Sensorized brake device for vehicle

Abstract

The invention relates to a braking device for a vehicle, comprising a piezoelectric sensor (2) comprising a piezoelectric material, two electrodes (6, 7), the piezoelectric material comprising a first flat surface (4) and a second flat surface (5) which extend in parallel planes defined by two orthogonal directions y and z, an electrical signal is collected by electrodes when the piezoelectric material is subjected to a normal force in the x direction and a shear force in the z direction at the same time, where a first electrode is positioned on the first face and a second electrode is positioned on the second face and has an extension (7a, 7b) on the first face that is separate from the first electrode, where the first electrode is positioned on the first face and the second electrode is positioned on the second face. Each of the extensions extends on a corresponding side of the first face, and wherein each of the extensions is symmetrically arranged with respect to a central axis of the first face.

Description

[0001] manual Technical Field

[0002] The following disclosure relates to a sensorized brake device for a vehicle, a piezoelectric shear force detection sensor, and a shear force detection method. Summary of the invention

[0003] Piezoelectricity is the property of certain materials to polarize when subjected to mechanical stress, resulting in a buildup of charge and, therefore, a potential difference.

[0004] Similarly, the opposite effect can occur, namely causing a material to deform by subjecting it to a voltage, in which case it is called the inverse piezoelectric effect.

[0005] Piezoelectric materials include quartz crystal, tourmaline, and Rochelle salt, which exhibit relatively small piezoelectric responses to external stresses, which is not optimal for some applications, such as the one under consideration.

[0006] To overcome this problem, some polycrystalline ferroelectric ceramics, such as barium titanate (BaTiO3) and lead zirconate titanate (PZT), have been synthesized so that the synthesized ceramics exhibit more significant piezoelectric properties, that is, higher voltage under the same mechanical stress, or larger displacement when subjected to electrical stress.

[0007] In order for piezoelectric ceramic materials to have piezoelectric properties, they must undergo a polarization process.

[0008] To this end, a strong electric field of several kV / mm is applied to create an asymmetry in the ceramic compound, which previously appeared to have randomly oriented domains and therefore no net polarization.

[0009] Application of an external electric field causes the material's dipoles aligned parallel to its direction to rearrange so that the total electric dipole is no longer zero, with the result that the material becomes polarized.

[0010] After poling, much of the reorientation is retained, even in the absence of an applied electric field, until the temperature of the material is above the so-called Curie temperature (TC), which is characteristic of the material.

[0011] At temperatures below TC, the lattice structure of the PZT grains may be distorted, for example, by external mechanical stresses, leading to a change in the overall polarization.

[0012] This is therefore a mechanism of interest for piezoelectric technology. At temperatures above TC, the piezoelectric ceramic material loses its asymmetry within the crystal lattice, resulting in a loss of its piezoelectric properties.

[0013] After sintering and poling, the piezoelectric ceramic material is very hard and dense and can be sawed and machined if necessary.

[0014] The compacted material comes in different shapes such as discs, plates, rods and cylinders. The final stage of the manufacturing process involves electrode deposition. The electrodes are applied to the piezoelectric ceramic material by screen printing technology, sputtering or PVD (sputtering), and then the electrodes are baked.

[0015] The thickness of the conductive material may vary between 1 μm and 10 μm, depending on the final application of the sensor.

[0016] The geometric arrangement of the electrodes defines two different types of sensors: electrodes on 2 opposite sides or two contacts on the same side of the piezoelectric ceramic.

[0017] The latter type is called a wrapped electrode (WAC) because one of the two electrodes is wrapped around the peripheral edge of the piezoelectric material to be on the same plane as the other electrode.

[0018] Polarized piezoelectric materials are characterized by various coefficients and relationships.

[0019] In short, the basic relationship between electrical and elastic properties can be expressed as follows:

[0020] D=d·T+ε T ·E

[0021] S=S E ·T+d·E

[0022] Where D is the electric flux density, T is the mechanical stress, E is the electric field, S is the mechanical stress, d is the piezoelectric charge coefficient, ε T is the dielectric constant, and S E is the elastic coefficient.

[0023] These relationships apply to small electrical and mechanical amplitudes, or so-called small signal values. In this range, the relationship between the mechanical deformation, elasticity S or stress T and the electric field E or electric flux density D is a linear relationship, and the coefficient value is constant.

