GB2443046A

GB2443046A - Method for Controlling a Valve for a Fluid.

Info

Publication number: GB2443046A
Application number: GB0716871A
Authority: GB
Inventors: Valerio Cascio; Fortunato Nocera; Lorenzo Morbidelli
Original assignee: Indesit Co SpA
Current assignee: Whirlpool EMEA SpA
Priority date: 2006-09-01
Filing date: 2007-08-30
Publication date: 2008-04-23
Anticipated expiration: 2027-08-30
Also published as: GB2443046B; ITTO20060628A1; GB0716871D0; DE102007040698A1

Abstract

A method for regulating a valve (1, fig.1) for a fluid, such as fuel gas, which is controlled by an electric signal input (S, fig.1), as a function of an electric parameter V of said electric signal (S), in particular voltage or current; the valve is of a type such that when the value of said parameter is below a lower threshold VP 1 said valve is fully closed/open, and when the value of said parameter is above an upper threshold VP2 said valve is fully open/closed; in order to set a desired open condition of the valve between said fully closed condition and said fully open condition, a variation of said electric signal is accomplished so that the value of said electric parameter corresponds, at least for an instant, to approximately said lower threshold ( and/or approximately said upper threshold. Thus, the valve is controlled with built in calibration, eliminating any hysteresis errors. Preferably, a piezoelectric valve is used in a household cooker appliance.

Description

METHOD FOR CONTROLLING A VALVE FOR A FLUID, AND

HOUSEHOLD APPLIANCE USING SUCH METHOD

DESCRIPTION

The present invention relates to a method for controlling a valve for a fluid, in particular for fuel gas, as well as to a household appliance using such method.

Gas cooking appliances, in particular gas cooking tops, with automatic valves are not widespread on the market, although this typology of household appliances is accepted by the applicable regulations.

In such household appliances, the regulation of the gas supplied to a burner takes place through an automatic valve, i.e. a type of valve having a shutter which is not controlled directly and manually by the user, but through an actuator being typically controlled by means of electric signals; by.acting on a knob or a slider and on push-buttons of a control panel of the cooking top, the user sets the desired flame level (which is related to the heat level provided by said burner, to the valve opening degree and to the quantity of gas flowing through the valve); the control panel is connected to a cooking top electronic control system which sends suitable electric signals to the valve, which is thus regulated (i.e. opened) to such an extent as to obtain the burner flame level set by the user.

Of course, it is important that a certain user setting always provides substantially the same flame level.

The Applicant realized that with many types of automatic valves, in particular with piezoelectric valves, identical control signals do not produce the same width of the valve opening. In piezoelectric valves, the phenomenon which mainly contributes to this problem is the hysteresis of the piezoelectric actuator during its movement in both directions.

Aiming at solving this problem, known regulation methods use feedback information about the valve opening condition, based on which the control system changes the control signal in order to obtain the flame level set by the user. However, these regulation methods suffer from the drawback that they require special components which increase the complexity and cost of the system, thus being hardly acceptable for use in consumer products like household appliances.

The general object of the present invention is to provide a method for regulating a valve for a fluid, in particular for fuel gas, in an accurate manner without using neither the valve opening condition nor the quantity of gas flowing through the valve as feedback information.

A first particular object of the present invention is to provide a method which can be easily implemented in general and in a gas cooking top in particular.

A second particular object of the present invention is to provide a reliable method.

A third particular object of the present invention is to provide a method which does not require substantial modifications to the valve structure.

These and other objects are achieved by the method having the features set out in the appended claims, which are intended as an integral part of the

present description.

The present invention is based on the idea of "calibrating" or "resetting" the valve at each regulation operation.

In particular, at each operation of regulation the valve is first supplied with electric signals that substantially bring it to a predetermined open or closed condition which is certain and constant in time, and is then supplied with electric signals that bring it to the desired open condition. In this manner, the obtained open condition will be essentially identical to the desired one.

This idea has proven to be particularly effective for those valves having a piezoelectric actuator subject to motion hysteresis, and especially for those piezoelectric valves which are particularly suitable for use in gas cooking appliances.

According to a further aspect of the present invention, it also relates to a gas cooking household appliance.

