Piezoelectric-deformation pressure-drop signalling device in a tyre, comprising a detector

Holder (s);

74) Agent (s):

Device for signaling a drop in piezoelectric deformation pressure in a tire, comprising a detector, (57) The present invention relates mainly to a device for signaling a drop in pressure in tires.

The drop in pressure in a tire 1 causes it to deform during its rotation. The device 2 which is the subject of the present invention detects th is deformation and signals the pressure drop to the driver. The detection of the deformation is advantageously carried out by a polarized dielectric such as for example polyvinylidene fluoride. The transmission of information is carried out for example by neck ** magnetic range.

I The invention mainly applies to road safety.

<img file="FR2580997A1_D0001.tif" />

FR 2 580 997

D

Sale of booklets at IMPRIMERIE NATIONALE. 27. rue de la Convention - 75732 PARIS CEDEX 15

The main subject of the present invention is a device for signaling the drop in pressure in a tire, characterized in that it includes a tire deformation detector, signal transmission means and signaling means.

Means of transport such as cars or trucks are fitted with tires which, inflated to a sufficient pressure, ensure the contact of the vehicle with the road. Maintaining this pressure is essential to maintain good braking efficiency, maneuverability, traction and grip. Thus, a drop in pressure in a tire leads to a deterioration in vehicle safety. In addition, if a sufficient pressure does not prevail in a tire, the latter deforms in its lower part under the weight of the vehicle which it supports. Any rolling under such conditions leads to deformations which risk damaging or destroying the tire.

The device according to the present invention uses said deformation to produce an electrical signal which, once transmitted, will signal to the driver that a tire is deflated. The latter may take appropriate measures, for example changing the wheel, before destroying the tire or endangering the vehicle.

The main object of the invention is a device for signaling the drop in pressure in a tire.

Other advantages and characteristics of the invention will appear in the description which follows, illustrated with the aid of the figures which represent:

- Figure 1, a car wheel equipped with the device according to the invention;

- Figure 2, the section of a tire;

- Figure 3, the magnetic signal transmission means;

- Figure 4, the radio transmission means;

- Figure 5, the radio reception means;

- Figure 6, a bimetallic strip of PVF2;

- Figure 7, a deformation detector.

In the figures, the same references designate the same devices.

In FIG. 1, one can see a wheel 3 fitted with a tire 1. Against the wall of the tire 1 is arranged a device 2 for detecting deformations of the wall of the tire. The device 2 for detecting deformation of the wall of the tire 1 is for example a piezoelectric device which, with a stress exerted on it, associates an electric voltage. Advantageously, the piezoelectric element is made of polyvinylidene fluoride, called PVF2 in the rest of this patent.

Advantageously, the device according to the invention comprises a bimetallic strip of PVF2. Such a Jjilame is illustrated in Figure 6.

The sheet 2 of PVF2 follows the shape of the tire 1. Thus, when the sheet 2 of PVF2 descends as it approaches the ground, it undergoes a first deformation. This deformation is, in particular, a bending. Going up, the PVF2 sheet undergoes reverse deformation. With each deformation, the sheet 2 of PVF2 produces electrical energy.

258997

In a first alternative embodiment, this electrical energy is used to power a radio transmitter 4. The vehicle body (not shown) has an antenna 8 allowing reception of the signal transmitted. Some tires have a metal frame forming a Faraday cage. Thus, in order to be able to transmit to the vehicle body, the antenna 6 is passed through the valve 5 of the wheel 3. In another embodiment of the device according to the invention, rim 7 is used as the antenna.

In a second embodiment of the device according to the invention, illustrated in FIG. 3, the current produced by the bimetallic strip 2 of PVF2 is outputted into an inductor, for example a winding. Said coil induced in a second coil, integral with the bodywork or a suspension element, an electric current.

In FIG. 2, a bimetallic strip of PVF2 can be seen inserted between the air chamber 9 and the tire 1. In the illustrated embodiment, the bimetallic strip 2 is placed on the internal sidewall inside the tire 1. In another example of embodiment, the bimetallic strip 2 of PVF2 covers the two internal sides passing through the internal face of the tread.

