WO2025172773A1

WO2025172773A1 - Sensor for measuring at least one electrical property of a fluid

Info

Publication number: WO2025172773A1
Application number: PCT/IB2025/050192
Authority: WO
Inventors: Matteo RONDANO; Giorgio Martinengo; Andrea LUPARIA
Original assignee: Eltek SpA
Current assignee: Eltek SpA
Priority date: 2024-02-14
Filing date: 2025-01-08
Publication date: 2025-08-21
Anticipated expiration: 2026-08-14

Abstract

A sensor device (1) for the measurement of at least one electrical property of a fluid comprises a device body (2) with a sensing duct (4) for the fluid, within the sensing duct (4) there being arranged a sensitive element (10) for the detection of the at least one electrical property. The sensitive element (10) comprises a first electrode (11) and a second electrode (12) which extends in part within a tubular wall (11a) of the first electrode (11), spaced therefrom. The first electrode (11) has a through-slit (14), which extends in the length direction (L) for at least a fraction of the tubular wall (11a), starting from the first longitudinal end (lib) towards the second longitudinal end (11c). The sensitive element (10) comprises a positioning element (15) of the second electrode (12), which is secured at the through-slit (14) of the tubular wall (11a) and is formed at least in part with an electrically insulating material.

Description

Sensor for measuring at least one electrical property of a fluid

DESCRIPTION

Field of invention

[0001] The present invention refers in general to sensors for the measurement of quantities of fluid substances, and has been developed with particular reference being paid to sensors designed to measure, in the presence of a flow of a fluid, the content or the concentration of a component of the fluid itself. The invention has a preferred use in the field of measuring the percentage of alcohol in a fuel, for example the percentage of ethanol in petrol.

Background art

[0002] Sensors of the type indicated are used for example on particular categories of vehicles defined as flexible fuel vehicles (or Fuel Flex), i.e., vehicles equipped with an engine that can run using different fuels or mixtures of fuels, generally alcohol and petrol. In such applications, the sensor, called Flex Fuel, measures the concentration of alcohol, usually plant-based ethanol, with respect to the petrol in the fuel.

[0003] Petrol and alcohol have a different stoichiometric ratio. To achieve an optimal combustion, an engine control unit must therefore vary the ignition advance and the amount of fuel injected, depending on the type of fuel present. For this purpose, the Flex Fuel sensor measures the alcohol concentration and transmits the information to the engine control unit, enabling the control unit to adjust the operating parameters in real time. For a faster and more efficient response, the Flex Fuel sensor is an in-line type sensor, that is, mounted along a fuel supply line to the engine.

[0004] The operation of these sensors is generally based on the different properties of the liquids that make up the fuel mixture. Among the physical properties of petrol and alcohol, the one that most distinguishes the two substances is the dielectric constant, or electrical permittivity sr. The dielectric constant of petrol (sr ~ 2) differs significantly from that of ethanol (sr ~ 24.3) and that of water (sr ~ 78.0). In practice, measuring a dielectric constant results in measuring an electrical capacitance.

[0005] Given that capacitive measurement alone is not sufficient in itself to quantify the water contained in ethanol (naturally or as a contaminant), in particular if it is conductive water, it is normally necessary to also measure an additional electrical quantity, and in particular the electrical conductivity (or the electrical resistance, given that conductivity is the inverse of resistance). The operating principle of Flex Fuel sensors of this type is in any case well known, and does not require a detailed description herein.

[0006] In sensor devices of the type indicated, it is known to use a sensitive element for detecting the electrical quantity or quantities of interest, which comprises at least two electrodes. In various known solutions, the two electrodes are arranged concentrically or coaxial, i.e., by providing a first tubular electrode and a second electrode that extends inside the first electrode.

[0007] A solution of this type is known, for example, from US 2014/069187 Al, wherein both electrodes of the sensitive element have a tubular shape, and wherein the outer electrode of metal material is configured to obtain also a duct for the fluid, directly exposed to the environment, equipped with hydraulic connection elements for connection in a fluid passage line.

[0008] Known solutions of this type generally prove to be complicated in terms of device assembly. Further complications occur in relation to the need of adequately insulating the two electrodes from each other, as well as to counteract possible leakage of the fluid subject to detection towards the electronic control part of the sensor device. The fact that the outer electrode of the sensitive element forms a portion of the duct for fluid passage which is directly exposed to the environment, configured for connection along the relevant supply line, can be a source of possible additional drawbacks with regard to reliability and measurement accuracy of the device.

Aim of the invention

[0009] In its general terms, the present invention is aimed to provide a sensor device of the type indicated at the beginning, for the measurement of at least one electrical property of a fluid, having an improved, economical and reliable construction, and distinguished by a remarkable simplicity of assembly. Another aim of the present invention is to provide a sensor device wherein precise insulation between two electrodes arranged at least in part coaxially is ensured, as well as a precise insulation or protection of these electrodes from the external environment. A further aim of the present invention is to obtain such a sensor device wherein the risks of leakage of the fluid subject to measurement towards the corresponding electronic control components are reduced.

[0010] One or more of the above aims is achieved, according to the present invention, by a sensor device for the measurement of at least one electrical property of a fluid, and by a method for producing a sensor device for the measurement of at least one electrical property of a fluid, having the characteristics indicated in the attached claims. The claims form an integral part of the technical teaching provided herein in connection with the invention.

Brief description of the drawings

[0011] Further aims, characteristics and advantages of the present invention will be apparent from the detailed description that follows, made with reference to the attached schematic drawings, provided purely as a non-limiting example, wherein:

- Figure l is a schematic perspective view of a sensor device according to possible embodiments of the invention;

- Figures 2 and 3 are schematic perspective views, partially sectioned, of a sensor device according to possible embodiments of the invention;

- Figure 4 is a schematic perspective view, in partial section, of a sensitive element of a sensor device according to possible embodiments of the invention;

- Figures 5 and 6 are schematic perspective views, from different angles, of an outer electrode of the sensitive element of Figure 3, including a corresponding electrical connection element;

- Figures 7 and 8 are schematic perspective views, from different angles, of an inner electrode of the sensitive element of Figure 3, with an associated positioning element;

- Figures 9 and 10 are schematic perspective views, from different angles, of a sensitive element obtained by assembling the components shown in Figures 5-6 and 7-8;

- Figures 11 and 12 are schematic views, respectively in perspective and from above, of a sensor body of a sensor device according to possible embodiments of the invention, integrating a sensitive element of the type shown in Figures 9-10;

- Figures 13 and 14 are schematic views, respectively in perspective and from above, of the sensor body of Figures 11-12, with the addition of further components;

- Figures 15 and 16 are schematic views, respectively in perspective and from above, of the sensor body of Figures 13-14, with the addition of further components;

- Figures 17, 18 and 19 are schematic perspective representations of two parts of a mould, in a respective open position, which can be used to overmould by injection a device body of the type shown in Figures 11-12 to a sensitive element of the type shown in Figures 9-10, under three corresponding different conditions;

- Figure 20 is a schematic section of the two mould parts of figures 17-19, in a respective closed position;

- Figures 21 and 22 are schematic sections of an inner electrode and a corresponding positioning element, respectively in exploded view and assembled together, according to a possible variant embodiment with respect to the case of Figures 7-8;

- Figure 23 is a schematic section similar to that of Figure 22, of a further possible variant embodiment;

- Figure 24 is a sectioned, partial and schematic view of a sensor device according to a possible variant embodiment of the invention; and

- Figure 25 is a schematic sectioned view of a sensor device according to a further possible variant embodiment of the invention.

Description of preferred embodiments of the invention

[0012] Reference to an embodiment within this description indicates that a particular configuration, structure, or characteristic described in relation to the embodiment is included in at least one embodiment. Thus, phrases such as "in one embodiment", "in various embodiments" and the like, which may occur in different places in this description, do not necessarily refer to the same embodiment. In addition, particular conformations, structures or characteristics described or illustrated may be combined in any appropriate way in one or more embodiments, even if different from those depicted. Certain conformations, structures or characteristics described or illustrated by reference to "one embodiment" or "in various embodiments" may be at least partially present or absent in other embodiments.

[0013] The references used here are for convenience only and therefore do not define the scope of protection or the scope of the embodiments. The spatial references (such as "upper", "lower", "top", "bottom", etc.) used herein are for convenience only and refer to the examples as shown in the figures.

[0014] In figures 1-3, reference 1 indicates a sensor device in accordance with the present invention. In the following, suppose that the sensor 1 is a sensor configured to detect characteristics of a fuel or fuel mixture, such as a Flex Fuel sensor, designed to detect the concentration of an alcohol, particularly ethanol, with respect to petrol in a fuel.

[0015] The device has a device body 2, which comprises a body part 3 defining at least one detection duct 4, preferably a duct having a circular cross-section. Body part 3 is preferably made of an electrically insulating polymer or plastic material. Preferably, the body of the device 2 also has at least one cavity 5, for housing a circuit arrangement that - in the example - includes a circuit support or PCB 6, on which electrical/electronic components for the connection and/or control of the device 1 are mounted. In a preferential embodiment, the body part 3 is shaped in such a way as to define in a single piece the duct 4 and the cavity 5, or a body portion generally box-shaped, designated by 3', which delimits said cavity.

