WO2007017009A1

WO2007017009A1 - A valve unit for controlling a combustible gas supply

Info

Publication number: WO2007017009A1
Application number: PCT/EP2006/006144
Authority: WO
Inventors: Stefano Zanella; Gianpiero Turrin; Luca Peron
Original assignee: Sit La Precisa SpA
Current assignee: Sit La Precisa SpA
Priority date: 2005-08-09
Filing date: 2006-06-26
Publication date: 2007-02-15
Anticipated expiration: 2008-02-09
Also published as: ITPD20050250A1

Abstract

A valve unit for controlling the supply of a combustible gas comprises a motor (S) for controlling the shutter (4), a control rod (5) with a first (5a) and a second rod portion (5b), an electromagnetic operating means (19) with a spring (20) acting on the shutter (4) shut off the valve irrespective of the operating position of the actuator rod (5) when a safety condition occurs and with a first and a second ferromagnetic core (21, 22) structurally independent from and coaxial with the actuator rod portions (5a, 5b) , and a spring (11) urging the second rod portion (5b) connected to the shutter (4) against the other portion (5a) coupled to the motor (6) so that the rod portions (5a, 5b) are kept rigid with one another in axial translation during the control movement of the shutter.

Description

A valve unit for controlling a combustible gas supply Technical field

The present invention relates to a valve unit for controlling a combustible gas supply having the characteristic features set out in the preamble of the main claim. Technological background

These units are used in particular to control the supply of combustible gas to a burner or like consumer unit in order to vary its supply pressure or the flow of gas supplied in a controlled manner, preferably with continuous modulation. A typical application is in the system controlling the supply of gas to burners of boilers for domestic heating and/or heating of domestic hot water.

An example of these known valve units is disclosed in Italian Patent Application PD99A000274 in the name of the Applicants. Valve units of this type are normally provided with motor-driven actuators adapted operationally to control a shutter which opens or closes a valve seat and which is generally adapted to carry out both the function of safe interception of the gas path and the function of regulation/modulation of the supply pressure (or flow). In this respect, they comprise an actuator rod acting on the shutter and coupled kinematically to a motor, such as a step-by-step motor, the coupling being such that an actuation in rotation of the motor entails a displacement in axial translation of the rod from and towards the position intercepting the seat. The control of the axial displacement of the shutter therefore provides the predetermined control modulating the supply pressure or flow through the valve seat. One of the main functions of these valve units is to ensure that the passage of gas through the valve seat is efficiently intercepted when particular conditions occur, for instance conditions in which safe closure of the valve seat has to be ensured because the electrical supply to the motor- driven actuator is discontinued. In the first place, these motor-driven actuators are controlled with relatively low powers which, although ensuring an efficient modulation function, with low consumption, do not make it possible to sustain the high resilient recall load needed to ensure safe closure of the valve seat, which also complies with current technical standards.

In practice, in the modulation phase, if the electrical supply to the motor-driven actuator is discontinued, the shutter may stop in an intermediate position of opening of the seat and may not therefore be able to ensure that the flow of gas through this seat is intercepted. In order to satisfy these requirements, solutions have been proposed in the prior art in which use is made of operating means of electromagnetic type actuated by the excitation of an electromagnet in opposition to resilient recall means acting on the shutter to urge it to close the valve seat when the above-mentioned conditions occur. An application of an electromagnetic safety device of this type is disclosed in the Italian Patent Application mentioned above. Although this solution ensures the safe closure of the valve seat in an extremely reliable manner, its structure is relatively complex largely because it comprises an electromagnet floating with the control rod of the shutter. A second known solution is disclosed in Italian Patent Application PD2001A000240 in the name of the Applicants. In this solution, no provision is made for the electromagnetic safety operator to have parts of the electromagnetic winding in movement, which facilitates its electrical supply and makes the electric insulation and gas seals less complex. A further known solution is disclosed in European Patent Application

0 271 3016. In this case, the control rod of the shutter is formed as two coaxial sections provided with portions of ferromagnetic material, capable of mutual attraction, in which the lower section, connected rigidly to the shutter, is directly urged by a resilient recall means into the position closing the valve seat.

