WO2013017768A1

WO2013017768A1 - Extra-flat piezoelectric detector and sensor for sensing the passage of travelling vehicles

Info

Publication number: WO2013017768A1
Application number: PCT/FR2012/051672
Authority: WO
Inventors: Marcel Guwang; Mathieu POQUE; Alain Ramond; Marwan ZEIDAN; Antoine JAURÉGUIBERRY
Original assignee: Sterela
Priority date: 2011-07-29
Filing date: 2012-07-13
Publication date: 2013-02-07
Also published as: EP2737465A1; FR2978563A1; FR2978563B1

Abstract

The invention relates to a piezoelectric detector including at least one piezoelectric sensing element inserted into an assembly suitable for transmitting pressure forces to each piezoelectric sensing element, said assembly including a rolling plate (16) having a surface (17) for measuring the pressure forces along a measuring direction perpendicular to said measurement surface, and a resiliently deformable device (22) suitable for subjecting each piezoelectric sensing element to compressive prestressing. The resiliently deformable device (22) has a height along the measurement direction that is less than the largest dimension thereof that is orthogonal to said measurement direction. The invention also relates to a sensor for sensing the passage of travelling vehicles, including a plurality of piezoelectric detectors according to the invention that are juxtaposed on a single base.

Description

PIEZOELECTRIC DETECTOR EXTRAPLAT AND PASSING SENSOR

OF ROLLING VEHICLES

The invention relates to an ultra-flat piezoelectric detector, and to a moving vehicle passage sensor comprising a plurality of ultra-flat piezoelectric detectors associated with a common support intended to be implanted on the ground across a passageway of said vehicles.

US5265481 discloses a dynamic force measurement sensor supposed to allow the determination of the axle load, speed, and weight of a vehicle. This sensor comprises a hollow tube incorporating vertically preloaded piezoelectric elements distributed along the tube and which, for a maximum resolution, can be connected in parallel to a signal processing device located on the side of the road. This tube is buried across the road, with a filling material that overcomes it, and rods or bands of transmission of forces between the surface of the road and the tube, the latter elements still being the subject of experiments. as of the filing date of this document. For the measurement of speed, such sensors are arranged 10 m apart from each other along the road.

Such a known sensor has several disadvantages. Firstly, it is in practice insufficiently precise and reliable to deliver a value of effort that can be exploited to reliably determine whether or not the vehicle meets predetermined regulations, for example maximum axle load standards or per vehicle. In particular, the values delivered by a sensor system 10 m distant with respect to the weight of a vehicle are not very precise.

This lack of precision derives in particular from the fact that the different piezoelectric elements of the sensor are not mechanically independent of each other, so that each piezoelectric sensitive element in such a known sensor delivers a signal which is not solely dependent on the vertical load applied above this piezoelectric sensing element. For example, when a vehicle wheel passes over a piezoelectric sensitive element, the other adjacent piezoelectric elements of the sensor necessarily also deliver a signal, since the vertical force applied by the wheel is transmitted to these adjacent piezoelectric elements via the common support tube of the different elements. Similarly, given the geometry of this sensor, the piezoelectric elements begin to deliver a signal well before the wheel arrives at the vertical of the sensor, due to the deformation of the road.

This defect is not compensated by the fact that, as indicated in this document, it is planned to calibrate each piezoelectric sensitive element after mounting the sensor on the road. Indeed this calibration is also influenced by the mechanical dependence of the piezoelectric elements between them. It should be noted in this respect that it is not possible to calibrate this sensor known in the factory, before it is mounted on the road, because its encapsulation in the road influences the deformation modes of the common support tube, and therefore the calibration values of sensitive elements that are mechanically dependent on each other.

In addition, the weight value obtained from the speed measurement with two separate sensors of 10 m (or even a distance of the order of 2 m) presents a significant uncertainty, the vehicle being able to accelerate or brake strongly. between the two sensors.

US5461924 also discloses a measuring rail intended to be installed across a passageway for the dynamic detection of reaction forces acting on the surface, such as for example speed or other. This rail incorporating in particular a tabular force transmission structure incorporating sensitive elements in the form of piezoelectric plates, this tabular transmission structure being elastically deformable so as to exert prestressing on these sensitive elements. US 5942681 discloses a truck tire pressure measuring rail comprising a plurality of force measuring elements, each force measuring element comprising an upper rolling plate, a lower plate, and a tabular structure transmission of forces connecting the upper rolling plate to the lower plate via a network of crystals as sensitive elements. Such a tabular structure of elastically deformable force transmission has a large height. However, the inventors have determined that such a height in fact significantly affects the accuracy of the measurement of the efforts at each sensing element. Indeed, this important height implies that horizontal shear forces are reflected with a significant lever at each sensing element. It also implies that the detector has a large transverse lateral contact zone with the remainder of the road surface, so that the deformations and vertical stresses imparted to the road surface at the moment of the passage of a vehicle wheel also induce parasitic forces, especially in terms of vertical shear, reflected on the sensitive elements. The same is true of adjacent detectors which also induce parasitic forces by vertical and / or horizontal shear due to the large height of the deformable tabular part. In addition, such a complex shaped tabular structure must be manufactured with very high accuracy and is therefore expensive.

The invention therefore aims to overcome these drawbacks by proposing a piezoelectric detector that makes it possible to provide signals with a high degree of accuracy, undisturbed by the deformations of the peripheral environment close to the detector, or by the non-orthogonal components-notably non-vertical- pressure forces applied to the detector.

It also aims at proposing a sensor for the passage of rolling vehicles capable of delivering signals of high accuracy (in particular less than 5%, in particular of the order of 2%) and of high reliability, making it possible in particular to determine load values with a sufficiently good accuracy to determine from these values whether the vehicle meets a predetermined regulatory constraint or not.

More particularly, the invention aims to provide such a piezoelectric sensor and such a sensor for determining sufficiently accurately selected load values among the axle load, the instantaneous speed of the vehicle, the total weight of the vehicle. The invention also aims at providing such a sensor for delivering, in a sufficiently precise and reliable manner, dimensional data of the vehicle, in particular chosen from the width of each wheel, the distance between the axles (the wheelbase), the track (distance between the two wheels of the same axle), the distinction between a narrow tire and a wide tire, the distinction between twin wheels and single wheels, and the detection of under-inflation.

The invention also aims at providing such a detector and such a sensor that are inexpensive in manufacturing, and whose integration in a passageway is simple, fast and inexpensive. The invention also aims at providing such a sensor which is less sensitive to integration defects in a passageway.

The invention also aims at providing a piezoelectric detector and a sensor that can be fully calibrated at the factory, before being mounted in a passageway.

To do this, the invention relates to a piezoelectric detector comprising at least one piezoelectric sensitive element interposed in an assembly capable of transmitting pressure forces to each piezoelectric sensitive element, said assembly comprising:

a plateau, called a rolling platform, having a planar face, called a measurement face, arranged to receive integrally said pressure forces exerted in a direction, called measuring direction, normal to the measuring face of this rolling plate,

an elastically deformable device capable of subjecting each piezoelectric sensitive element to a compressive prestress in said measurement direction,

characterized in that said elastically deformable device has a height in said measurement direction less than its largest dimension orthogonal to said measurement direction.

A detector according to the invention can be advantageously used in any situation and in any orientation to measure the pressure forces in any direction. Nevertheless, a detector according to the invention is more particularly (although not exclusively) advantageous with the measurement face of the horizontally oriented rolling plate, said measurement direction being vertical, and even more particularly in the context of measuring the pressure. vertical movement exerted by a vehicle wheel on a passageway. The invention therefore also relates more particularly to a piezoelectric detector adapted to be able to deliver an electrical signal, called a detection signal, representative of vertical pressure forces exerted on this piezoelectric detector-in particular by the passage of a vehicle wheel-comprising at least one piezoelectric sensitive element interposed in an assembly capable of transmitting said vertical pressure forces to each piezoelectric sensitive element, said assembly comprising:

a plateau, called a rolling platform, having an upper horizontal plane face, referred to as the measuring face, arranged to receive integrally the vertical pressure forces exerted on top of this rolling plate, in particular the vertical pressure forces resulting from the passage of a vehicle wheel rolling above this rolling plate, and for transmitting these vertical pressure forces to each piezoelectric sensing element of said piezoelectric detector,

- An elastically deformable device adapted to subject each piezoelectric sensitive element to a vertical compression prestress, characterized in that said elastically deformable device has a height less than its largest horizontal dimension.

Advantageously and according to the invention, said elastically deformable device has a height in said measurement direction (in particular in the vertical) less than half of the largest dimension, said larger orthogonal dimension, of said rolling plate orthogonal to said direction measurement (especially greater horizontal dimension) -in particular of the order of 10% to 20%, for example of the order of 12% to 15%, of said largest orthogonal dimension (especially horizontal) of said rolling plate- . In an advantageous embodiment of the invention, said largest orthogonal dimension (especially horizontal) of said rolling plate is less than 10 cm, in particular is of the order of 5 cm.

Advantageously and according to the invention, said elastically deformable device has a height in said measurement direction less than half of its largest dimension orthogonal to said measurement direction, for example of the order of 10% to 20%, for example in the order of 12% 15%, of its largest dimension orthogonally to said measurement direction. In particular, advantageously and according to the invention, said elastically deformable device has a height in said measurement direction of less than 15 mm, in particular between 3 mm and 10 mm.

In addition, advantageously and according to the invention, the rolling plate is of generally square shape with a side whose length is of the order of 5cm. However, nothing prevents other shapes and / or dimensions, depending on the applications, for example a rectangular rolling tray, or trapezoidal, or rhombus or any other polygon, regular or not, or other.

A detector according to the invention may in particular be dimensioned such that it has a total height between a soleplate supporting each piezoelectric sensitive element and said measurement face of said rolling plate (including a possible wear layer surmounting the plate rolling) less than 4 cm, for example of the order of 25mm.