[0016] In an alternative embodiment, the body part 3 could include at least two parts made of polymer and welded or fixed together, such as a first part shaped in order to define the duct 4 in a single piece, and a second part shaped to define the cavity 5, i.e., the body portion 3'. The device body 2 can also comprise a lid 7, for closing the cavity 5.

[0017] In one embodiment, the body part 3 also integrally defines one or more flanges 3a for fixing the device 1 in position. Each flange 3a may include a metal bushing 3b, at one through-opening thereof. In the example, two flanges 3a are defined in a lateral position with respect to the cavity 5, i.e., on opposite sides of the box-shaped portion 3' of the body part 3.

[0018] The device 1 has an electrical connector, for connection to an external unit, such as an engine control unit of a Fuel Flex vehicle. In a preferential embodiment, the aforementioned connector includes a connector casing 8, at least partly tubular in shape, inside which there extends an end portion of a plurality of electrical connection terminals (not visible in Figures 1-3, but indicated for example by 8a in Figures 11-18), the other end portion extending instead inside the cavity 5, for electrical connection to the circuit borne by the circuit support 6.

[0019] In a possible embodiment, the body part 3 is shaped in such a way as to define in a single piece at least the duct 4 and the box-shaped portion 3' defining the cavity 5. In a possible embodiment, the body part 3 is shaped in such a way as to define at least the duct 4 and the connector casing 8 in a single piece. In a preferential embodiment, the body part 3 is shaped in such a way as to define in a single piece the duct 4, the box-like portion 3' defining the cavity 5, and the connector casing 8.

[0020] The detection duct 4 extends axially along a respective axis A (Figures 2-3), and has an inlet 4a and an outlet 4b (or an inlet 4b and an outlet 4a), so that a fluid can flow therein. Preferably, therefore, the sensor device 1 is of the in-line type, that is, configured to be mounted directly in a supply line of a fluid on which the detection is to be carried out, preferably a line for supplying a fuel to an engine.

[0021] For this purpose, preferably, the detection duct 4 is shaped in such a way as to integrally define, in an external part thereof, connecting or fixing elements, in particular for respective connection elements of a served hydraulic circuit; these connecting or fixing elements, indicated by 4c, are preferably obtained in the form of reliefs or flanges which radially protrude from the duct 4.

[0022] In various embodiments, each connection element 4c obtains a fixing and/or coupling means for a respective female hydraulic connector of the fluid transit line, not represented; in this case, the end parts - indicated by 4d - of the duct 4 that are provided with the respective connection element 4c substantially obtain a corresponding male hydraulic connector, designated by HC in Figures 1 and 3 (see also Figure 25). Therefore, in various preferential embodiments, these hydraulic end connectors HC of the duct 4 are completely made of polymer, i.e., they comprise in one piece an annular relief or flange 4c and a respective end section 4d of the duct 4, both of which are made of polymer. The hydraulic connectors HC can therefore be advantageously integrated into the detection duct 4 made of polymer material, easily and cost-effectively.

[0023] On the two opposite ends portions 4d of the duct 4, i.e. on the hydraulic connectors HC, corresponding to the inlet 4a and the outlet 4b, the outlet end of a first pipe and the inlet end of a second pipe can be coupled, or the corresponding female hydraulic connectors, respectively, for the fluid, here the fuel to be supplied to the engine. In the case of fixing by means of pipes free of a female hydraulic connector, the flanges 4c could in any case define a position of maximum engagement of a corresponding portion of the end of a respective pipe on the corresponding portion of the end 4d of the duct 4.

[0024] In accordance with an important aspect, inside the detection duct a sensitive element is provided, for the detection of at least one electrical property of the fluid.

[0025] In the following, assume that the device 1 is configured to detect at least one of the electrical capacitance (representative of the dielectric constant) and the electrical resistance of the fluid, preferably of both these electrical quantities, as explained in the introductory part.

[0026] The sensitive element, designated in by 10 in Figures 2-4, comprises at least one first electrode 11 and one second electrode 12, with the second electrode 12 extending at least partially within the first electrode 11.

[0027] As can be seen in particular from Figure 4, the first electrode 11 - hereinafter also defined as the outer electrode for simplicity - extends in a respective length direction L and preferably has a substantially tubular wall Ila, with a first longitudinal end 11b and a second longitudinal end 11c opposite to each other. The two ends 11b and 11c of the tubular wall Ila are open, to enable the fluid to pass through the electrode 11. The wall Ila has, as mentioned, a substantially tubular shape and preferably has a circular crosssection, i.e., it preferably has a substantially cylindrical shape; however, the outer electrode 11 and/or its wall Ila may have other shapes suitable for the purpose.

[0028] The second electrode 12 - hereinafter also referred to as the inner electrode for simplicity - is shaped so that at least one part thereof extends inside the tubular wall 11 a, at a distance therefrom, in the same length direction of L as the outer electrode 11. In preferential embodiments, the inner electrode 12 is formed into a single or monolithic body, bent in such a way as to define different portions, as described below, for example.

[0029] In a preferential embodiment, the electrode 12 is substantially thread-shaped (wireshaped), preferably having a circular cross-section, i.e., with a substantially cylindrical shape; however, the inner electrode 12 may have another shape or cross-section suitable for the purpose.

[0030] In a preferential embodiment, the electrode 11 and at least a portion of the electrode 12 are arranged concentrically with respect to each other, i.e., coaxial. Referring for example to Figures 3-4, the electrode 11 and at least one detection portion of the electrode 12 (identified as 12a) can be coaxial with each other and with respect to the duct 4, sharing the axis A thereof.

[0031] In various embodiments, the outer electrode comprises an electrical connection element or portion. In Figure 4, reference numeral 13 designates, for example, an electrical connection element that is in electrical contact with at least one area of the outer surface of the tubular wall Ila. The element 13 is also preferably thread-shaped. The element 13 can be shaped or bent substantially into an L, as in the example shown, wherein 13a and 13b respectively designates a base portion and an upright portion of the element 13 (see also Figures 2-3), wherein portion 13b is substantially a portion for the electrical connection to the circuit support 6. The element 13 is preferably shaped to be in contact with at least two areas of the outer surface of the tubular wall 1 la. As will be shown later, the element 13 - for example welded to the tubular wall Ila - allows the connection of the outer electrode 11 to the circuit arrangement provided on the circuit support 6.

[0032] The two electrodes 11 and 12 are formed with electrically conductive material, although the case of one or both electrodes formed with an insulating material made electrically conductive, for example an electrically conductive polymer, is not excluded. It is also possible to cover the inner surface of a tubular wall Ila formed with an insulating polymer and/or the outer surface of an electrode 12 formed with an insulating polymer with a layer of electrically conductive material. In such a case, an electrical connection element technically equivalent to the element 13 can be made in a single piece with the outer electrode 11 and also be coated with a layer of electrically conductive material, in contact with the electrically conductive layer that covers the inside of the tubular wall.

[0033] In a preferential embodiment, the electrode 12 and the electrode 11 with the connection element 13 thereof are formed from metal material. A preferred material is AISI (stainless) steel. In the case of AISI steel, the inner electrode 12 may be subjected to surface treatment with nickel, while the outer electrode 11 may not be surface treated. The connecting element 13 can also be made of stainless steel, preferably superficially treated with nickel.

[0034] As mentioned, the outer electrode 11, i.e., the tubular wall Ila thereof, is preferably cylindrical in shape, and the inner electrode 12 is preferably shaped as a wire with a circular cross-section. The element 13 can also be thread-shaped with a circular crosssection, for example having the same diameter as the thread-like body of the electrode 12.

[0035] By way of example, the electrode 11 can have an external diameter of between 6 and 10 mm, for example 8.6 mm, and an internal diameter of between 4 and 8 mm, for example 6 mm; the electrode 12 can have an outer diameter of between 1 to 3 mm, for example 1.6 mm. Again by way of example, the electrode 11, i.e., the tubular wall 1 la thereof, can be between 20 and 24 mm long, for example 22 mm. The part of the electrode 12 that extends coaxially with respect to the outer electrode 11, i.e., the detection portion identified as 12a in Figure 4, may be slightly shorter in length than the tubular wall Ila, preferably of between 18 and 22 mm, for example 19 mm. Again by way of example, the duct 4 may have an inner diameter slightly smaller than the outer diameter of the tubular wall Ila and slightly larger than the inner diameter of the tubular wall Ila, preferably of between 5 and 9 mm, for example 7.05 mm.

[0036] In any case, it can be seen from Figures 2 and 3 that, preferably, the extension in length of the outer electrode 11 is equal to a fraction of the length of the duct 4, that the outer electrode 11 is positioned in an intermediate zone of the duct 4, and that the detection portion 12a of the inner electrode 12 is substantially centered in the length direction L with respect to the two ends 11b, 11c of the tubular wall.

