ITUA20164410A1 - SENSOR FOR DETECTION OF THE LEVEL OF A MEDIA - Google Patents

Description

"Sensor for detecting the level of a vehicle",

TEXT OF THE DESCRIPTION

Field of the Invention

The present invention refers to a sensor for detecting the level of a generic medium, such as a liquid, a fluid substance, a powdery or bulk material, etc. The invention was developed with particular reference to capacitive level sensors used on vehicles.

State of the art

Level sensors are used in various fields for detecting a residual quantity of a liquid present in a generic container, such as a tank. Some of these sensors are based on the use of a float: these sensors are generally complicated from a mechanical point of view and present some critical issues, such as jamming risks. These sensors are inevitably affected by problems related to the possible freezing of the medium being measured.

Level sensors are also known based on the measurement of electrical quantities, such as conductivity / resistivity or electrical capacitance. These sensors usually have an array of first electrodes, arranged according to the level detection axis - generally vertical - on a relative insulating support intended to be mounted inside the tank. The sensors then have a similar array of second electrodes, placed between or facing those of the first array, so that the fluid being measured enters between the electrodes of the two arrays. In some solutions, instead of a plurality of second electrodes, a common electrode is provided, having a height at least equal to that of the first array. In still other solutions, the tank itself has an internal surface made electrically conductive, for example by means of a surface metallization, in order to act as a common electrode. The electrodes are electrically connected to a circuit arrangement, often including a microcontroller, which by processing the value of the electrical quantity detected between the electrodes is able to identify a transition zone between the liquid and the air in the tank, considered indicative of the level of the liquid.

In these known solutions, the electrodes are directly in contact with the liquid and therefore subject to aging and premature wear. The operation of these sensor systems is then closely linked to the characteristics of the fluid, such as its conductivity / resistivity or its dielectric constant.

Referring to capacitive level sensors, these typically provide at least two electrodes facing each other, between which the liquid whose height is to be detected is intended to penetrate, with these electrodes being excited by an oscillator circuit, i.e. a circuit that generates an alternating or frequency modulated electrical signal. The circuit detects a change in the capacity between the facing electrodes which is proportional to the change in the dielectric interposed between the electrodes, or in proportion to the level of the interposed liquid, and therefore of the electrical capacity of the sensor element. In such sensors, an output signal proportional to the aforementioned capacity variation is therefore obtained. Known sensors of this type provide configurations with respective impedance which can also act as antennas and present the problem of generating electromagnetic disturbances (EMI), which disturbances are likely to interfere with other electronic systems, such as the electronic circuits on board the vehicle. This phenomenon increases with the increase in the extension of the electrodes, or with the increase in the length of the level sensor, which could behave like a transmitting antenna.

Further types of capacitive sensors provide for carrying out a measurement between at least two coplanar electrodes, for example in an interdigitated configuration, and facing an insulating wall that separates them from the liquid, where the presence of liquid beyond the insulating wall determines a variation of the dielectric between the two electrodes side by side, allowing a detection. A sensor of this type is known for example from US 7258005 B2. In these cases the spacing between the two electrodes must be much greater than the thickness of the insulating wall, typically greater than double this wall thickness (i.e. the sum of the wall thicknesses interposed between each of the two electrodes and the fluid to be detected), in so that any liquid can actually perturb the capacitance between the electrodes. In addition to creating problems of space, this type of solution has limits in resolution or measurement accuracy.

Other types of capacitive sensor are mounted outside a tank, such as a fuel tank or an additive in a vehicle. However, these types of sensors are penalized by the fact that the tank must have high wall thicknesses, in order to guarantee the necessary mechanical strength: this entails the need to use higher power frequency signals to detect the liquid level in the tank and this determines greater risks for the aforementioned electromagnetic disturbances.

Summary and purpose of the invention

In its general terms, the present invention proposes to provide a sensor of a simple and economical construction level, characterized by a high flexibility of use and manufacturing and substantially immune to the problems highlighted above.

According to its first aspect, the invention aims to create a level sensor that can be produced in different lengths, while ensuring precision and reliability.

According to a different aspect, the invention proposes to realize a sensor that is suitable for carrying out level measurements even in conditions of at least partial solidification or freezing of the medium subject to measurement.

According to a different aspect, the invention proposes to realize a level sensor capable of distinguishing the presence and / or the height of different layers and / or different states of the medium subject to detection, such as a sequence of states and / or "liquid - air or gas - solid" layers or a "liquid - solid" sequence, or a "air or gas - solid" sequence or "liquid - air or gas".

According to a different aspect, the invention proposes to realize a level sensor capable of detecting variations in height of different layers and / or states of the medium subject to detection, such as an increase or decrease in an icy or solidified layer. of the medium, for example a measurement of the level changes in a tank containing a liquid during a freezing and / or thawing phase.

According to a different aspect, the invention proposes to realize a level sensor provided with a suitable structure to allow its precise operation even in the face of stresses due to conditions of freezing and / or solidification and / or heating of the medium subject to detection.

At least one of the purposes of the invention are achieved by a level sensor and a related control method having the characteristics of the attached claims. The claims are an integral part of the technical teaching provided herein in relation to the invention.

Brief description of the drawings

Further objects, characteristics and advantages of the invention will emerge from the following description, made with reference to the attached drawings, provided purely by way of non-limiting example, in which:

- Figures 1 and 2 are schematic perspective views, partially sectioned, of two possible alternative configurations for mounting a level sensor according to the invention on a generic container, such as a tank;

- Figures 3 and 4 are schematic perspective views, from different angles, of a level sensor according to an embodiment of the invention;

- Figure 5 is a partially sectioned schematic perspective view of a level sensor according to a possible embodiment of the invention;

- Figure 6 is a partial exploded schematic view of a level sensor according to a possible embodiment of the invention;

- Figures 7 and 8 are schematic perspective views from different angles of a circuit of a level sensor according to a possible embodiment of the invention;

- Figure 9 is a schematic longitudinal section of a level sensor according to a possible embodiment of the invention;

- figure 10 is a first detail on a larger scale of figure 9;

- figure 11 is a detail on a larger scale of figure 10;

- figure 12 is a second detail on a larger scale of figure 9;

- Figure 13 is a schematic cross section of a detection portion of a level sensor according to a possible embodiment of the invention;

- figure 14 is an enlarged detail of figure 13;

- figure 15 is a detail on a larger scale of figure 14;

- Figures 16, 17 and 18 are perspective views, partial and schematic, of possible alternative mounting or fixing configurations of a level sensor in accordance with a possible embodiment of the invention;

Figure 19 is a partial and schematic perspective view of a portion of a container to which a level sensor according to Figure 18 can be associated;

- Figure 20 is a partial and schematic representation aimed at illustrating a possible configuration of connection of electrodes of a level sensor in accordance with a possible embodiment of the invention;

Figure 21 is a partial and schematic representation aimed at exemplifying a possible circuit configuration of a level sensor according to Figure 20;

Figure 22 is a partial and schematic representation similar to that of Figure 21, aimed at exemplifying an alternative circuit configuration of a level sensor according to Figure 20;

- Figures 23 and 24 are schematic representations aimed at illustrating further possible configurations of connection of electrodes of level sensors in accordance with possible alternative embodiments of the invention;

Figure 25 is a partial and schematic representation aimed at exemplifying a possible circuit configuration of a level sensor according to Figure 24;

- Figure 26 is a schematic representation, through graphics, aimed at exemplifying a possible principle of interpretation of signals or electrical values used in possible embodiments of the invention;

- figures 27 and 28 are schematic representations similar to those of figures 20, 23 and 24, aimed at illustrating further possible configurations of connection of electrodes of level sensors in accordance with possible alternative embodiments of the invention;

- Figure 29 is a schematic representation of some circuit elements of a level sensor according to a possible embodiment of the invention;

- Figure 30 is a partial and schematic representation similar to that of Figure 25, aimed at exemplifying a further possible condition of use of a level sensor in accordance with a possible embodiment of the invention; and - Figure 31 is a schematic perspective view, partially sectioned, of a possible variant of implementation of a level sensor according to the invention.

Description of preferred embodiments of the invention

The reference to "an embodiment" within this description indicates that a particular configuration, structure, or feature described in relation to the embodiment is included in at least one embodiment. Therefore, phrases such as "in an embodiment", "in an implementation" and the like, possibly present in different places of this description, do not necessarily refer to the same embodiment, but may instead refer to different embodiments. In addition, particular conformations, structures or characteristics defined within this description can be combined in any suitable way in one or more embodiments, even different from those depicted. The numerical and spatial references (such as "upper", "lower", "high", "low", "front", "back", "vertical", etc.) used here are only for convenience and therefore do not define the scope of protection or the scope of the forms of implementation. In the figures the same reference numbers are used to indicate similar elements or technically equivalent elements.

In Figure 1, 1 indicates as a whole a generic container, particularly a tank, for a generic fluid or bulk medium. The tank 1 has a main body preferably formed of electrically insulating plastic material. The tank 1 can optionally be associated with a heater of a per se known type, used to heat the tank itself and / or its contents, for example in the event of freezing. An electric heater is schematized in the figure by the block indicated with EH.

The tank 1 can be, for example, a tank that equips a motor vehicle. In an embodiment, such as the one exemplified here, the tank 1 is intended to equip a vehicle with a diesel engine and the liquid contained in the tank 1 is a liquid known as AdBlue, i.e. a 32.5% urea solution (minimum 31 , 8% - maximum 33.3%) in demineralised water, used by a SCR (Selective Catalyst Reduction) system, which is a system to reduce the emissions of nitrogen oxides from the exhaust gases produced by a diesel engine.

In the schematic example shown, the tank has an upper wall 2, in correspondence with which an opening is provided with a cap 3 for filling the liquid. A wall of the tank 1, for example its bottom wall 4, then has an outlet opening, not visible, through which the liquid escapes or is sucked in, for example by means of a pump, to feed the liquid to the SCR system. Still in correspondence with the upper wall 2, the tank 1 has a second opening, indicated with 5, in correspondence with which the body of a level sensor is tightly fixed according to a possible embodiment. The level sensor, indicated as a whole with 10, is mounted in such a way as to extend along a level detection axis, indicated with X, preferably substantially vertical but can, if necessary, be inclined with respect to the vertical.

The sensor 10 has a sensing part 11, intended to extend at least partially inside the tank 1. The distal end region of the sensing part 11 is preferably in contact with or at a slight distance from the bottom wall 4 of the tank, i.e. a height very close to that of the liquid outlet or suction opening, in order to detect the presence of even a very low level in the tank. In an embodiment not shown, the distal end region of the sensing part 11 is fixed internally to the wall of the tank 1 opposite the wall provided with the opening 5 for inserting and fixing the sensor 10, preferably by means of a coupling or quick release coupling. Preferably the proximal end region of the detection part 11 extends inside the tank 1 to a height relatively close to the upper wall 3.

In the illustrated embodiment, the sensor body 10 has, in its upper part, elements for its fixing to the upper wall 2 of the tank. In the example these means are represented by flange formations with associated screws, not indicated: this embodiment is not it must in any case be construed as limiting, since different fixing solutions for the sensor body 10 are also possible, some of which are exemplified below.

