WO2008025988A2

WO2008025988A2 - Solenoid actuators

Info

Publication number: WO2008025988A2
Application number: PCT/GB2007/003282
Authority: WO
Inventors: Richard Anthony Connell
Original assignee: Dialight Blp Limited
Priority date: 2006-08-30
Filing date: 2007-08-30
Publication date: 2008-03-06
Also published as: GB0617104D0; WO2008025988A3; GB0707725D0; EP2059700A2

Abstract

A solenoid actuator suitable for opening and closing an aperture to control fluid flow therethrough, comprises a closure member (630) and a solenoid plunger drive means (325). When the aperture is closed, the closure member is held in contact with a rim of the aperture (31) by a closure force. The solenoid plunger is slidably actuatable within a bore of a solenoid with a predetermined stroke, and is coupled to the closure member to transmit a plunger force to the closure member to open the aperture. The plunger is coupled to the closure member by a first resilient means (610) such that, when the plunger is actuated to open the aperture, the plunger is allowed to travel for a portion of its stroke before the plunger force transmitted to the closure member overcomes the closure force to open the aperture.

Description

SOLENOID ACTUATORS

The present invention relates to solenoid actuators and more particularly to solenoid actuators used for fluid flow control, such as, for example, gas flow in a domestic gas meter.

Background

Solenoid actuators are well known in fluid control, especially for air or gas control, where an orifice or aperture in a fluid flow path is opened or closed by means of a compliant closure member such as a flat seal, semi-spherical (mushroom-shaped) plug, or the like, under the control of an electric current drive.

Such actuators commonly comprise a magnetic circuit wound about by a flux- generating coil, with a central plunger of magnetic or magnetised material moving under the influence of the flux in a magnetic circuit, in response to current flow through the surrounding coil. The plunger is mechanically coupled to the compliant closure means, which opens or closes the aperture or orifice in the fluid path as the plunger moves within the magnetic circuit.

Such actuators frequently incorporate a coil spring, for example as a push-off spring, which is normally wound about the plunger to provide an axial force along the principle axis. This spring force is additional to that which would be exerted upon the plunger by the solenoid alone, and assists the opening or closing of the aperture orifice. To provide sufficient force for the purpose, the coil spring may have to be relatively long, which increases the overall axial dimension or size of the actuator. A coil spring also requires the generation of an electromagnetic force by the coil during the closure stroke that is additional to that necessary to move the plunger, solely for the purpose of overcoming the force due to the coil spring.

Known actuators of the type in question have hitherto most usually been constructed as an integral part of the fluid flow system in which they have been employed, and have often been indirectly acting, thereby giving rise to assemblies of greater complexity and size. Where such actuators have been of discrete construction, they have commonly been of a size preventing their employment or integration within a compact enclosed assembly, such as a modern domestic gas meter. The operating power of such prior art actuators is prohibitively high, especially if they are solidly linked and directly driven.

Valve actuators of the type in question are most commonly mounted in the inlet aperture of a gas meter, in which case the plunger and closure member are driven to close off the aperture or orifice against the prevailing supply pressure and closing flow. In order to achieve satisfactory shut-off and low leakage past the closed-off aperture or orifice, the closure member has to be adapted to provide an adequate limited force, derived from and exerted by the actuator or solenoid means; the actuator comprising a spring means, for example a short- stroke diaphragm spring within the drive.

The spring means may comprise one or more diaphragm springs, suitably incorporated and retained within the closure member assembly, for effective shut-off.

In the inlet-mounted version of the valve, the diaphragm spring preferably bears, directly or indirectly, upon the underside of that part of the closure member, which contacts and seals the inlet or orifice against the prevailing supply pressure and closing flow.

The closure member assembly may be carried directly by the solenoid plunger.

The solenoid means may include a permanent magnet (or magnets) the flux of which maintains the plunger in a stable latched state at one end of its travel, which may be the end at which the aperture or orifice is closed.