The present invention will become more apparent from the following description and from the annexed drawings, wherein: Figs.l show, in a very schematic manner, a piezoelectric automatic valve in the closed condition (Fig.1A) and in the open condition (Fig.IB), Fig.2 shows characteristic curves of the valve of Figs.1, Fig.3 shows a very schematic view of a valve similar to that of Figs.I, but implementing a teaching according to the method of the present invention, and Fig.4 shows characteristic curves of the valve of Fig.3 in the same scale as Fig.2.

Said description and said drawings are to be considered as non-limiting

examples.

Since the valves of Fig. I and Fig.3 are very similar, hereafter the same reference number will be used for the same components.

In Figs.l and Fig.3, the valve is designated as a whole by reference number Reference number 2 designates a piezoelectric element acting as an actuator of a regulating device 3 of valve 1; 31 designates the shutter of valve 1, belonging to regulating device 3; 32 designates a stem of the regulating device, included in regulating device 3 of valve 1.

Shutter 31 and stem 32 are rigidly joined together, thus forming regulating device 3, which is pushed by actuator 2.

Actuator 2 receives an electric signal S through two electric leads; actuator 2 is so conceived that, when a direct electric voltage is applied as an S signal, it will curve downwards (note the difference between Fig.IA and Fig.IB) and regulating device 3 will move downwards accordingly; the greater the amplitude of the voltage signal S, the more actuator 2 will curve; actuator 2 is subject to high motion hysteresis.

The valves of Fig. 1 and Fig.3 comprise a hollow body 6 having a gas inlet duct 7 and a gas outlet duct 8. The cavity of body 6 is divided by a rigid separator 4 into an upper outlet cavity 61 and a lower inlet cavity 62; inlet duct 7 ends in body 6, in particular in inlet cavity 62, while duct 8 starts in body 6, in particular in outlet cavity 61. Separator 4 has an aperture 40 (a flared hole) allowing the gas to flow from cavity 62 to cavity 61.

Shutter 31, for example having a cone-shape, is adapted to shut aperture 40 of separator 4 by perfectly coupling thereto, thus ensuring tightness.

Body 6 of the valve of Figs. 1 has a hole in its upper portion which allows stem 32 to slide without any substantial gas leakage from chamber 61.

Fig.1A shows a situation in which the S signal has a null voltage value (or a value below the minimum design voltage value); in this situation, the valve is "fully closed" because shutter 31 is shutting aperture 40; this is the idle or inoperative condition of the valve.

Fig.IB shows a situation in which S signal has the maximum design voltage value; in this situation, the valve is considered to be "fully open" because shutter 31 is far below aperture 40 and therefore cannot prevent the gas from flowing from chamber 62 to chamber 61.

An elastic element 5, in particular a spring, may also be provided in order to obtain or facilitate the return of the valve I to its idle or inoperative condition; in the cases shown in the examples of Fig. l and Fig.3, the downward motion of regulating device 3 is obtained through actuator 2, whereas the upward motion of regulating device 3 is obtained through elastic element 5. This elastic element may show some inertia of motion which may increase over time; however, this phenomenon will not hereafter be taken into account.

The operation of valve I of Figs.1 can be understood by referring to the exemplifying curves of Fig.2; in these curves, the X axis indicates the voltage V of the signal S applied to element 2, while the Y axis indicates the gas flow F through valve I, which is related, though in a non-linear manner, to the opening degree of valve I. Any point of the curve between the origin of the axes and point PI corresponds to the condition of Fig. IA, i.e. a "fully closed" valve 1; in fact, when the voltage of the signal S is not high enough to overcome the elastic force of spring 5, shutter 3 1 will stay inserted in aperture 40, thus sealing it.

The voltage value corresponding to point P1 is approximately 50 Volt.

Point P2 corresponds to the condition of Fig.lB, i.e. a "fully open" valve 1.

The voltage value corresponding to point P2 is approximately 250 Volt.

