Pressure Sensors

Abstract

A pressure sensor (1) for detecting fluid pressure, comprising a sensor body (2) having at least one first body portion (3) and one second body portion (4), each having a first surface and a second surface opposite each other, the first body portion (3) and the second body portion (4) being coupled to each other such that the first surface of the first body portion (3) faces away from the first surface of the second body portion (4), and at least one of the first body portion (3) and the second body portion (4) includes a membrane portion (7) that undergoes elastic bending or deformation toward the other of the first body portion (3) and the second body portion (4) as a result of fluid pressure, the membrane portion (7) defining the first surface of the first body portion (3) and the second body portion (4). The pressure sensor (1) has a circuit arrangement (8, 10) supported by the sensor body (2), the circuit arrangement (8, 10) comprising at least one first electric circuit (10) extending at least partially at a position corresponding to the membrane portion (7) and configured to detect its elastic bending or deformation via at least one respective detection component (R1, R2, R4). The first electric circuit (10) is associated with the first surface of one of the first body portion (3) and the second body portion (4), and the first surface of the other of the first body portion (3) and the second body portion (4) forms or is associated with at least one circuit element (20) that generates information or an alarm indicating at least one of excessive fluid pressure, inaccurate pressure measurement, and an abnormal state of the device when the elastic bending or deformation of the membrane portion (7) is at least substantially equal to a predetermined limit.

Description

[Technical field]

[0001] The present invention relates to pressure sensors and has been developed with particular reference to sensors having a sensor body with a membrane portion that undergoes elastic bending or deformation by the fluid whose pressure is to be measured. [Background technology]

[0002] Sensors of the above mentioned type are used in devices for detecting the pressure of fluids (liquids and gases) in various fields, such as the automotive field, the household and domestic appliances field, the heating, ventilation and air conditioning field, and the general hydraulic and sanitation field. These detection devices usually include a casing or support and define at least one housing with an inlet for the fluid whose pressure is to be measured, as well as a pressure sensor in the housing, the membrane part of which is exposed to the fluid.

[0003] The sensor generally has a sensor body made of an electrically insulating material, with a cavity closed at least at one end by the membrane portion described above. In some types of sensors (e.g., some sensors of the relative type), the axial cavity is essentially a blind axial cavity, closed only by a face of the sensor body, which for simplicity is defined here as the "top face".

[0004] Instead, the axial cavity is designed to be open at the opposite face of the sensor body (defined herein as the "lower face") and configured to communicate with an inlet of the device to receive the fluid. In other types of sensors (e.g., some sensors of the absolute type), the cavity is instead substantially closed at both ends and one of these ends is provided with a membrane portion, the outside of which is exposed to the fluid.

[0005] Regardless of the type of sensor, the sensor body may be monolithic or may be composed of several parts. For example, the sensor body may be monolithic in order to define in a single part a blind cavity with a corresponding membrane portion, or it may comprise an axially hollow body, which is a relatively thin element on its upper surface, defining a membrane portion, in order to close one end of the said cavity. In other solutions, in which the sensor body is composed of multiple parts, a body is provided, which integrally defines the blind cavity, closed on the upper surface by a part of the body itself and on the lower surface by an element defining a membrane portion applied to the body. Alternatively, the said body may envisage a hole for setting the cavity in communication with the external environment. In still other sensors, the two body parts are joined together by an annular layer of a fixing material having a certain thickness, and the cavity of the sensor body is delimited axially by two opposing surfaces of the two body parts and peripherally by an annular layer of fixing material. In these cases, one of the two body parts does not necessarily define the respective cavity.

[0006] In the type of sensor mentioned, the detection of pressure is obtained by utilizing the elastic deflection or deformability of the membrane portion caused by the action of the fluid to be detected, the degree of deflection or deformation, representative of the pressure of the fluid, being measured electrically through suitable circuit means provided directly on the membrane portion, these means usually being of the piezoelectric or other piezoresistive, or other resistive, or otherwise capacitive type.

[0007] The membrane part and the detection circuitry provided thereon represent an element of importance for the sensor, especially when they are subjected to excessive mechanical stresses due to the pressure of the fluid. Such stresses can be caused, for example, by occasional overpressure of the fluid to be detected or by an increase in the volume of the fluid due to its freezing. These circumstances can cause excessive bending of the membrane part, which can, for example, cause its failure and / or the interruption of the electrical connection tracks deposited thereon belonging to the detection circuitry. These problems of mechanical type are generally solved by providing the pressure sensor or the device integrating it with suitable mechanical compensation elements, as for example described in WO2008 / 078184A.

[0008] However, the applicant has discovered that in some types of pressure sensors, excessive stress by fluid on the membrane portion, i.e., excessive pressure, can sometimes cause inaccurate detection, even if it does not cause failure of the sensor itself or its components.

[0009] For example, as already mentioned, some pressure sensors consist mainly of a monolithic body without blind cavities, on whose underside the elements defining the membrane part are sealed via an annular layer of a suitable material, for example an adhesive. The material that seals and bonds the two parts thus defines the boundaries of the cavity. In such a configuration, the elements defining the membrane part are set substantially parallel to the underside of the monolithic body and at a certain distance from it. This distance, which depends on the thickness of the layer of fastening material, is generally relatively modest (on the order of a few tens of micrometers).

[0010] In these sensors, the sensor body usually supports a circuit arrangement having a first part including a first electrical circuit pattern made of a conductive material deposited on the upper surface of the monolithic body, to which various circuit components can be connected for processing the signal representative of the pressure value (for example for the purposes of amplification or processing). Instead, the electrical signal representative of the pressure value is obtained from a second part of the circuit arrangement, including a second electrical circuit pattern, which provides or is connected to a means designed to detect the deflection or deformation of the membrane part, for example a series of electrical resistors connected to form a Wheatstone bridge. The two circuit patterns are electrically connected through connecting elements extending in the axial direction of the sensor body. These connecting elements often include at least a through hole in the monolithic body, which extends in the axial direction between two opposing faces and on the inside of which there is a conductive material in contact with both circuit patterns.

[0011] The second electrical circuit pattern, for example the aforementioned Wheatstone bridge, is formed on the "inner" surface of the element defining the membrane portion, i.e. the surface facing the inside of the cavity of the sensor body (or in other words the surface of the membrane element opposite that exposed to the fluid). As already mentioned, the aforementioned inner surface is relatively close to the lower surface of the monolithic body.

[0012] The applicant has found, for example, that in sensors of the mentioned type, excessive bending of the deformation of the membrane portion due to excessive pressure of the fluid, sometimes resulting in contact between said membrane portion and the underside of the monolithic body or parts thereof in relief, and said contact, can result in significant errors in the detection of the pressure values. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] WO2008 / 078184A Summary of the Invention

[0014] The present invention has as its basic object the provision of a pressure sensor having a simple, cheap and reliable structure making it possible to solve the above problems. This and other objects which will become apparent hereinafter are achieved according to the present invention by a pressure sensor and a device integrating such a pressure sensor, having the characteristics mentioned in the appended claims, which form an integral part of the technical teachings provided herein in relation to the invention.