A detector according to the invention is extra flat which has been found to provide optimum accuracy and sensitivity characteristics, particularly in the case where the detector is used in a sensor for moving vehicles. This results in particular that each piezoelectric sensitive element is substantially not disturbed by any parasitic shear forces in the directions orthogonal to said measurement direction (including horizontal shear forces) imparted on the rolling plate. In addition, the detector offers a reduced lateral surface of contact with its external environment, so that any shearing forces in said measurement direction (especially in the vertical direction) can occur in use-especially by deformation of the road surface and or by displacement or deformation of the adjacent detector (s) during the passage of a vehicle wheel are also not likely to affect the accuracy of the measurement of the pressure forces exerted over the rolling. More generally, the low height of the deformable part of the detector gives it greater reliability (only the pressure forces in the vertical direction being essentially measured), greater robustness and better stability, facilitates its implementation and integration into any system and its use. In addition, advantageously and according to the invention said assembly connects the rolling plate and a sole supporting each piezoelectric sensitive element, and the assembly between the rolling plate and the sole is adapted to absorb the horizontal shear forces (or more generally orthogonal to said measurement direction) without transmitting them to each piezoelectric sensing element. In particular, advantageously and according to the invention, said elastically deformable device is adapted to absorb any shear forces orthogonal to said measurement direction (in particular horizontal shear forces) and / or any shear forces in said measurement direction ( in particular vertical shear forces). According to a variant of the invention, this function is exerted by the elastically deformable device itself only, which is adapted for this purpose, in particular to prevent any relative displacement of the rolling plate relative to this sole in the horizontal directions (or more generally orthogonal to said measurement direction). According to another variant of the invention, the rolling plate is further guided relative to the lower sole independently of said elastically deformable device, so as to prevent any relative displacement of the rolling plate relative to this sole in the horizontal directions ( or more generally orthogonal to said measurement direction). For this purpose, said assembly is arranged to form abutments in the horizontal directions (or more generally orthogonal to said measurement direction) between the rolling plate and the sole.

In addition, advantageously a detector according to the invention comprises a central receiving housing of an electronic circuit electrically connected to each piezoelectric sensitive element and adapted to be able to deliver an electrical signal, said detection signal, representative of said pressure forces. Advantageously and according to the invention, this central receiving housing is formed by said elastically deformable device and / or each piezoelectric sensitive element which is / are arranged (s) for this purpose.

Advantageously and according to the invention, said electronic circuit can be formed essentially of a charge amplifier and be adapted to generating the detection signal according to a predetermined value gain, and for reliably compensating the various offsets of the reference signal absolute value, which compensation simultaneously suppresses the low frequency variations of the signal, corrects the slack or progressive drifts of the reference value, does not require the addition of electronic circuits complementary to the charge amplifier, is compatible with the operation of a sensor for moving vehicles, and in particular with sudden and large variations in amplitude and in frequency from one cycle to another, such as those due to pyroelectricity, and is simple and inexpensive to implement.

This electronic circuit advantageously comprises a charge amplifier and a compensation circuit comprising:

a closed-loop servocontrol adapted, when active, to deliver an enslaved output signal on a predetermined constant value, referred to as the reference value Sr, independently of any untimely variations in the value of the detection signal normally corresponding to values constant,

an operational amplifier (in particular a charge amplifier) receiving as input the signal delivered by the sensor and outputting said output signal, said compensation circuit delivering, at the input of the operational amplifier, a current Icorr of compensation in parallel with the signal delivered by the sensor,

a detection circuit adapted to measure and memorize the value S (t) of the output signal for successive sampling instants t at a sampling frequency higher than the maximum frequency of the pulses expected in the detection signal,

and data processing means adapted to calculate, at each sampling instant, a value representative of an AS variation of the output signal, with respect to a past sampling instant,

and said compensation circuit is adapted for, at each sampling instant, if the absolute value of said variation AS is lower than a predetermined comparison value V, enabling said servocontrol to slave the output signal to said reference value Sr, the value of the output signal being a value normally corresponding to a constant value. In particular, advantageously and according to the invention, this electronic circuit can be in accordance with WO 2012031964 and / or FR 2969279.

According to another aspect, the invention also relates to a piezoelectric detector comprising at least one piezoelectric sensitive element interposed in an assembly capable of transmitting said pressure forces to each piezoelectric sensitive element, said assembly comprising:

a support sole of each piezoelectric sensitive element,

characterized in that the elastically deformable device comprises a peripheral sleeve connecting the rolling plate to said sole by laterally delimiting an internal space receiving each piezoelectric sensitive element, with a compressive preload according to said measuring direction of each piezoelectric sensitive element between the plate rolling and the sole.

The invention also extends to a piezoelectric detector adapted to be able to deliver a signal, said detection signal, representative of vertical pressure forces exerted on this piezoelectric detector-in particular by the passage of a vehicle wheel-comprising at least one piezoelectric sensitive element interposed in an assembly capable of transmitting said vertical pressure forces to each piezoelectric sensitive element, said assembly comprising:

a support sole of each piezoelectric sensitive element,

a plateau, called a rolling platform, having an upper horizontal plane face, referred to as the measuring face, arranged to receive integrally the vertical pressure forces exerted on top of this rolling plate, in particular the vertical pressure forces resulting from the passage of 'a wheel of a vehicle rolling above this rolling plate-, and for transmitting these vertical pressure forces to each piezoelectric sensitive element of said piezoelectric detector,

an elastically deformable device suitable for subjecting each piezoelectric sensitive element to vertical compression prestressing, characterized in that it comprises a peripheral sleeve connecting the rolling plate to said soleplate by laterally delimiting an internal space receiving each piezoelectric sensitive element, with vertical compression prestressing of each piezoelectric sensing element between the rolling plate and the sole.

Said sleeve is interposed between the rolling plate and the sole, and rigidly connected, for example by welding, at one of its axial ends, to the rolling plate, and at its other axial end, the sole. Said sleeve is further adapted to allow the optimal transfer of said pressure forces from the rolling plate to each piezoelectric sensitive element. Advantageously and according to the invention, said sleeve has a generally symmetrical shape of revolution about an axis parallel to said measurement direction (particularly vertical). It is elastically deformable in axial tension - and at least partly elastically deformed in axial tension after assembly of the various constituent elements of the detector - in the measuring direction, for example in the manner of a bellows or a portion of bellows. Advantageously and according to the invention, said peripheral sleeve is formed of a tight elastic bellows, in particular with a radial cross-section in the general shape of S. Other shapes are possible, for example a multi-ply bellows (waves), or radial section in V, in W ...

In addition, advantageously and according to the invention, said elastically deformable sleeve has a height less than its horizontal dimensions - in particular less than half of its largest outside diameter, for example of the order of 10% to 20%, for example of the order of 12% to 15%, of its largest outer diameter, when the sleeve has a symmetrical shape of revolution about an axis parallel to said measurement direction (including vertical) -. In particular, advantageously and according to the invention, said height of the elastically deformable sleeve is less than 15 mm, in particular between 3 mm and Advantageously and according to the invention, said peripheral sleeve is sealed and laterally delimits sealingly said inner space, protecting each sensitive piezoelectric element including moisture or runoff.

Such a low-height sleeve makes it possible in particular to obtain a super-flat detector; robust ; easy and inexpensive to manufacture, assemble, and integrate in a sensor comprising several such detectors or any other system; extremely sensitive, accurate and reliable; undisturbed by significant deformations and / or displacements of its peripheral environment; suitable for use in humid and / or outdoor environments; and having surprising mechanical properties.

However, nothing prevents the provision of other shapes and / or structures capable of acting as an elastically deformable device as mentioned above, for example a plurality of resilient flexible springs or blades or studs of elastic material connecting the tray. rolling and the sole.

Furthermore, the invention also relates to a piezoelectric detector -especially as mentioned above- characterized in that each piezoelectric sensitive element is formed of a block -particularly in the form of a wafer (that is to say having a thin and two parallel main faces) - in particular a washer of polycrystalline piezoelectric ceramic material, preferably lead-free. Nothing prevents alternatively to provide any other piezoelectric sensitive element, for example in the form of piezoelectric quartz crystals.

In addition, the invention also relates to a piezoelectric detector -especially as mentioned above- characterized in that each piezoelectric sensitive element is disposed in said assembly in an annular geometry relative to a planar support surface of each piezoelectric sensitive element. The said support face supports, generally via an electrical connection electrode, one of the main faces of the wafer forming each piezoelectric sensitive element. The said support face carrying each piezoelectric sensitive element is firmly held relative to the rolling plate, by means of said elastically deformable device-in particular the sleeve-. Advantageously and according to the invention, said support face is parallel to said measuring face. Such an annular geometry presented by the piezoelectric sensitive element (s) of a detector according to the invention is particularly advantageous for obtaining a super-flat detector as mentioned above. It delimits a central receiving housing of the electronic circuit and facilitates electrical connections between each piezoelectric sensitive element and the electronic circuit. It also gives great mechanical stability, especially for the application of said compression prestressing which can be performed uniformly and accurately.

It should be noted that there is nothing to prevent provision of said support face to be formed of a plurality of disjoint surface portions each receiving a piezoelectric sensitive element. Nevertheless, in a preferred embodiment, a detector according to the invention is advantageously characterized in that it comprises a single piezoelectric sensitive element in the form of an annular plate. Taking into account in particular the costs of piezoelectric quartz, this embodiment is more particularly advantageous in combination with the fact that this piezoelectric sensitive element consists of a washer of polycrystalline piezoelectric ceramic material, which is therefore in the form of an annular plate. .

A piezoelectric detector according to the invention is formed of a plurality of parts mechanically assembled to each other, comprising in particular at least one piezoelectric sensitive element and at least one other part forming at least one support plate receiving each piezoelectric sensitive element and / or or said rolling plate and / or said elastically deformable device.

