US20180266684A1

US20180266684A1 - Electro-pilotstatic valve for gas burners

Info

Publication number: US20180266684A1
Application number: US15/745,928
Authority: US
Inventors: Rosalino Usci; Michele Marcantoni; Daniele Belmonti; Roberto Onori
Original assignee: TRE P ENGINEERING Srl
Current assignee: TRE P ENGINEERING Srl
Priority date: 2015-07-23
Filing date: 2016-07-21
Publication date: 2018-09-20
Also published as: EP3325881B1; BR112018001029A2; EP3325881A1; WO2017013487A1; BR112018001029B1; ITUB20152426A1; CN107949748A

Abstract

The object of the present invention is hence an electro-actuator (1) for gas cooktops or the like, piloted by actuating means, comprising at least one safety electromagnet (4) forming part of a pilotstat, at least one cut-off means (2) of the fuel gas, substantially a sleeve provided with an outlet channel (22) and a conduit (23) of the fuel gas, of at least one safety shutter (20) whereon a pushing/pulling force (F_F) acts that operates the safety closing of said outlet channel (22), at least a service shutter (20), and a support structure (10) provided with a cavity (100) within which a stem (21) is placed sliding, whereto at least one ferromagnetic element (32) cooperating with said safety electromagnet (4) and said shutter (20) cooperating with the cut-off means (2) of the fuel gas are constrained, where said safety shutter (20) and said service shutter (20) coincide in a same shutter (20); said ferromagnetic element (32) being anchored to said safety electromagnet (4) through an anchoring force (F_P) of mutual attraction that arises when said safety electromagnet (4) is electrically powered, in particular through the flame sensor of pilotstat,

characterised in that:
said pressing/pulling force (F_F) is of magnetic nature and susceptible to be won by the command forces (F_S) exerted for the opening of said outlet channel (22) and by said anchoring force (F_P).

Description

The present invention relates to an electro-pilotstatic system for gas burners, in particular an electro-actuator for gas cooktops or the like equipped with a safety system.
Currently the prior art provides different solutions for the delivery and regulation of the fuel gas for cooktops and also contemplates different systems that ensure safety.
For example, the common cooktops are equipped with a safety system, advantageously comprising valves, which automatically stops the flow of the fuel gas to the burner in case of accidental switching off of the flame.
The most known and used solution provides the use of a linear shut-off valve mounted in series to a manual regulation valve, typically a rotary plug valve (tap).
The user, by interacting with the tap, performs a manual action that moves back the shutter of the safety valve, bringing a ferromagnetic keeper constrained thereto in contact with an electromagnet allowing the passage of gas for the ignition of the burner; said electromagnet being controlled and supplied by a flame detector.
Said flame detector generally makes use of a thermocouple placed in the proximity of the flame of the burner; in the presence of a flame said thermocouple generates a potential difference capable of producing an electric current that feeds the solenoid of said electromagnet.
The magnetic field created by the solenoid is sufficient to retain the shutter in its open position and to ensure the supply of the fuel gas to the burner.
In the event that the flame accidentally goes out, the thermocouple does no longer produce any potential difference, as a consequence it ceases the electrical supply to the solenoid of the electromagnet, which is no longer able to generate a magnetic field sufficient to retain the shutter, which under the thrust of an elastic means, such as a spring, returns to the rest position closing the valve and thus interrupting the gas flow; this avoids that in case of inadvertent switching off of the flame the gas continues to be delivered by the valve, dispersing in the surrounding indoor environment (normally kitchens or rooms for the preparation and cooking of foods and meals) with serious risks for people and things.
The electromagnet—thermocouple coupling is known as “pilotstat” and is widely used on each burner to ensure a safe use of the cooktops.
The various solutions proposed by the prior art provide to keep separate and distinct the devices adapted to the control and regulation of the gas flow from the devices adapted to safety.
Said division involves the installation of multiple components in cooktops or the like where the nature of the overall dimensions is extremely relevant and space saving is one of the objectives to be pursued for the designers and manufacturers.
Normally closed shut-off valves exist on the market, which carry out the passage of gas through a remote electrical control.
In fact, said shut-off valves are closed in the rest position, as a matter of safety, while in the working position they are constantly kept open through a continuous control signal.
This operating configuration involves a waste of energy and heating of the electrical and electronic equipment; the latter may generate over time a degradation of the insulator of the electric cables and a deterioration of the same circuit, leading to malfunctions or breakages.
The main object of the present invention is to provide an electro-actuator for gas cooktops or the like that combines in a single element both the part concerning safety and the part concerning the regulation of the flow.
In particular, the main object of the present invention is to provide an electro-actuator for gas cooktops or the like which integrates in a single element the regulation of the flow of the fuel gas and the automatic cut-off of the same in case of accidental switching off of the flame.
A further object of the present invention is to provide an electro-actuator for gas cooktops or the like which allows to feed the control and regulation devices of the gas flow only during the actuations of the same, by suspending the electrical supply once the regulation is complete.
This and other objects, which shall appear clear hereinafter, are achieved with an electro-actuator for gas cooktops or the like illustrated in the following description and in the annexed claims, which constitute an integral part of the same description.

