CA2914522A1 - System for measuring the thickness of a layer of rubber for a tyre - Google Patents
System for measuring the thickness of a layer of rubber for a tyre Download PDFInfo
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- CA2914522A1 CA2914522A1 CA2914522A CA2914522A CA2914522A1 CA 2914522 A1 CA2914522 A1 CA 2914522A1 CA 2914522 A CA2914522 A CA 2914522A CA 2914522 A CA2914522 A CA 2914522A CA 2914522 A1 CA2914522 A1 CA 2914522A1
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- measurement system
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- 230000002787 reinforcement Effects 0.000 claims abstract description 22
- 230000007423 decrease Effects 0.000 claims abstract description 8
- 238000005259 measurement Methods 0.000 claims description 69
- 230000035699 permeability Effects 0.000 claims description 18
- 229910000859 α-Fe Inorganic materials 0.000 claims description 15
- 230000005284 excitation Effects 0.000 claims description 14
- 230000035945 sensitivity Effects 0.000 claims description 7
- 239000002184 metal Substances 0.000 abstract description 15
- 238000004804 winding Methods 0.000 abstract 3
- 230000008901 benefit Effects 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 239000004020 conductor Substances 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/26—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring depth
Abstract
The invention concerns a system for measuring the thickness of a layer of rubber material for a tyre, the layer having a face connected to an adjacent metal reinforcement and a free face which is in contact with the air. The system comprises a sensor which can measure the distance d between the connected face and the free face of the rubber material layer, the sensor comprising a single exciting and measuring winding, and the exciting power and frequency of the winding being such that the inductance at the winding terminals increases as the distance d decreases.
Description
System for measuring the thickness of a layer of rubber for a tyre Technical field [0001] The present invention relates to a system for measuring the thickness of a layer of rubber, and more particularly to the measurement of the thickness of remaining rubber on a tread of a tyre.
Prior art
Prior art
[0002] In a known way, the tread of a pneumatic tyre, or more simply a tyre, regardless of whether it is to be fitted on a passenger vehicle, a heavy transport vehicle, a civil engineering vehicle, or other vehicle, is provided with a pattern comprising, notably, pattern elements or elementary blocks delimited by various main, longitudinal, transverse or oblique grooves, the elementary blocks also possibly comprising various finer slits or sipes. The grooves form channels intended to discharge the water during running on wet ground, and define the leading edges of the pattern elements.
[0003] The depth of the tread is at a maximum when a tyre is new. This initial depth may vary according to the type of tyre in question, as well as the use for which it is intended; by way of example, "winter" tyres generally have a pattern depth greater than that of "summer" tyres. When the tyre becomes worn, the depth of the elementary blocks of the pattern decreases and the stiffness of these elementary blocks increases. The increase in the stiffness of the elementary pattern blocks causes a reduction in some performance characteristics of the tyre, such as the grip on wet ground. The water discharge capacity also decreases markedly when the depth of the channels in the pattern decreases.
[0004] It is therefore desirable to be able to monitor the development of the wear of the tread of a tyre.
[0005] This monitoring is usually carried out by visual observation of the tread by the user or a mechanic, with or without actual measurement with a depth gauge.
However, this observation is not very easy to carry out, notably on rear tyres which are harder to access, and furthermore it is not very precise.
However, this observation is not very easy to carry out, notably on rear tyres which are harder to access, and furthermore it is not very precise.
[0006] Numerous proposals have been made to automate the measurement of the depth of tyre patterns. Such devices can be placed on the roadway on which vehicles run. These devices usually operate by two techniques, either based on optical systems with cameras or lasers, or based on eddy currents.
[0007] The systems based on optical systems are costly, have to be embedded in the roadway, and require regular maintenance. Moreover, the measurements are subject to interference due to soiling and the presence or spraying of water, mud, snow, etc.
[0008] Documents US 7,578,180 B2 and WO 2008/059283 propose systems for measuring the thickness of the tread of a tyre, comprising sensors sensitive to the eddy currents generated by an exciting magnetic field in the crown reinforcement of the tyre.
These systems are placed on a roadway.
These systems are placed on a roadway.
[0009] However, it has been found that these measurement systems are not entirely satisfactory in some cases. This is because the reinforcement of some tyres is such that the crown of the tyre is insufficiently conductive to allow the establishment of eddy currents.
These measurement systems are therefore unsuitable for measuring the thickness of the treads of these tyres.
Brief description of the invention
These measurement systems are therefore unsuitable for measuring the thickness of the treads of these tyres.
