FIELD OF THE INVENTION

This invention concerns a thermostat for protecting burners, of the type wherein the inflow of gas to the burner is adjusted by a safety valve supplied by a relevant thermocouple that detects the presence of a flame in the burner itself.

KNOWN PRIOR ART

The known art, especially in the field of gas burners for residential use, is to equip the burner with a safety valve, usually a solenoid electrovalve (i.e. activated through an electromagnet) that is kept in an open position to allow the inflow of the gas to the burner, thanks to the electric current generated by a thermocouple combined with the same burner and arranged at one or more of the holes of the flame spreader of that burner.

For example, the solenoid safety valve may be positioned in the inlet duct of the gas adjustment tap of the burner and may be kept in its closed position, thus preventing the inflow of the gas inside the tap and therefore inside the burner, by means of a spring whose thrust can be temporarily overcome manually by an operator when turning on the burner or by the magnetic field generated in the solenoid valve by the current generated by the thermocouple, once the burner is on.

As far as the safety of use of known burners is concerned, this solution does not prevent the possible backfiring, i.e. the presence of combustion within the burner, from damaging the burner itself or from constituting a potential risk for the user.

In the field of burners, there are various known solutions aimed to interrupt the flow of gas to a burner during emergency conditions, such as to prevent the backfiring.

For example, document JP H07-4651 A (in the name of RINNAI) describes a combustion apparatus equipped with a solution for closing a solenoid valve for the gas inflow to the combustion apparatus in the event of an outbreak of fire or whenever the temperature of the combustion apparatus should reach abnormal values.

Such system is equipped with an electric circuit that feeds a combustion sensor and a thermostat of electric/electronic type, and which are activated in the event any abnormal combustion and/or temperature values are detected in the combustion

l apparatus.

An aspect of such solution is that, since it involves the use of a thermostat of electric/electronic type, the same needs to be fed by an electric system external to the combustion apparatus and consequently cannot operate in case of electrical blackouts.

Alternatively, especially in the field of burners for gas cookers, the inflow of gas to the same burner is controlled whenever the overheating of a hob, or of a recipient heated by the burner, is detected.

Document WO2016162526A1 describes a cooker burner equipped with a safety system aimed to interrupt the delivery of gas whenever the overheating of a cooking container positioned on the burner is detected.

For this reason, the burner comprises thermoelectric means that generate voltage to address its overheating and the same are positioned in parallel to a thermocouple. By means of a diode (acting as a switch), the voltage generated by the thermoelectric means is imparted across the valve once a determined temperature threshold value has been reached and detected by the thermoelectric means.

Document US5769622A describes an apparatus comprising a burner equipped with a temperature sensor positioned in the center of the flame corona. The temperature sensor comprises a PTC (Positive Temperature Coefficient) thermistor adapted to detect the temperature of a pot positioned on the burner.

The resistance of the thermistor increases whenever the temperature increases.

Once a determined resistance threshold value is reached, the voltage across the same breaks the supply current to the winding and consequently closes the safety valve.

Document KR20140040909 A describes an apparatus comprising a control unit and a temperature sensor arranged as to penetrate through the center of the head of a cooker in order to detect the temperature of a container used to cook food on the flame.

The control unit drives a relay aimed to regulate the supply of a magnet through which a gas delivery valve is activated.

This known apparatus comprises a bimetallic switch adapted to directly detect the temperature of the container used to cook food. The switch is arranged between the relay and supply unit through which the relay is fed.

Whenever the temperature of the upper plate of the bimetallic switch falls within a predetermined temperature range, the switch will immediately cut-off the supply to the magnet controlling the valve to prevent the container used to cook food from overheating and from possibly generating soot.

However, these types of solutions do not make it possible to control the burner whenever the temperature inside the same should reach abnormal values, such as in case of undesired backfiring or other phenomena.

Purpose of the present invention is to increase the safety of use of burners by resolving the drawbacks of the aforementioned previous art.

Another purpose of the present invention is to implement a burner with a high safety of use in a simple and economic manner.

Still another purpose of the present invention is to implement a burner, especially of residential use, that prevents gas from being delivered to the burner itself both in the absence of a flame at the holes of the relevant flame spreader and whenever the same burner should overheat, such as because of backfiring.

BREIF SUMMARY OF THE INVENTION

These and other purposes are achieved by a system of a gas burner for residential use, and particularly for gas cookers, of the type in which a thermocouple detecting the external flame is combined with the burner and is connected to a safety valve through an electric circuit, and wherein the aforesaid safety valve is held in a position allowing a gas flow to the burner thanks to the electric current the thermocouple generates when the burner flames and whereby, in absence of the electric current generated by the thermocouple, it returns to a position preventing a gas flow to the burner, characterized in that a non-electric thermostat is further connected to the burner to detect the temperature of the burner itself, which thermostat is adapted to break the circuit connecting the thermocouple to the safety valve when the temperature inside the burner exceeds a predetermined threshold.