The translation of the plunger to or from the stable latched state may be by means of a magnetic pulse from the surrounding drive coil of the solenoid actuator. By way of example, an inlet-mounted solenoid actuator valve embodying the key elements as described above is shown in prior-art granted patent GB 2276701 , the disclosure of which is hereby incorporated by reference.

According to GB 2276701 , there is provided a solenoid actuator comprising a closure member suitably adapted to move to engage a fluid flow aperture or orifice; solenoid means for moving the closure member into or out of engagement with the aperture or orifice; and assembly comprising at least one diaphragm spring capable of exerting a force counter to the force exerted by the solenoid means; characterised in that the closure means is carried by the assembly, the diaphragm spring being adapted to deform in the direction of travel of the solenoid plunger when the closure member has contacted the fluid flow aperture, thereby to convey to the closure means, and to limit, the force exerted upon the closure means by the solenoid means, and to provide a force acting to displace the closure member from the aperture when the closure force due to the solenoid means is removed. The assembly may be mounted within and retained by the closure member, typically a moulded rubber seat.

In GB 2276701 the assembly is mounted upon the plunger end by a means permitting a degree of free movement of the assembly, whereby the closure member is able precisely to align itself orthogonally on axis with the aperture or orifice, giving good sealing and minimal leak past when closed off by the moulded rubber seat.

A solenoid actuator constructed in accordance with GB 2276701 has the advantage of providing a compact and energy-efficient construction and drive, which is particularly suitable for use where the actuator is required to operate upon a valve aperture or orifice not forming part of a common structure with the actuator, for example where the actuator is mounted within the casing of a gas meter, to open and close a gas inlet or outlet incorporated in the sealed casing.

It is particularly advantageous in these applications, as it lends itself to a low- voltage battery supply commonly employed in gas meters for metrology, whether driven directly from the battery via a suitable electronic circuit, or more - A - commonly, using a so-called capacitor-discharge drive, initiated from a similar electronic circuit.

With capacitor-discharge drive, there is an optimum relationship between the valve coil size, coil resistance, coil turns and magnetic flux capability, and the most cost-effective capacitor value and size, such that the valve latches and de-latches decisively during the exponential discharge period, with adequate residual voltage margin.

The solenoid-actuated valve mounted on the inlet connection of a gas meter has to close off against the prevailing working pressure and closing flow, involving the diaphragm spring incorporated within the closure member assembly, the shut-off pressure being above the seat and thus acting against the closure member. Where a solenoid actuated valve is mounted on an outlet connection of a gas meter, the actuator must work against the "back-pressure" within the meter in order to open the valve. This is not generally done as the large closure force requires a large solenoid to provide sufficient power to overcome the closure force and open the outlet.

Summary of the invention

The invention provides solenoid actuators and a method of opening an aperture as defined in the appended independent claims, to which reference should now be made. Preferred or advantageous features are defined in dependent sub- claims.

Accordingly, in a first aspect the invention may provide a solenoid actuator for opening and closing an aperture to control fluid flow therethrough, comprising a closure member that, when the aperture is closed, is held in contact with a rim of the aperture by a closure force, and a solenoid plunger, slidably actuatable within a bore of a solenoid and having a predetermined stroke or open gap, coupled to the closure member to transmit a plunger force to the closure member to open the aperture, in which the plunger is coupled to the closure member by a first resilient means such that, when the plunger is actuated to open the aperture, the plunger is allowed to travel a portion of its stroke before the plunger force transmitted to the closure member overcomes the closure force to open the aperture.

By allowing the plunger to travel a portion of its stroke during which it only needs to overcome a resilience of the first resilient means, the instantaneous force provided by the plunger may be increased to a point at which it can overcome the closure force. This may advantageously allow a lower powered solenoid actuator to be used than would be required if the plunger was directly connected to the closure member and was not permitted to travel a portion of its stroke before overcoming the closure force.

Preferably the solenoid actuator further comprises a second resilient means acting to urge the closure member towards the aperture. This second resilient means is preferably a coil spring such as a push-off spring and may also act to urge the plunger away from a latched position, for example by urging the plunger out of the bore of the solenoid.

