METHOD FOR ALERTING UNDERINFLATION ON A DUAL WHEEL TIRE

Abstract

The invention relates to a method for detecting underinflation of a tire on a dual wheel of a vehicle, comprising the steps: - Moving the dual wheel at a specified speed V on the same surface equipped with sensors capable of detecting contact between the tire and the surface, two adjacent sensors being separated by a distance Di; - Determining, for each sensor, an instant when the contact between the tire and the sensor changes state; - Determining a discrete metric contact line for each tire of the dual wheel; - Determining a parabolic arc that minimizes the deviation from the points on the discrete line for each tire; - Algebraically comparing the second-order coefficients of the parabolic arcs; - If the algebraic comparison exceeds a threshold S, alerting the user that one of the tires of the dual wheel is underinflated. Fig. 5

Description

Title of the invention: A warning system for underinflation on a dual-wheel tire. Field of the invention

[0001] The present invention relates to the field of vehicles transporting substantial loads, which requires the use of twin wheels on certain axles of the vehicle in order to reduce ground pressure. Technological background

[0002] In the field of freight transport in particular, dual-wheel vehicles are frequently used for long-distance journeys between warehouses. The driving force of this industry is speed of delivery, which requires the vehicles to be used continuously. However, underinflation of a tire, caused for example by a puncture, can lead to the vehicle being immobilized for tire repairs. If the puncture is not detected early, the damage to the tire can lead to its disposal or even the destruction of the wheel assembly. In the first case, this constitutes a financial loss for the carrier, along with a controlled immobilization of the vehicle.In the second case, this can lead to an interruption in the truck's operation, at best to change the tire, or even to repair the damage caused by the tire's destruction to the vehicle, not to mention any potential damage to the road. Retreading worn tires is common practice in the road transport industry. A new tire that has been driven underinflated can thus lose its "second life" and the corresponding value.

[0003] The difficulty in inspecting dual-wheel tires lies in the accessibility of the tire's internal components for instrumented checks such as inflation pressure, as well as visual inspections of the entire tire. These checks are generally performed while the vehicle is stationary, as workshop inspections, where accessibility is easier, only take place at the vehicle's service center. Consequently, the most efficient checks are scheduled and are generally too far apart to detect underinflation before it becomes a serious concern for the tire's integrity.

[0004] The introduction of electronic pressure sensors such as TPMS (Tyre Pressure Monitoring System) in tires is a solution for providing early warning of tire underinflation. However, this technological solution is costly since it requires equipping each tire with a pressure sensor. These sensors generally operate on batteries. This necessitates specific maintenance. Therefore, this solution is too costly and intrusive compared to the current practices used in the transportation industry.

[0005] Furthermore, the principle of estimating the contact patch of a tire using proximity or force sensors is known from French patent FR3030742A1. As a tire passes over it, the time signal from such a sensor successively shows an approach phase, a plateau phase corresponding to the rolling of the flattened tread in the contact patch, and a retreat phase. Appropriate signal processing makes it possible to estimate the duration of the plateau phase, given the speed, and its longitudinal extent, i.e., the length of the contact patch. Assuming that the contact width is constant and known, it is possible to estimate the surface area of ​​the contact patch.

[0006] However, dual wheels, by their geometric design, have an axis of rotation positioned at the same distance from the ground. Consequently, the contact patch area is virtually identical between the dual wheels, regardless of the inflation pressure. In other words, the contact patch is not very sensitive to variations in inflation pressure. Therefore, the contact patch between the ground and the tire is not a sensitive indicator of a drop in inflation pressure between the tires of the dual wheel.