In the example of figure 1, the sensor 10 is fixed from above, or associated with the upper wall 2 of the tank. In other embodiments, however, the sensor can be fixed from below, that is to the bottom wall 4. An implementation of this type is schematically illustrated in figure 2, where the sensor 10 is mounted tightly at the opening 5, here defined in the bottom wall 4. Also in this embodiment, a proximal end region of the sensing part 11 (here defined as lower) is in a position close to the bottom wall 4, while the distal end region (here defined as upper) is located at a height relatively close to the upper wall 3; even in a solution of this type, the distal end of the part 11 can be fixed to the wall 3 by means of suitable coupling means of the type indicated above.

In Figures 3 and 4 a sensor 10 according to an embodiment is shown in isolation, with different angles. At the proximal end of part 11, the body 10a of the sensor 10 defines a box-like housing 12, also including a generally hollow connector body 12a, provided with electrical terminals indicated below, preferably protruding from a side wall of the housing. The housing 12 is preferably provided with a closing cover 13, which can be secured in a sealed position, for example by welding between the plastic material of the housing 12 and the cover 13.

Between the housing 12 and the part 11, the body 10a of the sensor 10 preferably defines a portion or formation 14 for the sealing coupling at the respective mounting opening on the tank. The formation 14 defines at least one seat for at least one sealing element 15, which can possibly also perform functions of elastic mounting of the sensor 20 with respect to the tank. In one embodiment, at least two elastic elements of the o-ring type are provided, one of which performs sealing functions and the other is used to obtain an elastic mounting of the sensor 10 on the tank 1, for example for tolerance compensation purposes. by Assembly. In the example shown, the formation 14 has a substantially circular profile and the sealing element is an o-ring gasket. In figures 3 and 4, 12b indicates the aforementioned flange formations for fixing the sensor body 10a, defined here at the bottom of the housing 12.

In Figure 5, a sensor 10 according to an embodiment is shown partially sectioned, in order to highlight how its body 10a is internally hollow to house the level detection components. From the figure it can be seen in particular how the sensor body 10a defines, in correspondence with the detection part 11, a hollow casing 16, of generally elongated shape; in the example illustrated, the casing 16 has a generally prismatic shape, particularly substantially parallelepiped. As will be seen, in a variant of implementation, at least the casing 16 can be made through a direct over-molding of electrically insulating plastic material on a circuit support, described below. More generally, the sensor 10 has at least one layer of insulation, to electrically isolate its electrodes (described below) with respect to the inside of the tank 1.

In a preferred embodiment, the housing 12 with the formation 14 and the casing 16 are defined by a single body 10a of electrically insulating plastic material, as clearly visible for example in Figure 6. However, an embodiment is not excluded from the invention. of the body 10a in distinct parts made integral with a seal, for example by means of mutual coupling, or by welding or overmoulding.

In one embodiment, the body 10a, or at least its portion intended for direct or indirect exposure to the liquid (the casing 16 and possibly the attachment portion 14) is formed with a printable thermoplastic material, such as a polypropylene (PP) or with a high density polyethylene (HDPE). Practical tests carried out by the Applicant have also made it possible to ascertain that a particularly suitable material - also in view of the particular level detection methods described below - is a cyclo-olefin copolymer (COC - Cyclic Olefin Copolymer). Materials of this type - usually used in the medical field - have particularly advantageous characteristics for the application considered here, among which the low density, the very low water absorption, the excellent water vapor barrier properties, must be emphasized. the high rigidity, strength and hardness, the high resistance to extreme temperatures and thermal shocks, the excellent resistance to aggressive agents such as acids and alkalis, the excellent electrical insulation properties, the easy processing using common methods of treatment of thermoplastic materials , such as injection molding, extrusion, blow molding, injection blow molding.

The material, or at least one of the materials used for the construction of the body 10a of the sensor 10, can be analogous or chemically compatible with a material that forms at least part of the tank 1, for example in order to allow a seal weld between the body of the sensor and tank. One or more of the materials indicated above can be used for the construction of different portions of the body 10a, such as the housing 12 with the formation 14 and the casing 16, even when the body 10a is formed in distinct pieces made integral with each other. Naturally, the lid 13 can also be made of one of the indicated materials.

Again in Figure 5 it can be seen how the electrical and electronic detection components are housed in the cavity defined by the body of the sensor 10 - indicated as a whole with H -. In a preferred embodiment, such components are mounted on an electrically insulating substrate 20 which forms a circuit support. The support 20 is formed with material suitable for making printed circuits, such as for example FR4 or a similar composite material such as fiberglass, or again in ceramic or polymeric-based material, preferably a printable material for the purposes of making the support 20.

In the circuit support 20 a first portion 20a is identified, intended to be received in the housing 12, and a second portion 20b intended to be received in the casing 16. The portion 20a of the support 20 is mainly associated with the electronic control components of the sensor 10, as well as relative terminals for the external electrical connection of sensor 10; the detection components, including a series of electrodes, are instead associated with the portion 20b of the support 20; some of the above electrodes are indicated in figure 5 with the letter "J" followed by the number that identifies the position of the electrode in the series that extends from the proximal end (electrode J1) to the distal end (electrode Jn) of the detection part 11, i.e. of the portion 20b of the support 20.

In the illustrated example, a single circuit support is provided in which the parts 20a and 20b are defined, but in possible embodiment variants several circuit supports can be provided, connected to each other by suitable electrical interconnection means and possibly mechanical interconnection means (e.g. example a circuit support corresponding to the portion 20a and a circuit support corresponding to the portion 20b, with electrical conductors or connectors for connecting electrically conductive tracks of one portion to electrically conductive tracks of the other portion).

In figure 6 a sensor 10 according to an embodiment of the invention is represented by an exploded view, from which the various parts already identified above can be detected. In this figure, the aforementioned terminals, indicated by 21, preferably of generally flattened shape, for example made by molding and / or shearing from a metal strip, which form an interface for the connection with the connector body 12a integral with the housing 12, are visible. external connection of the sensor 10, for example to a control unit of the on-board SCR system of the vehicle.

In one embodiment, each terminal 21 has a foil-shaped contact portion 21a, intended for positioning inside the cavity of the connector body 12a and a restricted interconnection portion 21b, intended for electrical and mechanical coupling with respective contacts 22 present on the support 20, particularly in its portion 20a, hereinafter described.

Also in figure 6 the support 20 as a whole is visible, with the relative parts 20a and 20b, with relative associated electrical and electronic components; the same support 20 is also represented in isolation in figures 7 and 8, through opposite views of its major faces. The circuit support 20, of generally elongated and preferably flattened shape, has associated on one of its major faces - here conventionally defined "rear" - a control circuit arrangement, globally indicated with 23, preferably comprising an electronic controller 24, to example a microcontroller. The controller 24 preferably comprises at least one processing and / or control logic unit, a memory circuit and inputs and outputs, including analog / digital inputs.

The components of the circuit arrangement 23 are connected to electrically conductive tracks provided in the portion 20a, visible for example in Figure 8, not shown; on the back of the portion 20b of the support there is then provided a series of electrically conductive tracks 25, for the electrical connection of the electrodes J of figure 5 - preferably with metallized holes for the connection between tracks on different surfaces - and of any other components in the arrangement 23 .

In one embodiment, the circuit comprises at least one temperature sensor, particularly provided on the relative circuit support 20. Such a sensor, for example of the NTC type, can be mounted in correspondence with at least one of the distal end region and the region of the proximal end of the portion 20b of the support 20. In the example shown on the portion 20b of the support 20, particularly on its rear, two temperature sensors 26 and 27 are mounted, in opposite end regions of the portion 20b, connected to the circuit arrangement 23 through relative conductive tracks. Assuming a mounting of the sensor 10 in the tank 1 of the type illustrated in Figure 2, the temperature sensor 27 can be used for measuring the temperature of the liquid, while the sensor 26 - which in the assembled condition is located closer to the upper wall of the tank - it can be used to detect the temperature that exists in the internal volume of the tank above the liquid, for example the air temperature. A configuration of the type shown, in particular with two temperature sensors 26 and 27, allows the sensor 10 to be mounted in the tank 1 both in the configuration of Figure 1 and in the configuration of Figure 2, by inverting the functions at the software level, such as the functions of the two sensors and / or electrode functions J.

A sensor for detecting the temperature can optionally be provided within the portion 20a of the support, that is, within the housing 12. It is of course also possible to provide more than two temperature sensors, for example with one or more sensors in intermediate positions to those of sensors 26 and 27.

Figure 8 clearly shows the front of the support 20, in the portion 20b of which the electrodes J are arranged, only some of which are indicated. In the non-limiting example shown, the electrodes J - 37 in number - are arranged according to an array that extends along the length direction of the portion 20b of the support, or along the detection axis X, spaced apart. The electrodes J are formed with electrically conductive material, for example a metallic material or a metal alloy and are associated with the front of the portion 20b of the support 20. The electrodes J are preferably coplanar with each other and can be, for example, in the form of plates or sheets. engraved or applied on the support 20, or consisting of an electrically conductive layer - similar to the tracks 25 - deposited on the support 20, for example with a screen printing technique or the like.

As mentioned, in one embodiment the support 20 has through holes - partially visible in Figures 7 and 8, one of which indicated with F - containing conductive material for the electrical connection between the electrodes J provided on the front of the portion 20b and the tracks conductive 25 present on the back of the same portion of the support 20.

Returning to Figure 6, a part of the blind cavity H is visible which extends axially into the body 10a of the level sensor, or in its parts 12, 14 and 16. Within this cavity H, preferably elements of guide and positioning of the support 20, some of which are partially visible in Figures 5 and 6, where they are indicated with 16a and 12c, respectively in correspondence with the casing 16 and the housing 12. Positioning elements of the support 20 can optionally also be provided in the lid 13.

In Figure 9, the level sensor 10 is visible in a longitudinal section, from which the presence of the blind cavity H which extends into the housing 12, into the attachment formation 14 and into the casing 16, in this cavity H being the circuit support 20 is housed. From this figure it is well known how, in one embodiment, the temperature sensor 27 is in a position close to the formation 14 or, more generally - in a mounted condition of the sensor 10 - in a close to the wall of the tank 1 provided with the mounting opening of the sensor 10. From the comparison between figures 7-8, on the one hand, and figure 9 on the other side, it is also inferred that the electrode indicated with J1 is also , in the mounted condition of Figure 2, in a position close to the lower wall of the tank, preferably a position reachable by the liquid even in a condition of even minimal tank filling. As will be seen, in one embodiment, the electrode J1 is used to provide a reference value used during the liquid level detection. Moreover, one or more reference electrodes J can also be provided in other areas of the portion 20b of the support 20.

Figure 9 also shows the connector body 12a, with one of its terminals 21. The terminals 21 can be planted with interference in the relevant passages defined in the connector body 12a, or possibly at least the housing body 12 can be overmolded at the terminals. Preferably, the terminals - and the relative passages of the connector body - extend longitudinally in a direction substantially perpendicular to a plane identified by the circuit support 20 and / or by the electrodes J.

