GB2527062A

GB2527062A - Pressure switch

Info

Publication number: GB2527062A
Application number: GB1410282.6A
Authority: GB
Inventors: Simon Nicholas; Alexander David Norman; Congyi Huang; Chas Kilby; Gordon Leather
Original assignee: Intelligent Energy Ltd
Current assignee: Intelligent Energy Ltd
Priority date: 2014-06-10
Filing date: 2014-06-10
Publication date: 2015-12-16
Also published as: GB201410282D0

Abstract

A pressure sensing switch comprises a dome member supported on a substrate such as printed circuit board 3 at an intermediate position 4. An actuator 15 displaces an actuation portion of the dome inboard of intermediate position 4, flattening the dome and causing it to transition from a first configuration where an outboard contact 53 is in contact with a connector 54 to a second configuration where contact 53 is not in contact with connector 54. The dome may have a second contact 57 to contact a second connector 55 in a third, partial configuration intermediate the first and second configurations. Contact regions 53,57 may be on opposite legs of the dome (fig 3) which can flex with a non-linear characteristic including a negative stiffness portion for hysteresis. The actuator can comprise coaxial rods 7,15 and spring 14 and transmit force from a diaphragm 10. The pressure-sensing switch is optimal for use in sensing a high pressure condition in a reaction chamber to disable a pump pumping reactant to the reaction chamber. A particular application is to fuel supply cartridges for fuel cells.

Description

PRESSURE SWITCH

The present invention relates to pressure switches and in particular, though not exclusively to pressure switches suitable for sensing an over-pressure condition in, for example, a gas generator cartridge or a reactor module.

Electrochemical fuel cells require a source of fuel and oxidant to generate electrical energy. A common type of fuel cell uses hydrogen as a fuel source. In some applications, it is convenient to use a fuel supply cartridge which incorporates a reactor module to generate hydrogen as it is required. Such reactor modules may comprise a reaction chamber pre-charged with a first reactant, for example, a metal hydride (such as sodium borohydride) to which can be added a second reactant (e.g. water) to generate hydrogen as and when required. Where the second reactant is a fluid, control of the flow of hydrogen can be conveniently controlled by monitoring hydrogen pressure in the reaction chamber and controlling a pump delivering the fluid reactant to the reaction chamber.

It is desirable to provide a safety mechanism capable of shutting off such a pump in the event of an overpressure condition.

According to one aspect, the present invention provides a pressure-sensing switch comprising: a substrate; a dome member supported on the substrate at an intermediate position of the dome member and having a first electrical contact portion outboard of the intermediate position and an actuation portion inboard of the intermediate position; an actuator configured to displace the actuation portion to flatten the dome member such that the dome member transitions from a first configuration in which the first electrical contact portion is in electrical contact with a first electrical connector, and a second configuration in which the first electrical contact portion is not in contact with the first electrical connector, by rotation of a pivot portion of the dome member about the intermediate position.

The dome member may further include a second electrical contact portion, the second electrical contact portion being in contact with a second electrical connector when the dome member is in a third configuration and the second electrical contact portion being not in contact with the second electrical connector when the dome member is in the first configuration, the actuator being configured to displace the actuation portion such that the dome member transitions from the first configuration to the third configuration prior to completion of the transition to the second configuration. The first configuration may correspond to an unbiased condition of the dome member, the second configuration may correspond to a fully biased condition of the dome member and the third configuration may correspond to a partially biased condition of the dome member. The intermediate position of the dome member may be radially outward of the actuation portion. The first electrical contact portion may lie on a radially extending leg of the dome member. The first electrical contact portion may lie on a first radially extending leg of the dome member and the second electrical contact portion may lie on a second radially extending leg of the dome member.

The first and second radially extending legs may extend in opposite directions from the centre of the dome member. The actuator may comprise a first rod and a second rod, the first and second rods being coaxially mounted to one another and relatively displaceable along the common axis against a spring bias. The spring bias may be configured to enable axial compression of the actuator under a force which is sufficient to transition the dome member from the first configuration to the third configuration, but insufficient to transition the dome member from the third configuration to the second configuration. The actuator may comprise an end stop preventing further axial compression of the actuator thereby enabling transition of the dome member from the third configuration to the second configuration. The displacement of the actuation portion of the dome member as a function of force thereon applied by the actuator may have a non-linear characteristic. The non-linear characteristic may include a negative stiffness portion for hysteresis in switching between the first and second configurations. The substrate may comprise a printed circuit board, the printed circuit board including the first electrical connector. The substrate may comprise a printed circuit board the printed circuit board including the first and the second electrical connectors. The pressure-sensing switch may be incorporated into a fluid fuel supply module.