[0007] The object of the following invention is to offer a solution for early and reliable detection of underinflation of the dual wheel tires of a vehicle at low operating cost, even for small variations in inflation pressure. Description of the invention

[0008] The invention relates to a method for detecting underinflation of a tire forming part of a twin wheel of a vehicle comprising the following steps: • Moving at an identified speed V the two tires of the twin wheel of the vehicle on the same flat ground equipped with sensors, two neighboring sensors being separated from each other transversely in the direction of movement of the vehicle by a distance Di, so that each tire is located vertically above at least three sensors during the movement, said sensors being capable of detecting the contact between the tire and the ground; • Determine for each sensor at least one instant when the contact between the tire and the sensor changes state. • Determine a discrete metric line of contact between the tire and the ground for each tire of the dual wheel using the identified speed V, the transverse distances Di, and the instants of state change of at least three sensors located vertically above the tire. responding to the entry and / or exit of Making contact; • Determine a parabolic arc that minimizes the deviation from the points on the discrete line for each tire; • Compare algebraically the second-order coefficients of the parabolic arcs, preferably performing an algebraic difference; and • If the algebraic comparison exceeds a threshold S, alert that one of the tires of the dual wheel is underinflated.

[0009] The method is based on obtaining the entry and / or exit front of the contact area. Several sensors are necessarily required per tire. Given that the sensitive parameter according to the invention is the curvature of this entry and / or exit front of the contact area, a minimum of 3 sensors per tire is required to identify the equation of the parabola, which will minimize the difference between the points of this front and the theoretical parabola. By their very nature, tires have entry or exit fronts that resemble parabolas. Naturally, the greater the number of measurement points, the greater the robustness of the result by minimizing measurement noise and errors.

[0010] To obtain this theoretical curvature, it is first necessary to identify the instants of the sensor's state change. The sensor signal resembles a square wave consisting of a rising edge at the entrance of the contact area, a plateau during the crossing of the contact area, and a falling edge at the exit of the contact area.

[0011] The rising and falling edges reflect several phenomena simultaneously. First, the edge illustrates the spatial approach of the tire along its trajectory relative to the sensor. Indeed, regardless of the sensor technology used, the tire gradually approaches the measuring sensor, which rapidly transitions from a non-contact state to a progressively contacting state. The rising or falling edge reflects this evolution of the distance between the sensor and the tire. Second, the edge also reflects the length of the sensor's sensitive area along the direction of the tire's trajectory. The sensor's sensitive area has a certain length, and contact is progressive along this length. Part of the sensitive area is in contact while the other part is still effectively out of contact, and the resulting sensor signal reflects these two phenomena by averaging them.Therefore, it is impossible to identify the exact moment of contact from the sensor signal, since the contact is primarily spatial. The method thus proposes a morphological approach to signal processing on the sensor signal in order to, firstly, identify the plateau corresponding to complete contact across the entire active area of ​​the sensor, and secondly, identify the rising and falling edges corresponding to partial contact across the entire active area of ​​the sensor and to a distance between the sensor and the tire that varies significantly depending on the sensor's sensitivity.

[0012] Therefore, a single method must be defined for determining the beginning or end of the contact area, which is called the sensor's state change. A threshold approach relative to a maximum, similar to the sensor's response at the plateau, is one technical solution. More complex techniques can also be used. As long as the same technique is used on all sensors for the entry and / or exit of the contact area, the underinflation detection method is robust because the shape of the state change line remains identical. This is a strength of the method since the length of the contact area, and consequently its surface area, varies depending on the detection method used.

[0013] Next, the time signals must be converted into metric signals. For this, determining the speed V and the transverse distances Di between the sensors on the ground is essential. This yields a set of measurement points in a two-dimensional metric coordinate system. This allows for a method independent of the speed of the tires passing over the sensor-equipped ground and for determining a threshold S that is independent of the speed V, thus making the method reliable.

[0014] The speed V corresponds to an instantaneous average speed at the moment the tire passes over the sensors. Since the time spent passing the sensors is short, the speed changes only slightly during this period. This speed can be obtained by a specific measurement system located upstream or downstream of the ground sensors, depending on the vehicle's trajectory. This signal determination can also be performed on the sensor signal itself, taking into account the sensor's sampling frequency and the shape of the output signal.

[0015] Once the discrete metric definition of the contact between the ground and the tire has been established, the equation of the parabola which minimizes the deviation, generally the squared deviation, between the discrete measurement points and the equation of the parabola can be identified.

