WO2015104265A1 - Multizone piezoelectric road sensor - Google Patents

Abstract

The invention relates to a road sensor detecting pressure forces, comprising a base (20), a transmission plate (28), and a plurality of substantially piezoelectric elements (21) inserted between said base (20) and said transmission plate (28), characterised in that it has a plurality of detection areas which are different from each other.

Description

 MULTIZONE PIEZOELECTRIC ROAD SENSOR

 The invention relates to a piezoelectric pressure sensor comprising a plurality of piezoelectric sensitive elements and for detecting the passage of rolling vehicles and the characteristics of the rolling vehicles by being implanted on the ground across a passageway of said vehicles. vehicles.

 WO2013017768 discloses a road detector comprising a plurality of piezoelectric sensors, each sensor comprising in particular a piezoelectric sensitive element and a rolling plate independent of the rolling plates of the other sensors, so that each sensor can be actuated independently of its neighbors. In addition, each sensor comprises an electronic circuit for processing the signals of said piezoelectric sensitive element and an elastic sleeve for prestressing in compression of said piezoelectric element.

 Such a detector is of excellent quality and has a very good behavior over time, including following many passages of vehicles. However, it is expensive to manufacture, both in terms of purchase of equipment (the electronic circuits for signal processing being expensive) and in terms of manufacturing processes, since each sensor must be the subject of an independent, specific and complex assembly.

 This is why other simpler road detectors have been proposed. Thus, there are known detectors as described by WO2012038955, in which a plurality of piezoelectric elements are interposed between a housing and a cover, said cover being directly screwed to the housing in order to apply a compressive prestressing of each of the piezoelectric elements.

 However, such a detector does not make it possible to carry out measurements of vehicle characteristics such as the crossing zone of the detector, the detection of a double axle, the measurement of the width of the vehicle, etc.

The reliability of the measurements of such detectors is also quite low because their sensitivity varies according to the portion of the detector on which the wheel of a vehicle passes. Indeed, the cover does not transmit the same efforts to the piezoelectric elements as the wheel passes in a central portion or on an edge of the detector. Moreover, in such a detector, the compression preload applied to the piezoelectric elements is not controlled and degrades over time. Indeed, such detectors are subjected to a very high number of passages and therefore compression-decompression cycles. The assembly of the cover to the housing therefore tends to take the game-especially by matting. The compression preload applied to the piezoelectric elements therefore tends to decrease over time. This loss of precision is not measurable (and therefore can not be corrected) and is more irregular along the detector between the different piezoelectric elements.

 The invention therefore aims to overcome these disadvantages.

 The invention aims to provide a road detector that is both inexpensive, accurate and reliable.

 The invention aims in particular to provide a detector for collecting a large number of characteristics on a vehicle.

 The invention aims more particularly to provide a detector whose entire surface is useful and provided reliable measurements.

 The invention also aims at providing a detector having excellent reliability of measurements over time.

 The invention aims more particularly at providing a detector whose measurements remain accurate even after a very large number of vehicle passes.

 The object of the invention is to provide a detector whose number of components is reduced.

 The invention also aims at providing such a detector whose integration in a passageway is simple, fast and inexpensive.

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

 The invention also aims to propose a method of manufacturing such a detector.

The invention aims in particular to provide a manufacturing method for making such a detector at a lower cost while conferring lasting reliability over time. The invention therefore relates to a pressure force road detector comprising:

 - a sole in one piece,

 a plateau, said transmission plate, in one piece, adapted to be able to transmit in one direction, said measurement direction, forces received on an upper face of the detector,

 a plurality of piezoelectric sensitive elements interposed between said soleplate and said transmission plate, adapted to generate electrical signals under the effect of forces transmitted along said measurement direction by said transmission plate,

characterized in that

 at least one first group of piezoelectric sensitive elements comprising at least one piezoelectric sensitive element is connected by a first electrical connection to at least one electrical signal processing unit,

 at least one second group of piezoelectric sensitive elements comprising at least one piezoelectric sensitive element is connected by a second electrical connection to at least one signal processing unit,

 said first group and first electrical connection being electrically isolated from said second group and second electrical connection, to each treatment unit at least.

 In addition, advantageously and according to the invention, said first group and second group are distinct by at least one parameter chosen from:

 • the footbed area occupied,

 • the number of piezoelectric sensitive elements,

 · The surface density of piezoelectric sensitive elements,

• the distribution of piezoelectric sensitive elements,

 • the average distance between piezoelectric sensitive elements,

The processing of the electrical signals of the piezoelectric sensitive elements, in particular the gain applied to the electrical signals of the piezoelectric sensitive elements. In particular, each processing unit receives electrical signals only piezoelectric sensitive elements disposed between said sole and said transmission plate, not piezoelectric sensitive elements disposed between another sole and / or another transmission plate. In particular, each processing unit does not receive electrical signals of piezoelectric sensitive elements arranged between sole portions and / or separate transmission plate portions which would have been assembled together, including by welding.

 The invention also relates to a pressure force road detector comprising:

 - a sole,

 a plateau, said transmission plate,

 a plurality of piezoelectric sensitive elements interposed between said sole plate and said transmission plate,

said transmission plate being adapted to be able to transmit forces in a direction, called measurement direction,

 at least one connecting member of the transmission plate to the soleplate,

 characterized in that each assembly member comprises:

 at least one portion, said elastic portion elastically deformed in pulling traction of the transmission plate towards the sole so as to exert a compression prestress in the measurement direction on each piezoelectric sensitive element interposed between the transmission plate and the soleplate,

 at least one abutment, referred to as a control abutment, in contact along said measurement direction with a range, referred to as the control range, of an element chosen from said transmission plate and the soleplate, by an anchorage of the body of assembly to said element selected from said transmission plate and the sole.

 The invention relates to a road detector, that is to say a detector intended to be arranged in a way of passage of vehicles in the broad sense, for example automobiles, trucks, aircraft, etc.

A vehicle passageway generally has a "normal" traffic direction of a vehicle on that lane. Throughout the text, the term "width" of the track means a dimension transverse to a normal direction of circulation of a vehicle on this track.

 A detector according to the invention is intended to be implanted on the ground across a vehicle passageway (road for automobiles, airport runway, etc.). It can be adapted to be arranged orthogonally to a direction of flow, or at an angle to the direction of circulation. Therefore a detector according to the invention generally has a length much greater than its width, the length of the detector being generally disposed in the width of the track.

 The force sensor according to the invention is adapted to deliver at least one electrical signal representative of a pressure force exerted by the passage of a vehicle over at least a surface portion of said force detector. Indeed, a detector according to the invention is particularly suitable for detecting outstretched forces in the form of pressures on an upper face of the detector.

 A force sensor according to the invention advantageously comprises an assembly adapted to be able to transmit to each piezoelectric sensitive element pressure forces applied to said assembly, for example by the passage of a vehicle above said assembly. The assembly advantageously comprises a sole and a transmission plate.

 A detector according to the invention advantageously comprises a single sole and a single transmission plate. That is to say that the soleplate and the transmission plate are respectively obtained in one piece by manufacture, and are therefore not respectively constituted, in the length and width of the detector, of multiple elements assembled or welded to each other. posteriori sets.

 It is thus inexpensive to manufacture because it includes a simple mechanical assembly.

A detector according to the invention also has significant reliability. Indeed, the sole and the transmission plate being each in one piece, the rate of force transmission from one portion to the other of the detector varies little, unlike detectors in which several sections are assembled, for example by welding: indeed welded portions introduce significant local variations in the sensitivity of the detector.

 In addition a detector according to the invention is simple to install on a road because it is in one piece and therefore does not require to assemble several modules. The duration of the installation work is thus reduced (no assembly or welding to be done at the place of installation). However, a detector according to the invention also has the advantage of having several distinct detection zones.

 Indeed, the invention allows the detection and measurement of several information relating to a vehicle passing on the detector, as with a detector comprising several sensors assembled one after the other in the width of a track, but without the drawbacks such as the high cost and the non-linearity of the forces transmitted to the piezoelectric sensitive elements over the length of the detector. In addition, the transmission of forces to the piezoelectric sensitive elements by the transmission plate is more homogeneous over the entire surface of the detector with a detector obtained by assembly / welding of several modules.

 A detector according to the invention therefore comprises several detection zones that are electrically independent of each other. Thus, a detector according to the invention makes it possible to obtain a lot of information on a vehicle passing over the detector, for example the number of wheels per axle of the vehicle or the detection of a vehicle traveling in a stopping belt. 'emergency. On the other hand, the detection zones are mechanically integral with one another as they form part of a single detector comprising a single sole and a single transmission plate.

The transmission plate is advantageously adapted to allow the detection of a point pressure force by a single detection zone. That is, the transmission plate is adapted to allow localized detection of a vehicle wheel by a detection zone, without all detection zones of the detector being activated. In particular, the Young's modulus of the transmission plate is adapted to allow the detection of a point pressure force by a maximum of three detection zones, said detection zone situated under the point pressure force receiving at least 70%, advantageously of the order of 80%, of said force.

 A detector according to the invention is therefore more generally adapted to detect two point pressure forces applied separately at a distance from each other of at least 5cm.

 The transmission of forces by the transmission plate of a detector according to the invention is homogeneous over a large part of the detector, and varies, if necessary, only in the vicinity of the assembly point of the transmission plate to the sole, and in advantageous embodiments described below, only near the edges of the plate and the sole, particularly near the longitudinal ends of the detector. The invention further provides a simple and reliable solution to overcome local variations in the transmission quality of transmission plate forces to piezoelectric sensitive elements.

 Each piezoelectric sensitive element is adapted to deliver an electrical signal, said detection signal, representative of the pressure force exerted on this piezoelectric sensitive element by the passage of a vehicle wheel.

 Each piezoelectric sensitive element is advantageously a piece of polycrystalline piezoelectric ceramic material.

 The piezoelectric sensitive elements are for example in the form of cylindrical pellets. Nothing prevents the use of other forms of piezoelectric sensitive elements, for example annular.

