WO2009010642A2

WO2009010642A2 - Device for monitoring the physical parameter of a tyre condition using a freely movable sensor

Info

Publication number: WO2009010642A2
Application number: PCT/FR2008/000788
Authority: WO
Inventors: Thomas Ledoux; Nathalie Levain; Denis Martin; Bernard Perrier
Original assignee: Societe De Technologie Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2007-07-11
Filing date: 2008-06-10
Publication date: 2009-01-22
Also published as: FR2918606A1; WO2009010642A3; FR2918606B1

Abstract

The invention relates to a device for monitoring the physical parameter of a tyre condition, that comprises a sub-assembly (1) arranged inside said tyre and comprising a resonant electric circuit (11) including a magnetic induction coil (110). According to the invention, the resonant circuit (11) has a flat shape with a thickness (El), parallel to the axis (Z) of the coil (110), not exceeding one fifth of each of the other two dimensions, and said circuit is directly imbedded in a protection coating (12) having a flat shape with a thickness (E2) parallel to that of the resonant circuit (11), the sub-assembly (1) formed by said circuit (11) imbedded in said coating (12) being arranged so as to be capable of free movement in the tyre.

Description

DEVICE FOR MONITORING A PHYSICAL STATE PARAMETER OF A TIRE USING A FREELY MOBILE SENSOR.

The invention relates generally to the monitoring of a state of operation, in the automotive field.

More specifically, the invention relates to a device for monitoring a physical state parameter of a tire mounted in operation on a vehicle equipped with a chassis and wheels, this device comprising at least a first subassembly disposed in operation in the tire and including a resonant electrical circuit with a magnetic induction coil.

Such a device is for example described in US Patent 5,260,683.

This patent discloses an internal pressure monitoring system ^"of a tire, comprising, besides the first sub-assembly disposed within the tire, a second sub-assembly connected to the frame and equipped with magnetic excitation means and means reading to communicate with the first subset, which plays the role of sensor.

In the solution advocated by this patent, the first subassembly is fixedly mounted in the tire cavity and for example made integral with the wheel rim equipped with this tire.

However, such a solution generates significant constraints of assembly, sealing and maintenance, which the present invention aims to overcome.

To this end, the device of the invention, moreover, conforms to the generic definition given in the preamble above, is essentially characterized in that the resonant circuit has a flattened shape of which a first dimension, parallel to the axis of the coil, is strictly lower than the other two, in that the first subassembly comprises, in addition to the resonant circuit, a flat-shaped protective coating of which a smaller dimension is parallel to the first dimension of the resonant circuit, in that the resonant circuit is directly embedded in this coating, and in that the first subassembly is arranged freely mobile in the tire.

For example, the first dimension of the resonant circuit is at most equal to one fifth of each of the other two dimensions.

Preferably, the coating consists essentially of a porous elastomeric material with open cells, for example having a density at most equal to 0.5 g / cm ³ and advantageously between 0.1 g / cm ³ and 0.3 g / cm ³ .

To do this, this coating can in particular be made of polyurethane foam.

The first subassembly can thus have a mass of less than 10 grams, and preferably even at most equal to 6 grams.

Since the resonant circuit comprises several components electrically connected to each other by electrical conductors, it may be advisable to provide, to further reduce the mass of the first subassembly, that these components are mechanically connected to each other at least by these means. electrical conductors. In a variant, thin and flexible conductive wires are used for electrically connecting the components of the resonant circuit, and a more rigid material, such as an epoxy resin, is used to coat at least a portion of these conductors and these components to ensure the mechanical strength of the assembly.

Similarly, instead of having a rigid core, the coil can be shaped as a flat ring and consists of turns glued to each other, made by winding a insulated wire surface.

The monitoring device of the invention may also comprise a second subassembly operably linked to the chassis of the vehicle and provided with magnetic excitation means and reading means.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

FIG. 1 is an electrical diagram illustrating a possible embodiment of a resonant circuit that can be used in the device of the invention;

Figure 2 is a schematic perspective view cut away, on an enlarged scale, of a first subset used in the device of the invention;

- Figure 3 is a half-sectional view of a tire during rolling, in which is inserted the first subassembly of a device according to the invention;

FIG. 4 is a diagram representing, in ordinate, the resonant frequency, expressed in kilohertz, of a circuit resonant usable in a device according to the invention, depending on the internal pressure of the monitored tire, expressed in bars and abscissa; and

- Figure 5 is a schematic partial sectional view of a vehicle equipped with a device according to one invention.

As previously announced, the invention relates to a device for monitoring a physical parameter of the state of a tire 920 (FIG. 5) fitted to a wheel 92 of a vehicle 9.

Good . that this description makes reference more specifically, for the sake of concrete illustration, a _* di-sppsitif monitoring the internal pressure of ^a>;' tire, the skilled person will be able to adapt this - device to monitor any physical ^• Settings-.