An advantage of such embodiment is that the same makes it possible to intervene on the supply of the burner in the presence of phenomena that could lead to an abnormal increase in temperature within the burner.

Furthermore, such solution does not require connecting the thermostat or safety valve to an external electric supply line and is thus not affected by any blackouts. Note that the expression "connected for the detection of the temperature of same burner", used with reference to the link between the thermostat and burner, herein means that at least the part sensitive to the temperature of the aforementioned thermostat is applied to the structure of the burner, such as to the cup or body or mixer of the burner, or that it is also applied inside the burner itself in order to directly detect the temperature of the latter.

Likewise, as will be clear for the person skilled in the art, the expression "nonelectric thermostat" denotes that the thermostat used is of mechanic type, such as a fluid expansion thermostat.

According to a preferred aspect of the present invention, the gas burner system comprises at least one mixer with Venturi effect (Venturi mixer) obtained inside the burner itself and wherein the non-electric thermostat is arranged at one of the ends of the mixer with Venturi effect, said non-electric thermostat being configured to interrupt the circuit that connects the thermocouple to the safety valve whenever the temperature inside such mixer with Venturi effect exceeds a predetermined threshold.

An advantage of such embodiment is that the thermostat is positioned in an optimal manner with regard to the detection of the temperature inside the burner.

Preferably, the non-electric thermostat comprises a bulb fastened to the burner and wherein such bulb contains a fluid, such as liquid, adapted to be expanded depending on the temperature.

In this case, the expansion of the fluid, generally channeled within a duct of reduced dimensions, may make it possible to act mechanically on the electric circuit connecting the thermocouple to the safety valve in order to break it whenever the burner reaches a certain temperature.

As already mentioned, an advantage of such embodiment is that it allows the thermostat to operate even in the absence of electric current.

Preferably, the bulb is equipped with a bottom wall directed towards one of the ends of the mixer of Venturi type.

An advantage of such embodiment is that, in this manner, the bottom wall of the bulb is directly affected by the internal temperature of the mixer.

Preferably, the fluid adapted to be expanded depending on the temperature is oil.

According to a preferred embodiment of the invention, as already mentioned, the non-electric thermostat provides an expandable element configured to break the circuit that connects the thermocouple to the safety valve whenever the fluid contained in the bulb is subject to an expansion resulting from the temperature inside the burner when the aforementioned temperature exceeds a predetermined threshold.

According to another embodiment of the invention, the non-electric thermostat is configured to break the circuit that connects the thermocouple to the safety valve by acting, through its own expandable element, on a normally closed interrupter positioned in series to the thermocouple.

An advantage of such embodiment is that the same allows the burner to operate under normal conditions, and that it can nonetheless intervene on the supply of the burner in the presence of phenomena that could lead to an abnormal increase in temperature within the burner.

According to another alternative embodiment of the invention, the non-electric thermostat is configured to break the circuit that connects the thermocouple to the safety valve by acting, through its own expandable element, to change the position of a shunting switch positioned in series to the thermocouple.

An advantage of such embodiment is that it makes it possible to apply electrical circuits fed by the thermocouple to the burner and that operate whenever the temperature inside the burner exceeds a predetermined threshold.

According to another embodiment of the invention, the position of the shunting switch, achieved through the effects of the non-electric thermostat, allows a warning light to be switched on.

An advantage of such solution is that it makes it possible to advise a user of the presence of any anomalies inside the burner.

Still according to another embodiment of the invention, the non-electric thermostat is configured to operate at predetermined temperature thresholds ranging between 250°C and 400°C.

An advantage of such embodiment is that the predetermined temperature threshold can be selected, depending on the applications, to ensure that the non-electric thermostat intervenes in case of temperatures exceeding those determined for normal operations (even under particularly serious conditions), although lower than those determined for abnormal operations and that may damage the burner and/or its attachments and hob.

Other characteristics of the invention can be deducted from the dependent claims.

BREIF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the invention will be evident by reading the following description provided for illustration purposes and without limitation, with the aid of the figures illustrated in the attached tables, wherein:

• figure 1 is an axonometric view of a burner system provided with the thermostat according to an embodiment of the invention;

• figure 2 is an axonometric view, partly in section, of the burner system of figure 1 ;

· figure 3 is an axonometric view of a set of elements associated to the burner system of figures 1 and 2;

• figure 4 is a schematic view of the main elements of figure 3;

• figure 5 is a schematic view of a burner system according to another embodiment of the invention;

· figure 6 is a schematic view of a burner system according to still another embodiment of the invention;

• figure 7 is a schematic view of a self-reset system applicable to the burner system; and

• figure 8 is a schematic view of a variant of the self-reset system applicable to the burner system.

