METHOD FOR DETERMINING A MECHANICAL PROPERTY OF AGRICULTURAL SOIL

Description

Scope of the invention

[0001] The present invention relates to the determination of the mechanical properties of soil, in particular its real-time spatial evolution such as surface deformability. More specifically, the invention proposes to determine the surface mechanical resistance state of the soil and its evolution following the passage of agricultural machinery by means of a measurement signal representative of the circumferential curvature of the tire. Technological background

[0002] It is indeed useful to know the mechanical properties of the soil at all times, in order to interact with the driver or driver assistance systems, so as to inform them in real time of changing driving conditions and potentially react accordingly. In particular, knowing the soil's mechanical resistance allows for adjusting the operating conditions of a vehicle. For example, in the presence of loose soil, the inflation pressure of a tire can be lowered to increase the contact area between the tire and the soil, thus limiting soil compaction and the formation of ruts after the passage of agricultural machinery.

[0003] Furthermore, determining the soil's mechanical resistance locally allows for an assessment of the tire's influence on the soil's mechanical properties and helps identify opportunities to carry out certain operations dependent on this mechanical resistance. For example, driving machinery through excessively loose soil can damage the soil or cause the machinery to become bogged down. Soil cultivation can also be affected by the soil's mechanical resistance, such as by surface compaction.

[0004] By combining mechanical resistance data with synchronous geolocation data, it is possible to create a soil mechanical resistance map of a plot, potentially combined with other soil characteristics. Such a map can be useful for determining soil management strategies for the plot, such as implementing soil drainage or targeted decompaction based on soil needs.

[0005] Finally, soil, particularly agricultural soil, is complex and changes depending on the depth of observation. It is characterized by physical quantities such as its moisture content, texture, and structure. Generally, soil moisture, or its water content, is defined by the relative mass of water remaining in the soil once its "gravitational" portion has drained away. This is called mass moisture or gross weight moisture, expressed as a percentage and denoted H. However, the amount of water actually available to the plant, or capillary water, is lower than the mass moisture content because the plant must exert a suction effort to assimilate this water, which is called water potential, expressed in bars. Classically, a plant's water potential is limited to 16 bars; beyond this, the water is not available to the plant. Conversely, a soil at its maximum water retention capacity will require very little suction effort from the plant, on the order of 0.3 bar: the soil is said to be at its "field capacity" moisture content. It is useful to quantify the capillary water available at a given time or location in the field by calculating the ratio between the measured ponderable water (H) and its maximum value at the field capacity. This capillary water, "normalized" relative to the field capacity and also expressed as a percentage, is called HCC. Normalizing relative to the field capacity allows us to define a moisture value independent of soil texture and representative of the water actually available to the plant. Soil texture corresponds to the proportion of clay, silt, and sand that constitute it. These three components are distinguished by their particle size. Thus, an HCC value of 99% means that the capillary water available to the plant corresponds to 99% of the field capacity, a value very close to the maximum possible.However, this value of 99% for HCC corresponds to a weight moisture H of around 40% for a soil with small grain size and high capillary water retention such as a clay soil, but only to a weight moisture H of around 20% for a soil with large grain size and low capillary water retention, such as a sandy soil.

[0006] Finally, soil structure, which corresponds to the three-dimensional arrangement of soil material that can be observed at various horizons, i.e., at different soil depths, is classically characterized by its apparent density, denoted DA. This parameter can be impacted by tillage, particularly on the surface horizons (a few tens of centimeters), but also by the repeated passes of agricultural machinery in the field.

[0007] The combination of soil moisture, texture, and structure results in a complex material with specific mechanical properties.

[0008] French patent application FR3088249A3, registration number 1860481, describes a method for determining soil firmness in front of a tire based solely on measuring the change in curvature of a tire traveling over the soil. Soil firmness is related to the tire's flattening speed and the length of the contact patch. The soil firmness analysis, performed over a relatively significant depth, reflects the soil's bearing capacity.

[0009] However, this method cannot determine all the physical or mechanical characteristics of the soil that might be relevant to specific applications. In particular, it cannot quantify the soil's surface mechanical resistance, that is, analyze its deformability to a depth of a few tens of centimeters. Similarly, this method cannot assess the impact of the passage of a vehicle equipped with a measuring tire on the soil's mechanical characteristics, especially at the surface.

[0010] The objects of the invention which follow are intended to determine the mechanical properties of the ground and thus evaluate the impact of the passage of the tire on the ground in real time in order to adapt the rolling conditions of the tire as needed. Description of the invention

[0011] The invention relates to a method for determining the mechanics of a ground on which a tire mounted on a vehicle rolls, said tire being equipped with a sensor configured to acquire a measurement signal representative of the evolution of the tire's curvature during rolling on a ground, the method comprising the following steps: acquisition by the sensor of a measurement signal representative of the evolution of the curvature of the tire during rolling, determination from the measurement signal of measurement data comprising: a) a first parameter representative of a speed, preferably angular, of flattening of the tire upon contact with the ground during one wheel revolution of the tire, and b) a second parameter representative of a speed, preferably angular, of rounding of the tire upon separation from the ground during one wheel revolution of the tire, determination of the mechanical property of the soil as a function of the first parameter and / or the second parameter using a linear relationship linking said mechanical property of the soil and the first parameter and / or the second parameter, the mechanical property of the soil being included in the group comprising the rut depth, the mechanical resistance of the soil;The mechanical resistance of the soil at the entry point of the contact area, the mechanical resistance of the soil at the exit of the contact area, and the soil compaction caused by the tire.