In one embodiment, the contacts 22 are configured for elastic coupling with the terminals 21, in order to obtain the mutual electrical and mechanical connection between them. In figure 10, and even more in detail in figure 11, a possible coupling method is visible between the portion 21b of a terminal 21 with a relative contact 22 provided in the portion 20a of the support.

In the exemplified embodiment - see in particular Figure 11 - the contacts have a flat base 22a provided with a central hole or passage 22b; at least two tabs 22c converging towards each other depart from the base 22a on opposite sides of the passage 22b. The contact body 22 is formed with an electrically conductive material, such as a metal or a metal alloy, for example phosphor bronze, preferably coated with tin or gold or other material suitable for improving the electrical contact.

The tabs 22c are inserted in a relative through hole 20c defined in the portion 20a of the support and the base 22a is fixed and / or welded to a surface of the support itself or to its conductive tracks. Preferably the hole 20c is surrounded by electrically conductive material of one of the tracks of the circuit design of the circuit arrangement 23, with the base 22a of the contact 22 which is at least partially superimposed on the aforementioned conductive material, so as to obtain the electrical connection. As can also be seen in Figure 11, in the assembled condition, the passage 22b of a contact is substantially aligned with the hole 20c of the support 20, with the base 22a leaning against a surface of the support itself (here the rear surface) and with the tabs 22c which preferably they protrude from the hole 20c at the opposite surface (here the front surface) of the support 20.

For the purposes of assembling the sensor, the support 20, already provided with the relative electrical and electronic components, is inserted into the cavity H of the body 10a of the sensor 10 in correspondence with its open part, that is, from the housing 12. Following this insertion, therefore, the portion 20b of the support 20 is predominantly positioned within the housing 16, while the portion 20a is positioned within the housing 12. The position of the contacts 22 and of the holes 20c on the support 20 is such that, following the aforementioned insertion of the support 20 into the body 10a, these holes and contacts face the passages inside the connector body 12b. The terminals 21 are then inserted with interference in the relative passages of the connector body 12a, so that the respective interconnection portions 21b penetrate the holes 22a and 20c of the contacts 22 and of the support 20, respectively. The portions 21b of the terminals then slip between the fins 22c, causing an elastic spreading thereof, which guarantees an adequate electrical connection and a well-balanced mechanical connection. Preferably, this elastic electrical connection is also suitable for avoiding any damage to the support 20 and the related circuit, due for example to possible mechanical stresses during the use of the sensor 10, such as vibrations or stress applied to the terminals 21.

It will be appreciated that the assembly of the sensor is very simple and easy to automate, involving in themselves elementary operations, consisting of the insertion of the circuit support 20 into the cavity H of the body 10a and the subsequent insertion of the terminals 21 in the relative passages of the connector body 12a .

As mentioned, in one embodiment, the body 10a of the sensor 10 is provided with positioning and / or guiding elements of the support 20. The presence of these elements further simplifies the assembly of the sensor 10, while ensuring a high accuracy of assembly between parts and greater measurement accuracy. The aforementioned positioning elements can be provided within at least one of the housing 12 and the housing 16, preferably both in the housing and in the housing. As already mentioned, one or more positioning elements can be provided in the cover 13 of the housing 12.

Referring for example to Figures 10 and 11, in one embodiment, on the inner side of each of two opposite side walls of the housing 12 there are defined insertion and positioning guides, indicated with 12c, generally parallel to each other and between which there is an edge region of the support 20, particularly of its portion 20a, can be engaged. In the example illustrated, the guides 12c are defined in relief on the internal surface of the aforesaid opposite walls of the housing 12 (see also Figure 6, in which the top of a guide 12c is visible), but it is not excluded from the scope of the invention an embodiment in which guides having similar purposes to those of the guides 12c are constituted by recesses extending in the longitudinal direction of the sensor body 10. Preferably the top of the guides 12c is shaped so as to have a centering hole , here defined by an inclined surface, adapted to facilitate the entry of the opposite edges of the portion 20a of the support into the respective pairs of guides 12c. The portion 20a of the support 20 can be inserted with slight interference between the guides 12c or with minimal play.

From Figure 10 it is also visible how, in a preferred embodiment, the lid 13 also has, on the internal side of its top wall, a positioning formation 13a, defining a seat for the proximal or upper edge (referring to the figure) of portion 20a. Also in this case, preferably, the positioning formation 13a is shaped so as to define a centering hole, here comprising two converging inclined surfaces, in order to facilitate the entry of the proximal or upper edge of the portion 20a into the relative seat when the cover 13 is mounted on the housing 12. The formation 13a preferably comprises a surface or a stop element 13b suitable for avoiding unwanted axial movements of the support 20.

In a preferred embodiment, a free space or gap is defined between the distal end of the casing 16 and the distal end of the support 20 (or of its portion 20a), particularly to allow to compensate for any different dilatations between the material. which forms the casing 16 and the material which forms the support 20: such a port is indicated with H1 in figure 12, which represents an enlarged detail of figure 9, particularly of the distal end portion of the sensor 10. To clarify this aspect, consider that a preferential field of use of the sensor 10, such as the vehicle sector, provides for the achievement of very low temperatures, for example up to -40 ° C, with a production of the device which instead takes place substantially at room temperature, for example at 25 ° C: referring to this numerical example, the sensor 10 is therefore subject to a considerable thermal excursion, which corresponds to shrinkages of the casing 16 which vary in relation to the plastic material used.

In the hypothesis of having such a difference or thermal delta of 65 ° C (from 25 ° C to -40 ° C), the port H1 is therefore provided, so as to allow a free contraction of the envelope 16, without it coming into contact with the distal end or edge of the support 20 and / or a port H1 is provided to prevent said contraction of the envelope 16 from damaging one or more electrodes J. Referring to the materials mentioned above, the following expansion values can be considered thermal:

- HDPE => 200 ppm / ° C

- PP => 120 ppm / ° C

- COC => 60 ppm / ° C

- FR4 (support 20) => 20 ppm / ° C

Considering now the formula H1 [mm] = unit h [mm / mm] x length Lu of the sensor [mm], for the thermal delta exemplified here (65 ° C) the following values of unit h can be considered:

- h for HDPE = 0.012 mm / mm

- h for PP = 0.007 mm / mm

- h for COC = 0.003 mm / mm

Therefore, for example for a sensor body 10 with Lu = 150 mm in HDPE, the minimum value of H1 will be equal to 0.012 x 150 = 1.8 mm; for a sensor body of identical length Lu made of PP, the minimum value of H1 is equal to 0.007 x 150 = 1.05 mm; for the same sensor body made of COC, the minimum value of H1 is equal to 0.003 x 150 = 0.45 mm.

In a preferred embodiment, the portion 20b of the circuit support 20 is positioned within the casing 16 of the body 10a of the level sensor so that its front, or its face provided with the electrodes J, is adjacent or leaning against the relative internal surface, preferably at least partially in contact with it. For this purpose, one or more positioning elements are preferably provided inside the casing 16, tending to urge the portion 20b of the support towards a wall of the casing 16. In one embodiment, from the inner side of a wall of the casing 16 protrudes at least one said positioning element, which extends in the direction of the opposite wall of the casing itself.

A possible embodiment in this sense is visible in figure 13, which represents a cross section of the casing 16 (particularly according to a plane orthogonal to the X axis, passing for example through the line XIII-XIII of figure 4): from this figure it can be seen how, from the inner side of one of the major walls of the casing 16 protrude two reliefs 16a (one of which is also visible in figures 5 and 9), generally parallel to each other and extending in the longitudinal direction of the casing, preferably but not necessarily for its entire length (these findings may also present intermediate interruptions). The projections 16a, here defined integrally by the body 10a or by the casing 16, preferably have a tapered profile, so that a generally pointed or thinned top of them is pressed against the rear of the portion 20b of the support 20. As can be understood, a following the insertion of the support 20 into the cavity H, the projections 16a are able to urge the front of the part 20b against the internal surface of the wall of the casing 16 opposite to that from which the projections themselves rise. This stress advantageously has an elastic component, due to a certain elasticity of the plastic material constituting the casing 16.

In one embodiment, the positioning element 16a or each positioning element 16a is formed with a material different from that of the casing 16, such as an elastomer, for example mounted or co-molded or over-molded to the casing 16 and / or having another shape different from that shown, although able to operate in thrust and / or in an elastic manner on the support 20 and the electrodes J.

In a preferred embodiment, the relief or reliefs 16a are configured to be able to yield elastically and / or deform at least in their top area, so as to be able to possibly allow the insertion of the support 20 even if the thickness of the latter is greater than that of the distance between the tip of the projections 16a and the internal surface of the casing 16 facing this tip (a condition that could occur in the face of dimensional tolerances due to different shrinkage of the plastic material during the relative molding), however guaranteeing the aforementioned thrust.

In one embodiment, a non-electrically conductive filling fluid material is introduced inside the casing 16 - or in any case at least between the support 20 and the relative facing wall of the casing 16a, in order to preferably ensure the absence of bubbles. air - particularly between the electrodes J and the casing 16 - which could affect the correct level measurement, carried out according to the methods described below. The aforementioned filling material, which is preferably intended to encapsulate and / or be in contact with at least the portion 20b of the support 20, can be for example a polyurethane resin or, preferably, a gel, most preferably a silicone gel. A silicone gel suitable for application is for example the one called SilGel® 612, marketed by Wacker Chemie AG, Munich, Germany.

The presence of the aforementioned gel has the main function of filling any gaps that arise between the front of the sensor portion 20b and the wall of the casing 16 facing it: these gaps - even if of minimal volume - may exist for example at due to the surface roughness of the support 20 and / or the electrodes J, or again when the electrodes J have a thickness which causes a slight protrusion thereof with respect to the front surface of the portion 20b of the circuit support, or again due to the roughness and / or the possible deformation of the wall of the casing 16, for example following the surface finish of the relative mold and / or the different shrinkage of the polymeric and / or thermoplastic material in the case of molding the casing 16.

The above concepts are further clarified by the details in figures 14 and 15. In the detail in figure 14 the top of a relief 16 is clearly visible, which presses on the back of the portion 20b of the support, thereby pushing the electrodes - one of which indicated with J - against the internal surface of the facing wall of the casing 16. The further enlargement of figure 15 highlights the interface area between the electrode J and the aforementioned wall of the casing 16, from which it is possible to see how - in exemplified case - the facing surfaces of the two elements in question have respective micro-cavities, for example due to surface roughness and / or deformations of materials (for example different shrinkage of the material during molding, slight curvatures, etc.). In the presence of the aforementioned gel - indicated with G in Figure 15 at the interface between and said micro cavity - the reliefs 16a urge the part 20b of the support 20 against the internal surface of the envelope 16, thereby favoring the escape of the excess gel between the two parts in question: in this way, between these facing parts there remains only a film of gel G strictly necessary to fill the aforementioned micro-cavities. The aforementioned leakage of the excess gel G is preferably allowed by the presence of at least one vent chamber in the casing 16, for example comprising the part of the cavity H inside the casing 16 which is not occupied by the support 20 and by the projections 16a: such chamber is schematically indicated with H2 in figure 13 (chamber H2 may possibly include the space previously indicated with H1).