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, purely by way of a non-limiting example, in the annexed drawing tables, in which:

FIG. 1 shows a section view of the electro-actuator according to a first embodiment of the present invention in the closed or rest position;

FIG. 2 shows a section view of the electro-actuator according to the same first embodiment of the present invention in the open or work position;

FIG. 3 shows a section view of a second embodiment of the electro-actuator according to the present invention in the closed or rest position;

FIG. 4 shows a section view of a second embodiment of the electro-actuator according to the present invention in the open or work position;

FIG. 5 shows a section view of a further executive variant of the electro-actuator according to the present invention;

FIG. 6 shows the electro-actuator according to the present invention provided with a membrane;

FIG. 7 compares two section views of the electro-actuator according to the present invention shown in the open condition and in the closed condition;

FIG. 8 shows a summary table of the parameters and operating configurations of the electro-actuator according to the present invention;

FIGS. 9a and 9b show two examples of gas valves suitable for blown burners wherein the electro-actuator according to the invention could be used.

Unless otherwise specified, in this report any possible spatial reference such as the terms up/down, front/rear, right/left etc. refers to the position in which the elements are represented in the annexed figures.
The features of the invention are now described using the references in the figures.
In relation to the figures, the electro-actuator 1 for gas cooktops or the like according to the present invention, is provided with a safety electromagnet 4, shut-off means 2 of the fuel gas, substantially a sleeve equipped with an outlet channel 22 and a fuel gas duct 23, at least one service shutter 20 and at least one safety shutter 20, cooperating with said shut-off means 2, whereon a pressing/pulling force acts that operates the safety closing of said electro-actuator 1, advantageously said pressing/pulling force being of magnetic or elastic nature.
Said service shutter and said safety shutter coincide in a same shutter 20 that performs two tasks simultaneously:

- the cut-off of the fuel gas to be sent to the burner;
- the safety closing of the shut-off means 2 of the fuel gas when the burner or the flame are switched off.