In a first possible variant embodiment, a piezoelectric detector according to the invention is formed, in addition to each piezoelectric sensitive element, of at least one other piece forming the rolling plate and at least one other piece forming said elastically deformable device ( in particular said sleeve), these different parts being assembled in the form of a suitable mechanical assembly. A detector according to the invention further comprises a support plate of each piezoelectric sensitive element. In particular, the elastically deformable device is then advantageously rigidly and permanently fixed, in the elastically deformed state in axial traction under residual elastic stress, on one side to the rolling plate, on the other side to the sole, for example by welding. In this first embodiment, the various constituent parts of the detector according to the invention may be at least partly metallic. In particular, said sleeve may be formed of an elastically deformable metal alloy.

Advantageously and according to the invention, in this first embodiment, said elastically deformable device -in particular said sleeve- is fixed to the rolling plate and the sole so as to be in the elastically deformed state in axial tension (after the assembly of the different constituent elements of the detector) between the rolling plate and the sole so as to impart said compressive preload on each piezoelectric sensitive element by elastic return (exerted by said elastically deformable device -particularly by said sleeve-) of the rolling plate towards the soleplate, each piezoelectric sensitive element being thus elastically compressed between the rolling plate and the soleplate. Said compressive prestressing can thus in particular be obtained by axial axial deformation prior to axial traction of said elastically deformable device -particularly of said sleeve-obtained at the time of assembly of the assembly, when said elastically deformable device -in particular said sleeve- is flexible ( elastically deformable) axially. For this purpose, it suffices that the axial height of the elastically deformable device-especially the sleeve-at rest is less than the distance between the rolling plate and the sole.

In a second variant of possible embodiment of a detector according to the invention, at least a portion of the constituent elements of the detector are formed together of the same molded piece of synthetic material. Thus, advantageously and according to the invention, said elastically deformable device and / or a part of said rolling plate and / or said support sole are formed of a same piece of molded synthetic material. In a particularly advantageous embodiment, a detector according to the invention thus comprises a support sole (receiving each piezoelectric sensitive element), an elastically deformable peripheral sleeve in the measurement direction and a base plate of the rolling plate, formed together. of the same piece obtained from molding in synthetic material. Also in an advantageous embodiment and according to the invention, said base plate of said rolling plate is surmounted by a layer of leveling and wear -notamment a rigid resin layer (for example chosen from an epoxy resin charged with silica, a polyamide, a polyamide filled with glass fibers) overmolded on said base plate and / or in a formwork secured to the latter so as to have a parallel free face forming said measurement face receiving the pressure forces to measure.

Advantageously and according to the invention, said molded synthetic material is a rigid dielectric material of high hardness, for example a thermoplastic selected from the group consisting of polyetheretherketone (PEEK) and liquid crystal polymers (LCP). Other materials having suitable mechanical properties may be chosen.

In certain embodiments of this second embodiment, advantageously and according to the invention, the elastically deformable device -in particular the peripheral sleeve- and at least a part of said sole -particularly the part of the soleplate receiving each piezoelectric sensitive element- are formed together from the same piece of synthetic material from molding.

Advantageously and according to the invention, said elastically deformable device comprises a pressing piece bearing on said elastically deformable device -notamment on said sleeve- and applied with a clamping stress against each piezoelectric sensitive element so as to exert at least part of said compression prestress according to the direction of measurement. In particular, advantageously and according to the invention, this compressive preload applied to each piezoelectric sensitive element can be obtained at least partly by a pressure piece bearing on an extreme portion of the sleeve located on the side of the rolling plate, this pressure piece being applied - in particular by screwing with respect to said end portion of the sleeve - with a clamping stress against each piezoelectric sensitive element. This clamping stress has the effect of elastically deforming in axial tension:

- At least partly the sleeve (which is therefore in the elastically deformed state in axial tension at least partly by this clamping stress after assembly of the various constituent elements of the detector) and / or

at least in part the connecting members (for example a thread / tapping system admitting an axial deformation-in particular threading of said pressure piece and tapping of said end portion of the sleeve) from said pressure piece to the sleeve and / or

at least partly to said pressure piece which may itself be elastically deformable in axial compression.

Preferably, however, the rigidity of said pressure piece in axial compression and that of said connecting members are much greater than the stiffness of the sleeve, so that said compressive prestress mainly derives from the axial tensile deformation of the sleeve. , in particular in its portion extending between said sole and said end portion on which the pressure piece bears. In any case, this clamping constraint produces at least part of said compression preload. Thus, said compressive prestressing may be at least partially obtained by clamping, in particular by screwing, a pressure piece bearing on said elastically deformable device -particularly inside said end portion of said sleeve- and applied with a clamping stress against each piezoelectric sensing element.

Nothing prevents to provide a combination of these embodiments, for example a previously elastically deformed sleeve in axial tension during assembly performing a portion of the compression preload, and a pressure piece screwed inside this sleeve with a tightening torque able to complete the compression prestress in order to obtain the appropriate value. The invention also relates to a sensor for moving vehicles, comprising a plurality of piezoelectric detectors associated with a common support intended to be implanted on the ground across a vehicle passageway, each piezoelectric detector being adapted to deliver a signal electrical, said detection signal, representative of the pressure force exerted on the piezoelectric detector by the passage of a vehicle wheel, each piezoelectric detector comprising at least one piezoelectric sensitive element interposed in an assembly adapted to subject each piezoelectric sensitive element to vertical compression prestressing and transmitting to each piezoelectric sensitive element the compression forces generated by the passage of a vehicle wheel,

said common support comprising a flat rigid upper face, said base, carrying the piezoelectric detectors juxtaposed next to each other above the base,

each piezoelectric detector comprising a clean rolling plate (that is to say, specific to this piezoelectric detector) having an upper planar face, called measuring face, arranged to receive fully the force resulting from the passage of a wheel of vehicle traveling above-especially on this rolling platform, and for transmitting these forces to each piezoelectric sensing element of said piezoelectric detector,

said rolling plate of each piezoelectric detector being distinct and remote from the rolling plates of the piezoelectric detectors which abut it, so that each piezoelectric detector receives exclusively the force resulting from the passage of a wheel of a vehicle traveling above the in particular on the rolling plate of this piezoelectric detector,

characterized in that each piezoelectric detector is in accordance with the invention.

The invention thus makes it possible to propose a sensor which is not only sufficiently precise to be able to provide exploitable values for purposes of official control, but which, moreover, is particularly simple, resistant and economical. All the ultra-flat piezoelectric detectors according to the invention extend on and above the base of the common support and each detector receives directly and only measures the pressure forces resulting from the passage of a vehicle wheel on this detector. The sensor according to the invention can be particularly thin, which promotes its performance and facilitates its integration into any system, including a passageway, or even over a passageway, in a mobile system or semi mobile such as a speed bump.

Advantageously and according to the invention, the different piezoelectric detectors are identical to each other, extra flat and in accordance with the invention. They can therefore in particular be mass-produced at lower cost, and the manufacture of the sensor according to the invention is itself particularly simple since it is sufficient to juxtapose identical detectors next to each other on the same base.

Moreover, each piezoelectric detector can be prefabricated and precalibrated during manufacture (at the factory) so that a detection signal can be delivered accurately and reliably, that is to say whose value is strictly proportional to the force of the detector. pressure exerted on the rolling platform, independently of the temperature, the shear forces or the dynamic forces exerted.

Advantageously in a sensor according to the invention, said elastically deformable device of each piezoelectric detector has a total height less than the total length of said rolling plate the direction of vehicle wheel passage. More particularly, advantageously and according to the invention, said elastically deformable device of each piezoelectric detector has a total height less than -in particular less than half of its total length -in particular of the order of 10% to 20%, for example in the order of 12% to 15% of its total length - in the direction of passage of a vehicle wheel.

Moreover, advantageously and according to the invention, the rolling trays of the piezoelectric detectors are of rectangular shape - preferably square - and of the same dimensions, the different piezoelectric detectors being juxtaposed on the base parallel to each other forming a tiling the free upper surface of the sensor. Each rolling tray has one face free upper adapted to receive the contact of a vehicle wheel passing above the piezoelectric detector.

In addition, advantageously and according to the invention, said rigid planar base is formed of an upper face of a beam -in particular a cross-section I, H, or polygonal or other section, hollow or solid - having a longitudinal direction adapted and intended to be arranged across said passageway. Advantageously, a sensor according to the invention then comprises at least one-in particular a single-row of piezoelectric detectors juxtaposed in alignment along said rigid planar base, one side of the rectangular rolling trays of the piezoelectric detectors being parallel to said longitudinal direction of the beam forming the base.

Furthermore, advantageously and according to the invention, the rolling trays of the different piezoelectric detectors juxtaposed on the base are separated from each other in the longitudinal direction of the beam by a distance of less than 2 cm. Advantageously and according to the invention, when the sensor comprises a plurality of successive piezoelectric detectors in a direction orthogonal to the longitudinal direction of the beam, the rolling trays of the different piezoelectric detectors juxtaposed on the base are also separated from each other according to the invention. this direction orthogonal to the longitudinal direction of the beam from a distance also less than 2 cm, especially and advantageously of the order of 1 mm.

In addition, advantageously and according to the invention, the piezoelectric detectors are separated from each other by a filler material having negligible compressive strength compared to that of each piezoelectric detector.

Nothing prevents to provide in a sensor according to the invention that the different piezoelectric detectors are directly disposed on the base, in particular on the upper face of the beam, the latter acting as a bottom flange common to the different piezoelectric detectors. Nevertheless, preferably, advantageously and according to the invention, each piezoelectric detector comprises a sole that is specific to it (that is to say distinct from the sole of each another adjacent piezoelectric detector), and the soleplate of each piezoelectric detector is superimposed on the base.

Furthermore, advantageously and according to the invention the sensor comprises an electrical connection layer extending between the base and the different soles of the different piezoelectric detectors, for electrically connecting the piezoelectric detectors (in series or in parallel) to an end of the base intended to be located on the side of said passageway and provided with an electronic processing circuit receiving the different detection signals.

According to an advantageous embodiment, a sensor according to the invention is also characterized in that it comprises at least two parallel rows of piezoelectric detectors juxtaposed on the base. In a variant, a sensor according to the invention comprises a single row of piezoelectric detectors juxtaposed on the base.