Figure 14 also shows a deformation or slight removal of material from the top of the relief 16a, which in the example assumes a nominally rounded tip: as explained, the tapered shape of the reliefs 16a is aimed at allowing a deformation, particularly in the case of where the portion 20b of the circuit support is inserted forcibly into the cavity of the casing 16 (for example in the case of excessive dimensional shrinkage or tolerances due to the molding of the casing itself), and to ensure both the aforementioned thrust aimed at obtaining a good contact between the electrodes J and the internal surface of the envelope 16, both to allow the excess gel to flow out, for the purpose of a reliable and precise detection. In this regard, it should be considered that, in the preferred embodiment, the gel is introduced into the cavity of the envelope 16 in order to substantially fill it, but for practical purposes it is sufficient for the gel to be present in the interface area between the portion 20b of the support with the electrodes. J is the facing surface of the casing 16, where the excess gel can, as said, flow into the aforementioned vent chamber H2 inside the casing.

As already mentioned, the methods for fixing the body 10a of the level sensor 10 to the tank can be different from those previously exemplified. In general, the coupling can be based on the presence of raised elements associated with one between the body 10a of the sensor 10 and the tank 1, provided for coupling with cavities or seats present on the other between the tank and the body 10a of the sensor. , the coupling preferably taking place following a partly axial and partly angular movement. In one embodiment, the mechanical coupling between the body 10a and the tank is a quick coupling, for example a snap coupling or a threaded coupling or a quick coupling. Figure 16 exemplifies, for example, the case of a coupling between sensor 10 and tank 1 based on a substantially bayonet-type coupling system. In this example, the body 10a of the sensor is provided, in its attachment portion 14, with a plurality of teeth or surface hooking projections, only one of which is visible, indicated by 12d, intended for coupling into respective defined hooking seats 5a in peripheral positions with respect to the opening 5 of the wall of the tank 1 provided with the opening 5, here the lower wall 4. Preferably, this wall of the tank 1 has, in correspondence with the opening 5, a cylindrical housing for receiving the attachment portion 14 and of the relative gasket 15, with the seats 5a extending between the upper face of the wall 4 and the cylindrical surface of the aforementioned housing. For the purpose of coupling, the body 10a is inserted through the opening 5, until the gasket 15 abuts on a relative abutment surface defined in the aforementioned cylindrical housing, in which the attachment portion is also received. This insertion is carried out in such a way that the reliefs 12d enter a substantially vertical section of the respective seats 5a; a subsequent angular movement imparted to the body 10a determines the passage of the reliefs 12d in a substantially horizontal section of the seats 5a, with a consequent coupling between the parts, as typically occurs in bayonet couplings of a known type (it is also possible to provide inclined sections in the seats 5a ).

In one embodiment, additionally or alternatively, an internal coupling to the reservoir is provided, such as a coupling based on coupling reliefs associated with one of the distal end of the sensor 10 and the facing wall of the reservoir, which reliefs coupling devices are coupled to cavities present on the other between the aforementioned distal end and wall. For example, the distal end of the casing 16 can be provided with one or more hooking projections or teeth, preferably radial projections, intended for coupling in respective hooking seats defined in an element that rises from the tank wall facing the said distal end. This internal coupling to the tank can provide elements technically equivalent to those described with reference to the example of figure 16.

A coupling of the type illustrated in figure 16, in addition to not requiring specific tools, allows to obtain an elastic mounting of the body 10a of the sensor 10 on the tank 1. In the embodiment of figure 16 the shape of the housing 12 is substantially cylindrical , without prejudice to its characteristics described above.

In one embodiment, the fixing between the body 10a of the level sensor and the tank 1 is of the permanent type, for example made by gluing or welding. A solution of this type is exemplified in figure 17, according to which an annular relief 2a rises from the external side of the wall 4 of the tank 1 (but it could be the wall 2), here a substantially quadrangular relief, which circumscribes a region of the wall 4 in which the opening 5 is defined, here substantially consisting of a slot having section dimensions slightly greater than those of the casing 16. In this case the attachment portion 14 of the body 10a has a shape substantially complementary to the closed profile defined from the relief 2a, or quadrangular in the illustrated example, and is preferably provided with its own annular relief, complementary or specular to the relief 2a, not indicated. For the purpose of coupling, the casing 16 of the body 10a is inserted into the opening 5, until the attachment portion 14 is coupled with the relief 2a. The final fixing between portion 14 and relief 2a can be achieved by means of an adhesive deposited on at least one of the two parts in question (with this adhesive which also performs sealing functions) or by welding together the portion 14 and the relief 2a, for example by a laser or vibration or ultrasonic welding, or with remelting of material or of the type defined with hot blade. Naturally, in this case, the materials constituting the wall 2 or 4 of the tank 1 and the attachment portion 14 of the sensor body will be compatible materials in view of the welding.

In the embodiment of Figure 17, the wall of the housing 12 from which the connector body 12a protrudes and the connector body itself have a different structure than in the cases illustrated above, without prejudice to the characteristics of the device described with reference to Figures 1- 15. In Figures 16 and 17 also the connection between the internal terminals of the connector body 12a and the internal circuit of the sensor 10 is different from that previously exemplified. According to these variants, electrical connectors are preferably provided with a connector body 12a shaped so as to define coding means, suitable for allowing univocal coupling with a respective external electrical connector, and / or polarization means, suitable for allowing coupling with said external connector only in the correct direction, thereby avoiding polarity inversions or incorrect connections.

Figure 18 illustrates a variant of implementation similar to that of figure 16, but characterized by the presence of two elastic elements 15 'and 15 ", here represented by rings of the O-ring type, with the attachment portion 14 defining the relative seats for such items. Preferably, the coupling surface reliefs 12c are defined in the portion 14 in an intermediate position to the two elastic elements 15 'and 15 ", or in an intermediate position to the relative positioning seats. As can be seen in Figure 19, in such an embodiment, the cylindrical housing at the mounting opening 5 is shaped so as to have two axial bearing surfaces 5b and 5c for the elements 15 'and 15 ", respectively, with the coupling seats 5a for the projections 12d which are in an intermediate position with respect to these surfaces.

In such an embodiment, the lower gasket 15 "performs gasket functions, particularly as a radial seal between the portion 14 of the body 10a and the interior of the relative cylindrical housing. The elastic element 15 'is instead intended to be axially compressed between the relative resting surface of the portion 14 - indicated with 14a in figure 16 - and the surface 5b of the cylindrical housing: in this way, in the assembled condition, the elastic reaction of the element 15 'urges the body 10a as a whole towards the outside of the housing (towards the bottom, with reference to Figure 18), ensuring an elastic assembly and the recovery of possible tolerances between the parts in play.

As said, the mounting configurations described with reference to Figures 16-19 can also be used when the level sensor 10 is associated with the upper wall of the tank, similar to what is illustrated in Figure 1.

As it has been seen, in the embodiments cited up to now the level sensor 10 includes an array of capacitive elements which each include a single electrode J1-Jn ("n" being equal to 37, in the examples illustrated up to now). The term "single" here means that each electrode J belongs to a capacitive element that does not require an additional electrode, as typically occurs in known capacitive level sensors, which presuppose the presence of pairs of facing or interdigitated electrodes or plates, or the presence of a common electrode or armature facing a plurality of electrodes or armatures. In other words, in the solution proposed here each electrode J forms the armature of a sort of "virtual capacitor", the other armature of which is made by the means subject to detection present in the tank and where the interposed wall of the casing 16 - or another layer of insulation that replaces it - constitutes the dielectric or insulator between the plates of this virtual capacitor, to which the dielectric or insulator consisting of the aforementioned layer of gel G is possibly added.

In practice, therefore, each electrode J creates, together with the relative control electronics, a sort of capacitive proximity sensor, capable of detecting the presence or absence of the medium even without direct contact with the latter. This type of operation is based on the principle of detecting the electrical capacity of a capacitor: the electrode J is the sensitive side of the capacitor and constitutes an armature, while the possible presence in the vicinity of an electrically conducting medium realizes the other capacitor armature. In this way, the presence or absence of a medium in the vicinity of each electrode J determines an electrical capacity that the control electronics is able to detect.

In the application considered here each electrode J is therefore capable of creating at least two different capacitive structures depending on the presence or absence of the liquid in front of it, and precisely at least

- a first capacitive structure having a first value of electrical capacity, when an electrode J faces the liquid, or when the liquid level in the tank is at or above the electrode J considered, and

- a second capacitive structure having a second value of electrical capacity, when an electrode J is not facing the liquid, or when the level of the liquid in the tank is below the electrode J considered.

In the preferred embodiment illustrated, as we have seen, the electrodes J are isolated from the liquid, as they are contained in the electrically insulating and fluid-tight casing 16: the wall of the casing 16 which the electrodes J face, with the any interposed layer of gel G can therefore be assimilated to a sort of dielectric of the aforementioned “virtual capacitor”.

The thickness of the wall of the casing 16 facing the electrodes J, or of the insulation layer, can be approximately between 0.1 and 5 mm, preferably between 0.6 and 1 mm, most preferably about 0.8 mm. Furthermore, as already mentioned, the hollow casing 16 can be replaced by a direct overmolding of plastic material on the sensitive element or by a generic wall or layer of insulation of the electrodes J, with a thickness of the part facing the electrodes J similar to that indicated. for the homologous wall of the casing 16.

Each electrode J is electrically connected - alone or in common, particularly in parallel, with at least one other electrode J, as explained below - to a respective input of a plurality of inputs of the controller 24 belonging to the circuit arrangement 23. Preferably, a filter resistor is provided between each input of the controller and a relative electrode J (two of these resistors are indicated by R1 and Rn in Figures 6 and 7). The controller 24 is substantially arranged to discriminate the electrical capacitance value associated with each electrode J at least between the aforementioned first and second electrical capacitance values and consequently identify at least one liquid / air transition in the tank, indicative of the medium level when this is in the fluid state. In a preferred embodiment, the controller 24 carries out a sequential sampling of the electrical capacitance values present at the inputs to which the electrodes J are connected, in order to identify the aforementioned transition.

The controller 24 is preferably a digital electronic microcontroller provided with an analog-digital converter. By way of example only, a commercial microcontroller suitable for the application proposed here is the one identified by the code PIC16F1517 marketed by Microchip Technology Inc., Chandler, AZ, U.S.A. However, it should be noted that the functions of the controller 24 can be at least partially implemented through dedicated external circuits: for example, in a preferred embodiment, the controller 24 consists of a microcontroller that implements an analog-to-digital converter module, but in others embodiments the controller 24 can include a microcontroller (or a microprocessor or an ASIC or FPGA integrated circuit) and an integrated circuit (or external or independent) dedicated to perform the functions of an analog-to-digital converter.

Figure 20 schematically shows a controller 24 which, by way of example only, includes "n" signal inputs IN (here twenty in number), to which the same number of electrodes J in a single configuration are connected by means of relative conductive tracks 25 ( i.e. not connected in common or in parallel to other electrodes).