[0024] like Figure 1 As shown, the directions are represented by 1, 2 and 3, corresponding to the classic right-handed orthogonal axis set of X, Y and Z axes.

[0025] The axes of rotation are indicated by 4 , 5 and 6 .

[0026] The polarization direction (axis 3) is formed during the poling process by applying a strong electric field between the two electrodes and is usually above a specific critical value that depends on the piezoelectric material considered.

[0027] The basic characteristic parameter of a piezoelectric material is that the coupling between the mechanical deformation in a particular direction j and the potential generated on the surface in direction i is given by the coefficient d ij Control, the coefficients are grouped in the d matrix:

[0028]

[0029] Typically, piezoelectric sensors used in compression or traction force measurements are polarized in such a way that their polarization axis coincides with the direction of the mechanical deformation to be measured (z axis, 3), while the charge is collected from a face orthogonal to this direction (face 3).

[0030] As a result, the coefficient d 33 to control the response to sensor compression.

[0031] By similar reasoning, it can therefore be deduced that the sensor used in shear stress measurements (ie, in the case of relative creep between two opposing surfaces) is dominated by the coefficient d 15 (1 is the surface orthogonal to the x-axis, 5 is the shear deformation along the z-axis, polarization) control.

[0032] In the case where the mechanical deformation is not completely unidirectional, other coefficients can have an influence on the final signal, sometimes even with uncontrollable or destructive effects, as will be seen later in the case of sensors with reported electrodes.

[0033] A sensored brake device for a vehicle (particularly but not limited to a smart brake pad) is a brake device that is configured (e.g., configured with a suitable hardware and software system architecture and some algorithms) to measure one or more parameters, such as brake pad temperature and / or static and dynamic quantities, including normal force and shear force applied during braking.

[0034] The shear force detection sensor may include a piezoelectric material plate having a main placement plane defined by orthogonal y-direction and z-direction, a thickness defined by an x-direction orthogonal to the main placement plane yz, a polarization according to the z-direction, and configured to collect charge on a surface parallel to the main placement plane yz.

[0035] A limitation of this uniqueness is the fact that, when used to read shear force signals, the electrodes also pick up a significant amount of charge generated in the normal direction, which can somewhat complicate the correct interpretation of the signal. This phenomenon is known as "crosstalk."

[0036] The "crosstalk" consists of the electrical signal generated by the shear force sensor when force is applied in the x-direction only.

[0037] "Crosstalk" is a phenomenon that exists in every piezoelectric component, but some types of piezoelectric shear sensors are affected to a greater extent, such as the reported electrode sensors.

[0038] In particular, if a piezoelectric shear sensor is integrated into a braking device where the shear force is always correlated with the normal force during braking, "crosstalk" may make the measurement results unreliable and non-repeatable.

[0039] In the case of sensorized brake pads, the reported electrode sensors are the best solution for mass production processes, but they are also the most sensitive to “crosstalk” if not properly designed and manufactured.

[0040] If a shear force sensor of this type is integrated into the two brake pads constituting a disc brake, completely different read signals are obtained from the two shear force sensors, as the "crosstalk" signal creates a variable contribution that may or may not be consistent with the signal generated by pure shear force.

[0041] Industrially (high volume and low cost) it is preferred to use the reported electrode sensor, but if not designed properly this would render it unsuitable for use in brake pads.

[0042] IT 1020210021017 filed by the same applicant shows a sensorized brake device for a vehicle, a piezoelectric shear force detection sensor, and a shear force detection method.

[0043] The technical task of the present invention is to make up for the shortcomings of the known technology.

[0044] Within the scope of this technical task, an object of the present invention is to provide a shear force sensor and a sensorized brake device incorporating such a shear force sensor, which produces reliable and reproducible measurement results when the shear force sensor is simultaneously subjected to shear forces and normal forces.

[0045] Another object of the present invention is to provide a shear force sensor and a sensorized brake device incorporating such a shear force sensor, which can be easily industrialized and produces reliable and repeatable measurements when the shear force sensor is subjected to shear forces and normal forces simultaneously.