In order to allow the actuator to operate more efficiently it may be preferable to allow the plunger to travel at least 10% of its stroke, and preferably at least 20% or at least 30% of its stroke before the closure force is overcome.

Particularly preferably the plunger is allowed to travel between 25% and 75%, and preferably between 40% and 60% of its stroke before the closure force is overcome. It may be advantageous if about half of the stroke is taken up in acting solely against the resilience of the first resilient means, or against the combined force provided by the first and second resilient means.

The full open stroke or stroke or open gap may be in the range 2 to 20 mm, preferably 3 to 8 mm and particularly preferably about 5 mm. These ranges may be the most suitable for gas valve applications.

A push-off spring may provide a portion of the closure force. In fluid flow applications a portion of the closure force is likely to result from a fluid pressure acting on the closure member. This is likely to be the case where the actuator is for opening a valve on an outlet of a gas flow meter. Advantageously, the first resilient means may be a diaphragm spring, for example a short stroke diaphragm spring. The diaphragm spring may comprise an outer rim and a central boss, separated by resilient cantilevered fingers. Preferably the plunger may be connected to the diaphragm spring at the central boss. This may assist in centring the closure member during opening and closing of the aperture. Additionally, the second resilient means may preferably act through the central boss of the diaphragm spring and, again, this may aid the centring and symmetry of the actuator.

The closure member may comprise a closure seat assembly having a seat face for contacting the rim of the aperture, a substantially rigid plate, such as a washer disposed behind and supporting the seat face, and the first resilient means (for example a diaphragm spring). The seat face may be formed of a resilient material, for example rubber, for contact with, or seating against, a rim of the aperture.

Advantageously, the seat face may be part of a moulded housing that retains the plate and the first resilient means.

In some operating situations, back-pressure may become trapped behind the plate or washer and result in a delay in the closure response time of the actuator. Advantageously, the plate or washer may comprise a plurality of holes to enable back-pressure to escape when the aperture is opened. The holes may additionally have the advantage of reducing the weight of the closure member, thereby allowing a swifter closure response.

In a second aspect the invention may provide, a solenoid actuator for opening and closing an aperture to control fluid flow therethrough, comprising a closure member that, when the aperture is closed, is held in contact with a rim of the aperture by a closure force, a solenoid plunger, slidably actuatable within a bore of a solenoid and having a predetermined stroke, coupled to the closure member to transmit a plunger force to the closure member to open the aperture, and a push-off spring acting to urge the closure member towards the aperture, in which the plunger is coupled to the closure member at a central boss of a diaphragm spring such that, when the plunger is actuated to open the aperture, the plunger is allowed to travel a portion of its stroke before the plunger force transmitted to the closure member overcomes the closure force to open the aperture.

In a third aspect the invention may provide a solenoid actuator for opening and closing an aperture to control fluid flow therethrough, comprising; a closure member having a closure seat that, when the aperture is closed, is held in contact with a rim of the aperture by a closure force, the closure seat being supported by a substantially rigid plate or disc having a plurality of holes defined through its thickness.

In this third aspect the actuator may further comprise a solenoid plunger, slidably actuatable within a bore of a solenoid and having a predetermined stroke, coupled to the closure member to transmit a plunger force to the closure member to open the aperture, and a second resilient means acting to urge the closure member towards the aperture, in which, the plunger is coupled to the closure member by a first resilient means such that, when the plunger is actuated to open the aperture, the plunger is allowed to travel a portion of its stroke before the plunger force transmitted to the closure member overcomes the closure force to open the aperture.