[0016] For each tire of the dual wheel, the equation of the parabola is obtained. This equation describes the convexity or concavity of the contact line when viewed from the point of contact, respectively from the point of view outside the contact area, such as, for example, the geometric center of the contact area, or, respectively, any point on the tire's trajectory outside the contact area. The second-order coefficient of the parabola's equation describes the degree of convexity or concavity of the parabola. If the second-order coefficient is positive, the parabola, viewed, for example, from the contact area, is convex. If the second-order coefficient is negative, the parabola, viewed, for example, from the contact area, is concave.

[0017] The algebraic comparison of the second-order coefficients is then performed, whether it be the ratio of the coefficients or their difference. In the case of a twin wheel having Therefore, with the same distance between the wheel center and the ground for both tires, both tire assemblies being inflated to the same inflation pressure, and the tires and wheels being identical, the two coefficients are identical, and the comparison tends towards a target value: 0 for the difference and 1 for the ratio. As soon as one tire is underinflated relative to the other, the two coefficients differ. Under normal pressure and load conditions, the parabolas are generally convex from the point of view of the contact patch. The greater the difference in pressure between one of the tire assemblies, the further the second-order coefficients diverge from each other, to the point where the underinflated tire has a concave parabola viewed from inside the contact patch, and a convex one viewed from outside the contact patch. Thus, the comparison of the coefficients deviates from the target value.Since initially we do not know which tire is underinflated compared to the other, the difference in coefficients is insensitive to the order of the coefficients, unlike the ratio which will tend from the target value 1 towards the value 0 or infinity depending on whether the coefficient of the underinflated tire is in the numerator or denominator.

[0018] When the distance from this target value is greater than a threshold S, an underinflation of one of the sets of twin wheels is confirmed and an alert is sent to the operator operating the ground measuring device.

[0019] The method is more precise than that used with the contact surface, which is sensitive for dual wheels only when there are significant inflation differences between the two mounted sets, approximately half the inflation pressure, or about 4 bar for tires typically inflated to 7 or 9 bar. Here, a pressure difference of 2 bar, or about 20 percent, will be identified by the method, allowing for earlier detection of underinflation and intervention before a significant structural defect occurs in the tire itself.

[0020] Advantageously, the process comprises the following additional steps: • Identify the discrete line with the smallest coefficient of order two; • Identify the tire that generated the discrete line of smallest co efficient of order two, the identified tire is in a condition of underinflation.

[0021] While the detection of underinflation is a minimum for vehicle safety, the detection of the underinflated individual makes it possible to accelerate the repair or restoration of the vehicle, which constitutes a saving of time and therefore a monetary saving for the goods and people transport industry which generally employs dual wheels.

[0022] Having previously identified the two second-order coefficients of the parabolas, it You just need to evaluate the coefficients between them to identify the underinflated tire compared to the other.

[0023] Preferably, each tire has a trajectory supported by at least five sensors during its movement on the ground.

[0024] A minimum of three sensors is required to determine the equation of the parabola. However, increasing the number of measurement points improves the accuracy of the method by minimizing measurement errors. Furthermore, an odd number of measurement points is preferable for a theoretical parabola, whether convex or concave.

[0025] Specifically, the comparison of the second order coefficients being carried out by an algebraic difference, the threshold S corresponds to a curvature of value 5 m1.

[0026] The inventor has observed that for heavy goods vehicle tires, having generally rectangular contact areas with rather straight contact lines at the entry or exit of the contact area, a threshold value S of 5 allows us to state that one of the mounted sets of the vehicle is in a condition of underinflation relative to the other when the tires comply with the ETRTO standards (acronym in English for European Tyres and Rim Technical Organization).

[0027] According to a first embodiment, the contact between the sensor and the ground being previously identified on the sensor signal by a constant amplitude A of the signal, the change of state of the sensor signal corresponds to the crossing of a threshold T by the signal, the threshold T corresponding to a percentage of the amplitude A of the signal.