Brief description of the invention
[0010] One object of the invention is a system for measuring the thickness of a layer of rubber material of a tyre, the layer comprising a face joined to an adjacent reinforcement made with at least one material having a magnetic permeability greater than the magnetic permeability of air, and a free face in contact with the air, the system comprising a sensor capable of measuring the distance d between the joined face and the free face of the layer of rubber material. This system is characterized in that the sensor comprises a single excitation and measurement coil, and in that the excitation frequency and power are such that the inductance at the terminals of the coil increases when the distance d decreases.
[0011] According to one object of the invention, the sensor of the measurement system has the advantage of operating in reluctance mode, and therefore with a lower coil excitation frequency for a given power than in the case of a similar sensor operating in a mode sensitive to eddy currents.
[0012] Measurement in reluctance mode also makes use of the magnetic permeability of the adjacent reinforcement, and has been found to provide high measurement sensitivity to any variation of the distance d.
[0013] Preferably, the coil of the sensor is positioned around, or is surrounded by, a material having high electrical resistivity and high magnetic permeability.
[0014] The presence of this material with high electrical resistivity and high magnetic permeability, such as a ferrite, has the advantage of localizing the magnetic field lines and thus providing a more localized measurement of layer thickness.
[0015] The ferrite may be U-shaped.
[0016] The coil is then preferably positioned around one of the lateral branches of the U.
[0017] Alternatively, the coil may be positioned around the bottom of the U of the ferrite.
[0018] In this embodiment, the range of the sensor can be improved simply by increasing the spacing between the two ends of the U.
[0019] This range may also be increased by increasing the cross section of the poles formed by the two parallel bars of the U-shaped circuit.
[0020] According to another embodiment, the excitation and measurement coil is positioned around an E-shaped material having high electrical resistivity and high magnetic permeability.
[0021] In this embodiment, the coil is advantageously positioned around the central bar of the E.
[0022] In this embodiment, the range of the sensor can be improved simply by increasing the spacing between the central bar of the E and its two outer ends.
[0023] This range may also be increased by increasing the cross section of the poles formed by the three parallel bars of the E-shaped circuit.
[0024] According to a third embodiment, the excitation and measurement coil is positioned around a material having high electrical resistivity and high magnetic permeability, the material having an axis of symmetry and being E-shaped as seen in any axial section.
[0025] In this embodiment, known as a "potted" arrangement, the coil is positioned around the central axis of the magnetic circuit.
[0026] In this embodiment, the range of the sensor may be increased simply by increasing the outside diameter of the pot structure, so that the spacing between the central pole and the outer pole becomes greater.
[0027] This range may also be increased by increasing the cross section of the two poles of the pot structure.
[0028] This axisymmetrical embodiment has the advantage of being insensitive to the orientation of the metal cords forming the adjacent reinforcement. The sensor is therefore insensitive to the anisotropy of this adjacent layer.
[0029] Advantageously, the excitation and measurement coil is supplied by an alternating power source.
[0030] When an alternating power supply frequency is used, it is advantageous to limit this to not more than 150 kHz, thereby greatly limiting the generation of eddy currents in the adjacent reinforcement of the layer. Additionally, if a frequency of 10 kHz is exceeded, the conventional noises measured by an antenna in the near field can be avoided.
[0031] Furthermore, as the supply frequency increases for a given current, the time resolution of the measurement improves. Finally, increasing the frequency makes it possible to reduce the measurement time, which has a favourable effect on the power consumption of the whole system.
[0032] It has been found to be advantageous to use a supply frequency in the range from 40 to 80 kHz.
[0033] In order to evaluate the distance d between the sensor and the metal tyre reinforcement, it is possible to measure the complex impedance or only a part of this impedance, such as the resistance or inductance.
[0034] It is also possible to measure the phase or the modulus of the complex impedance.
[0035] Advantageously, the inductance of the coil is measured.
[0036] For example, the inductance of the coil may be measured by means of the following formula:
U = L(di/dt)
U = L(di/dt)
[0037] To do this, the coil can be supplied with a known stationary sinusoidal current, enabling the derivative with respect to time to be precisely known, and a device for measuring the amplitude of the voltage at the terminals of the coil can be used.
[0038] This device for measuring the voltage amplitude at the terminals of the coil may measure the voltage continuously or may use an amplitude demodulation system.
[0039] The measurement system is advantageously positioned in an electrically non-to conductive casing whose materials have a magnetic susceptibility equal to zero or sufficiently low to be similar to those of air or a vacuum.
[0040] Preferably, the coil has an axis of sensitivity and the casing has a face for application against the free face of the layer whose thickness is to be measured, and the application face of the casing is perpendicular to the axis of sensitivity of the coil.
[0041] The casing may be a portable casing.
[0042] In this case, the measurement system according to one object of the invention may be used for measuring the thickness of rubber material of a sidewall or of an internal rubber element of a tyre. This measurement can be performed during the manufacture of the tyre or after the completion of this operation.
[0043] The casing may also be suitable for positioning on, or embedding in, a roadway.
