Thermosensitive controller

Abstract

A control unit for a liquid heating appliance includes a leaf spring (44) including a fixed end (44a) and a movable portion (44b) movable relative to the fixed end between a closed position and an open position. The leaf spring (44) includes a kink (54) between the fixed end (44a) and the movable portion (44b). A movable electrical contact (50) is mounted on the movable portion (44b) and mates with a corresponding fixed electrical contact (52) in the power supply circuit when the leaf spring (44) is in the closed position. The control unit further comprises a thermal actuator operable at a predetermined temperature to move the leaf spring (44) to the open position to separate the movable contact (50) from the fixed electrical contact (52).

Description

Technical Field

[0001] The present invention relates to a thermally sensitive controller for a liquid heating appliance, the liquid heating appliance, a leaf spring and a method for manufacturing the leaf spring. Background Art

[0002] In a liquid heating appliance, such as a domestic kettle, an electric heater is typically arranged to heat liquid stored in a liquid heating vessel of the appliance. A control unit may be provided to control the supply of power to the electric heater, such as to start or stop a heating operation.

[0003] The control unit typically includes a switch for disconnecting the electric heater from the power supply when a predetermined temperature is sensed within the appliance. For example, the control unit may be arranged to disconnect the electric heater when the liquid within the liquid heating vessel has reached boiling (or a particular selected temperature) or when an overheating condition is detected. Typically, the control unit includes a thermally sensitive actuator (e.g. a snap-action bimetallic actuator) that operates at a predetermined temperature to move the switch to interrupt the power supply.

[0004] In some conventional control units, the switch includes a leaf spring that carries a movable electrical contact that is arranged to mate with a corresponding fixed electrical contact in the heater's power circuit. When a thermal actuator operates at a predetermined temperature, the leaf spring deflects, causing the electrical contacts to separate, thereby interrupting the supply of power to the heater. The electrical contacts are typically required to be separated by a minimum contact gap to avoid arcing between the contacts when the contacts separate in response to operation of the thermal actuator.

[0005] Reducing the size of the control unit may be desirable because it can advantageously save manufacturing time and costs, and can also help provide more freedom in the design phase of the liquid heating appliance. It can be expected that reducing the size of the control unit will generally require a corresponding reduction in the size of components within the control unit, such as the size of the leaf spring. However, the minimum contact gap between the electrical contacts is generally the same regardless of the reduced size of the control unit.

[0006] As the length of the leaf spring is reduced, flexing the leaf spring to provide a given desired contact gap results in increased bending stresses within the leaf spring (compared to the stresses induced in a longer leaf spring). This increased stress, combined with the repeated flexing of the leaf spring during use of the appliance, results in stress relaxation within the leaf spring.

[0007] This stress relaxation results in a reduction in the contact force between the electrical contacts, which in turn increases the electrical resistance between the contacts, exacerbating the self-heating effect caused by the current flowing through the leaf spring. This can lead to further stress relaxation, a further increase in resistance, and thermal runaway characterized by problems such as contact hissing and control failure.

[0008] Consequently, existing smaller control units are only suitable for appliances operating at low currents and cannot be safely used with higher powered appliances (eg, between 13 and 15 amps). Summary of the Invention

[0009] The object of the present invention is to provide an improved control unit which can be made smaller than conventional control units without necessarily limiting its use to low power appliances.

[0010] When viewed from a first aspect, the present invention provides a control unit for controlling a power circuit of an electric heater in a liquid heating appliance, the control unit comprising:

[0011] a leaf spring comprising a fixed end and a movable portion, the movable portion being movable relative to the fixed end between a closed position and an open position;

[0012] a movable electrical contact mounted on the movable portion of the leaf spring and mating with a corresponding fixed electrical contact in the power circuit when the leaf spring is in the closed position;

[0013] a thermally sensitive actuator operable at a predetermined temperature to move the movable portion of the leaf spring from a closed position to an open position, wherein the movable electrical contact separates from the fixed electrical contact to interrupt the power circuit;

[0014] wherein the leaf spring includes a kink between the fixed end and the movable portion.

[0015] When viewed from a second aspect, the present invention provides a liquid heating appliance comprising:

[0016] Liquid heating containers;

[0017] an electric heater for heating liquid contained in the liquid heating vessel, wherein the electric heater is powered by a power circuit; and

[0018] Control unit, including:

[0019] a leaf spring comprising a fixed end and a movable portion, the movable portion being movable relative to the fixed end between a closed position and an open position;

[0020] a movable electrical contact mounted on the movable portion of the leaf spring and mating with a corresponding fixed electrical contact in the power circuit when the leaf spring is in the closed position;

[0021] a thermally sensitive actuator operable at a predetermined temperature to move the movable portion of the leaf spring from a closed position to an open position, wherein the movable electrical contact separates from the fixed electrical contact to interrupt the power circuit;

[0022] wherein the leaf spring includes a kink between the fixed end and the movable portion.

[0023] It will be appreciated that the leaf spring is flexible such that kinking and flexing of the movable portion relative to the fixed end occurs as the movable portion moves between the closed and open positions. Furthermore, it will be appreciated that since leaf springs are by definition substantially planar, kinking may be understood as any deviation from the planar shape of the leaf spring.

[0024] Thus, the leaf spring provided by embodiments of the present invention has an increased effective bending length due to the presence of the kink, which allows the leaf spring to be shorter in terms of its footprint while helping to prevent stress in the leaf spring from exceeding the yield stress of the leaf spring's material. As a result, the entire control unit can be made smaller. This can reduce the cost of manufacturing the control unit and make the liquid heating appliance including the control unit more visually appealing.

[0025] Because the stress within the kinked leaf spring of the present invention can be reduced compared to a conventional non-kinked leaf spring of the same footprint, in some embodiments, the leaf spring of the present invention can carry higher currents (e.g., between 13 and 15 amps). As mentioned above, leaf springs operating at high currents experience increased stress relaxation due to the higher temperatures generated within the leaf spring caused by self-heating caused by the current flowing through the leaf spring. Introducing a kink into the leaf spring of the present invention allows the maximum bending stress in the leaf spring to be reduced, thereby helping to mitigate the effects of stress relaxation at high currents and facilitating safe operation of the leaf spring below its yield stress.

[0026] In some embodiments, the liquid heating appliance is a cordless appliance. The control unit may include a cordless electrical adapter component for mating with a corresponding base electrical connector component (e.g., of a corresponding power supply base station) to receive a power supply for the power circuit. The cordless electrical adapter component preferably includes one or more mating conductors for connecting to the (respectively) live or neutral pole of the corresponding base electrical connector component.

[0027] In some embodiments, the control unit includes a control body that defines the cordless power adapter component. The control body can be a one-piece (e.g., molded) plastic material body. The cordless power adapter component and the corresponding base electrical connector component can be of a type that can mate regardless of their relative angular orientation, or at least can mate over a wide angular range (e.g., at least 340°, preferably up to 360°). Suitable cordless connectors of this "360° type" are described in WO95 / 08024 and WO01 / 28294, and P72 or P76 connector components from Strix are available.

[0028] In some embodiments, the liquid heating appliance is arranged to be mounted on a power base, and the power base includes a corresponding base electrical connector component. The base electrical connector component may include a tab for connecting to a mains power cable, or the mains power cable may be integrated with the connector component. Preferably, the base electrical connector component is centrally mounted on the power base.

[0029] The cordless power adapter component in the control unit may include at least two mating conductors for connecting to a live pole and a neutral pole of the power circuit. Additional grounding connections may also be present. In some embodiments, the cordless power adapter component is a 3-pole connector component (e.g., for mating with Strix's P72). In other embodiments, the cordless power adapter component is a 5-pole connector component (e.g., for mating with Strix's P76). Such 5-pole connector components provide electronic signal connections and power connections. Preferably, the power circuit of the liquid heating appliance is arranged to receive (e.g., from the base electrical connector component) an electric current between 13 amperes and 15 amperes.

[0030] Preferably, the fixed end of the leaf spring is fixed to a mating conductor of the cordless electrical adapter component. The control unit preferably includes two leaf springs, wherein a first leaf spring is connected or fixed to the live conductor of the cordless electrical adapter component and a second leaf spring is connected or fixed to the neutral conductor of the electrical adapter component. Any or all features of the leaf springs described herein may (and preferably do) apply to either or both of the first leaf spring and the second leaf spring (if provided).

[0031] For example, the second leaf spring preferably includes a fixed end and a movable portion that is movable relative to the fixed end between a closed position and an open position. Preferably, the fixed end of the second leaf spring is fixed to a neutral, mating conductor of the electrical adapter component. Preferably, the second leaf spring extends substantially within a plane and includes a kink disposed between the fixed end and the movable portion, the kink extending out of the plane and reversing to return substantially to the same plane. The second leaf spring preferably has a thickness between 0.05 mm and 0.18 mm, for example approximately 0.15 mm thick.