[0028] While detecting the plateau on the measurement signal corresponding to complete contact between the sensor's active area and the tire is straightforward using a morphological, threshold, or optimum detection approach, a preliminary definition of the contact line between the tire and the ground is provided by exceeding a threshold T, which is a function of the amplitude level A of the signal corresponding to the plateau. This threshold T is a percentage of the plateau's amplitude A. The percentage depends on the sensor technology used to account for sensor non-linearity and measurement noise associated with the technology. Thus, the contact line, at the entry or exit of the contact area, corresponds to all measurement points that have crossed the threshold T, either rising or falling.

[0029] According to a second embodiment, the contact being previously identified on the sensor signal by a constant amplitude A of the signal, the instants of change of state of the sensor correspond to the intersection between the tangent of the sensor signal at the point of abscissa corresponding to the ordinate at mid-amplitude A / 2 and a straight line whose ordinate is equal to the value A.

[0030] If the detection of the plateau on the measurement signal that corresponds to complete contact between the active area of ​​the sensor and the pneumatics is easy by a mor approach phological or threshold or optimum detection, a second definition of the contact zone is given by the set of points between two particular points.

[0031] These specific points, which are not necessarily measurement points, are defined by the intersection of two lines. The first line corresponds to the line defining the plateau of amplitude A previously identified. The second line corresponds to the tangent of the sensor signal at the point whose abscissa is half the amplitude A of the plateau.

[0032] Regardless of the method used to identify the contact area on the measurement signals, as long as this area is the same across the various measurement sensors, the method remains robust. Indeed, the parabolic shape of the contact line is similar regardless of the definition of the identified state change points. Consequently, the comparison yields an equivalent result, possibly adjusting the threshold S to suit the method used.

[0033] According to a specific embodiment, the identification of the speed of passage of the tire over the sensor is obtained by the estimated duration of the rising edge and / or the falling edge of the sensor signal at the passage of the tire knowing that the distance of these edges is constant depending on the geometric characteristics of the tire, preferably its diameter.

[0034] It is entirely possible to use the sensor signal to evaluate the speed of the mounted assembly as it passes over the measuring sensor. Indeed, the inventor observed that the shape of the sensor signal, regardless of the technology used, is always trapezoidal, and that the inclined edges of the trapezoid have a constant spatial length depending on the tire's specifications, irrespective of the inflation pressure and the static load applied to the mounted assembly. This length can be adjusted according to the method used to define the contact line and then serve as a reference distance. Knowing the sensor's sampling frequency and the number of measurement points on the inclined edge of the trapezoid, it is possible to define an instantaneous speed of the tire passing over the measuring sensor. In fact, two measurements can be taken during the same passage, at the entry and exit of the contact area.By taking either of the values ​​or the median value, it is quite possible to identify a realistic passage speed that is a function only of the discretization of the measurement signal.

[0035] Preferably, having previously identified the two instants when the contact between the tire and the sensor changes state during the passage of the tire over the sensors, the signals from the sensors are recalibrated with each other by making the instants corresponding to the middle of the interval defining the contact state of each sensor coincide.

[0036] If the sensor signals are not phased with each other in time, it is It is important to temporarily realign the signals from each ground sensor to identify the equation of each parabola associated with each mounted assembly. The method relies on a characteristic of assemblies mounted under free-rolling conditions. Indeed, the geometric centroid of the contact patch is equidistant from the contact lines at the entrance and exit of the contact patch. Since each sensor identifies a so-called contact state between the tire and the sensor on the signal, the midpoint of this time interval corresponds to this geometric centroid of the contact patch. Thus, a potentially imaginary time point can be defined for each measurement signal that corresponds to this midpoint. It is then simply a matter of aligning these potentially imaginary points between the various measurement signals to phase all the sensors together. Brief description of the drawings

[0037] 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: • Fig. 1 illustrates an example of the application of the method according to the invention for a vehicle with twin wheels; • Figures [Fig. 2a] and 2b show two views of an evaluation system according to the invention; • Fig. 3 presents a signal measured at the output of a sensor of the system and a processing of the determination of the instants of change of state of the sensor according to the invention; • Fig. 4 presents the same signal measured at the output of a sensor of the system and another processing of determining the instants of change of state of the sensor according to the invention; • Fig. 5 presents a representation of the contact areas of the axles of a vehicle on a measuring system, one of the tires of a twin wheel being underinflated; • The [Fig.6] is a time representation of the second order coefficients of the parabolas of the tires of a twin wheel, one of the tires being deflated from a given instant. Detailed description of the implementation methods

[0038] Fig. 1 shows a convoy consisting of a tractor 12 and a semi-trailer 13 passing over a measuring system 200 as described in Figs. 2a and 2b.