The invention may, in a further aspect, provide a solenoid actuator comprising a closure member adapted to engage the upstream end of a fluid flow aperture or orifice; solenoid means having a movable solenoid plunger attached or linked to the closure member, for moving the closure member into or out of engagement with the aperture or orifice; a magnetic circuit forming part of the solenoid means, enabling the plunger to be latched at the extremity of its stroke within the solenoid means, and an associated spring, which may be a coil spring surrounding the plunger, linked to the movable solenoid plunger and able to exert an outwardly directed force upon the plunger; and an assembly comprising at least one diaphragm spring associated with the closure member capable of exerting a force counter to the force exerted upon the closure member to maintain the closure member in engagement with the aperture or orifice; the force acting upon the closure member to maintain closure of the orifice or aperture including back-pressure exerted upon the closure member by the fluid, and force due to the associated spring acting through the solenoid plunger; such that when the solenoid is energised to attract and magnetically latch the plunger, thereby removing the closure member from the aperture or orifice, the diaphragm spring acts or flexes in a direction such as to assist the attraction of the plunger into the solenoid, thereby aiding removal of the closure member from the aperture and allowing fluid flow through the aperture or orifice.

A solenoid actuator as described above may have the diaphragm spring arranged to provide a pre-travel distance in the direction of plunger travel when the solenoid is energised to attract and latch the plunger, thereby to assist overcoming the back-pressure in order to allow the closure member more readily to detach from the aperture or orifice. A gas valve employing a solenoid actuator in accordance with the invention may be mounted within a domestic gas meter housing to operate upon the inner end of the outlet aperture of the gas meter, to permit or prevent gas flow therethrough.

In a further aspect the invention provides a method of opening an aperture, closable by a closure member held closed by a closure force, using a solenoid actuator having a plunger slidably actuatable within the bore of a solenoid and coupled to the closure member by a first resilient means, comprising the steps of, activating the solenoid to actuate the plunger to transmit a plunger force to the closure member via the first resilient means, such that the plunger travels a portion of its stroke while deflecting or loading the first resilient means without applying sufficient force to the closure member to overcome the closure force, and allowing the plunger to travel further in its stroke overcoming the closure force to open the aperture.

The invention also provides a fluid flow valve or a gas valve comprising or incorporating an actuator as described above or defined in the claims.

A solenoid-actuated valve mounted on the outlet connection of a gas meter is assisted by the prevailing internal supply pressure and through-flow at closure; the so-called "back-pressure" building up behind the closure seat assembly. The value of the built-up "back-pressure" force behind the closure member will depend upon the aperture orifice area and the prevailing working pressure.

E.g. for an aperture or orifice of 27 mm diameter having an area of 5.73 sq.cm. and a test pressure of 50 mBar, the assisted "back-pressure" force behind the closure seat would be,

5.73 x 50 = 286 gF, or approximately 2.8 Newtons.

This "back-pressure" force being uniformly distributed and applied behind the closure seat, gives good reliable sealing of the orifice. Also any subsequent impulses or perturbations in instantaneous pressure (possibly due to the dynamic settling effect of up-stream pressure-regulators feeding an entire domestic zone or individual meters) automatically increases the "backpressure" force seen by the closure seat, thus sealing even more effectively. The higher the working pressure, the greater the applied "back-pressure", and hence more effective the seat closure and sealing.

Specific Embodiments

Specific embodiments of the invention will now be described by way of example, with reference to the drawings in which;

Figure 1 shows the basic arrangement of a prior art gas meter with a shut-off valve mounted on the inlet connection, controlling the flow through the so-called "measuring-group" to the outlet, closing off against the inlet pressure;

Figure 2 shows an alternative arrangement, with a shut-off valve mounted on the outlet connection, closing off with the assistance of the prevailing back- pressure;

Figure 3 shows a basic arrangement according to an aspect of this invention, with the valve mounted at the outlet connection, incorporating the "assisting" diaphragm spring; Figure 4 shows the arrangement of a closure seat assembly according to an aspect of the invention, incorporating a short-stroke "assisting" diaphragm spring and a flat washer with bleed holes (not shown);

Figure 5 shows a flat washer with bleed holes, for relieving "back-pressure" in the closure seat assembly during the solenoid power stroke (valve opening);

Figure 6 shows a valve opening stroke, with the driven plunger picking up and pre-travelling the "assisting" diaphragm spring, overcoming the "back-pressure" and push-off spring forces, for more efficient operation;

Figure 7 graphically illustrates a typical capacitor-discharge drive of a directly connected actuator when opening an outlet aperture in a gas valve;

Figure 8 graphically illustrates a typical capacitor-discharge drive of an actuator according to an aspect of the invention when opening an outlet aperture in a gas valve.