[0015] Further objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings, which are given purely by way of illustrative and non-limiting examples and are as follows: [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic perspective view of a pressure sensor according to a possible embodiment; [Diagram 2] FIG. 2 is a schematic perspective view of the sensor of FIG. 1 with the top protective layer removed. [Diagram 3] FIG. 3 is a schematic diagram and a partial cross-sectional view of the sensor of FIG. 2. [Figure 4] FIG. 3 is a schematic perspective view of the sensor of FIG. 2 with the monolithic body removed. [Diagram 5] FIG. 3 is a schematic top view of the sensor of FIG. 2. [Figure 6] 6 is a schematic cross-sectional view of the sensor in a first state taken along line VI-VI in FIG. 5. [Figure 7] FIG. 7 is an enlarged detailed view of FIG. 6. [Figure 8] 7 is a view similar to FIG. 6 with the sensor in a second state; [Figure 9] 8 is a view similar to FIG. 7, but showing the sensor in a second state; [Figure 10] 9 is a view similar to FIGS. 6 and 8, but showing the sensor in a third state; FIG. [Figure 11] 7 and 9, but with the sensor in a third state. [Figure 12]7 is a view similar to FIG. 6 for a sensor according to a further possible embodiment; [Figure 13] 9 is a view similar to FIG. 8 for a sensor according to a further possible embodiment; [Figure 14] 11 is a view similar to FIG. 10 for a sensor according to a further possible embodiment; [Figure 15] FIG. 15 is an enlarged detailed view of FIG. [Figure 16] 5A and 5B are schematic and partial cross-sectional views of a sensor according to further possible embodiments; [Figure 17] 1 is a schematic perspective view of a sensor according to a further possible embodiment; [Figure 18] 4 is a schematic view from below of a sensor according to a further possible embodiment; FIG. [Figure 19] 19 is a schematic cross-sectional view taken along line XIX-XIX in FIG. 18. [Figure 20] FIG. 20 is an enlarged detailed view of FIG. 19. [Figure 21] FIG. 19 is a schematic perspective view of the sensor of FIGS. 17 and 18 with some parts removed. [Figure 22] FIG. 19 is a schematic perspective view of the sensor of FIGS. 17 and 18 with some parts removed. [Diagram 23] 20 is a schematic cross-sectional view similar to FIG. 19, but with the sensor in a different state. [Figure 24] FIG. 24 is an enlarged detailed view of FIG. 23. [Diagram 25] 25 is a view similar to FIG. 24 with respect to a possible variant embodiment. [Figure 26] FIG. 2 is a schematic top view of a sensor according to a possible embodiment with some parts removed. [Figure 27] FIG. 2 is a schematic perspective view of a sensor according to a possible embodiment with some parts removed; [Figure 28] 27 is a view similar to FIG. 26 with respect to a further possible embodiment. [Figure 29] 27, with respect to further possible embodiments. [Diagram 30]27 is a view similar to FIG. 26 with respect to a further possible embodiment. [Diagram 31] 27, with respect to further possible embodiments. [Diagram 32] 27 is a view similar to FIG. 26 with respect to a further possible embodiment. [Diagram 33] 27, with respect to further possible embodiments. [Diagram 34] 27 is a view similar to FIG. 26 with respect to a further possible embodiment. [Diagram 35] 27, with respect to further possible embodiments. [Diagram 36] 27 is a view similar to FIG. 26 with respect to a further possible embodiment. [Figure 37] 27, with respect to further possible embodiments. [Figure 38] FIG. 38 is a schematic cross-sectional view of a sensor according to the embodiment of FIGS. 36 and 37. [Figure 39] FIG. 39 shows a detail of the enlarged view of FIG. 38. [Diagram 40] FIG. 2 is a schematic perspective view of a sensor according to a possible embodiment with some parts removed; [Diagram 41] FIG. 2 is a schematic perspective view of a sensor according to a further possible embodiment with some parts removed; [Diagram 42] 42A-42C are schematic cross-sectional views of a sensor according to the embodiment of FIG. 41 under two different conditions. [Diagram 43] 42A-42C are schematic cross-sectional views of a sensor according to the embodiment of FIG. 41 under two different conditions. [Diagram 44] FIG. 44 is an enlarged detailed view of FIG. 43. [Diagram 45] FIG. 2 is a schematic top view of a sensor according to a further possible embodiment with some parts removed; [Figure 46] FIG. 2 is a schematic top view of a sensor according to a further possible embodiment with some parts removed; [Figure 47] 5 is a view similar to FIG. 4, but for a possible alternative embodiment. [Figure 48]21 with respect to a possible alternative embodiment. FIG. [Figure 49] 4 is a schematic top view of a portion of a sensor according to a further possible embodiment; FIG. [Figure 50] FIG. 50 is a schematic cross-sectional view of the sensor including a portion of FIG. 49. [Figure 51] FIG. 1 is a schematic diagram intended to illustrate possible pressure detection errors of a sensor according to the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Reference to an "embodiment" or "one embodiment" in the framework of this specification is intended to indicate that a particular configuration, structure, or feature described in connection with the embodiment is included in at least one embodiment. Thus, phrases such as "in an embodiment," "in an embodiment," etc. that may be present at various points in this description do not necessarily refer to the same embodiment. Furthermore, the particular conformations, structures, or features defined in the framework can be combined in any suitable manner in one or more embodiments, even if different from those depicted. The reference numbers and spatial references used herein (such as "above," "below," "upper," "lower," etc.) are provided merely for convenience and thus do not define the scope of protection or the scope of the embodiments. In this specification and the appended claims, the general term "material" should be understood to include a mixture, composition, or combination of several different materials (e.g., multilayered or composite materials).

[0018] Typically, the pressure sensor of the invention has a sensor body with a cavity closed at least at one end by a membrane portion. The sensor body comprises at least two body portions, at least one of which defines a respective membrane portion and to which a deformation detection circuit is associated. The sensor body, or each of the at least two body portions constituting it, is preferably made of an electrically insulating material, such as a ceramic material, for example alumina. However, it is not excluded to use an electrically conductive material, for example a metal, at least partially coated with an electrically insulating material, for manufacturing one or more parts of the sensor body.

[0019] In a first type of sensor according to the invention, the two body parts are joined together by an additional fastening material such that the two body parts have respective first faces facing each other. In this way, the aforementioned first face and the fastening material delimit a cavity, the height of which depends on the thickness of the layer of fastening material. Associated with the first face facing the inside of the membrane part, i.e. the inside of the cavity, is a deformation detection circuit, the outside of which is exposed to the fluid. In this type of sensor, one of the two body parts may also define a respective recess in the first face, which defines at least a part of the cavity. In such a sensor variant, the depth of the cavity therefore also depends on the depth of the aforementioned recess.

[0020] In the first type of sensor mentioned above, the cavity of the body sensor can be hermetically closed via a fastening material. On the other hand, using a substantially similar structure, a second type of pressure sensor according to the invention can also be provided, in which the cavity of the sensor body is set to be in fluid communication with the external environment, for example, via a through-hole in a body part, in particular, different from the one defining the membrane part. The through-hole thus provides a duct that can be used to provide a reference pressure, if necessary, at the side of the membrane part inside the cavity, with respect to the pressure to be measured acting outside the membrane part itself. This solution can be adopted, for example, to perform differential pressure detection of a fluid, in particular with respect to the ambient pressure.

[0021] In a third type of pressure sensor according to the invention, one of the two body parts defines a blind axial cavity, i.e. a cavity closed at one end by a membrane part. The body part in question is preferably of monolithic type, even if it does not constitute an essential feature. Instead, the opposite end of the axial cavity is open so as to be able to receive a fluid. In these sensors, the second body part is fixed to the first body part, substantially at a distance from it by the membrane part, and for example supports part of the circuitry. Also in these cases, the two body parts face each other with their respective first faces with respect to the first face of the body part defining the membrane part associated with the detection circuit.

[0022] The sensor according to the invention can in any case be available in forms or versions different from those exemplified above.

