METHOD FOR DETERMINING THE HUMIDITY OF AN AGRICULTURAL SOIL

Abstract

A method for determining the moisture of a ground on which a tire mounted on a vehicle is running, the tire being fitted with a sensor configured to acquire a measurement signal representative of the change in the curvature of the tire as it runs over a ground, comprises the following steps: acquiring a measurement signal representative of the change in the curvature of the tire while it is running; determining measurement data comprising (a) a first parameter (KS.sub.in) representative of a rate at which the tire flattens on contact with the ground, and (b) a second parameter (KS.sub.out) representative of a rate at which the tire regains its shape on becoming separated from the ground; and determining the moisture of the ground as a function of the first parameter (KS.sub.in) and the second parameter (KS.sub.out).

Claims

1.-14. (canceled)

15. A method for determining a moisture of a ground on which a tire mounted on a vehicle is running, the tire being fitted with a sensor configured to acquire a measurement signal representative of a change in a curvature of the tire as it runs over the ground, the method comprising the following steps: acquiring, using the sensor, a measurement signal representative of the change in the curvature of the tire while it is running; determining, from the measurement signal, measurement data comprising: (a) a first parameter KS.sub.in representative of a rate at which the tire flattens on contact with the ground over a course of one revolution of a wheel bearing the tire, and (b) a second parameter KS.sub.out representative of a rate at which the tire regains shape on becoming separated from the ground over the course of one revolution of the wheel bearing the tire; and determining the mechanical property of the ground as a function of the first parameter KS.sub.in and/or the second parameter KS.sub.out.

16. The method according to claim 15, wherein, during running, over the course of one revolution of the wheel, the curvature of the tire changes according to a cycle exhibiting: a part where there is no contact with the ground, and a part where there is contact with the ground, wherein the first parameter KS.sub.in is determined from a part of the measurement signal corresponding to a transition in the curvature of the tire between the part where there is no contact with the ground and the part where there is contact with the ground, and the second parameter KS.sub.out is determined from a part of the measurement signal corresponding to a transition in the curvature of the tire between the part where there is contact with the ground and the part where there is no contact with the ground.

17. The method according to claim 15, wherein, during running, over the course of one revolution of the wheel, the curvature of the tire changes according to a cycle exhibiting: a part where there is no contact with the ground, characterized in the measurement signal by a stable curvature, a part where there is contact with the ground, characterized in the measurement signal by a contact curvature variation spike, a coming-into-contact transition between the part where there is no contact with the ground and the part where there is contact with the ground, characterized in the measurement signal by a coming-into-contact curvature variation spike that is opposite of the contact curvature variation spike, and a coming-out-of-contact transition between the part where there is contact with the ground and the part where there is no contact with the ground, characterized in the measurement signal by a coming-out-of-contact curvature variation spike that is opposite of the contact curvature variation spike, the first parameter KS.sub.in being determined by a gradient between the coming-into-contact curvature variation spike and the contact curvature variation spike, and the second parameter KS.sub.out being determined by a gradient between the coming-into-contact curvature variation spike and the contact curvature variation spike.

18. The method according to claim 15, wherein, having defined a third parameter KS representative of a variation in a recovery rate of the tire, the moisture of the ground is determined using a polynomial relationship connecting the moisture of the ground and the third parameter KS.

19. The method according to claim 18, wherein the polynomial relationship is of the order n, n being an integer of between 2 and 5, taking the following form: $F=a_0+a_1\mathrm{KS}+.Math.+a_n{\left(\mathrm{KS}\right)}^n$ where F is a moisture factor, KS is the third parameter, and a.sub.0 to a.sub.n are predetermined fixed coefficients.

20. The method according to claim 15, wherein the moisture of the ground is determined by calculating a moisture factor F from the first parameter KS.sub.in and the second parameter KS.sub.out, and by comparing the moisture factor to thresholds delimiting moisture categories for the ground.

21. The method according to claim 15, wherein the moisture of the ground is included in the group comprising a moisture content by weight relative to the field capacity HCC and an average moisture content by weight H.

22. The method according to claim 15, wherein the moisture is defined over a ground depth X of less than 50 centimeters.

23. The method according to claim 15, further comprising a step of locating the vehicle during the step of acquiring the signal that provides an at least two-dimensional position Ploc of the vehicle.