[0037] Figures 5 and 6 show only the outer electrode 11 with the connection element 13 thereof. As can be seen in these figures, in accordance with an important aspect, the electrode 11 has a through-slit or through-groove 14, which extends for at least one fraction of the length of the tubular wall Ila, starting from the first longitudinal end Ila towards the second longitudinal end 11b. In the example, the bottom 14a of the slit 14, opposite to the end 11b of the tubular wall Ila, has a generally curved or rounded profile, although this is not an essential feature.

[0038] In accordance with another important aspect, at the aforementioned through-slot or through-through groove, a positioning element for the inner electrode is secured, configured to support the inner electrode in its working position. An example of the above positioning element is designated as a whole with 15, for example in Figure 4.

[0039] The positioning element 15 has the function of supporting the electrode 12, allowing assembling thereof in a substantially predefined position on the electrode 11, under conditions of electrical insulation; for this purpose, the element 15 is formed at least in part from an electrically insulating material.

[0040] The positioning element 15 is secured on the outer electrode 11 , or on its tubular wall Ila, in a fixed position.

[0041] In preferential embodiments, the electrically insulating material of the element 15 is overmoulded to the inner electrode 12, which has been previously shaped for the purpose, as is visible for example in Figures 7 and 8. For this purpose, the body of the electrode 12, previously shaped, is inserted into a mold, having an impression or cavity suitable for receiving the electrode 12 and defining the external profile of the element 15. After the mould has been closed, the electrically insulating plastic material of the positioning element 15 is introduced into the mould in a fluid state and, after solidification of the aforementioned plastic material, the electrode 12 including the element 15 can be removed from the mould. In this way, at least a coupling portion of the electrode 12 is surrounded by the electrically insulating material of the element 15, in particular embedded thereinto (as will be seen, in other possible embodiments, the body of the element 15 is mounted on the body of the electrode 12, in any case in such a way as to at least partially surround a coupling part thereof, even in the absence of over-moulding).

[0042] The inner electrode 12 provided with the positioning element 15 is then coupled to the outer electrode 11, particularly by engaging the element 15 inside the slit 14 defined in the tubular wall Ila of the electrode 11. This can be done, for example, by pushing the element 15 into the slit 14 from above, or else by pushing the element 15 sideways into the slit 14 from the open end thereof. The result of the coupling can be seen, for example, in Figures 9 and 10.

[0043] Preferably, the positioning element 15 is received in the through-slit 14 so as to occupy the through-slit substantially completely; this is advantageous when, as in the preferred embodiments of the invention, the part of the body of the device that defines the detection duct 4 is over-moulded to the sensitive element 10.

[0044] The body of the positioning element 15 and the shaped body of the inner electrode 12 are made in such a way that, in the coupling position between the element 15 and the through- slit 14, the detection portion 12a of the electrode 12 is in the correct position within the tubular wall Ila, substantially coaxial thereto.

[0045] Regardless of the specific shape, and as can be seen particularly in Figure 4, in a preferred embodiment, the body of the inner electrode 12 is bent in such a way as to define a plurality of portions, among which at least: a. the aforementioned detection portion 12a, which extends at least partially inside the electrode 11, substantially in the length direction L, b. an electrical connection portion 12b, which extends at least partially outside the electrode 11, preferably in a transverse direction with respect to the length direction L, and c. a coupling portion 12c, having support and/or positioning functions, which is at least partially surrounded by electrically insulating material of the element 15, wherein - in the assembled condition - this coupling portion 12c is preferably in a position substantially corresponding to that of the through-slit 14.

[0046] In one or more embodiments , the thread-like body of the inner electrode 12 has a plurality of curvatures or curved portions. In the specific example depicted, there are provided three portions curved substantially at 90°, designated by 12', 12" and 12"' in Figure 4.

[0047] In various embodiments, as in the case exemplified in the figures, the thread-like body of the inner electrode 12 is bent in such a way that the electrical connection portion 12b, or at least a part thereof, is substantially orthogonal or transverse to the detection portion 12a, or at least a part thereof.

[0048] In various embodiments, as in the case exemplified in the figures, the thread-like body of the inner electrode 12 is bent in such a way that the electrical connection portion 12b, or at least a part thereof, is substantially orthogonal or transverse to the coupling portion 12c, or at least a part thereof.

[0049] In various embodiments, as in the case exemplified in the figures, the thread-like body of the inner electrode 12 is bent in such a way that at least part of the coupling portion 12c is substantially parallel or set side by side with respect to at least part of the detection portion 12a.

[0050] The fact that, in preferential embodiments, the coupling portion 12c, or at least a part thereof, extends substantially in the length direction of the outer electrode 11, may contribute to maintenance of the coaxiality between the same outer electrode and the detection portion 12a of the inner electrode 12; this can be particularly useful in cases wherein the electrode 11 and the element 15 are assembled parts, as in the case of the variant embodiment of Figures 21-22.

[0051] It should be noted, however, that the coupling portion of the sensitive element could have a different shape from the one represented, or be obtained by exploiting a part of a different portion of the inner electrode: for example, in the case of an inner electrode having a substantially L-shape (as in the variant embodiments of Figures 23 and 25), the coupling portion could be obtained by a section of the electrical connection portion 12b that passes through the positioning element 15.

[0052] In the case exemplified, and referring to Figure 4, a portion of the thread-like body of the electrode 12 is bent substantially in a U-shape, so as to define the detection portion 12a and at least part of the coupling portion 12c substantially set side by side or parallel to each other, and joined by an intermediate portion 12c', which can be at least partially curved, wherein the curvature 12' connects the detection portion 12a to one end of the intermediate portion 12c', and the curvature 12" connects the other end of the intermediate portion 12c' to the coupling portion 12c; however, the detection portion 12a and the coupling portion 12c could be joined in another way, for example by means of a U-bent intermediate portion, or they could be folded in a V shape without a substantial intermediate portion.

[0053] The curvature 12" can itself be considered as a part of the coupling portion 12c, as it is partially embedded (or inserted, in possible variant embodiments discussed below) into the body of the positioning element 15; the same applies to the curvature 12'", here completely embedded into the body of the element 15 (but could be inserted therein, in possible variant embodiments discussed below).

[0054] Still referring to the case exemplified, another portion of the thread-like body of the electrode 12 is bent at an angle - here substantially at 90° - with respect to the coupling portion 12c, in order to obtain the electrical connection portion 12b, with the curvature 12'" that connects the two portions 12c and 12b. An initial section of the electrical connection portion 12b that is immediately downstream of the curvature 12'" can also be considered as a part of the coupling portion 12c, as it is partially embedded (or inserted, in possible variant embodiments) into the body of the positioning element 15; the same applies to the curvature 12", here completely embedded into the body of the element 15 (or inserted, in possible variant embodiments).

[0055] In general, it is preferable that the connection element 13 of the outer electrode 11 has a body shaped such that at least part of its electrical connection portion 13b extends substantially parallel to at least part of the electrical connection portion 12b of the body of the inner electrode 11. As will be seen below, this is advantageous for the assembly and the electrical connection of the sensitive element 10 to the circuit support 6.

[0056] In view of an easy and cost-effective construction, all portions of the thread-like body of the electrode 12 and/or of the connection element 13 have the same size and/or crosssection, preferably a circular shape with a diameter of between 1 mm and 2 mm, preferably 1.6 mm; this size can also allow a greater mechanical stability of the inner electrode 12 and/or an easy transfer of the heat of the fluid to the control circuit, for the reasons explained below.

[0057] However, the above-mentioned portions and/or curvatures of the thread-like body of the electrode 12 and/or of the connection element 13 may possibly have at least a somewhat different shape or size, for example obtained by abrasion or partial deformation of lengths of the constituent thread (for example a narrow or shaped shape of at least one final length of the electrical connection portion 12b and/or 13b, to facilitate soldering or fixing to the circuit support 6).

[0058] The sensitive element 10, in order to be used for measuring the electrical properties of interest of the fluid, is englobed in a body made of electrically non-conductive material, here represented by the plastic or polymeric material of the detection duct 4. For this purpose, in preferential embodiments, a part of the device body that defines at least the detection duct is a part over-moulded to the sensitive element.

[0059] The aforementioned body part - which in the example is part 3 also defining the cavity 5 (or the portion 3' that defines said cavity) and the connector casing 8 - essentially has the functions of conveying and enabling passage of the fluid of interest through the sensitive element 10, while allowing the easy insertion of the sensor device 1 into the circuit in which the fluid flows (particularly through the connectors HC), ensuring fixing of the concentric electrodes 11, 12 assembled together by means of the positioning element 15, and keeping the two electrodes 11, 12 electrically isolated from each other.

[0060] The body part that defines at least the detection duct, in the example part 3, is preferably made of plastic material, by means of an injection molding process, where in particular this plastic material is over-moulded to the sensitive element 10. Over-moulding allows the integration of the sensitive element 10 into the plastic material that obtains at least the sensing duct 4, with the sensitive element 10 being completely contained within said duct, and therefore only exposed to the fluid subject to detection. As can be clearly seen, for example, in Figures 2 and 3, the over-moulded material that obtains the opposite end portions 4d of the duct extends beyond the two longitudinal ends of the sensitive element 10.