[0039] In this example, the tractor 12 consists of a front axle 401 and a rear axle 501, and the semi-trailer 13 consists of a group of three axles 601. In addition, the rear axle 501 of the tractor 12 is equipped with two "twin" tires at each of its ends.

[0040] Only the dual wheel 510 located on the right side of the axle 501 of the tractor 12 is underinflated. Since these are dual tires, the increase in length or contact area resulting from underinflating one of the tires will be distributed between the two tires on the side affected by the underinflated condition. Thus, even if only one tire of the dual wheel 510 is underinflated, the length and contact area of ​​both tires will increase. Consequently, it is impossible to determine which tire of the dual wheel 510 is underinflated.

[0041] The sensitivity to possible underpressure of a tire is therefore much lower than in the case where the axle is fitted with a single tire.

[0042] The measuring system 200, given here as an example, shown in Figures 2a and 2b, consists of: • A housing 10 consisting of two access ramps 15 and a measurement zone located between the two access ramps 15. • Two tire presence detection devices, each consisting of three piezoelectric sensors 110, positioned along a line transverse to the direction of travel of a vehicle approaching the housing. In this example, the piezoelectric sensors are buzzers glued to the structure of the housing 10. • A line of 100 measuring sensors positioned along a line transverse to the direction of travel of the vehicle, approaching the housing 10. These measuring sensors can be either variable reluctance sensors or eddy current sensors. Alternatively, this line of electromagnetic sensors can also be replaced by an optical measuring system applying the principle of laser triangulation. • A processing electronics unit 140 to which the measuring sensors 100 and the tire presence detection sensors 110 are connected. In this example, the processing electronics unit 140 also contains an RFID reader allowing the reading of RFID chips integrated into or glued onto tires whose underinflation is being evaluated.

[0043] When a tire 20 passes over the housing 10 of the measuring system, the presence of the tire is first detected by a first row of tire presence detection sensors, then, when the tire leaves the housing 10 of the measuring system, its presence is detected by a second row of tire presence detection sensors. Since the distance between the two tire presence detection devices is known, it is then possible to calculate the tire speed can be calculated using a very simple formula: Average speed = d / tO.

[0044] In this formula, the distance d is the distance separating the two transverse lines of tire presence detection sensors 110, and the time t0 is the time elapsed between the detection of the presence of the tire by any one of the sensors belonging to the first line of tire presence detection sensors 110 and the detection of the presence of the tire by any one of the sensors belonging to the second line of tire presence detection sensors 110. The speed of the tire being known, it is then very easy to estimate a local length of the contact area of ​​the tire, vertically from the sensor considered by taking into account the sampling frequency of the sensor as we will see in [Fig.3].

[0045] The [Fig.3] is the time representation of the output signal of a sensor of a measuring system over which a tire has passed as well as a first method of detecting the instants of change of state of the sensor.

[0046] Curve 1001 is the mathematical representation of the various measurement points recorded by the sensor. This curve 1001 takes the form of a trapezoid as it passes through the tire. From a low level, indicating the absence of contact between the sensor and the tire, a first rising edge is observed, reaching a plateau that lasts for a few moments before a falling edge returns to the initial level.

[0047] Here, the upper plate is almost constant and tangent to a straight line 1002 whose ordinate is equal to the value A. This value A is constant since when the sensor is under the tire, the detected value is constant during the passage of the tire over the sensor.

