WO2015083072A1

WO2015083072A1 - Sensor device adapted for vehicle tyres, vehicle tyres and method of monitoring depths of grooves of tyre treads

Info

Publication number: WO2015083072A1
Application number: PCT/IB2014/066511
Authority: WO
Inventors: Rolf LIENER; Franc Godler
Original assignee: Liener Rolf; Franc Godler
Priority date: 2013-12-03
Filing date: 2014-12-02
Publication date: 2015-06-11
Also published as: CH708954A2

Abstract

This disclosure relates to a vehicle tyre, comprising at least one sensor device having a sensing element adapted to be embedded into a vehicle tyre tread, comprising a block made of tyre rubber blend mixed with a powder of a ferromagnetic material, and a coil buried into the block having two terminals protruding out of the block, an electronic circuit connected with the two terminals and configured to generate in operation an output signal representative of a sensed impedance of the coil. The sensing element is embedded in the tyre and has a free surface that is part of the rolling surface of the tyre tread and the electronic circuit being installed on an inner surface of the tyre. A method of monitoring a depth of a groove of a tread portion of a vehicle tyre is also disclosed.

Description

SENSOR DEVICE ADAPTED FOR VEHICLE TYRES, VEHICLE TYRES AND METHOD OF MONITORING DEPTHS OF GROOVES OF TYRE TREADS

TECHNICAL FIELD

This disclosure relates to sensor devices and more in particular to a sensor device having a sensing portion that may be embedded in tyre treads for monitoring depths of tread grooves.

BACKGROUND

A safe adhesion of a vehicle on the road can be attained primarily by a good tire set. The higher the static friction (frictional grip) between tires and underground, the safer the vehicle keeps its trace. Different parameters affect negatively the static friction (frictional grip): wetness, smoothness, small depth of tread, wrong tyre pressure, great age of the tires, tire temperature etc. Road traffic regulations of individual states stipulate different tire parameters which can be kept forward (depth of profile, gas pressure). The defaults can be different from state to state. The vehicle owners are obliged to keep the limits value of the state laws as well the recommendations of the insurers.

Depth measures of a tyre profile are simply carried out on still vehicles using a vernier caliper. For moving vehicles up to 120 km/h laser systems are used, which are built in the road pavement.

Tire tread depths are measured at present mainly when the vehicle is still (not moved vehicle). The measurement of the depths of profile is made mechanically by a length comparison. In addition there are different vernier gauges, which use however all the same principle of one or two scales each movable in respect to the other.

More modern facilities admitted in workshops or measuring systems in road pavements permit an optical profile measurement (laser tri angulation). By fast CCD line sensors and a semiconductor laser which is diverted by a mirror, depth of profile measurements of moving vehicles up to 120 km/h can be done. These systems are however very expensive, cumbersome and therefore cannot be built into a vehicle.

Continuous measurement of the depth of profile was suggested by different tyre manufacturers by use of ultrasound transmitters and receivers inside the tyre. This system however is affected by substantial disadvantages of high power requirements and strong interferences (interfering signal) which are influenced very differently by the wheel arch on the road depending on its surface.

A further solution is a stepped profile measurement, with electrical conductor bow, which are embedded in the profile and interrupted by driving off. Here is a substantial disadvantage that the interrupted electrical conductor bow can get very low- impedance depending on floor covering again. Besides level data values for the assistance systems are not particularly suitable.

The company Michelin carries out continuous measurements of the depth of a tread profile by way of the reduction of a resistance or a condenser that is embedded in the profile. Also in this case no accurate depth of profile can be determined, because environmental influence on the tyres causes variations of the measures provided by the sensors.

The company Continental measures different additional tyre parameters, such as the torsion of the tyre walls, in order to infer more accurately the depth of tread profile.

The company Bridgestone uses a sound analysis to be able to deduce around statements about the static friction of the tire, without identification or to know the accurate depth of a tyre profile.

To the best knowledge of the inventors, there is so far no solution for direct, continuous and efficient control and measurement of the depth of tread profile of each tire on a moving vehicle for the driver and the assistance systems.

SUMMARY

A sensor device that obviates at least partially to the above limitations has been devised.