[0061] In cases such as the one exemplified, wherein the body part 3 defines the connector casing 8 and the fixing flanges 3a, over-moulding makes it advantageous to integrate the metal bushings 3b and the electrical terminals, indicated by 8a in Figures 11-18, into the same body part 3, for the external electrical connection of the device 1.

[0062] A possible method for producing a sensor device 1 having a device body that includes a detection duct made of electrically insulating material comprises the steps of: i) providing an outer electrode (11) having a substantially tubular wall (Ila), to which an electrical connection element (13) is preferably connected, ii) providing an inner electrode (12), comprising at least one detection portion (12a) and one electrical connection portion (12b), iii) providing a sensitive element (10) of the sensor device (1) by coupling the inner electrode (12) to the outer electrode (11), preferably by means of a positioning element (15), in such a way that the aforementioned detection portion (12a) extends at least partially substantially in a length direction (L) of the outer electrode (11), inside the substantially tubular wall (Ila) of the latter and spaced therefrom, the aforementioned electrical connection portion (12b) extends at least partially outside the outer electrode (11), in particular transversely with respect to the length direction (L) of the outer electrode (11), and iv) constraining the sensitive element (10) within a detection duct (4) of a body (2) of the device (1).

[0063] Step iii) indicated above preferably comprises the operation of securing a positioning element (15) to the inner electrode (12), this positioning element being formed at least in part of an electrically insulating material and configured to support the inner electrode (12), and the operation of coupling this positioning element (15) to the outer electrode (H).

[0064] Preferably, the positioning element (15) is moulded over a coupling portion (12c) of the inner electrode (12), which is substantially intermediate to the corresponding detection portion (12a) and electrical connection portion (12cb).

[0065] Step iv) indicated above preferably comprises the operation of moulding a part (3) of the body (2) of the device (1) that defines at least the detection duct (4) over the sensitive element (10).

[0066] In the specific case of the example of the preferential embodiment as illustrated in the figures:

- step i) comprises the operation of defining in advance in the tubular wall (Ila) of the outer electrode (11) a longitudinal through-slit or through-groove (14);

- step ii) comprises the operation of bending a body of the inner electrode (12) so as to present the detection portion (12a), the electrical connection portion (12b) and the coupling portion (12c),

- step iii) comprises the operation of securing the positioning element (15) in a through-slit or through-groove (14) of the substantially tubular wall (Ila) of the outer electrode (11), in such a way that the coupling portion (12c) is at least partially surrounded by electrically insulating material of the positioning element (15), at the through-slit (14) of the tubular wall (Ila) of the outer electrode (11).

[0067] Even more generally, a possible method to produce a sensor device (1) having a device body overmolded in order to define at least one detection duct made of an electrically insulating material comprises the steps of: a) providing an outer electrode (11) comprising a substantially tubular wall (Ila), extending in a length direction (L), the outer electrode (11) having a respective electrical connection portion (13b), b) providing an inner electrode (12), comprising a detection portion (12a) extending at least partially substantially in the length direction (L), the inner electrode (12) having a respective electrical connection portion (12b), c) obtaining a sensitive element (10) of the sensor device (1) by coupling the outer electrode (11) and the inner electrode (12), with the inner electrode (12) that extends at least partially within the outer electrode (11) electrically isolated therefrom, d) over-moulding the sensitive element (10) with an electrically insulating polymer or plastic material to obtain a body (2) of the device (1) which defines at least one sensing duct (4) within which the sensitive element (10) is integrated.

[0068] Preferably, step d) indicated above comprises the operation of over-moulding the electrically insulating polymer or plastic material in such a way as to integrally define, on the outside of the detection duct (4), connecting or fixing elements (4c), in particular in the form of radially protruding flanges, for the connection of the detection duct (4) along a line of passage of a fluid.

[0069] In the non-limiting example of Figures 11 and 12 a body part 3 is visible, that integrates the portion 3' delimiting the cavity 5, the duct 4, the flanges 3a and the connector casing 8, and which is moulded over the sensitive element 10 including the connection element 13. As can be seen, in the electrically insulating material forming the body part 3, there are already partially integrated or embedded the terminals 8a, the bushings 3b, as well as the sensitive element, of which only a terminal length of the portion 12b of the inner electrode 12, and a terminal length of the portion 13b of the connection element 13 of the outer electrode 11 are visible.

[0070] As will be seen, the cavity 5 preferably has a bottom, through which there extend respective parts of the portion 13b of the electrical connection element 13 and the portion 12b of the inner electrode 12. In this perspective, from Figures 11 and 12 it can be seen that, preferably, substantially cylindrical formations 3c and 3d rise from the bottom of the cavity 5, in each of which a respective part of the connection portion 12b of the inner electrode 12 and of the connection portion 13b of the connection element 13 extend axially; the function of these bushing-shaped formations, also visible in Figures 2-3 and having a larger diameter than the aforementioned connection portions 12b and 13b, is to house at least one sealing element associated with the aforementioned electrical connection portions 12b and 13b, as it will be explained below. From the same Figures 11 and 12 it can also be seen that, within the cavity 5, one or more support elements 3e and/or one or more positioning elements 3f for the circuit support 5 can be integrally defined.

[0071] Figures 13 and 14 further show how, on the top of the formations 3c and 3d referred to in Figures 11-12, respective plugs 21 and 22 can be mounted, for example in plastic or elastomer material, in any case of electrically insulating material. These plugs 21 and 22, also visible in Figures 2-3, each have a central passage, to allow the terminal length of the electrical connection portion 12b of electrode 12 and the terminal length of the upright portion 13b of the connection element 13 of the electrode 11 to protrude inwards into the cavity 5, for the purpose of connection with the circuit borne by the support or PCB 6.

[0072] Figures 15 and 16 further show the condition wherein the circuit support 6 is inserted inside the cavity 5. The circuit support 6 is provided with first holes (not indicated) in which respective portions of the terminals 8a are passing, with these portions which are set in an electrically conductive condition with respective electrically conductive tracks or pads of the circuit provided on the support 6 (for this purpose, the aforementioned first holes can also be metallized holes). Similarly, the circuit support 6 is provided with second holes (not shown, but visible in Figure 3) through which the respective terminal sections of portions 12b and 13b of the inner terminal 12 and the connection element 13, respectively, pass through (see also Figure 2 for reference). Also in this case, the above- mentioned terminal sections of portions 12b and 13b are set in a condition of electrical conduction with respective electrically conductive tracks or pads of the circuit provided on the support 6 (for this purpose, the aforementioned second holes can be metallized holes). As mentioned, in preferential embodiments, the inner electrode 12 and the connection element 13 are made of stainless steel coated at the surface thereof with nickel, and this coating facilitates tin welding of the end sections of portions 12b and 13b to the aforementioned tracks, pads or metallized holes.

[0073] In various preferential embodiments, the operation of moulding a part (3) of the device body (2) over the sensitive element (10) comprises:

- placing the sensitive element in a mould (10),

- closing, by means of corresponding movable mould elements, the two ends (11b and 11c) of the tubular wall (Ila) of the outer electrode (11),

- inject into the mould an electrically insulating plastic material in the fluid state, necessary for the formation of the part (3) of the device body (2) which defines at least the detection duct (4),

- waiting for the solidification of the electrically insulating plastic material, and

- removing from the mould the part (3) the device body (2), which defines at least the detection duct (4) integrating the sensitive element (10).

[0074] Preferably, the aforementioned mould is configured in such a way as to define, on the outside of the detection duct (4), connecting or fixing elements (4c), in particular in the form of radially protruding flanges, for connection of the detection duct (4) along a fluid passage line.

[0075] Figure 17 schematically represents a possible mould that can be used to carry out the over-moulding operation. In the example, the mould comprises two mould parts that can be closed one on top of the other (as shown in Figure 20): for the sake of clarity, in Figure 17 and in the following Figures 18 and 19 the two mould parts are represented side by side, in order to make the parts more clearly visible.

[0076] The two mould parts are designated by 30' and 30" in Figure 17 and each define a respective impression 31' and 31" which, when the parts 30' and 30" are closed on top of each other, delimit the mould cavity into which the plastic or polymeric material necessary for the formation of the body part 3 is injected (some parts of the mould cavity can also be defined by movable mould parts described below). In summary terms, the impression 31' can be understood as a male impression, aimed at defining most of the internal surfaces of the body part 3 (for example the cavity 5 and the connector casing 8), while the impression 31" can be understood as a female impression, aimed at defining most of the external surfaces of the body part 3. Respective parts of the impression 31' and 31" (for example the parts indicated by 30b' and 3 lb' in Figure 20) are configured for the positioning of the sensitive element 10, which is provided with the connection element 13. In this specific example, other parts of the impression 30' are configured for the positioning of the terminals 8a and the bushings 3b.

[0077] On a mould part, here part 30', movable mould parts 32' are mounted, which are linearly displaceable and configured so that corresponding shaped portions 32a' close the two open ends (11b, 11c, Figures 1-3) of the tubular wall Ila of the outer electrode 11, on which the positioning element 15 is mounted with the inner electrode 12 (Figures 3-4), preferably by also securing the inner electrode 12 in position (as will be seen in relation to Figure 20).