[0023] As already mentioned, the sensor body includes at least two parts fixed to each other. These parts may be monolithic or formed by several assembled components. For example, with reference to the above third type of sensor, the body part defining the membrane portion may be monolithic so as to define also the corresponding blind axial cavity in a single part. However, said body part may also be formed by a first axially hollow component, i.e. a component having a through hole sealingly fixed to an end face of a second, relatively thin component, which defines the membrane portion and closes the through hole at one end.

[0024] In FIG. 1, indicated generally at 1 is a pressure sensor according to a possible embodiment of the invention, in particular of the first type mentioned above.

[0025] In the illustrated embodiment, the sensor 1 has a sensor body generally indicated by 2. In various embodiments, the body 2 comprises several parts, at least one first body part indicated by 3 and one second body part indicated by 4. In the illustrated example, the two parts 3 and 4 are hermetically joined via suitable means, represented here by a layer of fastening material 5, for example an adhesive or a sinterable material, with part 3 facing a corresponding first face (here the upper face) of part 4 at a distance therefrom. The layer 5 is annular in shape and is placed between the lower face of part 3 and the upper face of part 4. Thus, defined between the two body parts 3, 4 is a cavity or chamber, here of the closed type, indicated for example by 6 in FIG. 6.

[0026] In various embodiments, part 3 is substantially monolithic, although it is not essential that this is so, although it is relatively thick, whereas part 4 is relatively thin and defines, at least in its central region, an elastically deformable membrane part, for example indicated at 7 in figures 3 to 6. It is preferred that the body parts 3 and 4 are of an electrically insulating material, such as a ceramic material (e.g. alumina), or a polymeric material, although it is not excluded from the scope of the invention that both parts 3 and 4 are made of an electrically conductive material (e.g. a metallic material) optionally at least partially coated by a layer of an electrically insulating material.

[0027] The body part 3 is preferably approximately cylindrical with two opposing faces, for example indicated by 3a and 3b in FIG. 3, as well as several peripheral reference or positioning seats, indicated by 3c only in FIG. 1. In various embodiments (not shown), the body part 3 may have a different shape, for example generally parallelepiped or in any case prismatic. The body part 4 preferentially has a peripheral profile that substantially coincides with that of the part 3, which in the example shown is substantially circular. In this example, the part 4 has substantially the shape of a disk, which provides at least in its central region the above-mentioned membrane part 7, which undergoes elastic bending or deformation towards the body part 3 and, as a result of the fluid, the pressure of which is detected.

[0028] The thicker or rigid body portion 3 and the thinner, at least partially flexible body portion 4 may have a parallelepiped shape, i.e. a substantially square or rectangular cross section. These shapes can be obtained, for example, by cutting a plurality of bodies 3 and 4 from sheets of larger dimensions, respectively the thicker and thinner, preferably by cutting the bodies 3 and 4 after the corresponding sheets have been fastened together.

[0029] The sensor 1 includes circuitry supported by a sensor body 2, which in various preferred embodiments includes at least two portions or circuits each supported by a corresponding body portion 3 and 4.

[0030] With particular reference to Figures 2-4, in various embodiments, the aforementioned circuitry comprises an electrical circuit, generally designated 8, associated with the upper surface 3a of the body portion 3. The circuitry 8 comprises a plurality of respective tracks of conductive material, some of which are designated by 8a in Figures 2-5, made, for example, of a metal or metal alloy (such as a silver-palladium alloy), and such tracks can be screen-printed or in any case deposited on the surface 3a of the body portion 3. In a preferred embodiment, the electrically insulating material constituting the portion 3 is then directly utilized as a substrate for at least a part of the circuitry. However, as previously mentioned, the surface 3a can also be coated with a layer of electrically insulating material that is conductive, but which is, for example, the circuitry 8.

[0031] The circuit 8 may include corresponding circuit components, for example components configured for processing the electrical signal representative of the first information, e.g. in terms of a pressure value, for filtering, amplifying, processing thereof, etc. Also, one or more of the aforementioned components may be formed directly on the face 3a, for example as screen printed resistors.

[0032] In FIG. 2, indicated at 8b are several connection pads located underneath corresponding conductive tracks 8a of the circuit 8, which are used to connect the sensor 1 to a general external system (e.g. the electronic control unit of an internal combustion engine).

[0033] It should be noted that in Fig. 1, the circuit 8 and corresponding circuit components are at least partially coated with a protective layer 9 made of an electrically insulating material, such as a layer of a polymeric or glassy material, except in some areas where the pads 8b (and possibly further components that are not covered) are located. In other figures, the representation of layer 9 has been omitted.

[0034] The circuitry of the sensor 1 in each case comprises an electrical circuit, generally indicated at 10 in Figures 3 and 4, associated with the upper surface of the body portion 4, i.e. facing and remote from the lower surface 3b (see Figure 3) of the body portion 3. As can be clearly seen in Figure 4 (wherein the representation of the body portion 3 has been omitted for greater clarity), the circuit 10 extends at least partially to a position corresponding to the membrane portion 7.

[0035] At least a part of the circuit 10 is configured to detect the elastic bending or deformation of the membrane portion 7. This circuit part may be obtained according to any type known in the art, and is preferably selected among resistive, piezoelectric and piezoresistive type detection circuits.

[0036] Also, the circuit 10 preferentially comprises a number of tracks made of a conductive material, for example a metal or a metal alloy (such as a silver-palladium alloy), some of which are indicated by 10a in Figs. 3 and 4. Preferably, they are deposited (for example screen-printed) directly on said top surface of the body part 4, as well as one or more detection circuit components electrically connected to the tracks. One or more detection components may also be formed directly on said top surface of the body part 4, for example resistors, or piezoelectric or piezoresistive elements, deposited by screen-printing or some other deposition technique. Also, in this case, as mentioned above, the considered surface of the body part 4 may be made of a conductive material, for example a metal material, but at least the part on which the circuit 10 is present is coated with an electrically insulating material.

[0037] In this example, given that the part of the circuit 10 detecting the deformation of the membrane portion 7 is of the resistive type, in particular of the piezo-resistive type, it comprises four resistors, in particular piezo-resistives, designated R1, R2, R3 and R4, connected via tracks 10a in a Wheatstone bridge configuration, with at least two resistors (here the two central resistors of the bridge, designated R3 and R4) preferentially located in a generally central position of the membrane portion 7. In the following, the four resistors R1, R2, R3 and R4 will also be designated collectively as R1, ..., R4.

[0038] Thus, in the considered example, the resistors R1, ..., R4 forming part of the resistive detection bridge are made of a resistive or piezoresistive material (e.g. a resistive or piezoresistive paste) deposited on the upper surface of the body part 4, on the membrane part 7. If the circuit components for detecting the deflection are made of a piezoelectric material, different suitable configurations can be adopted.

[0039] The two circuits 8 and 10 are connected together by suitable electrical connection elements extending in the axial direction of the sensor body 2. In a preferred embodiment, the means for connecting the two circuits 8 and 10 comprise at least one conductive material set in a number of through holes in the body part 3, extending in the axial direction between the corresponding faces 3a and 3b. Two of such holes are indicated at 11 only in FIG. 3, while indicated at 12 are corresponding fillings made of a conductive material (see also FIG. 4). It should be noted that instead of a filling, the conductive material 12 present in the holes 11 may consist of a layer of material extending on the inner surface of each hole 11 for its entire length and / or surface, up to both ends. Regardless of the particular technique used, the material 12 is preferentially applied in such a way that a part of the metal or other conductive material protrudes to the corresponding end outside the hole 11.