In addition, advantageously a sensor according to the invention comprises an electronic circuit for processing the detection signals from the different piezoelectric detectors, and said electronic processing circuit is adapted to produce digital data representative of the pressure force measured by each piezoelectric detector. , the speed of passage of each wheel of the vehicle, and the weight of the vehicle transmitted at each wheel of the vehicle. The calculation of the passage speed and the weight of the vehicle can be easily obtained in the embodiment in which the sensor according to the invention comprises several parallel rows of detectors juxtaposed on the same base, so that each wheel of a vehicle rolling rolls successively on several piezoelectric detectors (of several successive rows). Nevertheless, this calculation can also be obtained with other configurations, for example with a single row of piezoelectric detectors oriented non-orthogonal to the longitudinal direction of the passageway, so that each wheel of a vehicle comes into contact with several piezoelectric sensors of the sensor according to the invention, which are thus offset in the longitudinal direction of the passageway. The invention also relates to a piezoelectric detector and a sensor characterized in combination by all or some of the characteristics mentioned above or below.

Other objects, features and advantages of the invention will appear on reading the following non-limiting description which refers to the appended figures in which:

FIG. 1 is a schematic perspective view of a piezoelectric detector according to a first embodiment of the invention,

FIG. 2 is a diagrammatic exploded perspective view illustrating the various component parts of the detector of FIG. 1,

FIG. 3 is a partial perspective view illustrating a longitudinal end of a sensor according to a first embodiment of the invention,

FIG. 4 is a partial schematic view in longitudinal vertical section of a sensor according to the invention provided with piezoelectric detectors according to the first embodiment of the invention and implemented in a vehicle passageway,

FIG. 5 is a partial schematic view in partial transverse vertical section of a sensor according to a second embodiment of the invention provided with piezoelectric detectors according to the first embodiment of the invention and set up in a way of passage of vehicles,

FIG. 6 is a block diagram of an electronic circuit of a piezoelectric detector of a sensor according to one embodiment of the invention,

FIG. 7 is a flowchart of an embodiment of a signal processing method implemented by the compensation circuit of the circuit of FIG. 6 at each iteration,

FIG. 8 is a three-dimensional graph illustrating an example of signals delivered by a sensor according to the first embodiment of the invention during the passage of a vehicle wheel,

FIG. 9 is a two-dimensional graph illustrating one of the signals of FIG. 8, FIG. 10 is a three-dimensional graph illustrating an example of signals delivered by a sensor according to the second embodiment of the invention during the passage of a vehicle wheel,

FIG. 11 is a two-dimensional graph illustrating one of the signals of FIG. 10,

FIG. 12 is a block diagram of an embodiment of a main circuit for processing a sensor according to the invention,

FIG. 13 is a schematic exploded perspective view of a piezoelectric detector according to a second embodiment of the invention,

FIG. 14 is a partial schematic view in transverse vertical section of a detector of FIG. 13, during a step of assembling the latter, the rolling plate being in particular not shown,

FIG. 15 is a partial schematic view in longitudinal vertical section of the detector of FIG. 14 in the fully assembled state,

FIG. 16 is a partial schematic view in partial transverse vertical section of a sensor according to a third embodiment of the invention provided with a row of piezoelectric detectors according to the second embodiment of the invention and put in place in a vehicle lane.

A sensor according to the invention comprises a beam 1 1 intended to be placed across a passageway for moving vehicles so that the sensor has a free upper surface 12 on which the wheels of vehicles traveling along said passageway roll. .

This beam 1 1 is preferably rigid, that is to say adapted to undergo substantially no deformation under the effect of the passage of the heavier vehicles considered, for example up to 40t in the case of roads or highways. It should be noted, however, that the invention eliminates the mechanical characteristics of the beam 1 1, which can be made of inexpensive material, for example aluminum alloy, steel or polymeric rigid synthetic material and / or composite.

The beam 1 1 has a flat horizontal top face, said base 13, on which are juxtaposed piezoelectric detectors 14 mechanically independent of each other (in addition to being carried by the same rigid base 13), so as to form a tiling of said upper face 12 of the sensor according to the invention. The beam 1 1 is preferably formed of a cross-section section I in the example shown in the figures, but which may alternatively be a cross-section section in H, or polygonal hollow or solid ... It should be noted in particular that the use of a hollow beam 1 1 allows the insertion of accessories, for example a main circuit 50 signal processing as described below, in the central volume of the beam by an open longitudinal end of the latter.

Each piezoelectric detector 14 comprises at least one piezoelectric sensitive element 15 capable of delivering an electric charge signal as a function of the compression forces it undergoes, for example and preferably a block of piezoelectric synthetic material, more particularly and advantageously a piezoelectric washer. polycrystalline piezoelectric ceramic, preferably lead-free.

Each piezoelectric sensitive element 15 is interposed in a proper assembly on the one hand to subject each piezoelectric sensitive element 15 to a vertical compression prestress, and on the other hand to transmit to each piezoelectric sensitive element 15 the compression forces generated by the passage of a vehicle wheel above the piezoelectric detector 14.

Each piezoelectric detector 14 is adapted to deliver an electrical signal, said detection signal, representative of the pressure force exerted on this piezoelectric detector 14 by the passage of a vehicle wheel. This detection signal is preferably developed and delivered by an electronic circuit 18 integrated in each piezoelectric detector 14. This electronic circuit 18 is electrically connected to each piezoelectric sensitive element 15 to receive charging signals.

In the preferred embodiment of the invention, each piezoelectric detector 14 comprises at least one-in particular a single-piezoelectric sensitive element 15 which is a plate-shaped flattened annular washer (ring) symmetrical of revolution about an axis 19 , which makes it possible in particular to provide a hollow central space 20 forming receiving accommodation for said Electronic circuit 18. This central space is preferably then filled with a soft plastic protective material 23 - in particular silicon - protecting the electronic circuit 18 from vibrations and moisture. The dimensions of this piezoelectric washer are for example the following: outer diameter between 25mm and 35mm, for example of the order of 30mm; inner diameter between 15mm and 25mm, for example of the order of 20mm; thickness between 0.1mm and 1mm, for example of the order of 0.5mm.

This embodiment is particularly advantageous in that it makes it possible to optimize the quantity of piezoelectric material necessary and sufficient for the sensitivity of the piezoelectric detector 14, the geometry of the assembly and the overall bulk of the piezoelectric detector 14 which is particularly compact in horizontal directions and thin (extra flat), given its performance, especially in sensitivity. It should be noted in this regard that a small thickness of the piezoelectric detector 14 is particularly advantageous, in particular to avoid the disturbance of the signals by the shear effects in the horizontal directions, the deformations induced on the passageway by the wheels of the front vehicle. that these do not arrive above the sensor, and the adjacent detectors.

Each piezoelectric detector 14 comprises a clean rolling plate 16 having an upper planar face, called measuring face 17, arranged to receive fully the force resulting from the passage of a wheel of a vehicle running above this plate 16 of rolling and in contact with this measurement face 17, and for transmitting this force to each piezoelectric sensitive element 15 of said piezoelectric detector. The measurement face 17 is orthogonal to the axis 19 of symmetry of the piezoelectric sensitive element 15, this axis 19 constituting the direction of measurement of the pressure forces. In the examples shown in the figures and in particular in the case of a sensor for moving vehicles, the measurement face 17 is horizontal flat (parallel to the base 13), and the measurement direction corresponding to the axis 19 is vertical (orthogonal to the base 13 and the face 17 of measurement).

The rolling plate 16 of each piezoelectric detector 14 is distinct and remote from the trailing plates 16 of the other piezoelectric detectors. 14 that adjoin it, so that each piezoelectric detector 14 receives exclusively the force resulting from the passage of a wheel of a vehicle running over the rolling plate of this piezoelectric detector 14.

The rolling plate 16 comprises a rigid base plate 16a - in particular aluminum alloy, steel or polymeric rigid material and / or composite-, rectangular or square, defining the size, size and horizontal dimensions of the piezoelectric detector 14, this base plate 16a being surmounted by a layer 16b leveling and wear, formed of a rigid and hard synthetic material -in particular a silica-filled epoxy resin whose thickness can be adjusted by polishing after integration of the sensor in a passageway to ensure proper leveling of the different piezoelectric detectors 14 (outcropping with the road surface) and form said measuring face 17 on which a vehicle wheel can come rolling.

Each piezoelectric detector 14 also comprises a rigid sole 21 formed of a rigid plate -particularly aluminum alloy, steel or polymeric rigid material and / or composite-, rectangular or square, the same size and dimensions as the plateau 16 of driving.

The soleplate 21 is applied to the base 13. The plate 16a of the rolling plate 16 is connected to the sole 21 by a flexible peripheral sleeve 22 which holds them together by applying the plate 16a (and thus the rolling plate 16) on each piezoelectric element 15 with a vertical compression prestress.

The sleeve 22 may be formed of an elastic bellows - in particular with a radial cross-section in the general S-shape as in the example shown - in aluminum alloy, in steel or in synthetic material elastic in polymeric bending and / or composite . The sleeve 22 has a circular lower edge 24 welded to the sole 21, and a circular upper edge 25 welded with vertical compression prestressing under the plate 16a of the rolling plate 16. Thus, the sleeve 22 is sealed and delimits an internal space receiving each piezoelectric sensitive element 15, the various constituent elements of the mechanical assembly, as well as the electronic circuit 18. The sleeve 22 is elastically deformable compression / vertical traction, and is also adapted to absorb any horizontal shear forces experienced by the sensor.