These sketches and diagrams are used to explain the main points and operational advantages of embodiments of this invention.

Figure 1 illustrates a typical inlet-mounted actuating valve for a gas flow meter (as described in, for example, GB2276701). Figure 1 shows a sealed meter casing 10 having an inlet 20 and an outlet 30, with a valve 40 mounted on the inlet to control the flow 50 through the "measuring group" 60.

Figure 2 illustrates an alternative arrangement with the valve 40 mounted on the outlet 30 rather than the inlet 20. In this arrangement the "back-pressure" force exerted by the gas passing through the measuring group acts to close the valve, and this force must be overcome by an actuator means to open the valve.

With reference to Figure 3, showing an outlet-mounted valve in the open condition (the outlet flow 32 is illustrated), a solenoid actuator comprises a U-frame 305 containing a central bobbined coil 310 containing, on axis, a single disc magnet 315 at the bottom attached to a cylindrical stop 320, whose geometry compliments that of a plunger (that is slidable within the bobbined coil) for efficient drive and latching at a relatively large open stroke or open gap 330 (in this case about 5 mm). This approach maximises the length and hence the available turns of the actuating coil, thus giving more efficient operation.

The solenoid assembly is solidly integrated to a bridge-plate 335 through which the plunger 325 passes on axis, with a small defined linkage clearance. The outer ends of the bridge plate 335 are strongly staked to the tops of the U-frame legs 305. A crinkled pressure-washer (not shown) placed around the plunger, located strongly between the inside face of the bridge-plate 336 and bobbin top cheek 337, keeps all magnetic parts solidly intimate for best integrity and performance.

Attached to the top end of the plunger 326 is the closure seat assembly 340 comprising an "assisting" diaphragm spring 610, a flat washer 620, a moulded containment seat 630 and a push-off spring 350, conveniently, a moulded orifice bracket (not shown) may be clipped onto the bridge-plate, linking the main valve and closure seat assembly with the outlet 30, suitably sealed into the outlet in one of several ways with an O-ring, for example at an outlet lip or orifice lip 31.

The release from the latched state, for seat closure, is aided by the push-off spring 350 that surrounds the plunger 325. When the push-off spring is extended, it provides additional seat closure force, over and above that due to the "back-pressure" force built-up behind the seat 630 due to the fluid pressure, thus giving enhanced sealing of the orifice or outlet, and minimal leakage. This aspect is shown in Figure 6.

The solenoid power stroke attracts the plunger and moving seat assembly in to latch, thus opening the valve sufficiently to allow full-bore flow through the outlet orifice and aperture. This gives minimal pressure-drop through the valve at full flow when opened by the nominal stroke. In this opening power-stroke, the solenoid not only has to the break the "backpressure" force built-up behind the seat assembly 340 due to the prevailing working pressure, but also overcome the plunger push-off spring force. The power stroke preferably results in latching speedily, especially if driven with a capacitor-discharge drive as described above with reference to GB 2276701.

One innovative aspect of the present invention is the relationship between the available power-drive from the solenoid, and in particular, the role of the incorporated "assisting" diaphragm spring within the seat closure member, for reducing the open drive power requirement. This is achieved by enhancing the large-stroke performance, at a lower voltage than a conventional direct-drive method that does not employ an "assisting" diaphragm spring.

The incorporated "assisting" diaphragm spring 610 has a special role, in that although integrated with the closure seat assembly 340 solidly for effective orifice sealing on the released closing stroke, it is arranged to behave in an independent way on the opening stroke. The opening stroke is when the plunger is being power-driven into the solenoid for efficient latching.