Said pressing/pulling force acts on said shutter 20 operating the safety closing of said electro-actuator 1, in particular said pressing force operates the safety closing of said outlet channel 22 of the fuel gas.
The electro-actuator 1 comprises a support structure 10, of substantially tubular shape and preferably made of non-magnetic material, at the ends whereof a safety electromagnet means 4 and a cut-off means 2 of the fuel gas, substantially a sleeve, are respectively arranged.
Inside the said support structure 10 a cavity 100 is provided within which a stem 21 provided with an element 30 sensitive to the magnetic field is placed sliding.
The stem 21, suitably controlled, operates the opening and/or closing of the shut-off means 2 of the fuel gas.
A detailed description of the figures, brought by way of a non-limiting example is provided below.
FIG. 1 shows a section of the electro-actuator 1 according to the present invention in the closed or rest position.
Inside the said support structure 10 a cavity 100 housing a bottom 101 is provided, within which a cursor 30 integral with a stem 21 is placed, said cursor 30 being sensitive to the magnetic field.
Said bottom 101 cooperates with the cursor 30 to achieve the magnetic force that operates the safety closing of the electro-actuator 1 according to the present invention.
In this construction variant said cursor 30 comprises a permanent magnet, while said bottom 101 comprises a ferro-magnet.
Nothing prevents, in accordance with alternative embodiments, that said cursor 30 may advantageously comprise a ferro-magnet, while the bottom 101 may comprise a permanent magnet, without altering the correct operation of the electro-actuator 1, or that both may comprise permanent magnets.
In general, the magnetic interaction between the bottom 101 and the cursor 30, due to the materials with which they are made and to their reciprocal position, must ensure for any condition of use and for any position of the shutter 20 or the electromagnet 4, the “normally closed” condition.
The position of the cursor 30 and the bottom 101, the materials with which they are created and the switching on and/or off modes of the burner, are thus parameters to be chosen and defined in order to ensure the “normally closed” condition of the electro-actuator 1.
Said bottom 101, comprising a disk of ferromagnetic material, is provided with a central hole 111 for the passage and the sliding of the stem 21, said stem 21 being integral with said cursor 30.
One end of said stem 21, advantageously made of non-magnetic material, is provided with at least one ferromagnetic element 32 that cooperates with the safety electromagnet means 4; the other end of the stem 21 is integral with the shutter 20.
The shutter 20 cooperates with the sleeve 2 of the fuel gas; in particular said shutter 20 opens or closes the outlet channel 22 of the fuel gas, allowing the passage of the fuel gas from the conduit 23 to said outlet channel 22, towards the corresponding burner (not shown).
The safety electromagnet 4 is advantageously controlled through the thermocouple placed in the proximity of the flame zone of the burner, according to what shown and described above with reference to the prior art.
When the burner is switched off, therefore, the thermocouple does not provide any type of electric current to said electromagnet 4, which is then de-energized and does not produce any magnetic field; in this case there is not any kind of significant interaction between the electromagnet 4 and the ferromagnetic element 32.
In FIG. 1, the electro-actuator 1 is in the closed position and the shutter 20 closes the outlet channel 22 of the fuel gas.
The closing of the electro-actuator 1 according to this variant of the invention is guaranteed by the magnetic force existing between the cursor 30 and the bottom 101; said magnetic force keeps the stem 21 fixed and stable, so as to lock the shutter 20 at the mouth of the outlet channel 22 of the fuel gas, preventing the entry to the fuel gas.
By analysing in more detail the closed configuration represented in FIG. 1 it can be deduced that the only active force is that magnetic between the bottom 101 and the cursor 30.
In fact, the electromagnet 4 is de-energized, so there are not significant attractive magnetic forces between said electromagnet 4 and the ferromagnetic element 32; the stem 21, therefore, is translated toward the sleeve 2 by the attractive magnetic force between the bottom 101 and the cursor 30.
Said magnetic force achieves and ensures the closing of the electro-actuator 1, engaging the shutter 2 at the mouth of the outlet channel 22 of the fuel gas, so as to occlude it.
FIG. 2 shows a section view of the electro-actuator according to the present invention in the open or work position.
In the figure the electro-actuator 1 is visible in the open position, i.e. with the outlet channel 22 of the fuel gas communicating with the conduit 23 of the fuel gas.
Considering FIG. 1 and FIG. 2 let us assume that the switching on of the burner of the cooktop is desired.
The user, by means of suitable actuating means (not shown), manually activates the electro-actuator 1, by translating the stem 21 towards said electromagnet 4, bringing the ferromagnetic element 32 in contact with said electromagnet 4.
The shutter 20, being positioned on the stem 21, is moved away from said outlet channel 22 of the fuel gas 22, thus allowing the gas to enter from the outlet channel 22 and reach the burner, allowing the switching on thereof.
When the flame of the burner is switched on, the thermocouple starts to generate an electric current that energizes the electromagnet 4, ensuring the magnetic coupling between said electromagnet 4 and the ferromagnetic element 32.
In fact, the attractive magnetic force between the electromagnet 4 and the ferromagnetic element 32 is greater than the attractive magnetic force present between the cursor 30 and the bottom 101; this allows to keep the electromagnet 4 and the ferromagnetic element 32 integral.
With the flame switched on the mechanical action (exerted by the user through the actuating means) that kept the electromagnet 4 and the ferromagnetic element 32 in contact is suspended, and the opening of the valve is ensured by the thermocouple, which generates the electric current necessary to keep the electromagnet 4 energized.
