FR2584348A1 - Method for monitoring and signalling the squashed state of the tyres of a moving vehicle and device for implementing it - Google Patents

Abstract

This method consists in comparing, at each wheel revolution, the light energy of a reference beam following a predetermined path inside the wheel with the energy of a second light beam following, inside the tyre of the same wheel, a path capable of giving rise to losses or variations in energy couplings, when the tyre undergoes deformations in the zone of contact with the ground, due to an underinflation and/or overload. The paths of the reference beam and of the second light beam are produced by means of optical fibres respectively 2, 5, 11; 2, 3, 4, 8, 9, 10 and means 12, 13, 16 are provided for transforming the light energy received through the optical fibres into electrical signals and for making use of the latter.

Description

"State monitoring and reporting process
flat tires of a moving vehicle
and device for its implementation. "
The subject of the present invention is a method and a device intended to monitor the state of crushing of the tires of a moving vehicle and in particular to trigger an alarm of any type when the state of crushing of these tires becomes critical due to underinflation or overloading of these or a combination of these two factors.

 In fact, insufficient inflation or an excessive load on the tires results in rolling overheating thereof, which can become very significant if the speed and / or the ambient temperature are high and can lead to the bursting of these tires, in addition to the increased wear and fuel consumption linked to the excessive crushing of these tires.

 In addition, it turns out that 9 to 11% of motorway accidents are due to tires, and that two vehicles out of three run on under-inflated tires.

 Devices have already been designed to signal the condition of the tires of a motor vehicle.

 For example, patent FR 2,543,069 shows a device for detecting the pressure inside a tire in which the pressure inside the tire is measured by a sensor and transformed into a light signal which is permanently transmitted to the "fixed" part of the vehicle via two optical cables arranged coaxially in the axis of the hub.

 In another patent FR 2 455 220, a piezoelectric element mounted against the wall of the tire produces electrical signals when pressure is exerted on this tire due to the deformation of the tire, these signals being transmitted to the "fixed" part of the tire. vehicle in the form of radio signals.

 Finally, FR 2 312 772 shows a detection device producing a periodic signal indicating a normal state or a second signal indicating an abnormal state, and essentially aimed at measuring the pressure inside the tire.

 In all these devices, the detection of the condition of the tire is based on a measurement of pressure or of pressure variation inside the tire. However, this varies with the temperature and the speed of rotation of the wheel and such devices based solely on the measurement of an essentially variable quantity are unreliable.

 The object of the present invention is therefore to provide a method and a device which is reliable, relatively simple to set up, inexpensive and which makes it possible to effectively monitor and report the state of flattening of the tires of a vehicle.

 This object is achieved in that the method according to the invention consists in comparing, at each revolution of the wheel, the light energy of a reference beam performing a determined path inside the wheel with the energy of a second light beam carrying out inside this same wheel and its tire a counter path during which the light energy can be modified, when the tire undergoes deformations due to underinflation or overload.

 Indeed, during the path of the second light beam, there are losses or, on the contrary, a gain in light energy so that the comparison of the energies of the two light beams makes it possible to highlight a deformation of the tire.

 Furthermore, the comparison of the two light beams coming from the same source and, consequently, the fact that a differential and not absolute energy is measured makes it possible to eliminate the effects of variable influence factors such as temperature, time, and therefore eliminating the risk of errors linked to a sudden change in these factors.

 Advantageously, in the device for implementing this method, the path of each light beam and the measurement of the deformation of the tire are carried out by means of optical fibers.

 According to a preferred embodiment, this device comprises at least two mobile optical fibers arranged inside the wheel, each optical fiber being capable of ensuring the transmission of the reference beam and the second light beam respectively, a fixed optical fiber integral of the chassis of the vehicle, this fixed optical fiber being excited by a light source also disposed on the chassis and being able to come into coincidence with a first end of the two mobile optical fibers at each turn performed by the wheel, as well as two fixed optical fibers disposed inside the chassis and able to also come into simultaneous coincidence with the second end of the optical fibers respectively at each rotation of the wheel, means being further provided for transforming the light energy received into electrical signals and for exploiting those -this.

 Different organizations of the optical fibers are provided to allow the weakening of the energy of the second light beam in its path in the tire and the electrical signal processing circuit includes timing means making it possible to eliminate accidental variations due for example to poor soil condition.