24. A tire comprising a sensor sensitive to a change in a curvature of the tire and configured to generate a measurement signal representative of the change in the curvature of the tire as it runs over a ground, comprising an active part and an electronic circuit board, the active part being configured to generate the measurement signal, the electronic circuit board being configured to determine measurement data comprising: (a) a first parameter KS.sub.in representative of a rate at which the tire flattens on contact with the ground over a course of one revolution of a wheel bearing the tire, and (b) a second parameter KS.sub.out representative of a rate at which the tire regains shape on becoming separated from the ground over the course of one revolution of the wheel bearing the tire, the sensor being configured to transmit the measurement data to outside the tire.

25. A data processing unit configured to receive measurement data derived from a measurement signal representative of a change in a curvature of a tire as it runs over a ground, the measurement data comprising: (a) a first parameter KS.sub.in representative of a rate at which the tire flattens on contact with the ground over a course of one revolution of a wheel bearing the tire, and (b) a second parameter KS.sub.out representative of a rate at which the tire regains shape on becoming separated from the ground over the course of one revolution of the wheel bearing the tire, the data processing unit being configured to determine the moisture of the ground as a function of the first parameter KS.sub.in and the second parameter KS.sub.out.

26. A vehicle comprising: at least one tire; at least one sensor sensitive to a change in a curvature of the tire and configured to generate a measurement signal representative of the change in the curvature of the tire as it runs over a ground; a data processing unit configured to receive measurement data derived from the measurement signal representative of the change in the curvature of the tire as it runs over a ground and to determine the moisture of the ground as a function of at least one of the measurement data, the measurement data comprising: (a) a first parameter KS.sub.in representative of a rate at which the tire flattens on contact with the ground over a course of one revolution of the wheel bearing the tire, and (b) a second parameter KS.sub.out representative of a rate at which the tire regains shape on becoming separated from the ground over the course of one revolution of the wheel bearing the tire, the vehicle being configured to implement the method according to claim 15.

27. The vehicle according to claim 26, wherein the at least one sensor is disposed inside the tire.

28. The vehicle according to claim 27, wherein the at least one sensor comprises an active part and an electronic circuit board, the active part being configured to generate the measurement signal, the electronic circuit board being configured to determine the measurement data, and wherein the data processing unit is disposed outside the tire.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The invention will be better understood on reading the following description, which is given solely by way of non-limiting example and with reference to the appended figures, in which the same reference numbers denote identical parts throughout, and in which:

[0050] FIG. 1 schematically illustrates a tyre mounted on a rim of a vehicle;

[0051] FIG. 2 shows an example of a measurement signal read by a sensor sensitive to the curvature of the tyre as the tyre runs;

[0052] FIG. 3 shows a flowchart of the steps of the method for evaluating the moisture of a ground according to possible embodiments of the invention;

[0053] FIG. 4a and FIG. 4b each show an example of the statistical categorization and relationship between the two parameters derived from the measurement signal for a front tyre of a vehicle in various conditions of moisture of the ground;

[0054] FIG. 5 shows an example of a map of the non-uniformity of the moisture of the ground on a plot of land, the map being obtained from the measurement signal for one vehicle tyre.

DETAILED DESCRIPTION OF EMBODIMENTS

[0055] FIG. 1 illustrates a tyre 1 mounted on a rim 2. Such a tyre 1 comprises, on the one hand, a crown region 3, constituting a tread exhibiting tread patterns, and, on the other hand, sidewalls 4 ending in lower sidewall regions. The latter generally comprise a bead wire and a bead for mounting the tyre 1 on the rim 2. The rim 2 is itself connected to the vehicle 9 by an axle (not depicted). The tyre 1 thus forms the contact system providing the connection between the vehicle 9 and the ground 7.

[0056] Thus, what is meant by a tyre is a resilient solid designed to be mounted on the rim 2 of a wheel, generally in the form of a tyre band, to form the contact system providing the connection between the vehicle 9 and the ground 7, comprising a tread that undergoes a change in its circumferential radius of curvature when subjected to a load. The tyre 1 is typically made of elastomers (for example rubber) and possibly other textile and/or metallic materials. The tyre 1 may be airless, for example having flexible polyurethane spokes supporting the tread. However, as a preference, a tyre 1 comprises a flexible casing containing a pressurized gaseous interior, typically air. As this is the commonest form of tyre 1, the following description is given non-limitingly with reference to such a tyre 1 having an internal pressure of pressurized gas.