[0040] In the example shown, the holes 11 are filled with a conductive material 12, e.g. a conductive paste, forming a substantially cylindrical electrical track, as described above. Alternatively, as described above, the material 12 can be set in the holes 11 to coat only the cylindrical surface of the latter, without filling the holes 11, e.g. via a metallization process. Additionally or alternatively, at least two of the axial grooves 3c of the body part 3 may be provided with a connecting layer or conductive track performing the functions as described (Figure 1).

[0041] As will be noted, for example in Figures 3 and 4, the conductive material 12 of each hole 11 is in electrical contact on the upper surface 3a of the component 3 with a respective terminal pad 8c connected to a track 8a of the circuit 8. On the lower surface 3b of the body part 3, the material 12 is instead electrically connected to the circuit 10, for example to contact layers 13 made of a conductive material obtained on the upper surface of the body part 4, these contact layers 13 being substantially axially aligned with the holes 11 and below the corresponding tracks 10a of the circuit 10. To allow the connection between the material 12 and the layer 13, the layer of the fastening material 5 is provided with respective passages or openings, some of which are indicated by 14. The layer 13 can also be obtained after mutual fastening between the body parts 3 and 4, for example by taking advantage of the holes 11 and introducing therein a conductive material providing such a layer 13.

[0042] According to one aspect of the invention, the face of the body portion 3 set in front of the membrane portion 7 forms or is associated with at least one further circuit element configured to interact with an electrical circuit present in the membrane portion in order to generate a second information representative of an excessive pressure of the fluid, i.e. an excessive bending of the membrane portion 7, when the elastic deflection or deformation of the latter is at least substantially equal to a predetermined limit.

[0043] In various embodiments, the aforementioned circuit elements are utilized to generate a signal or value of an electrical quantity indicative of excessive fluid pressure and / or excessive bending of the membrane portion 7 .

[0044] In various preferred embodiments, the aforementioned circuit element is configured to modify, in a clearly distinguishable and distinct manner, the output signal of the electric circuit that detects the deformation of the membrane portion. In this way, the same output signal of the detection circuit designed to provide the aforementioned first information regarding the normal measurement of pressure can be utilized to infer second information regarding an overpressure condition of the fluid or an excessive deformation of the membrane. The circuit element in question is a functionally distinct component from the detection circuit, i.e., it does not contribute to the effective measurement of pressure, but is instead configured to "perturb" or modify in a clearly distinguishable manner the output signal of the detection circuit in case of an overpressure or in case of an abnormal condition of the pressure sensor.

[0045] The fact that the same output signal of the detection circuit, especially a signal of analog type, can provide both the measurement value and an indication of the abnormal condition, has the advantage of being able to provide multiple pieces of information even when there are only a few electrical connections. However, the sensor according to the invention can be provided with suitable circuitry for controlling, processing and transmitting the data, for example in the form of a chip attached to the sensor body, in order to transmit multiple pieces of data, including also the information on the measurement value and the abnormal condition, in digital form (for example serial data), if necessary, or the control circuitry can identify the single measurement signal and the status signal and separate it into its two components (pressure measurement and abnormal condition) before supplying them separately to an external user circuit on their respective electrical connections.

[0046] Preferably, in order to detect the pressure of the fluid included in a nominal working range between a minimum pressure and a maximum pressure, a pressure sensor 1 is prearranged with an electric circuit for detecting the deformation of the membrane configured to provide an output signal representative of the pressure value of the fluid. The output signal is expressed as an electric quantity, for example a voltage, and can take values ​​included in a range of nominal values ​​between a minimum and a maximum value corresponding to the aforementioned minimum and maximum pressures, respectively. Thus, contact between the aforementioned circuit element and the aforementioned part of the electric detection circuit determines a variation of the output signal such that the value of the corresponding electric quantity is not included in the aforementioned nominal range.

[0047] To give a concrete example, let us assume, purely by way of example, that the sensor 1 operates in a nominal pressure range comprised between 8 and 13 bar, with an electrical quantity at the output from the circuit consisting of a voltage between 0.035V and 0.065V, corresponding respectively to the minimum (8 bar) and maximum (13 bar) values ​​of the sensor's nominal operating range. Contact between the circuit element provided according to the invention and the corresponding part of the detection circuit will decisively modify the value of the output voltage, for example making it 0.01V, or alternatively 0.09V, or in any case to a voltage value clearly distinguishable from the voltage value (for example 0.03-0.07) that would be generated if the pressure of the fluid were comprised in the nominal operating range of 8-13 bar.

[0048] With reference to the examples described so far, the aforementioned circuit element shown at 20 in FIG. 3 is associated with face 3b of body portion 3 and is preferably comprised of electrically conductive elements, this definition being understood to also include electrically resistive elements.

[0049] As can be seen from Figure 3, an element 20, in particular in the form of a contact or a plate or a pad, is associated with face 3b of body portion 3 so as to at least partially cover, at a distance therefrom, circuit 10. Element 20 can for example be glued to face 3a or alternatively be obtained via deposition of a conductive material (including a resistive material) on the face, for example via screen printing.

[0050] In various embodiments, the circuit element 20 is set in an area of ​​the face 3b that substantially corresponds to a central area of ​​the membrane portion 7, even if this does not constitute an essential characteristic. If the face 3b is not planar, the element 20 may be associated with a portion of the relief of said face. If the body portion 3 is not monolithic, in particular if it is formed by a number of components assembled together, the element 20 may be associated with one of such components located in a position generally facing the body portion 4.

[0051] In various embodiments, such as those considered so far, the circuit element 20 is then placed in contact with a portion of the electrical circuit 10 following the aforementioned elastic bending or deformation of the membrane portion 7 at least to an extent substantially equal to the aforementioned predetermined limit. In various preferred embodiments in which the detection circuit comprises a Wheatstone bridge, the element 20 is in a position that substantially corresponds to at least one of the two central resistors R2, R3 of the bridge, in particular having as reference the axial direction of the sensor.

[0052] To facilitate an understanding of the operation of circuit element 20, reference may be made to FIGS.

[0053] FIG. 6 shows the body 2, in a schematic cross-sectional view, in the inoperative or rest state of the sensor, i.e. in a state where no fluid impinges on the "outside" of the membrane portion 7 (i.e. on the underside of the body portion 4) or impinges on it with an insignificant pressure, i.e. insufficient pressure to determine a noticeable deformation of the portion 7. The pressure of the fluid is therefore zero or in any case lower than the lower limit of the nominal operating range of the sensor. The membrane portion 7 is substantially in a resting state, for example substantially planar and parallel to the underside 3a of the body portion 3, and the circuit 10 is at a distance from the surface 3a and from the element 20, as can also be seen from the detail of FIG. 7. As mentioned above, the circuit element 20 covers at least a part of the circuit 10. Let us assume for example that this part corresponds to the resistor R2.

[0054] Instead, FIG. 8 shows operating conditions where acting on the outside of the membrane portion 7 is a fluid pressure P that is within the nominal operating range of the sensor, which again can be considered to consist of 8 to 13 bar (obviously the operating range may vary depending on the class of sensor).

[0055] The pressure P is such that it causes an elastic deformation of the membrane part 7, which bends towards the face 3b, but without coming into contact with the circuit 10, as can be seen from the detail of Fig. 9. The deformation of the membrane part 7 also causes a deformation of one or more resistors R1, ..., R4 of the detection circuit, in particular the resistors R2 and R3 located at least in the central region of the membrane part 7. This deformation causes a variation in the resistance values ​​of R2 and R3 and thus a variation in the output signal, preferably a voltage signal, of the detection circuit R1, ..., R4.

[0056] The above-mentioned change in the output signal, such as the change in voltage value relative to the quiescent value generated in the conditions of Figure 6, is therefore representative of the pressure P generated by the fluid. The signal reaches the circuit 8 through a connection means represented by the axial track formed by the material 12 and can be processed and made available to an external system via pad 8b (Figure 1).

