IMPROVED ELECTRONIC AND ELECTRO-MECHANICAL THERMOSTAT

DESCRIPTION

The object of the present invention is a thermo-regulator device for household heating appliances, in particular for storage water heaters, even more in particular with electrical power supply.

More precisely, the present invention relates to a control, regulation and safety device for such electrical storage water heaters which integrates the control and regulation features of an electronic system in a single and compact device with the safety modes of an electromechanical system.

In prior patents filed by the same applicant company (or by companies belonging to the same industrial group) as the present patent, construction solutions have already been described suitable for improving the operation of the thermostats and thermo-protectors used in electrical storage water heaters.

For an exhaustive description of the prior art in the field, reference should be made to documents EP 0651412 and EP 1652017; herein, to summarise the description, it is sufficient to note that the electrical storage water heaters include two types of thermostats, usually integrated in a single device, for controlling the temperature of the water contained in the storage tank: the first one is a regulation thermostat (thermo-regulating thermostat) suitable for keeping the water heater temperature at the value set by the manufacturer and/or selected by the user; the second one is a thermal protector thermostat suitable for cutting off the power supply to the electrical resistances when a limit temperature is reached. In this type of water heater devices, the use of a thermo-sensitive element is widespread, which extends within the storage tank consisting of a heat expanding tube, generally of brass, wherein a rod with a low heat expansion is coaxially arranged, generally made of INVAR (hereinafter, the "heat expanding tube/low heat expansion rod" pair shall be briefly referred to as "tube and rod actuator"). As the storage water temperature increases, the brass tube is subject to an elongation that also pulls the INVAR rod, constrained thereto at the outermost end. Said rod therefore performs the action of mechanical actuator on the contacts within the thermostat, cutting off/restoring the power supply to the electrical resistances.

The simplest and most renown versions provide for the tube and rod actuator to serve as sensor and actuator for the thermo-regulation only, due to the fact that a monostable elastic sheet micro-switch is operated through it, so as to cause subsequent opening closing of the contacts for the electrical power supply of the heating elements. On the other hand, the thermal protection function is performed by an actuator consisting of a known bistable thermo-sensitive bimetallic element (commonly called "clickson"), arranged within the thermostat box in a position that is sufficiently close to said thermo-expansible tube of the tube and rod actuator so that its temperature is strongly influenced by the water heater temperature through the same thermo-expansible tube, which passively serves as heat conductor. If the temperature reached by the clickson exceeds a safety value, it triggers irreversibly opening electrical contacts.

On the other hand, in the above-mentioned document EP 0651412, also the thermo- protection function is based on the tube and rod actuator, besides the thermo-regulation one. According to said document, the tube and rod actuator also acts on a bistable bimetallic disc capable of inverting the convexity of its concavity, in a non reversible manner, under the action of the rod when a limit temperature is reached, so as to cause the opening of the contacts and set the water heater to a safe condition.

On the other hand, the above-mentioned document EP 1652017 describes a thermo- regulating and thermal protecting thermostat entirely electronic.

According to prior techniques, the microprocessor of electronic thermostats, with the relevant temperature sensors, is obtained on a very narrow and elongated board, with overall dimensions similar to those of the tube and rod actuator so that it is easily seated in place of said "heat expansible tube/INVAR rod" pair in the same sheath.

The use of electronics and of the corresponding electronic sensors (generally NTC) allows an adjustment accuracy that cannot be achieved by the electro-mechanical thermostats and offers the possibility of managing a series of functions of the water heater (such as temperatures, usage mode learning, or others) which greatly improve the energy efficiency thereof.

However, besides the higher cost of a fully electronic device, the thermal protection function performed by the electro-mechanical device described before has an excellent level of reliability, meeting all the safety requirements of the regulations in force.

Therefore, it is certainly advantageous to prevent wasting the economical and operating advantages resulting from an electro-mechanical safety device made according to the prior art, but it is also appropriate to use the advances allowed by the electronic means of an electronic regulation device.

However, it is impossible to seat both the board of an electronic thermo-regulator and the tube and rod actuator of an electro-mechanical thermal protector within a same sheath of the current dimensions.

The object of the present invention is to provide a single and compact control device suitable for serving as electronic thermo-regulator and electro-mechanical thermal protector in an electrical storage water heater, thus adding up the reliability of an electromechanical system with the adjustment accuracy and the management flexibility of an electronic system.

A further object of the present invention is to allow all the temperature sensors of such devices to be seated in the sheaths of the current dimensions and currently provided for the alternative seating of either the board of an electronic thermo-regulator or of the tube and rod actuator.