[0057] The tyre 1 is subjected to a force applied by the vehicle 9 via the axle and the rim 2 towards the ground 7. This force stems from the axle load, resulting from the weight of the vehicle 9. Because the rim 2 is non-deformable, this force, applied to the tyre 1, deforms the latter when the tyre 1 is in contact with the surface 8 of the ground 7: the part of the crown 3 below the rim 2 flattens, increasing the area of the contact patch 6 in which the tyre 1 is in contact with the ground, while the sidewalls 4 become distended. This deformation is all the more pronounced when the pressure inside the tyre is low. The nature of the ground 7 also has an influence on this deformation, and particularly the mechanical condition of this ground 7. Specifically, resistant ground deforms little if at all, whereas soft or loose ground deforms under the action of the tyre 1, so that the deformation of the tyre 1 is less as part of it is transferred to the ground 7.

[0058] The deformation of the tyre 1 results in a change to the circumferential curvature of the tyre 1, namely the curvature of the crown region 3. When the tyre 1 is running, this change to the curvature travels around the circumference of the tyre 1. For a given point on the tyre 1, the curvature will therefore vary periodically with each revolution of the wheel.

[0059] The tyre 1 is fitted with a sensor 10 configured to acquire a measurement signal representative of the change in the curvature of the tyre. This sensor 10 is situated inside the casing of the tyre 1. The sensor 10 is preferably situated against the crown region 3. The sensor 10 may be embedded in the structure of the casing of the tyre 1, or may be attached thereto, and for example held in place by an adhesive layer. The sensor 10 comprises an active part 11 secured to the casing of the tyre 1, so that the deformation of the tyre 1 leads to a corresponding deformation of the active part 11 of the sensor 10, which generates a measurement signal that is a function of the deformation of its active part 11. The measurement signal is therefore truly representative of the change in the curvature of the tyre.

[0060] As a preference, the sensor 10 is a piezoelectric sensor, which generates a voltage proportional to the variation in bending. More specifically, the sensor 10 may for example comprise an active part 11 made up of a piezoelectric layer between two conducting layers. It is also possible for the sensor 10 to be a resistive sensor, the impedance of which is proportional to the bending of the active part 11 of the sensor. It is also possible to use an accelerometer, although these are far more complex to use and require more processing of the signal. The sensor 10 may also be suited to measuring other parameters, particularly the pressure. The sensor 10 may be incorporated into another piece of electronic equipment installed inside the tyre 1, such as a pressure and/or temperature sensor of TMS (tyre monitoring system) type.

[0061] The sensor 10 also comprises an electronic circuit board 12 connected to the active part 11 of the sensor 10 and configured to receive the measurement signal coming from the active part 11. This electronic circuit board 12 comprises at least a processor and a memory, and is suited to processing data such as the measurement signal, in order to determine measurement data from the measurement signal, and to communicate these measurement data. As a preference, the sensor 10 is associated with a wireless transmitter, notably of the radiofrequency type, for example of the type using Bluetooth Low Energy technology, or of the low-power device type operating in the 433 MHz band (LPD 433) able to relay the measurement signal to an automated data processing unit, preferably disposed outside the tyre 1, in order to be processed. The wireless transmitter may form part of the sensor 10, for example as a component of the electronic circuit board 12, or may be separate from the sensor 10. It is thus possible, for example, to provide an antenna inside the tyre 1. In the case of wireless communication, an external receiver may receive the signals sent by the wireless communication means associated with the sensor 10, and relay them to the automated data processing unit.

[0062] Of course, the sensor 10 may comprise other elements involved in its correct operation, notably an electrical power supply module, for example consisting of a battery.

[0063] When the tyre 1 is running over the ground, the sensor 10 acquires (step S1) the measurement signal representative of the change in the circumferential curvature of the tyre. This measurement signal may be directly connected to the curvature (and therefore be a curvature measurement signal), and therefore monitor the change therein, or may be indirectly connected to the curvature. This is notably the case for a sensor 10 of which the active part 11 is a piezoelectric sensor, because the measurement signal then corresponds to the curvature after the signal has passed through a charge amplifier. It is this type of sensor that will be used in the examples which follow. The measurement signal, generated by the active part 11 of the sensor 10, is then processed by the electronic circuit board 12 to determine measurement data from the measurement signal. The purpose of processing the measurement signal is to extract the useful information in this signal, which information is then exploited later on in the method.