 Each piezoelectric sensing element is interposed in an assembly -particularly between a face, said support face, of a sole and a face, called the compression face, of a transmission plate proper to subject each piezoelectric sensitive element to a compression prestress in one direction, called the measuring direction, in particular in a vertical direction.

Advantageously, the compression face of said transmission plate abuts against each piezoelectric sensitive element in said measurement direction. Said transmission plate is adapted to be able to receive, on an upper face, opposite to the lower face (in particular opposite to the compression face), pressure forces - in particular the forces generated by the passage of a vehicle wheel on the detector - according to the measurement direction at least and transmit them to at least one piezoelectric sensitive element interposed between the face compression and the bearing face.

 In a detector according to the invention, the piezoelectric sensitive elements are not all electrically connected to each other. In particular, at least one piezoelectric sensitive element is electrically connected to at least one electrical signal processing unit, independently of at least one other piezoelectric sensitive element.

 Thus, the piezoelectric sensitive elements form at least two groups of piezoelectric sensitive elements (each group comprising at least one piezoelectric sensitive element) electrically connected independently. Thus, the surface of the detector is divided into at least two zones, called detection zones, each zone comprising the piezoelectric sensitive elements of the same group of piezoelectric sensitive elements. The surface of the detector here corresponds to its spatial extent in two dimensions, in particular its extent parallel to the surface of the ground when it is installed.

 The invention also makes it possible, for example, to compensate for a poor localized transmission of forces by the transmission plate: this is particularly often the case on the edges of the detector and / or in the vicinity of connection members between the sole and the plate of the transmission. transmission which locally maintain the transmission plate at a predetermined distance from the soleplate.

 Another advantage provided by the invention is therefore to provide a detector whose entire measurement surface (especially between a bearing surface of the sole and a compression face of the transmission plate) is really useful. The electrical signals of any portion of the detector surface are reliably exploitable.

Indeed, since the detector comprises several detection zones, the sensitivity of each detection zone can be corrected. Thus, the electrical signals produced by the piezoelectric sensitive element (s) of a detection zone located near a longitudinal end of the detector and therefore in which the transmission of forces by the transmission tray is logically smaller- can be corrected by a signal processing unit. Thus, by applying an appropriate gain to the electrical signals of at least one detection zone, and in particular of each detection zone, of the detector, the sensitivity of the latter is good and reliable over its entire surface.

 A detector according to the invention is furthermore advantageously characterized in that:

 the first group of piezoelectric sensitive elements occupies a first detection zone, called high sensitivity zone,

 the second group of piezoelectric sensitive elements occupies a second detection zone, called a low-sensitivity zone,

 said high sensitivity zone is distinct from said low sensitivity zone.

 Edge effects occur in peripheral areas of the detector by rapidly varying the sensitivity of the piezoelectric sensitive elements between the edge of the detector and a more interior area. The high sensitivity zones make it possible to decouple these peripheral zones from the other zones of the detector (where low sensitivity zones are arranged). Thus their electrical signals can be adequately processed (for example by the application of a gain) to allow the exploitation of electrical signals produced by the peripheral areas.

 In addition, said high sensitivity zone and said low sensitivity zone advantageously have different surfaces and / or a different number of piezoelectric sensitive elements and / or a different piezoelectric sensitive element density and / or a distribution of piezoelectric sensitive elements. different and / or the signals of their piezoelectric sensitive elements are treated differently (for example by applying a different gain).

In particular, advantageously and according to the invention, the surface of said high sensitivity zone is smaller than the surface of said low sensitivity zone. Thus, said high sensitivity area covers a detector surface smaller than the surface of the detector covered by said low sensitivity area.

 The fact that the high sensitivity areas are of smaller surface area than the low sensitivity areas makes it possible to improve the measurement in the edge zones -in particular the longitudinal ends of the detector. Indeed, while the measurements made in end zones or junction between detector portions are generally unusable because of a significant local linear variation of the transmission rate of force by the transmission plate, the invention proposes dividing the surface of the detector into a plurality of detection zones and forming high sensitivity areas of smaller dimensions for fine-tuning the linearity variations of the transmission rate of forces by the transmission plate. Indeed, the higher a high sensitivity area is small (especially narrow in the direction of the detector length), and less variation in the transmission rate of forces by the transmission plate is important within this detection zone. Thus, the detection resolution of the detector is increased, and the local structural variation in sensitivity (or transmission of pressure forces) is linearised. Therefore, the electrical signals produced by the piezoelectric sensitive elements that form a detection zone - especially a high sensitivity area - can be corrected by appropriate processing. An appropriate treatment is for example a linear processing, such as the application of a determined gain to the electrical signals of each group of piezoelectric sensitive elements of the same detection zone.

 Thus, advantageously and according to the invention, the detection zones are smaller and more numerous in portions of the detector in which the transmission of forces by the transmission plate varies greatly.

Each high sensitivity zone is advantageously arranged in a portion of the detector in which transmission of forces by the transmission plate varies greatly and / or is less than its average transmission of forces (edges, proximity of an assembly member, etc. .). Alternatively or in combination, the detection zones are smaller and more numerous in portions of the detector in which a higher spatial detection resolution is required. For example, it is possible to provide a larger number of detection zones, respectively smaller in size than the mean dimension of the detection zones of the detector, in portions of the detector or a higher wheel-passing frequency is expected than in other portions of the detector.

 In particular, advantageously and according to the invention, at least one high sensitivity zone is located near each longitudinal end of the detector.

 Each low sensitivity zone is instead arranged in a portion of the detector of the transmission plate whose transmission of efforts is good and homogeneous.

 However, there is nothing to prevent the provision of one or more high sensitivity zones in at least a portion of the detector in which a greater spatial resolution of detection is required, for example in portions of the detector in which the passage of vehicle wheels is more common than in other parts of the detector, once the detector is installed in a lane.

 Alternatively or in combination, advantageously and according to the invention, the number of piezoelectric sensitive elements in said high sensitivity zone is different from the number of piezoelectric elements in said low sensitivity zone.

 Thus, in a detector according to the invention, the number of piezoelectric sensitive elements in said low sensitivity zone may be greater than the number of piezoelectric sensitive elements in said high sensitivity zone. This is for example the case if the surface density of piezoelectric sensitive elements is homogeneous over the entire surface of the detector, and that said low sensitivity area covers a larger area of the detector than the area covered by a high sensitivity area.

Alternatively, in other embodiments of a detector according to the invention, the number of piezoelectric sensitive elements in the high sensitivity area is larger than the number of piezoelectric sensitive elements in the low sensitivity area. The surface density of piezoelectric sensitive elements in the high sensitivity zone is then higher than in the low sensitivity zone. The piezoelectric sensitive elements are therefore non-uniformly distributed on the surface of the detector, so that the surface density of piezoelectric sensitive elements is variable on the surface of the detector.

 The surface density of piezoelectric sensitive elements for each detection zone (high sensitivity and low sensitivity) therefore depends both on their surfaces and on the number of piezoelectric sensitive elements they contain. Also, if necessary, the density of piezoelectric sensitive elements can be modified by modifying the characteristics (size, type, etc.) of each piezoelectric sensitive element.

 Advantageously and according to the invention, the density of the piezoelectric sensitive elements in each high sensitivity zone and in each low sensitivity zone is adapted to compensate the surface variations of a transmission rate of a force exerted on a measurement face by the plateau. of transmission.

 Said low sensitivity zone comprises at least two piezoelectric sensitive elements.

 Said high sensitivity zone comprises at least two piezoelectric sensitive elements.

 Each low sensitivity zone and each high sensitivity zone advantageously comprises between 3 and 9 piezoelectric sensitive elements, in particular advantageously of the order of 4 to 6 piezoelectric sensitive elements.

In addition, advantageously and according to the invention, alternatively or in combination, the piezoelectric sensitive elements of said high sensitivity zone can be distributed in said high sensitivity zone according to a pattern different from the distribution of the piezoelectric sensitive elements of said low sensitivity zone in said of said low sensitivity zone. In addition, advantageously and according to the invention, the electrical signals delivered by the piezoelectric sensitive elements of a first detection zone are treated differently from the electrical signals delivered by the piezoelectric sensitive elements of a second detection zone.

 In particular, a different gain is applied to the electrical signals delivered by the piezoelectric sensitive elements of each type of zone (surface, number of piezoelectric sensitive elements, patterns, etc.) of the same characteristics. In particular, a different gain is applied to each high sensitivity area of the gain applied to each low sensitivity area. More particularly, the gain applied is advantageously distinct in each detection zone.

 With separate detection zones according to the invention, it is thus possible to obtain a simple assembly detector, which is, after manufacture, in one piece, and which has, after calibration (ie after assigning a determined gain to each detection zone), an identical sensitivity over its entire surface, so that its entire surface is useful for the recovery of data on vehicles passing over the detector.

 Furthermore, advantageously and according to the invention, the piezoelectric sensitive elements of the same detection zone are adjacent and connected in parallel with each other.

 The piezoelectric sensitive elements of the same zone are electrically connected in parallel, that is to say that the electrical signals - in particular the electric charges - that they deliver are summed between them. Thus, an area (high sensitivity or low sensitivity) of the detector according to the invention corresponds to a surface portion of the detector in which piezoelectric sensitive elements are electrically connected to each other.

 Moreover, advantageously and according to the invention, all the piezoelectric sensitive element piezoelectric sensitive elements are identical to each other (in particular of identical material and size, in particular of the same model).

Advantageously, a detector according to the invention is also characterized in that it comprises a unit, called a central processing unit, electrical signals delivered by the piezoelectric sensitive elements disposed between said sole plate and said transmission plate.

 Advantageously, said central unit is electrically connected to the piezoelectric sensitive elements of each high sensitivity zone and to the piezoelectric sensitive elements of each low sensitivity zone, directly or indirectly.

 A detector according to the invention can, in some particular embodiments, be realized at lower cost with a single signal processing unit. The central unit then processes the electrical signals of all the piezoelectric sensitive elements located between the sole plate and the transmission plate. Said central unit advantageously comprises several signal input connectors, or a multiplexed input.

 Said central processing unit of the detector signal is advantageously adapted to be able to process in parallel the signals of each high sensitivity zone and of each low sensitivity zone.

