in terms of a road roughness based on the first parameters P1 and the second parameters P2 (of the two bandpass filtered acceleration signals "A").

In this example, an aquaplaning risk is determined when for the first bandpass filtered acceleration signal "A" (i.e. with information in the interval from 400 to 750 Hz) the first parameter P1 is relatively low (e.g. lying below a predetermined threshold value) and the second parameter P2 is relatively high (e.g. lying above a predetermined threshold value).

Furthermore, a road roughness is determined in this example when for the second bandpass filtered acceleration signal "A" (i.e. with information in the interval from 200 to 500 Hz) the first parameter P1 is relatively high (e.g. lying above a predetermined threshold value).

Fig. 3 is an example for a signal "a", which causes such a determination of an aquaplaning risk in step S5.

Namely, as can be seen in Fig. 3, the frequency spectrum of the signal "a" in the interval [400 Hz... 750 Hz] (cf. dashed lines in Fig. 3) shows an increased intensity of frequency components (here: around 600 Hz) at the time t = 0,03 s, whereas for all other times (of the same revolution (3600) of the tire 2) no such significant increase can be seen.

This apparently leads in step S4 to a low value of P1 and a high value of P2 and thus in step S5 to the determination of an aquaplaning risk.

Fig. 4 illustrates in the lower part another example of the acceleration signal "a" versus time t, namely for the case that the vehicle drives on a rough road. Also in the example of Fig. 4, the signal "a" is more or less close to a value of "av" corresponding to the centrifugal acceleration (approx. 150 g in this example). Furthermore, also the signal "a" in Fig. 4 shows a characteristic deviation from the value "av", when the electronic tire unit 10 passes the footprint. In this example, the deviation can be found in a time span approximately from 0,09 s to 0,11 s.

Fig. 4 is an example for a signal "a", which causes a determination of road roughness in step 85.

Namely, as can be seen in Fig. 4, the frequency spectrum of the signal "a" in the relevant interval [200 Hz... 500 Hz] (cf. dashed lines in Fig. 4) shows a remarkably high intensity of frequency components (here: around 400 Hz) for the whole time (of the revolution of the tire 2).

This apparently leads in step S4 to a high value of P1 and a low value of P2 and thus in step S5 to the determination of road roughness.

Fig. 6 illustrates an example of a vehicle 1 having four wheels W1 to W4 each comprising a tire equipped with an electronic tire unit 10-1 to 10-4.

It is assumed that each of the electronic tire units 10-1 to 10-4 is designed as the electronic tire unit 10, which has already been described with reference to Fig. 5.

In Fig. 6, the RF signals (cf. signal R in Figs. 2 and 5) sent by the individual units 10-1 to 10-4 are designated by the reference signs R1 to R4.

The vehicle 1 has an electronic control unit (ECU) 30 comprising a program-controlled processing unit 34 and a storing unit 36 coupled with the processing unit 34 and storing a software code by which the operation of the processing unit 34 is controlled.

The electronic control unit 30 is coupled with an RF receiver 32 for receiving the RF signals R1 to R4 from the units 10-1 to 10-4.

In this embodiment, in the determination of indications of the instantaneous behaviour of the tires 2 at the wheels W1 to W4 in terms of a road roughness, the processing unit 34 may advantageously also conduct an overall evaluation of the received volatility measures VM1 to VM10 (for the respective bandpass filtered acceleration signal "A" and for the tires of all wheels W1 to W4) and/or received (or determined) first and second parameters P1, P2.

In the determination of indications in terms of an aquaplaning condition, the processing unit 34 may advantageously also conduct an overall evaluation of received volatility measures VM1 to VM10 and/or received (or determined) first and second parameters P1, P2 (for the respective bandpass filtered acceleration signal "A"). In this case, however, it is suitable to evaluate these data only for the tires of the front wheels, i.e. the wheels W1 and W2 in the shown example.

Based on a result of this evaluation, which may comprise e.g. a determination whether for at least two of a plurality of tires installed at the vehicle the determined instantaneous behaviour is substantially the same or not, it can e.g. be decided whether a warning has to be output or not.

A respective algorithm conducted by the processing unit 34 may provide that such output (e.g. a warning output) is provided only if more than one of the indications of the behaviour (determined at different tires) fulfil a predetermined criterion, e.g. when at least two of the units 10-1 to 10-4, or at least two of the units 10-1 to 10-4 arranged at a same axle of the vehicle 1. transmit data fulfilling a particular criterion.