Such a device comprises, at least in operation, - first subassembly 1 disposed in the tire 920, and a second subset * 2 connected to the chassis 91 of the vehicle 9. ^•>

The first subassembly 1 itself comprises a resonant electrical circuit 11 (FIG. 1), for example formed of a magnetic induction coil 110, of a capacitive sensor 111 of variable capacitance and in this case sensitive to pressure. internal tire, a resistor 112, and optionally an additional capacitor 113 of fixed capacity mounted in parallel on the sensor 111 to adjust the resonance frequency, all of these components being connected to each other by conductors electric 114. On the other hand, and as symbolically shown in FIG. 5, the subset 2 comprises magnetic excitation means 21 and reading means 22, which enable this second subset to communicate with the first subset. 1 by mutual magnetic influence, as described for example in the aforementioned US Pat. No. 5,260,683.

According to the invention (FIG. 2), the resonant circuit 11 has a flattened shape.

For example, its smallest dimension, or thickness E1, which extends parallel to the axis Z of the coil 110, is at most equal to the fifth of each of the two other dimensions of this circuit 11.

As further shown in FIG. 2, the subassembly 1 comprises, in addition to the resonant circuit 11, a protective coating 12 of flattened shape, in which the resonant circuit 11 is directly embedded.

The smallest dimension, or thickness E2, of the coating 12 extends in the same direction as the thickness E1 of the resonant circuit, that is to say parallel to the axis Z of the coil 110.

Thanks to these characteristics, the first subassembly 1 can be freely movably arranged in the tire 920, that is to say without any fixation, this sub-assembly 1 being pressed against the inner face of the tire by centrifugal force ( Figure 3) as soon as the vehicle reaches a moderate speed, lower than that for which the monitoring of the condition of the tire becomes desirable for reasons of safety.

Preferably, the coating 12 consists essentially of a porous elastomeric material with open cells, such as polyurethane foam, this feature being illustrated symbolically only on the left side of the fiqure 2 to keep the latter a sufficient readability.

This coating 12 advantageously has a density at most equal to 0.5 g / cm ³ and, even more advantageously, a density of between 0.1 g / cm ³ and 0.3 g / cm ³ .

Subassembly 1 may thus have a mass of less than 10 grams and in fact typically not more than 6 grams.

Several measures can be taken to reduce the mass of this subset.

In particular, the components 110 to 113 of the resonant circuit 11 may for example be mechanically connected to each other essentially through the electrical conductors 114 of this circuit.

In addition, instead of having a core, the coil 110, which is shaped as a flat ring, can be formed of turns glued to each other, each turn being made by winding a conductive wire, for example copper, isolated surface.

As known to those skilled in the art, a resonant circuit 11 such as that of FIG. 1 has a resonant frequency fr equal to:

and a quality factor Q equal to

where L is the inductance of the coil 110, C the overall capacitance of the sensor 111 and the additional capacitor 113, and R the value of the resistor 112.

The measurement of the resonance frequency fr therefore gives access to the value of the variable capacitance C if the inductance L is fixed, and vice versa.

The measurement of quality factor Q gives access to the value of capacitor C, inductance L, or resistor R if one of these electrical quantities is variable while the other two quantities are fixed.

It is therefore possible, by changing one of the magnitudes L, C and R according to the parameter chosen to monitor the state of the tire 920, to give the subset 1 many different embodiments.

In particular, instead of monitoring the pressure, it would be possible to monitor for example the temperature or the hygrometry.

Moreover, instead of using a capacitive sensor, it would be possible to vary the inductance L of the coil 110 as a function of the parameter to be monitored; the resistance of another component can also be varied according to the parameter to be measured.

In addition, the adjustment of the resonant frequency could be realized by an additional coil of fixed inductance instead of capacitor capacitance fixed, or a combination of both, it being understood that these components remain anyway optional.

On the other hand, the coating 12 must, in all cases, allow the chosen sensor to be influenced by the parameter to be monitored, which for example forbids the use of a water vapor-tight coating 12 in the case where the monitored parameter is the hygrometry of the tire.

In the case of a temperature measurement, the coating must be temperature-conductive.

In the case of monitoring the internal pressure of the tire, the coating 12 could thus be made of a material that does not allow the pressure to pass, provided that a communication channel is provided in the coating between the cavity of the tire. tire and the> sensor.

The coating 12 could also optionally be made of a material that does not let the pressure, provided that the thickness of this coating is then sufficiently low so that the deformation of the latter ^'is transmitted to the variable capacity.

The material of the coating 12 may also be chosen to have, at least on the surface, optimal adhesion to the tire inner liner.

The resonant circuit 11 preferably has a resonant frequency within the electromagnetic bands of the radio transmissions, for example of the order of 150 kHz or less.

Due to the flattened shape of the coating 12, the coil 110 is placed in a plane substantially tangential to the tread of the tire 920 as soon as the vehicle 9 is traveling at a speed greater than a relatively low limit value, of the order of 20 to 30 km / h and can thus receive and transmit a magnetic field through this tread.

In a possible embodiment, given by way of purely illustrative example, the subassembly 11 can be made in the following manner.