According to another aspect, the invention provides a fuel supply cartridge comprising the fluid fuel supply module described above and a detachable reaction chamber module configured to engage with the fluid fuel supply module, the reaction chamber module including a displaceable diaphragm configured to communicate pressure within a reaction chamber of the reaction chamber module to the actuator. The actuator of the fuel supply cartridge may comprise a first end for bearing on the actuation portion of the dome and a second end for engaging with the diaphragm, the second end of the actuator further comprising an end stop configured to engage with the housing of the reaction chamber module. The end stop and housing of the reaction chamber module may be configured to axially compress the actuator to transition the dome member to the third configuration when the reaction chamber module is coupled to the fluid fuel supply module. The fuel supply cartridge may further include a pump configured to pump reactant fluid to the reaction chamber, the pump being disabled when the dome member is in the first configuration and the second configuration, but not when in the third configuration. The pressure-sensing switch may be configured to switch from the third configuration to the second configuration of the dome when the pressure in the reaction chamber module between 500 mbar gauge and 830 mbar gauge.

According to another aspect, the present invention provides a fuel supply cartridge comprising a control module and a detachable reaction chamber module configured to engage with the control module, the reaction chamber module including a diaphragm configured to communicate pressure within a reaction chamber of the reaction chamber module to the control module; a pressure-sensing switch in the control module configured to separately sense (i) a disconnected state of the reaction chamber module from the control module; (U) a connected state of the reaction chamber module to the control module; and (iii) an overpressure condition of the reaction chamber in the reaction chamber module via the diaphragm.

The fuel supply cartridge may incorporate a pressure-sensing switch as defined above, configured such that the disconnected state of the detachable reaction chamber module effects the first configuration; the connected state of the reaction chamber effects the third configuration; and the overpressure condition of the reaction chamber effects the second configuration. The fuel supply cartridge may further include a pump configured to pump reactant fluid to the reaction chamber, the pump being disabled by the pressure-sensing switch when the reaction chamber module is disconnected and when the reaction chamber is in an overpressure condition.

According to another aspect, the present invention provides a method of operating a pressure-sensing switch having a substrate and a dome member supported on the substrate at an intermediate position of the dome member and having a first electrical contact portion outboard of the intermediate position and an actuation portion inboard of the intermediate position, the method comprising: operating an actuator to displace the actuation portion to flatten the dome member such that the dome member transitions from a first configuration in which the first electrical contact portion is in electrical contact with a first electrical connector, and a second configuration in which the first electrical contact portion is not in contact with the first electrical connector, by rotation of a pivot portion of the dome member about the intermediate position.

The dome member of the pressure-sensing switch may further include a second electrical contact portion, the second electrical contact portion being in contact with a second electrical connector when the dome member is in a third configuration and the second electrical contact portion being not in contact with the second electrical connector when the dome member is in the first configuration, the method further comprising operating the actuator to displace the actuation portion such that the dome member transitions from the first configuration to the third configuration prior to completion of the transition to the second configuration.

The method may further comprise disposing the pressure-sensing switch in a fluid fuel supply module of a fuel supply cartridge comprising the fluid fuel supply module and a detachable reaction chamber module configured to engage with the fluid fuel supply module, and using a displaceable diaphragm in the reaction chamber module to communicate pressure within a reaction chamber in the reaction chamber module to the actuator of the pressure-sensing switch in the fluid fuel supply module to thereby disable a pump in the fuel supply cartridge when the dome member is in the first configuration and the second configuration, and to enable the pump when the dome member is in the third configuration.