Alternatively, such algorithm e.g. may provide that such warning will be outputted if at least one of the data transmitted from the units 10-1 to 10-4 leads to a fulfilment of a predetermined warning criterion.

list of reference signs 1 vehicle 2 tire 3 rotation W1 to W4 vehicle wheels length of footprint 10-1 to 10-4 electronic tire units R1 to R4 RF signals 12 pressure sensor 14 acceleration sensor 16 processing unit 18 storing unit RE transmitter 30 electronic control unit 32 RE receiver 34 processing unit 36 storing unit pressure signal t time a acceleration signal number of data points per revolution index of data point A bandpass filtered acceleration signal M number of signal intervals per revolution index of signal interval 11 to 110 signal intervals VM1 to VM10 volatility measures P1 first parameter P2 second parameter

Claims

Claims 1. A method for monitoring an instantaneous behaviour of a tire (2) of a vehicle (1) in a rolling condition of the tire (2), comprising: a) acquiring (Si) an acceleration signal (a) representative of an acceleration of a specified point of the tire (2), b) bandpass filtering (52) of the acceleration signal (a) for providing a bandpass filtered acceleration signal (A), c) separating (S3) the bandpass filtered acceleration signal (A) for one revolution of the tire (2) into M signal intervals (11-110), wherein M is an integer between 4 and 20, and determining for each of the M signal intervals (11-110) a volatility measure (VM1-VM10) representative of a volatility of the bandpass filtered acceleration signal (A) within the respective signal interval (11-110), d) determining (54) a first parameter (P1) representative of a mean value of the volatility measures (VM1-VM 10) determined for the M signal intervals (11-110) belonging to one revolution of the tire (2) and/or determining a second parameter (P2) representative of a maximum difference between the volatility measures (VM1-VM 10) determined for the M signal intervals (11 -11 0) of the one revolution of the tire (2), e) determining (55) an indication of the instantaneous behaviour of the tire (2) based on the first parameter (P1) and/or the second parameter (P2).
2. The method according to claim 1, wherein the steps a) to c) or the steps a) to d) are realized by means of an electronic tire unit (10) which is arranged at the tire (2).
3. The method according to any of the preceding claims, wherein the steps d) and e) or the step e) are/is realized by means of an electronic control unit (30) of the vehicle (1).
4. The method according to any of the preceding claims, wherein in the step b) a lower limiting frequency of the bandpass filtering amounts to at least 100 Hz, in particular to at least 200 Hz, and an upper limiting frequency of the bandpass filtering amounts at most to 1000 Hz, in particular at most to 800 Hz.
5. The method according to any of the preceding claims, wherein in the step c) the bandpass filtered acceleration signal (A) for one revolution of the tire (2) is separated into M equally long signal intervals (11-110).
6. The method according to any of the preceding claims, wherein in the step c) the volatility is defined as a sum of absolute values of differences between values of the bandpass filtered acceleration signal (A) at equidistantly consecutive points in time within the respective signal interval (11-110).
7. The method according to any of the preceding claims, further comprising a step of outputting an information to a driver of the vehicle (1) and/or outputting an information to at least one electronic system of the vehicle (1) when the determined indication of the behaviour of the tire (2) fulfils a predetermined information criterion.
8. The method according to any of the preceding claims, wherein for monitoring the instantaneous behaviour of the tire (2) in terms of a road roughness, in the step d) at least the first parameter (P1) is determined and in the step e) an indication regarding the road roughness is determined based on at least the first parameter (P1).
9. The method according to any of the preceding claims, wherein for monitoring the instantaneous behaviour of the tire (2) in terms of an aquaplaning condition, in the step d) at least the second parameter (P2) is determined and in the step e) an indication regarding the aquaplaning condition is determined based on at least the second parameter (P2).
10. The method according to claim 9, wherein in the step d) the first parameter (P1) and the second parameter (P2) are determined and in the step e) the indication regarding the aquaplaning condition is determined based on the first parameter (P1) and the second parameter (P2).
1 1. A device (10) for monitoring an instantaneous behaviour of a tire (2) of a vehicle (1) in a rolling condition of the tire (2), comprising: an acceleration sensor (14) arranged at the tire (2) for acquiring an acceleration signal (a) representative of an acceleration of a specified point of the tire (2), bandpass filtering means (16, 18) for bandpass filtering of the acceleration signal (a) for providing a bandpass filtered acceleration signal (A), first determining means (16, 18) for separating the bandpass filtered acceleration signal (A) for one revolution of the tire (2) into M signal intervals (11-110), wherein M is an integer between 4 and 20, and for determining for each of the M signal intervals (11-110) a volatility measure (VM1-VM10) representative of a volatility of the bandpass filtered acceleration signal (A) within the respective signal interval (11-110), second determining means (16, 18) for determining a first parameter (P1) representative of a mean value of the volatility measures (VM1-VM10) determined for the M signal intervals (11-110) belonging to one revolution of the tire (2) and/or for determining a second parameter (P2) representative of a maximum difference between the volatility measures (VM1-VM10) determined for the M signal intervals (11-110) of the one revolution of the tire (2), third determining means (16, 18; 34, 36) for determining an indication of the instantaneous behaviour of the tire (2) based on the first parameter (P1) and/or the second parameter (P2).
12. A computer program product comprising software code for performing the method of any of claims 1 to 10 when the software code is run on a computer.