Assuming that a signal S having a voltage value starting from zero and growing gradually over time is applied to element 2, the characteristic curve to be considered will be the lower curve shown in Fig.2. As mentioned, up to a value of approximately 50 Volt shutter 31 cannot move because of spring 5; between approx. 50 Volt and approx. 100 Volt, the downward motion of shutter 31 is very small (almost null) due to the hysteresis of element 2; at this point, shutter 31 begins moving downwards; between approx. 100 Volt and approx. 150 Volt, the relationship between voltage and flow is more than linear; between approx. 150 Volt and approx. 200 Volt, the relationship between voltage and flow is substantially linear; between approx. 200 Volt and approx. 250 Volt, the relationship between voltage and flow is less than linear; over approx. 250 Volt, no perceptible increase in flow takes place as voltage increases.

Once point P2 has been reached, a signal S having a voltage value which decreases gradually to zero over time is applied to clement 2; the characteristic curve to be considered will then be the upper curve shown in Fig.2. The first 50V increase (i.e. up to approx. 200 Volt) determines a very small (almost null) upward movement of shutter 31 because of the hysteresis of element 2; at this point, shutter 31 begins moving upwards; the process will then proceed with a sequence consisting of a section with a more than linear slope, a section with a substantially linear slope, and a section with a less than linear slope ending at point P1 at approx. 50 Volt, where valve 1 is fully closed; as already mentioned, with lower voltage values valve I will stay closed; it is worth pointing out that, in this second characteristic curve, the linear section is comprised between approx. 100 Volt (point B) and approx. 150 Volt (point A).

It will now be assumed that valve I is in a condition corresponding to point C, and therefore that the signal S has a voltage value of 125 Volt; if the voltage of signal S is decreased to 100 Volt, the valve will enter a condition corresponding to point B and will follow the section comprised between C and B of the second characteristic curve; if the voltage is increased to 150 Volt, the valve will not follow the section comprised between C and A of the second characteristic curve, but will follow a section of a third characteristic curve which is intermediate between the first and the second ones (see Fig.2).

Said third characteristic curve always ends at point P2. This remark applies to all characteristic curves followed by valve I due to an increase in the voltage V of the signal S. Likewise, all characteristic curves followed by valve I due to a decrease in the voltage V of the signal S will end at point P1. This is the reason why the method according to the present invention is fully effective even in the presence of hysteresis.

The method according to the present invention is therefore suitable for regulating a valve for a fluid, in particular for fuel gas, controlled by an electric signal sent to a control input thereof as a function of the value of an electric parameter of said electric signal, in particular voltage or current; the valve is of a type such that when the value of said parameter is below a lower threshold (e.g. VPI in Fig.2) said valve is fully closed or open, and when the value of said parameter is above an upper threshold (e.g. VP2 in Fig.2) said valve is fully open or closed (as opposed to the previous case).

In general, according to the method of the present invention, in order to set a desired open condition of the valve between said fully closed and fully open conditions, a variation of the electric control signal is accomplished so that the value of said electric parameter corresponds, at least for an instant, to approximately said lower threshold (VP1 in Fig.2) or approximately said upper threshold (VP2 in Fig.2).

Referring to the example of Fig.2, it can be said in less rigorous terms that whatever condition the valve is in (whether it is fully closed, fully open or partially open), according to the invention the valve can only be brought to a different condition after having been brought to a condition substantially (i.e. not necessarily accurately) corresponding to point P1 or P2.

This provides, with sufficient accuracy, the characteristic curve that will be followed by the valve after such a "reset" or "calibration" action with subsequent changes in the electric control parameter, i.e. the control voltage V in the example of Fig.2.

With reference to the example of Fig.2, it can be said in less rigorous terms that the valve will substantially always follow the upper characteristic curve when point P2 is used, and the lower characteristic curve when point P1 is used.

For example, if the valve is open to such an extent that a gas flow corresponding to point C can flow through it, and the user wants to open the valve more in order to obtain a flow corresponding to point A, a control voltage corresponding to approx. VP2 (possibly even exceeding said value of 250 Volt) will first be applied to the valve in order to force it into the condition corresponding to point P2, and then a control voltage of approx.

Volt will be applied to the valve in order to ensure that the characteristic curve followed by it will be the upper one shown in the diagram, thus ensuring that the valve will be set to the condition corresponding to point A; this means that, when the valve must be opened a little more, it will first be opened completely for a short period of time.