[0057] FIG. 10 instead shows, with reference to the non-limiting example given above for a working range comprised between 8 bar and 13 bar, an abnormal condition in which excess fluid pressure P′ acts on the outside of the membrane portion 7, i.e. a pressure exceeding the nominal operating range of the sensor, for example a pressure of 14 bar.

[0058] As can be noted from the detail of FIG. 11, the elastic bending of the membrane portion 7 is such that a part of the circuit 10, here represented by a resistor R2, comes into contact with the circuit element 20.

[0059] As already mentioned, in this condition the characteristic output signal of the detection circuit, here represented by the Wheatstone bridges R1, ..., R4, is electrically modified so that the change in signal is detectable in a clear and unambiguous manner from the electrical signal, which instead is generated under conditions of pressure that are within the nominal operating range of the pressure sensor (i.e. when the pressure impinging on the membrane portion 7 is such that it does not cause contact between the element 20 and the circuit 10).

[0060] The proposed solution is based on the recognition of the fact that in conventional sensors, i.e. sensors without circuit element 20, the output signal of the detection circuit has a substantially defined characteristic plot in a nominal operating range (e.g. varying linearly or substantially according to a predefined curve), and that if, as a result of excessive pressure, the membrane part comes into contact with the body part above the sensor, this signal may diverge from the characteristic plot and a detection error may occur.

[0061] To make this concept clearer, reference may be made to FIG. 51, which shows a simplified representation of the operation of three conventional pressure sensors having a similar structure to those described so far, but without the circuit element 20. The graph in FIG. 51 shows the values, expressed in volts, of the output signals of the three sensors, designated S1, S2, and S3, as a function of the pressure, expressed in bar. For simplicity, it is assumed that the nominal operating ranges of the three sensors consist of 8-11 bar (signal S1), 8-12 bar (signal S2), and 8-13 bar (signal S3), respectively.

[0062] As will be noted, the output signals S1, S2 and S3 are substantially monotonic and linear in the nominal operating range of the three sensors. Instead, starting from pressures equal to at least 11.1 bar, 12.1 bar and 13.1 bar, corresponding to the contact of the membrane part of the sensor with the top of the sensor body, the output signal starts to decrease. This change in behavior is essentially due to the fact that with increasing deformation of the membrane part and increasing contact area with the body part above it, the central resistor of the measuring bridge is curved in the opposite direction (from a substantially concave configuration it tends to take a substantially convex configuration), so that the value of the output signal does not increase further but starts to gradually decrease. It will thus be understood that to one and the same value of the output signal, two values ​​of pressure clearly different from each other can correspond. See, for example, the value of the signal corresponding to an output voltage of 0.07 V. Here, For signal S1, this value may correspond to a pressure of approximately 11 bar or approximately 15.8 bar. For signal S2, this value may correspond to a pressure of approximately 9.8 bar or 12.8 bar. For signal S3, this value may correspond to a pressure of approximately 10.4 bar or 13.8 bar. This type of movement can obviously cause significant errors in the detection of pressure.

[0063] The solution according to the invention allows for accurate identification when the pressure of the sensed fluid exceeds the upper limit of the sensor's nominal operating range.

[0064] Returning to the example given so far (see in particular FIG. 11), the circuit element 20 may be made of a resistive material (or, alternatively, a metallic element or a highly conductive material) and is designed to be in direct contact with one of the resistors R1, ..., R4, here resistor R2. As can be seen, following contact between the circuit element 20 and resistor R2, the overall value of the resistance of the bridge R1, ..., R4 is radically modified, e.g. reduced, with respect to normal operating conditions (nominal range of pressures). The output voltage of the circuit 10 changes accordingly, so that it can be easily distinguished by the control electronics, e.g. electronics implemented in the circuit 8 or electronics implemented in the external system to which the sensor 1 is connected.

[0065] In the cases illustrated in Figures 6-11, the resistors R1, ..., R4, or at least one of them, extend at least partially to the end of the corresponding connecting track 10a, as is clearly shown, for example, from the details of Figures 7, 9 and 11. In this way, the element 20 can come into direct contact with the resistor considered following excessive deformation of the membrane part 7.

[0066] However, in other embodiments, the reverse arrangement is also possible, i.e. with the ends of the conductive tracks 10a extending at least partially beyond the resistors R1, ..., R4, or at least one of them. Such a case is illustrated in Figs. 12-15, and from the details of Fig. 15 in particular, it can be seen how in this case the circuit element 20 contacts the ends of the tracks designated 10a for the connection of the resistor R2. In this case, for example, the circuit element 20 can be a metallic element that is substantially fully conductive or has a very low electrical resistance, such as shorting the two tracks 10a. (On the other hand, also in this example, the circuit element 20 can be made of a resistive material). In this case, following an excessive deformation of the membrane part, i.e. contact by an excessive pressure P' of the fluid, the overall value of the resistance of the bridges R1, ..., R4 is radically modified with respect to normal operating conditions (nominal range of pressures), for example decreasing, while the output voltage of the circuit 10 changes accordingly, in particular exceeding the maximum voltage value allowed when the sensor operates in the nominal pressure range envisaged for the application of the sensor 1.

[0067] Shown in Fig. 16 is another pressure sensor according to the invention, substantially of the second type mentioned above. In this example, the sensor 1 has a substantially similar overall structure to the sensor of Fig. 1, except that the cavity or chamber delimited by the body parts 3, 4 and the layer of fastening material 5 is set to communicate with the external environment. For this purpose, in the case illustrated in Fig. 16, the body part 3 has a passage 11', here made like a hole 11, designed to connect the cavity or chamber to the external environment (see also Fig. 50). For this purpose, preferentially, the layer of fastening material 5 is also arranged at least at the lower end of the hole 11', allowing communication with the cavity or chamber defined between the parts 3, 4 and the layer 5. Of course, a possible protective layer 9 set on the upper surface 3a of the body part 3 will also be formed so as to be able to connect the upper end of the hole 11' with the external environment. For this purpose, in the case illustrated, the layer 9 has a passage or opening 9a at the upper end of the hole 11'.

[0068] 17-25 illustrate further possible embodiments of the present invention, particularly with reference to a third type of pressure sensor previously described, generally designated 1', having a body portion defining a respective cavity.

[0069] With particular reference to Figures 17-19, in this case the thicker portion 3' of the sensor body 2' defines a blind axial cavity, indicated as 6' in Figures 18-19, closed at its upper end by a corresponding membrane portion 7', preferably made of a ceramic material such as alumina, and defined integrally with the body portion 3'. As will be noted, particularly in Figure 19, the cavity 6' is instead open at its lower end, i.e. at the lower surface 3b of the portion 3', so that the cavity 6' can receive the fluid to be detected therein.

[0070] Attached to the upper surface 3a of the body part 3' is a second body part 4' which is thinner than the body part 3' (excluding the membrane part 7') and is preferably relatively stiff, for example in the form of a PCB or a planar support. Mounted on the upper surface of the body part 4' is a circuit 8 which, in the case of FIG. 17, is partially coated with a corresponding protective layer 9.

[0071] The body parts 3' and 4' are located away from a first face of the body part 3' (here the upper face 3a) or in any case a first face to which its membrane part 7' corresponds (here the lower face of the body part 4', as clearly shown in Figures 19 and 20), and in this case the circuit 10 is also at least partially set in the area corresponding to the membrane part 7', for example in a similar modality as already illustrated before.