The device disclosed herein has a sensing element and an electronic circuit. The sensing element comprises a block made of a tyre rubber blend charged with powder of a ferromagnetic material, and a coil buried in the block of tyre rubber blend. The electronic circuit is coupled with the coil so as to read the impedance of the coil when an AC current at a nominal frequency is forced therethrough.

According to an embodiment, the concentration of powder of ferromagnetic material is sufficient to make the relative magnetic permeability of the whole sensing element greater than one. According to an embodiment, the electronic circuit comprises a bias network functionally connected to the terminals of the coil so as to apply at the terminals of the coil in operation an AC bias voltage at a nominal frequency, and an operational amplifier coupled to a first terminal of the two terminals of the coil and to a reference terminal at which a reference voltage is made available, configured to generate the output signal with an amplitude corresponding to a sensed impedance of the coil.

Another object of this disclosure is a vehicle tyre, comprising at least one sensor device of this disclosure, wherein the sensing element is embedded in the tyre and has a free surface that is part of the rolling surface of the tyre tread, and the electronic circuit is installed on an inner surface of the tyre.

This disclosure provides also a method of monitoring a depth of a groove of a tread portion of a vehicle tyre of this disclosure, the method comprising the steps of applying an AC voltage having a nominal frequency at the terminals of the coil of the sensor device, generating the output signal, representative of a sensed inductance of the coil, as the amplitude of an AC voltage difference between the voltages available at a terminal of the coil and at a reference terminal of the electronic circuit, and determining the depth of the groove in accordance with the output signal.

The claims as filed are integral part of this specification and are herein incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a vehicle tyre according to this disclosure embedding a single sensing element B in the tyre tread D.

Figure 2 shows a vehicle tyre according to this disclosure embedding two sensing elements A and C in the tyre tread D on the left and on the right.

Figure 3 shows a vehicle tyre according to this disclosure embedding three sensing elements A, B and C in the tyre tread D on left, in the center and on the right.

Figure 4 shows the principle structure of an inductive tread measuring for sensor.

Figure 5 shows a sensing element of a sensor device according to this disclosure, comprising a tyre rubber blend block (A) which contains a coil (B) whose terminals (C) and (D) protrude out of the tyre rubber blend block.

Figure 6 depicts a sensing element similar to that of figure 5 containing a coil arranged longitudinally.

Figure 7 shows an embodiment of an electronic circuit of the sensor device of this disclosure for sensing the impedance of the coil in the sensing element comprising a constant AC power source (J) connected to the terminals of the coil (K) and a measurement amplifier (L) with a relatively great input resistance (R_is— *∞).

Figure 8 shows another embodiment of an electronic circuit of the sensor device of this disclosure wherein the coil (K) is connected in series with a resistor Rv of known value.

Figure 9 shows yet another embodiment of an electronic circuit of the sensor device of this disclosure wherein the coil (K) is inserted in a measuring bridge network.

DETAILED DESCRIPTION

In the following revelation of the invention a new sensor is described, which is adapted to be built directly in tires and is adapted to measure continuously the depth of profile of a tyre tread. The inquiry of the sensor is carried out with the help of well- known transponder technologies. From the tire data, warnings and forecasts can be derived about the use of the vehicle and the way of driving it or for the driver's way of driving. The results can be communicated to the driver over a display or they are provided to the different assistance systems. The owner/driver of a vehicle has always an overview of current tire data and thus of the compliance with the limits. Assistance systems may perform optimally their service in dependence of the current tire parameters.

The invention describes a new, low cost sensor, which is adapted to be built directly into the profile of a tire. The sensor becomes at the same time smaller with the profile reduction by wear geometrically and changes thereby its physical characteristics. Depending upon of the tires on passenger car, truck/lorry or special vehicles/motor vehicles the sensor may be placed in different positions separately or several instances of the sensor may be embedded in the tread of a tire.

The length of the sensor in direction of movement of the tire may be likewise varied depending upon use. Preferably the length in direction of movement is between 1 mm up to 10 mm to receive a sufficient large measuring accuracy of the depth of profile measurement. The larger is the sensor volume, the more exact and simpler is to have the measured value of the profile depth.