In the transitional period that goes from the switching on command imparted by the user and the entry into operation of the thermocouple, the passage of the gas is ensured by said mechanical action that maintains the ferromagnetic element 32 in contact with the electromagnet 4.
In case of accidental switching off of the flame, the thermocouple does not generate any potential difference, as a consequence the electromagnet 4 is no longer fed electrically and the magnetic coupling with the ferromagnetic element 32 of the stem 21 is lost; this results in the closing of the electro-actuator 1 due to the magnetic force of attraction between the bottom 101 and the cursor 30.
If wished to proceed with the voluntary switching off of the burner, the user, through suitable actuating means, uncouples the ferromagnetic element 32 from the electromagnet 4, or stops the passage of electric current to the electromagnet; also in this case the closing of the electro-actuator 1 is given by the attractive force between the cursor 30 and the bottom 101.
The closing command may further be obtained by means of a microswitch on the thermocouple circuit or through a by-pass circuit of the electromagnet 4, through which when the user closes, all or part of the electric current generated by said thermocouple passes, making the magnetic field of the electromagnet 4 so small as to allow the pressing force to close the passage of the fuel gas.
The embodiment shown in FIG. 1 and FIG. 2 described above, provides to keep the valve in the closed position through a magnetic force generated by at least one ferromagnetic element and at least one permanent magnet.
In the case just described, an attractive force that brings the cursor 30 towards the bottom 101 is employed, bringing the stem 21 to translate towards the sleeve 2 and engage the shutter 2 at the mouth of the outlet channel 22 of the fuel gas occluding it.
A construction variant (not shown) provides to employ a repulsive force.
Said configuration (valve closed in the rest condition) remains such until the user manipulates the electro-actuator 1 through the actuating means to switch on the burner of the cooktop.
In the existing electro-actuators, an elastic force is used, normally exerted by a compression helical spring in order to achieve the “normally closed” condition.
The electro-actuator 1 according to the embodiment just described, is characterised in that it achieves the “normally closed” condition through a magnetic force and uses it to ensure the closing of the outlet channel 22 of the fuel gas when said electric actuator 1 is closed or in rest condition.
The replacement of the spring with a magnetic force implies several advantages, first of all the elimination of an element subject to wear.
In fact, the spring is a component subject to constant mechanical stress, resulting in deterioration and wear of the elastic element that may lead to operating problems.
Furthermore, the spring may jam or stop compromising the safety of the valve, while the magnetic force existing between a ferro-magnet and a permanent magnet, by its nature, does not present issues of this kind.
With ref. to FIGS. 3 and 4 a second possible embodiment of the present invention is now described, illustrated by way of a non-limiting example. FIG. 3 shows a section of the electro-actuator 1 according to the present invention in the closed or rest position.
In this construction variant the electro-actuator 1 in addition to the elements already described, advantageously comprises a solenoid 33 connected to the walls of the said support structure 10 through the support element 330.
Said solenoid 33 is coaxial with respect to the support structure 10 and cooperates with the cursor 30 to achieve the closing and opening of the electro-actuator 1.
In FIG. 3, the electro-actuator 1 is in the closed position and the shutter 20 closes the outlet channel 22 of the fuel gas, as previously described (i.e., through a magnetic force).
FIG. 4 shows a section view of the electro-actuator according to the present invention in the open or work position, that is with the outlet channel 22 of the fuel gas communicating with the conduit 23 of the fuel gas.
Considering FIG. 3 and FIG. 4 let us assume that the switching on of the burner of the cooktop is desired.
The user, by means of suitable actuating means (not shown), activates the electrical supply to the solenoid 33, which immediately creates a magnetic field inside the support element 330.
Said induced magnetic field exerts a force on the cursor 30 forcing the stem 21 to translate towards the electromagnet 4, the force generated by said induced magnetic field being greater and of opposite direction with respect to the attractive magnetic force existing between the bottom 101 and the cursor 30.
The translation of the stem 21 brings the ferromagnetic element 32 in contact with the surface of the electromagnet 4 and opens the outlet channel 22 of the fuel gas.
The electrical supply to the solenoid 33, which no longer generates any type of magnetic field, is suspended when the flame is switched on, and the keeping of the valve open is ensured by the attractive magnetic force between the ferromagnetic element 32 and the electromagnet 4.
In the transitional period that goes from the switching on command imparted by the user and the entry into operation of the thermocouple, the gas passage is ensured by the solenoid 33, which continues to be fed electrically for said time interval, so as to maintain, through the interaction between the induced magnetic field and the cursor 30, the ferromagnetic element 32 in contact with the electromagnet 4.
In case of accidental switching off of the flame, the electromagnet 4 is no longer fed electrically by the thermocouple and the magnetic coupling with the ferromagnetic element 32 is lost; the closing of the electro-actuator 1 is carried out by the magnetic force of attraction between the bottom 101 and the cursor 30.
If wished to proceed with the voluntary switching off of the burner, the user, through suitable actuating means, activates the electrical supply to the solenoid 33, but with reversed polarity compared to the switching on signal, so as to generate a magnetic field in the opposite direction to the previous, or interrupting the passage of electric current in the electromagnet 4.