[0046] The technical task and this purpose and other purposes according to the present invention are achieved by a sensorized braking device for a vehicle, the sensorized braking device comprising: at least one piezoelectric shear force sensing sensor, a circuit configured to collect signals from the at least one sensor, wherein the sensor comprises: a piezoelectric material, a first reading electrode and at least one second reading electrode, wherein the piezoelectric material comprises a first flat surface and a second flat surface opposite to the first flat surface, the first flat surface and the second flat surface extend in parallel planes determined by two orthogonal directions y and z, wherein the piezoelectric material has a polarization axis along the z direction, and wherein when the piezoelectric material is in the same When subjected to a normal force along the x direction orthogonal to the two directions y and z and the shear force along the z direction, the electrical signal can be collected by the reading electrode, the first electrode is positioned on the first plane, and the second electrode is positioned on the second plane and has one or more extensions on the first plane separated from the first electrode, wherein each of the one or more extensions extends from a corresponding side of the first plane, and is characterized in that each of the one or more extensions of the second electrode on the first plane of the piezoelectric material is symmetrically configured relative to the central axis of the first plane of the piezoelectric material oriented along the y direction.

[0047] Advantageously, the first electrode is also arranged symmetrically with respect to a central axis of the first planar surface of the piezoelectric material oriented along the y-direction.

[0048] In a preferred embodiment, a sensorized brake device for a vehicle includes a brake pad, which includes a backing plate and a friction material block, wherein the circuit is inserted between the backing plate and the friction material block, and the at least one sensor is inserted between the circuit and the friction material block.

[0049] The present invention also discloses a piezoelectric shear force sensing sensor, which includes a piezoelectric material, a first readout electrode and at least one second readout electrode, wherein the piezoelectric material includes a first flat surface and a second flat surface opposite to the first flat surface, the first flat surface and the second flat surface extend in parallel planes determined by two orthogonal directions y and z, wherein the piezoelectric material has a polarization axis along the z direction, and wherein, when the piezoelectric material is simultaneously subjected to a normal force along the x direction orthogonal to the two directions y and z and the shear force along the z direction, an electrical signal can be collected by the readout electrode, the first electrode is positioned on the first surface, and the second electrode is positioned on the second surface and has one or more extensions on the first surface separated from the first electrode, wherein each of the one or more extensions extends from a corresponding side of the first plane, and is characterized in that each of the one or more extensions of the second electrode present on the first surface of the piezoelectric material is symmetrically configured relative to the central axis of the first surface of the piezoelectric material oriented along the y direction.

[0050] Finally, the present invention discloses a shear force sensing method using a sensorized brake device for a vehicle, the sensorized brake device comprising:

[0051] At least one piezoelectric shear force sensing sensor; a circuit configured to collect signals from the at least one sensor; wherein the sensor comprises: a piezoelectric material, a first readout electrode and at least one second readout electrode, wherein the piezoelectric material comprises a first flat surface and a second flat surface opposite to the first flat surface, the first flat surface and the second flat surface extending in parallel planes determined by two orthogonal directions y and z, wherein the piezoelectric material is polarized along the z direction, wherein the first electrode is positioned on the first surface, and the second electrode is positioned on the second surface, wherein the second electrode is extended on the first surface by one or more extensions separated from the first electrode, wherein each of the one or more extensions of the second electrode is extended on a corresponding side of the first plane, characterized in that each of the one or more extensions of the second electrode on the first surface of the piezoelectric material is symmetrically configured relative to a central axis of the first surface of the piezoelectric material oriented along the y direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The various implementations depicted in the drawings are for illustrative purposes and should in no way be construed to limit the scope of the present disclosure.

[0053] The various unique features of the different disclosed implementations may be combined to form additional implementations as part of the present disclosure.