[0048] The rising and falling fronts reflect, on the one hand, the progressive approach of the rotating tire towards the sensor and, on the other hand, the progressive overlap of the tire on the active part of the sensor. Since these phenomena occur both during the contact movement on the sensor and during the movement of the tire away from the sensor, it is normal that the rising and falling fronts are symmetrical.

[0049] According to a first embodiment, the detection of the sensor's state change is achieved using a threshold value T that is proportional to the value A of the plateau. In this case, the mid-amplitude of A corresponds to the value of T. Therefore, a straight line 1003 corresponding to this value can be defined, which intersects the curve 1001 at the rising edge by a point 1011 and at the falling edge by a second point 1012.

[0050] The interval between the sensor measurement points and these two reference points defines the contact zone of the tire with the sensor. Points outside this zone are considered out of contact. Thus, points 1011 and 1012 define the Instants of sensor state change. The duration of the zone between 1011 and 1012 represents the time length of the contact between the two structures, which will allow the metric distance of this contact to be determined by multiplying this duration by the instantaneous speed of the tire passing over the sensor.

[0051] Finally, the symmetry of this signal 1001 makes it possible to determine an axis of symmetry passing through the point 1015 which therefore corresponds to a given instant which is defined by the abscissa of this point 1015. By construction, this abscissa of the point 1015 corresponds to the median plane of contact of the tire which is common to the entire transverse width of the tire, which makes it possible to phase the signals 1001 of the various sensors measuring the passage of the tire over the measuring system.

[0052] Fig. 4 is the same time representation of the output signal of a sensor of a measuring system over which a tire has passed as well as a second method of detecting the instants of change of state of the sensor.

[0053] Curve 1001 is the mathematical representation of the various measurement points recorded by the sensor. This curve 1001 takes the form of a trapezoid as it passes through the tire. From a low level, indicating the absence of contact between the sensor and the tire, a first rising edge is observed, reaching a plateau that lasts for a few moments before a falling edge returns to the initial level.

[0054] Here, the upper plate is almost constant and tangent to a straight line 1002 whose ordinate is equal to the value A. This value A is constant because when the sensor is located under the tire, the detected value remains constant during its passage through the tire over the sensor. Of course, depending on the sensor technology and the tire dimensions, the value may vary.

[0055] The rising and falling fronts reflect, on the one hand, the progressive approach of the rotating tire towards the sensor and, on the other hand, the progressive overlap of the tire on the active part of the sensor. Since these phenomena occur both during the contact movement on the sensor and during the movement of the tire away from the sensor, it is normal that the rising and falling fronts are symmetrical.

[0056] According to a second embodiment, the detection of the sensor's state change is achieved using a property of curve 1001. Generally, at mid-amplitude A / 2 of the plateau, the rising and falling edges exhibit inflection points. It is then possible to draw a tangent 1005 across the rising edge of signal 1001, passing through the inflection point of the rising edge. Similarly, a tangent 1006 can be drawn across the falling edge. Here, the inflection points were determined by the intersection of line 1003 with signal 1001. The equation of line 1003 is that its abscissa is equal to half the amplitude A of the plateau of signal 1001.

[0057] The intersection of the tangent 1005, respectively 1006, with the curve 1002 re presenting the signal plateau, defines a unique point which is called the sensor state change point whose time abscissa is referenced 1011, respectively 1012.

[0058] The interval between the sensor's measurement points and these two reference points defines the contact zone of the tire with the sensor. Points outside this zone are considered out of contact. Thus, points 1011 and 1012 define the instants of the sensor's state change. The duration of the zone between 1011 and 1012 represents the contact time between the two structures, which allows the metric distance of this contact to be determined by multiplying this duration by the instantaneous speed of the tire passing over the sensor.

[0059] It should be noted here that the contact times are not identical depending on the method used. However, this does not affect the metric parabola, which will be based on the moment of state change 1011 of the sensor, or respectively, moment 1012.

[0060] Finally, the symmetry of this signal 1001 makes it possible to determine an axis of symmetry passing through the point 1015 which therefore corresponds to a given instant which is defined by the abscissa of this point 1015. By construction, this abscissa of the point 1015 corresponds to the median plane of contact of the tire which is common to the entire transverse width of the tire, which makes it possible to phase the signals 1001 of the various sensors measuring the passage of the tire over the measuring system.