On the contrary, if for example the valve is open to such an extent that a gas flow corresponding to point C can flow through it and the user wants to open the valve less in order to obtain a flow corresponding to point C, the method described above in general terms provides for bringing the valve first to a condition corresponding to point P2 and then to a condition corresponding to point C. However, regulating times may be reduced in this case by going directly from point C to point B. It is apparent that the above considerations about the characteristic curves and about the states and state changes of the valve, more in particular of the actuator thereof, are not to be understood in a strictly mathematical sense but within the limits of technical implementations of these physical principles.

It is clear from the above description that the method disclosed herein in general terms may also not be applied to all regulations of the valve, but only to those regulations which would imply deviations from the predefined characteristic curve.

The method according to the present invention therefore requires that one or two characteristic curves be identified and that the regulation of the valve be carried out by always using said one or said two characteristic curves; of course, this is true within reasonable technologic bounds.

Studies and tests carried out by the Applicant have shown that it is preferable that null values of the electric parameter of the control signals (in particular null control voltage or current) correspond to a fully closed condition of the valve (as in the example of Fig.2); in such a case, in fact, in the event of a power failure the valve will stay closed, and thus any risks of gas leaks will be easily avoided.

For regulation purposes, one may use only the lower threshold (VP1 in Fig.2), only the upper threshold (VP2 in Fig.2) or both thresholds (VPI and VP2).

The use of both thresholds (VPI and VP2) can be related to different regulation strategies. A first strategy may use just one threshold, i.e. the closest one; according to a second strategy, at each regulation the control signal is first decreased to the lower threshold and then raised to the upper threshold; according to a third strategy, at each regulation the control signal is first raised to the upper threshold and then decreased to the lower threshold; there are also strategies providing for the control signal to have at least for an instant a value corresponding to the upper threshold (VP2) and/or to the lower threshold (VP1) cyclically more than once.

When using the lower threshold (VPI) for the regulation, it must be remarked that it substantially corresponds to a fully closed condition of the valve, i.e. null gas flow. In such a case, in order to avoid extinguishing the flame and having to put it on again (which would not be acceptable for the user), one may use a very short regulation time and/or exploit the gas accumulated in the ducts downstream of the valve and in the burner chambers.

When using the upper threshold (VP2) for the regulation, it must be remarked that it substantially corresponds to a fully open condition of the valve, i.e. maximum gas flow. In such a case, in order to prevent the burner from blazing during the regulation (which would not be acceptable for the user), one may use a very short regulation time.

Although for regulation purposes the threshold values may be exceeded (e.g. voltage values higher than VP2 and/or voltage values lower than VP 1), this will lead to a longer regulation time and possibly also to greater stress on the actuator, in particular of the piezoelectric element; therefore, it is preferable to keep to the threshold value, approximately (a little more or a little less than).

As mentioned, the regulation of the valve implies a large variation of its control signal (and, accordingly, also of the gas flow and flame level) even for small regulation differences; also in the light of the above considerations, said variation should therefore last for a time shorter than a predetermined time, in particular approx. 5OmS and more preferably approx. lOmS, so that the user can hardly notice it at all.

The variation corresponds to a final value of the parameter of the valve control signal, which is determined on the basis of at least one characteristic curve of the valve itself; the variation is preferably accomplished on the basis of only one or two predetermined characteristic curves of the valve; with reference to Fig.2, said two characteristic curves are the upper curve and the lower curve. When two characteristic curves are used, two threshold values (VP! and VP2) will be used as well.

The above-described method has been conceived and is particularly suitable for a valve comprising a movable shutter driven, either directly or indirectly, by an electrically controlled piezoelectric actuator.

It is also suitable and particularly advantageous when applied to a valve wherein the shutter is driven, either directly or indirectly, through an element subject to motion hysteresis, e.g. the above-mentioned piezoelectric element.

The valve of Fig.3 differs from the valve of Figs. I essentially in that the top wall of body 6 is not rigid; said wall consists of a diaphragm 9, e.g. a membrane made of an elastic material and circular or square in shape. In particular, said diaphragm 9 is so shaped that its area is enlarged; in fact, the drawing clearly shows the bends around the stem 32.