According to another aspect, the present invention provides a method of operating a fuel supply cartridge comprising a control module and a detachable reaction chamber module configured to engage with the control module, the reaction chamber module including a diaphragm configured to communicate pressure within a reaction chamber of the reaction chamber module to the control module; and actuating a pressure-sensing switch in the control module by connection to the diaphragm to separately sense (i) a disconnected state of the reaction chamber module from the control module; (ii) a connected state of the reaction chamber module to the control module; and (iii) an overpressure condition of the reaction chamber in the reaction chamber module via the diaphragm.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 shows cross-sectional side view of a pressure-sensing switch coupled to a pressure vessel; Figures 2a to 2c show cross-sectional side views of the pressure sensing switch of figure 1 in three different configurations during operation; Figure 3 shows a perspective view of a snap-dome suitable for use in the pressure switch of figure 1; Figure 4 shows a cross-sectional side view of the snap-dome of figure 3 mounted on a boss; Figure 5 shows a perspective view of a snap-dome suitable for use in the pressure switch of figures 1 and 2; and Figure 6 shows a schematic view of a fuel supply cartridge suitable for use of the pressure-sensing switch of figure 1 Throughout the present specification, any descriptors relating to relative orientation and position1 such as "top", "bottom", "horizontal", "vertical", "left", "right", "up", "down", "front", "back", as well as any adjective and adverb derivatives thereof, are used in the sense of the orientation of component parts as presented in the drawings. However, such descriptors are not intended to be in any way limiting to an intended use of the described or claimed invention.

With reference to figure 1 there is shown a pressure-sensing switch 1 suitable for electrically connecting and disconnecting a circuit dependent on the pressure sensed in a pressure vessel 2. The pressure-sensing switch 1 comprises a substrate 3 in or on which is mounted a support member 4 which may be in the form of a boss having support points 5. The support points 5 may comprise a circumferential ridge of the boss or may be discrete points. The support member 4 may alternatively form an integral part of the substrate 3. The substrate 3 thus generally supports a dome member 6 which is preferably in the form of a snap-dome, the properties of which will be described in greater detail later.

The pressure-sensing switch 1 is configured so that, in use, a central portion of the dome member 6 is contacted by the first end 7a of an actuator 7 which is displaceable along its long axis (the vertical axis as shown in figure 1). A second end 7b of the actuator 7 can be brought into contact with a diaphragm 10 which is in communication with pressurized fluid 11 within the pressure vessel 2. The second end 7b of the actuator 7 further comprises an end stop 8 which may be in the form of a shoulder 9 which butts against or otherwise engages with a face 13 of the housing 12 of the pressure vessel 2.

The actuator? comprises a first rod 15 and a second rod 16 which are coaxially mounted to one another and are relatively displaceable along the common axis against a spring bias provided by spring 14. The actuator 7 is thereby axially compressible against spring force until the spring 14 is fully compressed, after which both the first rod 15 and the second rod 16 will move in unison. The actuator rod 15 may include an adjustment member 17, for example in the form of a threaded portion which enables lengthening or shortening of the rod 15 by rotation about the axis, independent of the length variation occasioned by the spring 14.

In at least one particular application illustrated in more detail in relation to figure 6, the pressure-sensing switch 1 including the actuator 7 is incorporated into a durable part 18, for example a fluid fuel supply module, and the diaphragm 10 and pressure vessel 2 are incorporated within a disposable part 19, for example a reaction chamber module.

Figure 2 illustrates in greater detail the configuration and operation of the pressure-sensing switch 1. The dome member 6 is attached to the substrate 3 by at least the support member or support position shown at 4a. One form of dome member 6 is shown in figure 3 (dome member 30) and another form of dome member is shown in figure 5 (dome member 50). The dome member 30 includes a set of radially extending legs 31a -31d extending from a central dome portion which is generally arcuate between each pair of opposing legs 31a, 31c and 31b, 31d. The dome member 50 is similar but in this arrangement one of the legs 51d is shortened, The function of the dome member 50 is shown schematically in the figures 2a to 2c. In figure 2a, the pressure-sensing switch 1 is in a first configuration corresponding to an "at-rest" or unbiased configuration, which may be described as "convex outwards". In this configuration, the dome member 50 is supported on the substrate at 4a at an intermediate position 52 of the dome member 50. An actuation portion 56 of the dome member 50, where the actuator 6 can be brought into pressing relation with the dome member, is positioned inboard of the intermediate position 52 (e.g. radially inward from the support position 4a). A first electrical contact portion 53 of the dome member 50 is positioned outboard of the intermediate position 52 (e.g. radially outward from the support position 4a). The first electrical contact portion 53 of the dome member is in physical and electrical contact with a first electrical connector 54 on the substrate 3. A second electrical contact portion 57, outboard of a support position 4b is close to, but not in physical or electrical contact with, a second electrical connector 55 on the substrate 3. The actuator 6 is in a free unbiased configuration applying no or negligible pressure on the actuation portion 56 of the dome member 50. In this configuration, an intermediate position 52b of the dome member is not in contact with the support position 4b.