[0044] In this case, the measurement system is preferably used for measuring the thickness of remaining rubber material on a tyre tread.
[0045] Evidently, the excitation and measurement coil of the measurement system according to one object of the invention may be formed by a plurality of coils connected in series or in parallel.
[0046] The invention is particularly applicable to tyres having metal reinforcers in their crowns and/or their carcass plies, such as those to be fitted on vehicles of the passenger or SUV ("Sport Utility Vehicle") type, or on industrial vehicles selected from among vans, heavy transport vehicles ¨i.e. light rail vehicles, buses, heavy road transport vehicles (lorries, tractors and trailers), and off-road vehicles such as civil engineering vehicles¨, and other transport or handling vehicles.
Description of the Drawings 100471 The attached figures show a number of embodiments of a measurement system according to one object of the invention, taking as the principal example the application of the invention to the measurement of the thickness of tyre treads:
- Figure 1 is a perspective view of a vehicle, a tyre of which is passing over a casing comprising a measurement system according to one object of the invention;
- Figure 2 shows a casing with a measurement system;
- Figure 3 shows a cross section of a tyre in contact with the casing of the measurement system;
- Figure 4 shows the operating principle of a measurement system in the case of an air-cored coil, in the absence (a) and in the presence (b) of a metal plate;
- Figure 5 shows schematically an example of the operation of the measurement system in the case of a coil with a U-shaped ferrite element;
- Figure 6 shows an alternative embodiment of the system of Figure 5;
- Figure 7 shows a second embodiment with an E-shaped ferrite element;
- Figure 8 shows a third embodiment with a pot-shaped ferrite element; and - Figure 9 shows schematically a structure of the electronic circuitry of a measurement system.
Detailed description of the invention 100481 Figure 1 shows a vehicle 5 whose tyre 8 is running over a casing 6 comprising a wear measurement system. The drawing shows a passenger vehicle, but the measurement system can also be used for any other vehicle, such as a heavy transport vehicle or a coach.
The remaining thickness of rubber material on the tread of the tyre 8 is measured when the tyre runs over the casing 6, without any need to stop the vehicle or remove the tyre from the vehicle.
[0049] Figure 2 shows a casing 12 according to one of the objects of the invention. This casing takes the form of a portable assembly which can be placed on a roadway.
It has a substantially trapezoidal cross section. The casing comprises two inclined portions, namely an access ramp 15 and an exit ramp 16. Between these two portions there is a substantially horizontal portion 18. The portion 18 of the casing 12 protects a sensor or a row of sensors 50 for making the distance measurements. The base 20 of the casing is placed against the roadway and gives the casing the necessary stability during the operation of the system.
The casing 12 also comprises electronic circuitry 40 with a power source which supplies the sensors 50 with alternating current. The measurements are made when the tyre contact area rests on the horizontal portion 18. This horizontal portion is the face of the casing which is applied to the surface of the tyre tread. The casing 12 is made of a non-conductive material whose magnetic properties are similar to those of air, to avoid interference with the measurements.
[0050] According to other embodiments, the casing may be embedded in a roadway or may have suitable dimensions and weight for application against a sidewall or an internal rubber element of a tyre.
[0051] The measurement of the thickness of remaining rubber material on a tyre tread is illustrated in Figure 3. This drawing shows a partial cross section of a tyre 8 bearing on the application face 18 of a casing 12. The tyre 8 comprises, notably, a tread 80 with patterns 82, a crown reinforcement 84 consisting of two or more plies of metal reinforcers (not shown), and sidewalls 86. The casing 12 comprises an application face 18, a base 20 and a row of sensors 50. The running surface 88 of the tread 80 bears against the application face 18 of the casing 12.
[0052] The sensors 50 measure, as will be explained below, the distance DI
which separates them from the metal reinforcement 84 of the crown of the tyre 8. DI
has three components. Two of these components are fixed, namely the distance D2 which separates the bases of the patterns 82 from the reinforcement 84, and the distance D3 which separates the sensors 50 from the application face 18 of the casing 12. One component is variable with the degree of wear of the tread, namely d, which corresponds to the remaining thickness of the tread. Thus:
d = D1- D2 - D3 [0053] The distance D2 can be known on the basis of the identification of the type of tyre being measured. This identification may be manual or automatic, being performed, for example, by retrieving identification data recorded in a transponder such as an RFID
device incorporated in the tyre structure.
[0054] Figure 4 shows the operating principle of the sensor of a measurement system according to one object of the invention.
[0055] Figure 4(a) shows an air-cored coil 10 with an axis of symmetry and sensitivity A.
When the terminals of the coil are supplied with a direct current, the magnetic field lines 54 emitted by this device extend in the air all around the coil, as shown schematically in Fig. 4(a).