The sensor described here is simple in the production, needs little material and is very low cost. In practice the dimensions of the finished sensor depend on the depth of profile of the new tire and on the type of tire. The sensor thickness may be for example only approx. 1 mm up to 5 mm. The height corresponds to the depth of profile plus some millimeters, from which the minimum value of the sensor is derived after 100% loss of the profile.

Examples of the installation show the pictures Figure 1 to Figure 3. A section of a tyre of this disclosure is shown crossways to the direction of motion. A, B, C are the sensors, D is the tyre coat.

According to an embodiment, an arrangement with only a sensor in the tyre centre is shown in figure 1. This arrangement is sufficient for relatively narrow tires, like e.g. tires of a motorcycle or of small cars.

According to an embodiment, an arrangement with two sensors on the left and on the right is shown in figure 2. With this arrangement, an uneven driving off of the tire tread can be recognized. This arrangement is sufficient for most passenger cars.

According to an embodiment, an arrangement with three sensors on the left, in the center and on the right is shown in figure 3. This arrangement is for broad tires and seizes all cases of possible depth of profile wear. This arrangement may be used for example in tires for lorries and special vehicles.

The sensor described here has a material with certain physical characteristics, brought in a defined volume. The material is a magnetically sensitive material like e.g. tyre rubber blend mixed with iron powder or tyre rubber blend mixed with ferrite. The measurement of the physical characteristics of the defined finite volume is obtained by a magnetic alternating field generated by a coil which is embedded in this material. The frequency of the signal current can be chosen in such a way that there is no interference caused by road surfaces.

The coil terminals are led through the steel plaiting into the inner surface of the tyre and are connected to an electronic circuit, that may operate as a meter circuit for sensing the impedance of the coil, with a transponder. The transponder provides for the power supply and the transmission of the data to the vehicle.

Admits is the Ampere law according to which magnetic fields are not produced by sources, but by moved electrically loads/charges. A swirl magnetic field develops around the moving electrical loads/charges (here electrons in a conductor). Therefore reads the differential and vector description for the moved loads/charges, the magnetic field and the source freedom of the field in the vacuum:

rot I? = |¾ j or rot H = j

8¾^! S = Q

rot 3 = local swivel strength of the vector field

3 = magnetic induction

= magnetic field strength

t = current density

f½ = magnetic field constant = 4xl€r⁷—

With the help of Stokes' integral law for steadily differentiable vector fields one gets the integral forms of the Ampere' s law to:

i¾ f = f § as or ί = 4s

I = electron current

§ = circulation integral about boundary curve

tti^" = infinitesimal integration path

If one rolls an electric conductor up to a coil, then the winding number and her length go in the magnetic induction (here only a coordinate; e.g. x-axis):

μ_: si = IS or rJ = I

= number of coil windings

i = length of the coil

If the coil gets filled a material matter, a change of the magnetic induction can appear. This change is indicated by the relative permeability of the material matter and arises from the relationship of induction with a material matter to induction of a vacuum coil of equal making geometry: ¾ = magnetic induction (only an axis) in the vacuum

B = magnetic induction (only an axis) in a material matter

The relative magnetic permeability can be subdivided into three groups: it_j, » 1 — > ferromagnetic substances (great gain of the induction.) μ_τ > 1 — > paramagnetic substances (low gain of the induction.)

μ_τ < i — > diamagnetic substances (low weakening of the induction.)

Further distinctions are (soft or magnetically hard) hit in dependence of its rest magnetism for ferromagnetic substances after magnetizing only.

The permeability number is not constant and is strongly nonlinear. It depends on the frequency and the strength of the magnetic field, on the temperature and on the material, which is brought into the magnetic field. In calculations it is therefore treated to the simplification and general validity as complex number. The real part stands for the inductive effects, the imaginary part for the losses.

The further considerations are made assuming the material as if it were ideal and thus loss-free.

Tyre rubber blend is typically a diamagnetic material and thus not suitable for any form of a magnetic-field-dependent sensor, because a is approx. 1.4 i0~⁵.

To get a sensor with a sensitivity as big as possible (large effect), a reinforcement of the induction of the coil is needed. It is already sufficient, if the coil itself and a fraction of its surrounding volume are filled with a material, which possesses ferromagnetic characteristics. In this material there is thus a concentration of the magnetic lines of flux and thus a reinforcement of the induction.