This and other objects, which shall appear clear hereinafter, are achieved with the device illustrated in the following description and in the annexed claims, which constitute an integral part of the description itself.

Further features of the present invention shall be better highlighted by the following description of a preferred embodiment, in accordance with the patent claims and illustrated in the enclosed designs. Such figures should be considered as having an illustrative and non-limiting purpose, in which:

figure 1 shows a perspective view of the device according to a first version of the invention;

figure 2 shows a detailed view of what shown in figure 1;

figure 3 shows the interior of the device according to a second version of the invention;

figure 4 shows an exploded view of a device according to the invention;

figure 5 shows a perspective view of the device according to a useful possibility provided by the invention;

figure 6 shows the interior of the device according to a further possibility provided by the invention.

The teachings of the invention are particularly useful for facilitating the assembly and mounting of a thermostat with electronic thermo-regulation and electro-mechanical thermal protection in a water heater.

The teachings of the invention are further as much useful for facilitating the assembly of a thermostat with electronic thermo-regulation and thermal protection.

The features of the invention are now described using the references in the figures.

With reference to figure 1, reference numeral 1 globally indicates the device suitable for performing, at least, the thermo-regulation and the thermal protection functions, in particular of an electrical storage water heater. Hereinafter, said device 1 shall be generically referred to with the term "thermostat". It is also noted that any dimensional and spatial term (such as "lower", "upper", "underneath" and the like) refers to the position according to which the devices are shown in the annexed figures.

Thermostat 1 comprises a containment box 2 consisting of a base 2.1 and a cover 2.2, wherein an electronic board 8 is seated (see figs. 2, 3 4 or 6) seating, among the others, a microprocessor suitable for controlling at the least the thermo-regulation function.

On top of said base 2.1 of box 2, special fastens 2.6 (or equivalent electrical connectors) power one or more electrical resistances (not shown in the figure), intended for heating the water contained in the storage tank.

Box 2, at least in the preferred versions of the invention, also contains the elements intended for the safety function (not shown in the figure).

A probe holder element 3 extends from base 2.1 of said box 2.

As shown in fig. 1, said probe holder element 3, according to the main version of the invention, consists of a metal tube 3 having the function of supporting the probes intended for the electronic thermo-regulation function. However, such probe holder element 3 is also an essential element of the electro-mechanical thermal protection function.

If the electro-mechanical thermal protection is of the traditional type, ensured by a thermo- sensitive bimetallic element (clickson), said probe holder element 3 acts as heat conductor for making the clickson temperature to be strongly influenced by the water heater temperature.

On the other hand, if the electro-mechanical thermal protection is of the type taught in EP 0651412, said probe holder element 3 is the thermo-expansible tube of the tube and rod actuator.

As said, box 2 of thermostat 1 seats not only the actuating safety means, actuated by the movement of the probe holder element 3 and intended for opening/closing the electrical contacts of the circuit powering the connecting fastens 2.6 of the resistances; it also seats an electronic board 8, capable of receiving the signals coming from special electronic sensors, to then transmit them to the microprocessor the electrical appliance is provided with.

Said electronic sensors are indicated with reference numeral 5 and are arranged on the probe holder element 3. As per prior art, such electronic sensors 5 are preferably of the NTC type and are in a variable number according to the functions they should perform. A single sensor may be provided, but in general there are more than one arranged at different heights to allow actuating various improving ancillary functions or other than thermoregulation, such as the estimate of the mean temperature or of the energy content of the water heater. In any case, for simplicity of description, hereinafter reference shall be made to the version with two electronic sensors 5, as is shown in the annexed figures.

One of the technical problems solved by the present invention consists in the particular embodiment of the conductive paths and in the connecting methods of sensors 5 and of such paths to the electronic board 8.

The element that is common to all versions lies in the fact that the electrical conductive paths that connect sensors 5 to box 2 of the thermostat and/or directly to the electronic board 8, are made by silkscreen printing, a printing technique that has long been used although not in the field of thermostats.

For an exhaustive description of the silkscreen printing technique on elements usable in electrical equipment, see the prior document No. 1290381 filed by the applicant of the present patent, which describes an electrical tubular resistance provided with an external silkscreen printed surface, that is, whereon one or more layers of dielectric material are progressively laid, and an electric printed circuit obtained by the affixing of a conductive paste that forms an actual electric circuit.

Figs. 1 and 2 show a first version of the invention wherein said conductive paths 6 are silkscreen printed directly on the probe holder element 3 by a portion that goes from said sensors 5 to the lower end of said probe holder element 3 in contact with base 2.1 of the box of thermostat 1.