[0056] If a metal reinforcement 14, which is a good magnetic field conductor and a poor electrical conductor, such as a crown ply of a tyre consisting of parallel metal reinforcers embedded in two layers of low-conductivity rubber material, is brought towards this device, the field lines will naturally attempt to pass through this metal reinforcement rather than through the air, because the reluctance of air is greater than that of the metal reinforcement. A localization of the magnetic field lines 54 through the metal reinforcement 14 can be observed.
[0057] The result is that the magnetic flux density will increase in the area located between the coil 10 and the metal reinforcement.
[0058] Thus the variation of the position of the metal reinforcement 14 relative to the coil 10 can be measured by measuring the variation of the inductance of the coil 10.
[0059] Figure 5 shows a schematic example of the operation of an embodiment of a measurement system in the case of a coil and a U-shaped ferrite element.
[0060] The layer 21 whose thickness d is to be measured comprises a layer of rubber material 24 adjacent to a reinforcement 22 formed by reinforcers whose magnetic permeability is greater than the magnetic permeability of air, such as those normally used for carcass plies or crown plies of tyres, notably those of heavy transport vehicles.
[0061] The casing 12 of the measurement system comprises a sensor 50 which comprises a coil 10 positioned around one of the lateral branches 36 of a U-shaped ferrite element 30.
The presence of the ferrite 30 makes it possible to localize the flow of the magnetic field lines through it and thus localize the measurement area. The two bars of the U
are spaced apart by a distance 11.
[0062] The casing 12 has its application face 18 bearing against the free face 26 of the layer 21.
[0063] According to an essential characteristic of the measurement system, the excitation frequency and power of the coil 10 are such that the inductance at the terminals of the coil increases when the distance d decreases.
[0064] Thus the operating mode of the sensor is a reluctance mode, and is therefore related to the magnetic permeability of the different parts of the magnetic circuit.
[0065] The magnetic permeability of the rubber material is much lower than that of the adjacent reinforcement, which is itself lower than that of the ferrite.
[0066] Consequently, the reluctance of the layer 24 of rubber material is much higher than that of the adjacent reinforcement 22, which is itself higher than that of the ferrite 30.
This means that the variation of inductance measured at the terminals of the coil 10 is mainly due to the variation of the distance d which is the thickness of the layer of rubber material, since any variation in the reluctance of the adjacent reinforcement caused, for example, by the number of reinforcers or their construction has only a minor effect on the accuracy of the measurement. The accuracy and sensitivity of this sensor in reluctance mode are therefore good. The range of the sensor is dependent on the distance 11, which is the distance between the two bars of the U, and on the cross section of the poles formed by these two parallel bars.
[0067] Figures 6 to 8 show alternative embodiments of sensors.
[0068] In Figure 6, the sensor 60 comprises a U-shaped ferrite element 64 and a coil 62 positioned around the central bar of the U.
[0069] In Figure 7, the sensor 70 comprises an E-shaped ferrite element 74 and a coil 72 positioned around the central bar of the E.
[0070] In Figure 8, the sensor 90 comprises a pot-shaped ferrite element 94 with an axis of symmetry and a central bar positioned substantially along this axis of symmetry, and a coil 92 positioned around the central bar of the pot. Figure 8(a) shows a perspective view of the sensor, and Figure 8(b) shows a cross section along the axis of symmetry.
[0071] This pot structure has the advantage of being insensitive to the anisotropy of the metallic architecture inside the tyre.
[0072] Figure 9 shows an example of the structure of the electronic circuitry 40 for measuring the thickness of a layer of tyre rubber.
[0073] This electronic circuitry is formed by a "sensor module" 100 and a "motherboard"
120. It can therefore be used to measure the thickness of a layer at a single point.
[0074] In order to extend the principle of this arrangement to a system consisting of multiple sensors, it is simply necessary to use a plurality of "sensor modules", all connected to the same "motherboard".
[0075] In reluctance mode, the inductance L of the sensor increases when the distance d between the sensor and an adjacent layer, formed by metal tyre cords, decreases. The purpose of this electronic circuitry is therefore to measure the inductance L
of the sensor coil, so that this distance between the sensor and the adjacent layer can be deduced.
[0076] The "sensor module" 100 is formed, in part, by a sensor 102 as described above, supplied with a current I which is considered to be the phase reference (4)=0). This current 1 is generated by a current amplifier 104, which is itself driven by an oscillator 106 whose frequency is set by a time base 107. The amplifier, oscillator and time base form part of the "sensor module-.
[0077] The voltage U for the phase 4, which is non-zero relative to the current I, collected at the terminals of the sensor, is first amplified by the amplifier 108 and then injected into a double demodulator 110, together with the output signal of the oscillator 106.
