Patent Application
20240326518
This application claims priority to French Patent Application No. 2302953, filed Mar. 28, 2023, the contents of such application being incorporated by reference herein.
The present invention relates to a method for monitoring the wear of a motor vehicle tire and a tire pressure monitoring module for implementing said method.
Conventionally, a tire comprises on its outer surface a zone referred to as the “tread”, corresponding to the outer surface of the tire that is in contact with the roadway.
The tread comprises a relief, also called the “tread pattern”, making it possible in particular to discharge rainwater, snow, dust, heat, etc., in order to limit loss of grip of the tire or prevent aquaplaning.
Over the course of the kilometers traveled by the vehicle, the tread of the tire wears and becomes smooth, which increases the risk of loss of grip. Beyond a certain wear, it is thus necessary to replace the worn tire with a new tire.
In order to detect the wear of a tire, it is known practice to use methods for monitoring the state of wear of the tire.
A first type of method, referred to as “direct methods”, makes it possible to deduce the deterioration of the tire through the use of a device that wears at the same time as the tire.
These methods can be manual, by means of a colored wear strip incorporated into the tread. This solution is however not very satisfactory in that the owner of the vehicle must visually inspect their tire in order to determine whether it should be replaced. They must also remember to inspect their tires themselves. A person with average attention does not systematically inspect their tires and after a certain amount of time, there is a risk that they will travel in a vehicle fitted with worn tires with only little grip, which poses an obvious hazard.
There is also a growing need for autonomous monitoring of the wear of a tire, in particular in the context of vehicle fleet management, which model forms part of the growing development of new modes of mobility in which the driver is not the owner and in which tracking and maintenance are carried out by specific organizations on large groups of vehicles. Autonomous monitoring of the wear of a tire also applies to an even greater extent to autonomous vehicles.
The autonomous methods for monitoring tire wear also include direct methods that make it possible to deduce the deterioration of the tire and are implemented in particular by measuring variations in impedance of tubes that pass through the tire.
A second type of method, referred to as “indirect methods”, makes it possible to deduce a state of wear of the tire by using data originating from one or more parameters of the wheel or of the motor vehicle.
The indirect methods for automatic monitoring of tire wear include a method known as tread depth monitoring, or TDM.
This method mainly uses signals originating from systems on board the motor vehicle to deduce a state of wear of the tires therefrom.
These onboard systems comprise in particular:
The indirect methods for automatic monitoring of tire wear also include a method known as tread depth sensing, or TDS, which aims to more directly use a signal that is perceived by the TPMS module and in which the state of wear of the tires is almost exclusively taken from this signal.
Unlike the aforementioned TDM method, in which a set of information acquired by different sensors of the motor vehicle is compiled, the TDS method is applied as close as possible to the source of the parameter to be monitored, which makes it possible to reduce the cause and effect chain used to deduce a state of wear of the tires of the motor vehicle therefrom.
Therefore, with the TDS method, the cause and effect chain is much shorter and thus more precise than the chain obtained using the TDM method.
A TDS method known from the prior art consists in using the acceleration signal in the contact zone between the tire and the ground, to deduce a state of wear of the tire therefrom.
This signal, also referred to as the “acceleration gradient in the contact zone” corresponds to the acceleration signal perceived by the TPMS module that is mounted in the tire and attached on the tread of the tire.
The accelerometer of the TPMS module monitors the acceleration gradient on rotation of the wheel on which the tire to be monitored is mounted.
Currently, the data acquired by the TPMS module is transmitted by radiofrequency to a central processing unit comprising an electronic control unit, or ECU.
Using the data acquired, the electronic control unit will develop a transfer function in order to correlate the gradient value acquired to a thickness of the tire.
Communication between the TPMS module and the processor of the central unit is relatively difficult to achieve.
This is because communication between the TPMS module that acquires the data and the processor of the central unit that processes the data requires a phase of pairing of the TPMS module and the processor of the central unit.
A strategy for communication between the TPMS module and the processor of the central unit must therefore be specifically developed to allow this communication.
In addition, it would not be obvious to implement a solution for migrating the architecture allowing direct processing in the TPMS module since some data is only accessible to the central processor and not to the TPMS module.