[0032] Preferably, the fixed end of (e.g., each) leaf spring is directly fixed to (e.g., a respective) mating conductor of the cordless power adapter component. The leaf spring(s) may be joined to the mating conductor(s), for example, by welding or soldering. The leaf spring(s) may be fixed to the mating conductor(s) by friction. The leaf spring(s) may be fixed to the mating conductor(s) by cooperation between paired fastening elements, such as tabs or hooks and corresponding holes.

[0033] In some other embodiments, the liquid heating appliance comprises a power socket for receiving a power cord for connection to a mains power supply. In some embodiments, the liquid heating appliance comprises an integrated power cord.

[0034] In various embodiments, the liquid heating appliance may include a heat diffuser plate arranged in thermal communication with the electric heater. Preferably, the control unit is arranged to be mounted to the underside of the heat diffuser plate. In some embodiments, the control unit includes a mounting plate for mounting the control unit to the underside of the heat diffuser plate. The mounting plate is preferably metal. The mounting plate is preferably substantially flat.

[0035] The thermally sensitive actuator is preferably arranged to detect a temperature within the liquid heating appliance. This temperature may represent the temperature of the liquid within the liquid heating vessel. This temperature may be the temperature of the electric heater. This temperature may be the temperature of the heat diffusion plate.

[0036] The predetermined temperature may be variable (e.g., adjustable). The predetermined temperature may correspond to a desired temperature to which the liquid in the liquid heating vessel is to be heated. The predetermined temperature may correspond to a desired state of the liquid in the liquid heating vessel (e.g., boiling). In some embodiments, the predetermined temperature corresponds to a temperature within the appliance (e.g., the temperature of a heat diffuser plate) during an overheating (e.g., "dry boil") condition.

[0037] In some embodiments, the control unit comprises an "overheat" thermal actuator and a "liquid temperature condition" thermal actuator. The overheat thermal actuator is preferably arranged to operate at a predetermined temperature corresponding to the temperature within the appliance during an overheat condition. The liquid temperature condition thermal actuator is preferably arranged to operate at a predetermined temperature corresponding to a desired state of the liquid in the liquid heating vessel (e.g. boiling).

[0038] Preferably, both the overheat thermal actuator and the liquid temperature condition thermal actuator are arranged to move the movable portion of the leaf spring from a closed position to an open position in which the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit.

[0039] In embodiments where the control unit comprises an "overheat" thermal actuator and a liquid temperature condition thermal actuator, the control unit may be considered an "integrated" controller.

[0040] In some embodiments, the control unit does not include a liquid temperature condition thermistor actuator. Instead, the control unit may only include an overheat thermistor actuator. A control unit according to such an embodiment may be suitable for use in a liquid heating appliance comprising an electric switching device that is physically separated from the control unit but electrically connected to the control unit. The electric switching device preferably includes a liquid temperature condition thermistor actuator for disconnecting the switch to interrupt the power supply to the heater. The liquid temperature condition thermistor actuator is preferably arranged to disconnect the switch when a predetermined temperature corresponding to a desired state (e.g., boiling) of the liquid in the liquid heating container is detected.

[0041] This liquid heating appliance can be considered a "split switch" appliance because the switch used to interrupt the power supply to the heater in the event of overheating is separate from the switch used to interrupt the power supply to the heater when a liquid temperature condition (such as boiling) is detected. In contrast, in an integrated control, the same switch (i.e., the same set of contacts in the control unit) is disconnected in both cases. The liquid temperature condition thermal actuator may comprise a thermomechanical switch, such as a bimetallic switch. In some embodiments, the electrical switching device comprises an electronic switching device, such as a controller connected to a thermistor. The electrical switching device is preferably arranged in a different part of the liquid heating appliance from the controller. This can increase the design flexibility of the liquid heating appliance. In some embodiments, the control unit is arranged at the base of the appliance, and the electrical switching device is arranged at the upper part of the appliance (e.g., on the handle of the appliance). The electrical switching device is preferably connected in series with a switch comprising a movable electrical contact and a fixed electrical contact of the control unit.

[0042] In some embodiments (e.g., where the control unit is an integrated control unit), the control unit includes a trip bar. The trip bar is preferably movable (e.g., pivotable). The trip bar is preferably movable so as to act on a movable portion of a leaf spring and move the movable portion of the leaf spring from a closed position to an open position, in which the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit. The liquid temperature condition thermally sensitive actuator is preferably configured to move the trip bar at a predetermined temperature. The liquid temperature condition thermally sensitive actuator is preferably configured to move the trip bar so as to move the movable portion of the leaf spring from the closed position to an open position, in which the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit.

[0043] Preferably, the (e.g., overheating) thermal actuator is mounted on the upper surface of the control unit. Preferably, the thermal actuator is mounted on the upper surface of the mounting plate. This means that when the control unit is mounted to the underside of the heat diffuser plate, the thermal actuator can be arranged in good thermal communication with the heat diffuser plate. As a result, the thermal actuator can more reliably detect the predetermined temperature, for example by accurately detecting the temperature of the heat diffuser plate (and therefore, for example, the temperature of the liquid within the appliance). This can allow the thermal actuator to operate more reliably at the predetermined temperature.

[0044] The thermally sensitive actuator may comprise a bimetallic element. The bimetallic element is preferably a snap-action bimetallic actuator. Preferably, the bimetallic element is arranged to operate (eg, snap-action) when a predetermined temperature is detected.

[0045] The bimetallic element may act directly on the leaf spring. However, preferably, the control unit (e.g., a thermal actuator) includes an intermediate component that is operated by the bimetallic element at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position. The bimetallic element preferably includes an actuating portion configured to deflect at a predetermined temperature. The actuating portion is preferably arranged to act on the intermediate component to move the intermediate component. Preferably, the intermediate component is moved by the same distance as the actuating portion of the bimetallic element deflects.

[0046] In a preferred embodiment, the intermediate component comprises a push rod which is operated by a (e.g. bimetallic) actuator at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position. Preferably, the push rod extends downwardly from the thermally sensitive actuator towards the movable portion of the leaf spring.

[0047] In some embodiments, a thermal actuator (e.g., a push rod of the thermal actuator) is arranged to push against a contact point of the movable portion of the leaf spring to move the movable portion from the closed position to the open position. Preferably, the contact point is arranged at a distal end of the leaf spring relative to the fixed end and the movable electrical contact. Preferably, the movable electrical contact is mounted on the movable portion of the leaf spring between the kink and the contact point.

[0048] The distance travelled by the movable portion of the leaf spring at the contact point is preferably substantially equal to the deflection of the actuating portion of the bimetallic element.

[0049] It may be beneficial for the manufacturer to use the same thermal actuator for a small control unit as for other (larger) sized control units in order to save costs and minimize design effort. However, due to the reduced length of the leaf springs in conventional smaller controllers, this is generally not possible because the force exerted by the thermal actuator on the shorter leaf spring would cause the stress within the leaf spring to exceed the yield stress. However, as discussed herein, providing a kink in the leaf spring of the present invention can reduce the maximum stress within the leaf spring. Therefore, in some embodiments, the thermal actuator provided in the control unit to act on the leaf spring can advantageously be of the same size as the type used in the larger controller.

[0050] Furthermore, by arranging the thermal actuator (e.g., the push rod of the thermal actuator) such that the distance from the fixed end of the leaf spring to the contact point is greater than the distance from the fixed end to the movable electrical contact, a vertical displacement of the thermal actuator (e.g., the push rod of the thermal actuator) at the contact point can result in a proportionally smaller vertical distance at the electrical contact position, i.e., at the location where the contact gap is generated. The location of the contact point between the thermal actuator (e.g., the push rod of the thermal actuator) and the movable portion of the leaf spring can be selected during the design phase to provide a desired separation distance between the movable electrical contact and the fixed electrical contact for a given vertical displacement of the thermal actuator when the movable portion of the leaf spring is moved to the disconnected position.

[0051] In some embodiments, the leaf spring defines a hole in which the movable electrical contact is disposed. The movable electrical contact can be disposed within the hole by an interference fit. Preferably, the leaf spring includes a (e.g., integral) projection that extends out of the plane of the leaf spring around the periphery of the hole. This means that there is a larger contact area between the leaf spring and the movable electrical contact than would be possible if the leaf spring did not include the projection. This can improve the bond (e.g., a cold bond) between the movable electrical contact and the leaf spring, thereby helping to reduce self-heating (and overall stress) in the leaf spring.