 Said central unit is adapted to be able to apply a determined value gain stored in a memory to the electrical signals of each detection zone.

 The central unit can be adapted, if necessary to perform operations from the electrical signals of different detection zones. Thus, said central unit may be adapted to summing the electrical signals of several detector fields, if necessary, in order to calculate, for example, the weight of a vehicle.

 Advantageously, a detector according to the invention is also characterized in that it comprises:

 a unit, called local unit, for processing the electrical signals delivered by the piezoelectric sensitive elements of said high sensitivity zone, for each high sensitivity zone,

a local unit for processing the electrical signals delivered by the piezoelectric sensitive elements of said low sensitivity zone, for each low sensitivity zone. Each local electrical signal processing unit has at least one analog input of analog electrical signals to which are connected in parallel the piezoelectric sensitive elements of the same detection zone.

 Each piezoelectric sensitive element according to the invention is adapted to deliver an electric charge depending on the pressure forces to which it is subjected. The instantaneous sum of the charges of all the piezoelectric sensitive elements of the detector is therefore received by said local signal processing unit.

 Each local unit is, advantageously and according to the invention, electrically connected to said central unit. Thus, each local unit makes it possible to transform the analog electrical signals delivered by the piezoelectric sensitive elements.

 In some embodiments, each local unit converts electrical signals in the form of electrical charges received from the piezoelectric sensitive elements into electrical signals in the form of electrical voltage, and transmits a digital signal to the detector's central processing unit.

 In other embodiments, each local unit converts the analog electrical signals delivered by the piezoelectric sensitive elements into digital signals, applies a gain to the received signals, and transmits a digital signal to the detector's central processing unit.

 The central unit is advantageously adapted to perform operations from the signals coming from each local unit of each detection zone.

 In addition, advantageously and according to the invention, each local unit is disposed near the piezoelectric sensitive elements to which it is electrically connected.

Each local processing unit is arranged near the piezoelectric sensitive elements to which it is connected, that is to say that it is arranged in the detection zone of the detector from which it collects the electrical signals. It can be arranged in the same plane as the sensitive elements piezoelectric of its detection zone, or above, or well below the plane of said piezoelectric sensitive elements.

 Placing the local unit near the detection zone whose electrical signals it processes makes it possible to locally measure additional information such as, for example, the local temperature of the detector.

 Indeed, the temperature of the detector can vary from one zone to another. This is for example the case on a lane, part of which is shaded, and the other is directly exposed to the sun. However, the sensitivity of the piezoelectric sensitive elements depends on the temperature. Therefore, the local measurement of the temperature makes it possible to correct the measurements of the piezoelectric sensitive elements as a function of their temperature.

 Advantageously, each local unit is a specialized integrated circuit.

 In addition, advantageously and according to the invention, the detector comprises a plurality of high sensitivity zones.

 Similarly, advantageously and according to the invention, said detector comprises a plurality of low sensitivity zones.

 In addition, advantageously and according to the invention, said detector comprises a plurality of high sensitivity and / or low sensitivity zones in the length of said detector.

 A detector according to the invention comprises a plurality of detection zones in the length of the detector.

 A detector according to the invention advantageously comprises, for each passageway, in the width of the passageway (that is to say along the length of the detector) a total number of detection zones of between 5 and 50 zones. , in particular between 10 and 30 zones, and more particularly advantageously between 15 and 20 zones.

Advantageously and according to the invention, the dimensions of each low-sensitivity zone and of each high-sensitivity zone are adapted to enable the detection - and more particularly the distinction - of a single wheel and a double axle. Thus, the width of a low sensitivity zone-the width being measured according to the main dimension (length) of the detector corresponding to a direction transverse to a normal direction of circulation on a track is advantageously less than 30 cm, especially advantageously less than 20 cm, more particularly advantageously of the order of 10 cm. The width of a high sensitivity zone is advantageously less than the width of a low sensitivity zone.

 Similarly, a detector according to the invention comprises a plurality of high sensitivity areas and / or low sensitivity in the width of said detector.

 A detector according to the invention comprises a plurality of detection zones in the width of the detector.

 Advantageously, a detector according to the invention comprises several rows of piezoelectric sensitive elements, successive in the direction of the width of the detector (that is to say in the normal direction of flow on a path).

 This allows for example to obtain by calculation the speed of an axle and therefore its equivalent weight.

 According to another aspect, the invention also relates to a pressure force road detector comprising:

 - a sole,

 a plateau, said transmission plate adapted to be able to transmit in one direction, said measuring direction, forces received on an upper face of the detector,

 a plurality of piezoelectric sensitive elements interposed between said sole plate and said transmission plate,

 at least one connecting member of the transmission plate to the soleplate,

characterized in that each assembly member comprises:

at least one portion, said elastic portion elastically deformed in pulling traction of the transmission plate towards the sole so as to exert a compression prestress in the measurement direction on each piezoelectric sensitive element interposed between the transmission plate and the soleplate, at least one abutment, referred to as a control abutment, in contact along said measurement direction with a range, referred to as the control range, of an element chosen from said transmission plate and the soleplate, by an anchorage of the body of assembly to said element selected from said transmission plate and the sole.

 More particularly, advantageously and according to the invention, the transmission plate is urged against said piezoelectric sensitive element by each elastic portion of each assembly member. The compression preload is therefore exerted on each piezoelectric sensitive element by elastic return of the transmission plate to the sole in the measurement direction.

 The assembly member is anchored on the one hand to the transmission plate and on the other hand to the sole. The assembly member may be anchored by any anchoring means to the transmission plate and the sole, including by anchoring means to the transmission plate different anchoring means to the sole. Among the anchoring means are, for example, screwing, welding, brazing, crimping, etc. One can also realize an assembly member according to the invention in one piece with the transmission plate or with the sole and assemble by another means of assembly to the other element of the transmission plate or the sole .

 The invention makes it possible to obtain a pressure force detector in which the compression prestressing of each piezoelectric sensitive element is controlled and durable over time.

 Indeed, the control stop allows to control the preload applied to said piezoelectric sensitive elements during the manufacture of a detector according to the invention, as described below.

In addition, during the passage of a vehicle on a detector, the elastic portion of each assembly member accompanies the pressure forces in the measuring direction. Thus, the (s) mechanical anchoring (s) fixed (s) of each assembly member to the transmission plate and / or the sole do not undergo (or little) deterioration -notement not (or little) deterioration by matting. In addition, advantageously and according to the invention, the stiffness of said elastic portion of each connecting member is adapted so that the stiffness of an assembly comprising each assembly member of said detector is at least 10 times less than the stiffness of an assembly comprising each piezoelectric sensing element of said detector.

 The assembly comprising each assembly member of said detector provides an elastic assembly of the transmission plate to the sole.

 Thus, the stiffness of the elastic assembly of the transmission plate to the sole is much lower than the stiffness of the set of piezoelectric sensitive elements. The compressive deformation of the elastic portion during the passage of a vehicle is negligible and even zero, so that the compression preload remains constant, regardless of the pressure forces experienced by the detector in use.

 More particularly, the stiffness of the elastic assembly of the transmission plate to the soleplate is much lower, particularly at least 10 times less than the stiffness of a set of elements interposed between the compression face and the bearing face. . The stiffness of said elastic assembly of the transmission plate to the soleplate is advantageously at least 20 times less than the stiffness of all the elements interposed between the compression face and the bearing face, more particularly it is advantageously of the order 30 times less than the stiffness of all the elements interposed between the compression face and the bearing face.

 Each elastic portion of each connecting member is elastically deformable globally in the measurement direction and at least for elastically deformed part globally in the measuring direction after assembly of the different constituent elements of the detector in the measuring direction.

Such assembly members also make it possible to reduce the local variations in the transmissivity of the forces by the transmission plate. Thus, when the transmission plate was for example screwed to the sole in detectors prior to the invention, the transmission plate was locally kept at a distance from the sole, thus locally varying the rate of transmission of efforts. An assembly member according to the invention makes it possible to avoid such transmission defects and to transmit to the piezoelectric sensitive elements forces more faithful to the forces received on a measuring face.

 In addition, advantageously and according to the invention, the transmission plate is assembled to the soleplate by an assembly absorbing shear forces orthogonal to said measurement direction (in particular horizontal) without transmitting them to each piezoelectric sensitive element. In particular, advantageously and according to the invention, each assembly member is adapted to absorb any shear forces orthogonal to said measurement direction (including horizontal shear forces).

 According to a variant of the invention, this function is exerted by each assembly member only, which is adapted for this purpose, in particular to prevent any relative displacement of the transmission plate relative to this sole in the directions orthogonal to said direction of rotation. measure (especially in horizontal directions).

 According to another variant of the invention, the transmission plate is further guided relative to the sole independently of each connecting member, so as to prohibit any relative displacement of the transmission 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 transmission plate and the sole.

 In addition, advantageously and according to the invention, each assembly member is made of a Young's modulus material greater than 50 GPa, said elastic portion having a thickness and a shape adapted to be deformed elastically in said measurement direction. Each assembly member is made of a Young's modulus material of the order of 70 GPa.

More particularly, each assembly member is adapted -by its material, by its dimensions and by its geometric shape- to be able to at least partly elastically deformed in tension overall in said measurement direction. More particularly, each assembly member is elastically deformed in extension between the sole plate and the transmission plate.

 On the other hand, the elastic portion of each assembly member is advantageously locally elastically deformed in bending. The elastic portion has for this purpose at least a secant main direction portion-that is to say non-collinear- to said measuring direction.

 More particularly, the elastic portion advantageously has bent portions elastically deformed in flexion. Thus, the elastic portion advantageously has a shape generally "S".

 The deformation in extension of the elastic portion of the assembly member between said control stop and the transmission plate is obtained by flexural deformation, locally, of the elastic portion, in particular by elastic deformation in bending of the branch intermediate and / or angular links bent between upper branch and intermediate branch and between lower branch and intermediate branch.

 Thus, in a particular embodiment of the invention, the elastic portion of each connecting member advantageously has, in profile through a cross section to the detector, an upper branch, directly projecting from the underside of the transmission plate and substantially parallel to the measurement direction. This upper branch is connected to a lower branch extending substantially parallel to the measurement direction. The lower branch and the upper branch are therefore generally parallel, non-collinear.