To allow the connection by welding of the sleeve 22 to the sole 21 and the plate 16a of the rolling plate, the constituent materials of these different parts are chosen to be compatible with such a welded joint. Advantageously, they are made of the same material -particularly aluminum alloy, steel or rigid synthetic material and elastic polymeric bending and / or composite-. In a variant, nothing prevents the sleeve 22 from being formed from one and the same piece of manufacture (in particular after molding) as the soleplate 21 or the plate 16a of the rolling plate. The sleeve 22 has a low vertical axial height, less than its largest diameter, and less than 15 mm, in particular between 3 mm and 10 mm, typically of the order of 6 mm to 7 mm. The largest outer diameter of the sleeve 22, which preferably corresponds as closely as possible to the horizontal dimensions of the rolling plate, is for example between 40 mm and 60 mm, in particular of the order of 50 mm -1. Thus, the ratio between the axial height of the sleeve 22 on its radial space is advantageously between 1/12 and 1/2, for example of the order of 1/6. In this sense, the sleeve 22 and the detector according to the invention can be called extra flat. The smallest inner diameter of the sleeve 22 is for example between 26mm and 36mm, for example of the order of 31mm.

To obtain the vertical compression prestressing, the sleeve 22 is stretched axially elastically before the two welds of these edges 24, 25 are made to the sole 21 and, respectively, to the plate 16a of the rolling plate. For example, in a first step, welding of the edge 24 below the sole 21 is performed, then the assembly of the piezoelectric element is carried out and the rolling plate 16 is assembled inside the sleeve 22, compressing the 16 tray rolling against the washer 32, then axially elastically constrains the sleeve 22 (by stretching it slightly upwards by bearing on the shoulder formed by the S or by one of the bellows of the sleeve 22) so its upper edge comes into contact with the plate 16a of the rolling plate, then the upper edge 25 is welded under the plate 16a of the rolling plate while the sleeve 22 is held axially stretched. The sleeve 22 and elastically deformed in axial tension during assembly ensures the axial prestressing of the assembly. The order of these steps may be different.

The sole 21 has a cylindrical housing 26 receiving a disc 27 made of rigid dielectric material of high hardness, for example a thermoplastic selected from the group consisting of polyetheretherketone (PEEK) and liquid crystal polymers (LCP). The cylindrical housing 26 has the particular function of enabling the piezoelectric detector 14 to withstand any horizontal shear stresses, by preventing the transfer to the piezoelectric washer of horizontal shear forces possibly imparted on the rolling plate 16. The disk 27 is embedded in the housing 26 and blocked horizontally in the latter. The disc 27 receives a ring 29 of electrically conductive material of horizontal dimensions corresponding to those of the piezoelectric washer 15 which surmounts said ring gear 29. The ring 29 has at least one radial band 30 of electrical connection to an input terminal of the electronic circuit 18.

The piezoelectric washer 15 is surmounted by a washer 31 upper rigid -notamment aluminum alloy, steel or polymeric rigid material and / or composite-. The cylindrical housing 26 of the soleplate 21 is sufficiently high to accommodate the insulating disk 27, the conductive ring 29, the piezoelectric washer 15, and the upper conductive washer 31, the peripheral edge 32 of which is welded, for example by laser welding. upper edge 33 of the wall 34 of the sole 21 forming said cylindrical housing 26, so as to connect the upper face of the piezoelectric washer 15 to the electrical ground of the piezoelectric detector 14, and preferably with a slight vertical compression prestressing of the together so stacked in the housing 26, and therefore in particular of the piezoelectric washer 15, so as to ensure the contacts between its different parts. It should be noted, however, that the cylindrical wall 34 of the sole 21 forming the cylindrical housing 26 has a stiffness of deformations in tension / vertical compression much lower than that of the stack of the piezoelectric washer and the washer 31 upper, so the puck 15 In this embodiment, the piezoelectric element is vertically preloaded in compression mainly by the sleeve 22.

The plate 16a of the rolling plate 16 has a central skirt 35 projecting downwardly so as to have a face 36 of the same dimensions and size as the piezoelectric washer 15, and applied in contact with the upper face 37 of the washer 31 upper which bears against the piezoelectric washer 15. It should be noted that the faces 36 and 37 in contact can slide relative to each other horizontally, which makes it possible to isolate the upper face of the piezoelectric washer 15 from the possible shearing forces horizontally.

The trays 16 for rolling the various piezoelectric detectors 14 are of the same rectangular shape - particularly and preferably square as in the example shown - and of the same dimensions, the different piezoelectric detectors 14 being juxtaposed on the base 13 in parallel with each other their free upper plane faces 17 forming a tiling of the free upper face 12 of the sensor according to the invention. In this regard, several variants are possible depending on the application. In a first variant embodiment shown in FIG. 3, the pavement comprises only a single row of piezoelectric detectors 14, aligned one beside the other along the beam 11, the base 13 having a width corresponding to that of the flange 21 of a piezoelectric detector 14. In a second variant embodiment represented in FIG. 5, the sensor according to the invention comprises two successive rows of piezoelectric detectors 14, the base 13 having a width adapted to receive two soles 21 of two piezoelectric detectors 14, with a separation space between these two flanges 21. In FIG. 5, a piezoelectric detector 14 of the first row is shown in section through a vertical median plane on the left of the figure, while a second detector 14 piezoelectric of the second row is shown uncut on the right of the figure. Other variants are possible, and for example a sensor according to the invention may be formed of a pavement comprising more than two successive rows in the longitudinal direction of the passageway.

The rolling plate 16 of each piezoelectric detector 14 has a width (dimension parallel to the longitudinal direction of the base 13 and the beam 1 1) less than 10cm, for example between 4cm and 6cm, especially preferably of the order of 5cm. The width of each rolling plate 16 is in any case less than the width of a vehicle wheel intended to be detected by a sensor according to the invention, so that a wheel which passes on such a sensor is necessarily detected by several separate piezoelectric detectors 14. The length of the rolling plate 16 (dimension orthogonal to the longitudinal direction of the common support and corresponding to the direction of passage of a vehicle wheel on the rolling plate) is preferably greater than or equal to the width of the rolling plate 16. . In the embodiments shown, the rolling plate 16 of each piezoelectric detector is of square shape.

The thickness of a piezoelectric detector 14, between the sole 21 and the upper face of the plate 16a of the rolling plate 16 (that is to say without taking into account the filling layer 16b leveling and 'wear) may be less than 20mm, for example of the order of 15mm. Consequently, the total thickness of such a piezoelectric detector 14 according to the invention between the lower face of the soleplate 21 and said measurement face 17 depends on the thickness given to the filling layer 16b, but can be less than 4cm, for example of the order of 25mm.

The trays 16 of rolling of the different piezoelectric detectors 14 juxtaposed on the base 13 are separated from each other in the longitudinal direction of the beam 1 1 by a distance ds of separation which is different from zero, the different piezoelectric detectors 14 do not not touching and thus being mechanically independent of each other with respect to the forces applied to the rolling plates, but this separation distance ds is preferably as low as possible, especially less than 2cm, for example between 1mm and 10mm. Advantageously, the distance ds separation is less than half the width of a tray 16 rolling. In the case of a sensor comprising several parallel rows of piezoelectric detectors, the piezoelectric detectors 14 are also separated from each other by a non-zero separation distance ds in the horizontal direction orthogonal to the longitudinal direction of the beam 1 1 which corresponds to the longitudinal direction of the passageway when the sensor according to the invention is placed with the beam 1 1 orthogonal to the latter. More generally, a piezoelectric detector 14 of a sensor according to the invention is separated from all the other piezoelectric detectors 14 which adjoin it with such a distance ds of non-zero separation and as low as possible but nevertheless sufficient, in particular to take into account Consider the possible deformations of the beam by avoiding any mutual interaction of the adjacent detectors. Preferably, this distance ds of separation is the same in all directions, but nothing prevents, if the need arises, to achieve a different tiling, with separation distances that vary in the direction between the detectors piezoelectric 14 which are adjacent. The detection signals delivered by the different piezoelectric detectors 14 are thus totally independent of one another.

The soles 21 of the different piezoelectric detectors 14 are fixed rigidly on the base 13, for example by gluing and / or screwing and / or crimping, ... The base 13 of the beam 11 may be provided with lateral rails defining facing stirrups adapted to receive the sole 21 of each piezoelectric detector 14 so that the sole 21 can slide longitudinally between these stirrups while being clamped by the latter so as not to be dissociated from the base 13 other than by longitudinal sliding along the beam 1 1 between the stirrups. The stirrups can also be adapted to be plastically deformed at each sole 21 after insertion of the latter, in order to fix it rigidly to the base 13. In addition to these possible stirrups, the piezoelectric sensors 14 are worn by the base 13 of the beam 1 1 and therefore extend completely upwardly above the base 13 and the beam 1 1.

Preferably, a filling material 40 is inserted into the spaces separating the different piezoelectric detectors 14 of the sensor according to the invention. This filler material is chosen so as to have negligible compressive strength with respect to that of each piezoelectric detector 14 and also a negligible modulus of elasticity with respect to that of each piezoelectric detector 14, in particular less than 50 MPa. . It may in particular be chosen from synthetic materials that can be molded, in particular from a silicone and a rubber. This filling material is in everything chosen to preserve the mechanical independence of the different piezoelectric detectors 14 against each other. In other words, it must form no connection between the different trays 16 of rolling, so that a tray 16 rolling a piezoelectric detector 14 can undergo a vertical force so that the piezoelectric detector 14 delivers a detection signal of the corresponding force, without any of the other adjacent piezoelectric detectors 14 delivering any detection signal and being influenced by this effort. It should be noted that the fact that the detectors are extra flat also largely contributes to achieving this independence between adjacent detectors.

Such a filling material 40 may be introduced into the manufacture of the sensor according to the invention, and also at its periphery and around the upper part of the beam 1 1 before its integration in a passageway, as illustrated for example on the FIGS. 4 and 5. This filling material 40 can thus be molded around the upper part of the beam 1 1 and all the piezoelectric detectors 14, including the spaces which separate them from each other.

For the integration of such a sensor according to the invention in a road crossing lane (highway, highway, taxiway, airport runway ...), a transverse groove is formed in the lane, then a volume 42 of resin - in particular a silica-filled epoxy resin - is deposited at the bottom of the groove, then the sensor is put in place with the lower part 41 of the beam 1 1 which is embedded in said resin mass before hardening. Preferably, the volume 42 of epoxy resin is in sufficient quantity to occupy the entire volume of the groove which is not occupied by the sensor itself.