[0078] On the same mould part 30' a further movable mould part 33' is mounted, which is linearly displaceable and configured in such a way that a corresponding shaped portion 33a' defines the internal surface and the bottom of the connector casing 8 (Figures 1-3), through which the terminals 8a are intended to pass through. Of course, the mould part 30' is configured to enable the movable parts 32' and 33' to slide from the respective rest positions, shown in Figure 17, to the respective working positions, shown in Figure 18. Similarly, the mould part 30" is configured to enable the movable parts 32" and 33" to be displaced, for example through appropriate sliding passages 32" and 33".

[0079] As mentioned, in Figure 18, the movable parts 32' and 33' of the mould part 30' are shown in the respective working positions, i.e., in an advanced position with respect to the positions of Figure 17. It can therefore be noticed that the shaped portions 32a' of the movable parts 32' obstruct the two open ends of the tubular wall 1 la of the outer electrode 11 (Figures 3-4), and that the shaped portion 33a' of the movable part 33' receives inside an end part of the terminals 8a.

[0080] Figure 19 shows the result of the over-moulding, with the body part 3 now formed, and which therefore includes the portion 3' that defines the cavity 5 (Figures 11-16), the duct 4 that integrates the sensitive element 10, the connector casing 8 that integrates the terminals 8a, and the flanges 3a that integrate the bushings 3b. After solidification of the over-moulded material, the two mould parts 30' and 30" can be opened, the movable parts 32' and 33' can be moved back to their initial positions, and the body part 3 can be removed.

[0081] Figure 20 is a schematic view of the mould, according to a vertical section plane, in a position corresponding to the sensitive element 10.

[0082] It can be seen how the mould parts 30' and 30", or the corresponding impressions, have respective shaped zones 30b', 31b' for positioning and supporting the sensitive element 10 in the mould, and how the shaped portions 32a' of the movable mould parts 32' can be configured to close the tubular wall (Ila, Figures 3-4) of the sensitive element 10 at both ends thereof, so as to prevent the over-moulding fluid material from spreading inside said wall. Figure 20 also shows how the above-mentioned shaped portions 32a' can also be advantageously configured to interact with respective parts of the inner electrode (12, Figures 3-4) and/or of the corresponding positioning element (15, Figures 3-4), in order to ensure the correct reciprocal positioning between the electrodes (11 and 12, Figures 3- 4).

[0083] Again from Figure 20 it can be seen how, in preferential embodiments, the movable parts 32" of the mould can conveniently define respective impressions 32a" for forming the opposite end portions (4d, Figures 1-3) of the detection duct (4, Figures 1-3) with the corresponding fixing formations or flanges (4c, Figures 1-3), or for the formation of the hydraulic connectors HC. The cavity parts necessary for the formation of the above- mentioned fixing formations or flanges are here defined between the movable parts 32' and the corresponding facing surfaces of the shaped zones 30b', 31b' used for the positioning and support of the sensitive element 10.

[0084] The shaped portions 32a' of the movable parts 32' press securely on the two opposite longitudinal ends of the sensitive element 10, so that the inside of the tubular wall Ila is isolated from the injection cavity. The aforementioned shaped portions 32a' press on substantially flat surfaces at the two ends 11b and 11c of the tubular wall Ila; it will be appreciated that, on the side of the sensitive element 10 where the positioning element 15 is positioned, one of the shaped portions 32a' will also press on the end surface of the element 15 opposite the slit (the end designated by B in figure 10). [0085] As mentioned, during moulding of the body part 3, it is necessary to prevent the injected material from escaping from the mould cavity and spreading inside the sensitive element 10, with the risk of occluding the space between the concentric electrodes, and therefore closing the passage for the fluid.

[0086] For this reason, in addition to configuring the mould in such a way that the two open ends of the sensitive element 10 are closed during moulding, it is preferable that the positioning element 15 of the inner electrode 12 be received into the through-slit 14 so as to occupy said slit substantially completely.

[0087] In order to further reduce the risk that some of the injected material may spread between the positioning element 15 and the slit 14, the positioning element 15 can be advantageously shaped so as to have a coupling portion, which is received in the through- slit 14. Preferably, this coupling portion is provided at the surface thereof with at least one sealing protrusion, configured to cooperate with the surface - designated by lid for example in Figures 5-6 - of the tubular wall Ila that delimits the through-slit 14. Such a coupling portion of the element 15 is designated by 15a for example in Figures 7-8.

[0088] The sealing protrusion, or the sealing protrusions, may extend along the perimeter part of the coupling portion 15a which faces the surface lid delimiting the through-slit 14.

[0089] In the case exemplified, the coupling portion 15a defines two sealing protrusions, designated by 15a' in Figures 7-8, which are generally parallel and extend over the entire profile of interference with the outer electrode 11 (i.e., the part of the portion 15a that is inserted into the slit 14). In the example, the protrusions 15a' essentially obtain sealing seams having a substantially triangular profile which, when the positioning element 15 is coupled to the slit 14, interfere with the surface lid, with a consequent deformation at the contact area.

[0090] In various embodiments the positioning element 15 has a containment portion, having lateral dimensions greater than the through-slit 14, for at least partial support on the outside of the tubular wall Ila of the outer electrode 11. One said upper containment portion, such as the one designated by 15b for example in Figures 7-8, further assist in reducing the possibility that the material injected into the mould may infiltrate into the inside of the sensitive element 10.

[0091] The fact that the containment portion 15b has a larger overall dimension with respect to the slit 14 also has the effect of counteracting the thrust exerted by the plastic material on the positioning element 15, during the over-moulding step, that is, preventing the positioning element from displacing towards the inside of the sensitive element 10 under the pressure of the polymeric material injected in the fluid state into the mould.

[0092] Considering that the moulding pressure can be relatively high, in various embodiments, the containment portion 15b is configured in such a way as to present additional mechanical elements to oppose the thrust of the material injected into the mould. In preferential embodiments, these mechanical elements may include at least one of a pair of opposite lateral protrusions and a longitudinal protrusion of the containment portion 15b.

[0093] Referring to the example in Figures 7 and 8, the containment portion 15b may have a pair of opposite projections 6a, each at a respective longitudinal side of the portion 15b, the lower surfaces of which may rest on corresponding regions of the outer surface of the tubular wall Ila, at the edge of the through-slit 14.

[0094] Again referring to the example in Figures 7 and 8, in addition or as an alternative to the protrusions 16a, the containment portion 15a may have a longitudinal or front projection 16b, the lower surface of which may rest on a corresponding region of the outer surface of the tubular wall that lies beyond the through-slit 14, in the direction towards the end 11 c of the tubular wall Ila.

[0095] The positioning element 15, or the containment portion 15b thereof, can be further strengthened, for example to oppose possible bending thereof, by providing at least one upper rib. Again in the example of Figures 7-8 there is shown the case of an upper rib 17a- 17b that extends for most of the length of the containment portion 15b.

[0096] The body of the positioning element 15 may be provided, at the containment portion 15b thereof, with an upper bushing-shaped formation, through which a corresponding length of the vertical portion of the inner electrode extends. This bushing-shaped formation, designated by 18, which in the example is defined in an intermediate position of the upper rib 17a- 17b, can be useful for sealing purposes.

[0097] By using a positioning element 15 as shown in Figures 7-8 in a sensitive element 10 having dimensions as previously exemplified, the Applicant found that, even with a minimal overall contact area between the containment portion 15b and the outer surface of the tubular wall Ila (here a contact surface of 0.023 ± 0.003 cm²), it is possible to inject the material necessary to obtain the body part 3 at high pressures, for example pressures of 300 ± 50 bar, without causing the displacements or the extrusion of the positioning element 15.

[0098] The sensor device 1 is designed to measure the electrical characteristics of interest of the fluid, for example capacitance and conductivity (resistance), as mentioned above, according to methods known in themselves that are independent from the present invention. For this purpose, the electrode 11 and part of the electrode 12 are arranged in an area wetted by the fluid (i.e., the inside of the detection duct 4), and the circuit arrangement including the circuit support 6, configured to perform the necessary detections and processing, is arranged in a dry area. An important function for the correct operation of the sensor device is therefore its hydraulic seal, in order to avoid damages to the electronic part implemented on the support 6, and the dispersion of the fluid subject to detection into the environment.

[0099] A main sealing function with respect to the fluid is achieved by means of the electrically insulating material over-moulded to the sensitive element 10, which evidently fills the gaps between the components present between the wet and dry areas of the device 1.

[0100] The sealing functionality can be further enhanced by associating suitable seals to the electrical connection portions 12b and 13b of the inner electrode 12 and the connection element 13, respectively.

[0101] As already mentioned, in preferential embodiments, at the bottom of cavity 5 cylindrical formations 3c, 3d (Figures 2-3 and 11-12) are defined, through which the aforementioned electrical connection portions 12b and 13b extend. Advantageously, on the part of each of these portions 12b or 13b that extends through the aforementioned formations 3c or 3d, a suitable seal can be fitted, for example an o-ring seal, intended to ensure a seal (mainly a radial seal) between the portion itself and the internal surface of the respective formation 3c or 3d. The concept is shown, for example, in Figures 2-3 (see also Figure 25), where it can be seen that an o-ring seal 19 is mounted on the portion 12b of the inner electrode 12, which operates a sealing action with respect to the internal surface of the cylindrical formation 3d. In addition, in the case shown in Figures 2-3, a top area of the bushing-like formation 18 of the positioning element 15 also protrudes within the formation 3d.

