Control unit, liquid heating appliance and plate spring

Abstract

The utility model discloses a control unit, a liquid heating appliance and a plate spring. 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. 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 leaf spring defines an aperture in which the movable electrical contact is disposed, and the leaf spring includes a projection extending around a periphery of the aperture out of a plane of the leaf spring. The control unit further comprises a bimetallic element operable at a predetermined temperature to move the leaf spring (44) to an open position to separate the movable contact (50) from the fixed electrical contact (52).

Description

Technical Field

[0001] The utility model relates to a control unit for a liquid heating appliance, the liquid heating appliance and a leaf spring. Background Art

[0002] In a liquid heating appliance, such as a domestic kettle, the 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, for example to start or terminate 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 switch off 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-acting bimetallic actuator) that operates at a predetermined temperature to move a switch to interrupt the power supply.

[0004] In some conventional control units, the switch includes a leaf spring carrying a movable electrical contact arranged to cooperate with a corresponding fixed electrical contact in a power circuit of the heater. When the thermal actuator is operated at a predetermined temperature, the leaf spring deflects so that the electrical contacts are separated, thereby terminating the supply of electrical energy to the heater. The electrical contacts are generally required to be separated by a minimum contact gap to avoid arcing between the contacts when the contacts separate in response to the operation of the thermal actuator.

[0005] Reducing the size of the control unit may be desirable because it can advantageously save manufacturing time and cost, 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 generally requires a corresponding reduction in the size of the 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 in the leaf spring compared to the stresses induced in a longer leaf spring. The increased stresses, combined with repeated flexing of the leaf spring during use of the tool, result in relaxation of the stresses in the leaf spring.

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

[0008] Therefore, existing smaller control units are only suitable for appliances running at low currents and cannot be safely used with higher powered appliances (eg, between 13 and 15 amps). Utility Model Content

[0009] The utility model aims to provide an improved control unit which can be made smaller than a conventional control unit without limiting its use to only low-power electrical appliances.

[0010] When viewed from a first aspect, the utility model 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 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;

[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 in which the movable electrical contact is separated 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] From the second aspect, the utility model provides a liquid heating device, 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, comprising:

[0019] 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;

[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 in which the movable electrical contact is separated 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 so that when the movable portion moves between the closed position and the open position, kinking and deflection of the movable portion relative to the fixed end occurs. 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] Therefore, the leaf spring provided by the embodiment of the utility model 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 length, while helping to prevent the stress in the leaf spring from exceeding the yield stress of the material of the leaf spring. As a result, the entire control unit can be made smaller. This can reduce the cost of manufacturing the control unit and can make the liquid heating appliance including the control unit more visually attractive.

[0025] Because the stress within the kinked leaf spring of the present invention can be reduced compared to a conventional non-kinked leaf spring having the same footprint length, the leaf spring of the present invention can carry higher currents (e.g., between 13 amps and 15 amps) in some embodiments. As described above, leaf springs operating at high currents can suffer from increased stress relaxation due to higher temperatures in 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, for example, mating with a corresponding power 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 pole 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 an integral (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 be matched regardless of their relative angular orientation, or at least of a type that can be matched 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 of Strix are available.

[0028] In some embodiments, the liquid heating appliance is arranged to be seated on a power base platform, and the power base platform includes a corresponding base electrical connector component. The base electrical connector component may include a lug 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 platform.

[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 a power circuit. Additional ground connections may also be present. In some embodiments, the cordless power adapter component is a 3-pole connector component (e.g., for mating with the P72 of Strix). In other embodiments, the cordless power adapter component is a 5-pole connector component (e.g., for mating with the P76 of Strix). 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 matching conductor of the cordless electrical adapter part. The control unit preferably comprises two leaf springs, wherein a first leaf spring is connected or fixed to a live conductor of the cordless electrical adapter part and a second leaf spring is connected or fixed to a neutral conductor of the electrical adapter part. Any or all features of the leaf springs described herein may (and preferably are) applied to either or both of the first leaf spring and the second leaf spring (if provided).

[0031] For example, preferably, the second leaf spring comprises 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. Preferably, the fixed end of the second leaf spring is fixed to a neutral mating conductor of the electrical adapter part. Preferably, the second leaf spring extends substantially in a plane and comprises a kink, the kink being arranged 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 thickness of the second leaf spring is preferably 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 the (e.g. respectively) matching conductor of the cordless power adapter part. (One or more) leaf springs can be bonded to the matching conductors, for example, by welding or soldering. (One or more) leaf springs can be fixed to (one or more) matching conductors by friction. (One or more) leaf springs can be fixed to (one or more) matching conductors by cooperation between a pair of fastening elements, such as a lug or hook and a corresponding hole.