Diaphragm 9 is secured in a substantially tight manner to the walls of the body 6 and to the stem 32; due to its elasticity, it allows the stem 32 and thus the whole regulating device 3 of valve I to move, in particular vertically, at the same time preventing any gas in chamber 61 from flowing out, except through duct 8.

In order to understand the effect provided by diaphragm 9, it is necessary to observe valve 1 of Fig.3 in operation.

When valve I is closed, the pressure in chamber 61 corresponds to the pressure downstream of duct 8 (in substance, downstream of the burner, not shown), i.e. to the atmospheric pressure; the very same pressure is also found outside body 6; in this condition, the forces exerted outside and inside the diaphragm are the same, so that the diaphragm does not transmit any force to stem 31 and thus to whole device 3. When the valve begins to open, i.e. when device 3 begins to go down, the pressure in chamber 61 rises a little, so that diaphragm 9 is subjected to a small upward force which is directly proportional to its area and to the pressure difference between chamber 61 and the atmospheric pressure; said force is applied upwards to device 3, and therefore tends to counter the downward force exerted by element 2. When the valve is fully open, the pressure in chamber 61 is at the highest level and produces the greatest counteracting force tending to shut the valve again.

When designing diaphragm 9, it must be taken into account that the pressure in gas pipe typically exceeds the atmospheric pressure by just 20-30 mBar.

It is for this reason that it is normally necessary to enlarge the area of diaphragm 9 in order to fully use its resistant effect; in general, and in particular for valves connecting to V4in. GAS piping, the extension of diaphragm 9 has one characteristic dimension (diameter or side) comprised between 10mm and 30mm, preferably between 15mm and 20mm.

Diaphragm 9 involves a modification of the characteristic curves with respect to the previous case (Fig.! and Fig.2); Fig.4 shows two of them by

way of example.

Said curves are longer to the right (since a higher voltage is required to open the valve due to the resistant force exerted by the diaphragm), and therefore are less steep and more linear.

Thanks to this measure, the regulation of the valve is carried out much better and the regulation method is even more effective. However, said measure is also valid in itself, since the use of diaphragm 9 (as described above) is in any case advantageous for the purpose of obtaining a better regulation of a valve.

In general, said measure can be summarized by saying that, in order to improve the regulation method, a resistant action which is proportional (linearly proportional or non-linearly proportional) to the pressure of the fluid downstream of the shutter is applied mechanically (either directly or indirectly) to the valve shutter.

More in particular, the resistant action is exerted by a diaphragm, in particular an elastic membrane (appropriately shaped and sized), which is adapted to confine said fluid within the valve and which is coupled mechanically (either directly or indirectly) to the movable shutter; thus, the resistant action is advantageously obtained without using any additional components.

As already mentioned, the method according to the present invention is particularly suitable for gas cooking household appliances, in particular for gas cooking tops, gas ovens and gas cookers, the term "gas cookers" meaning any household appliance comprising at least one gas cooking top.

In general, the gas cooking household appliance according to the present invention comprises a burner, at least one automatic valve for regulating the gas flow to the burner, and an electronic control system adapted to control said valve electrically; the electronic control system is adapted to control the valve electrically in such a way as to implement the regulation method according to the present invention.

It is worth pointing out that, as per the current regulations, a second automatic valve must be installed in series along the gas line (as a safety measure) in addition to the above-mentioned automatic regulation valve.

Since the regulation of the gas flow can be carried Out by means of just one valve, the second valve installed in series does not necessarily require the method of the present invention, even if its actuator is subject to motion hysteresis; in fact, the second valve can simply be used in just two different conditions, i.e. fully open and fully closed.

in the above general description, reference has been made to one burner; of course, the household appliance will typically comprise several burners (e.g. four or five) to which the same considerations may apply.

The electronic control system will typically be provided through a microcontroller; in such a case, the microcontroller can be so programmed as to control the valve electrically in accordance with the regulation method of the present invention.

The valve of the household appliance may advantageously be of a type comprising a movable shutter and an electrically controlled piezoelectric actuator adapted to move (either directly or indirectly) the shutter.

Said valve may also comprise movable means adapted to drive its actuator which are subject to motion hysteresis; by using the method according to the present invention, it will thus be possible to overcome any problems caused by said hysteresis.