An aspect of the present invention aims to overcome the drawbacks of the prior art, and to this end relates to a method for monitoring the wear of a motor vehicle tire, implemented by a tire pressure monitoring module mounted in said tire to be monitored, said module comprising a pressure sensor and a radial accelerometer, said method being notable in that it comprises the following steps of:
An aspect of the present invention provides a solution for monitoring the wear of the tire carried out solely by the tire pressure monitoring module mounted in the tire to be monitored, which makes it possible to make said solution autonomous and easily operational.
No particular system integration is then necessary. Implementing the method according to an aspect of the invention by means of a tire pressure monitoring module mounted in the tire to be monitored avoids having to transmit information to the central processor of the central processing unit of the motor vehicle, which in particular has a direct influence on the power consumption and service life of the monitoring module.
The information can also be used more directly compared to the prior art, and therefore more efficiently. The tire pressure monitoring module thus gives more refined information, which makes it possible to increase the relevance of the development of a wear processing strategy.
The monitoring method according to an aspect of the invention makes it possible to monitor and process the dynamics of the acceleration gradient, making it possible to deduce a significant level of wear therefrom, which will make it possible to transmit a warning if applicable.
Thus, unlike in the solutions known from the prior art, use is not made of a transfer function converting an acceleration gradient unit into a consumed thickness of the tread of the tire.
According to optional features of the method according to an aspect of the invention:
An aspect of the invention also relates to a tire pressure monitoring module, comprising hardware and/or software means for implementing the method according to an aspect of the invention, notable in that said hardware and/or software means are implemented in an integrated circuit.
Other features, aims and advantages of aspects of the invention will become apparent upon reading the following detailed description, in order to understand which reference will be made to the appended drawings, in which:
In the description hereinafter, elements with an identical structure or similar functions are denoted by the same reference sign.
Reference is made to
The tire 1, mounted on a motor vehicle wheel (not shown) rests on the ground 3.
The tire 1 comprises a nominal radius Rn defined by the radius of the tire 1 when the wheel is unladen, that is, not mounted on the vehicle.
The laden tire 1 is deformed in the contact zone 5 between the tire 1 and the ground 3, on its tread.
In this contact zone, the radius of the tire 1 is defined by the laden radius Rc, which corresponds to the distance between the axis of rotation 7 of the wheel and the ground 3.
The tire 1 comprises a tire pressure monitoring system, or TPMS, module 9 according to an aspect of the invention, which makes it possible to acquire the tire pressure.
The TPMS module 9 according to an aspect of the invention comprises hardware and software means capable of implementing the method of an aspect of the invention. The software means comprise computer program code means, comprising in particular the algorithm implemented to execute the method of an aspect of the invention, while the hardware means comprise an electronic module comprising a tire pressure sensor and a radial accelerometer capable of monitoring the acceleration of the wheel.
In one embodiment of the invention, the hardware and/or software means for implementing the method according to an aspect of the invention may be implemented in an integrated circuit.
In the position of the wheel illustrated in
The periodic signal representing the acceleration curve fluctuates around a static value Z0 equal to the product of the nominal radius Rn defined by the following formula:
where:
At the moment when the TPMS module 9 arrives almost in contact with the ground when the tire 1 is rotating in the direction of the arrow shown in
This pinching zone 11 is reflected in a local reduction in the nominal radius Rn of the tire 1.
Since the TPMS module 9 continues to rotate at the rotation speed ω, the local reduction in the nominal radius Ry of the tire 1 in the pinching zone 11 causes an increase in the radial acceleration Z perceived by the TPMS module 9.
This increase in the radial acceleration Z perceived by the TPMS module 9 is represented in
Once the TPMS module 9 has gone through the pinching zone 11 and arrived in the contact zone 5 with the ground 3, the acceleration Z2 perceived by the TPMS module 9 is zero, as the TPMS module 9 is no longer in motion.
Likewise, when the TPMS module 9 leaves the contact zone 5 with the ground 3, a pinching zone 13 of the tire 1 (visible in
The peaks in radial acceleration Z1 or Z3 perceived by the TPMS module 9 are reflected in a phenomenon commonly referred to as “overshoot”.
The portion 15 of the acceleration curve between Z1 and Z2 defines an entry acceleration gradient Gradentry with respect to the contact zone 5 with the ground 3 and the portion 17 of the acceleration curve between Z2 and Z3 defines an exit acceleration gradient Gradexit with respect to the contact zone 5 with the ground 3.