The closure member seat assembly 340 not only contains the "assisting" diaphragm spring 610 but also a flat washer 620 in front. Both the diaphragm spring and the washer are incorporated behind the periphery of the moulded seat face, for guaranteeing that a flat and uniform front face is presented to the shut-off orifice, for good reliable sealing of the outlet orifice or aperture.

With reference to Figures 4 and 5; the actuating plunger end 326 is attached on axis to the diaphragm spring central boss 611. The radial fingers 612 of the diaphragm spring are linked to its peripheral annular ring 613, which tightly abuts the periphery of the flat washer 620, forward and within the seat moulding assembly. The cantilevered radial fingers 612 determine the short-stroke pull- force characteristic of the diaphragm spring, nominally equalling about 200 gF/mm deflection. Bleed holes 622 in the flat washer 620 allow the "back pressure" within the closure seat assembly 340 to normalise through gaps in the "assisting" diaphragm spring during the opening stroke. With reference again to Figure 6. When the coil is energised (with the intention of attracting the plunger in to latch and open the valve for full-bore outlet flow through the orifice), the plunger 325 is allowed to move independently of the seat and washer being attached only to the central boss 611 of the diaphragm spring 610. Deflection of the diaphragm spring takes up approximately half the stroke (i.e. about 2.5 mm) before the plunger force, transmitted through the diaphragm spring, overcomes the "back-pressure" force and the valve is opened. The total closure force (a combination of the push-off spring force and the "back-pressure" force) may be in the order of say 500 gF at a test pressure of 50 mBar.

The stop 320 and the face of the plunger that mates with the stop form two opposite poles when the solenoid is energised to latch the plunger. The instantaneous plunger force is dependent on the distance the poles are apart and, in general, the force is inversely proportional to the square of the distance between pole faces. This means that the closer the plunger is to the stop during the latching stroke, the greater the instantaneous force provided by the plunger. The diaphragm spring allows the plunger to move independently into a pre-travel region on its pull characteristic (governed by the related plunger-to- stop geometry and diaphragm spring pull-force characteristic) where the instantaneous pull force capability of the solenoid increases. At the full open stroke the plunger cannot provide enough force to open the aperture as it cannot overcome the closure force. After a pre-travel period, where the plunger force only has to overcome the resistance of the diaphragm spring (or the combined resistance of the diaphragm spring and a push-off spring), the instantaneous plunger force is sufficient to overcome the combined "backpressure" and push-off spring forces (the closure force).

As the solenoid drive capability at this pre-travel instant exceeds the crucial force-balance point, the seat rapidly peels away from the outlet orifice releasing the "back-pressure", and the plunger rapidly latches over the remaining partial stroke. The only loading now is that due to the compressed push-off spring. At the same instant the deflected diaphragm spring reverts to its flat, relaxed state as shown in Figure 3 while the closure seat assembly opens, thus guaranteeing full open stroke. The capacitor-discharge drive method is well suited to this "assisted" diaphragm spring principle and operation, as the initial high peak voltage applied to the drive coil, accelerates the closure seat assembly and plunger for opening and full-bore flow more efficiently, with adequate residual voltage margins at latch.

Figures 7 and 8 illustrate the overall inventive drive improvement as described, especially due to the employment of the "assisted" diaphragm spring, and its plunger pre-travel adaptive control, in reducing the effective stroke to great advantage. Similar peak capacitor-discharge voltages are used in each example, derived from a notional voltage multiplier circuit off the nominal battery supply, being typically 3.6 V in a domestic gas meter. It is evident that direct-battery valve drive at 3.6 V would not be adequate for the configuration as employed in the design.

The following references are made in the graphs of Figures 7 and 8; A is the minimum peak voltage (voltage multiplier derived), B shows exponential discharge loading, C shows residual voltage at the latch point, D is the direct drive envelope, and E is the response time.

Figure 7 shows the typical capacitor-discharge drive of a valve not employing the "assisted" diaphragm method. This direct drive has a slower fill-stroke latching response (E), giving borderline residual voltage toward the end of the drive duration. The plunger being directly linked to the closure member assembly, the full-stroke drive (without pre-travel control) is more demanding and less reliable.