[0061] Fig. 5 is a representation of the contact areas of the tires of a vehicle along their entire width for various axles of a vehicle.

[0062] Here, at the top of [Fig. 5] is the right side of the vehicle when one is the driver of the vehicle. Knowing that the convoy moves in a straight line according to the solid arrow shown in the middle of [Fig. 5].

[0063] The footprints on the left of the figure represent the front of the convoy. The footprints on the right of the figure correspond to the rear of the convoy. The first axle of the vehicle consists of a single wheel, for which the method does not apply. However, implementing the method on this steering axle demonstrates a symmetrical behavior between the right and left sides of the vehicle, which is expected by the method due to the vehicle's trajectory, as indicated by the solid arrow.

[0064] The second and third axles of the vehicle consist of twin wheels of different sizes. The second axle, which traditionally represents the drive axle, carries only the weight of the engine, which rests vertically on this axle. The third axle, which corresponds to the vehicle's loading area, is equipped with twin wheels of larger dimensions to support a much greater load than the first two axles. Here, intentionally, a tire on one of the twin wheels of this third axle has been deflated. This is the twin wheel on the right side of the vehicle and the tire located in external to the vehicle. Generally, inspecting this casing is difficult due to its placement on the vehicle.

[0065] The vehicle traveled at a speed of 30 km / h on the straight-line measurement system. The measurement signals were recorded by each sensor. Here, for the third axle, we can see that each tire passed over approximately 7 sensors as it went over the system.

[0066] After signal processing as illustrated in [Fig. 3] or [Fig. 4], the contact time between the tire and the sensor, measured by the vehicle's speed, was converted into a metric length. Furthermore, since the system, including the sensors, is placed on the ground, the transverse distances Di between two adjacent sensors are known, whether the sensors are aligned transversely to the direction of vehicle travel or staggered. All of this information allows for the construction of a metric contact length for each sensor and the spatial and temporal phasing of the sensors relative to each other using imaginary time points representing the center of contact along the tire's direction of travel.

[0067] The set of contact lines from each sensor and the spacing of these lines using the distances Di allow us to obtain a representation of the contact area of ​​each tire. Each measurement line of the contact area begins and ends using the previously identified instants of the sensor's state change.

[0068] It is then possible to determine for the input line, respectively the output line, of the contact area of ​​each tire, a parabola which minimizes the gap with the points of change of state at the input of Making contact, respectively the points of change of state at the output of Making contact.

[0069] Here, in the figure, a parabola has been identified for the inlet and outlet lines. Then, the second-order coefficient of the parabola, which is similar to the curvature of the parabola, was extracted from the equation of the parabola. And the average "a" of these coefficients, which are shown for each tire in [Fig. 5], was taken.

[0070] It is noted that the average "a" between the right and left tires of the vehicle are almost identical for the first two axles, which is expected.

[0071] However, for the third axle, on the right side, there is a significant difference in curvature between the two tires of the twin wheel, unlike what occurs on the left side. This is normal since the inner tire of the right twin wheel of the third axle is intentionally underinflated. Here, there is a difference of 7 units on the right side compared to a difference of only one unit on the left.

[0072] Figure 6 is a time-domain representation of the second-order coefficients of the parabolas of the tires of a dual wheel, one of the tires being in to deflate from a moment on.

[0073] Fig. 6 is a graph whose abscissa is time with periodic measurements of the second-order coefficient of the parabola best describing the contact line of the tire with the ground at the entrance of the contact area according to the direction of passage of the vehicle over the measuring system.