The acceleration gradient in the contact zone defines a signal commonly referred to as a “footprint” signal.
Reference is made to
The entry Gradentry and exit Gradexit acceleration gradients of the second tire each have a slope greater than the slopes obtained for the first, less worn tire.
As the second tire is thinner than the first tire due to its greater wear, the radius of curvature of the second tire in the pinching zones 11, 13 is smaller than that of the first tire.
Note that other parameters can however influence the acceleration gradient. These parameters are, for example, the tire pressure, the load applied to the tire, and the speed of the vehicle.
In the context of an aspect of the present invention, the acceleration gradient value used is a compensated value, in other words the value of the gradient used only reflects the wear of the tire.
The method implemented to compensate the acceleration gradient with the other parameters does not form part of an aspect of the present invention and is therefore not described in greater detail.
Reference is made to
The monitoring method according to an aspect of the invention is implemented by the TPMS module 9 of the tire 1 and comprises the following steps of:
The method according to an aspect of the invention thus aims to monitor the changes in the acceleration gradient over time and transmit a warning signal when the gradient exceeds a certain threshold.
The monitoring method according to an aspect of the invention thus makes it possible to deduce a significant state of wear of the monitored tire on the basis of the monitoring of changes in its acceleration gradient.
An aspect of the present invention thus provides a solution for monitoring tire wear carried out solely by the TPMS module 9 of the tire 1.
The acceleration gradient measurements acquired in the context of an aspect of the present invention are:
Reference is made to
The acquisition step E1 comprises a first sub-step E11 of learning initial conditions.
The learning step E11 is typically initiated when the tire to be monitored is new.
The purpose of the learning step E11 is to determine a reference acceleration gradient Grad0.
To this end, in the learning phase E11, acceleration gradient measurements of the tire 1 are acquired, which may be entry acceleration gradient Gradentry measurements or exit acceleration gradient Gradexit measurements or entry Gradentry and exit Gradexit acceleration gradient measurements in order to deduce therefrom a relative difference between the entry Gradentry and exit Gradexit acceleration gradient.
A reference acceleration gradient Grad0 is determined, which may be the initial reference acceleration gradient averaged over a predetermined number of kilometers in the life of the tire 1 to be monitored.
The reference gradient Grad0 may be equal to the mean of the acceleration gradients measured for example over the first thousand kilometers in the life of the tire 1.
The learning phase thus makes it possible to indicate the value of the gradient that the monitored tire is supposed to have at the start of its life.
As a variant, the learning step E11 may be omitted and the reference gradient value Grad0 may be determined by any other means. In particular, the reference gradient value Grad0 may be read from charts and entered into the algorithm for implementing the method of an aspect of the invention.
The acquisition step E1 then comprises a second sub-step E12 of acquiring continuous measurements of acceleration gradients, initiated when the reference gradient Grad0 has been set.
The sub-step, step E12, of acquiring continuous measurements comprises in a first embodiment the acquisition of instantaneous gradient Grad(t) measurements.
In a second embodiment of the sub-step, step E12, the acquisition of continuous measurements is carried out by finding the mean of consecutive gradient measurements.
For example, a series of measurements is taken over a predetermined number of kilometers, and the mean of these measurements is found in order to deduce a mean gradient Gradmean. therefrom.
The consecutive measurements with a view to calculating the mean thereof may be taken over a distance range, for example equal to around 50 kilometers.
The step E2 of processing the gradient measurements acquired in step E1 is carried out using an “identity” function, which is an affine function of the changes in gradient over time.
On the basis of this identity function, in step E2 the difference is calculated, as an absolute value, between the instantaneous gradient Grad(t) and the reference gradient Grad0, or between the mean gradient Gradmean and the reference gradient Grad0.
In step E3, the value obtained in the processing step E2 is compared to a predetermined threshold value Gradthreshold 1.
If |Grad(t)−Grad0|>Gradthreshold 1, then a tire wear warning is generated (step E4).
The warning may be transmitted by radiofrequency, for example.
If the gradient threshold value Gradthreshold 1 is exceeded, this means that the gradient has increased relative to the reference gradient Grad0, and therefore that the tire is worn.