[0072] Also in this case, the means for joining the body parts 3' and 4' together may comprise a layer of fastening material 5', for example an adhesive or a sinterable material, set between the parts in question. It should be noted, however, that in this application it is not necessary for the layer 5' to seal the two parts 3' and 4' fluid-tight, and it is not essential that a closed chamber exists between them.

[0073] FIG. 21 shows a body part 3' with a corresponding circuit 10, which, as mentioned above, can be made in the same way as already described. In the illustrated case, the conductive tracks 10a of the circuit 10 are respectively under an electrical connection layer 13', for example similar to that previously designated by 13, deposited on the upper face 3a and can rise axially from there. Such a layer 13' can be advantageously used to connect the circuit 10 to the circuit 8. For this purpose, for example, the body part 4' can be provided with through holes, for example, at positions corresponding to the formations 13', as can be seen from FIG. 17, so that the layer 13' at least partially penetrates the said holes. The said holes can be provided with a surface metallization connected to the corresponding conductive tracks of the circuit 8. Alternatively, the said conductive tracks can be connected to the layer 13' by an applied welding material.

[0074] Figure 22 is similar to Figure 21, but further shows a circuit element 20 which, in various embodiments, is configured to contact two detection components of the circuit, here represented by central resistors R2 and R3. As can be seen from Figures 19 and 20, in this case element 20 is set on the underside of body portion 4', again preferentially in a position corresponding to the central region of membrane portion 7'.

[0075] As can be seen from Figures 23-24, the operating principle of the sensor 1' is similar to that already described above. Also in this case, in fact, an excess of pressure P' with respect to the nominal operating range of the sensor 1' leads to excessive deformation of the membrane part 7', causing, for example, a contact of at least a part of the circuit (here represented by resistors R2-R3) with the conductive circuit element 20 carried by the body part 4', as highlighted in Figure 24. This contact, regardless of the type of conductive material forming the element 20 (resistive or highly conductive material), causes a sudden fluctuation in the output signal of the measuring bridges R1, ..., R4, which can be clearly identified by the control electronics, i.e. indicates an excess of pressure with respect to the nominal range.

[0076] In the case of FIG. 17-244, the resistors R1, ..., R4 extend at least partially into the corresponding ends of the connecting track 10a, but of course, as highlighted in FIG. 25, an opposite configuration of the type already described above is also possible, in which the ends of the connecting track 10a extend at least partially beyond the resistors R1, ..., R4.

[0077] Figures 26-27, 28-29, 30-31, and 32-33 show, by way of example only, some of the possible alternative configurations of circuit element 20. Figure 26-27 shows the case of element 20 designed to contact resistor R2, effectively shorting it out or alternatively connecting the resistance obtained in element 20 in parallel with resistor R2 (thus reducing the value of resistor R2), while Figure 28-29 shows a similar case involving resistor R3.

[0078] 30-31 show the case of two separate circuit elements 20 designed to separately contact two resistors R2 and R3 with each other to short them out or reduce their resistance value.

[0079] 32-33 instead highlight the already mentioned case of a single element 20 which contacts resistors R2 and R3 simultaneously and in particular causes a reduction or shorting of both the value of the individual resistors and the resistance between resistors R2 and R3, i.e. a shorting between the corresponding parts of the measuring bridge, leading to a larger signal variation.

[0080] In various embodiments, the circuit element 20 and the circuit 10 may be pre-positioned to contact each other at a position different from at least one detection component of the circuit 10. For example, referring to Figs. 34-35, two different conductive tracks 10a of the circuit 10 (here, two conductive tracks that come under the resistors R2 and R3, respectively) are formed so as to present two corresponding pads 10b. On the other hand, Figs. 36-37 show possible configurations of a circuit element 20 configured to contact the two aforementioned pads 10b and short them or to connect them with a resistance obtained by the element 20 itself, without contacting the resistors R2 and R3. In this example, this contact element includes two ends 20a connected to each other by a middle portion 20b set at a position corresponding to the pads 10b, in a position corresponding to the space that separates the resistors R2 and R3 from each other. In this way, as illustrated in the following figures 38-39, in the presence of an excess pressure P' of fluid, i.e. a pressure P' exceeding the nominal operating range of the sensor 1, the pad 10b contacts the part 20a of the element 20, while its intermediate part 20b does not contact the resistors R2 and R3. For this purpose, the upper part of the pad 10b is preferably arranged at a height higher than the resistors R2 and R3. Also, in this case, the element 20 may comprise a resistive material to define a resistor, or may comprise a metallic material or a highly conductive material to define a short-circuit element or bridge. Also, in such an embodiment, the net effect is the one already explained above, consisting of a discernible change in the output signal of the circuit 10.

[0081] The circuit element 20 may also be electrically connected to one or more branches of the measurement bridges R1, ..., R4. Such a case is illustrated in Fig. 40, where under the element 20 is a respective conductive track 20c, which is also set away from the surface of the part (not shown here) of the sensor body (not shown here) facing the membrane part 7. The other end of the track 20c is connected to one of the branches of the bridges R1, ..., R4, for example via one of the metallizations 12 used to connect the circuit 10 to the circuit 8. It will be understood that also in such an embodiment, the net effect of the contact between the element 20 and the circuit 10, for example at the position corresponding to the resistor R2, causes an abrupt change in the output signal of the bridges R1, ..., R4, which can be recognized by the control electronics as representing an overpressure of the fluid.

[0082] Although preferred, circuit element 20 need not necessarily be in a location that corresponds substantially to one or more central detection components of circuit 10, such as resistors R2 and R3. Element 20 may in fact be configured to interact with one or both of the other resistors R1 and R4.

[0083] 41, where the circuit element 20 has a substantially annular shape and is arranged such that, following an overpressure of the fluid, it can be contacted by the resistors R1 and R4 (i.e. by the termination of the corresponding conductive track 10a), as already explained above. However, the circuit element 20 can provide contact with only one of the resistors R1, R4, or in any case can have another shape designed to provide contact with both resistors R1 and R4 (for example a semicircular shape or a shape including two pads connected to each other by at least one conductive track).

[0084] Preferably, in this case the thickness of the element 20 is relatively greater than in the case exemplified above. On the other hand, the element 20 can be placed in a relief portion of the corresponding face of the body portion 3, i.e. in its plane close to the membrane 7.

[0085] As can be seen from figure 42, in the absence of fluid pressure, the membrane portion 7 is substantially flat or stationary, so that all resistors R1, ..., R4 (or the corresponding ends of the corresponding connecting tracks 10a) are located away from the element 20. Setting a fluid pressure that is within the nominal operating range of the sensor 1 results in a deformation of the membrane portion 7 to such an extent that it does not cause contact between the resistors R1 and R4 and the element 20, as previously described.

[0086] Instead, if the pressure P' applied to the membrane part 7 exceeds the nominal pressure of the sensor, an excessive deformation of said part 7 towards the overlying body part 3 occurs in any case. The central area of ​​the membrane part 7 is free to undergo deformation towards the body part 3, thanks to the presence of the central passage of the element 20. The membrane part 7 also undergoes deformation in its peripheral areas, which correspond to the resistors R1 and R4, so that the latter rise. In this way, contact is made between the resistors R1 and R4 and the ring-shaped element 20, as shown diagrammatically in Fig. 43 and highlighted in Fig. 44 with reference to the resistor R4. Thus, again in this case, a sudden fluctuation of the output signal of the circuit 10 occurs, which can be identified and detected by the control electronics.

[0087] It should be noted that in other variant embodiments not shown, circuit element 20 may be shaped and positioned so as to be able to contact or interact with all resistors R1, R2, R3, R4, or different combinations of at least some of the resistors (e.g., R1 and R2, or R1 and R3, or R2 and R4, or R3 and R4).