[0052] This arrangement for mounting the movable electrical contact may be particularly beneficial for leaf springs that are thinner than conventional leaf springs (ie, less than 0.2 mm thick), as conventional methods of mounting electrical contacts to leaf springs (such as welding or riveting) are difficult to achieve at such low thicknesses.

[0053] This is considered novel and inventive in itself. Therefore, from another aspect, the present invention provides a leaf spring comprising:

[0054] a proximal end and a distal portion movable relative to the proximal end; and

[0055] An electrical contact is mounted on a distal portion of a leaf spring for mating with a corresponding electrical contact; wherein the leaf spring defines a hole in which the electrical contact is disposed, and wherein the leaf spring includes a projection extending out of the plane of the leaf spring around a periphery of the hole to surround the electrical contact.

[0056] When viewed from another aspect, the present invention provides a control unit for controlling a power circuit of an electric heater in a liquid heating appliance, the control unit comprising:

[0057] a leaf spring including a fixed end and a movable portion, the movable portion being movable relative to the fixed end between a closed position and an open position;

[0058] a movable electrical contact mounted on the movable portion of the leaf spring and mating with a corresponding fixed electrical contact in the power circuit when the leaf spring is in the closed position;

[0059] a thermally sensitive actuator operable at a predetermined temperature to move the movable portion of the leaf spring from a closed position to an open position, wherein the movable electrical contact separates from the fixed electrical contact to interrupt the power circuit;

[0060] Wherein the leaf spring defines an aperture in which the movable electrical contact is disposed, and wherein the leaf spring includes a projection extending out of the plane of the leaf spring around a periphery of the aperture.

[0061] When viewed from another aspect, the present invention provides a liquid heating device comprising:

[0062] Liquid heating containers;

[0063] an electric heater for heating liquid contained in the liquid heating vessel, wherein the electric heater is powered by the power circuit; and

[0064] A control unit, comprising:

[0065] a leaf spring including a fixed end and a movable portion, the movable portion being movable relative to the fixed end between a closed position and an open position;

[0066] a movable electrical contact mounted on the movable portion of the leaf spring and mating with a corresponding fixed electrical contact in the power circuit when the leaf spring is in the closed position;

[0067] a thermally sensitive actuator operable at a predetermined temperature to move the movable portion of the leaf spring from a closed position to an open position, wherein the movable electrical contact separates from the fixed electrical contact to interrupt the power circuit;

[0068] Wherein the leaf spring defines an aperture, the movable electrical contact is disposed in the aperture, and wherein the leaf spring includes a projection extending out of the plane of the leaf spring around a periphery of the aperture.

[0069] Viewed from another aspect, the present invention provides a method of manufacturing a leaf spring comprising a proximal end portion and a distal portion movable relative to the proximal end portion, the method comprising:

[0070] forming a hole through the distal end portion of the leaf spring; and

[0071] installing an electrical contact on the distal portion of the leaf spring by inserting the electrical contact into the hole;

[0072] Wherein forming the hole includes forming a projection that extends out of the plane of the leaf spring around a periphery of the hole.

[0073] As described above, in some embodiments, the movable electrical contact can be arranged in the hole with an interference fit. Preferably, the leaf spring includes a (e.g., integral) protrusion that extends out of the plane of the leaf spring around the periphery of the hole. This means that there is a larger contact area between the leaf spring and the movable electrical contact than would be possible if the leaf spring did not include the protrusion.

[0074] In some embodiments, the leaf spring includes a kink (e.g., a feature of any one or more embodiments of the other aspects discussed herein). However, the leaf spring can be substantially flat (e.g., at least between the proximal end and the distal end). Preferably, the leaf spring has a thickness of less than 0.2 mm. In some embodiments, the leaf spring has a thickness between 0.05 mm and 0.18 mm. In some embodiments, the leaf spring is approximately 0.15 mm thick.

[0075] The leaf spring and the projection can be separate components. However, the leaf spring is preferably a single component including the projection. The projection is preferably formed from the same material as the leaf spring. The projection is preferably formed at the same time as the hole (e.g., in the same operation). This can simplify the leaf spring manufacturing process while helping to ensure the beneficial geometry of the hole and projection as described above.

[0076] For example, the hole may be formed by stamping, which preferably causes the material of the leaf spring around the periphery of the hole to flex in the direction of the stamping, thereby forming the protrusion.Thus, in some embodiments, the method may include forming the protrusion by stamping through the leaf spring to form the hole.

[0077] The projection may extend around a portion of the hole. Preferably, the projection extends around most (eg the entire) circumference of the hole. The projection may be formed to surround the electrical contact.

[0078] In embodiments of any aspect disclosed herein, the movable part of the leaf spring is preferably biased to a closed position. The bias may be provided by a separate component, i.e. a biasing member. However, preferably, the bias is provided in the form of the leaf spring itself. The thermal actuator is preferably operable to move the movable part against the bias when moving the movable part from the closed position to the open position. Following the operation of moving the movable part from the closed position to the open position, the thermal actuator is preferably configured to reset to allow the movable part to return to the closed position. The thermal actuator may be manually reset. However, preferably, the thermal actuator is configured to automatically reset (e.g., when the temperature detected by the thermal actuator drops sufficiently below a predetermined temperature).

[0079] In some embodiments, the control unit also includes a trip bar, for allowing a user to manually move the movable part of the leaf spring from the closed position to the disconnected position and / or from the disconnected position to the closed position. The trip bar can be movable between an "OFF (disconnect)" position and an "ON (connection)" position. In the "ON" position, the movable electrical contact preferably contacts with a fixed electrical contact. In the "OFF" position, the movable electrical contact may or may not contact with the fixed electrical contact. However, preferably, the control unit is configured so that when the trip bar is in the "OFF" position, no current flows through the electrical contacts. Therefore, the provision of the trip bar can allow the user to manually interrupt the heating operation and / or start the heating operation of the liquid heating appliance.

[0080] As mentioned above, the trip bar may also be arranged to be moved by a liquid temperature condition thermally sensitive actuator of the control unit (eg upon detection of boiling).

[0081] Preferably, the control unit includes a stopper for preventing movement of the movable portion of the leaf spring after the movable portion has moved from the closed position to the open position. The movable portion of the leaf spring is preferably arranged to contact the stopper after moving from the closed position to the open position. Thus, the stopper can be provided to limit the overshoot distance traveled by the movable portion of the leaf spring. This helps prevent the leaf spring from plastically deforming during use due to (e.g., repeated) flexing.

[0082] In some embodiments, a stopper is disposed on a control body of the control unit. In some embodiments, the stopper is disposed on a trip bar of the control unit. When the stopper is disposed on the trip bar of the control unit, the position of the trip bar can be reset (e.g., reset to an "OFF" position) by a force exerted on the stopper by the movable portion of the leaf spring when the movable portion contacts the stopper. Thus, the stopper can act as a force-transmitting spacer, providing the dual functions of resetting the trip bar position and reducing overshoot in the leaf spring.

[0083] Preferably, the stopper is arranged vertically (e.g., directly) below the contact point (i.e., the point where the thermo-sensitive actuator or its push rod contacts the leaf spring). Positioning the stopper directly below the contact point means that the leaf spring can be stopped more quickly without inducing a bending moment in the leaf spring between the stopper and the contact point. Such a bending moment could damage the leaf spring.

[0084] In some embodiments, the control unit includes a return stop for preventing the movable portion of the leaf spring from moving from the open position to the closed position (for example, after the movable portion has been moved to the open position by the thermal actuator and when it returns to the closed position under its own bias). The return stop is preferably arranged to prevent the leaf spring from returning to the closed position after the movable portion has moved to the open position. The return stop is preferably arranged on a trip bar of the control unit.

[0085] In some embodiments, the trip bar includes a stopper (e.g., a force-transmitting spacer) and a return stopper. The stopper (e.g., the force-transmitting spacer) is preferably disposed below the movable portion of the leaf spring (i.e., in the direction in which the movable portion is moved by the thermal actuator). The return stopper is preferably disposed above the movable portion of the leaf spring.

[0086] The return stop may be configured to move the movable portion of the leaf spring from the closed position to the open position when the trip bar is moved from the "ON" position to the "OFF" position (e.g., by a user or by operation of a liquid temperature condition thermally sensitive actuator).

