WO2005088194A1

WO2005088194A1 - A valve unit for cotrolling the supply of a fuel gas, particularly for cooking hobs and the like

Info

Publication number: WO2005088194A1
Application number: PCT/IT2004/000131
Authority: WO
Inventors: Salvatore Pappalardo; Stefano Zanella; Massimo Giacomelli
Original assignee: Sit La Precisa, S.P.A.
Priority date: 2004-03-18
Filing date: 2004-03-18
Publication date: 2005-09-22
Also published as: EP1730443A1; TW200532145A

Abstract

A valve unit (1) for controlling the supply of a fuel gas to at least one burner, particularly for cooking hobs and the like, is described and comprises a pressure modulator device (10) including a gas supply duct (2) extending between an inlet opening (3a) and an outlet opening (3b) of the unit (1), a valve seat (12) in the duct (2) and a closure member associated with the seat (10), and an actuator element (14) which is active on the closure member (11) for the control thereof in the opening/closure of the valve seat (12), wherein the actuator element (14) comprises a diaphragm (16) fixed firmly to the closure member (11), the diaphragm being subject, on one side, to the atmospheric pressure and to a force exerted by first resilient means (15) and, on the opposite side, to the gas output pressure and to a force exerted by second resilient means (17).

Description

A valve unit for controlling the supply of a fuel gas, particularly for cooking hobs and the like

Technical field The present invention relates to a valve unit for controlling the supply of a fuel gas, particularly for cooking hobs and the like, according to the preamble to Claim 1. Technological background Within the technical field in question, the need for the user to modulate and control the gas supply so as consequently to vary the intensity of the flame in a burner, for example, in one of the burners of a gas cooking hob, is known. The required modulation must allow for considerable flame variations from a minimum to a maximum with a plurality of intermediate configurations, whilst conforming to the safety regulations that are in force on the subject. In particular, the regulations that are in force require the presence of at least two solenoid valves which can shut off the fuel gas in the duct which leads to each burner to ensure the safety of the cooking hob. Valve units that are arranged for the control and modulation of the gas supply in cooking hobs are known, for example, from French patent application No. 2779214. This application, describes a valve which comprises a closure member that engages in the gas-outlet opening to a greater or lesser extent, thus varying the flow-rate of gas directed to the burner. However, this valve unit does not ensure adequate regulation of the intensity of the flame since small movements of the closure member produce considerable variations in the gas flow. Great accuracy is therefore required in the production of the mechanical parts in order to achieve the desired variations of the gas flow-rate for the smallest movements of the closure member. Description of the invention A principal object of the invention is to provide a valve unit which is designed structurally and functionally to permit accurate modulation of the flow-rate of gas to the burner. A further object is to produce a device for controlling the supply of a fuel gas which ensures safety in accordance with the regulations that are in force on the subject. These and other objects are achieved by the invention by means of the valve unit and a device for controlling the supply of a fuel gas which are formed in accordance with the appended claims. Brief description of the drawings Further characteristics and advantages of the invention will become clear from the following detailed description of some preferred embodiments thereof which are described, by way of non-limiting example, with reference to the appended drawings, in which:

- Figure 1 is a perspective and sectioned view of a valve unit according to the invention,

- Figure 2 is a view of the valve unit of Figure 1 in longitudinal section, - Figure 3 is a block diagram of a device for controlling the supply of a fuel gas, comprising a plurality of the valve units of Figure 1, and

- Figure 4 is a schematic plan view of a user interface of the control device of Figure 3.