[0012] The process allows for the real-time determination of soil mechanical properties, ideally at the overall tire scale, such as rut ​​depth, but also at a local scale, such as the soil's mechanical resistance factors over a given depth from the ground on which a tire mounted on a vehicle is traveling. This determination is achieved simply, accurately, and reliably, without considering vehicle pressure or load, using only the measurement signal representing the tire's curvature evolution. By taking angular velocity into account, the process automatically eliminates the need for consideration of the tire's rolling speed.

[0013] Here, the first and second parameters are linked to local effects of the contact patch, that is, the change in curvature at the entry or exit of the contact patch, observed by observing the rate of this change. These are not parameters at the global scale of the contact patch, such as, for example, the length of the contact patch. Because these quantities are local, their sensitivity is much greater than a global quantity at the scale of the contact patch. Consequently, their individual observation allows us to trace back to local mechanical properties of the surface on which the tire rolls, which is not necessarily possible, if not impossible, with a global quantity, such as the length of the contact patch, which will naturally average the effect over the entire contact patch.Using a single variable allows the analysis to focus on a local area of ​​the contact surface, i.e., the area at the inlet or outlet of the contact surface. Conversely, combining local variables allows for the estimation of mechanical properties across the entire contact surface by differentiating the sensor's mechanical responses at the inlet and outlet of the contact surface.

[0014] Preferably, the determination of the mechanical property of the soil takes into account the texture, the water status of the soil as well as the depth in order to refine the quality of the evaluation of the mechanical property of the soil.

[0015] This process is advantageously complemented by the following characteristics, taken alone or in any technically possible combination thereof: During rolling, over the course of one wheel revolution, the curvature of the tire evolves according to a cycle presenting: a part out of contact with the ground, a part in contact with the ground, in which the first parameter is determined from a part of the measurement signal corresponding to a transition of the curvature of the tire between the part out of contact with the ground and the part in contact with the ground, and the second parameter is determined from a part of the measurement signal corresponding to a transition of the curvature of the tire between the part in contact with the ground and the part out of contact with the ground. During rolling, over the course of one wheel revolution, the curvature of the tire evolves according to a cycle presenting: a part out of contact with the ground characterized on the measurement signal by a stable curvature, a part in contact with the ground characterized on the measurement signal by a peak in variation of contact curvature.an input transition between the part not in contact with the ground and the part in contact with the ground, characterized on the measurement signal by a peak in input curvature variation opposite to the peak in contact curvature variation, an output transition between the part in contact with the ground and the part not in contact with the ground, characterized on the measurement signal by a peak in output curvature variation opposite to the peak in contact curvature variation, the first parameter being determined by a slope between the peak in input curvature variation and the peak in contact curvature variation, the second parameter being determined by a slope between the peak in input curvature variation and the peak in contact curvature variation, the linear relationship is of the form: , F = a + b × KS i ou j , Or F = a + b × KS i + c × KS j With F a mechanical property factor, KS i or j the first or second parameter, and a, b, c predetermined fixed coefficients, the mechanical property of the soil is determined by calculating a mechanical property factor from the first and / or second parameter and comparing this mechanical property factor to thresholds defining soil mechanical property classes. The mechanical property of the soil is defined at a soil depth X of less than 40 centimeters, potentially less than 20 centimeters, or even less than 10 centimeters. A vehicle localization step is performed during the signal acquisition step, providing at least a two-dimensional position of the vehicle.

[0016] Here, rut depth and soil compaction caused by the passage of the tire are considered global soil parameters at the tire scale. Conversely, the soil's mechanical resistance at the contact patch and the soil's mechanical resistance at the contact patch, which correspond to the soil's surface deformability, are local soil parameters at the tire scale. The invention also relates to mapping the heterogeneity of the soil's mechanical properties on a surface where a tire mounted on a vehicle rolls, said tire being equipped with a sensor configured to acquire a measurement signal representative of the tire's curvature evolution during rolling on the surface, comprising at least two determinations of the soil's mechanical properties corresponding to at least two two-dimensional vehicle positions obtained by the method according to the invention.

[0017] According to an example not forming part of the invention, this description also relates to a tire comprising a sensor sensitive to the evolution of the tire's curvature, configured to generate a measurement signal representative of the evolution of the tire's curvature when rolling on a surface, comprising an active part and an electronic board, the active part being configured to generate the measurement signal, the electronic board being configured to determine measurement data comprising: a) a first parameter representing a speed, preferably angular, of flattening of the tire during contact with the ground during one wheel revolution of the tire, and b) a second parameter representing a speed, preferably angular, of rounding of the tire during separation from the ground during one wheel revolution of the tire, the sensor being configured to transmit the measurement data outside the tire.

[0018] The invention also relates to a data processing unit configured to receive measurement data derived from a measurement signal representative of the evolution of tire curvature during rolling on a surface, said measurement data comprising: a) a first parameter representing a speed, preferably angular, of flattening of the tire upon contact with the ground during one wheel revolution of the tire, and b) a second parameter representing a speed, preferably angular, of rounding of the tire upon separation from the ground during one wheel revolution of the tire, the data processing unit being configured to determine the mechanical property of the soil as a function of the first parameter and / or the second parameter using a linear relationship linking said mechanical property of the soil and the first parameter and / or the second parameter, the mechanical property of the soil being included in the group comprising the rut depth, the mechanical resistance of the soil at the entry of the contact area, the mechanical resistance of the soil at the exit of the contact area, the compaction of the soil generated by the tire.

[0019] Preferably the data processing unit is configured to receive at least two-dimensional vehicle position associated with measurement data.

[0020] The invention also relates to a vehicle comprising: at least one tire, at least one sensor sensitive to the evolution of the tire's curvature, configured to generate a measurement signal representative of the evolution of the tire's curvature during rolling on a surface, preferably the sensor is located inside the tire, a data processing unit configured to receive measurement data derived from the measurement signal representative of the evolution of the tire's curvature during rolling on a surface and to determine the mechanical property of the surface as a function of at least one of the measurement data, the measurement data comprising a) a first parameter representative of a speed, preferably angular, of the tire flattening upon contact with the surface during one wheel rotation of the tire, and b) a second parameter representative of a speed, preferably angular,of the tire's circular shape during separation from the ground during one wheel rotation, the vehicle being configured to implement the method according to the invention.