[0064] FIG. 2 shows a schematic example of a measurement signal read by a sensor 10 sensitive to the variation in curvature of the tyre when the tyre 1 is running. The measurement signal is represented here by its voltage (in V) and designated by curvature, as a function of the rotation of the wheel expressed in degrees.

[0065] During running, over the course of one revolution of the wheel, the curvature of the tyre changes according to a cycle exhibiting: [0066] a part where there is no contact with the ground, [0067] a part where there is contact with the ground.

[0068] The sequence illustrates two passes into the contact patch in which the tyre 1 is in contact with the ground, of that region in which the sensor 10 is located, which are separated by a part of the cycle where there is no contact with the ground. The part of the cycle where there is no contact with the ground is characterized by a stable curvature, which manifests itself in stability of the measurement signal. The part of the cycle where there is contact with the ground is characterized in the measurement signal by a contact curvature variation spike 20, 30. In FIG. 2, the contact curvature variation spikes 20, 30 are directed downwards. This is because the contact curvature variation spikes 20, 30 correspond to the flattening of the tyre 1 in the contact patch 6.

[0069] The curvature also exhibits a transition referred to as the coming-into-contact transition between the part where there is no contact with the ground and the part where there is contact with the ground, characterized in the measurement signal by a coming-into-contact curvature variation spike 21, 31 that is the opposite of the contact curvature variation spike 20, 30, namely in this instance directed upwards. The variation in curvature also exhibits a transition referred to as the coming-out-of-contact transition between the part where there is contact with the ground and the part where there is no contact with the ground, characterized in the measurement signal by a coming-out-of-contact curvature variation spike 22, 32 that is the opposite of the contact curvature variation spike, namely in this instance directed upwards. The coming-into-contact curvature variation spike 21, 31 and the coming-out-of-contact curvature variation spike 22, 32 correspond to the sudden variations in the radius of curvature of the tyre 1 on entering and leaving the contact patch.

[0070] Because the tyre is turning, this same cycle is repeated, with a measurement signal that is stable where there is no contact with the ground, followed by a coming-into-contact curvature variation spike 21, 31, a contact curvature variation spike 20, 30, a coming-out-of-contact curvature variation spike 22, 32, and lastly another stable measurement signal where there is no contact with the ground. This cycle corresponds to one revolution of the wheel, and therefore to 360, which is shown in FIG. 2. For each cycle, the coming-out-of-contact curvature variation spike 22, 32 affords the major advantage of being a sharp spike and especially of being essentially independent of the conditions of the ground and of the tyre 1. Specifically, the coming-out-of-contact curvature variation spike 22, 32 corresponds to the change in curvature of the tyre 1 on leaving the contact patch, when the region of the tyre 1 in which the sensor 10 is located changes abruptly from the flat state characteristic of the part where there is contact with the ground to the curved state characteristic of the part where there is no contact with the ground. On loose ground, as the tyre 1 runs it compacts the ground beneath it, forming a rut, and therefore a rut bottom that is fairly firm and on which the tyre 1 rests as it leaves the contact patch. Furthermore, the forward progress of the vehicle 9 takes the strain essentially towards entering the contact patch. The tyre 1 on leaving the contact patch thus has a coming-out-of-contact behaviour, in terms of curvature, very similar to the way in which a tyre 1 behaves on a road.

[0071] It is thus easy to identify each cycle corresponding to a revolution of the wheel by identifying each coming-out-of-contact curvature variation spike 22, 32. It is also possible to identify the cycles using a dedicated device, such as a rev counter. On that basis, the data can be expressed as a function of the degree of angle in each cycle. That notably means that the cycles and their data can be compared independently of the speed of the vehicle 9. The method steps require just one cycle in order to be implemented, and can therefore be implemented on each cycle. However, in order to make the method more robust with respect to potential isolated unpredictable incidents (the presence of a stone for example), it is possible to use a combination of several measured cycles, for example using a moving average.