Disclosure of the invention

The main object of the present invention is therefore structurally and operationally to improve the solutions made available up to now by the prior art, in particular to make the modulation function in the valve unit as independent as possible from the safe closure function in order advantageously to improve overall reliability and precision of operation as regards safe closure.

These and other objects to be set out in detail in the following description are achieved by the invention by means of a valve unit for controlling the supply of a combustible gas embodied in accordance with the accompanying claims. Brief description of the drawings

Further characteristic features and advantages of the invention are set out in detail in the following description of two preferred embodiments thereof, given solely by way of non-limiting example, made with reference to the accompanying drawings, in which:

Figs. 1 to 4 are views in axial section of a first embodiment of a valve unit of the invention in respective and different operating conditions;

Figs. 5 to 8 are views in axial section of a second embodiment of a valve unit of the invention in respective and different operating conditions;

Fig. 9 is a view in axial section of a further variant of the embodiments of the preceding Figures. Preferred embodiments of the invention

With reference firstly to Figs. 1 to 4, a first embodiment of a valve unit for controlling the supply of a combustible gas to a burner or like consumer unit in accordance with the present invention is shown overall by 1.

The unit 1 comprises a supply duct 2 for the transfer of gas from a supply member (not shown) to a burner apparatus (not shown) provided with a valve comprising a first valve seat 3 associated with a shutter 4 adapted to carry out both the function of opening/closing of the gas path (on/off function) and the function of modulation of the flow of gas through the seat 3, as will be explained below.

It will be appreciated that the above-mentioned valve device may be further associated with a second on/off safety electrovalve Ia and a pressure regulator (not shown), both known per se and provided in the duct

2, and preferably disposed upstream of the valve seat 3 so as to provide a multifunctional valve unit in keeping with specific needs.

The valve unit 1 comprises a motor-driven actuator means for the control of the shutter 4 in relation to the seat 3, including a control rod 5 having a first and a second rod portion, shown respectively by 5a and 5b, which are structurally independent from one another and disposed coaxially with one being an axial prolongation of the other. The first rod portion 5a is coupled kinematically to a motor 6, the coupling being such that an angular rotation of the motor 6 corresponds to an axial translation of the rod portion 5a. This coupling may for instance be embodied as a screw-nut coupling (not shown) between a nut obtained in the rotor of the motor and a screw obtained by external threading of the rod portion 5a. The motor 6 is advantageously an electric motor of the step-by-step type with reversible rotation.

The second rod portion 5b is connected rigidly to the shutter 4 at the location of an intermediate section 10 thereof. A spring 11 also acts on the rod portion 5b, on the side axially opposite the portion 5a, the function of this spring being substantially to urge the rod portion 5b into contact with the portion 5a so that these portions are kept rigid with one another in both directions of axial displacement, from and towards the seat 3, in the operating phases of modulation of the flow of gas supplied.

In further detail, the spring 11 is keyed coaxially on the second rod portion 5b and is housed in a seat obtained in a housing 13 in which the valve seat 3 is defined. Openings 14, 15 opening into the duct 2 are also provided in the housing 13, respectively upstream and downstream of the seat, via which the gas supplied by the valve seat 3 passes.

A member connected to the shutter 4 is shown by 16 and has an ogive shape adapted to vary the gas passage section in the valve seat according to a predetermined law of variation correlated with the axial displacement thereof. It will be appreciated that the end section of the rod portion 5b forms a support member for all the components associated with the housing 13 which can be readily made rigid with the valve body, thus providing a self-contained system which can be individually handled (with the components associated therewith) and which can be readily inserted and replaced.

The spring 11 has axial ends 11a, lib respectively in abutment on a base 13a of the housing 13 and the ogive member 16.

An electromagnetic operating means is shown overall by 19 and is associated with a resilient recall means comprising a spring 20 adapted to urge the shutter 4 to close the valve seat 3 irrespective of the operating position of the actuator rod 5 when a predetermined condition requiring the gas path to be intercepted occurs.

The operating means 19 comprises a first and a second core shown respectively by 21 and 22, made from ferromagnetic material and associated with a magnetic circuit with an excitation coil 23 made rigid with the stationary structure of the valve unit 1.

The cores 21, 22 are structurally independent from and coaxial with the actuator rod portions 5a, 5b and are capable of mutual magnetic attraction, by means of excitation of the coil 23, at the location of respective surfaces 21a, 22a facing one another and forming an air gap 24.