Preferred embodiment of the invention With reference initially to Figures 1 and 2, a valve unit for controlling the supply of a fuel gas, particularly for cooking hobs and the like, formed in accordance with the present invention, is generally indicated 1. The valve unit 1 comprises a gas-supply duct 2 for the supply of fuel gas from a source (not shown) to a burner (also not shown), the duct being delimited by an gas-inlet opening 3a and a gas-outlet opening 3b. The valve unit 1 includes a solenoid valve 5, arranged in the duct 2, for shutting off the flow of gas in predetermined situations in order to maintain safety conditions, as explained in detail below. The solenoid valve 5 is of the normally-closed type and comprises a conventional electromagnetic actuator 6 including resilient biasing means 7 arranged so as to move a first closure member 8 of the solenoid valve 5 to a position of closure of a first valve seat 9 in the duct 2 in the absence of a supply of electrical current to the electromagnet. However, any solenoid valve of the on/off type may be used in the construction of the valve unit 1 of the present invention. The valve unit 1 further comprises, upstream of the solenoid valve 5 with reference to the direction of the gas-flow, a pressure modulator device 10 which can modulate the pressure of the gas at the outlet from the valve unit 1. This modulator device 10 comprises a second closure member 11 and a respective second valve seat 12, formed in the duct 2 and associated with the closure member 11. The second closure member 11 is connected, in the manner described below, to a linear actuator element, generally indicated 14 and including a substantially shaft-like control rod 13 of axis X which can translate along the said axis so as to move the closure member 11, indirectly, away from or towards the valve seat 12 and thus to regulate the flow-rate of gas which flows along the duct 2. In particular, the control rod 13 is moved by an electric motor 18, for example, of the stepping type, and its position along the axis X is consequently determined by the number of steps performed by the motor 18. By way of example, the control rod 13 comprises a first portion and a second portion (not shown) which are coaxial with one another and are connected to one another by means of a male and female screw coupling. More specifically, the second portion includes an externally threaded surface which is housed and screwed into a female thread formed in a blind hole of the first portion. The first portion in turn is fixed for rotation with a rotor of the electric motor 18 and is slidable axially relative thereto by virtue of the male and female screw coupling. Rotations of the motor 18 thus correspond to translations of the rod 13. The actuator element 14 further comprises first resilient means 15, in particular a spring which is fixed by a first end 15a to a free end 13a of the control rod 13 and is connected by the opposite end 15b to a face 16a of a diaphragm 16 which extends substantially perpendicularly relative to the axis X. The diaphragm 16 is also fixed firmly to the second closure member 11. Movements of the rod 13 therefore bring about greater or lesser compressions of the spring 15 with corresponding variations in the equilibrium position of the diaphragm 16 which lead to translations of the closure member 11, the size of which translations depends, amongst other things, on the resilient force exerted. In particular, the equilibrium position of the diaphragm 16, and hence the position of the closure member 11, depends on the resultant of the forces acting on the diaphragm, as indicated in detail below. Second, safety resilient means 17 are also provided, acting with a predetermined resilient force on the closure member 11 and positioned on the side of the diaphragm 16 remote from the resilient means 15 so as to urge the closure member 11 towards a position of closure of the valve seat 10. The resilient force of the second resilient means 17 acts substantially along the axis X in the opposite direction to that exerted by the first resilient means 15. The diaphragm 16 is therefore acted on, on one side corresponding to the face 16a, by the resilient force of the first resilient means 15 along the axis X and by the atmospheric pressure whereas, on the opposite side, that is, on the face 16b, it is acted on by the resilient force of the second resilient means 17, which is also directed along the axis X, as well as by the output pressure (P_u) of the fuel gas in the duct 2 (or, more generally, the pressure downstream of the closure member 11), if the pressure loss caused by the solenoid valve 5 with the closure member 8 open is considered to be substantially negligible. Since the control rod 13 is translatable and can therefore adopt a plurality of different positions, the intensity of the resilient force of the first resilient means 15 is variable, depending on the position of the rod; the closer the position of the rod is to the diaphragm 16, the greater is the resilient force which the first means 15 exerts on the diaphragm 16 because of the greater compression of the means 15. Similarly, the resilient force exerted by the second means 17 is also variable according to the position of the closure member 11; a greater opening of the closure member 11 increases the resilient force of the means 17 which tends to return the closure member 11 to a closure position. The position of the closure member 11 is therefore determined, as stated above, by the equilibrium position adopted by the diaphragm 16, according to the balance of the forces acting on it, which forces are variable and depend, once the elastic constants of the resilient means 15 and 17 have been set, on the position of the control rod 13 of the pressure regulator device 10 and on the gas input pressure (Pi). Moreover, the first and second resilient means 15, 17 have dimensions such that, when the control rod 13 exerts the least compression force on the first resilient means 15, the force exerted by the second means 17 on the closure member 11 is such that the closure of the closure member 11 is ensured. The value of this force exerted by the second means such that the closure member 11 is brought to the closure position is established at the calibration stage and is not changed again during the normal use of the valve unit 1. The precision of the regulation of the gas output pressure (P_u) which is achieved by the pressure modulator device 10 of the present invention is particularly important. In fact, owing to the indirect control, by resilient means, of the diaphragm 16 fixed to the closure member 11, relatively large movements of the control rod 13 result in smaller movements of the closure member 11 thus achieving a fine adjustment of the output pressure (P_u) without the need for micrometric movement of mechanical elements. The valve unit 1 preferably performs a modulation of the output pressure P_u within the range of from 0.5 to 25 mbar. The value of P_u is a substantially linear function of the number of steps imparted by the stepping motor 18, at least within a predetermined range. Figure 3 shows a block diagram of a device 100 for controlling the supply of gas to a cooking