In this case the magnetic field induces the cursor 30 to move toward the sleeve 2, by uncoupling the ferromagnetic element 32 from the electromagnet 4, and locking the shutter 20 at the mouth of the outlet channel 22 of the fuel gas, through said magnetic force.
Said configuration, that is of closed valve in rest condition, remains such until the user manipulates the electro-actuator 1 through the actuating means to switch on the burner of the cooktop.
The electro-actuator 1 according to the present invention provides for powering the solenoid 33 only during the switching on and voluntary switching off step of the burner, while as regards the normal activity of the burner the solenoid 33 is de-energized.
Said solution allows to reduce the energy absorption of the electro-actuator 1 according to the present invention and protects from excessive heating of the electrical parts due to the long operating times.
Preferably the typical operating voltage for the solenoid 33 is substantially less than or equal to 24V in direct current and the number of solenoid coils is substantially greater than or equal to 200.
In order to further reduce heating of the solenoid 33 and to increase its operational life, it can be advantageously fed with a square wave with variable duty cycle so as to obtain the maximum movement force.
The duty cycle, or useful work cycle is the fraction of time that an entity passes in an active state in proportion to the total time examined, for example considering a square-wave signal the duty cycle is the ratio between the duration of the active signal and the total period of the signal, and serves to express how much portion of period the signal is active for.
Furthermore, the electro-actuator 1 according to the present invention allows the switching on and switching off of the burner from remote locations, because the actuating commands carried out by the user are essentially of the electrical and non-mechanical type.
FIG. 5 shows a section view of a further possible executive variant of the electro-actuator according to the present invention.
In FIG. 5 the electro-actuator 1 is in the closed position and the shutter 20 closes the outlet channel 22 of the fuel gas.
In this construction variant, the pressing force is of elastic nature and the electro-actuator 1 is maintained in its normally closed position by an elastic loading means, advantageously a compression helical spring 200.
In fact, by observing the figure it is understood that the spring 200 insists on the shutter 20 while keeping the outlet channel 22 of the fuel gas closed.
Compared to previous embodiments, the magnetic force (that keeps the outlet channel of the fuel gas closed) has been replaced with an elastic force given by said spring 200.
In this construction variant a cursor 210 is provided comprising a ferromagnetic element.
Said cursor 210 cooperates with the bottom 102, also made of ferromagnetic material, placed inside the cavity 100.
With respect to what previously described, let us assume that the switching on of the burner of the cooktop is desired.
The user, by means of suitable actuating means (not shown), activates the electrical supply to the solenoid 33, generating a magnetic field that induces the cursor 210 to translate towards the electromagnet 4, the force generated by said induced magnetic field being greater and of opposite direction with respect to the elastic force that the compression helical spring 200 exerts on the shutter 20.
The shutter 20 is moved away from said outlet channel 22 of the fuel gas, thus allowing the gas to enter from the outlet channel 22 and reach the burner.
The translation of the stem 21 brings the ferromagnetic element 32 in contact with the surface of the electromagnet 4.
When the ferromagnetic element 32 and the electromagnet 4 are in contact and said electromagnet 4 is powered by the thermocouple (or flame sensor) exposed to the flame, it is intuitive that the magnetic force existing between said ferromagnetic element 32 of the stem 21 and said electromagnet 4 is greater than the elastic force generated by the compression helical spring 200.
The closing command is obtained substantially with the annulment of the electric current generated by the thermocouple.
Alternatively the variant of FIG. 5 may provide the use of the cursor 210 only, eliminating the bottom 102, provided that said cursor 210 is made of magnetic material so as to be able to be controlled by the solenoid 33.
In short, the electro-actuator 1 according to the present invention comprises at least a pressing/pulling force that achieves the normally closed condition, interrupting the passage of the fuel gas to the burner.
Said pressing/pulling force may advantageously be of elastic or magnetic nature, according to the construction variants.
Where the pressing/pulling force is of elastic nature, the electro-actuator 1 comprises at least an elastic means, such as for example a compression spring, while in the case of pressing/pulling force said electro-actuator comprises at least one ferromagnetic element and at least one permanent magnet, suitably arranged and cooperating with each other.
In general said pressing/pulling force is susceptible to be won by the command forces exerted for the opening of said outlet channel 22 and from said anchoring force between the ferromagnetic element 32 and the electromagnet 4.
With regards to the opening and closing command of the electro-actuator 1 according to the present invention, it can be advantageously manual or electrically controlled.
In the case of manual opening and closing the user, through appropriate control means, translates the stem 21 of the valve bringing the ferromagnetic element 32 in contact with the electromagnet 32, while in the case of closing the user uncouples said elements.
The opening and closing by electric control takes place through the interaction between a cursor, sensitive to the magnetic field, and an electromagnet, advantageously a solenoid 33.
If said cursor comprises a permanent magnet the opening and closing command may be exerted through said solenoid 33, in particular through the inversion of its poles.
In the case in which said cursor comprises a ferromagnetic element, the opening of the electro-actuator 1 takes place via the solenoid 33 that pushes said cursor towards the bottom 102, while the closing command may be obtained substantially causing the annulment of the electric current generated by the thermocouple.
This can be obtained at least in two ways:

- through a single normally closed switch on the thermocouple circuit, which the user opens to cut-off the current, provided that the cooktop is equipped with a suitable certified electronics;
- through a by-pass circuit of the coil of the normally open electromagnet that the user closes diverting on it substantially all the current passing in the coil significantly reducing the magnetic field thereof.

Nothing prevents to apply these switching off modes also to the variant in which the cursor is a permanent magnet.
FIG. 6 shows the electro-actuator 1 according to the present invention provided with an interference membrane 230 placed in proximity of the stem 21 inside the conduit 23 of the fuel gas, in order to prevent the inflow of said fuel gas inside the same electro-actuator.
Advantageously said interference membrane 230 is applicable to all the executive variants described.
FIG. 7 compares two section views of the electro-actuator according to the present invention shown in the open condition and in the closed condition.
In figure the numerals of the various components are not provided in order to facilitate the reading and understanding, and advantageously the terms and the concept expressed by FIG. 7 extend to all the embodiments previously illustrated and described.
Referring then to the numerals of FIGS. 1, 2, 3, 4, 5 and 6, a legend of the terms of FIG. 7 is provided below, where:

- D is the outer diameter of the valve body (or the maximum dimension thereof if of a non-cylindrical section);
- X is the instant position of the reference (e.g., the barycentre) of the element 30, 210 with respect to a reference integral with the body of the valve (e.g., the bottom 101) that varies between a minimum value Xmin, in correspondence of which said outlet channel 22 is closed, and a maximum value Xmax, in correspondence of which said outlet channel 22 is open;
- C is the maximum stroke of the translating elements 20, 21, 30, 32, 210, between them constrained, and being C=Xmax−Xmin;
- F_Fis the force of mutual attraction between the element 30 and the bottom 101, variable as a function of the instant position X, and such that F_F=F_F _{_} _MAXwhen X=Xmin; F_F=F_F _{_} _minwhen X=Xmax, where obviously F_F _{_} _MAXis the maximum attraction force, while for F_F _{_} _minis the minimum attraction force;
- the command force Fs is the resultant on the element 30 along the direction “x” of the forces generated by the solenoid 33, that is said command force Fs is the resultant of the forces generated by the solenoid 33 acting on said cursor 30, the direction and intensity whereof depend on the sign and intensity of the current circulating through the coils of the solenoid;
- the anchoring force FP is the force of mutual attraction between the element 32 and the electromagnet 4, which arises when the flame is lit and thermocouple active; variable as a function of the instant position X.

Said force F_Fis the pressing/pulling force that operates the safety closing of said electro-actuator 1, and is susceptible to be won by the command forces F_Sexerted for the opening of said outlet channel 22 and by said anchoring force F_P. Additionally the anchoring force F_Pis such that:

- F_P=0 when the flame is switched off (electromagnet 4 not powered);
- F_P≠0 when the flame is switched on (electromagnet 4 powered) and is worth: F_P=F_P _{_} _MAXwhen X=XMAX, FP=F_P _{_} _minwhen X=Xmin, where obviously F_P _{_} _MAXis the maximum anchoring force, while for F_P _{_} _minis the minimum anchoring force. In a preferred embodiment the electro-actuator according to the present invention is characterised by the simultaneous existence of all the following conditions (where the modules of the forces must be considered):
- D≤20 [mm];
- 0.08 D<C<0.4 D;
- F_P _{_} _MAX>F_F _{_} _min;
- F_F _{_} _MAX>F_P _{_} _min;
- F_S _{_} _MAX(+)>F_F _{_} _MAX;
- (F_S _{_} _MAX(−)+F_F _{_} _mm)>F_P _{_} _MAX.

In particular, once the geometry is fixed the intensity and direction of the current being equal F_Smay be considered approximately constant as the position X varies and equal to F_S _{_} _MAX(+)when the resultant of the forces on the element 30 acts in the positive direction of the axis x (opening command of the outlet channel 22); F_S _{_} _MAX(−)when said resultant acts in the negative direction of the same axis (closing command of the outlet channel 22).
Additionally F_Smay take a positive value FS_MAX(+) and a negative value F_S _{_} _MAX(−)corresponding to the sign of the electric current that feeds the solenoid 33.
FIG. 8 shows a summary table of the parameters and possible operating configurations of the electro-actuator according to the present invention.
The table shows:

- State: indicates the state of the electro-actuator 1 and fuel gas burner that is:
  - “rest”: the electro-actuator 1 is in a normally closed position and the burner is switched off;
  - “transitional”: the electro-actuator is switching from the closed position to the open position or vice versa and the burner may be switched on if the switching on is commanded or switched off if the switching off is commanded;
  - “switched on”: the electro-actuator 1 is in the open position and the burner is switched on;
  - “switched off”: the electro-actuator 1 is in the normally closed position and the burner is switched off.
- Flame: indicates the presence of the flame to the fuel gas burner (ON the flame is present; OFF the flame is absent).
- Solenoid: indicates the electrical supply to the solenoid, being ON(+) a positive electrical supply and ON(−) a negative electrical supply of the solenoid 33.