In figure 2b, the pressure-sensing switch 1 is in a second configuration corresponding to a partially-biased configuration. (Note that the expressions "first configuration", "second configuration" and "third configuration" are in order of introduction in any given context, and may be introduced in a different order in the statements of invention and in the claims.) In this second configuration, the actuator 7 has been engaged with a face 13 of the housing 12 of the pressure vessel 2 (not shown in figure 2, see figure 1) such that the end stop 8 has driven the second rod 16 to the right as shown in figure 2b, against the bias of the spring 14. The diaphragm 10 remains in an unbiased condition. The spring 14 provides sufficient bias against the actuation portion 56 to flex the dome member 50 about the support position 4a such that the second electrical contact portion 57 is brought into physical and electrical contact with the second electrical connector 55 on the substrate 3, while the first electrical contact portion 53 remains in physical and electrical contact with the first electrical connector 54. However, the spring bias of spring 14 is not sufficient to flex the dome member to a third configuration now described in connection with figure 2c.

In figure 2c, the diaphragm 10 is shown displaced to the right from its unbiased condition, e.g. corresponding to an overpressure state of the pressurized fluid 11 in the pressure vessel 2. As the diaphragm 10 displaces outwards (to the right as shown), it drives the rod 16 until spring 14 is fully compressed andlor until a stop end isa of the rod 15 is brought into compressive relationship with a stop end 1 6a of the rod 16. Thereafter, the entire actuator 7 (both rods 15 and 16) moves towards the dome member 50 as the diaphragm displaces further outwards. The actuator 7 movement compresses the actuation portion 56 of the dome member 50 against the support member positions 4a, 4b so that the dome member flattens, and preferably until the dome member "snaps" to a compressed configuration in which the curvature of the dome inverts from convex outwards to concave outwards, as shown in figure 2c, This flattening or inversion of the dome curvature lifts both the first electrical contact portion 53 and the second electrical contact portion 57 respectively away from the first and second electrical connectors 54, 55, by rotation of a pivot portion of the dome member 6 about the intermediate positions 52a, 52b).

The substrate 3 may be a printed circuit board. The first and second electrical connectors 54, 55 may be electrical traces or contact regions on the substrate 3. The first and second electrical connector portions 53, 57 may be configured as one common electrical terminal of a pair of switches suitable for making and breaking contact with the first and second electrical connectors 54, 55. In the first configuration of figure 2a, the first switch 53, 54 is on' and the second switch 55, 57 is off; in the second configuration of figure 2b, the first and second switches are both on'; and in the third configuration of figure 2c, the first and second switches are both off.

The dome member 50 of the pressure-sensing switch I may be entirely electrically conductive and therefore may be used to switch current between the first electrical connector 54 and the second electrical connector 55 on and off by providing an electrically conductive path between the connectors 54, 55 only when in the second configuration of figure 2b. Thus, the switch 1 may be configured as a pressure-sensing switch which is off' in an unbiased or low-biased state, on' in a partially-biased or mid-biased state and off again in a fully-biased or high-biased state, An exemplary application of this pressure-sensing switch will be discussed with reference to figure 6.

In an alternative, simpler configuration, the dome member 30 of figure 3 may be used.

This dome member 30 does not have a short leg 51d; rather, all of the legs 31 a-31 d may be of similar length. With this arrangement, the dome member may provide the pressure-sensing switch with the functionality of the second and third configuration of figures 2b and 2c, without the functionality of the first configuration of figure 2a.