Figure 8 shows the improved capacitor-discharge drive of a similar valve, but employing the "assisted" diaphragm method. This drive method has a faster latching response (E), giving a much higher residual voltage well within the drive duration. In this case, the plunger being linked only with the "assisting" diaphragm allows pre-travel for reduced effective stroke, and much improved drive.

If the valve operation is closely observed within a clear sealed casing, while the peak discharge-drive voltage is increased in small incremental steps, the plunger and "assisting" diaphragm spring can be seen to pre-travel towards full latching and falling back, until the closure seat finally begins to peel off the orifice. This happens only when the plunger pull capability exceeds combined "back-pressure" and push-off spring force at that instant. Past this crucial force balance point, with slightly increased peak drive, the solenoid latches decisively with a good fast response.

This "assisted" diaphragm spring principle and operation demands little additional drive voltage if the working pressure varies unexpectedly, as the diaphragm spring simply deflects a further pre-travel distance, automatically, still achieving decisive latching and a full bore opening, with slightly increased peak drive voltage.

For example, for a particular outlet valve of 4 Ohm coil resistance at 5 mm nominal stroke, driven with peak-discharge drive using a 5,700 micro. Farad capacitor at a test pressure of 50 mBar, latching occurs decisively at about 8.6 V peak. This is well within the permissible 10 V peak as specified in a particular gas meter specification.

Increasing the test pressure to 75 mBar (the value at which the local pressure- regulator is deemed to have failed or locked-up) only requires a peak-voltage of about 9.5 V to open, this not being a requirement in the specification.

The "assisted" diaphragm spring principle and operation is capable of working in excess of 100 mBar "back-pressure", still within the allowable 10 V peak- voltage drive. Again, this is not a requirement of the specification.

The direct drive method - not employing the "assisted" diaphragm spring principle - would not be able to match this superior performance. Although this application has majored on the solenoid-actuated outlet valve for domestic gas meters, (for example for remote shut-off of the gas supply, for pre-payment or bad-payment control, or for safety shut-off) the basic inventive concept employing an "assisted" diaphragm spring for enhancing or reducing the drive necessary, and minimising the size of the valve package as well, especially when using capacitor-discharge drive, is applicable to any gaseous fluid control. It is not restricted to the enclosed application embodiments as illustrated.

Claims

1. A solenoid actuator for opening and closing an aperture to control fluid flow therethrough, comprising; s a closure member that, when the aperture is closed, is held in contact with a rim of the aperture by a closure force, and

a solenoid plunger, slidably actuatable within a bore of a solenoid ando having a predetermined stroke, coupled to the closure member to transmit a plunger force to the closure member to open the aperture,

in which the plunger is coupled to the closure member by a first resilient means such that, when the plunger is actuated to open the aperture, thes plunger is allowed to travel a portion of its stroke before the plunger force transmitted to the closure member overcomes the closure force to open the aperture.

2. A solenoid actuator according to claim 1 further comprising a second0 resilient means acting to urge the closure member towards the aperture.

3. A solenoid actuator according to claim 1 or 2, in which the plunger is allowed to travel at least 10% of its stroke, preferably at least 20% or at least 30% of its stroke before the closure force is overcome. 5

4. A solenoid actuator according to claim 1 or 2, in which the plunger is allowed to travel between 25% and 75%, and preferably between 40% and 60% of its stroke before the closure force is overcome. 0

5. A solenoid actuator according to any of claims 2 to 4 in which the second resilient means is a push-off spring, or a spring acting to urge the plunger out of the bore of the solenoid.

6. A solenoid actuator according to any of claims 2 to 5 in which the second5 resilient means provides at least a portion of the closure force.

7. A solenoid actuator according to any preceding claim in which fluid pressure provides at least a portion of the closure force.

8. A solenoid actuator according to any preceding claim, in which the first resilient means is a diaphragm spring.

9. A solenoid actuator according to any preceding claim in which the first resilient means is a diaphragm spring having an outer rim and a central boss, and the plunger is connected to the diaphragm spring at the central boss.