[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 diffusion plate arranged to be in thermal communication with the electric heater. Preferably, the control unit is arranged to be mounted to the bottom side of the heat diffusion plate. In some embodiments, the control unit includes a mounting plate for mounting the control unit to the bottom side of the heat diffusion plate. The mounting plate is preferably metal. The mounting plate is preferably substantially flat.

[0035] The thermosensitive actuator is preferably arranged to detect a temperature within the liquid heating appliance. The temperature may represent the temperature of the liquid within the liquid heating vessel. The temperature may be the temperature of the electric heater. The 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" thermosensitive actuator and a "liquid temperature condition" thermosensitive actuator. The overheat thermosensitive 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 thermosensitive 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. Instead, the control unit may only include an overheat thermistor. A control unit according to such an embodiment may be suitable for use in a liquid heating appliance comprising an electrical switch device that is physically separated from the control unit but electrically connected to the control unit. The electrical switch device preferably includes a liquid temperature condition thermistor for disconnecting a switch to interrupt the power supply to the heater. The liquid temperature condition thermistor 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 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 include a thermomechanical switch, such as a bimetallic switch. In some embodiments, the electrical switch device includes an electronic switch device, such as a controller connected to a thermistor. The electrical switch device is preferably arranged in a portion of the liquid heating appliance that is different 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 switch device is arranged at the upper portion of the appliance (e.g., on the handle of the appliance). The electrical switch device is preferably connected in series with a switch including 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 the movable portion of the 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 arranged to move the trip bar at a predetermined temperature. The liquid temperature condition thermally sensitive actuator is preferably arranged to move the trip bar so as 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.

[0043] Preferably, the thermosensitive actuator is mounted on an upper surface of the control unit. Preferably, the thermosensitive actuator is mounted on an upper surface of a mounting plate. This means that when the control unit is mounted to the underside of the heat diffuser plate, the thermosensitive actuator can be arranged in good thermal conductive communication with the heat diffuser plate. As a result, the thermosensitive 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 in the appliance). This may allow the thermosensitive 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-acting bimetallic actuator. Preferably, the bimetallic element is arranged to operate (eg snap-acting) when a predetermined temperature is detected.

[0045] The bimetallic element may act directly on the leaf spring. Preferably, however, the control unit (e.g. a thermal actuator) comprises an intermediate component which is operated by the bimetallic element at a predetermined temperature to move the movable part of the leaf spring from the closed position to the open position. The bimetallic element preferably comprises an actuating portion which is arranged 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 the same distance as the distance over which 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 (eg bimetallic) actuator at a predetermined temperature to move the movable part 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 part of the leaf spring.

[0047] In some embodiments, the thermal actuator (e.g., a push rod of the thermal 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. 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 part of the leaf spring between the kink and the contact point.

[0048] The distance travelled by the movable part of the leaf spring at the contact point is preferably substantially equal to the deflection of the actuating part 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 applied by the thermal actuator on the shorter leaf spring will 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 have the same size as the type used in the larger controller.

[0050] Furthermore, by arranging the thermal actuator (e.g., a 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., a push rod of the thermal actuator) at the contact point can result in a proportionally reduced 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., a push rod of the thermal actuator) and the movable portion of the leaf spring can be selected at the design stage 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 arranged. The movable electrical contact can be arranged in the hole by 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 there would be if the leaf spring did not include the protrusion. This can improve the bond (e.g. cold bond) between the movable electrical contact and the leaf spring, thereby helping to reduce self-heating (and combined 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), since conventional methods of mounting electrical contacts to leaf springs (eg, welding or riveting) are difficult to achieve at such low thicknesses.

[0053] This is considered novel and creative in itself. Therefore, from another aspect, the utility model provides a leaf spring, which comprises:

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

[0055] an electrical contact mounted on a distal portion of the leaf spring for mating with a corresponding electrical contact;

[0056] 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.

[0057] From another aspect, the utility model provides a control unit for controlling a power circuit of an electric heater in a liquid heating device, the control unit comprising:

[0058] 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;

[0059] 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;

[0060] 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 in which the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit;

[0061] Wherein the leaf spring defines a hole 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 hole.

[0062] From another aspect, the utility model provides a liquid heating device, comprising:

[0063] Liquid heating containers;

[0064] an electric heater for heating liquid contained in the liquid heating vessel, wherein the electric heater is powered by the power circuit; and

[0065] A control unit, the control unit comprising:

[0066] 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;

[0067] 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;

[0068] 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 in which the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit;

[0069] The leaf spring includes a kink between a fixed end and a movable portion.

[0070] From another aspect, the utility model provides a method for manufacturing a leaf spring, the leaf spring comprising a proximal end portion and a distal portion movable relative to the proximal end portion, the method comprising:

[0071] forming a hole through a distal end portion of the leaf spring; and

[0072] installing an electrical contact on a distal portion of the leaf spring by inserting the electrical contact into the hole;

[0073] Wherein forming the hole includes forming a projection that extends out of the plane of the leaf spring around a periphery of the hole.