hob comprising a plurality of valve units 1 (of which three are shown, but the preferred number of valve units 1 used is five) each connected to a respective burner (not shown). The control device 100 comprises, upstream of the valve units 1, a general, safety solenoid valve 20 which has standard characteristics and is substantially similar to the solenoid valve 5, including an electromagnet (not shown) which can allow or interrupt the flow of gas towards the valve units 1. Additionally, the inlet of gas to the general solenoid valve 20 is optionally protected by a filter 25. In the event of a lack of electrical energy in the system or in the event of the identification of an operating anomaly, the general solenoid valve 20 is closed and the gas cannot flow to any of the units 1. In addition, each solenoid valve 5 also shuts off the gas-supply duct 2 to each burner, thus ensuring "double safety" of the gas-supply control device 100. The control device 100 further comprises an electronic control unit 22 to which the general solenoid valve 20 and the valve units 1 are subservient. In particular, the electronic control unit 22 sends an electrical signal to the general solenoid valve 20 upon the occurrence of any malfunctions of the device 100 which involve the closure of the solenoid valve as described above. The device 100 also includes a plurality of thermocouple sensors, all indicated 23, each of which is associated with a respective burner and can indicate the presence or absence of a flame in the burner. The electrical signals coming from the thermocouple sensors 23 are processed by the control unit 22 which compares the signals received with a stored reference signal; in the absence of a flame in the burner, the control unit 22 sends a signal to the valve unit 1 so that the solenoid valve 5 is brought to the closure position. Alternatively, it is possible to provide for three attempts to light the burner before the solenoid valve 5 is closed. Additionally, the actuator 14 is controlled so that the control rod 13 is brought to a position spaced from the diaphragm 16 so that the resilient force of the means 15 on the diaphragm 16 is minimal and the closure member 11 is brought to the closure position by virtue of the action of the second resilient means 17. In the event of the accidental extinguishing of a single burner, the flow of gas is shut off (by means of two distinct closure members 8 and 11 as required by the regulations in force, again ensuring double safety) solely in the malfunctioning burner, allowing the remaining burners to be used. In operation, an initial condition is represented by the configuration of the device 100 in which the general solenoid valve 20 is closed, that is, the gas duct 2 is shut off and gas is not caused to flow to the valve units 1, and in which the first and second valve seats 9 and 12 of each unit 1 are closed by the respective closure members 8 and 11 of the solenoid valve 5 and of the modulator device 10. By means of a first signal coming from the control unit 22, caused, for example, by the operation of a burner lighting and regulation device 200 (see Figure 4) by the user in order to light a preselected burner on the cooking hob, the first, general solenoid valve 20 is operated so as to allow the supply of gas through the duct 2 (if a flame were already present in another burner of the cooking hob, then the general solenoid valve 20 would already be in this condition); similarly, the closure member 5 of the burner in question is opened by means of a second signal coming from the control unit 22, and a third signal is sent to the motor 18 in order for the control rod 13 to be translated so as to bring about a compression of the first resilient means 15 and hence a translation of the diaphragm 16 and consequently of the closure member 11. The initial movement of the rod 13 along the axis X due to the third signal of the control unit 22 is such that the closure member 11 is substantially in the position of maximum opening and hence maximum gas supply. The lighting of the flame of the burner by lighting means 24, also operated by means of an electrical signal coming from the control unit 22, is thus facilitated. As mentioned above, in the event of a failure to light, it is possible to set a predetermined number of further lighting attempts before the solenoid valve 5 and the modulator 10 are closed. Preferably, the general lighting and extinguishing operation, that is, of the entire control device 100, and the lighting and regulation of each individual burner are activated by two different commands sent by the burner lighting and regulation device 200 to the control unit 22. In particular, a general ON/OFF push-button 28 and a pair of push-buttons 26, 27 for each burner are provided. The buttons 26, 27, which are identified visually, for example, by the symbols "+" and "-", respectively, perform the function of modifying, that is, increasing or reducing, respectively, the level of the flame in each burner up to a maximum of 6 levels. However, a different number of modulation levels may be set in the control device 100 of the invention. As stated above, the functions of the cooking hob are accessible from the device 200, which is connected directly to the control unit 22 and the function of which is that of a user interface. The device 200 can be constructed in accordance with the user's specific requirements; for example, as an alternative to the push-buttons 26, 27 and 28 shown in Figure 4, it may include touch panels. A display 29 is also provided for displaying the functions set and any error messages. Additionally, a timer 30 may be provided for automatically extinguishing the flame in each burner after a predetermined period of time. The intensity of the flame is then modulated, as soon as the thermocouple sensor 23 has detected the presence of flame in the burner, by means of a further electrical signal sent from the control unit to the pressure modulator device 10, to achieve the intensity desired by the user which has been set by means of the buttons 26 and 27 of the burner lighting and regulation device 200. Regulation takes place by alteration of the position of the rod 13 along the axis X by means of the motor 18. In particular, in order to reduce the intensity of the flame, the rod 13 is moved to a position farther from the diaphragm 16, or closer if an increase in intensity is required. The resilient force due to the resilient means 15 and acting on the face 16a of the diaphragm 16 is thus reduced/increased and the diaphragm 16, which is fixed firmly to the closure member 11, therefore moves in the direction of the movement of the rod 13 to reach a new equilibrium position. According to the position of the rod 13 along the axis X, it is therefore possible to change from a maximum flow-rate configuration to a minimum flow-rate configuration, according to the user's requirements. The invention thus achieves the objects proposed, affording many advantages over the prior art mentioned. A first advantage consists in the provision of gas modulation which is easy to implement and does not require complex calibrations. Furthermore, double safety is always ensured in the device of the invention.