 The lower branch and the upper branch are interconnected by an intermediate branch non-collinear to the measurement direction. The intermediate branch forms angled angular connections between 60 ° and 120 ° with the upper branch and with the lower branch. The intermediate branch is for example substantially orthogonal to the measurement direction.

 The lower branch ends at the control stop.

The elastic portion advantageously extends between: a control stop in abutment against a control range of a first element chosen from the transmission plate and the soleplate,

 and an anchorage to the second of said transmission plate and sole.

 In a non-exclusive preferred embodiment of the invention, the first element is advantageously the sole, the second element being the transmission plate. Said elastic portion of each assembly member therefore extends between the control stop and the transmission plate.

 In such embodiments, each assembly member is advantageously in one piece with the transmission plate, that is to say that the transmission plate comprises said connecting members. Each assembly member protrudes from a lower face of the transmission plate. Said lower face of the transmission plate comprises said compression face.

 Furthermore, said control range is advantageously opposite said second element of said transmission plate and sole.

 It is therefore in particular opposite the underside of the transmission plate in the embodiments in which each assembly member is in one piece with the transmission plate.

 Each assembly member is anchored to said at least one member selected from said transmission plate and the soleplate, by plastic deformation of a portion, said plastic portion, said assembly member on a stop, said anchor stop, said selected from said transmission plate and the sole

 Advantageously and according to the invention, each assembly member is anchored to the sole by plastic deformation of a portion, said plastic portion, said assembly member on a stop, said anchor stop, the sole.

 Each assembly member is therefore advantageously crimped on the sole.

In compatible embodiments, the anchor stop is on a face of the sole generally opposite to said bearing face. The anchoring of each assembly member to the soleplate is adapted to maintain the resiliently deformed elastic portion in pulling tension in the measuring direction, and to maintain each control stop of said assembly member in contact with a bearing surface. sole control.

 The control stop is advantageously projecting laterally from the assembly member.

 The control abutment is, on each connecting member, between the elastic portion and the plastic portion of said assembly member.

 Furthermore, a detector according to the invention advantageously comprises a plurality of assembly members distributed on either side of the compression face of said transmission plate. Similarly, said assembly members distributed on either side of the bearing face of said sole.

 A detector according to the invention advantageously comprises two assembly members distributed on either side of the compression face of said transmission plate.

 Each assembly member forms a thin wall projecting generally in the measurement direction from the lower face of the transmission plate. Said assembly members each advantageously form a thin wall on either side of the bearing face and the compression face, so as to form a housing for accommodating said piezoelectric sensitive elements between the compression face, the bearing face, and between the two assembly members.

 Said connecting members are advantageously continuous along the detector. In addition, they are advantageously anchored sealingly to the transmission plate (especially when they form a single piece with it), and the sole. More particularly, the detector advantageously comprises a seal between each control abutment and each control surface.

The detector further comprises end covers adapted to close the two longitudinal ends of the detector tightly. Thus, the receiving housing of said piezoelectric sensitive elements is sealed and protects said piezoelectric sensitive elements (and any other internal elements such as electrical circuits and / or electronic) external attacks such as water, dust, etc..

 In addition, a detector according to the invention advantageously further comprises a tray, said rolling tray:

 - separate from the sole plate and transmission plate,

 adapted to be able to receive pressure forces on a face, called measuring face,

 adapted to transmit pressure forces received on the measurement face in said measurement direction,

 - Mounted on and in contact with the transmission plate, so as to transmit the pressure forces received on the measurement face to said transmission plate in said measurement direction.

 The transmission plate is thus interposed between said rolling plate and at least one piezoelectric sensitive element.

 The rolling plate has an upper face, said plane measurement face, adapted to receive, in the measurement direction at least, the forces resulting from the passage of a wheel of a rolling vehicle directly on this rolling plate, and to transmit these efforts by a lower face of the rolling plate. The lower face of the rolling plate is advantageously in surface contact with the upper face of the transmission plate so that the forces in the measurement direction resulting from the passage of a vehicle wheel on the measurement face are transmitted via the transmission plate, to at least one piezoelectric sensitive element of said piezoelectric detector, in particular to at least one piezoelectric sensitive element situated vertically below a zone of the measuring face receiving said pressure forces.

The rolling plate is advantageously of great rigidity. Similarly, the transmission plate is advantageously in its thick portion of transmission of the efforts at least a high rigidity. Thus, the deformation of the transmission plate and the rolling plate under the effect of the passage of a vehicle is minimal and substantially all efforts applied by the vehicle to the measuring surface is transmitted to the piezoelectric sensitive elements.

 A detector according to the invention may advantageously be 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.

 Furthermore, the sole forms a common support for all the piezoelectric sensitive elements. In a non-exclusive advantageous embodiment of the invention, the sole is a profile forming a support beam of all the piezoelectric sensitive elements.

 Similarly, the transmission plate is advantageously a profile. Advantageously and according to the invention, the transmission plate is in one piece. That is to say that the transmission plate, including each assembly member is made profiled in a single substantially homogeneous material. For example, the transmission plate is a profile in an aluminum-based alloy.

 The profile of the transmission plate advantageously has a thick portion between a lower face (comprising the compression face) and an upper face, and two connecting members projecting from the lower face, on either side of the face of the compression.

 In certain advantageous embodiments of the invention, the piezoelectric sensitive elements are aligned in a single row, one after the other, along the largest dimension of the sole.

 In alternative and advantageous embodiments of the invention, the piezoelectric sensitive elements are aligned in several rows - in particular in two rows and arranged in staggered rows.

Nothing prevents us from considering other configurations of the piezoelectric sensitive elements. In addition, advantageously and according to the invention, the percentage difference between the value of the sensitivity of each piezoelectric sensitive element and the value of the average sensitivity of all the piezoelectric sensitive elements at least in the same zone is less than one. percent (1%).

 In a detector according to the invention, the set of piezoelectric sensitive elements substantially delivers a signal of the same amplitude for the same force undergone in the measurement direction.

 Advantageously and according to the invention, a detector further comprises at least one centering film interposed between the transmission plate and the soleplate. Each centering film has at least one housing-advantageously a plurality of housings-adapted to each receive a piezoelectric sensitive element. Each centering film makes it possible to maintain the position of each piezoelectric sensitive element when assembling a detector according to the invention.

 Advantageously, a detector according to the invention comprises a single centering film per detection zone.

 In some embodiments, the detector includes a single centering film.

 Advantageously and according to the invention, a detector further comprises a first thin band, said conduction band, comprising at least one conductive electrical circuit, said conduction band being interposed between said piezoelectric sensitive elements and the transmission plate.

 Advantageously and according to the invention, a detector further comprises an electrically insulating thin strip interposed between said first conduction band and the transmission plate.

 Advantageously and according to the invention, a detector further comprises a second conduction band comprising at least one conductive electrical circuit, said second conduction band being interposed between said piezoelectric sensitive elements and the soleplate.

Said first and second conduction strips comprise electrical circuits electrically connected to one or more units signal processing. Said first conduction band (respectively the second conduction band) puts the upper faces (respectively the lower faces) of each group of piezoelectric sensitive elements of the same zone (high sensitivity or low sensitivity) in series electrical connection with the treatment unit of said zone (respectively high sensitivity or low sensitivity).

 The invention also relates to a method of manufacturing a road detector according to the invention.

 The invention therefore relates to a method for manufacturing a pressure force road detector in which a plurality of piezoelectric sensitive elements are interposed between a sole plate and a transmission plate, in one piece, adapted to be able to transmit forces in a direction, said measurement direction, said piezoelectric sensitive elements being adapted to generate electrical signals under the effect of forces transmitted in said measurement direction by said transmission plate,

characterized in that

 a first electrical connection is created between at least a first group of piezoelectric sensitive elements comprising at least one piezoelectric sensitive element and at least one electrical signal processing unit,

 a second electrical connection is created between at least one second group of piezoelectric sensitive elements comprising at least one piezoelectric sensitive element and at least one signal processing unit,

 said first group and first electrical connection being electrically isolated from said second group and second electrical connection, to each treatment unit at least.

 In particular, in a process according to the invention:

 a first group of piezoelectric sensitive elements is arranged in a first surface portion of the detector so as to form a first detection zone, called a high sensitivity zone,

a second group of piezoelectric sensitive elements is arranged in a second surface portion of the detector so as to form a second detection zone, called a low sensitivity zone, said high sensitivity zone is made distinct from said low sensitivity zone.

 The invention also relates to a method for manufacturing a pressure force road detector in which:

 several piezoelectric sensitive elements are interposed between a soleplate and a transmission plate adapted to be able to transmit forces in a direction, referred to as a measurement direction,

 said transmission plate is assembled to said soleplate by at least one connecting member,

characterized in that

 - Elastically deforming a portion, said elastic portion, of each assembly member, in pulling force of the transmission plate to the sole in the measuring direction, so as to exert compression prestressing on each piezoelectric sensitive element interposed between the transmission plate and the sole,

 an abutment, called said control abutment, of each abutment member is brought into abutment in said measuring direction against a bearing surface, referred to as the control surface, of said element chosen from said transmission plate and the soleplate to which said abutment member is anchored; 'assembly.

 Advantageously and according to the invention, each control abutment of each abutment member is brought into abutment along said measurement direction against a control surface, said element selected from said transmission plate and the soleplate to which said body is attached. assembly, by canceling a game, said prestressing play, predetermined between said control stop and said control range. The prestressing clearance makes it possible to control the compression preload applied to each piezoelectric sensitive element in a device according to the invention.

Advantageously, to assemble the transmission plate to the soleplate, each assembly member is anchored to at least one element selected from said transmission plate and the soleplate. More particularly, in embodiments in which an assembly member is a separate part of the transmission plate and the sole, said assembly member is anchored by a first end to the transmission plate and a second end to the sole. In other alternative embodiments or in combination, in which an assembly member is in one piece with the transmission plate (or with the sole), said assembly member is anchored by a free end to the soleplate. (respectively to the transmission plate).