[0074] As mentioned above, in some embodiments, the movable electrical contact may be arranged in the hole by an interference fit. Preferably, the leaf spring comprises 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 comprise a protrusion.

[0075] In some embodiments, the leaf spring includes a kink (e.g., having features 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 portion). 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.

[0076] The leaf spring and the projection may be separate components. However, the leaf spring is preferably an integral 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 is formed (e.g., by the same operation). This can simplify the manufacturing process of the leaf spring while helping to ensure that the beneficial geometry of the hole and projection as described above is provided.

[0077] 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 projection.

[0078] The projection may extend around a portion of the hole. Preferably, the projection extends around most (eg the entire) circumference of the hole.

[0079] 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. After the operation of moving the movable part from the closed position to the open position, the thermal actuator is preferably arranged 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 arranged to automatically reset (e.g., when the temperature detected by the thermal actuator drops sufficiently below a predetermined temperature).

[0080] In some embodiments, the control unit also includes a trip bar, which is used to allow 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 (disconnected)" position and an "ON (connected)" position. In the "ON" position, the movable electrical contact is preferably in contact 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 contact. Therefore, the provision of the trip bar can allow the user to manually interrupt the heating operation of the liquid heating appliance and / or start the heating operation.

[0081] 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 when boiling is detected).

[0082] Preferably, the control unit comprises 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. The movable part of the leaf spring is preferably arranged to contact the stopper after moving from the closed position to the open position. Thus, a stopper may be provided to limit the overshoot distance travelled by the movable part of the leaf spring. This helps to prevent the leaf spring from plastically deforming in use due to (e.g. repeated) flexing.

[0083] In some embodiments, the stopper is arranged on the control body of the control unit. In some embodiments, the stopper is arranged on the tripping bar of the control unit. When the stopper is arranged on the tripping bar of the control unit, the position of the tripping bar can be reset (e.g., reset to the "OFF" position) by the force applied by the movable part of the leaf spring to the stopper when the movable part contacts the stopper. Therefore, the stopper can act as a force transfer pad to provide the dual functions of resetting the tripping bar position and reducing overshoot in the leaf spring.

[0084] 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 a faster stop can be brought to the leaf spring without causing a bending moment of the leaf spring between the stopper and the contact point. Such a bending moment could damage the leaf spring.

[0085] In some embodiments, the control unit comprises a return stop for preventing the movable part of the leaf spring from moving from the open position to the closed position (e.g. after the movable part 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 part has been moved to the open position. The return stop is preferably arranged on a trip bar of the control unit.

[0086] In some embodiments, the trip bar includes a stopper (e.g., a force transmission pad) and a return stopper. The stopper (e.g., a force transmission pad) is preferably arranged 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 arranged above the movable portion of the leaf spring.

[0087] The return stop may be arranged 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 (eg by operation of a user or by a liquid temperature condition thermally sensitive actuator).

[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 closest to the fixed end that 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 with the highest stress. 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 itself. Therefore, when viewed from a third 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 a fourth aspect, the present invention provides a method of manufacturing a leaf spring, the 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 is mounted on the distal end portion of the leaf spring for mating with a corresponding electrical contact.

[0099] In some embodiments, a method of manufacturing a leaf spring includes forming a hole 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 may 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 arranged adjacent to the kink to blend the geometry of the kink with the geometry of the rest of the leaf spring. In some embodiments, the kink includes an arcuate portion arranged 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, such as 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, such as approximately 0.65 mm.

[0102] The leaf spring may 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 a control unit that is smaller than a conventional control unit. The leaf spring may have a (footprint) length of between 5 mm and 30 mm, such as between 15 mm and 25 mm, such as approximately 22 mm. The leaf spring may be between 1.5 mm and 5 mm wide, such as between 2.0 mm and 4.0 mm, such as approximately 3.5 mm.

[0103] The leaf spring may be of any suitable or desired thickness. However, in a preferred embodiment, the thickness of the leaf spring is 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 stress generated in the leaf spring. This means that the leaf spring can be made shorter without 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 0.3 mm thick. 2 and 1.5mm 2 Between, for example, 0.2mm 2 and 0.8mm2 Between, for example approximately 0.5mm 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. The 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 so 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 so that the movable electrical contact applies a preload of between 10 grams and 30 grams, such as a preload of 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 A perspective view showing a liquid heating device according to an 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 It shows that when the push rod 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 Shows when the trip lever is operated via the control unit. 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 von Mises stress in a conventional leaf spring of different lengths;

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

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

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

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

[0120] Fig.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] Fig.12a , Figure 12b , Fig.12c and Fig.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 an embodiment of the present invention is shown. The appliance 2 comprises a liquid heating container 4, a container mouth 6 and a handle 8. The top of the appliance 2 is closed with a lid 10. The appliance 2 is arranged to rest on a power base 12 having a 360-degree base electrical connector part 14 arranged in the center for powering the appliance.