Said valve may advantageously comprise means adapted to apply mechanically (either directly or indirectly) to its actuator a motion resistant action which is linearly or non-linearly proportional to the pressure of the fluid downstream of the shutter; as already explained, the regulation will thus be improved.

In particular, said means may comprise a diaphragm (appropriately shaped and sized), in particular an elastic membrane, which is adapted to confine said fluid within the valve and which is coupled mechanically (either directly or indirectly) to the movable shutter.

Not even these measures are required for the second valve, if the latter is not used for regulating the gas flow.

The teaching of the present invention allows to obtain, in particular, an accurate, reliable and simple regulation of the valve used for regulating the fuel gas supplied to a burner of a cooking household appliance, in particular comprising a cooking top or an oven; consequently, it is possible to obtain an accurate, reliable and simple regulation of the flame level on the burner and of the heat provided by the burner without using neither the valve opening condition nor the quantity of gas flowing through the valve as feedback information.

The regulation of the valve can be needed for various reasons and triggered and/or controlled by various devices of the household appliance.

The household appliance according to the present invention may typically comprise a control panel allowing the user to set the flame level of the burner and/or to display the set flame level; therefore, the control panel will be connected to the electronic control system.

Said household appliance may also comprise a device for determining, either directly or indirectly, the food temperature and/or moisture (to be used when cooking and/or warming food), which device will be connected to said electronic control system in order to regulate the heat provided by said burner; thanks to the accurate electronic control of the burner, it will be easy to implement an automatic food warming function in addition to an automatic food cooking function.

Said household appliance may additionally comprise a timer connected to or built in said electronic control system for regulating the flame level or the heat provided by said burner, in particular for closing the gas regulating valve.

Said household appliance may also comprise a safety device, in particular a flame detector device for detecting the flame of said burner, connected to said electronic control system for closing the gas regulation valve.

Said household appliance may also comprise a flame igniter device, in particular a sparking device, connected to the electronic control system for lighting the flame on a burner of said appliance.

The electronic control system may be adapted to trigger and/or regulate the spark under a burner ignition command received from the user according to appropriate times related to the opening of the corresponding gas valve; this allows to obtain a better and more reliable ignition of the burner.

Furthermore, the electronic control system may be adapted to trigger the ignition of the burner in relation to a food cooking and/or warmingprogram and/or user setting; thus it will be easy to implement an automatic food warming function in addition to an automatic food cooking function.

Also, the household appliance may comprise communication means, in particular operationally connected to its electronic control system. In such a case, the household appliance can be connected to a communication network and/or to an external device in order to send and receive information to/from said network and/or said device. In particular, said information may be adapted to allow one or several of the following activities: i) monitoring the operation of the household appliance through the remote device, in particular as concerns the gas valves of said appliance; ii) controlling the household appliance remotely by changing its state and/or its operating parameters, in particular as concerns the gas valves of said appliance; iii) updating the list of cooking programs possibly stored in the household appliance; and iv) performing diagnostic and/or statistic analyses of the household appliance, in particular as concerns the gas valves of said appliance.

As explained, an accurate and reliable electronic regulation of the flame of the burners allows to easily provide the household appliance with many advanced functions which can improve the quality and safety of life.

The present invention has been described with reference to particular embodiment examples, but it is clear that many changes may be made thereto by those skilled in the art, and that all such changes will still fall within the scope defined by the appended claims.

*******

Claims

1. Method for regulating a valve (1) for a fluid, in particular for fuel gas, controlled by an electric signal (S) provided to a control input thereof as a function of the value of an electric parameter (V) of said electric signal (S), in particular voltage or current, said valve (1) being of a type such that when the value of said parameter (V) is below a lower threshold (VPI) said valve is fully closed/open, and when the value of said parameter (V) is above an upper threshold (VP2) said valve is fully open/closed, characterized in that, in order to set a desired open condition of the valve (1) between said fully closed and said fully open conditions, a variation of said electric control signal (S) is carried out so that the value of said electric parameter corresponds, at least for an instant, to approximately said lower threshold (VPI) or approximately said upper threshold (VP2).