[0072] The mechanical condition of the ground influences the characteristics of the profile of the measurement signal. The invention therefore seeks to extract parameters from the measurement signal in order to deduce the mechanical condition of the ground therefrom. The method thus comprises determining (step S2), from the measurement signal, measurement data comprising at least one first parameter KS.sub.in representative of an angular rate at which the tyre flattens on contact with the ground over the course of one revolution of the wheel bearing the tyre 1, and one second parameter KS.sub.out representative of an angular rate at which the tyre regains its shape on becoming separated from the ground over the course of one revolution of the wheel bearing the tyre 1. The measurement data may comprise other parameters or values derived from the measurement signal.

[0073] The first parameter KS.sub.in and the second parameter KS.sub.out are determined from a part of the measurement signal corresponding to a transition of the curvature of the tyre between the part where there is no contact with the ground and the part where there is contact with the ground. More specifically, the first parameter KS.sub.in is determined from a gradient between the coming-into-contact curvature variation spike 31 and the contact curvature variation spike 30. More specifically, the first parameter KS.sub.in may correspond to the maximum variation (in terms of absolute value) in the curvature between the coming-into-contact curvature variation spike 31 and the contact curvature variation spike 30, which is to say may correspond to the maximum gradient. In the example, with the measurement signal being expressed in volts V as a function of angular degrees , the first parameter KS.sub.in may have the units V/, which is to say may correspond to the first derivative of the curvature of the tyre 1.

[0074] The second parameter KS.sub.out is determined from a gradient between the coming-out-of-contact curvature variation spike 32 and the contact curvature variation spike 30. More specifically, the second parameter KS.sub.out may correspond to the maximum variation in the curvature between the coming-out-of-contact curvature variation spike 32 and the contact curvature variation spike 30, which is to say may correspond to the maximum gradient. In the example, with the measurement signal being expressed in volts V as a function of angular degrees , the second parameter KS.sub.out may have the units V/, which is to say may correspond to the first derivative of the curvature of the tyre 1.

[0075] The parameters KS.sub.in and KS.sub.out may be approximated in several ways. For example, the parameters KS may correspond to the maximum (in the sense of absolute value) of the derivative of the measurement signal between the coming-into-contact curvature variation spike 31 or the coming-out-of-contact curvature variation spike 32 and the contact curvature variation spike 30, the derivative being estimated from the difference between two successive (or closely-spaced) measurement points, obviously taking their angular separation into consideration. As this is a falling gradient for KS.sub.in in the example, the same will hold true for KS.sub.out with a rising gradient, and this maximum in the sense of absolute value corresponds to a minimum of the derivative of the measurement signal between the coming-into-contact curvature variation spike 31 and the contact curvature variation spike 30. It is also possible, rather than looking for a derivative extremum, to choose fixed measurement points, such as for example those situated equidistantly from the peaks of the coming-into-contact curvature variation spike 31 and of the contact curvature variation spike 30, and calculate the derivative using these points. It is also possible to use the measurement points corresponding to a measurement signal value, such as for example the signal passing through zero in the case illustrated. It is also possible to use more complex approaches, such as for example the Savitzky-Golay algorithm. However, choosing a relatively low sampling frequency, typically less than or equal to 500 Hz, and preferably less than or equal to 400 Hz, such as the frequency of 300 Hz in the example, amounts to smoothing the measurement signal and makes it possible to select approaches, such as those set forth above, that are less demanding in terms of computation.

[0076] Considered individually, the parameters KS may depend on the load, the pressure and/or the speed. However, taking into account both the first parameter KS.sub.in and the second parameter KS.sub.out makes it possible to determine variables representative of the water condition of the ground, such as the moisture content by weight relative to the field capacity over a depth X quite close to the surface of the ground, HCC 0-X caused by the passage of the tyre 1, from just these parameters, without knowing the load, the pressure, the speed of the tyre 1 over the ground.

[0077] As a preference, it is the electronic circuit board 12 of the sensor 10 which, from the measurement signal, determines the measurement data comprising the first parameter KS.sub.in and the second parameter KS.sub.out. These measurement data are then transmitted by the sensor 10 to a data processing unit 15 which implements the next part of the method. This data processing unit 15 is preferably disposed outside the tyre 1, for example in the vehicle 9, but the processing unit 15 may also be remote from the vehicle 9, and the transmission of the data may then involve intermediate transmission means. The transmission of the measurement data between the sensor 10 and the data processing unit 15 is then performed wirelessly. The data processing unit 15 typically comprises a processor and a memory and is suited to receiving and processing the measurement data when implementing the next part of the method for determining the water condition of the ground.