The sole 21 of each piezoelectric detector 14 is provided with at least one insulating bushing 45 extending through its thickness and through which a conductor 46 for transmitting the detection signal passes so as to connect an output 128 of the electronic circuit 18 delivering said detection signal to a ply 47 of electrical connection extending between the base 13 and the different flanges 21 of the different piezoelectric detectors 14, along the base 13. The disc 27 is also provided with a passage opening of the conductor 46 for transmitting the detection signal.

The electrical connection layer 47 has parallel tracks, each track being electrically connected to one of the conductors 46 for transmitting the detection signal of one of the piezoelectric detectors 14 of the sensor, so that all the detection signals are, in this embodiment, delivered in parallel to a main electronic circuit 50 for processing the signals delivered by the different piezoelectric detectors 14 placed at one end of the base 13 intended to be itself located on a side of a passageway. For the passage of the ply 47 of electrical connection without extra thickness, each sole 21 may be provided with a central recess 51 extending in central part and over the entire length of the sole 21 parallel to the axis of the beam 1 1 .

The electronic circuit 18 of each piezoelectric detector 14 is adapted to provide a detection signal in the form of a voltage proportional to the vertical force experienced by the piezoelectric detector 14, without drift. For this purpose it comprises, for example, a charge amplifier and a closed-loop compensation circuit, for example as described by WO 2012031964 and / or FR 2969279. It is in practice formed of a printed circuit in the general form of a disk housed at center of the washer forming the piezoelectric sensitive element 15 and receiving an integrated circuit (ASIC, FPGA, ...).

The piezoelectric sensitive element 15 delivers, on a terminal 11 1, a signal (formed of electrical charges) processed by the electronic circuit 18 comprising a charge amplifier comprising, in the embodiment shown in FIG. 6, an operational amplifier 12 high gain inverter and a capacitive feedback capacitance 1 16 C. The terminal 1 1 1 of the piezoelectric element 15 is connected to the inverting input 1 13 of the operational amplifier 1 12, whose non-inverting input 1 14 is connected to ground, and whose output 1 15 delivers a voltage proportional to the load produced by the piezoelectric element 15. The capacitive branch 1 16 is connected in parallel between the output 15 and the inverting input 1 13 of the operational amplifier 1 12 receiving the signal from the piezoelectric element 15. The piezoelectric sensitive element 15 delivers a signal in the form of pulses, relatively brief and corresponding to the vehicle wheel passages on the piezoelectric detector 14, these pulses being separated by trays of longer duration corresponding to values at least substantially constants of the pressure experienced by the rolling plate 16 of the piezoelectric detector 14, which corresponds to the atmospheric pressure in the absence of passage of a vehicle wheel.

It should be noted that, depending on the applications and the constraints, the operational amplifier 1 12 can be the subject of different embodiments, and in particular can be realized with more or less complex architectures.

The electronic circuit 18 furthermore comprises a compensation circuit 1 17 forming a closed-loop servocontrol delivering a compensation current to the input of the operational amplifier of the electronic circuit 18, in parallel with the signal delivered by the piezoelectric element 15. This compensation circuit 1 17 receives the output signal (in voltage) from the output 1 of the charge amplifier. The compensation circuit 1 17 provides a voltage correction signal Ucorr on an output 1 18 connected to a terminal of a series resistor 1 19 whose other terminal is connected to the input 1 13 of the charge amplifier receiving the signal delivered by the piezoelectric element 15. The resistor 1 19, of value, converts the voltage correction signal Ucorr into an intensity correction signal Icorr which is added to the signal delivered by the piezoelectric element 15 and makes it possible to compensate for untimely changes in absolute value.

The voltage signal supplied by the charge amplifier on the output 1 is thus said compensated detection signal and delivered on an output 128 of the electronic circuit 18, allowing its operation by connection with a main circuit 50 for processing the signals delivered by the different piezoelectric detectors 14.

The compensation circuit 1 17 comprises an analog / digital converter 120 which delivers a digital signal S corresponding to the analog voltage of the output 1 of the charge amplifier. This digital signal S is fed to an input of an integrated circuit 127 (which may be formed of an ASIC, an FPGA, or a microcontroller or the like), comprising a circular buffer memory 121 successively memorizing the sampled measurements. S (t) of the signal S according to a sampling clock frequency delivered by a clock 123 of the circuit 127. The integrated circuit 127 also comprises at least one microprocessor 124, at least one read-only memory 125 and at least one random access memory 126 associated with this microprocessor. The microprocessor 124 executes the processing method according to the invention on each sampled value of the signal S as represented in FIG. 7. The microprocessor 124 delivers at the output of the integrated circuit 127 a correction digital signal Corr supplied to a digital / analog converter 122. delivering an analog voltage correction signal Ucorr on the output 1 18 of the compensation circuit 1 17.

An example of the signal processing method S carried out by the compensation circuit 1 17 at each iteration, that is to say at each sampling of the output signal, is represented in FIG.

In the first step 131, the current value S (t) of the signal S is stored on a sampling clock edge in the location of the circular buffer 121 activated by this clock edge.

In the second step 132, the variation AS of the output signal S is calculated between the current value S (t) at the instant t of the clock edge, and one of the previous values of the signal S, called S ( t-aT), stored in the circular buffer 121 for a clock edge closest to the value t-αΤ, where T is a natural integer and has a rational number between 0 and 1. For example, one chooses between 0.05 and 0.5, in particular of the order of 0.2. aT represents the duration over which the variation AS is calculated, which is therefore a fraction of a total duration represented by T whose value lies between a non-zero minimum value Tmin and a maximum value Tmax. These values are chosen according to the maximum and respectively minimum possible frequencies for the passage of vehicles. Thus, Tmin is less than the duration of the trays for the maximum frequency of passage of the vehicle wheels, and Tmax is greater than the duration of the trays for the minimum passage frequency of the vehicle wheels. In the third step 133, the absolute value | S | of this variation is compared with a predetermined comparison value V stored in the memory 125. In practice, this comparison value can be adjusted from the intrinsic noise contained in the signal during the trays, by setting it to a value greater than maximum value of the derivative of this intrinsic noise.

If the absolute value | S | the variation of the output signal is less than the comparison value V, this means that the signal delivered by the piezoelectric element 15 corresponds to a plateau of the pressure by the piezoelectric detector 14, and a servo-control 134 is activated.

This servocontrol 134 consists, in a first step 135, of calculating a value of the corrective correction signal enabling the output signal S to be servocontrolled to the predetermined reference value Sr, independently of any untimely variations in the absolute value of the signal delivered by the piezoelectric element 15. This reference value Sr constitutes an instruction of the servocontrol 134 and can be chosen and stored in the memory 125 as a function of the constraints of the electronic components located downstream of the electronic circuit 18 and receiving the output signal .

This step of calculating the value of the corrective correction signal may be subject to various variants. Preferably, advantageously and according to the invention, this calculation is carried out by a PID (proportional integral derivative) regulator receiving as input the current value S (t), calculating the error with respect to the reference value Sr and applying a regulation of type PID on this error. It should be noted that the corrective correction signal is a digital voltage signal.

During the subsequent step 136 of the servocontrol 134, the current value of the corrective correction signal is stored and an average M of this corrective correction signal is calculated on the current value and different previously stored values of this corrective correction signal. .

This average is preferably an algebraic average calculated on a number of previous samples. For example, at each iteration, this average is calculated on the preceding βΤ samples, β being a rational number between 0 and 1, for example of the order of 0.5, chosen to filter the slight variations of the signal during the trays of the pressure undergone by the piezoelectric detector 14.

In the subsequent step 137 of the servocontrol 134, T is incremented by one and the duration used for calculating the variation AS is increased by a, unless the current duration is equal to a predetermined maximum duration aTmax. . Tmax corresponds for example to the greatest possible duration of the trays, that is to say to the maximum time separating two successive passages of vehicle wheels (s). To do this, if this value Tmax is not reached, the value of T is incremented by one unit at each iteration for which the servocontrol has been activated, that is to say after each calculation of a value Corr correction signal. Thus, the duration is an increasing function of the number of sampling times spent for which the absolute value | S | the variation has remained lower than said predetermined comparison value, that is to say for which the signal delivered by the piezoelectric element 15 corresponds to the same plate. In other words, the duration of calculation of the variation of the output signal increases as long as the signal delivered by the piezoelectric element 15 remains on the same pressure plate. In this way, the detection sensitivity of the trays is independent of the actual frequency of passage of the vehicle wheels (s).

It should be noted that the number βΤ of the passed samples used for the calculation of the average M also increases with each iteration by incrementing T as long as the signal delivered by the piezoelectric element 15 remains on the same pressure plate.

If the comparison step 133 determines that the absolute value I S | the variation of the output signal is not less than the comparison value V, this means that the signal delivered by the piezoelectric element 15 corresponds to a pressure peak, and the servocontrol 134 is inactivated. In this case, the corrective correction signal is set in step 138 to the last recorded value of the average M calculated during the last execution of step 136 of the servocontrol 134.

In the subsequent step 139, the value of T is reset to a minimum non-zero initial value Tmin. Tmin corresponds for example to the most small possible duration of the trays, that is to say the smallest time separating two successive passages of vehicle wheels (s). During a peak pressure and immediately after such a pressure peak, the value of T is therefore set at Tmin, so that the minimum duration taken into account for calculating the variation AS at the beginning of a plateau phase is equal to to aTmin. This duration is then gradually increased by the value a at each iteration.

In any event, the processing method implemented in the electronic circuit 18 of each piezoelectric detector 14 delivers, during the final step 140, for each sampling instant t, that is to say after each clock edge, a value Corr of the correction signal.

It should be noted that other embodiments of the compensation circuit can be used in an electronic circuit 18 of a piezoelectric detector 14 of the sensor according to the invention. Whatever the case, the electronic circuit 18 outputs a detection signal in the form of a voltage whose value is proportional to the pressure experienced by the piezoelectric detector 14, and remains constant regardless of the temperature, the phenomena of pyroelectricity being permanently automatically compensated in real time.