As more readily visualised in figureS, the other legs Sla, Sic (or analogously 31a, 31c) may be used to anchor, bond or otherwise couple the dome member 30, or 50 to the substrate 3, and optionally to electrical connectors 24, 25

S

With reference to figure 6, the pressure-sensing switch 1 may be deployed within a fluid fuel supply cartridge 60. In the particular arrangement of figure 6, the fuel supply cartridge is fabricated as a two part cartridge having a first, durable part 18, referred to as a fluid fuel supply module 61 or a control module and a second, disposable part 191 referred to as a reaction chamber module 62. The disposable part l9is detachable from the durable part 18 and is configured to engage therewith at interface 70 when connected. The reaction chamber module 62 may include a reaction chamber 63 pre-charged with a first reactant1 for example, a metal hydride (such as sodium borohydride). The reaction chamber may lie within a pressure vessel 2 as shown in figure 1. The reaction chamber module 62 may also include a reservoir 64 containing a second reactant, such as water.

The fluid fuel supply module 61 may include a pump 64 and control circuitry 65 for actuating the pump. The fluid fuel supply module 61 may also include an interface 66 for coupling to a fuel cell assembly (not shown) and a fuel conduit 67 for passing fluid fuel (e.g. hydrogen) from the reaction chamber 63 to the interface 66. The control circuitry 65 may also control a valve 68 in the fuel conduit 67, and may have a control interface 69 to coupling to the fuel cell assembly.

The pump 64 may be configured to pump second reactant fluid from the reservoir 64 to the reaction chamber 63 where it reacts with the first reactant to generate hydrogen. As the hydrogen is generated, it can be delivered to a fuel cell assembly via the fuel conduit 67. The pump 64 may be used to control the fuel (e.g. hydrogen) supply rate. The pump may include a mechanical or pneumatic link 64a to the reaction chamber module 62 via interface 70 if it is desired to provide the pump 64 in the durable part 18 rather than the disposable part 19. In an alternative arrangement, the pump could be provided in the disposable part and suitable electrical connections made across the interface 70.

The flow of second reactant fluid from the reservoir 64 to the reaction chamber 63 may be controlled by monitoring the pressure in the reaction chamber 63, using a pressure transducer, not shown. However, a pressure transducer could fail in a way that might cause a system to under-read pressure, or software errors could occur. In either situation, a fuel supply cartridge could over-produce hydrogen. Overproduction may lead to a pressure relief valve (PRV) opening, so that hydrogen can be released to atmosphere.

However, it may not always be optimal to release hydrogen to atmosphere, particularly if the fuel supply cartridge is being used in a confined space or in the presence of ignition sources. Also, continuing release of hydrogen to atmosphere may consume all remaining reactants and is thus wasteful.

Thus, it may be desirable to provide a further mechanism for ensuring that, in the event of an overpressure condition, electrical power to the pump 64 is shut off. It is preferable that the pump 64 is shut off when pressure exceeds a normal working range, but before a PRV opens. This can be particularly challenging, as in some designs the PRV should open before 830 mbar gauge (mbarg), and has some tolerance associated with it. The normal operating range of the reaction chamber may be 300-500 mbarg. Therefore, both the pressure switch and the PRV would need to function within very tight tolerances. However, both space and cost are tightly constrained. The pressure-sensing switch 1 described in connection with figures 1 to 5 can be manufactured as a very compact assembly and the pressure control range can be very tightly controlled by suitable design on the dome member 6 and other components.

One embodiment deploying the dome member 30 provides a simple and efficient method to switch off the pump when expansion of the diaphragm 10 displaces the actuator 7 thereby inverting the dome member from its convex-outward configuration to its concave-outward configuration, thereby lifting the first and second electrical contact portions 53, 57 away from the respective first and second electrical connectors 54, 55. In general, it can be seen that this arrangement corresponds to switching from a first configuration (which may be exemplified by either of the first or second configurations shown in figures 2a and 2b) in which at least a first electrical contact portion of the dome member 6 is in contact with a first electrical connector 54 on the substrate 3, to a second configuration (exemplified by the third configuration shown in figure 2c) in which the first electrical contact portion 53 is deflected away from the first electrical connector 54 on the substrate 3.

Another embodiment deploying the dome member 50 provides an additional safety functionality by way of the short leg 51d. In this arrangement, the unbiased dome member does not make electrical contact between the second electrical contact portion 57 and the second electrical connector 55, and the pump remains disabled. This corresponds to the situation when the disposable part 19 (e.g. the reaction chamber module 62) is not connected to the durable part 18 (eg. fluid fuel supply module). Once the disposable part 19 is connected to the durable part 18 at the interface 70 between the parts 18, 19, the actuator is driven to the partially-biased position exemplified in figure 2b and the dome member reaches the second configuration. The pump 64 is thereby electrically connected, or enabled, and can be switched on and off under the control of the control circuitry 65.