[0078] At the output of the demodulator 110, the signals X and Y are found, representing the two complex components describing the voltage at the terminals of the sensor, such that:
U = KVX2 + Y2 where K is a factor dependent on the amplification present along the electronic circuit.
[0079] The two signals X and Y are then filtered by the filters 112 and digitized by means of analogue/digital converters (ADC) 114, and are then injected into the microcontroller 122 of the "motherboard" 120.
[0080] The microcontroller 122 deduces from X and Y the value of the inductance L of the sensor 102. It initially calculates the value of the amplitude of the voltage U at the terminals of the sensor, using the above formula.
[0081] In a second stage, it deduces from this value the inductance L of the sensor coil, the value of the current I injected into the sensor being known, using the following formula:
L = ___________________________________ di 1 I dt [0082] The motherboard is also provided with a number of additional functional units, namely:
= a memory 124 for recording the measurements made by the sensor 102;
= an RFID decoder 126 for identifying the tyre, by means of an antenna 128, if this can be done by using the presence of an RFID device incorporated in the tyre structure;
= a wireless communication module 130 for sending data over a distance, via a supplementary antenna 132; and = a power supply 134 distributing the current required for the whole system from a battery 136.
The assembly is able to perform numerous measurements on tyres without a battery change, giving the system several years of service life without human intervention.
Description of the Drawings 100471 The attached figures show a number of embodiments of a measurement system according to one object of the invention, taking as the principal example the application of the invention to the measurement of the thickness of tyre treads:
- Figure 1 is a perspective view of a vehicle, a tyre of which is passing over a casing comprising a measurement system according to one object of the invention;
- Figure 2 shows a casing with a measurement system;
- Figure 3 shows a cross section of a tyre in contact with the casing of the measurement system;
- Figure 4 shows the operating principle of a measurement system in the case of an air-cored coil, in the absence (a) and in the presence (b) of a metal plate;
- Figure 5 shows schematically an example of the operation of the measurement system in the case of a coil with a U-shaped ferrite element;
- Figure 6 shows an alternative embodiment of the system of Figure 5;
- Figure 7 shows a second embodiment with an E-shaped ferrite element;
- Figure 8 shows a third embodiment with a pot-shaped ferrite element; and - Figure 9 shows schematically a structure of the electronic circuitry of a measurement system.
Detailed description of the invention 100481 Figure 1 shows a vehicle 5 whose tyre 8 is running over a casing 6 comprising a wear measurement system. The drawing shows a passenger vehicle, but the measurement system can also be used for any other vehicle, such as a heavy transport vehicle or a coach.
The remaining thickness of rubber material on the tread of the tyre 8 is measured when the tyre runs over the casing 6, without any need to stop the vehicle or remove the tyre from the vehicle.
[0049] Figure 2 shows a casing 12 according to one of the objects of the invention. This casing takes the form of a portable assembly which can be placed on a roadway.
It has a substantially trapezoidal cross section. The casing comprises two inclined portions, namely an access ramp 15 and an exit ramp 16. Between these two portions there is a substantially horizontal portion 18. The portion 18 of the casing 12 protects a sensor or a row of sensors 50 for making the distance measurements. The base 20 of the casing is placed against the roadway and gives the casing the necessary stability during the operation of the system.
The casing 12 also comprises electronic circuitry 40 with a power source which supplies the sensors 50 with alternating current. The measurements are made when the tyre contact area rests on the horizontal portion 18. This horizontal portion is the face of the casing which is applied to the surface of the tyre tread. The casing 12 is made of a non-conductive material whose magnetic properties are similar to those of air, to avoid interference with the measurements.
[0050] According to other embodiments, the casing may be embedded in a roadway or may have suitable dimensions and weight for application against a sidewall or an internal rubber element of a tyre.
[0051] The measurement of the thickness of remaining rubber material on a tyre tread is illustrated in Figure 3. This drawing shows a partial cross section of a tyre 8 bearing on the application face 18 of a casing 12. The tyre 8 comprises, notably, a tread 80 with patterns 82, a crown reinforcement 84 consisting of two or more plies of metal reinforcers (not shown), and sidewalls 86. The casing 12 comprises an application face 18, a base 20 and a row of sensors 50. The running surface 88 of the tread 80 bears against the application face 18 of the casing 12.
[0052] The sensors 50 measure, as will be explained below, the distance DI
which separates them from the metal reinforcement 84 of the crown of the tyre 8. DI
has three components. Two of these components are fixed, namely the distance D2 which separates the bases of the patterns 82 from the reinforcement 84, and the distance D3 which separates the sensors 50 from the application face 18 of the casing 12. One component is variable with the degree of wear of the tread, namely d, which corresponds to the remaining thickness of the tread. Thus:
d = D1- D2 - D3 [0053] The distance D2 can be known on the basis of the identification of the type of tyre being measured. This identification may be manual or automatic, being performed, for example, by retrieving identification data recorded in a transponder such as an RFID
device incorporated in the tyre structure.