[0087] Preferably, the trip bar is arranged such that movement of the trip bar from the "OFF" position to the "ON" position releases the movable portion of the leaf spring, allowing the movable portion to move from the open position to the closed position (e.g., due to the bias of the leaf spring). Preferably, movement of the trip bar from the "OFF" position to the "ON" position does not directly move the movable portion of the leaf spring to bring the movable electrical contact into contact with the fixed electrical contact. For example, preferably, the range of motion of the stop (upon movement of the trip bar) is insufficient to allow the stop to directly move the movable portion of the leaf spring to bring the movable electrical contact into contact with the fixed electrical contact. This can help improve safety by preventing a user from overriding the control unit by manually closing the electrical contacts before the thermal actuator is reset. Preferably, the movable portion is moved from the open position to the closed position solely by the bias of the leaf spring.

[0088] The leaf spring is preferably a single uniform component, preferably comprising at least a fixed end, a movable part and a kink. Preferably, the leaf spring is elongated. The leaf spring is preferably mounted in the control unit as a cantilever, i.e. fixed at its fixed end (proximal end) and unsupported (preferably movable) at its opposite end (distal end). The kink may be separated from the fixed end by a further movable part of the leaf spring. However, preferably, the kink is arranged adjacent to the fixed end of the leaf spring. Preferably, the kink is arranged at the flexure point of the leaf spring. The flexure point is the point of the leaf spring that is closest to the fixed end and still flexes when the movable part moves relative to the fixed end. Arranging the kink at the flexure point of the leaf spring helps to reduce the stress of the leaf spring at the flexure point, which is usually the part of the leaf spring where the stress is highest. Reducing the stress in this area can improve the durability of the leaf spring.

[0089] The kink may be of any suitable or desired shape to provide an increased effective bending length. Preferably, the kink extends out of the plane of the leaf spring and returns substantially to the same plane. The kink may be arcuate. The kink may be substantially semicircular. The kink may be U-shaped, S-shaped, V-shaped, W-shaped, M-shaped or C-shaped. The kink may be substantially sinusoidal. The kink may include a folded portion. Preferably, the kink is a continuous bend. The kink may have the approximate shape of a normal distribution (bell) curve. Preferably, the kink includes an arcuate portion. Preferably, the leaf spring includes one or more continuously bendable transition features (e.g., fillets) between the substantially planar leaf spring and the kink (e.g., the arcuate portion). This helps to avoid high stress concentrations in the leaf spring, which may allow the leaf spring to be made smaller while not exceeding the yield stress of the leaf spring material.

[0090] As described above, by providing a kink in the leaf spring to increase the effective bending length of the leaf spring, the stress within the leaf spring can be reduced for a leaf spring of a given footprint. As a result, the leaf spring can be made smaller without exceeding the yield stress of the leaf spring material.

[0091] The leaf spring of the present invention is considered to be novel and inventive in its own right. Thus, when viewed from another aspect, the present invention provides a leaf spring comprising:

[0092] a proximal end and a distal portion movable relative to the proximal end; and

[0093] an electrical contact mounted on a distal portion of the leaf spring for mating with a corresponding electrical contact;

[0094] wherein the leaf spring includes a kink between the proximal end and the distal portion.

[0095] When viewed from another aspect, the present invention provides a method of making a leaf spring comprising a proximal end portion and a distal portion movable relative to the proximal end portion;

[0096] The method includes:

[0097] forming a kink in the leaf spring between the proximal end and the distal portion; and

[0098] An electrical contact for mating with a corresponding electrical contact is mounted on the distal end portion of the leaf spring.

[0099] In some embodiments, a method of manufacturing a leaf spring includes forming a hole extending through a distal portion of the leaf spring. The method preferably includes mounting an electrical contact on the distal portion of the leaf spring by inserting the electrical contact into the hole. The electrical contact may be press-fit into the hole. The step of forming the hole may include punching the hole. Preferably, forming the hole includes forming a protrusion that extends out of the plane of the leaf spring around the periphery of the hole. As described above, this can increase the contact area between the electrical contact and the leaf spring, thereby helping to improve the bond (e.g., cold bond) between the electrical contact and the leaf spring.

[0100] The proximal end of the leaf spring is preferably adapted to be mounted on a control unit of a (eg domestic) liquid heating appliance.Preferably, the electrical contacts are adapted to cooperate with corresponding electrical contacts in a control unit of a (eg domestic) liquid heating appliance.

[0101] The leaf spring may include one or more fillets positioned adjacent to the kink to blend the geometry of the kink with the geometry of the remainder of the leaf spring. In some embodiments, the kink includes an arcuate portion positioned between two fillets. Preferably, the arcuate portion of the kink has a radius of curvature between 0.3 mm and 1.5 mm, such as between 0.5 mm and 1.0 mm, or approximately 0.8 mm. Preferably, the radius of curvature of the one or more fillets is between 0.1 mm and 1.35 mm, such as between 0.35 mm and 0.8 mm, or approximately 0.65 mm.

[0102] The leaf spring can be of any suitable or desired length. However, in a preferred embodiment, the leaf spring has a footprint length of less than 25 mm. This allows the leaf spring to be used in control units that are smaller than conventional control units. The leaf spring can have a (footprint) length between 5 mm and 30 mm, such as between 15 mm and 25 mm, or approximately 22 mm. The leaf spring can have a width between 1.5 mm and 5 mm, such as between 2.0 mm and 4.0 mm, or approximately 3.5 mm.

[0103] The leaf spring may be of any suitable or desired thickness. However, in a preferred embodiment the leaf spring has a thickness of less than 0.2 mm. Reducing the thickness of the leaf spring increases the self-heating effect of the leaf spring because less cross-sectional area is provided for the current to flow through the leaf spring. However, the applicant has found that reducing the thickness of the leaf spring may also reduce the stresses generated in the leaf spring. This means that the leaf spring can be made shorter without still exceeding the yield stress of the material. The thickness of the leaf spring may be between 0.05 mm and 0.3 mm, for example between 0.1 mm and 0.2 mm, for example approximately 0.15 mm thick. Preferably, the cross-sectional area of ​​the leaf spring in a plane perpendicular to the largest dimension (i.e. the length) of the leaf spring is between 0.07 mm and 0.15 mm thick. 2 and 1.5mm 2 between, for example, 0.2 mm 2 and 0.8mm 2 between, for example approximately 0.5 mm 2 .

[0104] In some embodiments, the leaf spring has a thickness between 0.05 mm and 0.18 mm, such as between 0.1 mm and 0.15 mm, such as approximately 0.15 mm thick.

[0105] Preferably, when the movable portion of the leaf spring is in the open position, the movable electrical contact is separated from the fixed electrical contact by a contact gap of between 0.3 mm and 1.5 mm, such as 0.7 mm to 1.2 mm, such as approximately 0.9 mm. This separation distance may be the minimum distance required to avoid arcing between the contacts when the movable portion moves between the closed position and the open position. The leaf spring is preferably shaped such that, when the leaf spring is arranged in the controller and the movable electrical contact is in the closed position, the deflection in the leaf spring provides a preload force applied by the movable electrical contact to the fixed electrical contact. In a preferred embodiment, when the movable portion is in the closed position, the leaf spring is arranged such that the movable electrical contact applies a preload of between 10 grams and 30 grams, such as between 15 grams and 25 grams, such as a preload of approximately 20 grams, on the fixed electrical contact.

[0106] The leaf spring may be made of any suitable or desired material. Preferably, the leaf spring is electrically conductive, such as metal. In a preferred embodiment, the leaf spring material is a (eg hardened) copper alloy, such as C7025.

[0107] It will be appreciated that any aspect described herein may (and preferably does) include one or more (eg all) of the optional and preferred features outlined herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Certain preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0109] Figure 1 shows a perspective view of a liquid heating appliance according to one embodiment of the present invention;

[0110] Figure 2a and Figure 2b Shows Figure 1 A perspective view of a control unit of a liquid heating appliance;

[0111] Figure 3 Shows Figure 2a and Figure 2b A cross-sectional front view of a control unit;

[0112] Figure 4 Shows Figure 2a and Figure 2b A perspective view of the various components of the control unit;

[0113] Figure 5a 、 Figure 5b and Figure 5c Displays when the actuator of the control unit is operated Figure 2a and Figure 2b A cross-sectional front view of a leaf spring of a control unit;

[0114] Figure 6a and Figure 6b Displays when the trip lever of the control unit is operated Figure 2a and Figure 2b A cross-sectional front view of a leaf spring of a control unit;

[0115] Figure 7 is a graph showing the von Mises stress in conventional leaf springs of varying lengths;

[0116] Figure 8 shows a cross-sectional front view of a control unit of a liquid heating appliance according to another embodiment of the present invention;

[0117] Figure 9a and Figure 9b Shows Figure 8 A cross-sectional front view of a leaf spring of a control unit;

[0118] Figure 10 A perspective view of a "split switch" liquid heating appliance according to an embodiment of the present invention is shown;

[0119] Figure 11a Shows Figure 8 A front view of a leaf spring of a control unit;

[0120] Figure 11b A front view showing a leaf spring of a control unit of a liquid heating appliance according to another embodiment of the present invention; and

[0121] Figure 12a、 Figure 12b 、 Figure 12c and Figure 12d Alternative geometries for leaf spring kinks are shown. DETAILED DESCRIPTION

[0122] Figure 1 A perspective view of a liquid heating appliance 2 (hereinafter appliance 2) according to one embodiment of the present invention is shown. The appliance 2 comprises a liquid heating vessel 4, a vessel spout 6 and a handle 8. The top of the appliance 2 is closed by a lid 10. The appliance 2 is arranged to rest on a power base 12 having a centrally located 360-degree base electrical connector component 14 for powering the appliance.