[0088] As can be seen, the element 20 can then be an electrical resistive element configured to provide an electrical resistance in contact with and thus electrically connected to at least a portion of the circuit 10, for example to provide a parallel connection to at least one electrical resistance R1, ..., R4 of the detection circuit, or to provide a connection between a plurality of electrical resistances R1, ..., R4 of the detection circuit, or between the connection tracks 10a of the detection components R1, ..., R4 belonging to the detection circuit. Alternatively, as mentioned above, the element 20 can also be a metallic element or a highly conductive element, designed to contact and thus provide a shorting element electrically connected to at least a portion of the circuit 10, such as a shorting connection across at least one electrical resistance R1, ..., R4 of the detection circuit, or a shorting connection between a plurality of electrical resistances R1, ..., R4 of the detection circuit, or between the connection tracks 10a of the detection components R1, ..., R4 belonging to the detection circuit.

[0089] From the foregoing description, the characteristics of the invention as well as its advantages will become apparent.

[0090] The sensor according to the invention comprises means designed to detect and / or signal (warning) a contact or excessive proximity of its membrane part with another part of the sensor body. This detection or signal (warning) can be obtained through a predefined change in the output signal of a measurement circuit in charge of detecting the deformation of the membrane part for the purpose of pressure detection. On the other hand, as we have seen, according to the invention, in addition to the aforementioned measurement circuit, it is also possible to envisage a second electric or electronic circuit designed to detect a contact with the membrane part or, even in the absence of direct contact, an excessive proximity to another fixed part of the sensor body. The proposed solution makes it possible to prevent, in a simple, inexpensive and reliable way, the risk of false detections in case of deformations of the membrane part of the sensor exceeding those permitted by the nominal operating range of the sensor.

[0091] It is clear that many modifications can be made by a person skilled in the art to the pressure sensor described by way of example without thereby departing from the scope of the invention, as defined in the appended claims.

[0092] The circuit 10 can be configured to make available a safety or fault signal, i.e. a signal indicating an excess of pressure, which is additional and independent to the output signals of the measuring bridges R1, ..., R4.

[0093] For example, the circuit 10 may present specific pads which are shorted or in any case connected together by an element 20, also in the form of a resistive element, to give rise to the aforementioned safety signal. More generally, the circuit element 20 may be a conductive element which, together with the dedicated pads and conductive tracks present in the membrane portion, provides a switch or electrical contact suitable for supplying a fault signal.

[0094] Such a case is illustrated in Figures 45-46, in which the circuit 10 includes two additional conductive tracks 10a', which are located under the respective layers 13 (and therefore under the respective tracks such as those made of material 12 in Figure 4) and define respective pads 10b', which are electrically isolated or independent from the tracks 10a of the detection circuits R1, ..., R4. In this case, the contact element 20 can be of a similar concept to that described with reference to Figures 36-39, i.e. formed to be contacted by pads 10b', rather than by resistors R2 and / or R3. The element 20 can thus include two ends 20a and a middle portion 20b, as already described above.

[0095] In this case, the output signal of the measuring circuit will not be modified by the circuit element 20 if excessive pressure is present. However, the latter, when connecting the two pads 10b', will generate an additional signal representative of excessive deformation of the membrane part 7, and instead, no signal will be present if the sensor is operating in its nominal operating range. Also, if the output signals of the measuring circuits R1, ..., R4 are affected by the problem described in relation to Fig. 51, the simultaneous presence of the aforementioned additional signal determined by the contact of the element 20 with the pads 10b' will be interpreted by the control electronics of the sensor as indicating the presence of an excessive pressure of the fluid. Thus, in this type of embodiment, the pads 10b' and the circuit element 20 form a kind of switch, which closes a signal (alarm) circuit when a pressure of the fluid is reached that exceeds the nominal pressure of the pressure sensor. This type of switch may comprise a contact element 20 designed to provide a short-circuit bridge between the pads 10b' or it may provide an electrical resistance between the pads 10b' and, in any case, provide a signal that can be detected by a suitable control circuit.

[0096] In the example of Figures 45-46, the output signal of the detection circuit, representing the pressure measurement value, is different from the aforementioned additional safety signal, representing the abnormal state. However, the sensor according to the invention may also be equipped with suitable circuits (for example in the form of a chip belonging to the circuit configuration) for control, processing and transmission of data, and may be arranged to combine and transmit a set of information regarding the measurement values ​​and the abnormal state, preferably via a single electrical connection, for example of serial type.

[0097] The circuit element 20 provided according to the invention may also include, together with at least one further component provided in the membrane portion (preferably a component not belonging to the deformation detection circuit), a metallic or conductive element providing a proximity or position detector configured to provide a fault signal even in the absence of contact between the element 20 and the aforementioned further component.

[0098] Figure 47 shows an example in this sense for a sensor 1 having a basic structure of the type shown in Figures 1-4, where corresponding to the circuit elements 20 on the membrane part 7 are similar elements 20" connected to the circuit 8 via respective tracks 10a" and respective axial tracks 12".

[0099] In this example, it can be assumed that the elements 20 and 20″ function as opposing plates of a capacitor, for example made of a metallic material, one (20) in a fixed position and the other (20″) in a variable position and connected to a control electronics. In this application, the two plates 20, 20″ determine between them a capacitance that can be detected by the circuitry of the sensor 1 (or by an external system to which the sensor 1 is connected) if the deformation of the membrane part 7 is excessive, i.e. if it exceeds a safety limit, this indicates an excessive pressure. A similar case is illustrated in FIG. 48, in connection with a sensor 1′ having a basic structure of the type shown in FIG. 17-19, in which the element or plate 20″ is connected to a conductive track 10a″ underneath a corresponding formation 13″.

[0100] In the examples of Figures 47 and 48, elements 20 and 20" effectively provide a proximity sensor of the capacitive type, with element or plate 20 having no electrical connection, but preferably in the form of a metal pad, which interacts with element or plate 20" and causes a variation in its capacitance. However, if required, element or plate 20 can also be provided with respective electrical tracks for connection to other parts of the circuitry of circuit 8 or sensor 1.

[0101] A similar structure is valid for the purpose of manufacturing sensors of the inductive or possibly magnetic type. For example, the element 20" may comprise a coil or winding made of a conductive material and suitable electrical connections to the circuit 8, which can be activated by the element 20, preferably of ferromagnetic type, to generate a separate fault signal. In such a case, the coil or winding may be in the fixed body part and the element 20 may be in the membrane part. Alternatively, the element 20 may comprise a permanent magnet and the element 20" may comprise a magnetic sensor, such as a Hall effect type sensor. Again, the magnetic sensor 20" may be in the fixed body part and the magnetic element 20 in the membrane part.

[0102] Figures 49 and 50 refer to an embodiment conceptually similar to that of Figures 34-37 (or possibly Figures 45-46), but the circuit element 20 present in front of the membrane portion 7 has a simplified shape. In this example, the element 20 has the shape of a simple plate or pad, square, preferably rectangular, with an inclined profile relative to the circuit 10 so as to be able to make contact with the pad 10b, preferably (but not necessarily) without making contact with the resistors R2 and R3. If the aim is to prevent contact with the resistors, as is the case in Figures 34-37 (or Figures 45-46), the top of the pad 10b is preferably placed at a higher height than the resistors R2 and R3, as can be seen in Figure 50.

[0103] The various conductive tracks and / or resistors and / or circuit elements mentioned above can be obtained on the corresponding parts of the sensor body 2 by means of techniques different from screen printing, even if this is the preferred technique. For example, alternative techniques in this sense can be chosen from among lithography, photolithography, spraying of conductive materials, surface metallization, plating, etc.