Preferably the command ON(+) provides for the opening of the electro-actuator 1, while the command ON(−) provides for the closing of the said electro-actuator 1.
The state is explained for various operating conditions of the burner controlled by the electro-actuator 1 according to the present invention where:

- “normal switching on” indicates the switching on of the said burner and the opening of the electro-actuator 1;
- “voluntary switching off” indicates the switching off of the said burner and the closing of the said electro-actuator 1;
- “accidental switching off” indicates the switching off of the said burner and the closing of the said electro-actuator 1;
- “attempted switching on” indicates the failed switching on attempt of said burner and the closing of the said electro-actuator 1.

In short the active forces in the electro-actuator 1 may be summarised as follows:

- valve closed: only F_Fis present that carries out the normally closed;
- valve open: both F_Fand F_Pare present, where F_Pkeeps the valve open being F_P>F_F;
- F_F, F_Pand F_Sare present in the transitional.

It is clear that the combination in various ways of the variants just described may lead to further variants without departing from the scope of the invention as well as many embodiments and applications are possible.
The electro-actuator according to the invention may for example be very useful for the supply of the premix burners for cooktops, both of the atmospheric type and blown type such as those described in documents AN2014A000130, AN2014A000176, AN2015A000041, AN2015A00042, AN2015A000060, AN2015A000061 and 102015000018411.
By “premix burner” it is meant a burner in which the primary air is fed in amounts sufficient for the complete combustion without the need for the supply of secondary air on the flames.
By “blown burner” it is meant a burner in which the primary air intended to take part in the combustion is not drawn by Venturi effect but is fed into the same burner through a fan and in precisely controlled amounts. In such burners the primary air therefore enters through calibrated orifices and in many cases it is appropriate that it is fed into or intercepted simultaneously upon the feeding/interception of the gas.
FIGS. 9a and 9b show two examples of gas valves 25 suitable for blown burners and wherein the electro-actuator according to the invention, which is not shown in details, may be used.
Both figures with 21 indicate the stem whereto one or more shutters 20 are constrained that intercept the passage of gas and air from the respective distribution conduits 23 and 24 towards the outlet channel 22 to the burner.
In particular, FIG. 9a shows two valves 25 in each of which a corresponding single shutter 20 intercepts two concentric air and gas orifices while in FIG. 9b the stem 21 carries two shutters 20 dedicated the one to the interception of the gas and the other of the air.

Claims

1. Electro-actuator (1) for gas cooktops or the like, piloted by actuating means, comprising at least one safety electromagnet (4) forming part of a pilotstat, at least one cut-off means (2) of the fuel gas, substantially a sleeve provided with an outlet channel (22) and a conduit (23) of the fuel gas, of at least one safety shutter (20), cooperating with said cut-off means (2) of the fuel gas, whereon a force (FF) acts that operates the safety closing of said outlet channel (22), at least a service shutter (20), where said safety shutter (20) and said service shutter (20) coincide in a same shutter (20), and a support structure (10) provided with a cavity (100) within which a stem (21) is placed sliding, where one end of said stem (21) is provided with at least one ferromagnetic element (32) that cooperates with said safety electromagnet means (4), while the other end of the stem (21) is integral with said shutter (20); said ferromagnetic element (32) being anchored to said safety electromagnet (4) through an anchoring force (FP) of mutual attraction that arises when said safety electromagnet (4) is electrically powered, in particular through the flame sensor of pilotstat,

I. characterised in that:

said force (FF), that operates the safety closing of said outlet channel (22), is of magnetic nature and susceptible to be won by a command force (FS) exerted for the opening of said outlet channel (22) and by said anchoring force (FP);

wherein said force (FF), that operates the safety closing of said outlet channel (22), is given by the magnetic mutual attraction between a cursor (30) placed on said stem (21) and a bottom (101) placed in said cavity (100);

wherein said force (FF), that operates the safety closing of said outlet channel (22), achieves and ensures the closing of the electro-actuator (1), engaging the shutter (20) at the mouth of the outlet channel (22) of the fuel gas, so as to occlude it.

2. Electro-actuator (1) according to claim 1, wherein the instant position (X) of said cursor (30) in relation to said bottom (101) varies between a minimum value (Xmin), in correspondence of which said outlet channel (22) is closed, and a maximum value (Xmax), in correspondence of which said outlet channel (22) is open, characterised in that:

the force of mutual attraction (FF) between said cursor (30) and said bottom (101) is variable as a function of the instant position (X), and such that said force is maximum (FF=FF_MAX) when the instant position is minimum (X=Xmin); while this force is minimum (FF=FF_min) when the instant position is maximum (X=Xmax);

the anchoring force (FP) between the ferromagnetic element (32) and the electromagnet (4) is variable as a function of the instant position (X), and such that said force is maximum (FP=FP MAX) when the instant position is maximum (X=Xmax), while the said force is minimum (FP=FP_min) when the instant position is minimum (X=Xmin);

II. and characterised in that:

said maximum anchoring force (FP=FP_MAX) is greater than the minimum mutual attraction force (FF=FF_min) between said cursor (30) and said bottom (101);

said maximum mutual attraction force (FF=FF MAX) between said cursor (30) and said bottom (101) is greater than said minimum anchoring force (FP=FP_min).