[0021] Preferably, the sensor comprises an active part and an electronic board, the active part being configured to generate the measurement signal, the electronic board being configured to determine the measurement data, and in which the data processing unit is disposed outside the tire.

[0022] According to an example not included in the invention, this description also relates to a computer program product comprising program code instructions for executing the process according to the invention, when said program is executed on a computer. The computer program product may take the form of a computer-readable non-transient medium storing code instructions for executing the process according to the invention, when said computer-readable non-transient medium is read by a computer. Brief description of the drawings

[0023] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the accompanying figures, in which the same reference numbers designate identical parts throughout and in which: there Fig. 1schematically illustrates a tire mounted on a vehicle rim; the Fig. 2 presents an example of a measurement signal recorded by a sensor sensitive to tire curvature as the tire rolls; the Fig. 3 presents a synoptic diagram of the steps in the method for evaluating the mechanical properties of soil according to possible embodiments of the invention; Fig. 4a and Fig. 4b Each shows an example of a statistical relationship and classification between the two parameters derived from the measurement signal for a vehicle's front tire according to different states of corresponding local mechanical properties of the ground: the mechanical resistance of the ground at the entry and exit of the contact area; the Fig. 5shows an example of mapping the heterogeneity of an overall mechanical property of the soil, the compaction caused by the passage of a tire, on two plots, obtained from the measurement signal for a vehicle tire; the Fig. 6 shows an example of the relationship between the overall mechanical property of the soil, rut depth, and one of the parameters derived from the measurement signal for a front tire of a vehicle. Detailed description of implementation methods

[0024] There Fig. 1Figure 1 illustrates a tire 1 mounted on a rim 2. Such a tire 1 comprises, on the one hand, a crown area 3 constituting a tread with grooves, and on the other hand, sidewalls 4 ending in lower sections. These lower sections generally include a bead and a rim strip to allow the tire 1 to be mounted on the rim 2. The rim 2 is itself connected to the vehicle 9 by an axle (not shown). The tire 1 thus provides the connection between the vehicle 9 and the ground 7.

[0025] A tire is defined as a flexible solid designed to be mounted on the rim 2 of a wheel, generally in the form of a band, to provide contact between the vehicle 9 and the ground 7. It has a tread whose circumferential radius of curvature changes when subjected to stress. The tire 1 is typically made of elastomers (e.g., rubber) and possibly other textile and / or metallic materials. The tire 1 may be airless, for example, with flexible polyurethane spokes supporting the tread. Preferably, however, a tire 1 comprises a flexible casing containing a pressurized gas, typically air. As this is the most common type of tire 1, the following description is non-limiting and refers to such a tire 1 with an internal gas pressure.

[0026] Tire 1 is subjected to a force applied by the vehicle 9, via the axle and rim 2, directed towards the ground 7. This force originates from the axle load, resulting from the weight of the vehicle 9. Since the rim 2 is rigid, this force acting on tire 1 deforms it when it is in contact with the ground surface 7 8: the crown 3 under the rim 2 flattens, increasing the contact area 6 of tire 1 with the ground, while the sidewalls 4 bulge. This deformation is more pronounced when the pressure inside the tire is low and / or the load carried by the tire is high. The nature of the soil 7 also influences this deformation, and in particular the mechanical state of this soil 7. Indeed, a resistant soil does not deform or deforms very little, while a soft or loose soil deforms under the action of the tire 1, so that the deformation of the tire 1 is less, partly transferred to the soil 7.

[0027] The deformation of tire 1 results in a change in the circumferential curvature of tire 1, that is, the curvature of the apex area 3. When tire 1 rolls, this change in curvature travels around the circumference of tire 1. For a given point of tire 1, the curvature will therefore vary periodically with each wheel rotation.

[0028] The tire 1 is equipped with a sensor 10 configured to acquire a measurement signal representative of the tire's curvature evolution. This sensor 10 is located inside the tire's casing. Preferably, the sensor 10 is positioned against the crown area 3. The sensor 10 can be embedded in the structure of the tire's casing, or it can be attached to the casing and, for example, held in place by an adhesive layer. The sensor 10 has an active part 11 attached to the tire's casing, such that the deformation of the tire 1 causes 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 representative of the tire's curvature evolution.

[0029] Preferably, the sensor 10 is a piezoelectric sensor, which generates a voltage proportional to the change in deflection. More precisely, the sensor 10 may, for example, include an active part 11 consisting of a piezoelectric layer between two conductive layers. It is also possible for the sensor 10 to be a resistive sensor, whose impedance is proportional to the deflection of the active part 11 of the sensor. An accelerometer can also be used, although its operation is much more complex and requires more extensive signal processing. The sensor 10 can also be adapted to measure other parameters, and in particular pressure. The sensor 10 can be integrated into other electronic equipment installed in the tire 1, such as a TMS (Tire Monitoring System) pressure and / or temperature sensor.

[0030] The sensor 10 also includes an electronic board 12 connected to the active part 11 of the sensor 10 and configured to receive the measurement signal from the active part 11. This electronic board 12 includes at least one processor and memory, and is adapted to process data such as the measurement signal, to determine measurement data from the measurement signal, and to communicate this measurement data. Preferably, the sensor 10 is associated with a wireless transmitter, in particular of the radio frequency type, and for example of the type using Bluetooth Low Energy technology or of the type of low-power device operating in the 433 MHz band (LPD 433), enabling the measurement signal to be relayed to an automated data processing unit, preferably located outside the tire 1, for further processing.The wireless transmitter can be part of the sensor 10, for example as a component of the electronic board 12, or be separate from the sensor 10. For example, an antenna can be provided inside the tire 1. In the case of wireless communication, an external receiver can receive the signals sent by the wireless communication means associated with the sensor 10, and relay them to the automated data processing unit.