[0074] Series 2002 corresponds to measurements of the outer tire's contact patch on the vehicle sidewall of the dual wheel, and series 2003 corresponds to measurements of the inner tire's contact patch on the same dual wheel. Initially, although a difference remains between the two values ​​of the second-order coefficient of the parabola, this difference is stable over time and small. Thus, a master curve 2001 can be defined, representing the theoretical average evolution of the coefficient. From a certain point, the inner tire began to gradually deflate. Looking at series 2003, we observe that the coefficient has begun to drift relative to master curve 2001. The same level of drift is observable in series 2002, which corresponds to measurements of the outer tire's contact patch on the vehicle sidewall of the dual wheel.Thus, the difference between the two Aa values, represented by the double vertical arrow, increased until it exceeded a threshold S, indicating that one of the two tires of the twin wheel is underinflated. To identify the faulty wheel, it is necessary to identify the one whose coefficient decreases instead of increases.

[0075] The proposed method thus makes it possible to detect early and robust underinflation of a tire on a dual wheel. Furthermore, the method makes it possible to identify which of the two tires is underinflated relative to the other.

Claims

Demands

1. A method for detecting underinflation of a tire forming part of a dual wheel of a vehicle comprising the following steps: - Moving the two tires of the dual wheel of the vehicle at an identified speed V on the same flat ground equipped with sensors, two neighboring sensors being separated from each other transversely in the direction of movement of the vehicle by a distance Di, so that each tire is located vertically above at least three sensors during the movement, said sensors being capable of detecting the contact between the tire and the ground; - Determining for each sensor at least one instant when the contact between the tire and the sensor changes state.- Determine a discrete metric contact line of the tire with the ground for each tire of the dual wheel via the identified speed V, the transverse distances Di and the instants of change of state of the at least three sensors located vertically of the tire corresponding to the entry or exit of the contact area; - Determine a parabolic arc that minimizes the deviation with the points of the discrete line for each tire; - Compare algebraically the second-order coefficients of the parabolic arcs, preferably performing an algebraic difference; and - If the algebraic comparison exceeds a threshold S, alert that one of the tires of the dual wheel is underinflated.

2. A method for detecting underinflation of a tire forming part of a dual wheel of a vehicle according to claim 1, wherein the method comprises the additional steps: - Identify the discrete line exhibiting the smallest coefficient of order two; - Identify the tire that generated the discrete line with the smallest coefficient of order two, the identified tire is underinflated.

3. Method for detecting underinflation of a tire forming part of a twin wheel of a vehicle according to any one of claims 1 to 2 wherein each tire has a trajectory supported by at least five sensors simultaneously during its movement on the ground.

4. Method for detecting underinflation of a tire forming part of a twin wheel of a vehicle according to any one of claims 1 to 3 wherein the comparison of the second order coefficients is carried out by an algebraic difference, the threshold S corresponds to a curvature of value 5 m1.

5. Method for detecting underinflation of a tire forming part of a twin wheel of a vehicle according to any one of claims 1 to 4 wherein, the contact between the sensor and the ground being previously identified on the sensor signal by a constant amplitude A of the signal, the change of state of the sensor signal corresponds to the crossing of a threshold T by the signal, the threshold T corresponding to a percentage of the amplitude A of the signal.

6. Method for detecting underinflation of a tire forming part of a twin wheel of a vehicle according to any one of claims 1 to 4 wherein, the contact being previously identified on the sensor signal by a constant amplitude A of the signal, the instants of change of state of the sensor correspond to the intersection between the tangent of the sensor signal at the point with abscissa corresponding to the ordinate at half amplitude A / 2 and a straight line whose ordinate is equal to the value A.

7. Method for detecting underinflation of a tire forming part of a dual wheel of a vehicle according to any one of claims 1 to 6 wherein the identification of the speed of passage of the tire over the sensor is obtained by the estimated duration of the rising and / or falling edge of the sensor signal at the passage of the tire knowing that the distance of these edges is constant depending on the geometric characteristics of the tire, preferably its diameter.

8. A method for detecting underinflation of a tire forming part of a dual wheel of a vehicle according to any one of claims 1 to 7, wherein, having previously identified the two instants at which the contact between the tire and the sensor changes state during the passage of the pneumatic on the sensor, the sensor signals are time-adjusted between them by making the instants corresponding to the middle of the interval defining the contact state of each sensor coincide.

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