3. Electro-actuator (1) according to claim 1, wherein said bottom (101) comprises a ferromagnetic element and said cursor (30) comprises a permanent magnet.

4. Electro-actuator (1) according to claim 1, wherein said bottom (101) comprises a permanent magnet and said cursor (30) comprises a ferromagnetic element.

5. Electro-actuator (1) according to claim 1, wherein said bottom (101) comprises a permanent magnet and said cursor (30) comprises a permanent magnet.

6. Electro-actuator (1) according to claim 1, where for the opening of the outlet channel (22), that is for the switching on of the burner, through a manual or automatic action, the ferromagnetic element (32) of the stem (21) with the safety electromagnet (4) are brought into contact and kept integral at least until the activation of said safety electromagnet (4) subsequent to the switching on of the burner.

7. Electro-actuator (1) according to claim 1, where for the opening or the voluntary closure of the outlet channel (22), that is for the voluntary switching on and off of the burner, the user manually couples and uncouples said ferromagnetic element (32) of said stem (21) with said electromagnet (4) through said actuation means.

8. Electro-actuator (1) according to claim 1, further comprising at least a solenoid means (33) cooperating with said cursor (30) through a suitable magnetic field, so as to achieve the opening or the voluntary closure of the outlet channel (22), that is the voluntary switching on or switching off of the burner, through electrical supply to said solenoid (33).

9. Electro-actuator (1) according to claim 8, wherein said command force (FS) is the resultant of the forces generated by the solenoid (33) acting on said cursor (30), the direction and intensity whereof depend on the sign and intensity of the current circulating through the coils of the solenoid (33); said command force (FS) being characterized in that:

to command the opening of said outlet channel (22) said command force (FS=FS_MAX(+)) is greater than said maximum mutual attraction force (FF=FF_MAX);

to command the closing of said outlet channel (22) the sum of the command force (FS=FS_MAX(−)) and the minimum mutual attraction force (FF=FF_min) is greater than the maximum anchoring force (FP=FP_MAX).

10. Electro-actuator (1) according to claim 9, where for the opening of the outlet channel (22), that is for the switching on of the burner, the user, through said actuating means, activates the electrical supply to said solenoid (33), which remains energized at least until the activation of said electromagnet (4) subsequent to the switching on of the burner.

11. Electro-actuator (1) according to claim 8, wherein said cursor (30) is a permanent magnet and for the voluntary closure of the outlet channel (22), that is for the voluntary switching off the user, through said actuating means, activates the electrical supply to the solenoid (33), reversing the polarity of said solenoid (33) with respect to that provided for the opening of the outlet channel (22), that is for the switching on of the burner.

12. Electro-actuator (1) according to claim 8, wherein said solenoid (33) can be fed with a square wave with duty cycle.

13. Electro-actuator (1) according to claim 7, wherein said cursor (30) is a ferromagnetic element and for the voluntary closure of the outlet channel (22), that is for the voluntary switching off, the user, through the actuating means, cuts off the electrical supply to the safety electromagnet (4).

14. Electro-actuator (1) according to claim 13, wherein said cut-off of the electrical supply to the electromagnet (4) takes place by closing a by-pass circuit of the electromagnet (4).

15. Electro-actuator (1) according to claim 13, wherein said cut-off of the electrical supply to the electromagnet (4) takes place through a normally closed microswitch on the circuit of the safety electromagnet (4), which the user opens to cut-off the electric current.

16. Electro-actuator (1) according to claim 1, characterised in that it further comprises an interference membrane (230) placed in the proximity of said stem (21) inside the said conduit (23) of the fuel gas.

17. Cooktop with blown burners that use the electro-actuator (1) according to claim 1.

18. Electro-actuator (1) according to claim 8, wherein said cursor (30) is a ferromagnetic element and for the voluntary closure of the outlet channel (22), that is for the voluntary switching off, the user, through the actuating means, cuts off the electrical supply to the safety electromagnet (4).

19. Electro-actuator (1) according to claim 18, wherein said cut-off of the electrical supply to the electromagnet (4) takes place by closing a by-pass circuit of the electromagnet (4).

20. Electro-actuator (1) according to claim 18, wherein said cut-off of the electrical supply to the electromagnet (4) takes place through a normally closed microswitch on the circuit of the safety electromagnet (4), which the user opens to cut-off the electric current.