In a preferred implementation, the measurement of the electrical capacity value at each of the IN inputs is carried out indirectly, based on the measurement of a voltage. In such a case, preferably, the inputs IN of the controller 24 are analog inputs and the controller implements or has associated an analog-digital converter.

In a preferred embodiment, each input IN is associated with a circuit including a controllable switch and a capacitor, here also referred to as sampling switch and sampling capacitor. The controllable switch is switchable between a first position, in which the sampling capacitor is connected to a voltage source, and a second position, in which the same capacitor is connected to a respective electrode J or to several electrodes J connected in common ( in parallel). Preferably said voltage is a direct voltage, for example the supply voltage of the circuit arrangement 23. The controller 24 has means for causing the switching of the controllable switch from the first position to the second position, so as to discharge the sampling capacitor in a manner proportional to the electric capacitance value associated with the relative electrode J or group of electrodes J connected in common. Furthermore, the controller 24 has means for determining the voltage at the input IN when the controllable switch is in its second position, this voltage being indicative of the electrical capacitance associated with the electrode J or the group of electrodes J. The controller 24 then has means comparators, to compare the determined voltage present at the input IN with at least one relative reference threshold, and thereby deduce whether the liquid faces or does not face electrode J or at least one of the electrodes of the group of electrodes J connected in common .

In a preferred embodiment, the scanning or sampling of the inputs IN is carried out using a Sample and Hold circuit associated with an analog-to-digital converter and the measurement of the capacitance of each electrode J or group of electrodes J takes place as a measurement comparison with respect to the intrinsic capacity of this circuit.

An example of operation of a sensor according to the configuration of Figure 20 - that is with single electrodes connected to respective inputs of the controller 24 - is shown schematically in Figure 21. It should be noted that this figure shows, only for the sake of greater clarity, a level sensor mounted from above, ie in the configuration of Figure 1: the relative electrodes J, however, are shown in the same order as in Figure 20 (therefore with the lower electrode J1 and the upper electrode Jn).

Figure 21 shows the tank 1, with inside the detection part 11 of the sensor, that is the electrodes J1-Jn contained in the relative casing 16 which is at least partially embedded in the AdBlue liquid, indicated with L (the support 20 is not here represented for reasons of clarity, or considering that - in a possible embodiment - the same casing 16 could fulfill the functions of the support 20). In the example shown, the analog inputs IN of the controller 24 are only connected to an MTP multiplexer implemented in the controller itself, which essentially operates as an electronic diverter, to which a sampling or Sample and Hold circuit is associated, including a Hold CHOLD capacitor (holding capacitor) and a sampling switch SS (sampling switch). The switch SS is switchable between a first position, for connection to the VDD voltage (for example the power supply voltage of the controller 24) and a second position, for connection to an output of the multiplexer MTP, or a position for connection to the electrodes J .

Through the MTP multiplexer the inputs IN, and therefore the electrodes J, are sequentially connected to the switch SS. The SS switch is switched cyclically, synchronized to the operation of the MTP multiplexer, between the first position, for charging the CHOLD capacitor, and the second position, for connecting the same capacitor to the IN input currently selected by the MTP multiplexer, and then to the relative electrode J. With the switch SS in its second position, a charge balance is essentially determined between the capacitance of the CHOLD capacitor and the capacitance associated with the electrode J; in other words, with this charge balance the CHOLD capacitor discharges in a manner proportional to the capacity of the "virtual capacitor" defined by the electrode J. The amount of charge is then determined through the ADC converter, that is a residual voltage of the CHOLD capacitor, which it is then compared with a predefined reference threshold, in order to deduce whether the electrode J faces the liquid L or not, or if the electrode J has assumed the first capacitive structure or configuration or the second capacitive structure or configuration indicated above.

As previously explained, when an electrode J faces the liquid L (for example electrode J1 of figure 21) it is associated with a first value of electric capacitance, while in the opposite case (as for the electrode Jno Jn-1 of figure 21) it is associated with a second electrical capacity value, lower than the first value. In figure 21 the block in hatched line indicated with VE is intended to represent in a schematic way the functionality of the electrode or "virtual" armature realized by the liquid L, as explained above.

Following the aforementioned balancing between the charges of the CHOLD capacitor and electrode J1, the voltage value across the capacitor and / or at the IN1 input may substantially coincide with or be greater or less than a certain reference threshold, previously stored in the controller 24 For example, in one embodiment, the controller 24 can be programmed so that the detection at an input IN of a voltage equal to or higher than the predefined threshold is indicative of the fact that the considered electrode is not facing the liquid. L (as for the Jn electrode), while the detection at the IN input of a voltage below the threshold is indicative of the fact that the electrode faces the liquid (as for the J1 electrode).

As can be understood, by carrying out the sequential sampling described, the controller 24 is able to identify the two electrodes J corresponding to the liquid / air transition in tank 1: once the presence of the liquid / air transition has been detected, the controller can infer the liquid level based on the fact that the one between the two electrodes J to which the voltage value equal to the threshold or above it is associated is the first in the air (or conversely, the electrode to which the voltage value below the threshold is associated threshold turns out to be the last one facing the fluid).

For this purpose, the circuit 24 preferably contains information representative of values in length (height) corresponding to the position of each electrode J, or in any case of the distance between the electrodes J in the direction of the measurement axis X, so as to be able to establish or calculate the level according to the default unit of measurement. The electronics of the sensor 10 transmits or generates signals to the outside and / or the electrical connector of the sensor 10, representative of the level information.

It will be appreciated that the functionality described with reference to Figure 21 can also be obtained with different but technically equivalent circuits to the one exemplified: for example, each input IN of the controller 24 could be associated with a respective circuit performing the functions of the Sample and Hold circuit described above. , with an MTP multiplexer between these circuits and the ADC converter. Another possibility is to equip each input IN with a circuit performing the functions of the Sample and Hold circuit described above, interfaced directly to an ADC converter: such a case is for example schematized in figure 22.

Preferably, the electronics of the sensor object of the invention is suitably initialized and / or calibrated in the production phase, with storage of the relative software or program and / or of at least some of the variables (such as one or more thresholds used in level measurements), for example dependent on the physical configuration of the sensor and the installation system, represented here by tank 1.

In one embodiment, the calibration step includes a reading of all the values of the electrodes J dry or in air (i.e. not facing the liquid), for the purpose of defining first reference thresholds and / or defining a cancellation of the initial offset. , or to compensate for the parasitic capacities due to materials, structures, thicknesses, etc. of the sensor and / or the installation system. This value is stored as a threshold reference for detections, such as a maximum threshold in electrical voltage detectable on the CHOLD capacitor and / or by the ADC circuit, this threshold value being able to subsequently be varied in the face of measurements made during the useful life of the sensor, for example by means of a dedicated reference electrode. This calibration operation is preferably performed only once in the production line, but for some applications where the tank has critical geometries that may have a bearing on the measurement of the raw data of the electrodes J (such as for example very small volumes and the presence of material metallic) it is possible to use this calibration or auto-calibration directly on the sensor 10 installed, in order to have an optimal calibration in the real system and / or cancel all the possible effects of noise due to the external environment.

The operating principle described is to a certain extent dependent on the temperature and aging of the system, if observed absolutely. For this reason, in a preferred embodiment, the controller 24 is programmed to carry out a measurement of the differential type, preferably using for the purpose at least one reference electrode. Given that the effect of the temperature is represented by an offset on the measurement of the voltage value determined at an input IN of the controller 24, by performing a differential measurement between a detection electrode and a reference electrode it is possible to obtain both the measurement on the electrode of detection, both to subtract the common mode effect present on the detection electrodes, and therefore to cancel any thermal and / or structural drift produced by the change in temperature and / or by aging; the aforementioned thermal drift can also be compensated by means of a temperature sensor, for example of the type indicated with 26 and 27. According to this embodiment, therefore, the determined voltage value, used for the comparison with the at least a reference threshold, is preferably a differential value.

The aforementioned reference electrode is preferably the lowest electrode inside the tank 1 and therefore, referring to the examples illustrated so far, the electrode J1. It is also possible to provide even more reference electrodes (for example the first three electrodes J starting from the bottom), which can be used to carry out the differential measurement, as well as to program the controller 24 to choose any one of the electrodes J1 each time. - as a reference electrode for the purpose of carrying out the differential measurement (the controller 24 is in fact able to identify an electrode facing or not facing the liquid, due to the fact that the electrical capacity in the two conditions is different and the presence of the cited maximum threshold).

In an implementation of this type, the controller 24 scans all the electrodes J with the acquisition of the relative raw voltage data, to verify the presence of the liquid: in this phase, the controller 24 calculates the difference between the raw data of each detection electrode and the raw data of the reference electrode J1, obtaining a relative measurement. This difference is compared with at least a minimum threshold defined in the design phase: in a possible implementation, if at least one of the differences calculated between each detection electrode J2- Jn and the reference electrode J1 is below the minimum threshold, then it means that the the detection electrode in question is at least partially facing the liquid L; otherwise, the electrode in question is in the air, or at a height above the level of the liquid L.

As already indicated, the level search is substantially based on the identification, by the controller 24, of the two detection electrodes corresponding to the transition between liquid and air. The evaluation is carried out by comparing the relative information (the differential measurement) with predefined thresholds for each electrode and defined in the design phase (possibly replaceable with thresholds defined and stored following a test with liquid in the production phase), in order to deduce whether a electrode is facing the liquid or not. Following the scan performed, the controller can thus identify two adjacent detection electrodes, one of which faces the liquid and the other, i.e. the height position of the liquid / air transition in tank 1.

In an embodiment which is inventive in itself, the electronic circuit of the sensor 10 is subjected to a calibration or configuration based on the type and / or conductivity of the medium subject to level detection, particularly considering that in the case of low conductive or resistive means , it would also determine a sort of electrical resistance virtually connected in series to the measuring capacitor, which resistance could determine an increase in the time necessary to reach the final threshold value (such as an increase in the charging time of the "virtual capacitor" to which it belongs an electrode J and / or an increase in the discharge time of the CHOLD capacitor); from this point of view, the aforementioned calibration can be foreseen, for example, in order to take into account any delays in the sampling measurement, and to avoid incorrect measurements on values that are not yet well stabilized.

In an embodiment which is inventive in itself, the electronic circuit of the sensor 10 is configured to detect the charge curve of the "virtual capacitor" corresponding to the measuring electrode J and / or to detect the discharge curve of a sampling capacitor, such as the CHOLD capacitor, where the charge and / or discharge curve is variable at least in proportion to the conductivity and / or electrical impedance characteristics of the medium subject to measurement, so as to be able to determine characteristics of the medium subject to detection. The electronic circuit can use the information thus acquired for the purpose of carrying out one or more of the detection operations, processing operations, comparison operations, storage operations, compensation operations, reporting operations. For this purpose, structural and / or circuit elements at least partly analogous to those previously described can be used.