[0123] The appliance 2 also includes an electric heater ( Figure 1 The heater (not shown) is used to heat a volume of liquid contained in a liquid heating vessel 4. The heater includes an electric heating element mounted on the underside of a heat diffuser plate. The heating element is arranged to be in thermal communication with the base 23 of the liquid heating vessel 4 via the heat diffuser plate when electrical energy is supplied to the heater, thereby heating the contents of the liquid heating vessel 4.

[0124] Control Unit ( Figure 1 The power supply unit 12 (not shown) is also mounted on the bottom side of the heat diffusion plate and controls the supply of power from the power base 12 to the electric heater.

[0125] Figure 2a Shows Figure 1 A perspective view of the control unit 16 of the appliance 2 is shown.

[0126] The control unit 16 comprises a moulded plastics control body 26 on the bottom side of which is formed a cordless power adapter part 28. The cordless power adapter part 28 is arranged to mate with the base power connector part 14 of the power base 12.

[0127] The control unit 16 includes fixed electrical tabs 29 that are electrically connected to the cordless electrical adapter component 28 via a power circuit, which will be described in more detail below. As is known in the art, flying leads or other electrical connections can be used to fix the electrical tabs 29 to connect the power circuit to the electrical terminals of the electric heater.

[0128] The control unit 16 also includes first and second thermal actuators 30a, 30b supported by a metal mounting plate 32 secured to the top side of the control body 26. The thermal actuators 30a, 30b are snap-acting bimetallic actuators, each set to operate independently at a predetermined temperature.

[0129] The actuators 30a, 30b are located on the top surface of the control unit 16 so that when the control unit 16 is mounted on the underside of the heat diffuser plate, the actuators 30a, 30b are in thermal communication with the heat diffuser plate. This means that the actuators 30a, 30b are arranged to detect the temperature of the diffuser plate.

[0130] As will be discussed in more detail below, the arrangement of the thermally sensitive actuators 30a, 30b is such that their operation at (one or more) predetermined temperatures causes a switch within the control unit 16 to open, thereby interrupting the supply of electrical energy to the heater. As is known in the art, this allows the heater to be switched off in the event of a "dry boil" where there is no liquid in the liquid heating vessel 4.

[0131] The control unit 16 also includes a trip bar 36 that is pivotally mounted on the control body 26 of the control unit 16 and is manually operable to open and close electrical contacts within the power circuit, as will be described in more detail below.

[0132] Figure 2b Shows Figure 1 A perspective view of the bottom side of the control unit 16 of the appliance 2.

[0133] Control unit 16 includes a third thermal actuator 30c mounted on control body 26 below the distal end of trip bar 36. The proximal end of the trip bar is adjacent first and second thermal actuators 30a, 30b and electrical contacts of the power circuit.

[0134] The third thermally sensitive actuator 30c is in fluid communication with the liquid heating vessel 4 of the appliance 2 via a conduit (not shown) which, in this example, extends through the handle 8 of the appliance 2, such that steam generated within the liquid heating vessel 4 is directed to the third thermally sensitive actuator 30c. The thermally sensitive actuator 30c is a snap-acting bimetallic actuator which is set to operate at a predetermined temperature which indicates that the liquid within the liquid heating vessel 4 has reached boiling temperature and has been converted to steam.

[0135] As will be described in more detail below, the thermally sensitive actuator 30c is arranged so that its operation at its predetermined temperature exerts a force on the distal end of the trip bar 36, causing the trip bar 36 to pivot to the "OFF" position, thereby opening electrical contacts within the power circuit and interrupting the supply of electrical energy to the heater. As is known in the art, this allows the heater to be switched off when the liquid in the liquid heating vessel 4 reaches a boil.

[0136] Figure 3 Shows Figure 2a and Figure 2bFIG2 is a cross-sectional front view of a control unit 16 mounted on the bottom side of a heat diffusion plate 18 b of an electric heater 18 . The electric heater 18 further includes an electric heating element 18 a , which is also mounted on the bottom side of the heat diffusion plate 18 b and surrounds the control unit 16 .

[0137] The cordless electrical adapter part 28 is a three-pole connector comprising a ground pin 28a, a live ring 28b and a neutral ring 28c. The live ring 28b and the neutral ring 28c are concentrically arranged around the ground pin 28a in the center. Figure 3 28a) comprises a central hole for receiving a ground pin 28a, and coaxial annular holes for receiving a live ring 28b and a neutral ring 28c.

[0138] Electrical contacts received in the coaxial bores contact the live and neutral rings 28b, 28c, respectively, to connect the live and neutral poles of the power circuit when the connector parts 14, 28 are connected together. The electrical contact received in the central bore contacts the ground pin 28a.

[0139] The control unit 16 includes a first push rod 40a and a second push rod 40b. The first push rod 40a is arranged directly below the first actuator 30a, and the second push rod 40b is arranged directly below the second actuator 30b. The first push rod 40a and the second push rod 40b are arranged to facilitate vertical downward movement when the first actuator 30a and the second actuator 30b are respectively operated.

[0140] Figure 4 Shows Figure 2a and Figure 2b 1 , wherein some components of the control unit 16 are omitted for ease of illustration.

[0141] The control unit 16 includes a live leaf spring 42 and a neutral leaf spring 44. The live leaf spring 42 includes a fixed end 42a that is mounted to and electrically connected to the live ring 28b. The live leaf spring 42 also includes a movable portion 42b that extends from a flexure point of the live leaf spring 42. The first push rod 40a is arranged to contact the distal end of the movable portion 42b of the live leaf spring 42.

[0142] The neutral leaf spring 44 includes a fixed end 44a which is mounted to the neutral ring 28c and is electrically connected to the neutral ring 28c. The neutral leaf spring 44 also includes a movable portion 44b which is movable from a flexure point 45 (e.g., Figure 5a and 5b The second push rod 40b is arranged to contact the distal end of the movable portion 44b of the neutral leaf spring 44.

[0143] Live and neutral leaf springs 42, 44 are directly secured to live and neutral rings 28b, 28c, respectively. The leaf springs 42, 44 include holes for receiving corresponding tabs projecting from live and neutral rings 28b, 28c to facilitate this direct securing.

[0144] The control unit 16 also includes a live securing tab 29 a located above the movable portion 42 b of the live leaf spring 42 , and a neutral securing tab 29 b located above the movable portion 44 b of the neutral leaf spring 44 .

[0145] The leaf springs 42 and 44 are respectively arranged below the push rods 40a and 40b, so that when the push rods 40a and 40b are moved downward by the corresponding operation of the actuators 30a and 30b, the movable parts 42b and 44b of the leaf springs 42 and 44 are deflected downward by the push rods 40a and 40b. The tripping rod 36 of the control unit 16 includes a force transmission pad 48b, which is arranged below the movable part 44b of the neutral leaf spring 44 to transmit the downward movement of the push rod 40b to the tripping rod 36 via the movable part 44b of the leaf spring 44, which moves the tripping rod 36 to the "OFF" position, so that the contacts are then held in the disconnected position by the stopper 48a. The force transmission pad 48b is arranged directly below the push rod 40b. The tripping rod 36 also includes a force transmission pad ( Figure 4 ), the force transmitting pad is arranged below the movable portion 42b of the charged leaf spring 42 for the same purpose.

[0146] The trip bar 36 further includes return stoppers 49a, 49b disposed above the movable portions 42b, 44b of the live and neutral leaf springs 42, 44, respectively, for limiting upward movement of the movable portions 42b, 44b, as will be described in greater detail below. The return stoppers 49a, 49b are configured to contact and push downward the movable portions 42b, 44b of the leaf springs 42, 44 when the trip bar 36 is pivoted to the "OFF" position (e.g., by manual operation of the trip bar 36 or as a result of operation of the third thermal actuator 30c when steam is detected).