 The control abutment and the range of the sole have respectively adapted forms so that the contact reaction between the control stop and the range comprises at least one non-zero component parallel to the measurement direction.

 More particularly, the span advantageously has a surface orthogonal to the measurement direction. Similarly, the control stop advantageously has a surface orthogonal to the measurement direction.

 Advantageously and according to the invention, each assembly member is chosen with an elastic portion adapted so that the stiffness of an assembly comprising each assembly member of said detector is at least 10 times-especially 20 times and more advantageously 30 times- less than the stiffness of an assembly comprising each piezoelectric sensitive element of said detector.

 The stiffness of the elastic assembly being much lower than that of the set of piezoelectric sensitive elements - and more particularly of all the elements interposed between the compression face and the bearing surface - during the anchoring of each assembly member to the transmission plate and / or sole, only the elastic portion of each assembly member deforms elastically overall in the measurement direction.

 Advantageously and according to the invention:

 in a first step, the at least one piezoelectric sensitive element is interposed between a face, said support face, of a sole and a face, referred to as the compression face, of the transmission plate,

 in a second step, the transmission plate is assembled to the soleplate by anchoring each assembly member to the soleplate,

and in that between the first and the second step, a game, said prestress play, strictly positive remains between each control stop of each assembly member and each control surface opposite each control stop, said prestressing set being canceled by the second step.

 During the anchoring of each assembly member to the transmission plate and the sole to assemble the transmission plate to the sole, the elastic portion of said assembly member is elastically tensioned in the measurement direction.

 The shapes of the transmission plate and the soleplate are adapted so that, when in a first step all the elements interposed between the compression face of the transmission plate and the bearing face are interposed and brought into contact, the control stop is opposite a control range with a game, said prestressing game, strictly positive between said control stop and said control range.

 Before the anchoring of each assembly member to the transmission plate and / or the soleplate, the control stop is at a predetermined distance -forming a game, called prestressing game- in said direction of measurement of the control range .

 The compressive prestressing applied (after the assembly of the transmission plate to the soleplate) to the piezoelectric sensitive elements interposed between the transmission plate and the soleplate is determined by the prestressing play. The respective shapes, of the transmission plate, of each assembly member, of the sole, and of all the elements interposed between the compression face and the bearing face (in particular the piezoelectric sensitive elements) determine the set of prestressing and thus the compressive prestressing experienced by said piezoelectric sensitive elements once the transmission plate assembled to the sole.

 The prestressing clearance is advantageously substantially the same between each control abutment and each inspection scope opposite. The particular prestressing clearance is advantageously substantially the same over the entire length of the control stops of the profiled connecting members and over the entire length of the control surface of the profiled sole.

Thus, once said transmission plate is elastically assembled to said sole, the percentage difference between the value of the compression preload applied to each piezoelectric sensitive element and the average value of the compression preload applied to all the piezoelectric sensitive elements of the detector is small.

 Advantageously and according to the invention, the transmission plate and the assembly members are produced in one piece. The transmission plate and the assembly members are advantageously made in a single profiled part.

 Advantageously and according to the invention, said second step of assembling the transmission plate to the sole by anchoring each fastener member to the soleplate is performed by plastic deformation of a portion, called the plastic portion, of each member. assembly on a stop, said anchor stop, of the sole, each elastic portion of said assembly member being simultaneously elastically deformed.

 The plastic deformation of the plastic and elastic portion of the elastic portion are substantially simultaneous during the anchoring of the transmission plate to the sole.

 Each assembly member is crimped on the sole, more specifically a plastic portion of each assembly member is crimped on an anchor abutment of the sole.

 Advantageously, the plastic portion does not differ from the elastic portion of material and thickness. Only the crimping of the plastic portion on the sole is adapted to deform the plastic portion mainly plastically, that is to say beyond its elastic limit.

 The sole advantageously has two anchor stops extending over the entire length of the sole and disposed respectively on either side of the bearing face. Each anchor stop is inclined with respect to the measurement direction.

 The detector advantageously comprises two connecting members continuous along the length of the detector, respectively on either side of the compression face.

The plastic portion of each assembly member advantageously comprises a free end, said anchoring end, said assembly member. Each anchoring end of each assembly member comes opposite an anchor stop during the first step -assembling- of placing the transmission plate on the sole (more precisely the compression face on the bearing face) with interposed elements comprising at least the piezoelectric sensitive elements.

 During the second step - anchoring - the plastic portion of each assembly member is crimped on an anchor abutment of the sole -notamment the plastic portion of each assembly member is crimped over its entire length over the entire length of an anchor stop of the sole-.

 The inclination of each anchor abutment makes it possible, during this step of crimping anchoring, to induce an elastic stretching of the elastic portion of said assembly member generally along the measurement direction, so that each elastic portion of each assembly member exerts a pulling force in return of the transmission plate to the sole.

 The inclination of each anchor abutment makes it possible, during this step of crimping anchoring, to induce a plastic stretching of the said plastic portion, capable of canceling the preloading clearance (each control abutment is brought into abutment against a scope of control).

 The control stop of said assembly member is thus brought into contact with the control range of the sole by anchoring said plastic portion on the sole.

Thus, during the crimping of the assembly members on the sole, the compressive stress of each piezoelectric sensitive element increases until the control stop is in contact with a control range of the sole. At this moment, the compressive stress exerted on each piezoelectric sensitive element reaches said compressive prestress. The compressive stress exerted on each piezoelectric sensitive element then remains constant regardless of the pressure exerted by the control stop on said control surface. Indeed, any additional deformation of the plastic portion after the control stop has been brought into contact with a control surface has the sole effect of increasing pressure exerted by the control stop (mainly in the measuring direction) on said control range. Indeed, the deformation of the elastic portion generally in the measurement direction with respect to its shape at rest is limited and predetermined by the prestressing game.

 The inclination of each anchor stop also ensures immobilization in translation of the transmission plate relative to the sole in a direction orthogonal to the measuring direction in addition to the immobilization provided in the measuring direction.

 Advantageously, in a process according to the invention, a group of piezoelectric sensitive elements having a sensitivity value of each piezoelectric sensitive element and a mean sensitivity value of the set of the piezoelectric sensitive lower elements are advantageously chosen for each detector. at least 1% in the same area.

 Furthermore, advantageously and according to the invention, a plate, said rolling plate, adapted to receive on a face, said measurement face, and transmit pressure forces in said measurement direction, is assembled to said transmission plate so that the transmission plate can receive and transmit said pressure forces to at least one piezoelectric sensing element.

 Advantageously and according to the invention, the rolling plate is made by molding. The transmission plate and the sole are advantageously profiled in a material chosen for its physical characteristics-especially for its Young's modulus in the case of the transmission plate. The transmission plate is advantageously made of a Young's modulus material greater than 50 GPa.

 The manufacture of the sole, the transmission plate and the rolling plate is thus simple and inexpensive.

The rolling plate is assembled to the transmission plate so as to prevent any relative displacement of the rolling plate relative to the transmission plate in directions orthogonal to said measurement direction, in particular in a direction corresponding to the direction of road traffic on a roadway. once the detector according to the invention installed across said roadway. Advantageously and according to the invention, the rolling plate is advantageously assembled to the transmission plate before assembly of the transmission plate to the sole. Thus, the realization of the rolling plate, which comprises a molding part and a synthetic liquid casting resin in said molding part - said resin then hardening - does not soil the elements of the detector, in particular the piezoelectric sensitive elements, or other electronic components and wiring.

 In addition, advantageously and according to the invention, the molding piece of the rolling plate is assembled by elastic deformation on said transmission plate so as to form, with the transmission plate, a mold for receiving said resin.

 Advantageously and according to the invention, said molding part is a two-component part comprising a rigid first part, made of a rigid material adapted to receive said resin, and to be assembled by permanent elastic deformation or not (sometimes the term " clipping "or" snapping ") on the transmission plate. For this purpose, the molding part advantageously comprises at least one-in particular two-lip (s) latching to the transmission plate.

 Advantageously and according to the invention, the molding part comprises a second portion, flexible, made of a material that is more flexible than the first material, adapted to be able to close an open housing in a sealed manner because of the shape of the transmission plate and the assembly members.

Advantageously and according to the invention, the flexible part of the molding piece is further adapted to allow separation in shear in measuring direction of the detector relative to the floor once it is installed therein. Such a function avoids any detection of a wheel before or after passing on the measurement surface of the detector. The flexible portion advantageously extends on the sides of the detector facing upstream and downstream of the roadway when the detector is installed across a roadway, upstream and downstream being considered in relation to to a normal vehicle traffic direction on this roadway. In addition, such a flexible part can absorb the thermal expansion of a roadway. Advantageously and according to the invention, the transmission plate has an upper face, opposite to the compression face, forming the bottom of said resin receiving mold. Said upper face of the transmission plate has cutouts for ensuring anchoring of the resin to the transmission plate once the resin cured. For example, the upper face of the transmission plate advantageously has inverted T-profile grooves so as to form a flow channel of the resin and two feet for anchoring the resin in the transmission plate. Similarly, the molding piece advantageously has recesses through which the resin can flow liquid and for securing said molding member and said resin once the latter hardened, so as to form said rolling plate. Hardened, said resin is adapted to be able to transmit pressure forces in the measurement direction. For example, a resin obtained from an epoxide polymer loaded with silica is chosen.

 In a manufacturing method according to the invention, the combination of elastically deformable connecting members, their symmetrical distribution on either side of the piezoelectric sensitive elements, and the crimping of the latter on the sole (while they are anchored to the transmission plate while being in one piece with it) makes it possible to obtain a very homogeneous compression prestressing over all the piezoelectric elements.

 Continuous connecting members continuously anchored to the transmission plate and to the sole over their entire length further improve this result. Indeed, thanks to a manufacturing method according to the invention, the deformation of each elastic portion of each assembly member is substantially the same throughout the detector, so that each piezoelectric sensitive element is substantially subjected to the same prestressing compression.