Claims

1. A valve unit (1) for controlling the supply of a fuel gas to at least one burner, particularly for cooking hobs and the like, comprising a pressure modulator device (10) including : - a gas supply duct (2) extending between an inlet opening (3a) and a outlet opening (3b) of the unit (1),

- a valve seat (12) in the duct (2) and a closure member (11) associated with the seat (10),

- an actuator element (14) which is active on the closure member (11) for the control thereof in the opening/closure of the valve seat (12), characterized in that the actuator element (14) comprises:

- a diaphragm (16) fixed firmly to the closure member (11), the diaphragm being subject, on one side (16a), to the atmospheric pressure and to a force exerted by first resilient means (15) and, on the opposite side (16b), to the pressure of the gas downstream of the closure member (11) and to a force exerted by second resilient means (17).

2. A valve unit (1) according to Claim 1 in which the actuator element comprises a control rod (13) acting, with a free end (13a), on the first resilient means (15).

3. A valve unit according to Claim 2 in which the rod (13) can translate along an axis (X) so that the resilient means (15) is compressed to a greater or lesser extent according to the position of the rod (13) along the axis (X).

4. A valve unit according to Claim 3 in which the translations of the rod (13) are brought about by drive means (8).

5. A valve unit (1) according to one or more of the preceding claims in which the first and second resilient means have dimensions such that, when the resilient force applied by the first means (15) is least, the force exerted by the second means (17) is such as to bring the closure member (11) to the position of closure of the valve seat (12).

6. A valve unit (1) according to one of more of the preceding claims, comprising a solenoid valve (5) including a valve seat (9) in the duct (2) and a closure member (8) associated with the seat (9).

7. A valve unit (1) according to Claim 6 in which the solenoid valve (5) is arranged downstream of the pressure modulation device (10) in the direction of flow of the fuel gas.

8. A valve unit (1) according to one or more of the preceding claims in which the gas pressure downstream of the closure member (11) is the output pressure (P_u).

9. A device (100) for controlling the supply of gas, comprising a plurality of valve units (1) and of burners associated therewith according to Claims 1 to 8, and further comprising a general solenoid valve (20) suitable for shutting off the supply of the gas directed towards the plurality of valve units (1) in the event of a lack of electrical energy or malfunction of one or more of the valve units/burners.

10. A device (100) according to Claim 9, comprising a flame sensor (23) associated with each burner to which the gas is supplied through the valve unit (1) and an electronic control unit (22) connected to the sensor means (23) so as to cause the closure member (11) to close the valve seat (12) in dependence on a signal generated by the sensor means (23) and indicative of the absence of flame in the burner.

11. A device (100) according to Claim 9 or Claim 10 in which the general solenoid valve (20) is controlled by the electronic control unit (22).

12. A device according to one or more of Claims 9 to 11, comprising a burner lighting and regulating device (200) which can determine the position of the control rod (13) along the axis (X).

13. A cooking hob comprising a device (100) for controlling the supply of gas formed in accordance with one or more of Claims 9 to 12.