[0054] Figure 1 schematically illustrates an orthogonal coordinate system for describing the properties of a poled piezoelectric material;

[0055] Figure 2 A schematic side elevation view of a brake device supporting a sensor for shear force detection;

[0056] Figure 2a The brake device is schematically shown in plan view;

[0057] Figure 3a and Figure 3b The axonometric and plan views schematically illustrate the integration of Figure 2 A first aspect of the shear force sensor in the brake device, wherein the second electrode provides an extension;

[0058] Figure 3c Show Figure 3a and Figure 3b AA cross section of the shear force sensor in;

[0059] Figure 4a and Figure 4b The axonometric and plan views schematically illustrate the integration of Figure 2 A second aspect of the shear force sensor in the braking device, wherein the second electrode has two extensions;

[0060] Figure 4c Show Figure 4a and Figure 4b AA cross section of the shear force sensor in;

[0061] Figure 5 A finite element model evaluating the effects of a combination of normal and shear forces on a force sensor with reported electrodes (WAC), attached to a metal plate, constrained at the edges and free to deform, is shown;

[0062] Figure 6 shows strain vectors in the yz plane of a force sensor with reported electrodes (WAC) attached to a metal plate, symmetric with respect to the z-axis and the y-axis, respectively;

[0063] Figure 7 shows different resultant strain vectors in the yz plane of a force sensor with reported electrodes (WAC) attached to a metal plate, symmetric with respect to the z-axis and the y-axis, respectively; DETAILED DESCRIPTION

[0064] In the following detailed description, reference is made to the accompanying drawings which form relevant parts.

[0065] In the drawings, similar reference numbers typically identify similar components, unless context dictates otherwise.

[0066] The illustrative implementations described in the detailed description and drawings are not intended to be limiting.

[0067] Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

[0068] Various aspects of the present disclosure, as generally described herein and as illustrated in the accompanying drawings, may be arranged, substituted, combined, and designed into a variety of different configurations, all of which are expressly contemplated and form a part of the present disclosure.

[0069] refer to Figures 1 to 4c The sensorized brake device 1 for shear force sensing comprises a piezoelectric shear force sensor 2 , which comprises a piezoelectric material 3 , such as a piezoelectric material sheet 3 , having a first main planar surface 4 and a second main planar surface 5 opposite to the first main planar surface 4 .

[0070] The first main plane 4 and the second main plane 5 extend in parallel planes which are determined by two orthogonal directions y and z.

[0071] The piezoelectric material 3 is electrically polarized in the z direction by the electric vector field P, and the z direction also determines the direction of the shear stress S of the piezoelectric material 3 .

[0072] As shown in the figure, the z direction is the direction along which the generally parallelepiped piezoelectric material 3 has a maximum length.

[0073] On the first main face 4 of the piezoelectric material 3 at least a first reading electrode 6 is placed.

[0074] On the second main face 5 of the piezoelectric material 3 at least a second reading electrode 7 is arranged.

[0075] When, during a braking event, the piezoelectric material 3 is simultaneously subjected to a normal force in the x-direction orthogonal to the two directions y and z and a shear force in the z-direction, electrical signals are collected by the electrodes 6 , 7 .

[0076] Advantageously, the second electrode 7 has at least one extension 7 a , 7 e separated from the first electrode 6 .

[0077] according to Figure 3a to Figure 3c In the illustrated first preferred embodiment of the invention, the force sensor 2 is provided with a single extension 7a.

[0078] according to Figures 4a to 4cIn the second preferred embodiment shown, the force sensor 2 has two extensions 7 a , 7 e .

[0079] Preferably, the piezoelectric material 3 has a parallelepiped quadrilateral structure, wherein the longest edge extends longitudinally in the z direction, parallel to the polarization vector P.

[0080] In fact, reference Figure 3a to Figure 3c In the first preferred embodiment shown, the second reading electrode 7 includes a first segment 7c arranged on the second flat surface 5 of the piezoelectric material 3, a second segment 7b folded from the first segment 7c and arranged along the peripheral edge of the piezoelectric material 3, and a third segment 7a folded from the second segment 7b and arranged along the first flat surface 4 of the piezoelectric material 3 and extending from the corresponding side of the flat surface 4.

[0081] refer to Figures 4a to 4c In the second preferred embodiment shown, the second reading electrode 7 includes a first segment 7c arranged on the second flat surface 5 of the piezoelectric material 3, a second segment 7b and an opposite third segment 7d folded from the first segment 7c and arranged along the opposite peripheral edges of the piezoelectric material 3, a fourth segment 7a and an opposite fifth segment 7e folded from the second segment 7b and the third segment 7d and arranged along the first flat surface 4 of the piezoelectric material 3 to define opposite extensions 7a, 7e and extending from corresponding sides of the flat surface 4.