In Figure 3, where ^ can see two embodiments of information transmission concerning the pressure drop in a tire i by magnetic coupling.

The bimetallic strip of PVF2 generates an electric current in an inductor 61. The establishment of the current in the inductor 61 causes a variation of magnetic field. Said variation of magnetic field induces a current in an inductor 81 made integral with the body or a suspension element.

The signal is transmitted by mutual inductance of the coils 61 and 81. The intensity of the current induced in the inductance 81 is increased due to the rotation of the wheel 3. Advantageously, the inductance 61 is flat, for example, produced under form of a multilayer and / or flexible printed circuit. Advantageously, for the tire 1, the metal armatures of which include slots, the inductor 61 is arranged so that the current lines induced in said armature are substantially perpendicular to the axis of said slots.

In an exemplary embodiment of the device according to the invention, the inductor 61 is photoetched on an insulating layer deposited on the bimetallic strip 2 of PVF2 or on a non-metallic part of this bimetallic strip. The photoengraving is carried out on a part of the bimetallic strip 2 which will be located opposite the receivers 8 when the bimetallic strip 2 of PVF2 is deformed.

In a first embodiment of the device according to the invention, the coupling is carried out through the tread of the tire 1. This coupling is carried out by sweeping the metal frame of the tire 1. In this embodiment, the distance between inductors 61 and 81 can be important.

In a second embodiment of the device according to the invention, the coupling is carried out through the tire blank 1. Advantageously, the device according to the invention comprises several inductors 61 making it possible to transmit signals coming from the two deformations that a wheel undergoes during a rotation of a turn. The inductor 81 has a size sufficient to pick up the signal emitted by the inductor 61 by compensating for the travel of the wheel.

8 0 99 Z

In FIG. 4, one can see a device for signaling the drop in pressure in a tire 1. The device in FIG. 4 comprises a device 2 for detecting deformation, a supply circuit 10, an oscillator 11 connected by a line 12 to an antenna 6.

The power supply 10 comprises for example a rectifier bridge charging a capacitor. If required by the oscillator 11, the power supply 10 includes a regulating device, for example a Zener diode. The oscillator 11 generates a high frequency electric current. The antenna 6 supplied by the oscillator 11 emits an electromagnetic wave.

In Figure 5, we can see the signaling device on board the vehicle. The device comprises an antenna 8 connected by a line 12 to an amplifier and / or detector 21. The amplifier 21 is for example a threshold amplifier. The amplifier and / or detector 21 controls and / or supplies a signaling device 22.

The signaling device 22 is for example an indicator light, an alphanumeric display, an audible signal and / or a voice message generated by a speech synthesizer. It is understood that the signaling device illustrated in FIG. 5 can be associated with magnetic coupling devices as illustrated in FIG. 3.

In FIG. 6, an exemplary embodiment of the device 2 for detecting deformations can be seen. The device 2 illustrated is a bimetallic strip of piezoelectric materials of opposite polarizations. The piezoelectric material is for example PVF2. The bimetallic strip 2 comprises a first layer 32 of electrically polarized PVF2, applied to a second layer 33 of PVF2 of opposite electric polarization.

On the layers 32 and 33 are deposited metal electrodes 31 and 34 respectively.

A bending of the bimetallic strip 2 generates a potential difference between the electrodes 31 and 34.

In an alternative embodiment of the bimetallic strip 2, not shown, a metal electrode is interposed between the layers 32 and 33 of PVF2. The electrical polarizations are chosen so that a bending of the bimetallic strip 2 generates a potential difference between the external electrodes 31, 34 and the central electrode.

In FIG. 7, an exemplary embodiment of the device 2 for detecting deformations can be seen, which is particularly well suited to tires having no air chamber. In the illustrated embodiment, the deformation detection device 2 comprises an inflatable structure allowing it to be pressed against the wall of the tire.

In an alternative embodiment of the invention, the deformation detection device 2 is bonded to the internal wall of the tire.

In an alternative embodiment of the device according to the invention, the metal wires forming the reinforcement of the tire are used to produce the inductor 61 making it possible to transmit the signal to the vehicle.

Advantageously, the bimetallic strip 2 of PVF2 is included in the sidewall of the tire during its construction or in those of the air chamber.