[0102] The operation of over-moulding of the body 15 and/or the body 3 to the electrical connection portions 12b and 13b, respectively, could lead to slight polymer leakage, or "burrs", from the mould impression on said portions 12b and 13b, with the risk that these burrs will result in some uneven surfaces, in particular at the top of the bushing-like formation 18 of the positioning element 15, and in the lower area of the cylindrical formation 3c.

[0103] To prevent the aforementioned o-ring seal 19 from operating in this potentially anomalous area, within the formation 3d a plastic spacer 20 is preferably provided, such as a washer, for example made of Teflon. The spacer 20 has a thickness suitable for having the upper surface thereof positioned higher than the aforementioned burrs, so that the seal 19 will remain safely in an area of the connecting portion 12b free of burrs.

[0104] A similar sealing arrangement is provided in the cylindrical formation 3c of Figures 2-3, with respect to portion 13b of the connection element 13 for the outer electrode 11; of course, in the case of the formation 3c, since a positioning element is not required for the connection element 13 (and therefore a bushing-like formation of the type designated by 18 is not required), a lower support step for the corresponding spacer 20 can be provided at the internal surface of the formation 3 c.

[0105] In various embodiments, the function of insulation between the wet and dry parts of the sensor device 1 can be further increased by depositing a resin inside the cavity 5, after the positioning and the electrical connection of the circuit support 6, with this resin, not shown in the figures, which embeds the components present in cavity 5.

[0106] Before insertion of the circuit support 6 into the cavity 5 and the electrical connection thereof, and therefore before the process of resin deposition, the aforementioned plugs 21 and 22 (see Figures 2-3) are installed, to close the cylindrical seats 3c, 3d for the seals 19; presence of the plugs 22 and 22 prevents the aforementioned resin from coming into contact with the seals 19 (the resin could interfere with the correct compression and therefore the sealing action of the seals).

[0107] In various embodiments, the sensor device according to the invention includes a sensor for detecting a temperature of the fluid passing through the detection duct 4, in particular an indirect temperature detection. Such a temperature value can be used for the purpose of compensation of the electrical quantity or quantities detected via the sensitive element 10, for example for compensating the measurement of the percentage of ethanol in the fluid and/or as stand-alone information (fuel temperature measurement).

[0108] In some known solutions, a temperature sensor having a "drop-shaped” sensitive part is provided for this purpose, which is typically inserted in a space of the device body, so as to be positioned in contact with the outer electrode that obtains the duct, or in any case near the fluid, and is used to indirectly measure the temperature of the fluid.

[0109] This known temperature sensor, usually a negative temperature coefficient thermistor (NTC), typically has leads inserted through and soldered into respective holes of the device's circuit support (assembly known as THT: Through Hole Technology), while the drop-sensitive part is located in a position at a distance from the circuit support, substantially near the fluid duct defined by the corresponding outer electrode; the sensitive part is not directly in contact with the fluid, but is typically placed as close as possible to the outer electrode that obtains the fluid metal duct.

[0110] In preferred embodiments of the invention, there is provided a temperature sensor which is configured to be mounted on a circuit support or PCB, such as an NTC-type sensor. Such a temperature sensor is preferably of the surface-mounted type (mounting known as SMD: Surface-Mounted Device). The sensor can be installed directly on the circuit support 6, in particular connected directly above corresponding electrically conductive tracks of the same support, without the mediation of leads or holes in the support, and placed near at least one of the electrical connection portions of the outer electrode and the inner electrode, represented here by the portions 13b of the connection element 13 and the portion 12b of the electrode 12. However, the aforementioned temperature sensor could be of another type suitable for the purpose, such as a sensor free of a casing, ox Dietype chip, with connections between the chip and the support 6 made by means of thin soldered wires (wire bonding), or it could be a temperature sensor of the traditional "drop" type with leads, but made to adhere to the circuit support by means of a glue designed to transmit temperature.

[0111] For this purpose, it is preferable to provide electrical connection portions having a sufficient diameter between the electrodes and the circuit support 6 (indicatively a diameter greater than 1 mm, in particular greater than 1.5 mm). This relatively large diameter allows the temperature of the fluid (with which the metal electrodes 11, 12 are in direct contact) to be quickly brought to the circuit implemented on the support 6. In other words, by positioning the temperature sensor on the circuit support 6 sufficiently close to at least one of the electrical connection portions 13b and/or 12b, the temperature sensor is able to quickly detect the temperature of the fluid of interest (and therefore without having to use - as in the known technique - a traditional NTC sensor with leads, having the corresponding drop-shaped sensitive part located near, or in contact with, an outer tubular electrode that directly defines a detection duct).

[0112] A solution in accordance with this preferential aspect is shown in Figure 3, wherein TS designates as an example an NTC temperature sensor of the SMD type, which in the example is installed on the lower face of the circuit support 6, i.e., the side thereof oriented towards the sensitive element 10. In this example, the temperature sensor TS is in a position adjacent to the connection portion 12b of the inner electrode 12, for example at a distance of 0 to 10 mm, preferably between 4 and 6 mm.

[0113] In the figure, W designates the mass of the welding material used for mechanically constraining and electrically connecting the electrical connection portion 12b of the electrode 12 to the circuit support 6, with this mass that contributes to the transfer of heat from said portion 12b to the circuit support 6, and therefore to the sensor TS. As mentioned, the output signal of the sensor TS is representative of the temperature of the portion 12b, which is in turn representative of the temperature of the fluid.

[0114] It is preferable that the sensor TS is placed in the immediate vicinity of the connection portion 12b of the electrode 12, given that the latter is preferably formed in a single shaped piece, and therefore more suitable for heat transfer; however, alternatively or additionally, the sensor TS could be placed in the immediate vicinity of the portion 13b of the connection element 13 of the electrode 11.

[0115] The solution of a sensor TS of a SMD type is distinguished by a considerably lower cost than a drop-shaped sensor with leads; the known temperature sensors, being THT-type components, require a specific soldering technology (hot iron) compared to the classic SMD soldering used for the other electronic components of the circuit implemented on the support 6: the solution according to the preferential version of the invention described herein avoids the aforementioned specific welding, allowing the optimization of the production process. In addition to this, the structure of a drop-shaped NTC sensor generally requires a plastic superstructure NTC holder) which can itself include terminals for soldering on a circuit support: not being easy to manage in a production process, the use of the drop-shaped version therefore also complicates the design of the circuit, its bill of materials and the production process as a whole.

[0116] From the given description, the characteristics and the advantages of the present invention are clear.

[0117] The sensor device according to the invention is distinguished by a remarkable simplicity of construction, which also translates into a low production cost. In accordance with one aspect, the particular construction of the sensitive element, provided with the positioning element for the inner electrode, in addition to contributing to the simplicity of assembly, avoids the risk of contact between the electrodes. The inner electrode can be obtained completely, or in large part, from a simple electrically conductive wire material, bent in a suitable way.

[0118] In accordance with another aspect, the simplicity of construction is increased by the fact that the detection duct can be formed by polymeric material moulded over the sensitive element, with the latter therefore having a comparatively reduced longitudinal dimension with respect to the known solutions. The related advantages in terms of protection of the sensitive element with respect to the environment are evident: the risks of corrosion of the metal and the risks of abnormal electrical contacts are avoided (corrosion of the outer electrode could, for example, be accentuated due to the presence of electrolytic or galvanic phenomena, as well as the presence of dirt and/or chemical agents - such as oil or salt - inside an engine compartment in which the sensor device is installed). The integration of the sensitive element into a conduit made of electrically insulating material also reduces the risk of abnormal electrical contact, such as the risk of contact with a high electrical voltage; the need - typical of the known solutions - to have to connect the outer electrode to the negative of the power supply, i.e., to the metal frame of the vehicle, is also avoided, as also avoided are the consequent limitations in the control circuit of the known devices (the connection to ground does not allow measurements to be carried out with electrodes connected to electrical or potential voltages that are not referred to the negative of the battery or to the ground).

[0119] Other advantages related to over-moulding are tied to the possibility of easy integration of the necessary connection/fixing means into the detection duct; in the cited known solutions, wherein the same outer electrode defines the detection duct, the connection/fixing means must be obtained by mechanical deformation of the electrode, or by machining the same electrode.