[0082] Advantageously, two opposite extensions 7 a , 7 e of the second reading electrode 7 extend from corresponding sides of the first planar face 4 along opposite edges of the piezoelectric material 3 .

[0083] Suitably, the first electrode 6 is separated from the extensions 7 a and 7 e of the second electrode 7 .

[0084] Advantageously, the opposite extensions 7 a , 7 e of the second reading electrode 7 are arranged and configured symmetrically with respect to a central Y symmetry axis of the flat face 4 of the piezoelectric material 3 oriented in the y direction.

[0085] Advantageously, the first electrode 6 is also arranged and configured symmetrically with respect to the central Y symmetry axis of the flat surface 4 of the piezoelectric material 3 .

[0086] The piezoelectric ceramic material 3 can be a screen-printed layer or a discrete component.

[0087] Piezoelectric materials may include synthetic polycrystalline ferroelectric ceramic materials such as barium titanate (BaTiO3) and lead zirconate titanate (PZT).

[0088] The piezoelectric materials in the present disclosure are not limited to synthetic ceramics and may include other types of ferroelectric materials.

[0089] Each reading electrode 6 , 7 may also consist of a layer deposited on the piezoelectric material 3 by screen printing or sputtering.

[0090] In some embodiments, the reading electrodes 6, 7 may be formed from a screen printed layer of a metal material such as silver, gold, copper, nickel or palladium. In a certain embodiment, the reading electrodes 6, 7 may be formed from silver ink or silver paste.

[0091] In some designs, one or more of the electrodes 6, 7 may be partially or completely covered by a protective material, such as an insulating glass layer or a ceramic layer, to electrically and thermally insulate the electrode and prevent oxidation.

[0092] In other solutions, the read electrodes are also discrete components.

[0093] Referring to the present invention and Figure 2 As shown, the sensorized brake device 1 may include a smart brake pad.

[0094] Smart brake pads are sensorized brake pads that are configured (e.g., with appropriate hardware and software system architecture and some algorithms) to measure one or more parameters, such as brake pad temperature and / or static and dynamic quantities, including normal and shear forces applied during braking.

[0095] The brake pad comprises a backing plate 9, a block of friction material 10 and an electrical circuit 12 provided with at least one shear sensor 2 of the type according to the present disclosure and preferably also with at least one other sensor 13, 14, such as a normal force sensor and / or a temperature sensor.

[0096] The normal force sensors may comprise piezoelectric ceramic sensors, but alternatively they may also be capacitive sensors or piezoresistive sensors.

[0097] The temperature sensor may be a thermistor such as PT1000, PT200 or PT100.

[0098] The circuit 12 has electrical terminals arranged in an area 15 to collect the signals from the brake pad.

[0099] The support plate 9 is preferably but not necessarily made of metal, and directly supports the circuit 12 .

[0100] The friction material block 10 is applied to the side of the carrier plate 9 on which the circuit 12 is located, so that the circuit 12 is embedded between the carrier plate 9 and the friction material block 10 .

[0101] In some designs, as shown, the brake pad also includes a damping layer 16 that surrounds the sensors 2 , 13 , 14 and is interposed between the circuit 12 and the friction material block 10 .

[0102] The smart brake device may include a limited number of sensors in order to limit the number of operations and the power budget of the electronics, making it suitable also for wireless systems for onboard applications.

[0103] During use, the brake pad may be able to transmit an electrical signal proportional to the braking force applied to the brake pad, due to contact with a braked element, such as a disc of the brake device 1 .

[0104] The cut sensor may preferably have a sheet of piezoelectric material having a thickness of at least 0.2 mm and an operating temperature above 200°C.

[0105] In various designs, shear force sensors make it possible to measure wear, residual resistance and / or braking torque.

[0106] The circuit 12 on which the sensors 2 , 13 , 14 are mounted is electrically insulated. The circuit 12 has branches shaped to arrange the sensors 2 , 13 , 14 in separate positions on the support plate 12 .

[0107] The circuit 12 may be a screen printed circuit.

[0108] In support of the present invention, provided below are experimental tests performed on a conventional WAC force sensor comparing reported electrodes that were not arranged symmetrically with respect to the Y-axis to reported electrodes that were arranged symmetrically with respect to the Y-axis.