Should an overpressure condition prevail, the diaphragm 10 will further displace the actuator 7 from the partially-biased position exemplified by figure 2b, to a fully-biased position exemplified by figure 2c. This causes the necessary switching of the dome member 50 and disconnection of the pump.

In general, it can be seen that the diaphragm 10 communicates a pressure force caused by the pressurized fluid 11 in the pressure vessel 2 to a spring element 6, 30, 50 in the form of a curved member or snap-dome, so that above a certain pressure the diaphragm defeats the spring element and an electrical contact is broken, cutting power to the pump 64.

This is generally achieved by way of an actuator 7 which has a first end 7a for bearing on the actuation portion 56 of the dome member 6 and a second end 7bforengaging with the diaphragm 10.

The dome member is preferably a snap-dome', which is effectively a highly nonlinear spring, with a negative-stiffness region, thereby giving a binary action from convex to concave configuration at a very well-controlled force, without taking up much space. This enables the pressure of actuation to be tightly-toleranced. The snap dome offers a non-linear characteristic with a negative portion of the force-displacement characteristic which is beneficial for providing switching hysteresis and thereby preventing rapid uncontrolled toggling close to the switching threshold.

The use of an electrically conducting dome member 6 can simplify the design in that the dome member can form one terminal of the switch, or one common terminal of two switches in the arrangement of figures 2a to 2c.

The diaphragm 10 may be any suitable type capable of generating the necessary displacement under pressure of the pressurized fluid 11. As shown, it may be a soft, rolling diaphragm, e.g. with a contoured profile best seen in the cross-sectional figures, to allow extended displacement, which can be matched with an appropriate force-displacement characteristic of the dome member 6.

Placing the diaphragm 10 on the disposable part 19, to actuate a snap-dome in the durable part 18, may be advantageous as there may be more space on the disposable part allowing a larger diaphragm and therefore a softer diaphragm for larger pressure force, enabling tighter tolerance on the pressure required to actuate the switch.

The use of a support member 4 under the dome member 6 at an intermediate position 52, to thereby enable the dome to invert from an unbiased, concave-outward, legs-down configuration to a biased convex-outward, legs-up configuration to break contact with the substrate makes the system fail-safe in the event of debris I contamination of the contacts.

Positioning the actuator 7 in the durable part 18 protects the snap dome 6 which can lie well inside the housing of the durable part 18, The three stage operation of first, second and third configurations of figures 2a to 2c provides a useful safety feature in that if any parts of the pressure switch are missing or broken, the pressure-sensing switch will assume that the disposable part is not present and therefore will therefore not activate the pump 64. This prevents a fuel supply module 61 from wasting electricity by activating the pump when the disposable part 19 is absent.

The use of an end stop 8 of the actuator 7 which seats against the disposable part 19 means that the diaphragm 10 does not need to provide the partial-bias actuation force to move the pressure-sensing switch 1 from the first configuration to the second configuration and so can be made softer, more sensitive to pressure and thereby more easily tuned for actuation to the third configuration within a tight pressure window. In a preferred arrangement, the pressure-sensing switch 1 triggers between 500 mbarg and 830 mbarg.

As the end stop face 13 is on the disposable part 19, and the substrate 3 carrying the dome member is on the durable part 18, there is considerable potential variation in the position of the end stop face 13 with respect to the substrate 3. The two part form of the actuator 7 transmitting force from the diaphragm 10 to the snap dome 6, with a soft spring 14 between the parts 15, 16 of the actuator 7, ensures that across variation in end-stop location, the force is large enough to move the dome member 6 from the first configuration (e.g. unbiased configuration) to the second configuration (e.g. partially biased configuration), but not enough to trip the dome to the third configuration (e.g. fully biased configuration).

The spring 14 between the two rods 15, 16 might be a compliant moulded part: the two rods 15, 16 could then comprise a unitary component with a compliant joint. The compliancy could also be provided at one end of the actuator 7, so that it could be a single rigid part with a compliant end essentially serving at the second rod. If the pressure-sensing switch 1 is configured only as an on-off switch (e.g. using the dome member 30 without a short leg), then only a single rigid rod actuator need be used. Where the dome member acts as a three position switch, the spring bias of the actuator may be generally configured to enable axial compression of the actuator under a force which is sufficient to transition the dome member from the first configuration to the second configuration, but insufficient to transition the dome member from the second configuration to the third configuration.