As mentioned, in a particularly advantageous embodiment, the detection electrodes comprise at least first detection electrodes, connected to respective inputs IN of the controller 24, and second detection electrodes which are electrically connected in common or in parallel to the first detection electrodes , the definition of parallel connection also referring to the parallel connection between the “virtual capacitors” defined by the electrodes J which are connected together in common with respect to a respective input IN.

An example of this type is shown schematically in figure 23, where the aforementioned first electrodes go from electrode J4 to electrode J20, while the second electrodes go from electrode J21 to electrode Jn; in this example the electrodes J1-J3 can be reference electrodes. In the configuration of figure 23 it is possible to substantially identify a first sub-array (or module or block or group) of first electrodes, which go from electrode J4 to electrode J20, and a second sub-array of second electrodes, which go from electrode J21 to electrode Jn, substantially connected to each other in common or in parallel; the number of electrode sub-arrays can be increased in order to obtain more or less long level sensors, or in order to allow different level measurements.

In an embodiment of this type, the comparator means implemented in the controller 24 are designed to compare the voltage determined at the IN input corresponding to two electrodes connected in common (for example the electrodes J4 and J21 in parallel) with at least two relative reference thresholds, in order to deduce if the liquid faces or does not face the first detection electrode (electrode J4) and / or the relative second detection electrode (electrode J21). The measurement can be carried out in the manner previously described. Preferably, also in this case the measurement is carried out by acquiring the raw data at the input IN which the two detection electrodes connected in common are connected, and then referencing this value with respect to a reference electrode, such as electrode J1, in order to pass from an absolute measurement to a differential measurement to cancel any common mode error effect due to the temperature and / or aging of the level sensor, as previously described.

In one embodiment, the value obtained from the differential measurement is compared with a number of thresholds equal to that of the number of electrodes connected in common increased by 1. Referring to the example considered here of two electrodes J in parallel, therefore, the differential value is compared with three distinct thresholds defined in the project or in the production phase: a value equal to a first threshold or within a determined neighborhood (for example / - 40%) indicates that both electrodes are not facing the liquid, a value equal to a second threshold or within a determined neighborhood (for example / - 40%) indicates that one of the electrodes (known based on its physical position) faces the liquid and the other electrode does not, a value equal to a third threshold or finally, within a determined neighborhood (for example / -40%) it indicates that both electrodes face the fluid.

In a different embodiment, a more simplified analysis logic is provided, according to which the value obtained from the differential measurement is compared with a number of thresholds equal to that of the number of electrodes connected in common. Referring again to the example considered here of two electrodes J in parallel, therefore, the differential value is compared with only two thresholds: a value above a first threshold indicates that both electrodes are not facing the liquid, a value between the two thresholds indicates that one of the electrodes (known on the basis of its physical position) faces the liquid and the other electrode does not, a value below the second threshold finally indicates that both electrodes face the fluid.

Naturally, according to the same principle described above, more than two electrodes connected in common can be provided, or more sub-arrays with the respective electrodes in parallel, in which case the number of reference thresholds for each input IN will be equal to the number of electrodes of each parallel increased by 1 or equal to the number of electrodes of each parallel, depending on the analysis approach implemented.

For example, Figure 24 illustrates the case of first, second and third detection electrodes connected in common or parallel. The first electrodes go from the J4 electrode to the J20 electrode, the second electrodes go from the J21 electrode to the J37 electrode and the third electrodes go from the J38 electrode to the Jn electrode; in this example the electrodes J1-J3 can be reference electrodes. In the example of figure 24 it is therefore possible to identify three sub-arrays of electrodes or "virtual capacitors", with the electrodes of one sub-array (J4-J20) which are substantially connected in common or in parallel with homologous electrodes of the other sub-arrays - Cups (J21-J37e J38-Jn).

In an embodiment of this type, the comparator means implemented in the controller 24 are arranged to compare the voltage determined at the input IN corresponding to three electrodes in parallel (for example the electrodes J4, J21 and J37) with three relative reference thresholds, in order to deduce whether the liquid faces or does not face the first detection electrode (electrode J4) and / or the relative second detection electrode (electrode J21) and / or the third detection electrode (electrode J37). An example of operation of an arrangement of the type illustrated in Figure 24 is described below with reference to Figures 25 and 26.

Figure 25 is a schematic representation similar to that of Figure 21, in which only two inputs IN4 and INnd of the controller 24 are highlighted (the representation of the reference electrode J1 is omitted here for reasons of clarity). As in the case of figure 21, the controller 24 carries out the sequential sampling of its analog inputs IN, with relative differential measurement for each of them and relative comparison with the three predefined thresholds for electrodes J facing the liquid L and / or at the predefined threshold for "dry" electrodes J, ie not facing the liquid L.

Figure 26 illustrates the measurement principle adopted for the various IN inputs, for example the IN4 input, in graphic and schematic form. Assume that the initial voltage of 5 V indicated in the graphs corresponds to the voltage VDD in figure 25. TH1, TH2 and TH3 indicate three predefined threshold values for the IN4 input, namely a maximum threshold, a minimum threshold and an intermediate threshold , respectively, for the condition of electrodes facing the liquid.

The graph in part a) of figure 26 expresses the condition that occurs <if none of the three electrodes J> 4 <, J> 21 <and J> 38 <faces the fluid, a> following the switching of the switch SS of figure 25 in its position in which the CHOLD capacitor is connected to the relative group of sensing electrodes J4, J21 and J38. In the figure, the falling edge of the voltage is intended to represent the decrease in the voltage value due to the differential measurement carried out in the manner described above and / or to the fact that, even if not facing the liquid L, the three electrodes in question are in any case associated with a minimum electrical capacity, due to the structure of the device. The voltage drop in the graph in part a) of figure 26 is also detected with reference to a certain "dry" threshold value, indicated by THD, higher than the maximum threshold value TH3, this threshold value THD being usable also for the purposes of discrimination with respect to the three detection thresholds TH1, TH2 and TH3. The voltage drop in graph a) remains within the determined range (for example the aforementioned / - 40%) of the THD threshold, and in any case above the maximum threshold TH3: controller 24 therefore deduces the absence of liquid in front to electrodes J4, J21 and J38.

The graph in part b) of figure 26 instead expresses the condition that occurs if one of the electrodes J4, J21 and J38 faces the liquid L. In this case the decrease in the voltage value is greater than in the previous case: in addition to the differential measurement, in fact, the overall electrical capacity associated with the three electrodes is greater than in the previous case, given that one of them faces the liquid L. The voltage value is now in the determined range of the TH3 threshold, and hence the controller 24 deduces the presence of liquid in front of only one of the electrodes; or the lowest electrode of the three (the physical position of the electrodes being known to the controller).

The graph in part c) of figure 26 instead expresses the condition corresponding to that of figure 25, i.e. the condition in which two of the electrodes J4, J21 and J38 face the liquid L. the voltage decrease is now greater than in the case of part b) of Figure 23 since, in addition to the differential measurement, in the condition in question the overall electrical capacity associated with the three electrodes is further increased with respect to the previous case. The voltage value is now in the determined range of the threshold TH2: the controller 24 therefore deduces the presence of liquid in front of the electrodes J20 and J37 and the absence of liquid in front of the remaining electrode Jn, i.e. the highest electrode among the three. This discrimination is also carried out considering that, in the case of freezing conditions or partial solidification of the liquid, it is possible to combine other measurements to better discriminate this condition, such as a check and comparison with the state of adjacent electrodes and / or a temperature measurement. Finally, the graph in part d) of figure 26 expresses the condition in which all three electrodes J4, J21 and J38 face the liquid L. the voltage decrease is evidently greater than in the case of part c) of figure 23 since , in addition to the differential measurement, in the condition in question the overall electrical capacity associated with the three electrodes is maximum. The voltage value is now in the determined range of the TH1 threshold, from which the controller 24 deduces the presence of liquid in front of the three electrodes J21 and J38.

As previously clarified, the same results can be obtained using a simplified logic, i.e. comparing the voltage value with only the three detection thresholds TH1, TH2 and TH3, as follows:

- part a) of figure 26: with the voltage value that remains above the TH3 threshold, the controller 24 deduces the absence of liquid in front of the electrodes J4, J21 and J38;

- part b) of figure 26: with the voltage value that is between the threshold TH3 and the threshold TH2, the controller 24 deduces the presence of liquid in front of the lower electrode among the three;

- part c) of figure 26: with the voltage value that is between the threshold TH2 and the threshold TH1, the controller 24 deduces the presence of liquid in front of the electrodes J20 and J37 and the absence of liquid in front of the remaining electrode Jn; And

- part d) of figure 26: with the voltage value falling below the threshold TH1, the controller 24 deduces the presence of liquid in front of the three electrodes J21 and J38.

By scanning the inputs IN with one of the methods illustrated above, the controller 24 is able to identify the liquid / air transition. In the specific case of figure 25, therefore, the controller 24 will be able to deduce the presence of a liquid / air transition between the electrodes J37 and J38, thereby identifying the level of the liquid in the tank 1.

From what has been described above it can be seen that the type of construction proposed is extremely flexible in relation to the possible lengths required for the level sensor. In other words, with a given controller 24 and substantially the number of its analog inputs IN being equal (or with a slightly higher number of inputs IN, as described below) it is possible to realize level sensors of different lengths, providing for the detection of the use of single electrodes J, or two electrodes J in parallel, or three electrodes J in parallel, and so on.

For example, by placing twenty single electrodes J having 2 mm in height and placed at a distance of 2 mm from each other, 78 mm of sensitive area for level measurement are reached ((20 electrodes 19 spaces between them) * 2 mm). When it is necessary to increase the length of the sensitive area (measurement of higher levels) while maintaining the same measurement resolution, it is possible to use two electrodes in parallel, or three, even maintaining the same controller 24.

Preferably, in the presence of first detection electrodes connected in common to further detection electrodes, it is preferable that the physical position of the various electrode sub-arrays be as far away from each other as possible, in order to increase the signal difference and therefore the quality of level information. For this reason, in a preferred embodiment, if several groups of sensing electrodes connected in common are provided, the electrodes of each group form respective sub-arrays arranged in sequence along the sensing axis of the sensor, as can be seen for example from Figures 23 and 24. In general, and referring for example to Figure 24, the rule can be applied according to which, given a number y (for example 17 electrodes) of first electrodes (J4-J20) in parallel to second electrodes (J21 -J37), y-1 electrodes (for example 16 electrodes) will be interposed between each first electrode and the relative second electrode.

Thanks to the construction typology described, it is also possible to have different level reading sensitivities: this can be obtained, during the construction of the part 20a of the support to which the relative electrodes J, positioning the electrodes themselves with a distance between centers equal to the desired resolution. It is also possible to provide at least two differentiated measurement resolutions on the sensitive portion 20b of the sensor, particularly at least a higher measurement resolution and a lower measurement resolution, in a low area and in a high area of the portion 20b, or vice versa. In such a case the electrodes in the lower region of the portion 20b may be closer to each other than the electrodes present in the upper region, or vice versa. The minimum distance between two electrodes can be, for example, 1 mm. It is also evident that the size of the electrodes define the amount of electrical capacity that can be measured by the control electronics, so a larger electrode will therefore offer a greater dynamic or measurement value.