[0054] Figure 4 shows the operating principle of the sensor of a measurement system according to one object of the invention.
[0055] Figure 4(a) shows an air-cored coil 10 with an axis of symmetry and sensitivity A.
When the terminals of the coil are supplied with a direct current, the magnetic field lines 54 emitted by this device extend in the air all around the coil, as shown schematically in Fig. 4(a).
[0056] If a metal reinforcement 14, which is a good magnetic field conductor and a poor electrical conductor, such as a crown ply of a tyre consisting of parallel metal reinforcers embedded in two layers of low-conductivity rubber material, is brought towards this device, the field lines will naturally attempt to pass through this metal reinforcement rather than through the air, because the reluctance of air is greater than that of the metal reinforcement. A localization of the magnetic field lines 54 through the metal reinforcement 14 can be observed.
[0057] The result is that the magnetic flux density will increase in the area located between the coil 10 and the metal reinforcement.
[0058] Thus the variation of the position of the metal reinforcement 14 relative to the coil 10 can be measured by measuring the variation of the inductance of the coil 10.
[0059] Figure 5 shows a schematic example of the operation of an embodiment of a measurement system in the case of a coil and a U-shaped ferrite element.
[0060] The layer 21 whose thickness d is to be measured comprises a layer of rubber material 24 adjacent to a reinforcement 22 formed by reinforcers whose magnetic permeability is greater than the magnetic permeability of air, such as those normally used for carcass plies or crown plies of tyres, notably those of heavy transport vehicles.
[0061] The casing 12 of the measurement system comprises a sensor 50 which comprises a coil 10 positioned around one of the lateral branches 36 of a U-shaped ferrite element 30.
The presence of the ferrite 30 makes it possible to localize the flow of the magnetic field lines through it and thus localize the measurement area. The two bars of the U
are spaced apart by a distance 11.
[0062] The casing 12 has its application face 18 bearing against the free face 26 of the layer 21.
[0063] According to an essential characteristic of the measurement system, the excitation frequency and power of the coil 10 are such that the inductance at the terminals of the coil increases when the distance d decreases.
[0064] Thus the operating mode of the sensor is a reluctance mode, and is therefore related to the magnetic permeability of the different parts of the magnetic circuit.
[0065] The magnetic permeability of the rubber material is much lower than that of the adjacent reinforcement, which is itself lower than that of the ferrite.
[0066] Consequently, the reluctance of the layer 24 of rubber material is much higher than that of the adjacent reinforcement 22, which is itself higher than that of the ferrite 30.
This means that the variation of inductance measured at the terminals of the coil 10 is mainly due to the variation of the distance d which is the thickness of the layer of rubber material, since any variation in the reluctance of the adjacent reinforcement caused, for example, by the number of reinforcers or their construction has only a minor effect on the accuracy of the measurement. The accuracy and sensitivity of this sensor in reluctance mode are therefore good. The range of the sensor is dependent on the distance 11, which is the distance between the two bars of the U, and on the cross section of the poles formed by these two parallel bars.
[0067] Figures 6 to 8 show alternative embodiments of sensors.
[0068] In Figure 6, the sensor 60 comprises a U-shaped ferrite element 64 and a coil 62 positioned around the central bar of the U.
[0069] In Figure 7, the sensor 70 comprises an E-shaped ferrite element 74 and a coil 72 positioned around the central bar of the E.
[0070] In Figure 8, the sensor 90 comprises a pot-shaped ferrite element 94 with an axis of symmetry and a central bar positioned substantially along this axis of symmetry, and a coil 92 positioned around the central bar of the pot. Figure 8(a) shows a perspective view of the sensor, and Figure 8(b) shows a cross section along the axis of symmetry.
[0071] This pot structure has the advantage of being insensitive to the anisotropy of the metallic architecture inside the tyre.
[0072] Figure 9 shows an example of the structure of the electronic circuitry 40 for measuring the thickness of a layer of tyre rubber.
[0073] This electronic circuitry is formed by a "sensor module" 100 and a "motherboard"
120. It can therefore be used to measure the thickness of a layer at a single point.
[0074] In order to extend the principle of this arrangement to a system consisting of multiple sensors, it is simply necessary to use a plurality of "sensor modules", all connected to the same "motherboard".
[0075] In reluctance mode, the inductance L of the sensor increases when the distance d between the sensor and an adjacent layer, formed by metal tyre cords, decreases. The purpose of this electronic circuitry is therefore to measure the inductance L
of the sensor coil, so that this distance between the sensor and the adjacent layer can be deduced.