[0078] It is possible to transmit the measurement signal to the processing unit 15 for implementing the next part of the method. However, determining the measurement data using the sensor 10 and transmitting these measurement data alone to the data processing unit 15 offers the advantage of reducing the amount of data transmitted between the sensor 10 and the data processing unit 15. As the transmission of data uses a great deal of energy, transmitting the measurement data rather than the measurement signal makes it possible to limit the electrical power consumption of the sensor 10, which has limited powering options inside the tyre 1.

[0079] It is also advantageous to not use the electronic circuit board 12 of the sensor 10 to implement the next part of the method but rather to use the data processing unit 15 to process the measurement data. This limits the calculations performed by the electronic circuit board 12 of the sensor 10, making it possible to save on power and memory for the electronic circuit board 12. In addition, it is easier to modify the ways in which the next part of the method is implemented on a readily accessible data processing unit 15 rather than on the sensor 10 which is inside the tyre 1.

[0080] Once the processing unit 15 has received the measurement data, the processing unit 15 can determine the mechanical property of the ground as a function of the first parameter KS.sub.in and of the second parameter KS.sub.in which are present in the measurement data and vary as a function of the mechanical resistance close to the surface of the ground, as shown below.

[0081] FIG. 4a and FIG. 4b are illustrations of the determination of the water condition of the ground which is overall at the scale of the tyre.

[0082] In these examples, the measurement data are derived from a measurement signal acquired by a piezoelectric sensor 10 disposed in a front tyre of an offset trailer pulled by an agricultural tractor while said tractor is passing over a ground. This makes it possible to place measuring instruments on the trailer that are necessary to determine the pressure and the load applied to the tyre in stable fashion. The offset of the trailer, in particular of the measurement tyre in relation to the tyres of the tractor, ensures that the ground is not packed down by the passage of the tractor but indeed only by the passage of the measurement tyre.

[0083] The tractor runs on a ground exhibiting three different ground moisture conditions: [0084] a ground of the wet type, denoted HH, which is to say moist on the surface and at a depth corresponding to wintry conditions for the countries in the northern hemisphere; [0085] a ground of the moist type denoted HS, which is to say moist on the surface but dry at a depth corresponding to autumnal conditions for the same countries as above; [0086] a ground of the dry type, denoted SH or SS, which is to say dry on the surface corresponding to springlike conditions (wet at a depth) or summery conditions (dry at a depth) for the countries cited above.

[0087] The water condition of the ground was characterized by the analysis of ground test specimens in the form of core samples at various depths X. The moisture content by weight or mass is evaluated by comparing the weight in the natural state of the core sample with its dry weight which was obtained after the core sample of ground was dried. The core samples of the ground were taken synchronously on the scale of a day with measurements taken on a tyre over a path adjacent to the measurement path of the tyre having the same physical ground features, which is to say the same physical variables in terms of texture, structure and moisture.

[0088] The results of FIG. 4a and FIG. 4b compile the data obtained for three types of ground having different textures (sandy loam, clay loam and loam). For each of these textures, the grounds were prepared according to three different structural conditions:

[0089] A packed-down or compacted condition, designated W0, corresponds to the condition of the ground left after a harvest, as a result of which the ground is packed down by an inflated and loaded tyre passing over it many times without any working of the ground after these passages.

[0090] A disturbed or soft ground condition made by harrowing the packed-down ground over a depth of 10 or 30 centimetres, designated W10 and W30, respectively.

[0091] Lastly, measurements using the sensor 10 on the tyre were taken under different load and pressure conditions applied to the tyre so as to be representative of the use of an agricultural tyre in a field. The measurements were taken for various running speeds below a maximum speed of 20 km/h.

[0092] FIG. 4a shows a quadratic relationship between the moisture content by weight of the ground over a depth of 40 centimetres, denoted H 0-40, and the variation in the recovery rate of the tyre KS. The dashed curved lines represent the 90% confidence band. In this case, the variation in the recovery rate of the tyre KS is obtained, such as the difference between the rate at which the tyre regains its shape KS.sub.out and the absolute value of the rate at which the tyre flattens KS.sub.in. This relationship continues to apply irrespective of the ground type and in particular its structure, its texture and its moisture.