[0120] In accordance with a further aspect, provision of a temperature sensor, in particular a surface-mounted sensor, on the circuit support that exploits for detection purposes the heat transmission by a connection element of one of the electrodes of the sensitive element, further simplifies manufacturing of the device, and increases the detection reliability. With regard to this last point, it should also be noted that, in traditional solutions, the drop-shaped sensitive part of the temperature sensor, in order to be located as close as possible to the fluid, must be housed in a seat of the device body having a thin wall with respect to the metal detection duct obtained by the outer electrode (the aforementioned wall must be thin to facilitate the transmission of heat to the sensitive part of the temperature sensor). In the preferential embodiment of the invention described herein, wherein the sensing duct is made of polymer, provision of a thin-walled seat for a drop-like temperature sensor could imply the risk of rupture (high fluid pressure could cause failure of the wall), resulting in fluid seepage into the cavity housing the control circuit of the sensor device. On the other hand, the described preferential positioning of the temperature sensor (on the circuit support 6, in a position close to at least one of the electrical connection parts of the electrodes 11, 12) makes it possible to maintain high thicknesses in the walls of the detection duct 4 made of polymer, such as to withstand the operating pressures of the fluid, and without jeopardizing the detection of the temperature (on the other hand, if a known drop-like sensor were adjacent to a thick wall of a polymer detection duct, correct temperature detection would not be allowed; the detection would be attenuated or in any case affected by a delay in propagation, with a delay in detection and consequent anomalies in the operation of the device).

[0121] It is clear that numerous changes are possible for the person skilled in the art to the device described by way of example, without departing from the scope of the invention as defined in the attached claims.

[0122] In possible variant embodiments, the body of the positioning element 15 can be formed separately, for example by injection moulding, by providing a through-opening in the same element, in which a corresponding coupling portion of the electrode 12 is either driven into it or blocked by mechanical interference, or glued. Such a case is shown schematically in Figures 21 and 22.

[0123] Figure 21 shows the unassembled condition of the electrode 12 and the element 15. In the example, the electrode 12 has a shape similar to the one already shown, while the element 15 is moulded separately so as to have a seat 15c at the bottom (with reference to the figures), suitable for receiving at least part of the intermediate coupling portion 12c of the electrode 12. In this example, the seat 15c is shaped to also receive the curvatures 12" and 12"'.

[0124] Figure 22 shows the result of the coupling between the two parts of Figure 21, with the connection portion 12b of the electrode 12 being inserted through the through-opening of the bushing formation 18, until the coupling portion 12c is fully inserted into the seat 15c. As already mentioned, maintenance of the relative position between the two parts can be achieved by mechanical interference or bonding, or even by coupling or deformation of the element 15.

[0125] It will be appreciated that also in this case the material of the positioning element 15 surrounds a large part of the coupling portion 12c of the electrode 12, guaranteeing electrical isolation with respect to the outer electrode 11, although the coupling portion is not completely embedded or incorporated in this material as in the previously described case of over-moulding of the element 15 to the electrode 11.

[0126] As already mentioned, the shape of the electrode 12 may be different from the one exemplified in the figures, for example with an L-shaped shape, as exemplified in Figure 23. In such a case, it is a length of the vertical portion of the L, i.e. the electrical connection portion 12b of the electrode 11, obtains the coupling portion 12c, surrounded by the electrically insulating material of the positioning element 15; depending on the case, this part will be embedded in the aforementioned material, in the event of over-moulding of the element 15, or inserted with interference and/or glued into a through hole in the body of element 15, previously obtained separately by moulding. The positioning element 15, herein having a reduced length compared to the cases previously shown, is secured at a corresponding slit 14 of the tubular wall Ila of the outer electrode 11 in a manner similar to those described above (in a different configuration, as in Figure 25, the element 15 can be secured in a through hole in the tubular wall).

[0127] In possible variants, the body of the inner electrode can be formed in several parts joined together, for example welded; even in these embodiments, at least one of the parts joined to form the inner electrode can be bent in order to define different functional portions, such as an electrical connection portion and a coupling portion.

[0128] An example of this type is shown in Figure 24, which uses the reference numbers of the previous figures to indicate elements technically equivalent to those already described. In this example, at least the detection portion - designated by 12a' - of the inner electrode 12 has a tubular structure, so that fluid can also pass through it. In the example, only the portion 12a' is tubular and can be welded to a remaining part of the electrode obtained from a bent wire in order to define the electrode portions 12b and 12c, with the corresponding curvatures 12" and 12"'.

[0129] The solution of providing an over-moulded detection duct that extends beyond the longitudinal ends of a sensitive element with an outer tubular electrode and an inner electrode does not depend on the specific methods of construction of the sensitive element.

[0130] In the case of the embodiment of Figure 25, for example, the sensitive element designated by 10' has a tubular wall 1 la' of an outer tubular electrode 11' in which the through-slit of the previous embodiments is replaced by a through-hole, in a position generally intermediate with respect to the two longitudinal ends of the same tubular wall Ila'. This through-hole is occupied by a positioning element 15' that supports an L-shaped inner electrode 12'. In this case, the detection part 12a of the electrode 12' can be inserted through the hole by tilting the electrode itself, until the coupling portion of the positioning element 15' is engaged in the hole in question. Also in this case the element 15' can be equipped with the bushing formation 18 already discussed.

[0131] As can be seen, even in this embodiment, the sensitive element 10' is completely inside the duct 4, which fully defines the connecting or fixing elements 4c.

[0132] In possible embodiments, such as the one exemplified, the detection duct 4 is also overmoulded to at least a portion of the tubular wall that extends beyond the detection area, in which the detection portion 12a of the inner electrode 12' is located. In this specific case, the tubular wall Ila' has two opposite longitudinal extensions, designated by lie, which in the example have an external diameter smaller than the external diameter of the central portion of the wall, i.e., the portion of the wall corresponding to the detection area (although this is not strictly necessary). The above-mentioned longitudinal extensions 4e can act as reinforcement for the detection duct 4 formed with polymeric material.

[0133] In possible variants, the detection duct 4 can also be over-moulded to other elements, such as at least one separate tubular element located at a respective hydraulic connector HC. Figure 25 also lends itself to showing a variant of this type, in which two of these tubular elements are provided, designated by 4e. The elements 4e can be made of metal or other material suitable for strengthening the corresponding portion 4d of the duct 4 and/or the corresponding hydraulic connector HC.

[0134] It will be appreciated that, despite the different specific design, the sensor device 1 of Figure 25 can be obtained with the methods described with reference to Figures 17-20.

[0135] The through-slit of the outer electrode may extend for the entire length of the tubular wall, in which case the positioning element for the inner electrode will have a corresponding length, and will be received into the slit itself so as to occupy it substantially completely.

[0136] In other embodiments, the through-slit of the outer electrode could extend into an intermediate zone for at least part of the circumference of the tubular wall, in which case the positioning element will have a corresponding curved shape, and will be received into the slit itself in such a way as to occupy it substantially completely.

[0137] The tubular wall of the outer electrode could be in two parts, i.e., cut in an intermediate area, substantially creating two outer tubular electrodes aligned longitudinally and equipped with corresponding elements for mutual electrical connection (without prejudice to the provision of a connecting element towards the circuit support 6, such as a connecting element of the type previously indicated with 13 in an electrical contact with at least one of the two aforementioned outer tubular electrodes). In such an embodiment, the positioning element for the inner electrode will have a substantially annular or tubular shape, substantially configured to create a sort of hydraulic connector between the two outer tubular electrodes (i.e., in an intermediate position to the two outer tubular electrodes and configured for coupling with the facing ends of the latter), in order to keep them fixed to each other and longitudinally aligned according to the same axis, to define a passage for the fluid in which the detection part of the inner electrode extends; such a positioning element could be associated with one or more inner electrodes.

Claims

1. A sensor device (1) for the measurement of at least one electrical property of a fluid, comprising a device body (2) with a detection duct (4) having an inlet (4a) and an outlet (4b) for the fluid, within the detection duct (4) there being arranged a sensitive element (10) for the detection of the at least one electrical property, wherein the sensitive element (10) comprises a first electrode (11) and a second electrode (12) that extends in part within the first electrode (11), wherein the first electrode (11) extends in a length direction (L) and has a substantially tubular wall (Ila) with a first longitudinal end (11b) and a second longitudinal end (11c) opposite to one another, wherein the first longitudinal end (11b) and the second longitudinal end (11c) of the tubular wall (Ila) are open to enable the passage of fluid through the first electrode (11), and the second electrode (12) extends in part in the inside of the tubular wall (Ila), spaced therefrom, wherein the first electrode (11) has a through-slit (14), which extends in the length direction (L) for at least one fraction of the tubular wall (Ila), starting from the first longitudinal end (11b) to the second longitudinal end (11c), wherein the sensitive element (10) comprises a positioning element (15) of the second electrode (12), which is secured at the through-slit (14) of the tubular wall (Ila), the positioning element (15) being formed at least in part with an electrically insulating material and being configured for supporting the second electrode (12).

2. The sensor device according to claim 1, wherein the second electrode (12) has a body shaped so as to have: a detection portion (12a) which extends at least partially substantially in the length direction (L) of the first electrode (11), within the first electrode (11), an electrical connection portion (11b) which extends at least partially outside the first electrode (11), in particular transversely with respect to the length direction (L) of the first electrode (11), a coupling portion (12c) which is at least partially surrounded by electrically insulating material of the positioning element (15), at the through-slit (14), wherein preferably the body of the second electrode (12): - is bent in such a way that at least a part of the electrical connection portion (12b) is substantially orthogonal to at least a part of the detection portion (12a), and/or

- is bent in such a way that at least a part of the coupling portion (12c) is substantially parallel to at least a part of the detection portion (12a), and/or

- is bent so as to have at least three curvatures (12', 12", 12"').