The invention also relates to a pressure force detector characterized in combination by all or some of the characteristics mentioned above or below. The invention also relates to a method of manufacturing a pressure force detector 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 an exploded schematic representation of a pressure force detector according to a first embodiment according to the invention, with a torn central part,

 FIG. 2 is a diagrammatic representation in longitudinal sectional view through a horizontal plane in the planes of the piezoelectric sensitive elements showing a distribution of piezoelectric sensitive elements in the detector according to the first embodiment according to the invention and FIG. 1, with a torn central part,

 FIG. 3 is a schematic representation in longitudinal sectional view through a horizontal plane in the planes of the piezoelectric sensitive elements showing a distribution of piezoelectric sensitive elements in the detector according to a second embodiment according to the invention, with a part central snatch,

 FIG. 4 is a schematic representation in longitudinal sectional view through a horizontal plane in the planes of the piezoelectric sensitive elements showing a distribution of piezoelectric sensitive elements in the detector according to a third embodiment according to the invention, with a part central snatch,

FIG. 5 is a schematic representation in longitudinal sectional view through a horizontal plane in the planes of the piezoelectric sensitive elements showing a distribution of piezoelectric sensitive elements in the detector according to a fourth embodiment according to the invention, with a part central snatch, FIG. 6 is a schematic cross-sectional representation of a detector after a first manufacturing step, in accordance with the embodiment of FIG. 1,

 FIG. 7 is a schematic cross-sectional representation of a detector after a second manufacturing step, in accordance with the embodiment of FIGS. 1 and 4,

 FIG. 8 is a schematic cross-sectional representation of a detector according to the invention after a third manufacturing step and installed in a roadway, in accordance with the embodiment of FIGS. 1, 4 and 5,

 - Figure 9 is a schematic representation of a cross section of a detector according to another manufacturing method according to the invention, after manufacture and installed in a roadway.

 The detector presented comprises a profiled sole 20 having an upper face, a flat part of which forms a bearing face 47.

 It further comprises a profiled transmission plate 28 having a lower face of which a flat part forms a compression face 49.

 Piezoelectric sensitive elements 21 are interposed between the bearing surface 47 and the compression face 49 mounted facing one another in a direction, referred to as the measuring direction 23.

 The transmission plate comprises a thick portion 22 between the compression face and an upper face, said thick portion 22 is adapted to transmit forces in the measurement direction and has a high rigidity in directions orthogonal to the measurement direction (width and length of the detector) to deform flexibly under the pressure forces of a wheel so as to transmit all the forces it receives.

The transmission plate further comprises two assembly members 52 to the sole. These two assembly members 52 project from the underside of the transmission plate 28, on either side of the compression face 49. Each assembly member 52 forms a thin sidewall. Each assembly member comprises: An elastic portion 27 directly projecting from the underside of the transmission plate,

 A control stop 25 protruding from the side formed by the assembly member, towards the interior of the detector, and having a plane lower surface to be able to abut against a control surface 33 of the sole plate 20,

A plastic portion 26 extending from the control stop 25 at a distal end of the assembly member, said plastic portion 26 being substantially straight before crimping, then plastically deformed after crimping on the sole,

 · An end, said anchoring end 31, distal, adapted to be crimped on the sole 20.

 The elastic portion 27 has, in profile, advantageously an upper branch, directly projecting from the lower face of the transmission plate and substantially parallel to the measurement direction 23. This upper branch is connected to a branch extending substantially parallel to the direction of measurement.

 The lower branch and the upper branch are offset relative to each other and are interconnected by an intermediate branch non-collinear to the measurement direction. The intermediate branch forms an angle between 60 ° and 120 ° with the upper branch and with the lower branch. In the example presented, the intermediate branch is for example substantially orthogonal to the measurement direction 23.

 The control abutment 25 projects inwardly from the detector, at the junction between the elastic portion 27 and the plastic portion 26.

 The deformation in extension of the elastic portion 27 of the assembly member is obtained by locally deforming bending of the elastic portion, in particular by an elastic deformation in flexion of the intermediate branch and / or bent connections between upper branch and intermediate branch and between lower branch and intermediate branch.

The soleplate comprises two bearing surfaces 33, said control surfaces 33, planes on either side of the bearing face 47, offset in the measurement direction 23 with respect to said bearing face. Each scope 33 presents a dimension adapted to be able to receive a control abutment 25 abutting in the measurement direction 23.

 In addition, the sole comprises two crimping abutments 32 on either side of the bearing face, opposite in the measurement direction 23 to the bearing surfaces 33 for receiving the control abutments 25. The crimping abutments 32 are furthermore inclined approximately 45 ° to the measuring direction. They are adapted to each receive an anchoring end 31 of an assembly member.

 The detector further comprises a plate, called a rolling plate 29, mounted on the transmission plate 28. Said rolling plate 29 comprises a molding piece 36 mounted on the upper part of the transmission plate by lips, called lip lips. snap-fastening 51. The molding piece 36 is a two-component extruded part comprising a first portion 37 made of rigid material, for example hard PVC, and a second portion 35 made of a more flexible material, for example flexible PVC. The rigid portion 37 ensures that the molding part is snapped onto the transmission plate 28. The flexible portion 35 ensures a lateral sealing of the detector and makes it possible to separate the detector from the roadway (see FIG. shear in the measurement direction, to avoid the detection of a vehicle before or after its passage on a face, said measuring face 30, upper detector. In addition, it makes it possible to absorb differences in thermal expansion between the roadway and the detector.

 Once the molding piece 36 is snapped onto the transmission plate 28, the latter forms, with the upper surface of the transmission plate, a mold for receiving a resin 38.

In a first step of a manufacturing method according to the invention, the molding piece 36 is snapped onto the transmission plate by its latching lips 51, each detent lip being accommodated in a lateral housing of the transmission plate. formed between the thick upper portion 22 of the transmission plate and the horizontal intermediate branch of the elastic portion 27 of each connecting member 52. The resin 38 is then poured liquid into the mold formed by said molding piece 36 and the upper face transmission plate 28. The resin is for example a resin obtained from a silica-filled epoxy polymer which cures with air.

 The rolling plate is thus manufactured and assembled to the transmission plate in a first step, before being assembled to the other components of the detector, including the piezoelectric sensitive elements and the sole. Thus any risk of flow of the resin on the piezoelectric sensitive elements 21 or any other electronic component or internal component of the detector is avoided.

 The upper face of the transmission plate 28 advantageously has grooves 34 in which the resin 28 can flow in the liquid state, the bottom of the grooves being wider than their opening on the upper face of the transmission plate (that is in the form of an inverted "T"), so as to ensure anchoring of the transmission plate 28 with respect to the rolling plate 29 in the at least measurement direction 23. This shape also makes it possible to anchor the transmission plate 28 with respect to the rolling plate 29 in a direction orthogonal to the measurement direction 23.

 Similarly, the molding piece 36 has two lateral edges forming the sides of the resin receiving mold 38, said latching lips 51 being formed on these lateral edges. The two side edges of the molding piece are interconnected by a horizontal portion having a plurality of holes through which the liquid resin can flow. This configuration of the molding piece 36 makes it possible to secure it to the rolling plate and once the resin 38 has hardened.

 In a second manufacturing step, the assembly formed of the transmission plate 28 and the rolling plate 29 is mounted on the sole 20. The result of the second manufacturing step is shown in FIG.

 Between the compression face 49 and the support face 47 is interposed, in the order:

 A thin band 46 electrically insulating,

 A first thin strip, called conduction band 45, made of electrically insulating material and having a plurality of conductive electrical circuits,

The piezoelectric sensitive elements 21, A centering film 44 of the piezoelectric sensitive elements,

A second thin strip, called conduction band 43, made of electrically insulating material and having a plurality of conductive electrical circuits.

 The conduction strips 43, 45 each have a plurality of conductive electrical circuits 57. Each conduction band 43, 45 provides, through its electrical conducting circuits 57, an electrical connection on one side of the piezoelectric sensitive elements 21. The conductive electrical circuits 57 form the collection electrodes of the charges delivered by the piezoelectric sensitive elements of the same zone (high sensitivity 55 or low sensitivity 56). The piezoelectric sensitive elements are thus electrically connected in parallel by groups of piezoelectric sensitive elements located in the same high sensitivity zone 55 or in the same low sensitivity zone 56.

 Each conductive electrical circuit 57 of a conduction band provides an electrical connection between the piezoelectric sensitive elements of the same zone (high sensitivity or low sensitivity) and a processing unit 54 of the electrical signal of the piezoelectric sensitive elements of this zone (respectively high sensitivity or low sensitivity).

 The conductive electrical circuits 57 are advantageously printed circuits on the conduction strips 43, 45.

 Advantageously, each processing unit 54 is dedicated to processing the electrical signals of a single high-sensitivity zone or a single low-sensitivity zone, and the processing unit 54 is disposed in said zone (high sensitivity or low sensitivity) of so that you can measure the temperature locally. Each processing unit 54 is adapted to correct the electrical signals of the piezoelectric sensitive elements of the zone (high sensitivity 55 or low sensitivity 56) whose electrical signals it processes, for example by applying a gain depending on the temperature to the sum of the signals. electrical piezoelectric sensitive elements of the same area.

The centering film 44 makes it possible to maintain in position all the piezoelectric sensitive elements, in particular relative to each other. to others, at least during assembly of the detector. Thus, the centering film determines the distribution of the piezoelectric sensitive elements 21.

 Two possible distributions of piezoelectric sensitive elements according to the invention are presented respectively in FIGS. 2 and 3. In a detector according to the invention, in particular according to an embodiment of FIGS. 1 and 4 to 7, any distribution of piezoelectric sensitive elements may be adopted, in particular one or the other of those shown in FIGS. 2 and 3.

 In the following, and generally throughout the text, when the high sensitivity areas and the low sensitivity areas are described, the references to the length and the width of the detector refer more specifically to the dimensions of the detector's working surface. between the bearing face 47 of the sole plate 20 and the compression face 49 of the transmission plate 28.

 An embodiment relating to the distribution of the piezoelectric sensitive elements in a detector according to the invention is proposed in FIG. 2. In this particular embodiment, the surface of the detector is divided in the sense of its length into detection zones 55. 56 of the same dimensions, and therefore of the same surface. To facilitate the reading of the figures, the zones are delimited by dashed lines.