[0093] It is possible to define categories of moisture or water condition of the ground particularly in three different levels, thereby making it possible to distinguish the water condition of the ground using a laboratory-type characterization over a certain depth X. In the case of FIG. 4a, the moisture content by weight H 0-40 corresponds to the average of the moisture measurements of the core samples taken at depths of 10, 20, 30 and 40 centimetres of the various grounds on the various paths of the plots of land. However, it is entirely possible to perform these moisture measurements over shallower ground depths but the results are generally not as good.

[0094] By way of non-limiting illustration, since they are highly dependent on the texture of the ground, the following categories can be used:

TABLE-US-00001 TABLE 1 H 0-40 (%) <=15 15-20 >20 Moisture categories dry moist wet KS >=1.2 1.2-0.6 <0.6

[0095] A surprising level of correlation was identified between this laboratory measurement and the variation in the recovery rate of the tyre KS which was obtained using the measurement from the sensor 10 mounted on the tyre. It was thus easy to determine the category of moisture of the ground over a depth of 40 centimetres close to the surface before the tyre passes over it solely by measuring the parameters KS.sub.in and KS.sub.out, irrespective of the texture, the moisture and the structure of the ground and the conditions of use of the tyre, i.e. the inflation pressure, the load applied and the running speed.

[0096] Thus, using F to denote the moisture factor of the ground, in this case moisture content by weight H over a depth of 40 centimetres, associated with the variation in the recovery rate of the tyre, and f to denote a function corresponding to the quadratic relationship and concerning the parameter KS, it is possible to write the following:

[00002]$\begin{array}{cc}F=f\left(\mathrm{KS}\right)& \left[\mathrm{Math}1\right]\end{array}$

[0097] More specifically, the quadratic relationship may take the following form:

[00003]$\begin{array}{cc}F=a_0+a_1*\mathrm{KS}+a_2*{\left(\mathrm{KS}\right)}^2+.Math.+a_n*{\left(\mathrm{KS}\right)}^n& \left[\mathrm{Math}2\right]\end{array}$

where F is the moisture factor of the ground over a depth of 40 centimetres, KS is the variation in the recovery rate of the tyre, such as being the difference between the rate at which the tyre regains its shape KS.sub.out and the rate at which the tyre flattens KS.sub.in, and a.sub.0 to a.sub.n are predetermined fixed real coefficients.

[0098] The fixed coefficients a.sub.0 to a.sub.n are preferably chosen to maximize the discrimination between moisture categories of the ground. It is possible for example to use a one-dimensional discriminant analysis. This discriminant analysis seeks to maximize the separations between the centres of gravity of each of the moisture categories of the ground, while at the same time minimizing the spread within the category.

[0099] By way of non-limiting illustration, the moisture content by weight factor of the ground over a depth of 40 centimetres (H 0-40) can be determined as follows:

[00004]$\begin{array}{cc}H0-40\left(\%\right)=23.63-4.98\mathrm{KS}+3.54{\mathrm{KS}}^2-3.28{\mathrm{KS}}^3& \left[\mathrm{Math}3\right]\end{array}$

[0100] FIG. 4b shows a quadratic relationship between the moisture relative to the field capacity of the ground over a depth of 40 centimetres, denoted HCC 0-40, and the variation in the recovery rate of the tyre KS. The dashed curved lines represent the 90% confidence band. In this case, the variation in the recovery rate of the tyre KS is obtained, such as the difference between the absolute value of the rate at which the tyre flattens KS.sub.in and the rate at which the tyre regains its shape KS.sub.out. This relationship continues to apply irrespective of the ground type and in particular its structure, its texture and its moisture or the conditions of use of the tyre.

[0101] A surprising level of correlation was identified between this laboratory measurement and the variation in the recovery rate of the tyre KS which was obtained using the measurement from the sensor 10 mounted on the tyre. It was thus easy to determine the moisture relative to the field capacity of the ground over a depth of 40 centimetres close to the surface solely by measuring the parameters KS.sub.in and KS.sub.out, irrespective of the texture, the moisture and the structure of the ground and the conditions of use of the tyre, i.e. the inflation pressure, the load applied and the running speed.