[0147] Figure 5a 、 Figure 5b and Figure 5c Shows Figure 2a and Figure 2b A cross-sectional front view of the neutral leaf spring 44 of the control unit 16. Figure 5a , the leaf spring 44 is in the closed position. Figure 5b The leaf spring 44 is shown after the push rod 40b has been moved downwardly. Figure 5c The leaf spring 44 is shown in the disconnected position.

[0148] The leaf spring 44 comprises a movable electrical contact 50 mounted on the movable portion 44b of the leaf spring 44 between the fixed end 44a and the portion of the leaf spring 44 arranged to contact the push rod 40b. Figure 5a As shown, the movable electrical contact 50 is in contact with the stationary electrical contact 52 of the neutral stationary tab 29b.

[0149] The leaf spring 44 is biased to the closed position (eg Figure 5a ), which means that the movable electrical contact 50 is biased by the leaf spring 44 into contact with the fixed electrical contact 52.

[0150] As described above, when the second thermo-sensitive actuator 30b is operated, the push rod 40b moves vertically downward so as to bend the leaf spring 44 by deflecting the movable portion 44b downward relative to the fixed end 44a. Figure 5b As shown in FIG. 1 , due to the force exerted by the push rod 40b on the movable portion 44b, the movable portion 44b of the leaf spring 44 continues to deflect downward even after the push rod 40b reaches the end of its stroke. The deflection of the movable portion 44b is stopped by the force transmitting spacer 48b of the trip bar 36, as shown in FIG. Figure 5b shown.

[0151] This deflection causes the movable electrical contact 50 to separate from the fixed electrical contact 52. Thus, operation of the actuator 30b moves the leaf spring 44 to the disconnected position (eg, Figure 5b and Figure 5c The force transmitting spacer 48b is pushed downward by the leaf spring 44, thereby pivoting the trip lever 36 to the "OFF" position. Figure 5b The positions of the force transmitting block 48b and the stop 49b of the trip bar 36 are shown before the trip bar has been moved to the "OFF" position. Figure 5c The positions of the force transmitting block 48b and the stop 49b are shown when the trip bar 36 is in the "OFF" position.

[0152] Due to the resilience of the leaf spring 44, the movable portion 44b of the leaf spring 44 then moves upward relative to the fixed end 44a toward the closed position of the leaf spring 44. However, this causes the distal end of the leaf spring 44 to be brought back into contact with the end of the push rod 40b and the return stop 49b of the trip bar 36 (now in the "OFF" position). As a result, the return stop 49b and the push rod 40b hold the leaf spring 44 in its open position, in which the movable electrical contact 50 is separated from the fixed electrical contact 52, as shown in FIG. Figure 5c shown.

[0153] In order for the leaf spring 44 to return to its closed position, the thermal actuator 30b needs to cool sufficiently to reset it (thereby allowing the push rod 40b to move upward), and the user needs to pivot the trip lever to the "ON" position, thereby lifting the return stop 49b out of contact with the leaf spring 44 and allowing the leaf spring 44 to move to the closed position (as shown in FIG. Figure 5a ). The force required to pivot the trip bar 36 is greater than the upward force exerted by the movable portion 44b of the leaf spring 44 on the return stop 49b due to the resilience of the leaf spring 44.

[0154] In addition to being movable to the disconnected position by the push rod 40b following operation of the thermal actuator 30b, the leaf spring 44 is also movable to the disconnected position by manual operation of the trip lever 36 or as a result of operation of the third thermal actuator 30c which causes the trip lever 36 to pivot when steam is detected. Figure 6a and Figure 6b Shown in.

[0155] Figure 6a Shows the Figure 5a The same view of the neutral leaf spring 44 is shown, with the leaf spring 44 in the closed position. Figure 6b The leaf spring 44 is shown after the trip bar 36 has been pivoted to the "OFF" position. As described above, the trip bar 36 includes a return stop 49b and a force transfer pad 48b, both of which are located in the Figure 6a and Figure 6b Shown in.

[0156] like Figure 6b As shown, instead of the push rod 40b moving vertically downward to contact and move the leaf spring 44, the trip bar 36 pivots so that the return stop 49b of the trip bar 36 moves downward and contacts the distal end of the movable portion 44b of the leaf spring 44, causing the movable portion 44b to flex relative to the fixed end 44a to separate the movable electrical contact 50 from the fixed electrical contact 52. The return stop 49b of the trip bar 36 holds the leaf spring 44 in this open position. In order to allow the leaf spring 44 to return to its closed position (as shown in FIG. Figure 6a ), the user pivots the trip lever to the "ON" position, thereby lifting the return stop 49b out of contact with the leaf spring 44 and allowing the leaf spring 44 to move to the closed position.

[0157] The vertical stroke of the push rod 40b is substantially equal to the vertical distance traveled by the thermal actuator 30b during operation. The vertical stroke of the movable portion 44b of the leaf spring 44 at the point where the push rod 40b contacts the leaf spring 44 (i.e., the "contact point") is substantially equal to the distance traveled by the flexure portion of the thermal actuator 30b during operation. The vertical movement of the movable electrical contact 50 depends on the relative distances between the flexure point 45, the movable electrical contact 50, and the push rod 40b. Because the push rod 40b is arranged to contact the leaf spring 44 at a point further distal to the movable electrical contact 50 along the leaf spring 44 than the movable electrical contact 50, the distance traveled by the movable electrical contact 50 is shorter than the distance traveled by the push rod 40b. This means that, although the leaf spring of the present invention can be shorter than conventional leaf springs, existing thermal actuators can still be used with embodiments of the present invention without requiring modification to provide a shorter stroke distance.

[0158] Because leaf spring 44 is thinner than conventional leaf spring, it may not be so hard, which means that leaf spring 44 may over-travel after thermal actuator 30b is operated. This over-travel may cause the stress generated in the leaf spring to exceed the yield stress of the leaf spring material. When leaf spring 44 is deflected by push rod 40b through thermal actuator 30b, force transfer pad 48b prevents leaf spring 44 from over-travelling via the inertia of trip bar 36. Thermal actuator 30b can apply high dynamic mechanical loads on leaf spring 44. However, by preventing excessive travel of leaf spring 44, the stress on leaf spring 44 can be limited. As described above, when force transfer pad 48b is arranged on trip bar 36, the impact between leaf spring 44 and force transfer pad 48b also causes trip bar 36 to pivot to the OFF position, thereby resetting trip bar 36.

[0159] The leaf spring 44 includes a kink 54 disposed adjacent to the flexure point 45 between the fixed end 44a and the movable portion 44b of the leaf spring 44. The cross-section of the kink 54 is substantially sinusoidal, extending out of the plane of the leaf spring 44 in an arc and returning to substantially the same plane (i.e., corresponding to approximately half a sine wave). The curved cross-section of the leaf spring 44 includes rounded corners on either side of the arc of the kink 54, thereby rounding the intersection of the sinusoidal kink 54 and the flat geometry of the leaf spring 44.

[0160] Figure 7 The von Mises stress diagram is shown for a straight (ie conventional) leaf spring having a thickness of 0.15 mm and different lengths, and an applied deflection of 0.9 mm, corresponding to the deflection of the leaf spring when it is deflected by a push rod.

[0161] It can be seen that for a conventional leaf spring with a yield stress of 540 MPa, the minimum length that the leaf spring can have while being deflected by 0.9 mm without exceeding the yield stress is 9 mm.

[0162] Figure 7 Also shown is a dot 200 representing the von Mises stress in a 0.15 mm thick leaf spring including a kink according to the present invention. It can be seen that by incorporating a kink into the leaf spring's shape, a leaf spring with an 8 mm footprint can be used without exceeding the material's yield stress. This is because the kink increases the effective bending length of the leaf spring, thereby helping to reduce the maximum induced stress without increasing the leaf spring's footprint.

[0163] Figure 4 The leaf spring 44 shown in Figures 5 and 6 is approximately 22 mm long, 3.5 mm wide, and 0.15 mm thick. The leaf spring 44 is made of C7025, a hardened copper alloy with a yield stress of approximately 540 MPa. The radius of curvature of the arc of the kink 54 is 0.8 mm, and the radius of curvature of the rounded corners on either side of the kink 54 is 0.65 mm.

[0164] The leaf spring 44 is shaped to provide a 20 gram preload on the fixed electrical contact 52. When the thermal actuator 30b is operated, the movable electrical contact 50 is separated from the fixed electrical contact 52 by 0.9 mm to sever the electrical connection between the contacts 50, 52.

[0165] Figure 8 A cross-sectional front view of a control unit 116 according to another embodiment of the present invention is shown. Figures 2 to 6 show an "integrated" control unit 16, wherein the control unit 16 itself includes a mechanism for interrupting the power circuit in an overheat condition (i.e., thermal actuators 30a, 30b), and a mechanism for opening the power circuit when a liquid temperature condition (e.g., boiling) is reached (thermal actuator 30c).