[0031] Of course, the sensor 10 may include other elements enabling its proper functioning, and in particular a power supply module, for example consisting of a battery.

[0032] When the tire 1 rolls on the ground, the sensor 10 acquires (step S1) the measurement signal representing the evolution of the tire's circumferential curvature. This measurement signal can be directly related to the curvature (and therefore be a curvature measurement signal), thus tracking its evolution, or it can be indirectly related to the curvature. This is notably the case for a sensor 10 whose active part 11 is a piezoelectric sensor, since the measurement signal then corresponds to the variation in curvature which, when integrated, for example at the level of a charge amplifier, becomes the curvature. This type of sensor will be used in the examples below. The measurement signal, generated by the active part 11 of the sensor 10, is then processed by the electronic board 12 to determine measurement data from the measurement signal.The processing of the measurement signal aims to extract useful information from this signal, which is then used in the subsequent stages of the process.

[0033] There Fig. 2 This shows a schematic example of a measurement signal recorded by a sensor 10 sensitive to the curvature of the tire when the tire 1 is rolling. The measurement signal is represented here by its voltage (in V), and designated by curvature, as a function of the wheel rotation expressed in degrees.

[0034] During rolling, over the course of one wheel rotation, the curvature of the tire changes according to a cycle that presents: one part out of contact with the ground, one part in contact with the ground.

[0035] The sequence illustrates two passes through the ground contact area of ​​the tire 1, where sensor 10 is located, separated by a non-ground contact area. The non-ground contact area is characterized by a stable curvature, which translates into a stable measurement signal. The ground contact area is characterized in the measurement signal by a peak in the variation of contact curvature 20, 30. On the Fig. 2 The peaks of contact curvature variation 20, 30 are directed downwards. Indeed, the peaks of contact curvature variation 20, 30 correspond to the flattening of the tire 1 in the contact surface 6, i.e. a curvature close to zero.

[0036] The curvature also exhibits a transition, known as the entry transition, between the part not in contact with the ground and the part in contact with the ground. This transition is characterized on the measurement signal by a peak in the entry curvature variation (21, 31) opposite to the peak in the contact curvature variation (20, 30), i.e., upwards in this case. The curvature variation also exhibits a transition, known as the exit transition, between the part in contact with the ground and the part not in contact with the ground. This transition is characterized on the measurement signal by a peak in the exit curvature variation (22, 32) opposite to the peak in the contact curvature variation (i.e., upwards in this case). The entry curvature variation peak (21, 31) and the exit curvature variation peak (22, 32) correspond to the more or less abrupt changes in the radius of curvature of the tire (1) as it enters and exits the contact patch.

[0037] Since the tire rotates, the same cycle repeats, with a stable measurement signal when not in contact with the ground, then a peak in the input curvature variation (21, 31), a peak in the contact curvature variation (20, 30), a peak in the output curvature variation (22, 32), and finally another stable measurement signal when not in contact with the ground. This cycle corresponds to one wheel rotation, therefore 360°, as shown on the diagram. Fig. 2For each cycle, the peak of the exit curvature variation 22, 32 has the significant advantage of being acute and, above all, essentially independent of the ground conditions and the tire 1. Indeed, the peak of the exit curvature variation 22, 32 corresponds to the change in curvature of tire 1 as it exits the contact patch, when the area of ​​tire 1 where sensor 10 is located abruptly changes from the flat state characteristic of the part in contact with the ground to the curved state characteristic of the part out of contact with the ground. On soft ground, as it rolls, tire 1 compacts the ground beneath it, forming a rut, and therefore a fairly firm rut bottom on which tire 1 rests as it exits the contact patch. Furthermore, the forward movement of the vehicle 9 primarily transfers the stresses towards the entrance of the contact patch.Tire 1 exiting the contact area thus exhibits an exit behavior, in terms of curvature, very close to the behavior of a tire 1 on a road.

[0038] Thus, it is easy to identify each cycle corresponding to a wheel rotation by detecting each peak in the output curvature variation 22, 32. It is also possible to identify the cycles with a dedicated device, such as a tachometer. From there, the data can be expressed as a function of the angular degree of each cycle. This makes it possible, in particular, to compare the cycles and their data independently of the vehicle's speed 9. The steps of the process require only one cycle to be implemented and can therefore be implemented for each cycle. However, in order to make the process more robust to potential one-off events (such as the presence of a stone), it is possible to use a combination of several measured cycles, for example, with a moving average.

[0039] The mechanical condition of the soil influences the characteristics of the measurement signal profile. The invention therefore aims to extract parameters from the measurement signal to deduce the mechanical condition of the soil. The method thus comprises determining (step S2), from the measurement signal, measurement data comprising at least a first parameter KSin representing the angular velocity of the tire's flattening during contact with the soil during one wheel rotation of tire 1, and a second parameter KSout representing the angular velocity of the tire's rounding during uncovering from the soil during one wheel rotation of tire 1. The measurement data may include other parameters or values ​​derived from the measurement signal.

[0040] The first KS in and second KS out parameters are determined from a portion of the measurement signal corresponding to a transition in the tire curvature between the part off the ground and the part in contact with the ground. More precisely, the first parameter KS in is determined by a slope between the peak of the input curvature variation 31 and the peak of the contact curvature variation 30. More precisely, the first parameter KS in can correspond to the maximum change in curvature between the peak of the input curvature variation 31 and the peak of the contact curvature variation 30, i.e., to the maximum slope (in absolute value). In the example, since the measurement signal is expressed in volts (V) as a function of angular degrees (°), the first parameter KS in can have units of V / °, i.e., the first derivative of the tire curvature 1.