 In addition, each detection zone comprises a single piezoelectric sensitive element 21. Each piezoelectric sensitive element 21 is electrically connected to a connection point 58 independently of the other piezoelectric sensitive elements by a conductive electrical circuit 57 formed in each conduction band 43 , 45 (only the lower conduction band 43 is visible).

 In this embodiment, the connection points 58 of each electrical conducting circuit 57 are electrically connected in parallel with each other to a single signal processing unit 40. The processing unit 41 therefore has at least as many connectors for the detector comprises detection zones 55, 56.

Advantageously, a different gain is applied to the electrical signals of the piezoelectric sensitive elements of the high detection zones. sensitivity 55 located at the longitudinal ends of the gain detector applied to the electrical signals of the piezoelectric sensitive elements of the low sensitivity detection areas 56 located in the central portion of the detector. In particular, a higher gain is applied to the electrical signals of the piezoelectric sensitive elements of the high-sensitivity detection zones 55 than to those of the piezoelectric sensitive elements of the low-sensitivity detection zones 56.

 In addition, a distinct gain is advantageously applied to the electrical signals of the piezoelectric sensitive elements of each detection zone. The gain of each detection zone is for example determined by calibration of each detection zone.

 Alternatively, another embodiment relating to the distribution of the piezoelectric sensitive elements in a detector according to the invention is proposed in FIG.

 In this particular embodiment, the surface of the detector is divided in the direction of its length into high-sensitivity areas 55 and low-sensitivity areas 56 which all extend over the entire width of the detector.

 The detector has two high sensitivity zones 55 identical to each other, each located at a longitudinal end of the detector. Between these two high sensitivity areas 55 the detector is subdivided into low sensitivity zones 56 identical to each other.

 The surface density of the piezoelectric sensitive elements on the detector is homogeneous. However, the high-sensitivity zones 55 are of smaller dimensions, in particular of lower surface area, than the dimensions of the low-sensitivity zones 56. Therefore, the low-sensitivity zones 56 comprise more (four) piezoelectric sensitive elements than the high-sensitivity zones. (which include two).

Each piezoelectric sensitive element of the same zone (high sensitivity or low sensitivity) is electrically connected in parallel with the other piezoelectric sensitive elements of the same zone (respectively high sensitivity or low sensitivity) by a conductive electrical circuit 57 of each conduction band. 43, 45 (only the lower conduction band 43 is visible). Each conductive electrical circuit 57 is terminated by a connection point 58. In this embodiment, the connection points 58 of each electrical conducting circuit 57 are electrically connected in parallel with each other to a single signal processing unit 40. The processing unit 41 therefore has at least as many connectors for input that the detector includes high sensitivity areas and low sensitivity areas.

 Alternatively, another embodiment relating to the distribution of the piezoelectric sensitive elements in a detector according to the invention is proposed in FIG. 4. In this particular embodiment, the surface of the detector is divided in the direction of its length into high zones. sensitivity 55 and low sensitivity zones 56 which all extend over the entire width of the detector.

 The detector has two high sensitivity zones 55 identical to each other, each located at a longitudinal end of the detector. Between these two high sensitivity areas 55 the detector is subdivided into low sensitivity zones 56 identical to each other.

 Each high-sensitivity zone 55 and each low-sensitivity zone 56 comprise the same number of piezoelectric sensitive elements 21. In the example shown, each high-sensitivity zone 55 and each low-sensitivity zone 56 comprises five piezoelectric sensitive elements 21 arranged in a staggered configuration.

 Each piezoelectric sensitive element of the same zone (high sensitivity or low sensitivity) is electrically connected in parallel with the other piezoelectric sensitive elements of the same zone (respectively high sensitivity or low sensitivity) by a conductive electrical circuit 57 of each conduction band. 43, 45 (only the lower conduction band 43 is visible). Each conductive electrical circuit 57 is terminated by a connection point 58.

In this embodiment, the connection points 58 of each electrical conducting circuit 57 are electrically connected in parallel with each other to a single signal processing unit 40. The processing unit 41 therefore has at least as many connectors for input that the detector includes high sensitivity areas and low sensitivity areas. Alternatively, another embodiment relating to the distribution of the piezoelectric sensitive elements in a detector according to the invention is proposed in FIG.

 In this particular embodiment, the surface of the detector is divided in the direction of its length and in the direction of its width into high sensitivity zones 55 and low sensitivity zones 56 which each extend over half the width of the detector .

 The detector has four high sensitivity zones 55 identical to each other, located two by two at the two longitudinal ends of the detector. Between these pairs of high sensitivity zones 55 the detector is subdivided into a plurality of low sensitivity zones 56 identical to each other and each having a width corresponding to half the width of the detector.

 Each high-sensitivity zone 55 and each low-sensitivity zone 56 comprises the same number of piezoelectric sensitive elements 21. In the example shown, each high-sensitivity zone 55 and each low-sensitivity zone 56 comprises two diagonally-arranged piezoelectric sensitive elements 21. To facilitate the reading of the figures, the zones are delimited by dashed lines.

 The two piezoelectric sensitive elements of the same zone (high sensitivity or low density) are electrically connected in parallel by conductive electrical circuits 57 of each conduction band 43, 45. The conductive electrical circuits 57 combine the piezoelectric sensitive elements of the same zone to a processing unit 54 electrical signals delivered by these piezoelectric sensitive elements.

 The detector comprises a unit, said local unit 54, high sensitivity zone processing 55 and a local unit 54 by low sensitivity zone 56.

Each processing unit 54 of the high sensitivity zones 55 applies a predetermined gain stored in memory to the electrical signals that it receives from the piezoelectric sensitive elements 21. Such a gain can be determined in a practical or theoretical manner and stored in the memory of all the units. of treatment 54 high sensitivity areas 55, or it can be adapted to each detector by factory calibration after fabrication or by in situ calibration.

 Each processing unit 54 delivers an analog or digital electrical signal through an output connector connected by the conductive electrical circuit 57 to a connection point 58. Each connection point 58 is connected to a central processing unit 40.

 In such an embodiment, a first set of high sensitivity and low sensitivity zones and a second set of high sensitivity and low sensitivity zones are separated into two rows in the width of the detector. Thus, when the detector is disposed across a roadway, one of the two rows is passed first by a vehicle.

 The elastic assembly members disposed on either side of the detection surface of the detector according to the width of the detector and extending over the entire length are therefore particularly advantageous and allow the transmission plate to tip slightly over the first row then on the second row, so for example to allow a speed calculation of a vehicle, for example by measuring a time interval between a maximum detection value on the first row (the electrical signals of the zones of the first row can be summed for this purpose) and a maximum detection value on the second row.

 Furthermore, two seals 42 are introduced between each assembly member and a portion of the sole. The seals 42 are advantageously arranged between each control surface 33 and each control abutment 25.

 After this second manufacturing step, the compression face 49 of the transmission plate 28 rests in contact with all the elements interposed between this face and the bearing face 47 of the sole 20. A game, said set of prestress 50 , strictly positive remains between each control abutment 25 and each span 33 facing the sole 20.

The prestressing clearance 50 is predetermined by the shape of the transmission plate 28, in particular by the shape of the connecting member 52, and more particularly by the shape of the elastic portion 27 and the abutment of control 25, as well as by the thickness of the elements interposed between the bearing face 47 and the compression face 49, and that by the shape of the sole 20 especially between the bearing face 47 and the control surfaces 33.

 The anchoring end 31 of each connecting member 52 is laterally facing an inclined anchor 32 of the sole.

 In a third manufacturing step, the anchoring ends 31 are crimped on the crimping abutments 32. They are in particular folded down plastically against the inclined crimping abutments 32.

 During crimping of the anchoring ends 31 on the soleplate, the assembly members are stretched elastically in the measurement direction 23. The elastic portion 27 of each assembly member is stretched elastically in the measurement direction 23 to each control stop 25 abuts against the bearing surfaces 33 of the soleplate. During this manufacturing step, the lower branch of the assembly member is pulled towards the sole until the control stop abuts against a bearing surface of the soleplate, so that the intermediate branch at least is elastically deformed in flexion.

 The plastic portion 26 of each assembly member is plastically deformed during crimping of the anchoring ends 31.

 During crimping, the prestressing clearance 50 between each control stopper 25 and each control surface 33 is canceled. The deformation after crimping of the elastic portion 27 of each connecting member 52 according to the measurement direction 23 thus depends on the play 50 of prestressing. However, the compressive prestress applied to the piezoelectric sensitive elements depends on the deformation of the elastic portion 27 of the assembly members 52. The compression preload is thus determined by the pre-stressing clearance 50 present between the control stops 25 and the staves. 33 control before crimping the fasteners on the sole.

In the example presented, for example, a preload set 50 of about 0.2 mm is chosen. The elastic portions 27 of the fasteners 52 each having a stiffness of approximately 1.67 GN.m ^"1, the total stiffness of the assembly between the transmission plate and the sole is 3.34GN.m ^_1, and the compressive prestressing applied to the piezoelectric sensitive elements results from a total force of 668kN applied to all the elements interposed between the compression face 49 and the bearing face 47.

The stiffness of the elements interposed between the compression face 49 and the bearing face 47 is much greater than the stiffness of said fasteners 52, so that under the effect of the weight of a vehicle applied to the upper face 30 , all the forces resulting from this weight are transmitted to the piezoelectric sensitive elements, without influence -particularly without deformation- of the resiliently deformed elastic portions 27 of the assembly members 52. In particular the stiffness of the stack formed of the electrically insulating thin strip 46 , the first conduction band 45, the piezoelectric sensitive elements 21, and the second conduction band 43, is of the order of 1 10 GN.m- ¹ . The stiffness of the elements interposed between the compression face 49 and the bearing face 47 is therefore at least 10 times greater than the stiffness of said connecting members 52, in particular at least 20 times greater, and more particularly advantageously at least 30 times higher.