[0166] However, Figure 8 The control unit 116 includes only an "overheat" protection mechanism. However, in the integrated control unit 16 of Figures 2 to 5, the "overheat" detection thermal actuators 30a, 30b and the "liquid temperature condition" detection thermal actuator 30c are arranged to disconnect the same set of electrical contacts 50, 52. Figure 8 The control unit 116 is adapted for use in an appliance in which the "overheat" detection mechanism and the "liquid temperature condition" mechanism open different sets of electrical contacts.

[0167] Figure 10 An example of such an apparatus 102 is shown, comprising Figure 8 The appliance 102 is a "split switch" appliance in which a separate electrical switching device 103 is provided for interrupting the power circuit when the liquid temperature condition is reached. The electrical switching device 103 is arranged separately from the control unit 116, which includes an "overheat" detection mechanism.

[0168] The separate electric switching device 103 includes a steam-sensitive bimetallic element (not shown) located on top of the handle 108. The electric switching device 103 is electrically connected to the control unit 116 via a cable 105 extending through the handle 108 of the appliance 102. The separate electric switching device 103, the electric heater (not shown), and the control unit 116 are electrically connected in series.

[0169] The control unit 116 does not include a trip bar, so instead of force transfer pads 48a, 48b, Figure 8 The control unit 116 includes stops 148a, 148b disposed on the molded control body 126 of the control unit 116 to prevent overshoot deflection of the live leaf spring 142 and the neutral leaf spring 144, respectively. The remaining components of the control unit 116 are substantially the same as the control unit 16 of Figures 2 to 6.

[0170] Figure 9a and Figure 9b Shows Figure 8 1. A front view of the components of the control unit 116 in FIG.

[0171] Figure 9a The neutral leaf spring 144 is shown in a closed position, with the movable electrical contact 150 in contact with the stationary electrical contact 152 . Figure 9b Shown is the leaf spring 144 in the disconnect position after the push rod 140b has been moved downwardly toward the stop 148b by the thermal actuator. In the disconnect position, the movable electrical contact 150 is separated from the fixed electrical contact 152 by 0.9 mm to cut off the electrical connection between the contacts 150, 152.

[0172] Figure 11a Shows Figure 9a and Figure 9b A front view and an enlarged cross-sectional front view of the mounting arrangement of the movable electrical contact 150 are shown for the leaf spring 144. The leaf spring 144 includes the kink 154 as described above.

[0173] The leaf spring 144 defines a punched hole 156 for receiving the movable electrical contact 150. The movable electrical contact 150 is received within the hole 156 by a press fit. When the hole 156 is punched into the leaf spring 144, the peripheral edge 156a of the hole 156 is bent downwardly out of the plane of the leaf spring 144, which means that when the contact 150 is received within the hole 156, the surface area of ​​the leaf spring 144 at its upper portion contacts the movable electrical contact 150. This means that even though the leaf spring 144 is thinner than conventional leaf springs, the contact surface area between the leaf spring 144 and the movable electrical contact 150 can remain the same, meaning that the flow of current between the leaf spring 144 and the movable electrical contact 150 is substantially unaffected by the thinning of the leaf spring.

[0174] Furthermore, this process forms a rigid cylindrical structure within the leaf spring 144 at the point of contact between the movable electrical contact 150 and the fixed electrical contact 152. This helps offset any reduction in the stiffness of the leaf spring 144 due to the relatively reduced thickness of the leaf spring 144 compared to known leaf springs, and helps ensure that a secure cold joint can be formed between the movable electrical contact 150 and the leaf spring 144. As a result, more of the force provided by the leaf spring 144 can be transferred to the electrical contacts 150, 152 to close the electrical contacts 150, 152.

[0175] It should be understood that Figure 11a The mounting arrangement of the movable electrical contact 150 shown and described above may be equally applied to either of the leaf springs 42 , 44 of the embodiments shown in FIGS. 2 to 6 .

[0176] According to another aspect of the present invention, the mounting arrangement may also be applied to leaf springs that do not include kinks. Figure 11b An example of such an arrangement is shown in which a substantially planar leaf spring 644 defines an aperture 656 in which the electrical contact 650 is disposed. A peripheral edge 656a of the aperture 656 is bent downwardly out of the plane of the leaf spring 644.

[0177] Although the above embodiments and FIG. 2 to FIG. Figure 11a The illustrated embodiment features a leaf spring having a kink corresponding to approximately half a sine wave, but many alternative geometries of the kink may be used to provide the same effect of increasing the effective bending length of the leaf spring. Figure 12a 、 Figure 12b 、 Figure 12c and Figure 12d Some examples of alternative geometries are shown.

[0178] Figure 12a An alternative leaf spring 244 is shown that includes an S-shaped or sinusoidal kink 254, ie, a sine wave corresponding to a full cycle.

[0179] Figure 12b An alternative leaf spring 344 is shown that includes an inverted V-shaped kink 354. The kink 354 extends linearly and diagonally out of the plane of the leaf spring 344 to a peak and symmetrically returns to the plane of the leaf spring 344.

[0180] Figure 12c An alternative leaf spring 444 is shown that includes a substantially M-shaped kink 454. The M-shaped kink is similar to Figure 12b The inverted V-shaped kink 354 in FIG. 3 is similar to the inverted V-shaped kink 354 in FIG. 3 , except that the peak itself is inverted so as to form two peaks and a valley between the peaks.

[0181] Figure 12dAn alternative leaf spring 544 is shown that includes a folded kink 554. The kink 554 bends upward at an angle of approximately 180° out of the plane of the leaf spring 544 and then continues in a distal direction again at the peak of the bend to return to the plane of the leaf spring 544. Thus, the folded kink 554 substantially resembles the shape of a breaking wave.

[0182] Those skilled in the art will recognize that many other alternative kink geometries may be suitable besides those shown and described herein.

Claims

1. A control unit for controlling a power circuit of an electric heater in a liquid heating appliance, the control unit comprising: a leaf spring comprising a fixed end and a movable portion, the movable portion being movable relative to the fixed end between a closed position and an open position; a movable electrical contact mounted on the movable portion of the leaf spring and configured to mate with a corresponding fixed electrical contact in the power circuit when the leaf spring is in the closed position; a thermally sensitive actuator operable at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position, wherein the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit; wherein the leaf spring includes a kink between the fixed end and the movable portion.

2. The control unit according to claim 1 further comprises a cordless electrical adapter part for cooperating with a corresponding base electrical connector part to receive a power supply, the cordless electrical adapter part comprising a cooperating conductor for connecting to a live pole or a neutral pole of the corresponding base electrical connector part, wherein The fixed end of the leaf spring is fixed directly to the mating conductor of the cordless power adapter part.

3. The control unit according to claim 2, wherein: The cordless electrical adapter part and corresponding base electrical connector part are of a type which can mate regardless of their relative angular orientation.

4. A control unit according to any one of the preceding claims, wherein The kink is disposed adjacent the fixed end at a flexure point of the leaf spring.

5. A control unit according to any one of the preceding claims, wherein The kinks are continuous bends.

6. The control unit according to claim 5, wherein: The kink includes an arcuate portion disposed between two rounded corners.

7. A control unit according to any one of the preceding claims, wherein The kink extends out of the plane of the leaf spring and returns substantially to the same plane.

8. A control unit according to any one of the preceding claims, wherein The thermally sensitive actuator is arranged to push a contact point of the movable part of the leaf spring to move the movable part from the closed position to the open position, and wherein the movable electrical contact is mounted on the movable part of the leaf spring between the kink and the contact point.

9. A control unit according to any one of the preceding claims, wherein The leaf spring defines a hole in which the movable electrical contact is disposed, wherein the leaf spring includes a projection extending out of the plane of the leaf spring around a periphery of the hole.

10. A control unit according to any one of the preceding claims, wherein The thickness of the leaf spring is between 0.05 mm and 0.18 mm.

11. The control unit according to claim 10, wherein: The leaf spring is approximately 0.15 mm thick.

12. A control unit according to any one of the preceding claims, further comprising a stop for preventing movement of the movable part of the leaf spring after the movable part has been moved from the closed position to the open position.

13. The control unit according to claim 12, further comprising a trip bar for allowing a user to manually move the movable part of the leaf spring from the closed position to the open position and / or from the open position to the closed position, wherein the stopper is arranged on the trip bar.

14. A liquid heating appliance comprising: Liquid heating containers; an electric heater for heating liquid contained in the liquid heating vessel, wherein the electric heater is powered by a power circuit; as well as A control unit according to any one of the preceding claims.