The main detection signal processing circuit 50 receives these detection signals in analog form as delivered by the outputs 29 of the electronic circuits 18, converts them into digital data and prepares from them data representative of the desired information. .

FIG. 8 represents an example of a temporal graph of the detection signals delivered by five adjacent piezoelectric detectors 14 of a sensor according to the invention. In this graph, the x-axis represents the x-position of the piezoelectric detector 14 along the beam 1 1 assumed to extend transversely to the passageway and having a single row of piezoelectric detectors 14.

As can be seen in FIG. 9, which represents the plot of one of the detection signals, it is possible to extract from each of the detection signals, in particular: the maximum value Fmax of the force measured by the piezoelectric detector 14,

the values of different instants ti for which the force measured corresponds to a predetermined proportion of the maximum value Fmax (for example the instants t1, t2, t4, t3, t4, t5 where the measured effort corresponds to 10% respectively, 60%, 100%, 60%, and 10% of the maximum effort as shown in Figure 9),

the values of statistical parameters such as the standard deviation or the symmetry coefficient,

the weight of a wheel brought back to a unit speed, that is to say the value of jFdt.

FIG. 10 is a graph similar to that of FIG. 8, obtained in the case of a sensor according to the invention formed of two parallel rows of piezoelectric detectors 14 as represented in FIG. 5. FIG. 11, which corresponds to FIG. in the case of the two-row sensor not only makes it possible to extract the same values as in the first embodiment of single-row embodiments, but also, for each pair of successive piezoelectric detectors 14 in the direction of the passageway, calculate the instantaneous speed v of the vehicle by intercorrelation of the two detection signals. Indeed, by intercorrelation one obtains the time difference δmax between the two pulses, and therefore the speed v = (D + ds) / δmax.

We can then calculate the weight P of the vehicle according to the formula:

P = (v / D) jFdt

D being the characteristic distance of the rolling plate 16 of each piezoelectric detector 14 in the direction of movement of the wheel, ie orthogonal to the beam 1 1. In addition, the detectors being independent, they make it possible to determine precisely the duration of passage of each wheel on the sensor, and to deduce a possible under-inflation of one of the wheels, and without measuring the internal pressure of the tires. Indeed, a duration of passage of a wheel on the sensor larger than the other durations of passage of the other wheels is representative of under-inflation. For optimum accuracy of the sensor, the main circuit 50 for processing the detection signals is clocked at a sampling frequency greater than 10 kHz, for example of the order of 100 kHz.

The main processing circuit 50 comprises as many inputs as there are piezoelectric detectors 14, and is adapted to be able to process the various signals and to develop and, where appropriate, store, digital data representative of the parameters to be measured. An exemplary embodiment of this main processing circuit 50 is shown in FIG.

This circuit 50 comprises a connector 61 receiving the signals from the various electronic circuits 18 of the different piezoelectric detectors 14. The connector 61 collects all the signals on a plurality of buses 62. Each bus 62 is connected to the input of a analog / digital converter 63 clocked at a predetermined sampling frequency, for example 100 kHz, the output of which is connected to an input of a programmable logic integrated circuit (for example of the FPGA type) 64 adapted to perform the detection of the pulses of pressure, the filtering of the signals, and their storage in a circular buffer memory 65. In the case where the sensor has a plurality of rows of piezoelectric detectors 14, the logic circuit 64 is also adapted to perform the intercorrelation calculation. The outputs of the circuit 64 are connected to a digital signal microprocessor (DSP) 66 programmed to control the logic circuit 64, to perform the various calculations and to manage the communications with an external measurement station 68 connected to the main circuit 50 of the sensor by a digital network 67, for example via an Ethernet or S 485 type link. The logic circuit 64 is programmed to deliver the signals to the microprocessor 66 with a sampling frequency compatible with said digital network 67, for example at 5 kHz. The microprocessor 66 is in particular programmed to detect the value of δmax and to calculate the linear weight as indicated above.

A sensor according to the invention may advantageously have a larger number of rows of detectors, for example three or four rows or more. These rows can be arranged on the same rigid common base, the width of which is adapted to receive the different rows of detectors piezoelectric juxtaposed, the whole being integrated in one piece in a passageway. Such a sensor comprising several rows may in particular be used in passageways likely to undergo severe deformation. Indeed, the fact of multiplying the rows ensures that the same vehicle wheel is, at least a given instant, fully carried by the sensor according to the invention, without being in contact with any portion of the road surface. Thus, regardless of the quality of the integration of the sensor with respect to the road surface, initially because of the wear of the latter, the quality of the detection remains good and reliable. Such a sensor comprising several rows may also be used for other applications, for example as weighing scales for low speed vehicles.

It should also be noted that it is possible to obtain the weight of the vehicle with a sensor having a single row, since this sensor extends in a direction inclined non-orthogonal to the passageway, a single vehicle wheel rolling successively on several adjacent detectors at different times, so that the intercorrelation of the detection signals is also possible.

In a variant, nothing prevents the provision that each electronic circuit 18 incorporates an analog / digital conversion module so as to directly supply the detection of digital detection signals to the sheet 47.

A piezoelectric detector according to the second embodiment shown in FIGS. 13 to 16 differs from the first embodiment mainly in that it comprises a molded plastic part 96 forming:

a soleplate 81 for supporting a piezoelectric washer 85,

a sleeve 82 that is elastically deformable in compression / vertical traction,

- And, from the end of the sleeve 82 opposite the sole 81, and extending radially outwardly, a base plate 102 of a rolling plate 86. The synthetic material making it possible to produce this part 96 is chosen so as to be sufficiently hard and rigid to be able to form a suitable support for the piezoelectric washer 85 (in particular by supporting the compressive prestressing substantially without deformation and more generally the pressure forces undergone by this piezoelectric washer 85). It is also chosen so as to obtain the appropriate mechanical properties of the sleeve 82 elastically deformable peripheral, given the shape imparted to this sleeve. In practice, excellent results have been obtained with a synthetic material selected from the group consisting of polyetheretherketone (PEEK) and liquid crystal polymers (LCP).

The soleplate 81 in particular forms a support face 1 10 in the lower part of the sleeve 82, this support face 1 10 being adapted to receive and support the piezoelectric washer 85, via an electrode 99 made of electrically conductive material as well. in the general shape of a ring similar to that of the piezoelectric washer 85. In this embodiment, the piezoelectric washer 85 is surmounted by a second upper electrode 98, also in the general shape of a ring. Preferably, the support face 1 is formed of the bottom of a peripheral groove formed in recess in the sole 81 in the lower part of the sleeve 82 to ensure proper centering and retention of the piezoelectric washer 85 and electrodes 98, 99 .

A printed circuit 97 is fixed in the central portion 141 of the soleplate 81 in the central housing delimited by the piezoelectric washer 85 and electrodes 98, 99. This printed circuit 97 carries in particular an integrated circuit 88 adapted to perform electronic functions, in particular as mentioned above with reference to the first embodiment. The upper electrodes 98 and lower 99 have lugs 100, 101 respectively for connection with the tracks of the printed circuit 97, so that the electrical charges delivered by the piezoelectric washer 85 are transmitted to the printed circuit 97.

Furthermore, the central portion 141 of the sole 81 is provided with recesses passing through its thickness for the passage of conductive tracks connecting tabs 94 which extend under the sole 81. After placing the various elements mentioned above in the piece 96, the piezoelectric washer 85 is compressed by screwing a ring 83 of pressure into the sleeve 82 (Figure 14). This pressure ring 83 has a thread 91 external to its upper part, adapted to cooperate with a thread 90 formed inside the upper part of the sleeve 82. The pressure ring 83 extends downwardly from this thread 91 with dimensions such that it does not come into contact with the inner wall of the sleeve 82. The compression ring 83 has a bottom face 142 in the form of a flat ring adapted to be superimposed on the upper electrode 98. The pressure ring 83 is provided with shapes 84 such as radial slots to allow its screwing and clamping with the aid of a suitable tool. The tightening torque imparted to the thrust ring 83 makes it possible to calibrate the compression preload of the piezoelectric washer 85. It should be noted in this regard that the adjustment of this compression prestressing can easily be carried out by simple measurement of the electrical detection signals delivered by the electronic circuit 97, so that their value corresponds to a predetermined value corresponding to the prestressing. desired compression.

The pressure ring 83 preferably has a central through bore 143 for subsequently introducing a layer 93 of a sealing and insulating filling material, for example silicone, which allows to seal and protect in this bore 143, the circuit printed 97 and the integrated circuit 88 it carries. This bore 143 is then itself closed by placing an upper plug 92 having a top plate 144 of generally square shape extending radially beyond the pressure ring 83, the corners of this plate 144 being endowed passing through holes 145 into which lugs 103 integral with the upper plate 102 of the molded piece 96 may be inserted.

A rolling plate 86 is then overmolded on the previously formed assembly so as to cover the peripheral edges of the plate 102, the ring 83 of pressure, the cap 92, and to be rigidly fixed thereto. This overmolding of the rolling plate 86 is made of a synthetic material suitable for forming a layer of leveling and wear-in particular a layer of resin rigid (for example selected from an epoxy resin filled with silica, a polyamide, a polyamide filled with glass fibers). The upper plate 102 of the molded part 96 advantageously has, in addition to the centering pins 103, forms which promote the fastening of the overmolded rolling plate 86, for example slots at these edges and / or its corners. The rolling plate 86 is generally parallelepipedal in shape, as in the first embodiment, and has an upper free plane face forming the measurement face 87 receiving the pressure forces exerted along the axis 89 of symmetry of the detector, which corresponds to the vertical when the detector is integrated in a sensor for moving vehicles.