In any case, the invention will be better understood and other characteristics will be highlighted with the aid of the description which follows with reference to the appended schematic drawing representing several embodiments:
Figure 1 is a schematic view of the device according to a first embodiment;
Figure 2 is a view similar to Figure 1 of a second embodiment;
Figures 3 to 6 are schematic views illustrating different possibilities of arrangement of the optical fibers.

 Figure 1 shows a first embodiment of the device according to the invention installed in one of the vehicle wheels.

 On the chassis is arranged a fixed light source (1) which excites an optical fiber (2) also fixed and disposed inside the chassis of the vehicle.

 This optical fiber (2) is mounted coaxially at a first end (3a) of a mobile optical fiber (3) secured to the hub of the wheel. This optical fiber (3) is capable of coming into coincidence with the optical fiber (2) at each revolution of the wheel on which it is mounted.

 The optical fiber (3) is split inside the hub into two optical fibers (3c, 5). The optical fiber (3c) lights up the measurement circuit, while the optical fiber (5) lights up the reference circuit.

 The end (3c) of the optical fiber (3) secured to the hub is in permanent coincidence with the end (4a) of the fiber (4) secured to the wheel. Similarly, the optical fiber (8) secured to the wheel at its end (8a) in permanent coincidence with the end (9b) of the optical fiber (9) secured to the hub. The end portions of the fibers (4) and (8) placed inside the tire are arranged side by side, parallel to each other so that their common end is at a certain distance from the internal wall of the tire (6) provided with a reflecting surface (7). The light energy conducted by the fibers (2), (3), (3c) and (4) at the instant of coincidence (2), (3) is partly returned by the reflecting surface (7) in the fiber optic (8).

 The amount of light energy collected by the fiber (8) varies with the distance between the ends (4b) and (8b) of the reflecting surface (7).

 As shown in FIG. 1, when the tire (6) crashes due to under-inflation and / or an overload thereof, the reflective surface (7) which covers the internal wall is displaced, for example, in position (7a) shown in dotted lines in the figure, so that the energy coupling increases.

 This results in a greater amount of light energy transmitted by the optical fibers (8) and (9).

 Two fixed optical fibers (10) and (11) are integral with the chassis and collect at the instant of the spatial coincidence of their ends (lob) and (I lb) respectively with the ends (5a) and (9a) of the optical fibers (5,9) the light energies of the reference circuit and of the measurement circuit at each wheel revolution.

 Each of these optical fibers (10, 11) is connected by its other end respectively (iota, lia) to a transducer respectively (12, 13) capable of transforming the light energy received into electrical energy.

 The electrical signals emitted by the two transducers (12,13) are compared in a threshold differential amplifier (14) whose output signal controls a monostable (15) which delivers a pulse only if the difference between the input signals of the amplifier (14) is greater than a determined threshold.

 The signals transmitted respectively by the transducer (13) and by the monostable (15) are then processed by a logic circuit of conventional type (16) disposed inside the chassis of the vehicle. This logic circuit includes two inverters (17,18), two AND gates (19,20) and two QU gates (21,22).

 The inputs of the AND gate (19) are respectively connected to the output of the transducer (13), after its signal has been inverted by the inverter (17), and to the output of the monostable (15). The inputs of the AND gate (20) are respectively connected to the output of the monostable (15), after inversion of its signal, and to the output of the transducer (13).

 The outputs of the two AND gates (19, 20) are connected to the input of the OR gate (21). In this way the output of the OR gate (21) is only true when the values of the output signals from the transducers (13) and (12) are similar, that is to say when the wall (7) s 'is brought closer to the ends (4b, 8b) of the optical fibers (4,8), due to the deformation of the tire (6).

 The output of the OR gate (21) is also connected to an input of another OR gate (22), the other inputs (22a) of which can be formed by signals from the other wheels monitored by the device.

 In this way, a signal is obtained at the exit from the last OR gate (22) indicating a malfunction of any of the tires monitored by the vehicle.

 The output signal from this OR gate is adapted by the amplifier (23) and is then sent to an alarm device such as a lamp (24), a siren or the like.

 A semi-integrator circuit with resistance (25) and capacitance (26) makes it possible to introduce a time constant into the circuit and therefore to achieve a certain time delay, intended to avoid false alarms which may result from significant irregularities in the ground. Thanks to this time delay device, the alert will only be effective after a certain number of successive repetitions of the anomaly.