[0076] The "sensor module" 100 is formed, in part, by a sensor 102 as described above, supplied with a current I which is considered to be the phase reference (4)=0). This current 1 is generated by a current amplifier 104, which is itself driven by an oscillator 106 whose frequency is set by a time base 107. The amplifier, oscillator and time base form part of the "sensor module-.
[0077] The voltage U for the phase 4, which is non-zero relative to the current I, collected at the terminals of the sensor, is first amplified by the amplifier 108 and then injected into a double demodulator 110, together with the output signal of the oscillator 106.
[0078] At the output of the demodulator 110, the signals X and Y are found, representing the two complex components describing the voltage at the terminals of the sensor, such that:
U = KVX2 + Y2 where K is a factor dependent on the amplification present along the electronic circuit.
[0079] The two signals X and Y are then filtered by the filters 112 and digitized by means of analogue/digital converters (ADC) 114, and are then injected into the microcontroller 122 of the "motherboard" 120.
[0080] The microcontroller 122 deduces from X and Y the value of the inductance L of the sensor 102. It initially calculates the value of the amplitude of the voltage U at the terminals of the sensor, using the above formula.
[0081] In a second stage, it deduces from this value the inductance L of the sensor coil, the value of the current I injected into the sensor being known, using the following formula:
L = ___________________________________ di 1 I dt [0082] The motherboard is also provided with a number of additional functional units, namely:
= a memory 124 for recording the measurements made by the sensor 102;
= an RFID decoder 126 for identifying the tyre, by means of an antenna 128, if this can be done by using the presence of an RFID device incorporated in the tyre structure;
= a wireless communication module 130 for sending data over a distance, via a supplementary antenna 132; and = a power supply 134 distributing the current required for the whole system from a battery 136.
The assembly is able to perform numerous measurements on tyres without a battery change, giving the system several years of service life without human intervention.
Claims (21)
1. System for measuring the thickness of a layer of rubber material of a tyre, said layer comprising a face joined to an adjacent reinforcement made with at least one material having a magnetic permeability greater than the magnetic permeability of air, and a free face in contact with the air, said system comprising a sensor capable of measuring the distance d between the joined face and the free face of said layer of rubber material, characterized in that the sensor comprises a single excitation and measurement coil, and in that the excitation frequency and power of said coil are such that the inductance at the terminals of said coil increases when the distance d decreases.
2. Measurement system according to Claim 1, wherein the coil of the sensor is positioned around, or is surrounded by, a material having high electrical resistivity and high magnetic permeability.
3. Measurement system according to Claim 2, wherein said material having high electrical resistivity and high magnetic permeability is U-shaped.
4. Measurement system according to Claim 3, wherein said coil is positioned around one of the lateral branches of the U.
5. Measurement system according to Claim 3, wherein said coil is positioned around the bottom of the U.
6. Measurement system according to Claim 2, wherein said material having high electrical resistivity and high magnetic permeability is E-shaped.
7. Measurement system according to Claim 2, wherein said material having high electrical resistivity and high magnetic permeability has an axis of symmetry and is E-shaped in any axial cross section.
8. Measurement system according to one of Claims 6 and 7, wherein said coil is positioned around the central bar of the E.
9. Measurement system according to any of Claims 2 to 8, wherein the material having high electrical resistivity and high magnetic permeability is a ferrite.
10. Measurement system according to any of the preceding claims, wherein said excitation and measurement coil is supplied by an alternating power source.
11. Measurement system according to Claim 10, wherein said excitation and measurement coil is supplied by an alternating power source having a frequency of more than 10 kHz and less than 150 kHz.
12. Measurement system according to Claim 11, wherein said excitation and measurement coil is supplied by an alternating power source having a frequency in the range from 40 kHz to 80 kHz.
13. Measurement system as claimed in any of the preceding claims, wherein the complex impedance, or a part of this impedance such as the resistance, the inductance, the phase or the modulus of the complex impedance, is measured.
14. Measurement system according to Claim 13, wherein the inductance of the coil is measured.
15. Measurement system according to any of the preceding claims, such that it is positioned inside an electrically non-conductive casing and is made of materials with a magnetic susceptibility equal to zero or sufficiently low to be similar to that of air or a vacuum.
16. Measurement system according to Claim 15, wherein the coil has an axis of sensitivity and said casing has a face for application against the free face of said layer, and said application face is perpendicular to the axis of sensitivity of the coil.
17. Measurement system according to one of Claims 15 and 16, such that said casing is a portable casing.
18. Measurement system according to one of Claims 15 and 16, such that said casing can be positioned on, or embedded in, a roadway.
19. Measurement system according to any of the preceding claims, wherein the excitation and measurement coil is formed by a plurality of coils connected in series or in parallel.
20. Use of the measurement system according to any of the preceding claims for measuring the thickness of remaining rubber material on a tread of said tyre.