Iron powder has a from 50 to 150 and can be used in the frequency domain up to 400 kHz. Manganese zinc and nickel zinc alloys are used as ferrites with different proportional weight quotas. For manganese zinc one gets 300 < < 20000 with working frequencies up to 20 MHz. The values at 40 < μ_Ύ < 1500 are with working frequencies up to 800 MHz noted for nickel zinc.

All ferromagnetic substances are suitable for the production of the sensor described here. To reach effects as big as possible, the skilled person may easily adjust the sensor volume must depending upon the used substance. The volume is preferably chosen to be relatively great at small μ₇ and smaller with a greater The proportional partitioning between tyre rubber blend and ferromagnetic material also plays a role in this; the more ferromagnetic material is inserted, the fewer availably the qualities of tyre rubber blend are in this volume.

The characteristics of the tire do not change if the sensor is made of a mixture of tyre rubber blend of the tyre and a ferromagnetic powder. This mixture can be injected during the production of maturing at the sensor position. Since the tyre rubber blend encloses the ferrite particle also in the microscopic range, there are no oxidations of the powder which wouldn't be particularly environmentally friendly.

Ferromagnetic powders are available in the micrometer range in different grain quantities and can for the optimization at different volume quantities and used frequencies the measuring electrical powers be selected optimally.

The needed coil is fastened before at the steel wire coat by arranging the conductors towards the inside of the tire, as well as at the sensor location, with the help of a mounting plate that has the same material characteristics as the mixture used for the sensor. In the tire inside is the meter circuit to which the coil is connected and the transponder that is used to transmit measured data and for power supply.

Self-induction voltage is directly proportional to the speed of the electrical current change in the coil. The proportionality factor is called inductance.

di

U; = L—

&t

Ui = self-induction voltage

I = inductance

= differential of the electrical current modification (speed of the electrical current modification is proportional to the frequency of the electric electrical current)

The proportionality factor inductance contains the geometry of the coil, its number of turns, the magnetic field constant and the material qualities: Λ₃ = effective coil cross-sectional area ¾?² = number of the coil turns to the square g = effective coil length (only a coordinate)

Figure 4 shows the basic structure of an inductive profile depth measuring sensor. K represents the tyre rubber blend mixed with ferromagnetic powder, J is the coil. Above the coil J there is a closed area, head of the magnetic field lines. This area gets smaller due to tire wear and the inductance of the coil decreases with increasing tire wear.

Substantially, any position of the coil can be provided in the sensor volume. There is always a measurable effect with the profile reduction. Two embodiments with great effect shown in the figures Figure 5 and Figure 6.

In Figure 5, the sensor volume (A), which contains the coil (B), the terminals (C) and (D) are routed through the steel wire coat inside the tire. The profile height (a) is worn during tire's life. If the tire tread is completely worn, the height (b) of the sensor is attained.

In Figure 6 is the sensor volume (E), comprising the coil (F), whose connections (G) and (H) are passed through the steel wire coat inside the tire. The profile height (c) is worn during the travel. If the tire tread is completely worn, the sensor height (d) is achieved.

The inductance electrically is characterized by its reactance (complex resistance):

X_L = i ω L = i 2 π f L

X_L = inductive reactance ω = angular frequency f = frequency The inductive sensor has largest inductance with full tread depth and proportionally the largest reactance. If the tread profile is worn by 100%, its inductance is the smallest and so is its resistance. The reactance value can be determined electrically in different ways. A constant a.c. source may supply it and the voltage drop at it (complex view) is:

¾, = complex sensor tension i_€ = complex constant alternating current

Figure 7 shows a constant a.c. current source (J), the sensor (K) and a measurement amplifier (L) with a very big input resistance (¾,→·>-»).