10. A solenoid actuator according to any preceding claim in which the closure member has a closure seat assembly comprising;

a seat face for contacting the rim of the aperture,

a substantially rigid plate, such as a washer disposed behind and supporting the seat face, and

the first resilient means.

11. A solenoid actuator according to claim 10, in which the seat face is formed as part of a moulded housing that retains the plate or washer and the first resilient means.

12. A solenoid actuator according to claims 10 or 11 , in which the plate or washer has a plurality of holes through its thickness.

13. A solenoid actuator according to any of claims 10 to 12 in which the seat face is a resilient diaphragm, such as a rubber diaphragm.

14. A solenoid actuator according to any of claims 2 to 13 in which the first resilient means is a diaphragm spring and the second resilient means acts through a central boss of the diaphragm spring.

15. A solenoid actuator according to any preceding claim in which the stroke of the plunger is between 2 and 20 mm.

16. A solenoid actuator according to any preceding claim in which the stroke of the plunger is between 3 and 8 mm.

17. A solenoid actuator according to any preceding claim in which the first resilient means is symmetrical about its centre.

18. A solenoid actuator according to any preceding claim in which the solenoid is a magnetically latching solenoid.

19. A solenoid actuator for opening and closing an aperture to control fluid flow therethrough, comprising;

a closure member that, when the aperture is closed, is held in contact with a rim of the aperture by a closure force,

a solenoid plunger, slidably actuatable within a bore of a solenoid and having a predetermined stroke, coupled to the closure member to transmit a plunger force to the closure member to open the aperture, and

a push-off spring acting to urge the closure member towards the aperture,

in which the plunger is coupled to the closure member at a central boss of a diaphragm spring such that, when the plunger is actuated to open the aperture, the plunger is allowed to travel a portion of its stroke before the plunger force transmitted to the closure member overcomes the closure force to open the aperture.

20. A solenoid actuator according to claim 19, in which the push-off spring acts on the closure member via the central boss of the diaphragm spring.

21. A solenoid actuator for opening and closing an aperture to control fluid flow therethrough, comprising;

a closure member having a closure seat that, when the aperture is closed, is held in contact with a rim of the aperture by a closure force, the closure seat being supported by a substantially rigid plate or disc having a plurality of holes defined through its thickness.

22. A solenoid actuator according to claim 21 , further comprising

a second resilient means acting to urge the closure member towards the aperture,

in which, the plunger is coupled to the closure member by a first resilient means such that, when the plunger is actuated to open the aperture, the plunger is allowed to travel a portion of its stroke before the plunger force transmitted to the closure member overcomes the closure force to open the aperture.

23. A solenoid actuator according to any preceding claim that is actuated by a capacitor discharge drive.

24. A fluid flow valve comprising a solenoid actuator as defined in any preceding claim.

25. A gas valve comprising a solenoid actuator as defined in any preceding claim.

26. A method of opening an aperture, closable by a closure member held closed by a closure force, using a solenoid actuator having a plunger slidably actuatable within the bore of a solenoid and coupled to the closure member by a first resilient means, comprising the steps of,

activating the solenoid to actuate the plunger to transmit a plunger force to the closure member via the first resilient means, such that the plunger travels a portion of its stroke while deflecting or loading the first resilient means without applying sufficient force to the closure member to overcome the closure force, and

allowing the plunger to travel further in its stroke overcoming the closure force to open the aperture.

27. A method of opening an aperture according to claim 26 in which the plunger is allowed to travel at least 10% of its stroke, preferably at least 20% or at least 30% of its stroke before the closure force is overcome.

28. A method of opening an aperture according to claim 26 in which the plunger is allowed to travel between 25% and 75%, and preferably between 40% and 60% of its stroke before the closure force is overcome.

29. A solenoid actuator substantially as described herein, with reference to the drawings.

30. A method of opening an aperture substantially as described herein, with reference to the drawings.