DETAILED DESCRIPTION OF SOME EMBODIMENT OF THE PRESENT INVENTION

Referring at first to figure 1, a burner for gas cookers, globally denoted with the numeral reference 10, is depicted and comprises at least one Venturi mixer 13 (more visible in the section of figure 2) obtained inside the burner 10.

In particular, the burner 10 herein illustrated, as shown by way of example in the scheme of figure 4, is of the type comprising a burner cup 11 aimed to be constrained below a hob (not shown) and equipped with a Venturi mixer 13 of the type with axial development, on which there is an intermediate body 12 equipped with a distribution chamber and a plurality of flame spreaders adapted to define two or more flame coronas 60, which are closed by their relevant upper covers. A similar burner may, for example, be achieved through the process described in EP2712334B.

Note that, although herein making reference to a similar type of burner, any other gas burner for residential use, such as of the type equipped with a radial Venturi mixer (such as in DE3123751 A) and/or equipped with only one flame corona, may be used for the implementation of the present invention.

Returning back to the equipment here illustrated, a valve tap 55, i.e. a tap equipped with a safety solenoid valve, connects the burner 10 to a gas supply tube 90 and allows, through an outlet 52, the flow of gas into a duct 54 connected to the gas inlet 53 of the mixer 13 of the burner 10.

A thermocouple 30 is combined with the burner 10 and connected, by means of an electric circuit 40, to a safety valve 50.

The thermocouple 30 is positioned at a flame corona 60 of the burner 10.

The electric circuit 40 comprises an insulated cable 32 that goes from a hot junction 37 of the thermocouple 30 and that is connected, by means of a normally closed interrupter (NC) 70, to a branch 33 of the circuit 40, said branch 33 being in turn connected to the safety valve 50 or to the solenoid activating the relevant shutter of such valve 50.

A second branch of the electric circuit 40 comprises a bare grounded cable 34 connecting the thermocouple 30 to the safety valve 50.

Generally, the safety valve 50 is held in an open position to allow the flow of gas to the burner 10, such as by means of an electromagnet (actuating solenoid) connected to the electric circuit 40 and acting on a shutter of the valve 50, thanks to the electric current generated by the thermocouple 30 in the presence of a flame on the burner 10.

As known instead, whenever there is no flame on the burner, the electromagnet

(solenoid) is not solicited and a spring brings the shutter of the valve 50 in closed position to block the flow of gas to the burner 10 and to avoid undesired gas leaks.

According to an aspect of the invention, the burner 10 is also combined, or connected, with a non-electric thermostat 20 that allows the temperature of the same burner 10 to be detected and is also configured to interrupt the circuit 40 that connects the thermocouple 30 to the safety valve 50 whenever the temperature T inside the burner 10 exceeds a predetermined threshold Ts.

The non-electric thermostat 20, or of a mechanical type, has its own section sensitive to temperature directly fastened to a component of the burner 10, such as to easily detect the temperature thereof, and preferably the non-electric thermostat 20 is positioned at one of the ends of the mixer 13 (shown, for example in figures 1 and 2) and is configured to interrupt the circuit 40 that connects the thermocouple 30 to the safety valve 50 whenever the temperature T inside the mixer 13 exceeds a predetermined threshold Ts.

Note that, although in the embodiment illustrated herein the non-electric thermostat 20 is positioned at an end of the Venturi mixer 13, such non-electric thermostat 20 may alternatively be arranged in any of the other positions on the cup or body of the burner 10 that allows the temperature inside such burner 10 to be effectively detected.

Preferably, the non-electric thermostat 20 comprises a bulb 24 fastened to the burner 10, such as by means of a flange 15 fastened to the cup 11 of the burner 10, for example by means of screws 16, and wherein the bulb 24 contains a fluid adapted to be expanded depending on the temperature T.

In particular, according to a preferred aspect of this invention, the bulb 24 of the non-electric thermostat 20 is equipped with a bottom wall 25 facing one of the ends of the Venturi type mixer 13.

As particularly shown in figures 2 and 4, the bottom wall 25 of the bulb 24 of the non-electric thermostat 20, in the particular embodiment of the invention herein illustrated, is arranged at that surface, or component (such as a closure cap of the Venturi mixer 13), of the cup 11 of the burner 10 towards which the flow of the gas- primary air combustible mixture coming out of the Venturi mixer 13 heads before being directed towards the distribution chambers and the relevant flame spreaders of the body 12 of the burner 10.