Both cores 21 and 22 advantageously have a tubular shape (with respective axial cavities 21b, 22b) so that they can be keyed, in axial alignment with one another, on the rod portions 5a, 5b and are free axially to slide with respect to the latter. The core 21 is also made rigid with the stationary part of the valve unit while the core 22 is received and guided in a sliding manner in the body of the valve unit and is thus capable of relative movement both with respect to the stationary part of the valve unit and with respect to the actuator rod 5.

An abutment plate of the spring 20 is shown by 25 and is rigidly connected to the end 22c of the core 22 opposite that facing the core 21. The end 22c of the core has a radial extension such that it is able axially to interfere with a shoulder surface 7 provided on the rod portion 5b, to the rear of the shutter 4, and thus to displace the shutter to close the seat 3 when there is no magnetic attraction between the cores, under the effect of the resilient action exerted by the spring 20, as will be explained in further detail below.

The valve unit operates as follows: In an initial condition closing the valve seat 3 (Fig. 1), the shutter 4 is indirectly urged by the resilient action of the spring 20, in opposition to the spring 11, against the seat 3, ensuring that the gas path is intercepted. When ignition of the burner is required, the control rod 5 is first displaced into a position in which the portion 5a is at an intermediate axial distance from the rod portion 5b comprised between the maximum opening and closure distances of the valve seat. In this condition, the core 22 is therefore raised by the excitation of the coil 23 until it contacts, by magnetic attraction, the core 21, in opposition to the resilient action of the spring 20 (Fig. 2 - loading). At the same time, the shutter 4 is raised to open the seat 3 under the resilient action of the spring 11 (greater than the pressure force exerted on the shutter by the supply pressure) and the rod portion 5b is displaced until it contacts the portion 5a. From this condition, in which the rod portions 5a, 5b are held rigidly in translation with one another, a corresponding variation of the lift of the shutter 4 with respect to the seat 3 is obtained by rotation of the motor 6 (Fig. 3 - modulation). As a result of the proportionality between the number of steps of the motor and the lift of the shutter, the gas flow Q is modulated between the minimum and maximum rates of flow as a function of the thermal requirement. In the modulation phase, the cores 21, 22 continue to be anchored to one another through their reciprocal magnetic attraction. When the electrical supply of the coil 23 is discontinued, the moving core 22 is resiliency urged by the spring 20 against the shutter 4 as a result of the interference between the end 22c of the rod and the shoulder 7 rigid with the shutter. Since the resilient action of the recall spring 20 is greater than that exerted by the spring 11, the shutter is urged against the valve seat 3 thus causing its closure and the resulting interception of the gas path (Fig. 4). Whatever the operating condition of the actuator rod 5, whenever the supply to the coil is discontinued, there is instantaneous safe closure of the seat 3 irrespective of the operational position of modulation of the rod 5. When it is wished to carry out a calibration of the modulation system, from the closed condition of the seat 3, with the coil 23 not excited, the rod portion 5a is brought into abutment against the portion 5b by appropriate rotation of the motor 6. In this position, a ZERO point is determined, from which the steps of the motor 6 are measured. Subsequently, the rod portion 5a is raised (by actuating the motor) to the ignition condition (Fig. 2) described above (corresponding therefore to a predetermined number of steps of the motor) thus preparing the device for subsequent ignition.

The fact that the opening of the seat 3, on ignition, always takes place with a well-defined relative distance between the core 21 and the core 22, makes it possible to optimise the characteristic of the traction force of the electromagnet, attempting to obtain a maximum force value in the closed position of the seat 3. This is achieved by appropriately selecting the shape of the surfaces 21a, 22a of the facing polar expansions of the cores

21 and 22. Preferred shapes include surfaces 26 with a conical profile and/or with front coupling recesses 27 as an alternative to simple planar

(radial) coupling profiles.

Among the features and advantages of this valve unit, it will be appreciated that modulation is substantially independent from the opening and closing function controlled by the electromagnetic operating means, Throughout the phase of modulation of the flow, the cores 21, 22 of the magnetic circuit therefore have no influence, as the actuator rod 5 is structurally independent from these cores.