[0102] Thus, using F to denote the moisture factor of the ground, in this case moisture relative to the field capacity HCC over a depth of 40 centimetres, associated with the variation in the recovery rate of the tyre, and f to denote a function corresponding to the quadratic relationship and concerning the parameter KS, it is possible to write the following:

[00005]$\begin{array}{cc}F=f\left(\mathrm{KS}\right)& \left[\mathrm{Math}1\right]\end{array}$

[0103] More specifically, the quadratic relationship may take the following form:

[00006]$\begin{array}{cc}F=a_0+a_1*\mathrm{KS}+a_2*{\left(\mathrm{KS}\right)}^2+.Math.+a_n*{\left(\mathrm{KS}\right)}^n& \left[\mathrm{Math}2\right]\end{array}$

where F is the moisture factor of the ground over a depth of 40 centimetres, KS is the variation in the recovery rate of the tyre, such as being the difference between the rate at which the tyre regains its shape KS.sub.out and the rate at which the tyre flattens KS.sub.in, and a.sub.0 to a.sub.n are predetermined fixed real coefficients.

[0104] The fixed coefficients a.sub.0 to a.sub.n are preferably chosen to maximize the discrimination between moisture categories of the ground. It is possible for example to use a one-dimensional discriminant analysis. This discriminant analysis seeks to maximize the separations between the centres of gravity of each of the moisture categories of the ground, while at the same time minimizing the spread within the category.

[0105] By way of non-limiting illustration, the moisture factor relative to the field capacity of the ground over a depth of 40 centimetres (HCC 0-40) can be determined as follows:

[00007]$\begin{array}{cc}\mathrm{HCC}0-40\left(\%\right)=90.3+8.5\mathrm{KS}-24.07{\mathrm{KS}}^2& \left[\mathrm{Math}4\right]\end{array}$

[0106] FIG. 5 is a map of the categories of moisture content by weight H of the ground evaluated on the basis of measurements taken during the passage of the measurement tyre over the ground at the scale of an agricultural plot of land. This plot of land having a loamy texture was initially highly irrigated over its entire width using an irrigation ramp in order to obtain a water condition of the HH type, i.e. wintery water conditions.

[0107] The moisture content by weight of the ground H is evaluated by measuring the rate at which the tyre flattens, KS.sub.in, and the rate at which the tyre regains its shape, KS.sub.out, for each revolution of the wheel bearing the tyre. Subsequently, the variation in the recovery rate of the tyre KS is evaluated by establishing the difference between the rate at which the tyre regains its shape KS.sub.out and the rate at which the tyre flattens KS.sub.in.

[0108] The columns of the map represent the longitudinal furrows made by the passage of the tyre equipped with the measuring sensor 10 over the agricultural plot of land under a consistent running condition of the tyre. However, from one furrow to the next, the conditions of use of the tyre can change with an increase in the load applied to the tyre or with a modification of the inflation pressure of the tyre, for example. In this case all the plot of land is considered to have the same physical properties in terms of texture and initial structure. However, some furrows have been subjected to specific preparation work that potentially makes the structure of this furrow different from the other furrows. Some furrows in the same plot of land have a structure of the W0, or W10 or W30 type.

[0109] For the same furrow, which is to say the same column for a given plot of land, the various lines correspond to linear units of the furrow corresponding to one revolution of the wheel bearing the measurement tyre, i.e. a distance of approximately 5 metres. For each revolution of the wheel, the rates at which the tyre flattens KS.sub.in and regains its shape KS.sub.out are measured. A variation in the recovery rate KS of the tyre is deduced from these values. The average moisture content by weight of the ground H is then evaluated over a depth of 40 centimetres for each revolution of the wheel.

[0110] The water condition of the linear unit of each furrow and the water condition of the furrow is then classified according to the three classifications defined above, which is to say wet, moist and dry, to obtain the map in FIG. 5.

[0111] A good correlation was observed between the water condition imposed on each furrow with the water condition obtained by the method in terms of statistical classifications, irrespective of the physical properties of the ground analysed. In particular, a strong disparity was observed in the centre of the plot of land, which was much dryer than at its edges. This disparity was attributed partially to problems with the nozzles of the irrigation ramp and to the non-uniform surface texture of the plot of land.

[0112] Such a map therefore shows clear agricultural potential by analysing the potential water non-uniformity of the ground of an agricultural plot of land, thereby making it possible to adapt the conditions of use of the tyre a priori to each region of the plot of land in question but also to adapt the irrigation of the plot of land to the spatial non-uniformity of the water condition of the plot of land.