Preferably, the fluid contained inside the bulb 24 and adapted to be expanded depending on the temperature is oil.

As shown in figures 3 and 4, the non-electric thermostat 20 provides a capillary tube 22 ending with an expandable bellow portion 26.

Such a configuration makes it possible to interrupt the circuit 40 that connects the thermocouple 30 to the safety valve 40 when the fluid contained in the bulb 24 is subject to expansion as a result of the temperature T inside the burner 10 when the aforementioned temperature T exceeds a predetermined threshold Ts.

In particular, in the event of an abnormal increase in the temperature T inside the burner 10, the fluid contained in the bulb 24 of the non-electric thermostat 20 expands and, through the capillary 22, reaches the expandable bellow portion 26 and the latter acts on the normally closed interrupter (NC) 70 to open it and thus to open the branch of the electric circuit 40 that connects the hot junction 37 of the thermocouple 30 to the safety valve 50.

In this case, the electromagnet (solenoid) of the valve 50 is no longer solicited and the spring brings the shutter of the valve 50 in a closed position to interrupt the flow of gas to the burner 10 and to protect it from other increases in temperature.

In a variant of the invention, illustrated in figure 5, the circuit 40 comprises, instead of the normally closed interrupter (NC) 70, a shunting switch 80 positioned in series to the thermocouple 30.

In this case, the non-electric thermostat 20 can act, in the event of abnormal increase in the temperature T inside the burner 10, on the shunting switch 80 so that the thermocouple 30 feeds the additional branch 71 of the circuit, the branch 71 being, for example, connected to a warning light 72 that signals an anomaly occurrence.

Even in this case, the changed position of the shunting switch 80 ensures that the electromagnet of the valve 50 is no longer solicited and that the spring brings the shutter of the valve 50 in a closed position to prevent the flow of gas to the burner 10.

In another variant of the invention, illustrated in figure 6, the non-electric thermostat 20 is configured to activate an auxiliary circuit 76 by an auxiliary switch 75 intervention. In particular, the auxiliary circuit 76 can provide an auxiliary supply 78 adapted to feed a warning light 72.

Also in this case, the non-electric thermostat 20 may act, in case of abnormal increase in the temperature T inside the burner 10, on the auxiliary switch 75 to activate a warning light 72 that signals an anomaly occurrence.

In the preceding examples, the term warning light means any type of known optical and/or acoustic detector.

Preferably, the non-electric thermostat 20 is configured to operate at predetermined temperature thresholds Ts ranging between 250 °C and 400 °C.

The temperature threshold is preferably established so that the non-electric thermostat 20 can intervene at higher temperatures than the normal operating temperatures (even in case of particularly serious conditions), although lower than those of abnormal operations, such as resulting from the ignition at the injector under to top of the hob, which can damage the burner and/or its accessories and the hob.

Still according to the invention, both the normally closed interrupter 70 and the auxiliary switch 75, as well as the shunting switch 80, can be equipped with a self- reset system 90, 90' that allows the same to return to their initial position whenever the temperature T inside the burner 10 drops under such a Tf threshold value to reset the initial conditions of the oil contained in the bulb 24 of the non-electric thermostat 20.

The self-reset system 90 may be automatic, such as by means of a spring 92 of appropriate dimensions, as illustrated in figure 7.

In alternative, the self-reset system 90' may be manual, such as by means of a reset button 94, as illustrated in figure 8.

Naturally, in both cases described, the safety valve remains closed because the thermocouple does not feed it since the flame of the burner is turned off.

Therefore, the effect of the self-reset system 90, 90' is only to turn on the burner again, but never automatically or without the intervention of the operator.

Generally, once confirmed that the burner 10 is turned off, such as by means of the switching on of the warning light 72, the operator of the same burner must verify the causes that led to the intervention of the non-electric thermostat 20 and thus to the turning off of the burner 10 operating under abnormal conditions. After having identified and resolved the problem, both in case of automatic 90 and manual 90' self-resets, the operator may turn on the burner 10 again. Whenever the causes have been resolved, the burner 10 will operate normally again, otherwise the thermostat 20 will intervene again each time an anomaly will arise.

Furthermore, the auxiliary circuit 76 provides, in alternative or in addition to the warning light 72, any other warning means, such as a beeper or the activation of a display.

Obviously, modifications or improvements may be added to the invention as described as a result of contingent or particular motivations, but without deviating from the scope of the invention claimed hereunder.