The coil 110 comprises 500 turns of copper wire of diameter equal to 0.08 mm, and itself has an inside diameter of 18 mm, an outside diameter of 23 mm, a thickness of 2 mm along the Z axis, a mass of 1.6 g, and an inductance of 8 mH.

The capacitive pressure sensor 111 takes the form of a chamber filled with air and closed by two brass discs, these discs having an outer diameter of 30 mm, a thickness of 0.05 mm, and forming both the front walls. of the chamber and the frames of a variable capacitor with the pressure.

These discs are sealingly welded to the respective coppered faces of a ring cut in an epoxy resin insulating plate, of the type used for printed circuits.

This ring, which forms both an axial separator for the brass discs and a side wall for the chamber, has for example a thickness of 0.4 mm, an outside diameter of 30 mm, and an internal diameter of 24 mm.

Finally, an insulating sheet, such as a sheet of paper or polymer of a few hundredths of a millimeter thick and preferentially high permittivity, is interposed between the two discs and possibly carried by one of them.

When the sensor 111 thus formed is subjected to a pressure to be measured, the discs come into contact with one another, through the insulating sheet, in an area of variable area with this pressure, this sensor having a varying capacity strongly with the pressure.

The sensor thus produced has a mass of 1.1 g.

The capacitor 113, with a fixed capacity of 150 pF, typically has a mass of 0.1 g.

Under these conditions, and by equating the resistor 112 with the parasitic resistance of the three aforementioned components, the resonant circuit 11 has a total mass of 2.8 g, a length of 5.5 cm, a width of 3.0 cm and a thickness of 0.2 cm. .

In other words, the thickness of this circuit 11 is only one-fifteenth of its width, while it could, without affecting the performance of the device, represent the tenth or even the fifth of this width.

Finally, the coating 12 has a length of 6.5 cm, a width of 4.0 cm, a thickness of between 0.5 cm and 1 cm, and a mass of about 3.2 g, so that the subassembly 1 illustrated in FIG. Figure 1 shows a total mass of the order of 6 g and therefore does not disturb the operation of the tire 920 rolling.

A circuit 11 produced according to the indications given above has (FIG. 4) a resonance frequency of 126 kHz at atmospheric pressure and 100 kHz under an additional pressure of the order of 3 bars, the frequency resonance fr thus varying from about 26 kHz for a pressure variation of 3 bar.

Claims

CLAIMS.

1. A device for monitoring a physical state parameter of a tire (920) mounted in operation on a vehicle (9) equipped with a chassis (91) and wheels (92), this device comprising at least one first subassembly (1) disposed in operation in the tire (920) and including a resonant electrical circuit (11) having a magnetic induction coil (110), characterized in that said resonant circuit (11) has a flattened shape of which a first dimension (El), parallel to the axis of the coil

(110), is strictly smaller than the two other dimensions, in that the first subassembly (1) comprises, in addition to the resonant circuit (11), a protective coating (12) of flattened shape, of which a smaller dimension ( E2) is parallel to the first dimension (El) of the resonant circuit (11), in that the resonant circuit (11) is directly embedded in this encapsulation (12), and in that the first subset (1) is freely movable in the tire (920).

2. Monitoring device according to claim 1, wherein the first dimension (El) of the resonant circuit is at most equal to fifth of each of the two other dimensions.

3. Monitoring device according to claim 1 or 2, characterized in that the coating (12) consists essentially of a porous elastomeric material with open cells.

4. Monitoring device according to any one of the preceding claims, characterized in that the coating (12) has a density at most equal to 0.5 g / cm ³ .

5. Monitoring device according to any one of the preceding claims, characterized in that the coating (12) has a density of between 0.1 g / cm ³ and 0.3 g / cm ³ .

6. Monitoring device according to any one of the preceding claims, characterized in that the coating (12) is made of polyurethane.

7. Monitoring device according to any one of the preceding claims, characterized in that the first subassembly (1) has a mass less than 10 grams.

8. Monitoring device according to any one of the preceding claims, characterized in that the first subassembly (1) has a mass at most equal to 6 grams.

9. Monitoring device according to any one of the preceding claims, characterized in that ^* the resonant circuit (11) comprises several components (110-113) electrically connected to each other by electrical conductors (114), and mechanically connected to each other at least by these electrical conductors (114).

10. Monitoring device according to any one of claims 1 to 9, characterized in that the resonant circuit (11) comprises several components (110-113) electrically connected to each other by thin and flexible electrical conductors (114). and mechanically connected to each other also by a more rigid material encasing at least a portion of said conductive wires and said components.

11. Monitoring device according to any one of the preceding claims, characterized in that the coil (110) is shaped as a flat ring and consists of turns glued to each other and made by winding a insulated wire surface.

12. Monitoring device according to any one of the preceding claims, characterized in that it comprises a second subassembly (2), this second subassembly being operatively connected to the frame (91) and provided with means (21). ) magnetic excitation and means (22) for reading.