2. Method according to claim 1, wherein said variation is such that the value of said electric parameter corresponds, at least for an instant, to said upper threshold (VP2) and/or said lower threshold (VP 1).

3. Method according to claim 2, wherein said variation is such that said parameter does not exceed said upper threshold (VP2) and/or said lower threshold (VP I) substantially.

4. Method according to claim 2 or 3, wherein said variation is such that the value of said parameter corresponds, at least for an instant, to said upper threshold (VP2) and/or said lower threshold (VP I) cyclically more than once.

5. Method according to any of the preceding claims, wherein the duration of said variation is shorter than a predetermined time, in particular 5OmS and more preferably lOmS.

6. Method according to any of the preceding claims, wherein said variation corresponds to a final value of said parameter, said final value being determined on the basis of a characteristic curve of said valve.

7. Method according to any of the preceding claims, characterized by being implemented on the basis of one predetermined characteristic curve or two predetermined characteristic curves of said valve.

8. Method according to any of the preceding claims, wherein said valve (I) comprises a movable shutter (31), characterized in that said shutter (31) is driven through an electrically controlled piezoelectric actuator (2).

9. Method according to any of the preceding claims, wherein said valve (1) comprises a movable shutter (31), characterized in that said shutter (31) is driven through an element (2, 5) which is subject to motion hysteresis.

10. Method according to any of the preceding claims, wherein said valve (1) comprises a movable shutter (31), characterized in that a motion resistant action proportional to the pressure of the fluid downstream of the shutter (31) is applied mechanically to said shutter (31).

11. Method according to claim 1 0, wherein said resistant action is exerted by a diaphragm (9) adapted to confine said fluid within said valve (1) and coupled mechanically to said movable shutter (31).

12. Gas cooking household appliance comprising a burner, at least one automatic valve (I) for regulating the gas flow to said burner, and an electronic control system adapted to control said valve (1) electrically, characterized in that said electronic control system is adapted to control said valve (1) electrically in such a way as to implement the regulation method according to any of claims Ito 11.

13. Household appliance according to claim 12, wherein said valve (I) comprises a movable shutter (3 1) and an electrically controlled piezoelectric actuator (2) adapted to move said shutter (3 1).

14. Household appliance according to claim 12 or 13, wherein said valve (1) comprises a movable shutter (31) and movable means (2,5) adapted to drive said shutter which are subject to motion hysteresis.

15. Household appliance according to claim 12 or 13 or 14, wherein said valve (1) comprises a movable shutter (31) and means (9) adapted to apply mechanically to said shutter (31) a resistant action to motion proportional to the pressure of the fluid downstream of the shutter (3 1).

16. Household appliance according to the preceding claim, wherein said means (9) comprise a diaphragm adapted to confine said fluid within said valve (1) and coupled mechanically to said movable shutter (31).

17. Household appliance according to any of claims 12 to 16, comprising a control panel allowing the user to set the flame level of the burner and/or to display the set flame level, said control panel being connected to said electronic control system.

18. Household appliance according to any of claims 12 to 17, comprising a device for determining, either directly or indirectly, the food temperature and/or moisture, which is connected to said electronic control system in order to regulate the heat provided by said burner.

19. Household appliance according to any of claims 12 to 18, comprising a timer connected to or built in said electronic control system for regulating the flame level or the heat provided by said burner, in particular for closing said valve (I).

20. Household appliance according to any of claims 12 to 19, comprising a safety device, in particular a flame detector device for detecting the flame of said burner, connected to said electronic control system for closing said valve (I).

21. Household appliance according to any of claims 12 to 20, characterized by comprising a flame igniter device, in particular a sparking device, connected to said electronic control system for lighting the flame on said burner.

22. Household appliance according to any of claims 12 to 20, characterized by comprising a kitchen cooking top or a kitchen oven.

23. Household appliance according to any of claims 12 to 22, characterized by comprising communication means, in particular operationally connected to an electronic control system thereof, for sending and/or receiving information to/from a communication network and/or an external device.

24. Method for regulating a valve for a fluid and gas cooking household appliance according to the innovative teachings of the present description and of the annexed drawings, which refer to preferred and advantageous embodiments thereof.

*******