Since the acceleration gradient value used is a compensated value that only reflects the wear of the tire, the other parameters that can influence the acceleration gradient value (in particular the tire pressure, the load applied to the tire, and the speed of the vehicle) do not affect the triggering of the steps of the method of an aspect of the invention, particularly step E4 for transmitting a warning when the predetermined threshold value Gradthreshold 1 is reached.
In this first embodiment of the method according to the invention, a step E5 of predicting the distance remaining before a predetermined level of wear of the monitored tire is reached may be initiated.
The predetermined level of wear may for example correspond to a level of complete wear of the monitored tire.
Step E5 may be implemented before the gradient threshold value Gradthreshold 1 is reached, that is, at any time after step E2 of processing the gradient measurements acquired during step E1 is finished, and before the warning transmission step E4 is initiated. A message to the central processing unit is then regularly transmitted without the gradient threshold value Gradthreshold 1 necessarily being reached.
As a variant, step E5 may be initiated when the gradient threshold value Gradthreshold 1 is reached, that is, following step E4.
In one exemplary embodiment, step E5 of predicting the distance remaining before a predetermined level of wear of the monitored tire is reached may be implemented periodically.
Reference is made to
In this exemplary embodiment of step E5, we go from a gradient Grad1 having a slope a to a gradient Grad2 having a slope b after having traveled a distance D1.
The assumption is that the evolution between the curve Grad1 and the curve Grad2 takes place linearly.
Based on this assumption, it is considered that to reach the value Grad3 having a slope c and representing a predetermined level of wear of the monitored tire, for example complete wear, the distance D2 to be traveled is equal to the distance D1.
The distance remaining may be extrapolated using the following formula:
where:
The monitoring method of an aspect of the invention may be implemented by a second embodiment.
It has been observed that, as the tire wears, the gradient stiffens substantially linearly as a function of the loss of thickness of the tire tread.
It has also been observed that, approaching a maximum gradient value corresponding to a highly advanced or terminal state of wear of the tire, the variations in gradient become much more dynamic. These variations in gradient are characterized by the derivative of the gradient relative to time.
Unlike in the first embodiment, the second embodiment does not comprise a step of learning a reference gradient Grad0 (step E11 of the first embodiment) or entering the reference gradient Grad0 read from charts into the algorithm for implementing the method of an aspect of the invention.
In the execution of the method according to the second embodiment of the invention, step E1 of acquiring acceleration gradient measurements may be carried out cyclically by taking a plurality of acceleration gradient measurements over a current cycle.
For example, for an iteration i performed over a predetermined distance window, the instantaneous gradient Grad(t) is measured periodically on a time basis.
The distance window may for example be equal to 100 kilometers.
The time base selected may for example be a minute, that is, a measurement is taken every minute.
As a variant, the instantaneous gradient Grad(t) may be measured periodically, over the aforementioned predetermined distance window, on a distance basis, for example every kilometer.
Given that there is a running-in phase during which certain parameters specific to the vehicle are set up, step E1 may be initiated after a predetermined number of kilometers has been traveled by the tire to be monitored.
Step E2 of processing the gradient measurements deduces a mean value of the gradient Gradmean
Step E2 of processing the gradient measurements then calculates the derivative in time of the mean gradient values Gradmean
In the exemplary embodiment shown, the value of the derivative of the gradient in time is zero over iterations i=1 to i=3.
From iteration i=4, the derivative increases until, between iteration i=5 and iteration i=6, it exceeds the predetermined threshold value Gradthreshold 2.
In step E3, the values Gradmean
If
then a tire wear warning is generated (step E4) and transmitted by radiofrequency.
According to a variant embodiment, step E2 of processing the gradient measurements deduces a mean value of the gradient Gradmean
The tire wear warning may thus be generated (step E4) not by comparison between iterations i and i−1 but by comparison between iterations i and i−2, i−3, etc.
By virtue of this second embodiment, the significant variations in gradient are detected, which makes it possible to deduce that the tire has exceeded its maximum wear level and therefore that the tire is close to the end of its life.
Of course, aspects of the present invention are not limited solely to the embodiments of this method for monitoring the wear of a motor vehicle tire and of this tire pressure monitoring module for implementing said method, which are described above purely by way of illustrative example, and it encompasses all variants involving technical equivalents of the means described.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2302953 | Mar 2023 | FR | national |