A further advantages lies in the fact that the modulation of the gas flow takes place with recovery of the play in the mutually coupled portions as a result of the resilient action of the spring 11 which keeps the actuator rod portions 5a, 5b rigid when the coil 23 is excited.

A further advantage lies in the fact that the opening of the seat 3 on ignition takes place with a snap movement and is not therefore linked to the manoeuvring time of the motor. Moreover, if there are short cuts in the supply voltage, the device may start to operate again without necessarily having to be subject to the above-described ignition sequence forming part of the initialisation phase. By appropriate dimensioning of the excitation coil 23 it is possible in practice to obtain the following operating sequence: - very short voltage cut, lowering of the moving core 22, closing the valve seat 3, restoration of the supply voltage, resulting mutual magnetic attraction of the cores 21, 22, opening the seat and re-admitting gas. If the burner flame has remained alight because the cut has been extremely short, there are no operating variations. If, however, the flame has been extinguished (in the case of short, albeit substantial, cuts) the flame ignition means react immediately and re-ignite the flame and, as the appliance is hot, with draught under way, the re-ignition may take place at the same flow as at the time of the CUt.

Figs. 5 to 8 show a variant of the valve unit 1 of the invention, in which details similar to those of the preceding embodiment bear the same reference numerals. This second embodiment differs from the preceding embodiment chiefly in that the core 21 may in practice move with respect to the stationary structure of the valve unit, and can in particular slide in a limited manner between a first and a second axially opposite end position. In further detail, the core 11 is mounted coaxially on the rod portion 5a (and can slide relative thereto) with an end 21c able to stop in abutment against a shoulder surface 28 of the portion 5a and with an opposite end 21d urged by a spring 29 (also coaxial with the rod portion 5a). In operation, with reference to the phase of initialisation with the valve seat 3 closed and the coil 23 not excited (Fig. 5), the rod portion 5a is brought (by actuation of the motor 6) into contact with the portion 5b (calibration zero setting) and is then raised into the intermediate ignition position (Fig. 6). In this operating stroke, the core 21 is also displaced together with the portion 5a as a result of the assembly configuration discussed above. When the rod portion 5a reaches the intermediate position (ignition position) the core 21 is therefore at a predetermined distance from the core 22 of a value lower than that of the preceding embodiment (with the core 21 made rigid with the valve body). The stroke needed for the core 22 to be brought into contact with the core 21 when the excitation coil 23 is supplied is therefore reduced. On reaching this ignition condition, the modulation phase may take place (when ignition is completed) in which the rod 5 is displaced with the portions 5a, 5b rigid with one another and the cores 21, 22 are displaced jointly with the rod (Fig. 7) thus regulating the flow to the instantaneous value required. The closure of the valve seat 3 takes place, as in the preceding embodiment, by disexcitation of the coil 23 entailing the resilient recall of the core 22 against the shutter 4 thereby intercepting the valve seat (Fig. 8). The configuration of the core 21 described above is particularly suited to applications in which it is wished to use, other conditions remaining the same, magnets of smaller power, weight and bulk (and therefore lower energy consumption, reduced costs and a longer duration due to a reduction of the damage to the polar surfaces caused by the repeated impacts between the latter which take place during operation). It is also possible, through the provision of the spring 29, to offset and/or recover any variations of length which may possibly exist in the rod portions 5a, 5b.

Moreover, since the cores are guided axially by the tubular formation externally keyed thereon and rigid with the stationary structure of the unit, the spring 29 is adapted to enable adaptation between the surfaces of the coupled cores.

The spring 29 is also adapted to recover the kinematic coupling play of the motor, thus providing a kinematic transmission in which play is recovered.

It may also be provided for both the electromagnetic operators provided for the respective control of the electrovalve Ia and the shutter 4 associated with the valve seat 3 to be supplied by a single coil, coupled to an appropriate magnetic circuit, in a configuration of the type illustrated in Fig. 9. A control of this type with a single coil reflects a substantially known application such as that disclosed, for instance, in US Patent Specification 4 921 011.

Since the traction characteristic of the electromagnet, i.e. the law of correlation between the traction force and the traction stroke, is a curve with a substantially hyperbolic course, it will also be appreciated that it is preferable to work in the zone of the curve with a lower stroke so that smaller powers are required for the mutual attraction of the magnets. In this case it may be advantageous to provide the upper core 21 of the electromagnetic means such that it can move in displacement between two axial end positions, so as to reduce the stroke of the second core 22, without thereby sacrificing the stroke of the shutter.