[0041] The second parameter KS out is determined by a slope between the peak of the output curvature variation 32 and the peak of the contact curvature variation 30. More precisely, the second parameter KS out can correspond to the maximum curvature variation between the peak of the output curvature variation 32 and the peak of the contact curvature variation 30, i.e., it corresponds to the maximum slope. In the example, since the measurement signal is expressed in volts (V) as a function of angular degrees (°), the first parameter KS out can have the unit V / °, i.e., the first derivative of the curvature of the tire (1).

[0042] The parameters KS in and KS out can be approximated in several ways. For example, the KS parameters can correspond to the maximum (in the sense of absolute value) of the derivative of the measurement signal between the peak of the input curvature variation 31 or output 32 and the peak of the contact curvature variation 30. The derivative is estimated from the difference between two successive (or nearby) measurement points, obviously taking into account their angular separation. Since the slope of KS in in the example is decreasing, the same will be true for KS out, with an increasing slope. This maximum in the sense of absolute value corresponds to a minimum of the derivative of the measurement signal between the peak of the input curvature variation 31 and the peak of the contact curvature variation 30.It is also possible, instead of searching for an extreme value of the derivative, to choose fixed measurement points, such as those equidistant from the peaks of the input curvature variation peak 31 and the contact curvature variation peak 30, and calculate the derivative from these points. Alternatively, one can choose measurement points corresponding to a measurement signal value, such as the zero crossing in the illustrated case. More complex approaches, such as the Savitzky-Golay algorithm, are also possible. However, choosing a relatively low sampling frequency, typically less than or equal to 500 Hz, and preferably less than or equal to 400 Hz, like the 300 Hz in the example, smooths the measurement signal and allows for less computationally intensive approaches, such as those presented above.

[0043] The first parameter, KS in, and the second parameter, KS out, have the advantage of exhibiting high variability depending on the soil's mechanical resistance and are easily obtained, as demonstrated above. More precisely, when soil resistance decreases, the parameters KS in and KS out decrease (in absolute value), and vice versa. Thus, the looser the soil, the lower the flattening or rolling speed. Conversely, when soil resistance increases, the parameters KS in and KS out, which are equivalent to the tire's deformation rates, increase.

[0044] Taken individually, the KS parameters can depend on the load, pressure, and / or speed. However, taking into account both the first parameter KS in and the second parameter KS out makes it possible to determine soil deformation quantities at the tire scale, such as the compaction over a rather shallow depth X of the soil C tire 0-X generated by the passage of tire 1, from these parameters alone, without knowing the load, pressure and speed of tire 1 on the soil.

[0045] Preferably, the electronic board 12 of the sensor 10 determines, from the measurement signal, the measurement data comprising the first parameter KS in and the second parameter KS out. This measurement data is then transmitted by the sensor 10 to a data processing unit 15, which implements the remainder of the process. This data processing unit 15 is preferably located outside the tire 1, for example, in the vehicle 9, but the processing unit 15 can also be located remotely from the vehicle 9, and the data transmission may then involve intermediate transmission means. The transmission of measurement data between the sensor 10 and the data processing unit 15 is then wireless.The data processing unit 15 typically includes a processor and memory, and is adapted to receive and process measurement data during the implementation of the subsequent process for determining the mechanical properties of the soil.

[0046] It is possible to transmit the measurement signal to the processing unit 15 for the subsequent steps of the process. However, determining the measurement data using the sensor 10 and transmitting only this measurement data to the data processing unit 15 has the advantage of reducing the amount of data transmitted between the sensor 10 and the data processing unit 15. Since data transmission consumes a significant amount of energy, transmitting the measurement data rather than the measurement signal limits the power consumption of the sensor 10, whose power supply options in the pneumatic system 1 are limited.

[0047] Furthermore, it is advantageous not to use the electronic board 12 of the sensor 10 for implementing the rest of the process, but rather to use the data processing unit 15 to process the measurement data. This limits the calculations performed by the electronic board 12 of the sensor 10, thus saving energy and memory on the electronic board 12. In addition, it is easier to modify the implementation of the rest of the process on an easily accessible data processing unit 15, rather than on the sensor 10 inside the tire 1.

[0048] Once the processing unit 15 has received the measurement data, the processing unit 15 can determine the mechanical property of the soil as a function of the first parameter KS in and the second parameter KS in contained in the measurement data, which vary according to the surface mechanical resistance of the soil, as shown below.

[0049] THE Fig. 4a and 4b are illustrations of the determination of a mechanical property of the soil which is local and not global at the scale of the tire.

[0050] In these examples, the measurement data is derived from a signal acquired by a piezoelectric sensor located in the front tire of an offset trailer pulled by an agricultural tractor as the tractor passes. This allows the trailer to carry the necessary measuring equipment to determine the pressure and load applied to the tire in a stable manner. The offset of the trailer, and in particular the measuring tire relative to the tractor tires, ensures that the soil is compacted not by the tractor's passage, but only by the passage of the measuring tire.

[0051] In the results of the two figures Fig. 4a and Fig. 4bThe tractor drove over several types of soil representing three different texture conditions: a medium silt type soil, a clayey silt type soil, a sandy type soil.

[0052] Furthermore, these different soils were put in all possible water states by varying the proportion of water both on the surface and in depth, either naturally according to the seasons (winter, spring, summer, autumn), or by irrigation.

[0053] These soils were also prepared according to three different initial structural conditions: A compacted or pressed-down soil condition, designated "WO," corresponds to the state of the soil left after harvest, compacted by the repeated passage of a loaded and inflated tire without any subsequent tillage. A loosened or disturbed soil condition, achieved by harrowing the compacted soil to a depth of 10 or 30 centimeters, is designated "W10" and "W30," respectively.