The diaphragm can comprise a hinged flap, or a piston arrangement.

The dome member 6 can have any force-displacement characteristic suitable for lifting one or two (or more) legs 31, 51 from the surface of a substrate 3 when the actuation portion 56 of the dome is displaced. This may include flattening the dome, e.g. reducing its convex-outward profile, or reducing its convex profile to a planar profile, or reducing its convex profile so far that it subsequently inverts to a concave outward profile. The force-displacement characteristic need not include a negative portion defining a "snap" transition. The dome member 6 generally provides a pivot portion at the intermediate position 52 about which at least a portion of the dome member 6 can pivot. The pivot portion (and thus the intermediate position 52) may comprise an annulus about the actuation portion 56. More generally, the dome member 6 may be elongate and may have discrete pivot portions at discrete intermediate positions. In an arrangement as shown in figure 5, the at least two legs forming first and second electrical contact portions may extend in opposite directions from a centre position of the dome member, although other arrangements are possible.

Other embodiments are intentionally within the scope of the accompanying claims.

Claims

CLAIMS1. A pressure-sensing switch comprising: a substrate; a dome member supported on the substrate at an intermediate position of the dome member and having a first electrical contact portion outboard of the intermediate position and an actuation portion inboard of the intermediate position; an actuator configured to displace the actuation portion to flatten the dome member such that the dome member transitions from a first configuration in which the first electrical contact portion is in electrical contact with a first electrical connector, and a second configuration in which the first electrical contact portion is not in contact with the first electrical connector, by rotation of a pivot portion of the dome member about the intermediate position.
2. The pressure-sensing switch of claim 1 in which the dome member further includes a second electrical contact portion, the second electrical contact portion being in contact with a second electrical connector when the dome member is in a third configuration and the second electrical contact portion being not in contact with the second electrical connector when the dome member is in the first configuration, the actuator being configured to displace the actuation portion such that the dome member transitions from the first configuration to the third configuration prior to completion of the transition to the second configuration.
3. The pressure-sensing switch of claim 2 in which the first configuration corresponds to an unbiased condition of the dome member, the second configuration corresponds to a fully biased condition of the dome member and the third configuration corresponds to a partially biased condition of the dome member.
4. The pressure-sensing switch of claim 1 or claim 2 in which the intermediate position of the dome member is radially outward of the actuation portion.
5. The pressure-sensing switch of claim 4 in which the first electrical contact portion lies on a radially extending leg of the dome member.
6. The pressure-sensing switch of claim 4 when dependent on claim 1 in which the first electrical contact portion lies on a first radially extending leg of the dome member and the second electrical contact portion lies on a second radially extending leg of the dome member.
7. The pressure-sensing switch of claim 6 in which the first and second radially extending legs extend in opposite directions from the centre of the dome member.
8. The pressure-sensing switch of claim 2 in which the actuator comprises a first rod and a second rod, the first and second rods being coaxially mounted to one another and relatively displaceable along the common axis against a spring bias.
9. The pressure-sensing switch of claim 8 in which the spring bias is configured to enable axial compression of the actuator under a force which is sufficient to transition the dome member from the first configuration to the third configuration, but insufficient to transition the dome member from the third configuration to the second configuration.
10. The pressure-sensing switch of claim 9 in which the actuator comprises an end stop preventing further axial compression of the actuator thereby enabling transition of the dome member from the third configuration to the second configuration.
11. The pressure-sensing switch of claim I in which the displacement of the actuation portion of the dome member as a function of force thereon applied by the actuator has a non-linear characteristic.
12. The pressure-sensing switch of claim 11 in which the non-linear characteristic includes a negative stiffness portion for hysteresis in switching between the first and second configurations.
13. The pressure-sensing switch of claim I in which the substrate comprises a printed circuit board, the printed circuit board including the first electrical connector.
14. The pressure-sensing switch of claim 2 in which the substrate comprises a printed circuit board, the printed circuit board including the first and the second electrical connectors.
15. The pressure-sensing switch of claim 1 incorporated into a fluid fuel supply module.