The invention therefore achieves the objects set out above and offers the above-mentioned advantages in comparison with known solutions.

Claims

1. A valve unit for controlling the supply of a combustible gas via a supply duct (2), comprising : a valve seat (3) in this duct (2) and a shutter (4) associated with this seat, actuator means adapted to control the shutter (4) to open and close the seat (3), comprising a control rod (5) with a first (5a) and a second rod portion (5b), structurally independent from one another and coaxially disposed with one being a prolongation of the other and respectively associated with a motor means (6) for the control of the actuator and with the shutter, an electromagnetic operating means (19) associated with a resilient recall means (20) acting on the shutter (4) in order to urge it to close the valve seat (3) irrespective of the operating position of the actuator rod (5) when a predetermined condition making it necessary to intercept this valve seat (3) occurs, characterised in that the electromagnetic operating means comprise a first and a second core (21, 22) of ferromagnetic material associated with a magnetic circuit with an excitation coil (23) made rigid with a stationary structure of the unit, these cores (21, 22) being structurally independent from and coaxial with the actuator rod portions (5a, 5b) and capable of mutual magnetic attraction, when the coil (23) is excited, at the location of respective surfaces (21a, 22a) defining an air gap (24) between the cores, in that it further comprises a spring (11) acting on the second rod portion (5b) connected to the shutter (4) in order to urge it against the other portion (5a) coupled to the motor means (6) so that the rod portions (5a, 5b) are kept rigid with one another in axial translation during the control movement of the shutter (4) from and towards this seat (3), and in that at least the second core (22) is capable of relative movement with respect to the actuator rod (5), the resilient recall means (20) acting directly on the second core (22) in order to urge it to interfere with the shutter (4) and therefore to displace this shutter to close the seat, when there is no magnetic attraction between the cores (21, 22) and in opposition to the action of the spring (11), irrespective of the operating position of the actuator rod (5).

2. A valve unit according to claim 1, wherein the first and second cores (21, 22) have a tubular shape, whose respective axial cavities (21b, 22b) receive, in a sliding manner, the rod portions (5a, 5b) which are free to slide axially in a relative manner.

3. A valve unit according to claim 1 or 2, wherein the cores (21, 22) are keyed on the rod portions (5a, 5b) in axial alignment with one another.

4. A valve unit according to one of the preceding claims, wherein the spring which keeps the rod portions (5a, 5b) rigid comprises a first spring (11) disposed coaxially with the second rod portion (5b) and acting thereon at the location of an end section of this second rod portion (5b) in an axially opposite position to the end of this second rod portion (5b) capable of contact with the first rod portion (5a).

5. A valve unit according to one of the preceding claims, wherein the recall means comprises a second spring (20) coaxial with the second core (22) and acting on an abutment member (25) made rigid with this second core (22), this second core being able to interfere with the shutter (4) during its axial movement under the resilient action of the second spring (20).

6. A valve unit according to one of the preceding claims, wherein the valve seat (3) is obtained in a housing (13) forming a seat housing the first spring (11).

7. A valve unit according to claim 6, wherein the housing (13), together with the shutter (4), the first spring (11) and the second rod portion

(5b) form a self-contained unit which may be individually handled and can be made rigid in a detachable manner with the stationary structure of the valve unit.

8. A valve unit according to one of the preceding claims, wherein the facing surfaces (21a, 22a) of the cores (21, 22) jointly defining the air gap (24) are provided with front recesses (27) for coupling one core to the other.

9. A valve unit according to one of the preceding claims, wherein the first core (21) is made rigid with the stationary structure of the valve unit.

10. A valve unit according to one of the preceding claims, wherein the first core (21) is at least partly rigid in axial translation with the first actuator rod portion (5a).

11. A valve unit according to claim 10, further comprising a spring (29) acting between a stationary portion of the unit and the first core

(21).

12. A valve unit according to claim 11, wherein the first core (21) has a first axial end (21c) able to stop in abutment against a shoulder surface (28) of the first rod portion (5a) and a second opposing end (2Id) urged by this spring (29).