[0054] Furthermore, other soil structural conditions were created by varying the number of tractor passes (up to three passes) over each of these initial conditions. Finally, measurements were taken under different load and pressure conditions applied to the tire, representative of field use of an agricultural tire. Measurements were taken at varying speeds below a maximum speed of 20 km / h.

[0055] The first mechanical property is the soil's resistance to the tire, denoted Cpc in, which corresponds to the determination of the soil's allowable elastic stress limit, expressed in bar. This is the maximum stress the soil can withstand before irreversibly deforming, thus altering its structure. Necessarily, the lower this stress, the weaker or looser the soil. Conversely, the higher this stress, the stronger the soil. Maximum resistance is obtained for a road-type soil that does not deform under the passage of an agricultural tire under normal operating conditions.

[0056] There Fig. 4aThis shows a linear relationship between the Cpc in and the tire flattening speed upon contact with the ground (KS in), regardless of the soil's physical state, i.e., its texture, structure, and moisture content. The two dashed lines represent the 90% confidence intervals.

[0057] It is possible to define soil resistance classes, specifically three different levels, which allows differentiation of the soil resistance type using a laboratory-type characterization of the soil resistance obtained by a uniaxial compression measurement of a cylindrical soil sample taken to a certain depth X. In the case of the Fig. 4a , the Cpc measurement was carried out at a depth of 10 centimetres on soil cores taken before or after the passage of the tire.

[0058] As an illustrative and non-limiting example, the following classes can be used: [Table 1] Cpc (bar) <= 0.5 bar 0.5 - 1.0 bar > 1.0 bar Soil resistance Weak or "cowardly" Average or "intermediate" Strong or "resistant" KS in >= -0.6 -1.1 - -0.6 < -1.1

[0059] A correlation level was identified between this laboratory measurement Cpc and a measurement of the tire flattening speed KS in obtained by measuring the sensor 10 mounted on the tire, specifically at a soil depth of 10 centimeters. Thus, it is easy to determine the soil resistance class at a surface depth of 10 centimeters before the tire passes over the ground, based solely on the KS in parameter measurement, regardless of the soil texture, structure, and moisture content, as well as the tire's operating conditions, such as inflation pressure, applied load, and rolling speed.

[0060] Thus, denoting F as the soil mechanical property factor associated with the soil resistance to the tire, denoted Cpc in, and f as a function corresponding to the relation and acting on the parameter KS in, we can write: F = f KS in

[0061] More precisely, the linear relationship can be of the form: F = a + b ∗ KS in with F the mechanical resistance factor of the soil in front of the tire over a depth of X centimeters, KS in the tire flattening speed and a, b fixed non-zero real coefficients previously determined.

[0062] The fixed coefficients a and b are preferably chosen to maximize the discrimination of soil mechanical property classes. A one-dimensional discriminant analysis can be used, for example. This discriminant analysis aims to maximize the differences between the centroids of each soil mechanical property class, while minimizing intra-class dispersion.

[0063] As an illustrative and non-limiting example, the mechanical resistance factor of the soil in front of the tire at a depth of 10 centimeters can be determined as follows: Cpc in 0 − 10 bar = − 0.092 − 1.109 × KS in

[0064] The dotted lines around the solid line illustrating the formula above delimit the 90% confidence interval.

[0065] The illustration of the Fig. 4b concerns a similar analysis that was carried out on the same soils in terms of structure, texture and water status as those of the Fig. 4a .

[0066] The second mechanical property observed is the soil resistance behind the tire, Cpc out, which corresponds to the determination of the allowable elastic stress limit of the soil, expressed in bar, after the tire has passed over it. If the soil has remained elastic, no variation in soil resistance is observed in front of or behind the tire; that is, generally, no rutting occurs. Generally, on agricultural soil, soil compaction is observed after the tire has passed over it, which is minimized, for example, by adjusting the tire's inflation pressure. Therefore, Cpc out is generally higher than Cpc in, reflecting the compaction or plastic deformation experienced by the soil due to the mechanical action exerted by the tire.

[0067] It is possible to define soil resistance classes, specifically three different levels, which allows differentiation of the soil resistance type using a laboratory-type characterization of soil resistance obtained by a uniaxial compression measurement of a cylindrical soil sample taken at a certain depth X. The same Cpc measurements were used as for the Fig. 4a .

[0068] As an illustrative and non-limiting example, the following classes can be used: [Table 2] Cpc (bar) <= 0.5 bar 0.5 - 1.0 bar > 1.0 bar Soil resistance Weak or "cowardly" Average or "intermediate" Strong or "resistant" KS out <= 0.8 0.8 - 1.6 > 1.6

[0069] A similar level of correlation was identified between the laboratory measurement of uniaxial compression Cpc, particularly for a soil depth of 10 centimeters, and the determination of the KS tire's rounding speed, as illustrated by the Fig. 4b .

[0070] It is therefore easy to determine the soil resistance class Cpc out over a surface depth of 10 centimeters before the passage of the tire by measuring only the parameter KS out, regardless of the texture, structure and water status of the soil as well as the conditions of use of the tire such as inflation pressure, applied load and rolling speed.

[0071] Thus, denoting F as the soil mechanical property factor associated with the soil resistance behind the tire, denoted Cpc out, and f as a function corresponding to the relation and acting on the parameter KS out, we can write: F = f KS out

[0072] More precisely, the linear relationship can be of the form: F = a + b ∗ KS out with F the mechanical resistance factor of the ground behind the tire, KS out the speed of tire rolling and a, b fixed non-zero real coefficients determined beforehand.