21. Use of the measurement system according to any of Claims 1 to 17 for measuring the thickness of rubber material of a sidewall or internal rubber element of said tyre.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR1355850A FR3007516B1 (en) | 2013-06-20 | 2013-06-20 | SYSTEM FOR MEASURING THE THICKNESS OF A GUM LAYER OF A TIRE |
| FR1355850 | 2013-06-20 | ||
| PCT/EP2014/062998 WO2014202746A1 (en) | 2013-06-20 | 2014-06-20 | System for measuring the thickness of a layer of rubber for a tyre |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2914522A1 true CA2914522A1 (en) | 2014-12-24 |
Family
ID=49474544
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2914522A Abandoned CA2914522A1 (en) | 2013-06-20 | 2014-06-20 | System for measuring the thickness of a layer of rubber for a tyre |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP3011264B1 (en) |
| JP (1) | JP2016529479A (en) |
| CA (1) | CA2914522A1 (en) |
| FR (1) | FR3007516B1 (en) |
| MX (1) | MX351684B (en) |
| WO (1) | WO2014202746A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113302486A (en) * | 2018-12-11 | 2021-08-24 | 倍耐力轮胎股份公司 | Method and apparatus for checking the electrical conductivity of a tyre being processed |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2019211430A (en) * | 2018-06-08 | 2019-12-12 | 株式会社ブリヂストン | Method for detecting distortion of rubber member and device thereof, and tire for detecting internal distortion |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4652820A (en) * | 1983-03-23 | 1987-03-24 | North American Philips Corporation | Combined position sensor and magnetic motor or bearing |
| JPH04343001A (en) * | 1991-05-20 | 1992-11-30 | Ishikawajima Harima Heavy Ind Co Ltd | Method and apparatus for inspecting position of cooling hole at end of turbine blade |
| JP2589420B2 (en) * | 1991-07-19 | 1997-03-12 | 古河電気工業株式会社 | Method and apparatus for inspecting conductive film |
| JPH07110203A (en) * | 1993-10-08 | 1995-04-25 | Japan Atom Energy Res Inst | Method and instrument for measuring thickness of build-up weld of reactor pressure vessel |
| DE19745734B4 (en) * | 1997-10-16 | 2007-07-05 | Bayerische Motoren Werke Ag | Abrasion sensor for detecting the tread depth of a tire of motor vehicles |
| JP4610062B2 (en) * | 2000-09-14 | 2011-01-12 | 株式会社ブリヂストン | Buffing method |
| US7112960B2 (en) * | 2003-07-31 | 2006-09-26 | Applied Materials, Inc. | Eddy current system for in-situ profile measurement |
| JP2005315734A (en) * | 2004-04-28 | 2005-11-10 | Jfe Steel Kk | Method and instrument for measuring displacement of ferromagnetic body |
| US20100139383A1 (en) * | 2006-11-17 | 2010-06-10 | Treadcheck Limited | Apparatus and method for monitoring tyre wear |
| US7578180B2 (en) | 2007-06-29 | 2009-08-25 | The Goodyear Tire & Rubber Company | Tread depth sensing device and method for measuring same |
| GB2470779A (en) * | 2009-06-05 | 2010-12-08 | Monitran Ltd | Eddy current proximity probe system and method of measuring that mitigates errors due to temperature fluctuations |
-
2013
- 2013-06-20 FR FR1355850A patent/FR3007516B1/en not_active Expired - Fee Related
-
2014
- 2014-06-20 EP EP14735491.4A patent/EP3011264B1/en active Active
- 2014-06-20 WO PCT/EP2014/062998 patent/WO2014202746A1/en active Application Filing
- 2014-06-20 MX MX2015016917A patent/MX351684B/en active IP Right Grant
- 2014-06-20 CA CA2914522A patent/CA2914522A1/en not_active Abandoned
- 2014-06-20 JP JP2016520504A patent/JP2016529479A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113302486A (en) * | 2018-12-11 | 2021-08-24 | 倍耐力轮胎股份公司 | Method and apparatus for checking the electrical conductivity of a tyre being processed |
Also Published As
| Publication number | Publication date |
|---|---|
| EP3011264A1 (en) | 2016-04-27 |
| JP2016529479A (en) | 2016-09-23 |
| WO2014202746A1 (en) | 2014-12-24 |
| EP3011264B1 (en) | 2019-01-09 |
| MX351684B (en) | 2017-10-25 |
| FR3007516A1 (en) | 2014-12-26 |
| FR3007516B1 (en) | 2017-04-28 |
| MX2015016917A (en) | 2016-04-04 |
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| EEER | Examination request |
Effective date: 20190410 |
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| FZDE | Discontinued |
Effective date: 20221012 |