 A judicious choice of the values of the resistance (25) and the capacity (26) will make it possible to adapt the time constant and to obtain the desired time delay.

 Of course, the time delay could be obtained using any other known time delay device, or could be replaced by a counting system.

 Switches (27, 28) allow the circuit to be tested at each wheel and during the movement of the vehicle.

 FIGS. 3 to 6 illustrate different possibilities of configuration of the measurement optical fibers similar to the optical fibers (4, 8) whose couplings or losses of light energy from the source (1) are liable to be modified, due to 'a deformation. In each of these Figures 3 to 6 are shown the light source (1) placed at the entrance to the light path and the transducer (16) placed at the exit thereof.

 In the example shown in FIG. 3, two optical fibers (33, 34) are twisted together, these fibers being integral with the sidewall of the tire.

 The light source (1) sends light rays to the optical fiber (33) which by its coupling with the optical fiber (34) transmits to the latter a part of its light energy.

 In the event of a tire being crushed, the light energy obtained in return at the outlet of the fiber (34) will be modified, due to the modification of the coupling between these two fibers, which makes it possible to detect such a crushing.

 In the case of FIG. 4, three sections of optical fibers (40, 41, 42) are placed end to end along the internal wall of the tire.

 In the event of a tire being crushed, the alignment of these optical fibers (40, 41, 42) will be modified and consequently the light energy transmitted between each optical fiber will be reduced. The loss of light energy between the entry of the first section (40) and the exit of the last section (42) will make it possible to determine the state of crushing of the tire.

The number of sections is obviously not limited to three.

 In the case of FIG. 5, a single optical fiber (46) is placed against the internal wall of the tire. The light source (1) is placed at the inlet of this fiber (46) while at its outlet is arranged the transducer (12).

As shown in FIG. 5, the light rays (45) coming from the source (1) are reflected inside the optical fiber (46) as long as their angle of incidence, 2, 3, S4 relative to normal to the
I 2 4 wall of this one is greater than a certain angle limit (, defined by the relation: n2
If not, =
n1 n2 and n1 being the respective refractive indices of the materials constituting the sheath (47) and the core (48) of the optical fiber (46). When the curvature of the optical fiber (46) increases, the angles of incidence of the light rays (10) decrease, when these angles become smaller than the angle, the light ray is no longer reflected inside the fiber optical (46) but refracted and exits therefrom, which is the case for the light ray (49) having the angle of incidence 495. Thus, bending of the optical fiber (46), due to a deformation of the tire, beyond a certain limit value, will cause a loss of light energy inside the optical fiber (46) making it possible to detect the deformation of the tire.

 Figure 6 shows another configuration using the bending effect of optical fibers.

 In this example, an optical fiber (50) is arranged between two plates (51, 52) having on their opposite faces corrugated profiles (51a, 52a) complementary.

 The penetration depth of the corrugations (51a, 52a) and their periodicity depend on the size of the optical fiber (50). One of the plates (51, 52) is fixed to the interior wall of the tire.

Since the two plates cannot slide relative to each other, any variation in the curvature of the assembly results in the plates being brought together in the central part.

 These corrugated plates (51, 52) make it possible to amplify the bending effect of the optical fiber (50) compared to the embodiment shown in FIG. 5 and consequently to increase the light losses of these optical fibers if the tire is crushed. This facilitates the detection of such a phenomenon.

 The different arrangements of the optical fibers shown in these FIGS. 3 to 6 could obviously replace the arrangement of the fibers (4,8) and the reflecting surface (7) shown in FIG. 1.

 Figure 2 shows a second embodiment of the device according to the invention, similar to that of Figure 1, and in which the fiber optic sensor and the signal processing circuit have been modified.

For simplicity, the elements of this figure 2 identical to those of figure 1 will therefore be designated by the same references as in this one.

 As in the example in FIG. 1, a light source (1) excites an optical fiber (2) arranged coaxially with an optical fiber (3) which splits into two optical fibers (3c, 5), the fiber ( 3c) being extended by the fiber (29). In this case, the fiber (29) only has, by way of example, three undulations (29a) of a sensor organized according to the data of the sensor in FIG. 6.