[0073] The fixed coefficients a and b are preferably chosen to maximize the discrimination of soil mechanical property classes. A one-dimensional discriminant analysis can be used, for example. This discriminant analysis aims to maximize the differences between the centroids of each soil mechanical property class, while minimizing intra-class dispersion.

[0074] As an illustrative and non-limiting example, the mechanical resistance factor of the soil behind the tire to a depth of 10 centimeters can be determined as follows: Cpc out 0 − 10 bar = 0.142 + 0.507 × KS out

[0075] The dotted lines around the solid line illustrating the formula above delimit the 90% confidence interval.

[0076] The values ​​of flattening or rounding speed of the tire for the same soil class are different because the interaction between the soil and the tire is different depending on whether one is at the entrance or exit of the contact area, which justifies specific relationships for each quantity.

[0077] There Fig. 5 is a mapping of the surface compaction of the soil C tire caused by the passage of the tire on the scale of two agricultural plots differing in texture but both heavily wet throughout the depth of the soil (winter condition).

[0078] The surface compaction of the soil (Ctire) caused by the passage of the tire is evaluated by comparing the mechanical strength of the soil in front of (Cpc in) and behind (Cpc out) the tire. In our case, the comparison consists of calculating the difference between the mechanical strength of the soil after the tire has passed and the mechanical strength of the soil before the tire has passed. The compaction is then expressed in bars. However, the comparison can also be based on the ratio between the two levels of soil mechanical strength, and the compaction is then expressed as a percentage.

[0079] The columns in the map represent the longitudinal furrows of the tire equipped with sensor 10 across the agricultural plot under homogeneous tire conditions. However, from one furrow to the next, tire usage conditions can change, for example, by increasing the load applied to the tire or modifying the tire inflation pressure. In the example given, the entire plot is assumed to have the same physical properties in terms of texture and initial structure. However, some furrows have undergone specific preparation, potentially resulting in a different furrow structure compared to other furrows. Some furrows within the same plot have a WO, W10, or W30 type structure and have been subjected to up to three tractor passes.

[0080] For the same furrow, that is, the same column for a given plot, the various lines correspond to linear units of the furrow, corresponding to one wheel rotation of the measuring tire, or approximately 5 meters. For each wheel rotation, the flattening speed (KS in) and the rounding speed (KS out) of the tire are measured. From these values, a Cpc in and a Cpc out are deduced based on the previous formulas. The surface compaction of the soil (C tire) is then evaluated at each wheel rotation. Finally, the surface compaction values ​​of the soil for each linear unit of furrow are averaged over all the linear units of the same furrow.

[0081] We observe that some furrows show no surface compaction of the soil, such as the first columns on the left, indicating that the passage of the tire does not alter the soil structure. In other words, the soil remains in an elastic state following the passage of the tire under the operating conditions of the tire on these furrows.

[0082] Conversely, other furrows, corresponding to furrows 4 to 7 from the left, exhibit high soil compaction rates caused by the tire, generally around 0.3 bar. This indicates significant plastic deformation of the soil by the tire's passage and leads to rutting. To prevent rutting, it is necessary to adjust the tire's operating conditions by reducing its inflation pressure or decreasing its transported load. However, if the soil is loose in this furrow, which will be detected by the relationship between the Cpc in and the tire's flattening speed, this compaction may be desirable. The behavior should be adapted according to the desired function in relation to the actual function achieved.

[0083] Such mapping reveals clear agricultural potential by analyzing the potential heterogeneity of the soil within a given agricultural plot. This allows for the proactive adaptation of tire operating conditions to each zone of the plot. Furthermore, real-time measurement and mapping enable real-time adjustments to tire operating conditions during fieldwork to minimize the impact of agricultural machinery on the soil's mechanical properties. For example, these measurements can be used to alert farmers to the risk of rutting that could be detrimental to the plot's operation, allowing for the rapid adaptation of tire operating conditions to the soil's mechanical properties at the linear furrow level.

[0084] The illustration of the Fig. 6 concerns a similar analysis that was carried out on the same soils in terms of structure, texture and water status as those of Fig. 4a and Fig. 4bBut this time the mechanical property is global, at the scale of the tire.

[0085] The observed mechanical property is the rut depth PO, which corresponds to the formation of a rut in the agricultural soil, expressed in centimeters, due to the plastic deformation the soil undergoes after the tire passes over it. The fact that this is the result of the tire passing completely over the soil justifies the global nature of this mechanical property of the soil. If the soil remains elastic, no plastic deformation is observed, meaning no rut formation. Generally, on agricultural soils with inherently low resistance, soil compaction is observed after the tire passes over them. This compaction is minimized, for example, by adjusting the tire's inflation pressure. Consequently, the mechanical action exerted by the tire on the soil generates a rut of varying depth.

[0086] A correlation has been identified between the measured rut depth after tire passage and the flattening speed (KS in) and rounding speed (KS) of the tire. This is linked to the variation in the soil's plasticity limit during tire passage, which translates into a variation in soil resistance (Cpc in) and (Cpc out) of the soil over a depth X.

[0087] However, the soil depth X to be taken into account to best correlate with rut depth depends heavily on the physical properties of the soil.

[0088] A general and global level of correlation has been identified between the rut depth PO and the tire's circling speed KS out through a simple relationship between the two quantities.

[0089] Indeed, the correlation links this field measurement, taken after the tire has passed, with a measurement of the tire's rutting speed (KS out) obtained by measuring the sensor 10 mounted on the tire, specifically for a soil depth of 10 centimeters. Thus, it is easy to determine the rut depth after the tire has passed using only the KS out parameter, regardless of the soil texture, structure, and moisture content, or the tire's operating conditions such as inflation pressure, applied load, and rolling speed.