[0109] according to Figure 6 And especially according to Figure 7 It is evident that the different resultant strain vectors in the yz plane of the force sensor with the reported electrodes (WAC) attached to the metal plate are symmetric with respect to the z-axis and the y-axis respectively.

[0110] In the case of symmetry with respect to the z-axis, the resultant force in the direction of the polarization axis P is not zero, and therefore there is a significant crosstalk effect.

[0111] Advantageously, in the case of symmetry with respect to the Y axis, the resultant force in the direction of the polarization axis P is zero and therefore there are no crosstalk effects.

[0112] like Figure 2a As shown, the sensor 2 must be positioned in the braking device 1 in the correct orientation, specifically, the polarization axis P must be parallel to the direction of the shear force acting on the braking device, which direction is indicated by the arrow F.

[0113] Arrow F indicates the direction of shear stress from right to left, but it is clear that shear stress can act in the opposite direction.

[0114] The scope of the present disclosure is not to be limited to the specific implementations disclosed above, but is to be determined only by a fair reading of the following claims along with their full scope of equivalents.

Claims

1. A sensorized brake device (1) for a vehicle, the sensorized brake device comprising a brake pad, the brake pad comprising a back plate (9), a friction material block (10) and an electric circuit (12), the electric circuit being equipped with at least one piezoelectric sensor (2) for detecting shear forces, the electric circuit (12) being configured to receive a signal from the at least one sensor (2), wherein: The sensor (2) comprises: a piezoelectric material (3), a first reading electrode (6) and at least a second reading electrode (7), wherein the piezoelectric material (3) comprises a first flat surface (4) and a second flat surface (5) opposite to the first flat surface (4), the first flat surface (4) and the second flat surface (5) extending in parallel planes determined by two orthogonal directions y and z, wherein the piezoelectric material (3) has a polarization axis (P) along the direction z, and wherein when the piezoelectric material (3) is simultaneously subjected to a normal force along a direction x orthogonal to the two directions y and z and the shear force along the direction z, an electrical signal can be received by the reading electrodes (6, 7), the first electrode (6) The piezoelectric material (3) is provided with a first flat surface (4) and a second electrode (7) is provided with a second flat surface (5) and a second electrode (7) is provided with one or more extensions (7a, 7e) on the first flat surface (4) and separated from the first electrode (6), wherein each of the one or more extensions (7a, 7e) extends from a corresponding side of the first flat surface (4), and characterized in that each of the one or more extensions (7a, 7e) of the second electrode (7) on the first flat surface (4) of the piezoelectric material (3) is symmetrically arranged with respect to a central axis (Y) of the first flat surface (4) of the piezoelectric material (3) oriented along the direction y.

2. The sensorized braking device (1) for a vehicle according to claim 1, characterized in that: The sensor (2) is positioned so that the polarization axis (P) is oriented parallel to the direction (F) of the shear force.

3. A sensorized braking device (1) for a vehicle according to any of the preceding claims, characterized in that The first electrode (6) is arranged symmetrically with respect to the central axis (Y) of the first flat surface (4) of the piezoelectric material (3).

4. A sensorized braking device (1) for a vehicle according to any of the preceding claims, characterized in that The piezoelectric material extends longitudinally along the direction z.

5. A sensorized braking device (1) for a vehicle according to any of the preceding claims, characterized in that The piezoelectric material (3) has a quadrilateral structure.

6. A sensorized braking device (1) for a vehicle according to any of the preceding claims, characterized in that The one or more extensions (7a, 7e) of the second electrode (7) consist of a single extension (7a) extending along the direction z.

7. The sensorized braking device (1) for a vehicle according to any one of claims 1 to 5, characterized in that: The one or more extensions (7a, 7e) of the second electrode (7) consist of two extensions (7a, 7e) extending along the direction z.

8. A sensorized braking device (1) for a vehicle according to any of the preceding claims, characterized in that The circuit (12) is interposed between the support plate (9) and the friction material block (10), and the at least one sensor (2) is interposed between the circuit (12) and the friction material block (10).

9. A sensorized braking device (1) for a vehicle according to any of the preceding claims, characterized in that The piezoelectric material is a piezoelectric ceramic.

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