The electrodes J are preferably (but not necessarily) equal to each other and can for example be made with dimensions of 20 mm (length) x 2 mm (height) and placed 2 mm away from each other; for sensors with a length of less than 100 mm - or if you want to increase the resolution in an area of the sensitive portion of the sensor - it is possible to reduce the size of the electrodes, and therefore also reduce the distance between them, just to obtain a resolution larger: in these cases the electrodes can have dimensions of 15 mm (length) x 1 mm (height) and be placed at 1 mm between them. To maximize the measurement dynamics with respect to the liquid, for example with respect to the AdBlue liquid considered here (or other solution with urea or different reducing agent), it is also preferable to size the electrodes, for any value of their length, so that the height of an electrode is equal to the distance between two contiguous electrodes.

Figures 27 and 28 show, with views similar to that of Figure 24, further possible arrangements which provide three groups of electrodes J in parallel: In the case of Figure 27, the two end electrodes of the illustrated array, i.e. the electrodes J1 and Jn, are not they are connected in parallel to other electrodes and constitute reference electrodes, respectively for the condition of presence and absence of liquid, or vice versa, whose function is preferably programmable or predeterminable, for example in order to allow the sensor 10 to be mounted in the tank 1 in the two conditions of figures 1 and 2.

Figure 27 illustrates a configuration, partly similar to that of Figure 24, where the electrode array includes three sub-arrays of first, second and third sensing electrodes connected in common (in parallel) with each other, the sub-arrays being however separated by single electrodes. The first electrodes go from the J2 electrode to the J17 electrode, the second electrodes go from the J19 electrode to the J34 electrode and the third electrodes go from the J36 electrode to the J51 electrode. In this example, the intermediate electrodes J18 and J35 are instead independent and interposed between the aforementioned three sub-arrays of electrodes: in particular, the single electrode J18 is interposed between the first sub-array (J2-J17) and the second sub-array (J19 -J34), while the single electrode J35 is interposed between the aforementioned second sub-array and the third sub-array (J36-J51).

The intermediate electrodes J18 and J35 allow a clearer distinction between the sub-arrays of electrodes connected in common, in particular in order to detect particular conditions or states of the liquid or other means subject to detection (such as a state of partial solidification or icing of the liquid or medium), particularly a more precise and / or clear distinction in the detection of transitions "liquid - air or gas" and / or "liquid - air or gas - solid or ice". To this end, consider that the interposed electrodes J18 and J35 make it possible to more quickly determine which and / or how many sub-arrays or parts of them are facing the vehicle (or vice versa not facing), thus being able to identify more quickly the areas of uncertainty in which to carry out. more accurate measurements, ie by detecting the transition areas between two adjacent electrodes, for example to detect the "liquid-air" transition area as previously indicated.

The presence of intermediate independent electrodes is also useful for better discriminating the values in relation to the aforementioned reference thresholds (such as TH1, TH2, TH3 and / or the "dry" threshold), in particular in the case of a high number of sub-arrays of electrodes in common (in parallel): in the case of many sub-arrays there will in fact be many reference thresholds that are closer to each other; for example, if it is preferable for cost reasons to use an analog / digital converter (ADC) with a lower resolution (for example 8 bits instead of 10 or 12 bits); the presence of said independent electrode J18, J35 allows a clearer and / or more certain detection, similarly to what is described with reference to graph b) of figure 26, where only the threshold TH3 is considered.

Figure 28 is substantially similar to Figure 27, distinguished by the fact that the intermediate electrodes J18 and J35 are not single, but in parallel with each other and connected to the same input IN. A configuration of this type can be useful for limiting the number of connections to the intermediate electrodes provided, while ensuring a good distinction of two thresholds (such as thresholds TH1 and TH2) associated with the same input IN.

With reference to the exemplary configurations described in figures 27 and 28, and considering a greater number of sub-arrays or groups of electrodes connected in common (for example equal to or greater than five sub-arrays), it is possible to provide more intermediate electrodes, individually connected or connected together in pairs in parallel.

Figure 29 illustrates some circuit components used in a possible practical implementation of the invention. Part a) of the figure shows the microcontroller 24 used, here the aforementioned PIC16F1517 by Microchip Technology Inc, with indication of the relative inputs and outputs. Part b) of the figure highlights the electrodes J, which here comprises electrodes J1-J17 connected in a single configuration to respective inputs of the microcontroller 24, as well as electrodes J18- J27 connected to respective inputs of the microcontroller 24 in common or parallel to electrodes J28- J37. It is noted, on the connection between each of the electrodes J1-J27 and the relative input of the microcontroller 24, the aforementioned filter resistance, which can possibly be omitted. Part c) of figure 29 illustrates a possible circuit diagram of a temperature sensor usable in the device according to the invention, such as for example the temperature sensor 26 and / or 27 of figure 7, while part d) of the figure illustrates a possible communication port or electrical connector belonging to the circuit arrangement 23 of Figure 7, usable for example for programming and / or calibration of the production phase level sensor. Naturally, the circuit arrangement 23 also includes a power supply stage, not shown, as it can be produced according to a per se known technique.

Thanks to its nature with discrete detection elements, the sensor according to the invention is able to perform level measurements in a variety of situations, which occur for example in SCR systems. A first situation is the typical one, already described previously, in which the liquid contained in the tank is entirely in the fluid state. A second situation is that which can occur in the event that the tank is operating in conditions of low temperature, such as to produce the total freezing of the liquid present in the tank. Also in this case the sensor 10 is perfectly capable of recognizing the electrodes facing the frozen mass, and therefore calculating its height. A third situation is that in which the tank contains a predominant liquid part in which frozen parts float or are immersed ("iceberg effect"): also in this case the level measurement performed by the sensor 10 can take place in the manner already described above, given that the presence of icy parts does not affect the operation of the sensor 10 and the calculation of the level. Similar considerations apply to the case in which there is a direct transition between liquid and ice.

The sensor 10 is also capable of detecting in mixed situations, when the liquid - ice system is freezing or thawing. A case of this type is schematically illustrated in figure 30, where in the upper part of the tank 1 there is frozen liquid, indicated with I, to form a partial or total "cap"; in the lower part of tank 1, at a higher temperature, the content L of the tank is already in liquid form and between the solid part I and the liquid part L there is air, indicated with A, or vacuum. For example, such a condition can occur in the case of use of the liquid L contained in the tank before it freezes completely or after a partial defrosting of the contents of the tank has been obtained by means of a heater: in this case, to the part of the liquid used substantially there is an empty intermediate zone or with air between the liquid and the ice. In accordance with an aspect of the invention, in a condition of this type it is advantageous to detect the level of the liquid in order to avoid its complete use, or in order to leave at least a part of liquid in the tank, for the reasons explained below.

Even in a condition of the type exemplified, the control electronics of the sensor 10 is able to correctly identify the presence of one or more electrodes (J4, J20) facing the liquid L, followed by the presence of one or more electrodes (J21, J37 ) facing the air A, followed in turn by one or more electrodes (J38, Jn0) facing the ice I. Advantageously, in a situation of this type, the control electronics of the sensor according to the invention is able to define both the quantity / level of liquid content L, which is important because it is the part directly usable at the moment by the SCR system, and the total quantity of liquid (L + I) present in the tank, which is important for planning the refilling of tank 1. A possible control logic that can be used for detecting the so-called "igloo effect" (presence of a layer of air topped by a layer of ice) can be the following:

- only all the detection electrodes that appear to be "dry", ie facing the air, are considered;

- the information acquired on a certain number (for example 3) of electrodes subsequent to a considered dry electrode is evaluated (meaning by subsequent electrodes those above the considered dry electrode, in case of mounting the sensor from below, or below the considered dry electrode, in case of mounting the sensor from above);

- occurs if above a "dry" electrode there is an electrode - between the aforementioned successive electrodes - which faces the liquid; for this purpose, in a preferred embodiment, the difference between the measurements performed on the aforementioned successive electrodes and that of the "dry" electrode considered is calculated, comparing the three individual results with absolute thresholds defined in the design phase: if at least one of these differences coincides or is in the determined neighborhood of the defined threshold in the presence of the “igloo effect”.

It is also possible that, starting from a situation of the type shown in figure 30, the tank is topped up, thus entering a part of liquid L which could be blocked by the ice cap I still present in tank 1. In on the basis of the above principles, also in this case the sensor according to the invention is evidently able to detect the increase in the total level of liquid present in the tank 1. Again with reference to situations of the type represented in figure 30, it will be appreciated that , in case of need, the electronics of the sensor 10 can be programmed to carry out successive measurements, spaced out by a certain period of time (for example 2 minutes), in order to verify the progressive progress of the melting of the ice cap I .

As already indicated, the electronics of the sensor object of the invention is initialized and calibrated in the production phase, with storage of the related software and related variables, including one or more of the reference thresholds depending on the physical configuration of the sensor - tank system. , including the minimum thresholds representative of the condition of an electrode or a group of electrodes not facing the fluid. The minimum threshold for the opposite case (liquid facing an electrode can be predefined in the face of experiments and / or possibly defined by further testing with the sensitive part 11 of the sensor completely immersed in the liquid. In the event that the sensor 10 includes electrodes in parallel, the intermediate thresholds between the minimum and the maximum are also experimentally defined.

The temperature information that can be acquired through the sensor 27 and / or 26 can be used by the electronics 23 to recognize the situation of the tank system, for example to infer the freezing condition of the liquid and activate a relative heater, and / or to compensate mathematically, the information on the level measurement, particularly in the case of applications at critical temperatures where the use of a differential measurement with the reference electrode may not be sufficient to guarantee error compensation.

It should be noted that in order to cause some frozen liquids to melt by means of a heater, such as the AdBlue additive considered here, it is necessary that a part of dissolved liquid is still present in the tank, so that the heater can continue to heat the liquid and these transmit the heat to the ice mass. In the application to an SCR system, when the vehicle engine is started, a withdrawal of the additive occurs, and this does not cause particular problems if a certain quantity of heated additive still remains in the tank, which can reach the mass. frozen by virtue of the movement of the vehicle and the consequent agitation of the hot liquid in the tank 1. If, on the contrary, the initial withdrawal of the additive determines the emptying of the residual liquid of the tank contents, the dissolution effect stops. For this reason, in a preferred embodiment, the sensor according to the invention can be arranged, for example at the software level, to detect the level of the dissolved liquid, so as to guarantee in any case the presence of a minimum level thereof, sufficient for the dissolution effect is not stopped; for this purpose, the sensor 10 can generate an appropriate signal or data to the outside, for example usable by the vehicle's on-board electronics and / or for appropriate signals.

It will of course be appreciated that with the sensor object of the invention the progressive melting of the frozen mass of liquid is also easily detectable, as this melting proceeds. The sensor 10 is naturally able to operate during the heating and / or thawing of the liquid or other means subject to level detection, as well as during its possible freezing.