[0090] Thus, denoting F as the soil mechanical property factor associated with rut depth PO and f as a function corresponding to the relation and acting on the parameter KS out, we can write: F = f KS out , Or F = f KS out KS in

[0091] More precisely, the linear relationship can also be of the form: F = a + b ∗ KS out , Or F = a + b ∗ KS out + c ∗ KS in with F the rut depth factor, KS out the tire rounding speed, KS in the tire flattening speed and a, b, c fixed non-zero real coefficients previously determined.

[0092] As an illustrative and non-limiting example, the rut depth factor PO can be determined from the tire's swashplate speed KS as follows: PO cm = 14.3 − 4.5 × KS out

[0093] The dotted lines around the solid line illustrating the formula above delimit the 90% confidence interval.

Claims

1. Method for determining the mechanical properties of a ground on which a tyre (1) mounted on a vehicle (9) is running, said tyre (1) being fitted with a sensor (10) configured to acquire a measurement signal representative of the change in the curvature of the tyre as it runs over a ground (7), the method comprising the following steps: - acquiring (S1), by way of the sensor (10), a measurement signal representative of the change in the curvature of the tyre (1) while it is running, - determining (S2), from the measurement signal, measurement data comprising: a) a first parameter (KSin) representative of a rate, preferably angular rate, at which the tyre (1) flattens on contact with the ground (7) over the course of one revolution of the wheel bearing the tyre, and b) a second parameter (KSout) representative of a rate, preferably angular rate, at which the tyre (1) regains its shape on becoming separated from the ground (7) over the course of one revolution of the wheel bearing the tyre, - determining (S4) the mechanical property of the ground as a function of the first parameter (KSin) and / or the second parameter (KSout) using a linear relationship connecting said mechanical property of the ground and the first parameter (KSin) and / or the second parameter (KSout) the mechanical property of the ground being included in the group comprising the rut depth (RD), the mechanical resistance of the ground on entering the contact patch (Cpcin), the mechanical resistance of the ground on leaving the contact patch (Cpcout), and the compaction of the ground caused by the tyre (Ctyre),2. Method according to Claim 1, wherein, during running, over the course of one revolution of the wheel, the curvature of the tyre (1) changes according to a cycle exhibiting: - a part where there is no contact with the ground, - a part where there is contact with the ground, wherein the first parameter (KSin) is determined from part of the measurement signal corresponding to a transition in the curvature of the tyre (1) 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 (KSout) is determined from part of the measurement signal corresponding to a transition in the curvature of the tyre (1) between the part where there is contact with the ground and the part where there is no contact with the ground.

3. Method according to Claim 1 or 2, wherein, during running, over the course of one revolution of the wheel, the curvature of the tyre (1) 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 (20, 30), - 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, 22) that is the opposite of the contact curvature variation spike (20, 30), - 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 (20, 30), the first parameter (KSin) being determined by a gradient between the coming-into-contact curvature variation spike (21) and the contact curvature variation spike (20), the second parameter (KSout) being determined by a gradient between the coming-into-contact curvature variation spike (31) and the contact curvature variation spike (30).

4. Method according to one of the preceding claims, wherein the linear relationship takes the following form: F = a + b × KS i or j , or F = a + b × KS i + c × KS j where F is a mechanical property factor, KSi or j is the first or the second parameter, and a, b and c are predetermined fixed coefficients.

5. Method according to one of the preceding claims, wherein the mechanical property of the ground is determined by calculating a mechanical property factor (F) from the first parameter (KSin) and / or the second parameter (KSout), and by comparing said mechanical property factor to thresholds delimiting mechanical property categories for the ground.

6. Method according to one of the preceding claims, wherein the mechanical property of the ground is defined over a ground depth X of less than 40 centimetres, potentially less than 20 centimetres, or even less than 10 centimetres.

7. Method according to one of the preceding claims, comprising a step of locating the vehicle (9) during the step of acquiring the signal that provides an at least two-dimensional position (Ploc) of the vehicle (9).

8. Data processing unit (15) configured to receive measurement data derived from a measurement signal representative of the change in the curvature of the tyre as it runs over a ground, said measurement data comprising: a) a first parameter (KSin) representative of a rate, preferably angular rate, at which the tyre (1) flattens on contact with the ground (7) over the course of one revolution of the wheel bearing the tyre, and b) a second parameter (KSout) representative of a rate, preferably angular rate, at which the tyre (1) regains its shape on becoming separated from the ground (7) over the course of one revolution of the wheel bearing the tyre, the data processing unit (15) being configured to determine the mechanical property of the ground as a function of the first parameter (KSin) and / or the second parameter (KSout) using a linear relationship connecting said mechanical property of the ground and the first parameter (KSin) and / or the second parameter (KSout) the mechanical property of the ground being included in the group comprising the rut depth (RD), the mechanical resistance of the ground on entering the contact patch (Cpcin), the mechanical resistance of the ground on leaving the contact patch (Cpcout), and the compaction of the ground caused by the tyre (Ctyre),, and the data processing unit (15) is preferably configured to receive that at least two-dimensional position (Ploc) of the vehicle (9) that is associated with the measurement data.

9. Vehicle (9) comprising: - at least one tyre (1), - at least one sensor (10) sensitive to the change in the curvature of the tyre and configured to generate a measurement signal representative of the change in the curvature of the tyre as it runs over a ground, - a data processing unit (15) according to Claim 8, the vehicle being configured to implement the method according to any one of Claims 1 to 6.

10. Vehicle (9) according to the preceding claim, wherein the sensor (10) is disposed inside the tyre (1).

11. Vehicle (9) according to the preceding claim, wherein the sensor (10) comprises an active part (11) and an electronic circuit board (12), the active part (11) being configured to generate the measurement signal, the electronic circuit board (12) being configured to determine the measurement data, and wherein the data processing unit (15) is disposed outside the tyre.