According to an alternative, the sensor may be connected through a resistance to a constant a.c. voltage source. The sensor is switched with an Ohmic resistor in series. Figure 8 shows these facts: (M) is the constant a.c. voltage source and delivers the a.c. voltage u_M. A switched resistance (Rv) and the sensor (K) with the reactance K_L are connected in series. The measuring is carried out again with a measurement amplifier (L) with a high-impedance input. With this arrangement, one gets for the sensor voltage

A measuring bridge, as it is shown into figure 9, delivers very accurate measurements. With this arrangement, two voltage divider conditions are compared. Both voltage dividers are supplied with electrical power from the same constant a.c. voltage source. The resistor (Rl) and (R2) form a voltage divider without phase shift, (R3) and (K) form a voltage divider with phase shift. The measuring of the detuning of the bridge is carried out with a measurement amplifier (L) with a high-impedance input also in this case. For the measurement carried out using the bridge, the following equation holds:

Claims

1. Vehicle tyre, comprising at least one sensor device comprising:

a sensing element adapted to be embedded into a vehicle tyre tread, comprising a block (A; E) made of tyre rubber blend mixed with a powder of a ferromagnetic material, and a coil (B; F) buried into the block (A; E) having two terminals (C, D; G, H) protruding out of said block (A; E), and

an electronic circuit connected with said two terminals (C, D; G, H) and configured to generate in operation an output signal representative of a sensed impedance of said coil;

said sensing element being embedded in the tyre and having a free surface that is part of the rolling surface of the tyre tread and said electronic circuit being installed on an inner surface of the tyre.

2. Vehicle tyre of claim 1, wherein said block (A; E) is made of the same tyre rubber blend of said vehicle tyre.

3. Sensor device, comprising:

a sensing element adapted to be embedded into a vehicle tyre tread, comprising a block (A; E) made of tyre rubber blend mixed with a powder of a ferromagnetic material, and a coil (B; F) buried into the block (A; E) having two terminals (C, D; G, H) protruding out of said block (A; E); and

an electronic circuit connected with said two terminals (C, D; G, H) and configured to generate in operation an output signal representative of a sensed impedance of said coil.

4. Sensor device or vehicle tyre of one of previous claims, wherein said block of tyre rubber blend contains an amount of the powder of ferromagnetic material sufficient to make greater than one the relative magnetic permeability of the block (A; E) made of tyre rubber blend mixed with the powder of ferromagnetic material.

5. Sensor device or vehicle tyre of one of previous claims, wherein said ferromagnetic material is chosen in the group consisting of: iron, ferrite, manganese- zinc alloys, nickel-zinc alloys and combinations thereof.

6. Sensor device or vehicle tyre of one of previous claims, wherein said electronic circuit comprises: a bias network functionally connected to said terminals (C, D; G, H) of the coil (B; F) so as to apply at the terminals of said coil in operation an AC bias voltage at a nominal frequency,

an operational amplifier (L) coupled to a first terminal of the two terminals of said coil (B; F) and to a reference terminal at which a reference voltage is made available, configured to generate said output signal with an amplitude corresponding to a sensed impedance of said coil (B; F).

7. Sensor device or vehicle tyre of claim 6, wherein said bias network comprises a resistor (Rv) connected in series with said coil (B; F) and an AC voltage generator functionally connected so as to power the series of said resistor (Rv) with said coil (B; F), said reference terminal being a second terminal of the two terminals of the coil.

8. Sensor device or vehicle tyre of claim 6, wherein said bias network comprises an AC voltage generator functionally connected so as to power said coil (B; F), said reference terminal being a second terminal of the two terminals of the coil.

9. Sensor device or vehicle tyre of claim 6, wherein said bias network comprises a resistor (R3) connected in series with said coil (B; F), a resistive divider (Rl, R2) connected electrically in parallel with the series of said resistor (R3) with said coil (B; F) and an AC voltage generator functionally connected so as to power the voltage divider (Rl, R2) and the series of said resistor (Rv) with said coil (B; F), said reference terminal being an intermediate tap of said voltage divider (Rl, R2).

10. Sensor device or vehicle tyre of one of previous claims, wherein said electronic circuit further comprises a transponder with a wireless transmitter functionally configured to transmit in operation said output signal.

11. A method of monitoring a depth of a groove of a tread portion of a vehicle tyre, the vehicle tyre being as defined in one of claims 1, 2, 4 to 10, the method comprising the steps of:

applying an AC voltage having a nominal frequency at the terminals of the coil of said sensor device;

generating said output signal, representative of a sensed inductance of the coil, as the amplitude of an AC voltage difference between the voltages available at a terminal of the coil and at a reference terminal of the electronic circuit; determining the depth of said groove in accordance with said output