The further connection of the conductive paths 6 to the electronic board 8 is ensured by a conductive flexible element 7, which connects the lower end of said paths 6 to a connector 7.1 of said electronic board 8.

Such conductive flexible element 7 consists in an FPCB, that is, a "flexible printed circuit board" (for shortness, also called "flex"), that is, a flexible tape whereon one or more resistive tracks are silkscreen printed, thus obtaining a conductive path totally similar to conductive paths 6.

In this way, the signals captured by the electronic sensors 5 reach the electronic board 8 located within box 2 of thermostat 1 to be then suitably directed towards microprocessor of the water heater through a usual connector that may be inserted in the connection plug 2.3. Fig. 3 shows a second version of the connection method between sensors 5 and the electronic board 8: in this case, the probe holder element 3 does not stop in contact with base 2.1 of box 2 but it extends within the same up to coming into direct contact with the electronic board 8 or better, with a coupling 8.1 constrained on said board. In this version, the conductive paths 6, always silkscreen printed on the length of the probe holder element 3 by a portion that goes from sensors 5 to the lower end of said element, come into contact with coupling 8.1, technically consisting of a connector suitable for receiving the electrical signals carried by said conductive paths 6 by contact.

Therefore, in such second version of the invention, the conductive paths 6 made on the probe holder element 3 substantially come into contact with the electronic board 8 without the aid of a further conductor cable, such as flex 7 of the first version, the end result of transferring the signal captured by the electronic sensors 5 to said board 8 through the silkscreen printed conductive paths remaining unchanged.

In any of the above versions, the electronic sensors 5 are standard NTC or PTC thermistors, affixed by welding or, in the case of PTC, also directly made by silkscreen printing, in this last case advantageously with the same technique used for the respective conductive paths 6.

It should be noted that the advantage of the technology just described is useful for making probe holder elements 3 for exclusively electronic thermostats.

This is shown in the figures just described wherein the probe holder 3 can still consist of a tube but not necessarily heat conductive. However, the probe holder 3 may also be shaped as in figs. 5 and 6.

In fig. 5, the probe holder element 3 acts as support for a flat bar 9 whereon the electronic sensors 5 and the conductive paths 6 are made. In this case, such conductive paths 6 consist of the same flex cable 7, affixed on the entire portion of said bar 9, between sensors 5 and up to the lower end thereof in contact with base 2.1 of the box of thermostat 1.

The same flex cable 7, without interruption with the conductive paths 6, also remains as connecting element between the lower end of the "probe holder element 3-bar 9" assembly and connector 7.1 of the electronic board 8.

Fig. 6 shows a further simplified version comparable to the version shown in fig. 3 as regards the direct connection of the conductive paths 6 to the electronic board 8, but similar to the version of fig. 5 as regards the support element of sensors 5 and of said conductive paths 6.

In such configuration, in fact, the tube 3 in the meaning of probe holder element described so far is missing since sensors 5 and the respective conductive paths 6 are affixed by silkscreen printing directly on a flat bar 9, which comes into contact with the electronic board 8, more precisely with a coupling 8.1 fixed to said board. In this case, therefore, the same flat bar 9 acts as probe holder element.

Fig. 4 shows an exploded view of thermostat 1, which highlights a possible feature of the thermostat described above, consisting in the fact that pins 2.4 (suitable for mechanically constraining base 2.1 of box 2 to the underlying electronic board 8 through reciprocal holes 2.5), or at least one of them, also perform the role of electrical connectors of the same board 8 to the electrical resistances and to the network.

The same pins 2.4 also have the role of spacers for the electromc board 8 from base 2.1 of the containment box 2, so as to prevent undesired overheating of the board and create an adequate space for the components thereof, such as the regulation and/or thermal protection relay 8.2 (the opening-closing whereof controls the power supply to the resistances) and the fuses that protect the contacts of the various relays from overcurrents that would cause the gluing of the same.

As can be understood from the description of the present invention, the main advantage of thermostat 1 resides in combining the typical safety features of an electro-mechanical device with the capabilities of regulation of an electronic device in a single body, using the elements and the dimensions of a standard rod thermostat.

This peculiarity is present, in particular, in the version of the invention wherein the probe holder element 3 is represented by the tube and rod actuator: in this case, the probe holder element 3 is already provided for regularly performing the function of thermal protection but without having to provide additional support elements, it also serves as support for the electronic sensors 5 and the conductive paths 6 used for the thermo-regulation function. It is clear that several variants to thermostat 1, object of the invention, are possible for those skilled in the art, without departing from the novelty scopes of the inventive idea, as well as it is clear that in the practical embodiment of the invention the various components described above may be replaced with technically equivalent ones.