16. A fuel supply cartridge comprising the fluid fuel supply module of claim 15 and a detachable reaction chamber module configured to engage with the fluid fuel supply module, the reaction chamber module including a displaceable diaphragm configured to communicate pressure within a reaction chamber of the reaction chamber module to the actuator.
17. The fuel supply cartridge of claim lOin which the actuator comprises a first end for bearing on the actuation portion of the dome and a second end for engaging with the diaphragm, the second end of the actuator further comprising an end stop configured to engage with the housing of the reaction chamber module.
18. The fuel supply cartridge of claim 17 in which the end stop and housing of the reaction chamber module are configured to axially compress the actuator to transition the dome member to the third configuration when the reaction chamber module is coupled to the fluid fuel supply module.
19. The fuel supply cartridge of claim 18 further including a pump configured to pump reactant fluid to the reaction chamber, the pump being disabled when the dome member is in the first configuration and the second configuration, but not when in the third configuration.
20. The fuel supply cartridge of claim 16 in which the pressure-sensing switch is configured to switch from the third configuration to the second configuration of the dome when the pressure in the reaction chamber module between 500 mbar gauge and 830 mbar gauge.
21. A fuel supply cartridge comprising a control module and a detachable reaction chamber module configured to engage with the control module, the reaction chamber module including a diaphragm configured to communicate pressure within a reaction chamber of the reaction chamber module to the control module; a pressure-sensing switch in the control module configured to separately sense (i) a disconnected state of the reaction chamber module from the control module; (ii) a connected state of the reaction chamber module to the control module; and (iii) an overpressure condition of the reaction chamber in the reaction chamber module via the diaphragm.
22. The fuel supply cartridge of claim 21 incorporating a pressure-sensing switch according to claim 2, configured such that the disconnected state of the detachable reaction chamber module effects the first configuration; the connected state of the reaction chamber effects the third configuration; and the overpressure condition of the reaction chamber effects the second configuration.
23. The fuel supply cartridge of claim 21 further including a pump configured to pump reactant fluid to the reaction chamber, the pump being disabled by the pressure-sensing switch when the reaction chamber module is disconnected and when the reaction chamber is in an overpressure condition.
24. A method of operating a pressure-sensing switch having a substrate and a dome member supported on the substrate at an intermediate position of the dome member and having a first electrical contact portion outboard of the intermediate position and an actuation portion inboard of the intermediate position, the method comprising: operating an actuator to displace the actuation portion to flatten the dome member such that the dome member transitions from a first configuration in which the first electrical contact portion is in electrical contact with a first electrical connector, and a second configuration in which the first electrical contact portion is not in contact with the first electrical connector, by rotation of a pivot portion of the dome member about the intermediate position.
25. The method of claim 24 in which the dome member of the pressure-sensing switch further includes a second electrical contact portion, the second electrical contact portion being in contact with a second electrical connector when the dome member is in a third configuration and the second electrical contact portion being not in contact with the second electrical connector when the dome member is in the first configuration, the method further comprising: operating the actuator to displace the actuation portion such that the dome member transitions from the first configuration to the third configuration prior to completion of the transition to the second configuration.
26. The method of claim 25 further comprising disposing the pressure-sensing switch in a fluid fuel supply module of a fuel supply cartridge comprising the fluid fuel supply module and a detachable reaction chamber module configured to engage with the fluid fuel supply module, the method comprising: using a displaceable diaphragm in the reaction chamber module to communicate pressure within a reaction chamber in the reaction chamber module to the actuator of the pressure-sensing switch in the fluid fuel supply module to thereby disable a pump in the fuel supply cartridge when the dome member is in the first configuration and the second configuration, and to enable the pump when the dome member is in the third configuration.
27. A method of operating a fuel supply cartridge comprising a control module and a detachable reaction chamber module configured to engage with the control module, the reaction chamber module including a diaphragm configured to communicate pressure within a reaction chamber of the reaction chamber module to the control module; actuating a pressure-sensing switch in the control module by connection to the diaphragm to separately sense (i) a disconnected state of the reaction chamber module from the control module; (H) a connected state of the reaction chamber module to the control module; and (Ui) an overpressure condition of the reaction chamber in the reaction chamber module via the diaphragm.