In this second embodiment, there is also provided a lower base 95 overmolded under and around the sole 81 and tracks 94, this base 95 having at its two opposite ends at the longitudinal ends of the tracks 94, rabbets assembly 104, respectively 107, conjugated to each other, adapted to allow rapid assembly of two similar detectors according to the invention next to one another, with an electrical connection of the tracks 94 of the two detectors established by the simple effect of this assembly. However, there is nothing to prevent an additional step, for example welding or crimping, to ensure the electrical connection.

In the example shown, a first rabbet 104 is formed at the right end of the base 95, this rabbet 104 having a horizontal upper free face on which open holes 105. A second rabbet 107 is formed at the left end of the base 95, this second rabbet 107 having a horizontal lower free face from which lugs 108 extend downwardly so as to be able to penetrate the holes 105 of a first rabbet 104 of another adjacent detector. The first rebate 104 is also provided with a central recess 109 in which ends of the tracks 94 extend so that these ends can be slightly deformed in flexion under the effect of the pressure of the assembly and the ends. tracks from another adjacent detector.

To ensure good electrical contact and improve the electrical connection, each track 94 is advantageously provided on at least one of its ends, of a connection boss, for example by stamping and / or addition of fuse electrically conductive material (for example tin alloy) allowing a hot soldering of the ends of superimposed tracks. Such fuse electrically conductive material facilitating welding can be added to each end of the tracks, or over their entire surface.

In the example shown, the detector comprises three parallel tracks 94, electrically insulated from each other, one of which serves for the power supply of the printed circuit board 97 and its components, while the other two are used for the transmission of detection signals delivered by the printed circuit 97 (each of these two tracks corresponding to one of the phases of the electric current for the transmission of these signals). The ends of the tracks 94 thus constitute, on each side, a series of terminals making it possible to establish an electrical connection with a series of conjugate terminals of another adjacent analog piezoelectric detector.

A moving vehicle passage sensor according to the third embodiment of the invention may be formed of a plurality of such piezoelectric detectors, according to the second embodiment described above, juxtaposed on the same beam 146 as described hereinabove. above with reference to the first embodiment of the sensor according to the invention, in particular with a filling material 40 in the spaces surrounding the detector (FIG. 16) and separating the different adjacent detectors.

The different tracks 94 of each detector establish an electrical connection between the different detectors from one end to the other of the sensor by simply assembling the detectors together. These tracks 94 thus form an electrical connection layer of the detectors, which are thus mounted and electrically connected in series with each other on the beam 146.

Each detector according to this second embodiment is also advantageously characterized in that it comprises an electronic circuit comprising a charge amplifier and a drift compensation circuit enabling an enslaved detection signal to be delivered at a predetermined constant value independently of the possible untimely variations in value piezoelectric signals. In particular, advantageously and according to the invention, this electronic circuit can also be in accordance with WO 2012031964 and / or FR 2969279, as indicated above, modified to present a digital output and / or supplemented in particular by at least one module. Analog / digital conversion adapted to convert the output analog voltage into a digital signal. It further preferably comprises at least one memory adapted to store the digital values of the measured voltage. Said electronic circuit is thus adapted to deliver detection signals in the form of digital data on the tracks 94 and at said terminals of the detector.

Two tracks 94 are used for the transmission of the detection signals (in the form of digital data representative of an output voltage) according to a digital serial link protocol, the third conductor being used to supply the power supply of the electronic circuit. Thus, each series of terminals and the corresponding tracks 94 act as a digital serial bus, for example of the UART, LIN, CAN type ...

At one of the longitudinal ends of the sensor, the latter advantageously comprises, as in the previous embodiment, a main electronic processing circuit (not shown) receiving the different detection signals, and connected to the tracks 94 of the last detector mounted to this longitudinal end of the sensor.

This sensor may be integrated in a groove formed in passageway as shown in Figure 16, in the same manner as described above in relation to the other embodiments.

The invention may be the subject of numerous variants with respect to the preferred embodiments described above and shown in the figures. In particular, the elastically deformable device of the detector may be formed other than a sleeve, for example a plurality of elastic blades uniformly distributed at the periphery; each detector does not necessarily incorporate an electronic circuit for processing the signals delivered by the piezoelectric sensitive element, the electrical charges delivered by each piezoelectric sensitive element of the different detectors juxtaposed on a beam for forming a same sensor that can be transmitted to a single electronic circuit placed at the longitudinal end of the sensor; the mechanical assembly and electrical connection structures may be the subject of various embodiments performing the same functions and to obtain a detector extra flat. A super-flat detector according to the invention which is extremely reliable, precise, precalibrated, robust and insensitive to external disturbances may also be the subject of other applications, particularly for the accurate and reliable measurement of high pressure forces, possibly with parasitic horizontal components of relatively large values and / or in harsh environments, for example on public works sites, on board an aircraft or space systems, in connection with machining centers or other machines. tool...

Claims

1 / - Piezoelectric detector comprising at least one piezoelectric sensitive element (15, 85) interposed in an assembly capable of transmitting pressure forces to each piezoelectric sensitive element, said assembly comprising:

a plateau, called a rolling platform (16, 86), having a planar face, called the measuring face (17, 87), arranged to receive integrally said pressure forces exerted in a direction, referred to as the measuring direction, normal to the measuring face (17, 87) of this rolling plate,

an elastically deformable device (22, 82, 83) capable of subjecting each piezoelectric sensitive element to a compressive prestress in said measurement direction,

characterized in that said elastically deformable device (22, 82, 83) has a height in said measurement direction less than its largest dimension orthogonal to said measurement direction.

21 - Detector according to claim 1, characterized in that said device (22, 82, 83) elastically deformable has a height less than 15mm in said measurement direction.

3 / - Detector according to one of claims 1 or 2 characterized in that said device (22, 82, 83) elastically deformable has a height in said measurement direction less than half the largest dimension of said rolling plate orthogonally to the said direction of measurement.

4 / - Detector according to one of claims 1 to 3 characterized in that said device (22, 82, 83) elastically deformable comprises a sleeve (22, 82) connecting the peripheral plate (16, 86) rolling to a sole (21, 81) supporting each piezoelectric sensitive element (15, 85), said sleeve (22, 82) laterally delimiting an internal space accommodating each piezoelectric sensitive element (15, 85), with compressive preload in said measurement direction of each piezoelectric sensitive element (15, 85) between the rolling plate (16, 86) and the sole plate (21, 81). 5 / - Detector according to claim 4 characterized in that said sleeve (22, 82) is formed of a sealed elastic bellows.

6 / - Detector according to one of claims 1 to 5 characterized in that said sleeve (22) is fixed to the plate (16) of rolling and the sole (21) in the elastically deformed state in axial traction between the plate (16) of rolling and the sole (21), so as to impart said compressive prestressing on each element (15) piezoelectric sensitive by elastic return of the plate (16) of rolling towards the sole (21), each element (15) piezoelectric sensitive being thus elastically compressed between the rolling plate (16) and the sole (21).

7 / - Detector according to one of claims 1 to 5 characterized in that said sleeve (82) and at least a portion of the sole (81) are formed together of a single piece of synthetic material after molding.

8 / - Detector according to one of claims 1 to 7 characterized in that said device (22, 82, 83) elastically deformable comprises a piece (83) of pressure bearing on said elastically deformable device and applied with a clamping stress against each piezoelectric sensitive element (85) so as to exert at least part of said compression preload in the measurement direction.

91 - Detector according to claims 4 and 8 characterized in that said piece (83) pressure is supported on said sleeve (82) by screwing said piece (83) of pressure relative to said sleeve (82).

10 / - Detector according to one of claims 1 to 9 characterized in that the tray (16, 86) of rolling is guided relative to a sole (21, 81) for supporting each piezoelectric sensitive element so as to prohibit any relative displacement of the bed (16, 86) of rolling relative to the sole (21, 81) in the directions orthogonal to said measuring direction.

1 1 / - Detector according to one of claims 1 to 10 characterized in that it comprises a housing (20) central receiving an electronic circuit (18, 97) electrically connected to each element (15, 85) sensitive piezoelectric and adapted to be able to deliver an electrical signal, said detection signal, representative of said pressure forces. 12 / - Detector according to one of claims 1 to 1 1 characterized in that each element (15, 85) sensitive piezoelectric is disposed in said assembly in an annular geometry relative to a support plane face.

13 / - Detector according to one of claims 1 to 12 characterized in that each element (15, 85) sensitive piezoelectric is formed of a washer of polycrystalline piezoelectric ceramic material.

14 / - A sensor for moving vehicles, comprising a plurality of piezoelectric detectors (14) associated with a common support (1 1) intended to be implanted on the ground across a vehicle passageway, each detector (14) piezoelectric sensor being adapted to deliver an electrical signal, said detection signal, representative of the pressure force exerted on this piezoelectric detector by the passage of a vehicle wheel, each piezoelectric detector comprising at least one piezoelectric sensitive element (15, 85). interposed in an assembly adapted to subject each piezoelectric sensing element to vertical compression prestressing and to transmit to each piezoelectric sensing element the compressive forces generated by the passage of a vehicle wheel,

said common support (1 1) comprising a rigid flat top face, said base (13), carrying the piezoelectric detectors (14) juxtaposed next to one another above the base (13),

each piezoelectric detector (14) comprising a clean rolling plate (16, 86) having an upper planar face (17, 87) arranged to receive in full the force resulting from the passage of a wheel of a vehicle running above it. rolling plate, and for transmitting these forces to each piezoelectric sensitive element (15, 85) of said piezoelectric detector (14),

said rolling plate (16, 86) of each piezoelectric detector (14) being distinct and remote from the trays (16, 86) for rolling the piezoelectric detectors which are adjacent thereto, so that each piezoelectric detector (14) receives exclusively the force resulting from the passage of a wheel of a vehicle traveling above the rolling plate (16, 86) of this piezoelectric detector (14), characterized in that each piezoelectric detector (14) is according to one of claims 1 to 13.

15 / - Sensor according to claim 14, characterized in that said device (22, 82, 83) elastically deformable of each piezoelectric detector has a total height less than the total length of said tray (16, 86) of rolling in the direction of passing a vehicle wheel.