3. The sensor device according to claim 1 or claim 2, wherein the positioning element (15) is an element overmolded to a part of the body of the second electrode (12).

4. The sensor device according to any one of claims 1-3, where a part (3) of the device body (2) that defines at least the detection duct (4) is a part over-moulded to the sensitive element (10).

5. The sensor device according to claim 4, wherein the detection duct (4) is shaped to integrally define at least one hydraulic connector (HC).

6. The sensor device according to any one of claims 1-5, wherein the positioning element (15) is received into the through-slit (14) so as to occupy the through-slit substantially completely.

7. The sensor device according to any one of claims 1-6, wherein the positioning element (15) has at least one of:

- a coupling portion (15a) which is received in the through-slit (14) and which is provided at the surface with at least one sealing protrusion (15a'), configured for cooperating with a surface (lid) of the tubular wall (Ila) which delimits the through-slit (14),

- a containment portion (15b) having greater lateral overall dimensions with respect to the through-slit (14), for an at least partial rest on an edge or an outer surface of the tubular wall (Ila).

8. The sensor device according to any one of claims 1-6, wherein the positing element (15) has a containment portion (15b) that defines at least one from among a pair of opposite lateral projections (16a), a longitudinal projection (16b), an upper strengthening rib (17a-17b), an upper bushing-shaped formation (18) through which a corresponding part of the second electrode (12) extends.

9. The sensor device according to any one of claims 1-8, comprising an electrical connection element (13) which is in electrical contact with an outer surface of the tubular wall (Ila).

10. The sensor device according to claim 9, wherein the electrical connection element (13) has a body shaped such that at least a part of an electrical connection portion thereof (13b) extends substantially parallel to at least a part of the electrical connection portion (12b) of the body of the second electrode (12), wherein preferably:

- the device body (2) has a housing cavity (5) for a circuit arrangement (6) to which the electrical connection portion (13b) of the body of the electrical connection element (13) and the electrical connection portion (12b) of the body of the second electrode body (12) are electrically connected,

- the housing cavity (5) has a bottom which is passed through by respective parts of the electrical connection portion (13b) of the body of the electrical connection element (13) and the electrical connection portion (12b) of the body of the second electrode (12), at least one sealing element (19) being associated to each one of said respective parts of said electrical connection portions (12b, 13b).

11. A sensor device (1) for the measurement of at least one electrical property of a fluid, comprising a device body (2) with a detection duct (4) having an inlet (4a) and an outlet (4b) for the fluid, within the detection duct (4) there being arranged a sensitive element (10; 10') for the detection of the at least one electrical property, wherein the sensitive element (10; 10') comprises a first electrode (11; IT) and a second electrode (12; 12') which extends in part within the first electrode (11; IT), wherein the first electrode (11; IT) extends in a length direction (L) and has a substantially tubular wall (Ila; Ila') with a first longitudinal end (11b) and a second longitudinal end (11c) opposite to each other, wherein the first longitudinal end (11b) and the second longitudinal end (11c) of the tubular wall (Ila; Ila') are open to enable passage of fluid at least through the first electrode (11; IT), and the second electrode (12; 12') is associated with respect to the first electrode (11; IT) to extend partly in the inside of the tubular wall (Ila; Ila'), spaced therefrom, wherein a part (3) of the device body (2) which defines at least the detection duct (4) is a part over-moulded to the sensitive element (10; 10'), in particular a polymer overmoulded part, the over-moulded part of the detection duct (4) preferably integrally defining at least one hydraulic connector (HC) and/or fixing elements (4c).

12. A sensor device (1) for the measurement of at least one electrical property of a fluid, comprising a device body (2) with a detection duct (4) having an inlet (4a) and an outlet (4b) for the fluid, within the sensing duct (4) there being arranged a sensitive element (10; 10') for the detection of the at least one electrical property, wherein the sensitive element (10; 10') comprises a first electrode (11; 11') and a second electrode (12; 12') which extends in part within the first electrode (11; 11'), wherein the first electrode (11; 11') extends in a length direction (L) and has a substantially tubular wall (Ila; Ila') with a first longitudinal end (11b) and a second longitudinal end (11c) opposite to each other, where the first longitudinal end (11b) and the second longitudinal end (11c) of the tubular wall (Ila; Ila') are open to enable passage of the fluid at least through the first electrode (11; 11'), and the second electrode (12; 12') is associated with respect to the first electrode (11; 11') to extend in part in the inside of the tubular wall (Ila; Ila'), spaced therefrom, wherein the device body (2) comprises a body part (3) which defines a housing cavity (5) for a circuit support (6), bearing a control circuit of the sensor device (1), to which an electrical connection portion (13b) of the first electrode (11; 11') and an electrical connection portion (12b) of the second electrode (12; 12') are electrically connected, wherein on the circuit support (6), preferably on a side thereof oriented towards the sensitive element (10; 10'), a temperature sensor (TS) is mounted, preferably of a SMD type, configured for detecting in an indirect way a temperature of the fluid transferred via the electrical connection portion (13b) of the first electrode (11; 11') and/or via the electrical connection portion (12b) of the second electrode (12; 12').

13. A method for producing a sensor device (1) for the measurement of at least one electrical property of a fluid, comprising the steps of: a) providing an outer electrode (11; 11') comprising a substantially tubular wall (Ila; Ila'), that extends in a length direction (L), the outer electrode (12; 12') having an electrical connection portion (13b), b) providing an inner electrode (12; 12'), comprising a detection portion (12a) that extends at least partially substantially in the length direction (L), the outer electrode (11; 11') having an electrical connection portion (12b), c) obtaining a sensitive element (10; 10') of the sensor device (1) by associating the outer electrode (11; 11') with the inner electrode (12; 12'), with the inner electrode (12; 12') that extends at least in part within the outer electrode (11; 11') electrically isolated therefrom, d) over-moulding an electrically insulating polymer or plastic material to the sensitive element (10; 10'), to obtain a part (3) of a device body (1) of the sensor device (1) that defines at least part of a detection duct (4) within which the sensitive element (10; 10') is integrated.

14. The method according to claim 13, wherein step d) comprises the operation of over-moulding the electrically insulating polymer or plastic material so as to integrally define connection or fixing elements (4c) on the outside of the detection duct (4), in particular shaped as radially protruding flanges, for connection of the detection duct (4) along a line for passage of a fluid.

15. The method according to claim 13, wherein:

- step a) comprise the operation of providing the tubular wall (Ila) with a through- slit (14) that extends in the length direction (L) for at least a fraction of the tubular wall (Ila), starting from a first longitudinal end (11b) towards a second longitudinal end (11c) of the tubular wall (Ila),

- step b) comprises the operation of shaping a body of the inner electrode (12) so as to have at least a detection portion (12a), an electrical connection portion (12b) and a coupling portion (12c),

- step c) comprises the operation of securing to the inner electrode (12) a positioning element (15) formed at least in part with an electrically insulating material and configured for supporting the inner electrode (12), and coupling the positioning element (15) to the through-slit (14) of the tubular wall (Ila) of the outer electrode (11), in such a way that the detection portion (12a) of the body of the inner electrode (12) partially extends substantially in the length direction (L) of the outer electrode (11), within the tubular wall (Ila) of the outer electrode (11) and spaced therefrom, the electrical connection portion (12b) of the body of the inner electrode (12) extends at least partially outside the outer electrode (11), in particular transversely with respect to the length direction (L) of the outer electrode (11), and the coupling portion (12c) of the body of the inner electrode (12) is surrounded at least partially by electrically insulating material of the positioning element (15), at the through-slit (14), where in particular step c) comprises the operation of over-moulding the positioning element (15) on a region of the inner electrode (12) which is substantially intermediate to the detection portion (12a) and the electrical connection portion (12c), and which includes at least part of the coupling portion (12c).

16. The method according to claim 13, wherein the operation of over-moulding of step d) comprises:

- positioning the sensitive element (10; 10") in a mould (30', 30"),

- occluding, by means of corresponding movable mould elements (32'), a first longitudinal end (11b) and a second longitudinal end (11c) of the tubular wall (Ila; Ila') of the outer electrode (11; IT),

- injecting into the mould (30', 30") an electrically insulating plastic material in a fluid state, required for forming the part (3) of the device body (2) that defines at least part of the detection duct (4),

- waiting for solidification of the electrically insulating plastic material, and

- remove from the mould (30', 30") the part (3) of the device body (2) which defines at least part of the detection duct (4) integrating the sensitive element (10; 11').

17. A sensor device (1) for the measurement of at least one electrical property of a fluid, comprising a device body (2) with a detection duct (4) having an inlet (4a) and an outlet (4b) for the fluid, within the sensing duct (4) there being arranged a sensitive element (10) for the detection of the at least one electrical property, wherein the sensitive element (10) comprises at least one first electrode (11) and at least one second electrode (12), preferably with at least one positioning element (15) associated to at least one of the first electrode (11) and the second electrode (12), the positioning element (15) being formed at least in part with electrically insulating material, wherein at least one part (3, 4) of the device body (2) is a part made of a polymer over-moulded to the sensitive element (10; 10').