 The choice of the material and the shape of the transmission plate 28 -in particular the thickness of the assembly members 52- is therefore important so that the elastic portion 27 of each assembly member has a suitable stiffness and the plastic portion 26 each assembly member is adapted to be deformed by crimping. The material must also be adapted so that the upper thick portion 22 of the transmission plate is sufficiently rigid to transmit the forces in the measuring direction 23 without undergoing plastic or elastic bending deformation.

 The transmission plate is for example made of an aluminum alloy, the thickness of the thick portion 22 of the transmission plate is about 8 mm and the thickness of the elastic portions 27 and plastics 26 of each assembly member 52 is about 2mm. The Young's modulus of the aluminum alloy chosen for the transmission plate is of the order of 70 GPa.

Advantageously, all the piezoelectric sensitive elements 21 in at least one zone of the same detector are chosen such that the percentage of difference between the value of the sensitivity of each piezoelectric sensitive element and the value of the average sensitivity of all the piezoelectric sensitive elements of the detector is less than 1%.

 In the example presented, the piezoelectric sensitive elements 21 are in the form of cylindrical pellets with a diameter of about 6 mm and a thickness of about 1 (one) mm, and are made of lead-free ceramic.

 When crimping the fasteners 52 on the sole 20, the seals 42 are compressed between the control stops 25 and the sole 20, so as to close the receiving housing of the piezoelectric sensitive elements and other components leakproof electronics.

 In a fourth manufacturing step, an electronic card 39 comprising a signal processing unit 40 is mounted using a part 41 in a housing of the sole 20. Said signal processing unit 40 is then connected electrically to each processing unit 57 of the high sensitivity zones 55 and the low sensitivity zones 56.

 In a fifth manufacturing step, end caps 48 close the two longitudinal ends of the detector so as to seal it tightly.

 The detector according to the invention is adapted to be mounted in a carriageway 53, across the carriageway with respect to the direction of travel, as shown in FIGS. 6 and 7. Advantageously, a trench is made across the carriageway 53, the detector according to the invention is placed there and the remaining volume of the trench is filled.

The detector according to the invention is installed so that the upper face, so-called measurement face 30, of the rolling plate is at the level of the roadway. Said measurement face 30 is adapted to receive pressure forces in the measurement direction 23 at least. The rolling plate 29, and more particularly the resin 38, transmits almost all the pressure forces received by the measuring face 30 in the said measurement direction 23. Similarly, the thick upper portion 22 of the transmission plate situated between the upper face of the transmission plate and the compression face 49 transmits almost all the pressure forces received along said measurement direction 23 at the interface between the rolling plate 29 and the transmission plate 28.

 In Figure 7 a third embodiment of a detector according to the invention is presented. The detector is identical in all respects to the detector presented as the first embodiment, with the exception of the assembly members 52 of the transmission plate 28 which do not have a plastic portion in their end. The anchoring end 31 of the fasteners 52, in this embodiment, is indeed directly welded to the sole 20.

 For this purpose, in a manufacturing method according to the invention, the transmission plate 28 and the sole 20 are maintained at a predetermined distance from one another, that is to say with a predetermined manufacturing constraint , so as to obtain a deformation of the elastic portion 27 of the assembly members 52 sufficient at least for the stops 25 to be in contact in the measurement direction 23 with the bearing surfaces 33 of the soleplate (the prestressing clearance is erased) then the anchoring ends 31 are welded to the sole 20. The manufacturing preload is then released.

 The invention can be the subject of many other embodiments not shown.

 Thus, many variations of distributions of the piezoelectric sensitive elements can be envisaged.

 Likewise, numerous geometrical divisions can be envisaged with regard to the high sensitivity zones and the low sensitivity zones. Thus, nothing prevents to provide high sensitivity areas and low sensitivity areas of non-rectangular shapes, for example hexagonal.

 In addition, the high sensitivity areas (respectively low sensitivity) can be shifted (not aligned) between them, for example arranged in staggered rows. Similarly, the high sensitivity areas can be shifted (not aligned) of low sensitivity areas.

In addition, a detector according to the invention may comprise several types of high sensitivity zones and / or several types of low zones. sensitivity, that is to say areas of high sensitivity (respectively low sensitivity) of shapes and / or density distinct from each other.

 In particular, the transmission plate can be assembled to the sole by other methods than by crimping, for example by welding.

 In addition, the assembly member and more particularly the elastic portion of the assembly member may have other shapes.

 Furthermore, in a detector according to the invention, the conduction strips can be adapted to collect the electrical signals from all the piezoelectric sensitive elements of the same detection zone and to connect the piezoelectric sensitive elements of the same zone of detection at a processing unit. Such conduction strips are, for example, electrically conductive thin strips -so the detector comprises two conducting conduction strips in each detection zone (one on each side of the piezoelectric sensitive elements). Alternatively conductive wires can be used.

 The centering film presented in the embodiments can be made in several parts, that is to say that the detector comprises several centering films, for example a centering film for each detection zone. In addition, the centering film may have one or more electrical connections of the piezoelectric sensitive elements with a signal processing unit. The centering film may further comprise one or more processing units and / or one or more electrical supply connections of each processing unit.

 Moreover, nothing prevents that the gain applied to the electrical signals of one or more low sensitivity zones is higher than the gain applied to the electrical signals of one or more high sensitivity zones.

Claims

 1 / - Pressure force road detector comprising: - a sole (20) in one piece,  - A plate, said transmission plate (28), in one piece, adapted to be able to transmit in one direction, said measuring direction (23), forces received on an upper face (30) of the detector,  a plurality of piezoelectric sensitive elements (21) interposed between said soleplate (20) and said transmission plate (28), adapted to generate electrical signals under the effect of forces transmitted along said measurement direction by said plateau of transmission, characterized in that  at least one first group of piezoelectric sensitive elements (21) comprising at least one piezoelectric sensitive element (21) is connected by a first electrical connection (57) to at least one processing unit (40, 54) of electrical signals,  at least one second group of piezoelectric sensitive elements (21) comprising at least one piezoelectric sensitive element (21) is connected by a second electrical connection (57) to at least one signal processing unit (40, 54),  said first group and first electrical connection being electrically isolated from said second group and second electrical connection, to each treatment unit (40, 54) at least,  said first group and second group being separated by at least one parameter chosen from:  · The footbed area occupied,  • the number of piezoelectric sensitive elements, The surface density of piezoelectric sensitive elements, • the distribution of piezoelectric sensitive elements, • the average distance between piezoelectric sensitive elements, The processing of the electrical signals of the piezoelectric sensitive elements, in particular the gain applied to the electrical signals of the piezoelectric sensitive elements.  21 - Detector according to claim 1, characterized in that:  the first group of piezoelectric sensitive elements (21) occupies a first detection zone, called a high-sensitivity zone (55),  the second group of piezoelectric sensitive elements (21) occupies a second detection zone, called low sensitivity zone (56),  the surface of said high sensitivity zone (55) is smaller than the area of said low sensitivity zone (56).  3 / - Detector according to one of claims 1 or 2, characterized in that the piezoelectric sensitive elements (21) of the same detection zone (55, 56) are adjacent and connected in parallel with each other.  4 / - Detector according to one of claims 1 to 3, characterized in that it comprises a unit, said central unit (40) for processing electrical signals delivered by all the piezoelectric sensitive elements (21) arranged between said sole plate (20) and said transmission plate (28).  5 / - Detector according to one of claims 1 to 4, characterized in that it comprises for each group of piezoelectric sensitive elements (21), a unit, called local unit (54), for processing electrical signals delivered by said piezoelectric sensitive elements (21) of said group of piezoelectric sensitive elements.  6 / - Detector according to claim 5, characterized in that each local unit (54) is disposed near the piezoelectric sensitive elements (21) to which it is electrically connected.  7 / - Detector according to one of claims 5 or 6, characterized in that each local unit (54) is adapted to apply a predetermined gain to the sum of the electrical signals it receives from said piezoelectric sensitive elements (21). 8 / - Detector according to one of claims 1 to 7, characterized in that it comprises a plurality of groups of sensitive elements piezoelectric elements (21) each forming a detection zone (55, 56), said detection zones (55, 56) being distributed in the length of the detector.  91 - Detector according to claims 7 and 8, characterized in that the local units (54) of at least two detection zones, said high sensitivity zones (55), located at the longitudinal ends of the detector are adapted to apply a gain more higher than the gain applied by the local units (54) of the detection zones, called low sensitivity zones (56), located longitudinally in the detector between said at least two high sensitivity zones (55).  10 / - Detector according to one of claims 1 to 9, characterized in that it comprises at least one connecting member (52) of the transmission plate (28) to the sole (20), and in that each assembly member (52) comprises:  - At least a portion, said elastic portion (27) elastically deformed in pulling traction of the transmission plate (28) towards the sole (20) so as to exert a compression prestress in the measuring direction (23) on each element (21) piezoelectric sensitive interposed between the transmission plate (28) and the sole plate (20),  at least one abutment, said control abutment (25), in contact in said measurement direction with a bearing surface, said control bearing surface (33), of a member selected from said transmission plate (28) and the soleplate ( 20), by anchoring the connecting member (52) to said element selected from said transmission plate (28) and the sole (20).  1 / - - Detector according to claim 10, characterized in that the stiffness of said elastic portion (27) of each connecting member (52) is adapted so that the stiffness of an assembly comprising each connecting member (52). ) of said detector is at least ten times less than the stiffness of an assembly comprising each piezoelectric sensitive element (21) of said detector. 12 / - Detector according to one of claims 10 or 1 1, characterized in that each connecting member (52) is made of a Young modulus material greater than 50 GPa, said elastic portion (27) having a thickness and a shape adapted to be elastically deformed along said measurement direction (23). 13 / - Detector according to one of claims 10 to 12, characterized in that it comprises a maximum of two connecting members (52) distributed on either side of the compression face (49) of said transmission plate (28).  14 / - Detector according to one of claims 10 to 13, characterized in that it further comprises a plate, said rolling plate (29):  - separate from the sole (20) and the transmission plate (28), adapted to be able to receive pressure forces on a face, called measuring face (30),  adapted to transmit pressure forces received on the measurement face in said measuring direction (23),  - Mounted on and in contact with the transmission plate, so as to transmit the pressure forces received on the measurement face to said transmission plate in said measurement direction.