As in the previous example, the outputs of each optical fiber (5,9) coincide at each turn of the wheel with two fixed optical fibers (11,10) each connected to a transducer respectively
As we have seen previously, the crushing of the tire carrying the sensor shown diagrammatically in (29a) will lead to an increase in the losses of the light energy introduced into the fiber (3c), therefore a decrease in the electrical signal delivered by the transducer (12).

 The circuit for processing the electrical signals comprises, like the diagram in FIG. 1, a threshold differential amplifier (14) and a monostable (15) whose output signal is processed with that of the transducer (13), by the circuit logic (30).

 The logic circuit (30) includes, as does the circuit (1) two AND gates (19,20), two OR gates (21,22), and two inverter circuits (17,18), the inverter (18) only used for the test function during driving controlled by the switches (27,28).

 As in the circuit of FIG. 1, a signal representative of the state of the tire is obtained at the output of the OR gate (22) which is then sent to the timed alarm device (24) as explained in the text relating to figure 1.

 Of course, the positions of the optical fibers, the energy coupling of which can be modified during the flattening of the tire, will be predetermined as a function of the tire and of the type of vehicle on which the device is mounted.

 It goes without saying that the present invention is not limited to the sole embodiments shown here by way of nonlimiting examples, but on the contrary embraces all similar or equivalent embodiments.

 Thus the circuits for processing the signals coming from the transducers could be produced quite differently, so as for example to also provide an identification of the under-inflated wheel, without thereby departing from the scope of the present invention. .

Claims (9)

 1- A method of monitoring and reporting the flattened state of a tire, characterized in that it consists in comparing, at each turn of the wheel, the light energy of a reference beam performing a determined path at l inside the wheel with the energy of a second light beam making a path inside the tire of the same wheel capable of causing losses or variations in energy couplings, when the tire undergoes deformations in the area contact with the ground, due to under-inflation and / or overload.  2- Device for implementing the method according to claim 1, characterized in that the path of each light beam and the sensitive element are made by means of at least one optical fiber.  3- Device according to claim 2, characterized in that it comprises at least two mobile optical fibers (5.3c) arranged inside the wheel, each optical fiber (5.3c) being capable of ensuring transmission respectively of the reference beam and of the measurement light beam, a fixed optical fiber (2) disposed inside the chassis of the vehicle, this fixed optical fiber being excited by a light source (1) also disposed inside the chassis and being able to come into coincidence with a first common end (3a) of the two mobile optical fibers (3c, 5) at each turn carried out by the wheel, as well as two fixed optical fibers (11,10) arranged inside the chassis and capable of coming into coincidence with the second end of the optical fibers respectively (5a, 9a) at each rotation of the wheel, means (12, 13, 16, 30) being further provided for transforming the light energy received into signals and to operate them.  4- Device according to claim 3, characterized in that each of the optical fibers (10, 11) is connected by its ends respectively (l0a, lla) to a transducer respectively (12, 13) and in that the electrical signals emitted by the two transducers (12, 13) are then processed in a logic circuit of the conventional type placed inside the chassis of the vehicle.  5- Device according to claim 4, characterized in that the logic circuit (16, 30) comprises an OR gate (21) whose output  is only true when the flattening of the tire exceeds a threshold  fixed or testing the device.  6- Device according to any one of claims 2 to 5, characterized in that the measuring light beam passes by coupling in two optical fibers (33, 34) attached to the sidewall of the tire, the coupling between these optical fibers being capable of '' be modified if the tire is crushed.  7- Device according to any one of claims 2 to 5, characterized in that the measuring light beam passes through a single optical fiber (29, 46) disposed against the inner wall of the tire, this optical fiber (29, 46) being liable to undergo light losses from a determined curvature.  8- Device according to any one of claims 2 to 5, characterized in that the measuring light beam passes through several sections (40, 41, 42) of optical fibers, arranged end to end against the internal wall of the tire and capable to be disoriented during a deformation of it.  9- Device according to any one of claims 2 to 5, characterized in that the measuring light beam passes through an optical fiber (50) disposed between two plates (51, 52) having on their opposite faces corrugated profiles ( 51a, 52a) complementary, one of the plates (51, 52) being fixed to the wall of the tire and being able to be brought closer to the other plate (52, 51) during a deformation of this tire.  the device according to any one of the preceding claims, characterized in that the position of the optical fibers, the energy coupling of which is liable to be modified during the crushing of the tire, is predetermined as a function of the type of tire and of the vehicle on which he is riding.