The sensor 10 is interfaced with an external control system, such as for example a control unit of the SCR system by means of the connector 12b. For this purpose, the control electronics 23 of the sensor is designed for data transmission, preferably in a serial format, most preferably through an interface and / or a SENT (Single Edge Nibble Transmission) protocol. The signals sent may include, in addition to information representative of the level of the medium subject to detection, also information representative of at least one of the temperature of the medium or of the air present in the tank, the presence of a condition of freezing or solidification of at least part of the means subject to detection, the presence of an abnormal operating condition, a warning and / or status signal.

From what has been described above, it can be seen that the operation of the level sensor described is substantially independent of the dielectric constant of the medium being measured. The sensitive element represented by the array of electrodes is able to carry out the level measurement even if completely isolated from the liquid, thereby guaranteeing its protection from contact with aggressive liquids, such as AdBlue or urea, and giving a good mechanical strength to the sensor structure. In this perspective, the thickness of the wall of the casing 16, in particular in the area facing the electrodes J, can be indicatively comprised between 0.1 and 5 mm, preferably comprised between 0.6 and 1 mm, most preferably approximately 0, 8 mm; as already mentioned, the casing can be replaced by a direct overmolding of plastic material on the sensitive element, or by a generic insulation wall of the electrodes J, with a thickness similar to that indicated.

The sensor described can have any length and is therefore easily adaptable inside any container. A problem present in the application of level sensors is represented by the length of the sensor, or the height of the level to be measured, which is a variable dependent on the installation tank. In this context, the invention allows

- to use standardized electronics, i.e. a minimum number of components as possible, with a microcontroller that, with the same or almost equal number of inputs, can manage a wide range of lengths thanks to the possible connection in common or parallel of several sub- arrays of electrodes;

- to use a highly flexible circuit diagram for the various possible lengths required for the sensor, or to maintain the same microcontroller with the same number of inputs also for level sensors of different lengths. As already mentioned, by positioning for example 20 2 mm high electrodes at 2 mm distance from each other, 78 mm of sensitive area is reached for the length measurement, or 78 mm of sensitive area for a group of first electrodes; when it is necessary to increase the length of the sensitive area, it is possible to use the same number of inputs by providing second electrodes in parallel with the first: it is thus possible to maintain the same microcontroller, both for cost reasons and in terms of design. By way of non-limiting example, with ten underlayers of electrodes it is theoretically possible to reach lengths close to 780 mm. For such high lengths, however, it is possible to reduce the number of electrode sub-arrays, if a lower measurement sensitivity or resolution is acceptable at least in certain parts or levels of the sensor: for this purpose, as already mentioned, it is possible to increase the distance between the electrodes in the areas where the measurement accuracy is less significant (such as a level close to the full tank) and instead decrease this distance to have greater resolution in areas considered more critical (for example near a minimum level in the tank ).

In various embodiments described above, a mounting of the sensor 10 on the lower wall of the tank has been assumed, so that the electrode indicated with J1 represents the lowest electrode within the tank itself. Obviously, as explained, the sensor can also be mounted in correspondence with the upper wall of the tank, in which case - referring to the illustrated examples - the electrode J1 will be the one next to the distal end of the portion 20b of the support 20 and the electrode Jns will be the one next to the proximal end of this portion 20b: naturally, the control software will be set up to allow the level detection according to the sensor installation point, to further advantage of the flexibility of use.

From the above description the characteristics of the present invention are clear, as well as its advantages, mainly represented by the simplicity of realization of the proposed level sensor, by its low cost, by its precision and reliability, by its high flexibility of use and configuration. .

It is clear that numerous variants are possible for the person skilled in the art to the devices and methods described as an example, without thereby departing from the scope of the invention as defined by the attached claims.

In accordance with possible variants of implementation or application, the level sensor object of the invention can be arranged outside the container or tank containing the means subject to detection (i.e. in correspondence with an external wall or in a seat obtained in correspondence of such an external wall of the container or tank), with the array of electrodes J set against a wall of this container, with the possible interposition of the gel G or the like. In this case, the aforementioned wall of the container is suitably configured in terms of material and thickness, in order to form the layer that electrically insulates the electrodes J from the inside of the container 1. A possible example of embodiment is illustrated in figure 31, in which the The casing of the sensor body 10 a is here a casing 16 'open laterally, so that the front of the portion 20b of the support, and therefore the electrodes J, face and / or lean against a respective portion 16 "of a side wall 6 of tank 1; in the example this portion 16 ", which here forms the insulation layer which electrically insulates the electrodes J with respect to the inside of the tank 1, is thinned with respect to the rest of the wall 6, for example with a thickness included between the aforementioned 0, 1 and 5 mm.

In accordance with other variants of implementation, the casing 16 and at least part of the related characteristics described above could be included in at least one part integrated or associated with the container or tank. As already mentioned, the electrodes could be associated directly to a wall or portion of the wall of the tank (for example the portion 16 "of figure 31), which in this case would constitute both the substrate for the electrodes J and the insulation layer with respect to the tank contents.

The invention has been described with particular reference to the detection of the level of a liquid medium, particularly a urea-based additive, but as already mentioned, the sensor described can be used in combination with different substances and materials, also potentially subject to solidification. for reasons other than freezing (think of a mass of a powdery material or the like, a part of which is compacted or solidified, for example due to excessive humidity).

Claims (8)

CLAIMS 1. A level sensor for detecting the level of a medium contained in a container (1), particularly a tank, the sensor (10) comprising an array of capacitive elements adapted to be associated with the vessel (1) and comprising a plurality of electrodes (J1-Jn) on an electrically insulating substrate (20), a control circuit (23, 24) having a controller (24) with a plurality of inputs (IN1-INn) to which the electrodes (J1-Jn) are connected, the controller (24) being arranged to infer the level of the medium (L) present vessel (1) based on electrical signals acquired through the capacitive elements, at least one layer of insulation (16; 16 ") to electrically isolate the electrodes (J1-Jn) from the inside of the container (1), wherein the array of capacitive elements is contained in an electrically insulating and fluid-tight casing (16), defining said at least one insulation layer and configured to be arranged inside the vessel (1) according to a detection axis ( X), the casing defining a respective cavity (H) for receiving the electrically insulating substrate (20) carrying the electrodes (J1-Jn), wherein the cavity (H) is provided with positioning means (16a) configured to urge at least a portion (20b) of the electrically insulating substrate (20) carrying the electrodes (J1-Jn) towards said at least one insulation layer and / or a free space or gap (H1) defined between a distal end of the electrically insulating substrate (20) and a distal end of said casing (16), particularly for compensating for any dilatations. The level sensor according to claim 1, wherein the positioning means (16a) are elastically yielding and / or deformable. 3. The level sensor according to claim 1 or claim 2, in which inside the casing (16) there is a non-electrically conductive filling fluid material (G). The level sensor according to any one of the preceding claims, wherein the capacitive elements comprise groups of electrodes (J4- J20; J21-J37; J38-Jn) connected in parallel with each other, each group of electrodes being connected to a respective input (IN1-INn) of the controller (24), in which the electrodes of respective groups form on the electrically insulating substrate (20) respective sub-arrays of electrodes (J4- J20; J21-J37; J38-Jn) arranged in sequence along a detection axis (X), where given a number y of first electrodes (J4-J20) connected in parallel to second electrodes (J21-J37), y-1 electrodes are interposed between each first electrode and the relative second electrode. The level sensor according to any one of the preceding claims, wherein the housing (16) belongs to a body (10a) of the sensor (1), the material or at least one of the materials used for making the body (10a) of the sensor being analogous or chemically compatible with a material which forms at least part of the container (1), particularly to allow a tight seal between the sensor body and the container. 6. The level sensor according to any one of the preceding claims, comprising at least one of: - a sensor body (10a) defining a cavity (H) for receiving the electrically insulating substrate (20) which is provided with guiding elements (12c) for the substrate (20); - a sensor body (10a) defining an attachment portion (14) configured for sealing coupling at a respective mounting opening (5) of the vessel (1), the attachment portion having at least one seat for a relative elastic element (15; 15 ', 15 "), the attachment portion preferably including two elastic elements of the O-ring type, one of which performs sealing functions and the other performs functions of elastic mounting of the sensor body (10a ); - a sensor body (10a) at least partially formed with a printable thermoplastic material, preferably selected from a polypropylene, a high density polyethylene, a cyclo-olefin copolymer; - a sensor body (10a) having a connector (12a) with electrical terminals (21), where the electrically insulating substrate (20) has electrical contacts (22) configured for coupling or elastic engagement with the terminals (21 ) of the connector (12a), the electrical contacts (22) being in particular arranged in correspondence with through holes (20c) of the substrate (20); - a sensor body (10a) having means (12d) designed for quick coupling to a wall (2, 4) of the container (1), in particular of the type with bayonet coupling; - a sensor body (10a) having a distal end designed for releasable coupling to a vessel wall (1); The level sensor according to any one of the preceding claims, wherein the electrically insulating substrate (20): - has a first portion (20b) carrying the plurality of electrodes (J1-Jn) and a second portion (20a) carrying a circuit arrangement (23) including the controller (24), on the substrate electrically conductive tracks (25) are preferably provided for the electrical connection of the electrodes (J1-Jn), and / or - has associated at least one temperature sensor (26, 27), and / or - has associated at least one reference electrode (J1) in at least one of its distal end portion and a proximal end portion thereof, and / or - has associated a plurality of reference electrodes (J1, Jn; J18, J35) , such as at least two reference electrodes (J1, Jn) each at a respective end of an array of the plurality of electrodes (J1-Jn) or reference electrodes (J18, J35) interposed to sub-arrays of detection electrodes (J2- J37; J19-J34, J36-Jn), and / or - has associated a plurality of reference electrodes each connected (J1, J18, J35, Jn) to a respective input (IN) of the controller (24) or at least some of which are connected in parallel (J18, J35) to the same input (IN ) of the controller (24), and / or - has first electrodes of the plurality of electrodes (J1-Jn) closer to each other in the direction of a detection axis (X) than second electrodes of the plurality of electrodes (J1-Jn) , the first electrodes determining a measurement resolution of a higher level than that determined by the second electrodes. A method of controlling a level sensor of a medium (L), particularly but not exclusively according to any one of claims 1-7, the sensor (10) having an array of capacitive elements adapted to be associated with a vessel ( 1), the array of capacitive elements comprising a plurality of electrodes (J1-Jn), the electrodes (J1-Jn) being connected to a plurality of inputs (IN1-INn) of a control circuit (23, 24), in which at least one of a level, a quantity, a state and a characteristic of the medium (L) present in the vessel (1) is deduced on the basis of electrical signals acquired through the electrodes (J1-Jn) of the plurality of electrodes, the method comprising : i) carry out a calibration phase of the level sensor which includes reading values of the electrical signals relating to the electrodes (J1-Jn) in a dry condition or in air, i.e. not facing the medium (L), in order to define first values of reference threshold for detections of the at least one of the level, quantity, state and characteristic of the medium (L), and memorize the first threshold values in the control circuit (23, 24), ii) vary the first threshold values of reference in the face of measurements made during the useful life of the level sensor by means of a dedicated reference electrode (J1 ).