[0104] As already mentioned, the presence of active or passive circuit components in the circuit 8 is not strictly necessary as regards the processing and / or manipulation of one or more signals generated by the circuit 10, but may be performed in an external system to which the pressure sensor is connected. Thus, in such an embodiment, the circuit 8 may present only pads 8b and corresponding connection tracks 8b to perform a simple interface or connection function.

[0105] The pressure sensor according to the invention may in any case include active or passive circuit components in a circuit 8, as for example illustrated in Figure 17. In this example, the circuit 8 of the sensor 1' includes a control and / or processing and / or transmission circuit MP, for example in the form of a chip or die, which may include a digital processor (such as a microprocessor or microcomputer circuit, or an integrated ASIC or FPGA circuit), which may be provided with or combined with electronic memory means, preferably of the non-volatile and / or electronically rewritable type.

[0106] Furthermore, such a circuit MP comprises inputs and outputs and preferably means for analog to digital conversion. The circuit MP can also, if necessary, very preferably envisage a data transmission circuit in serial form, using SENT (Single-Edge Nibble Transmission) or CAN (Controller Area Network) interfaces and / or protocols, or in Ethernet form.

[0107] The control circuit may be configured to provide a serial type digital signal suitable for representing multiple pieces of information at one and the same serial output, such as a pressure measurement and a possible abnormal condition, for example in the case of the type specified by MP in Figure 17. Such a control circuit may also be configured to distinguish information representing a pressure measurement from information representing a possible abnormal condition at a single input signal and to transmit them separately or successively.

[0108] The circuit elements provided according to the invention which interact with the circuitry present in the membrane portion of the sensor can be obtained directly from the corresponding part of the sensor body (part 3 or 4' in the case of sensor structures of the type described with reference to Figures 1-4 or 17-19, respectively), at least from that part which faces the membrane portion of the sensor, if this body part is made of metal or a conductive material.

Claims

1. A pressure sensor for detecting a pressure of a fluid, comprising a sensor body (2; 2') having at least one first body portion (3; 3') and one second body portion (4; 4'), each having a first surface and a second surface opposite each other; said first body portion (3;3') and said second body portion (4;4') are joined to each other such that said first surface of said first body portion (3;3') faces away therefrom said first surface of said second body portion (4;4'); at least one of said first body portion (3;3') and said second body portion (4;4') comprises a membrane portion (7;7') which undergoes elastic bending or deformation towards the other of said first body portion (3;3') and said second body portion (4;4') as a result of a fluid pressure, said membrane portion (7;7') defining at least a part of said first surface of said first body portion (3;3') and said second body portion (4;4'); said pressure sensor (1) having a circuit arrangement (8, 10) supported by a sensor body (2), said circuit arrangement (8, 10) including at least one first electric circuit (10) extending at least partially through said membrane portion (7; 7') and configured to detect at least one said elastic bending or deformation via at least one respective detection component (R1, R2, R3, R4) to provide a first information representative of a measurement of pressure, said first electric circuit (10) being associated with said first face of one of said first body portion (3; 3') and said second body portion (4; 4') and said first face of the other one of said first body portion (3; 3') and said second body portion (4; 4') forming or being associated with at least one circuit element (20); said circuit element (20) is pre-arranged to interact with said first electric circuit (10) when said elastic bending or deformation of said membrane portion (7; 7') is at least substantially equal to a predetermined limit, thereby generating a second information or signal representative of at least one of an excessive pressure of a fluid, an inaccurate pressure measurement, and an abnormal state of said pressure sensor (1); Pressure sensor.

2. The at least one circuit element (20) is an element functionally different from the first electric circuit (10). The pressure sensor according to claim 1 .

3. said at least one circuit element (20) comprises an element made of an electrically conductive material, such as a resistive material, a metallic material or a material having a high electrical conductivity, with which at least one portion of said first electric circuit (10) comes into contact after said elastic bending or deformation of said membrane portion (7; 7') to an extent at least substantially equal to said predetermined limit, The pressure sensor according to claim 1 .

4. The portion of the first electrical circuit (10) comprises: one said detection component (R1, ..., R4), a conductive track (10a) for connecting one of said detection components (R1, ..., R4); and contact pads (10b; 10b') electrically connected to the conductive tracks (10a; 10a') of said first electric circuit (10); At least one of the following: The pressure sensor according to claim 3.

5. said pressure sensor (1;1') being pre-arranged to detect the pressure of a fluid within a nominal operating range between a minimum pressure and a maximum pressure; said first electric circuit (10) being configured to provide an output signal representative of a pressure value of the fluid, said output signal being an electrical quantity that can assume values ​​comprised in a range of nominal values ​​between a minimum and a maximum value corresponding to said minimum and maximum pressures, respectively; contact between said circuit element (20) and at least a portion of said first electric circuit (10) causes a variation of said output signal such that the value of the corresponding electrical quantity is not included in said range of nominal values. The pressure sensor according to claim 3.

6. The circuit element (20) belongs to a signal circuit, an interaction between the circuit element (20) and at least a portion of the first electrical circuit (10) generates a corresponding signal representative of the second information or signal, the corresponding signal being independent of an output signal of the first electrical circuit (10) representative of the first information; The pressure sensor according to claim 1 .

7. said circuit element (20) comprising a first conductive element providing a proximity or position detector together with at least one second conductive element (20″) associated with said first surface with which said first electrical circuit (10) is also associated; The proximity or position detector detects if the elastic bending or deformation of the membrane portion (7; 7') is at least substantially equal to the predetermined limit. configured to generate the second information or signal even when there is no contact between the first conductive element and the second conductive element (20''); The pressure sensor according to claim 1 .

8. The proximity or position detector is of the inductive, capacitive or magnetic type, The pressure sensor according to claim 7.

9. said at least one detection component (R1, R2, R3, R4; 20″) being selected from among a resistive component, a piezoresistive component, a piezoelectric component, The pressure sensor according to claim 1 .

10. The circuit configuration (8, 10) further comprises: a second electrical circuit (8) associated with another of the second surfaces between the first body portion (3; 3') and the second body portion (4; 4'); a connecting means for electrically connecting the first electric circuit (10) to the electric circuit (8) and extending at least in the axial direction of the sensor body (2); The pressure sensor according to claim 1 .

11. The connection means is a plurality of through holes (11) in the other one of the first body portion (3;3') and the second body portion (4;4'), the through holes extending axially between the respective first and second faces; and a plurality of passages or openings (14) in the layer of material (5) set between said first surface of said first body portion (3; 3') and said first surface of said second body portion (4; 4'); At least one of the following: said connection means further comprising an electrically conductive material (12, 13; 12, 13, 12″; 13′; 13″) extending inside each of the through holes (11) and / or each of the passages or openings (14) and electrically connecting said first electric circuit (10) to said second electric circuit (8); The pressure sensor according to claim 10.

12. an annular layer of sealing material (5) is disposed between said first surface of said first body portion (3) and said first surface of said second body portion (4); the first face of the first body portion (3), the first face of the second body portion (4) and the annular layer of sealing material (5) delimit a cavity (7) in the sensor body (2); The pressure sensor according to claim 1 .

13. said at least one of said first body portion (3') and said second body portion (4') comprises an axial cavity (6') closed by said membrane portion (7') at a corresponding first face (3a); said axial cavity (6) opening at said corresponding second face (3b) for receiving said fluid whose pressure is to be sensed; The pressure sensor according to claim 1 .

14. A pressure detection device comprising a pressure sensor described in any one of claims 1 to 13.

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