15. The liquid heating appliance of claim 14, further comprising an electrical switching device physically separate from but electrically connected to the control unit, wherein: the electrical switching means comprising a liquid temperature condition thermally sensitive actuator arranged to open a switch to interrupt the supply of power to the heater upon detection of a predetermined temperature corresponding to a desired condition of liquid in the liquid heating vessel; and The thermally sensitive actuator of the control unit comprises an overheat thermally sensitive actuator, wherein the overheat thermally sensitive actuator is arranged to operate at a predetermined temperature corresponding to a temperature within the liquid heating appliance during an overheat condition.

16. The liquid heating appliance according to claim 15, wherein The electrical switching arrangement is arranged in a different part of the liquid heating appliance than the control unit.

17. A control unit according to any one of claims 1 to 13, wherein The thermally sensitive actuator of the control unit comprises an overheating thermally sensitive actuator, wherein, the overheat thermally sensitive actuator being arranged to operate at a predetermined temperature corresponding to the temperature within the liquid heating appliance during an overheat condition; and The control unit further comprises a liquid temperature condition thermally sensitive actuator arranged to separate the movable electrical contact from the fixed electrical contact to interrupt the power circuit upon detecting a predetermined temperature corresponding to a desired state of liquid in the liquid heating vessel.

18. The control unit of claim 17, further comprising a trip bar movable to act on the movable portion of the leaf spring and move the movable portion of the leaf spring from the closed position to the open position, wherein The liquid temperature condition thermally sensitive actuator is configured to move the trip bar at the predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position, wherein the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit.

19. A liquid heating appliance comprising: Liquid heating containers; an electric heater for heating liquid contained in the liquid heating vessel, wherein the electric heater is powered by a power circuit; as well as A control unit according to claim 17 or 18.

20. A leaf spring comprising: a proximal end and a distal portion movable relative to the proximal end; and an electrical contact mounted on the distal portion of the leaf spring for mating with a corresponding electrical contact; wherein the leaf spring includes a kink between the proximal end and the distal portion.

21. The leaf spring according to claim 20, wherein The kinks are continuous bends.

22. The leaf spring according to claim 21, wherein The kink includes an arcuate portion disposed between two rounded corners.

23. The leaf spring according to any one of claims 20 to 22, wherein The kink extends out of the plane of the leaf spring and returns substantially to the same plane.

24. The leaf spring according to any one of claims 20 to 23, wherein The leaf spring defines a hole in which the electrical contact of the leaf spring is disposed, wherein the leaf spring includes a projection extending out of the plane of the leaf spring around a periphery of the hole.

25. The leaf spring according to any one of claims 20 to 24, wherein The thickness of the leaf spring is between 0.05 mm and 0.18 mm.

26. A leaf spring according to any one of claims 20 to 25, wherein The leaf spring is approximately 0.15 mm thick.

27. A method of manufacturing a leaf spring comprising a proximal end and a distal portion movable relative to the proximal end, the method comprising: forming a kink in the leaf spring between the proximal end and the distal portion; as well as An electrical contact for mating with a corresponding electrical contact is mounted on the distal end portion of the leaf spring.

28. The method according to claim 27, comprising: forming a hole through the distal end portion of the leaf spring; as well as The electrical contact is mounted on the distal end portion of the leaf spring by inserting the electrical contact into the hole.

29. The method according to claim 28, wherein Forming the hole includes forming a projection that extends out of the plane of the leaf spring around a periphery of the hole.

30. A control unit for controlling a power circuit of an electric heater in a liquid heating appliance, the control unit comprising: a leaf spring comprising a fixed end and a movable portion, the movable portion being movable relative to the fixed end between a closed position and an open position; a movable electrical contact mounted on the movable portion of the leaf spring and configured to mate with a corresponding fixed electrical contact in the power circuit when the leaf spring is in the closed position; as well as a thermally sensitive actuator operable at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position, wherein the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit; wherein the leaf spring defines an aperture in which the movable electrical contact is disposed, and wherein the leaf spring includes a projection extending out of the plane of the leaf spring around a periphery of the aperture.

31. The control unit according to claim 30, wherein: The thickness of the leaf spring is between 0.05 mm and 0.18 mm, for example between 0.1 mm and 0.15 mm, for example approximately 0.15 mm.

32. A control unit according to claim 30 or 31, wherein: The movable electrical contact is disposed in the aperture with an interference fit.

33. A control unit according to any one of claims 30 to 32, wherein: The leaf spring is an integral component including the protrusion.

34. A control unit according to any one of claims 30 to 33, wherein The protrusion is formed to surround the electrical contact.

35. A control unit according to any one of claims 30 to 34, further comprising a stopper for preventing movement of the movable part of the leaf spring after the movable part has moved from the closed position to the open position.

36. The control unit according to claim 35, further comprising a trip bar for allowing a user to manually move the movable part of the leaf spring from the closed position to the open position and / or from the open position to the closed position, wherein the stopper is arranged on the trip bar.

37. A control unit according to any one of claims 30 to 36, further comprising a cordless electrical adapter part for cooperating with a corresponding base electrical connector part to receive a power supply, the cordless electrical adapter part comprising cooperating conductors for connecting to a live pole or a neutral pole of the corresponding base electrical connector part, wherein The fixed end of the leaf spring is fixed directly to the mating conductor of the cordless power adapter part.

38. A control unit according to claim 37, wherein The cordless electrical adapter part and corresponding base electrical connector part are of a type which can mate regardless of their relative angular orientation.

39. A liquid heating appliance comprising: Liquid heating containers; an electric heater for heating liquid contained in the liquid heating vessel, wherein the electric heater is powered by a power circuit; as well as A control unit according to any one of claims 30 to 38.

40. The liquid heating appliance of claim 39, further comprising an electrical switching device physically separate from but electrically connected to the control unit, wherein: the electrical switching means comprising a liquid temperature condition thermally sensitive actuator arranged to open a switch to interrupt the supply of power to the heater upon detection of a predetermined temperature corresponding to a desired condition of liquid in the liquid heating vessel; and The thermally sensitive actuator of the control unit comprises an overheat thermally sensitive actuator, wherein the overheat thermally sensitive actuator is arranged to operate at a predetermined temperature corresponding to a temperature within the liquid heating appliance during an overheat condition.

41. The liquid heating appliance of claim 40, wherein The electrical switching arrangement is arranged in a different part of the liquid heating appliance than the control unit.

42. A control unit according to any one of claims 30 to 38, wherein the thermally sensitive actuator of the control unit comprises an overheat thermally sensitive actuator, wherein the overheat thermally sensitive actuator is arranged to operate at a predetermined temperature corresponding to a temperature within the liquid heating appliance during an overheat condition; and The control unit further comprises a liquid temperature condition thermally sensitive actuator arranged to separate the movable electrical contact from the fixed electrical contact to interrupt the power circuit upon detecting a predetermined temperature corresponding to a desired state of liquid in the liquid heating vessel.

43. The control unit of claim 42, further comprising a trip bar movable to act on the movable portion of the leaf spring and move the movable portion of the leaf spring from the closed position to the open position, wherein The liquid temperature condition thermally sensitive actuator is configured to move the trip bar at the predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position, wherein the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit.

44. A liquid heating appliance comprising: Liquid heating containers; an electric heater for heating liquid contained in the liquid heating vessel, wherein the electric heater is powered by a power circuit; as well as A control unit according to claim 42 or 43.

45. A leaf spring comprising: a proximal end and a distal portion movable relative to the proximal end; and an electrical contact mounted on the distal portion of the leaf spring for mating with a corresponding electrical contact; wherein the leaf spring defines a hole in which the electrical contact of the leaf spring is disposed, and wherein the leaf spring includes a projection extending out of the plane of the leaf spring around a periphery of the hole to surround the electrical contact.

46. ​​The leaf spring according to claim 45, wherein The thickness of the leaf spring is between 0.05 mm and 0.18 mm.

47. The leaf spring according to claim 46, wherein The leaf spring is approximately 0.15 mm thick.

48. A leaf spring according to any one of claims 45 to 47, wherein The electrical contacts of the leaf spring are arranged in the holes by interference fit.

49. A leaf spring according to any one of claims 45 to 48, wherein The leaf spring is an integral component including the protrusion.

50. A method of manufacturing a leaf spring comprising a proximal end and a distal portion movable relative to the proximal end, the method comprising: forming a hole through the distal end portion of the leaf spring; as well as mounting the electrical contact on the distal portion of the leaf spring by inserting the electrical contact into the hole; Wherein forming the hole includes forming a protrusion extending out of the plane of the leaf spring around a periphery of the hole.

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