[0123] The apparatus 2 also includes an electric heater ( Figure 1 The heater is a heat exchanger (not shown) for heating a volume of liquid contained in a liquid heating container 4. The heater includes an electric heating element mounted on the bottom side of a heat diffusion plate. The heating element is arranged to be in thermal communication with a base 23 of the liquid heating container 4 through the heat diffusion plate when electrical energy is supplied to the heater, thereby heating the contents of the liquid heating container 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 plastic 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 electrical connector part 14 of the power base 12.

[0127] The control unit 16 includes fixed electrical tabs 29, which are electrically connected to the cordless electrical adapter component 28 through a power circuit, which will be described in more detail below. As 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 thermally sensitive actuators 30a, 30b supported by a metal mounting plate 32 secured to the top side of the control body 26. The thermally sensitive actuators 30a, 30b are snap-acting bimetallic actuators, each set to independently operate 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 bottom side of the heat diffuser plate, the actuators 30a and 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 (multiple) predetermined temperatures causes the switch in 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 absence of a "dry boil" situation in the liquid heating vessel 4 where liquid is not present.

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

[0136] Figure 3 Shows Figure 2a and Figure 2b 18 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 component 28 is a three-pole connector including a ground pin 28a, a live ring 28b, and a neutral ring 28c. The live ring 28b and the neutral ring 28c are arranged concentrically around the ground pin 28a in the center. Figure 3 28a) includes a central hole for receiving the ground pin 28a, and coaxial annular holes for receiving the live ring 28b and the neutral ring 28c.

[0138] The 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 2 is a perspective partial view of the control unit 16, in which some components of the control unit 16 are omitted for ease of illustration.

[0141] The control unit 16 includes a charged leaf spring 42 and a neutral leaf spring 44. The charged leaf spring 42 includes a fixed end 42a, which is mounted to the charged ring 28b and is electrically connected to the charged ring 28b. The charged leaf spring 42 also includes a movable portion 42b, which extends from the flexure point of the charged leaf spring 42. The first push rod 40a is arranged to contact the distal end of the movable portion 42b of the charged 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 (such as 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] The live leaf spring 42 and the neutral leaf spring 44 are directly fixed to the live ring 28b and the neutral ring 28c, respectively. The leaf springs 42, 44 include holes for receiving corresponding tabs protruding from the live ring 28b and the neutral ring 28c to facilitate such direct fixing.

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

[0145] The leaf springs 42 and 44 are arranged below the push rods 40a and 40b, respectively, 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 trip 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 trip rod 36 through the movable part 44b of the leaf spring, which moves the trip 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 trip rod 36 also includes a force transmission pad ( Figure 4 ), the force transfer pad is arranged below the movable part 42b of the charged leaf spring 42 for the same purpose.

[0146] The trip bar 36 also includes return stops 49a, 49b disposed above the movable portions 42b, 44b of the live leaf spring 42 and the neutral leaf spring 44, respectively, for limiting the upward movement of the movable portions 42b, 44b, which will be described in more detail below. The return stops 49a, 49b are arranged 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 includes 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 fixed electrical contact 52 of the neutral fixed tab 29b.

[0149] The leaf spring 44 is biased to a 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 temperature-sensitive actuator 30b is operated, the push rod 40b moves vertically downward so as to bend the leaf spring 44 by flexing the movable portion 44b downward relative to the fixed end 44a. Figure 5b As shown, due to the force applied by the push rod 40b on the movable portion 44b, the movable portion 44b of the leaf spring 44 continues to bend downward even after the push rod 40b reaches the end of its travel. The deflection of the movable portion 44b is stopped by the force transmitting pad 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 pad 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 be cooled 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 (such as Figure 5a ). The force required to pivot the trip lever 36 is greater than the upward force exerted by the movable portion 44b of the leaf spring 44 on the return stopper 49b due to the resilience of the leaf spring 44.

[0154] In addition to being movable to the disconnected position by push rod 40b following operation of thermal actuator 30b, leaf spring 44 is also movable to the disconnected position by manual operation of trip lever 36 or as a result of operation of third thermal actuator 30c causing 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 lever 36 has been pivoted to the "OFF" position. As described above, the trip lever 36 includes a return stop 49b and a force transfer pad 48b, both of which are located at 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 stopper 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 so that the movable electrical contact 50 is separated from the fixed electrical contact 52. The return stopper 49b of the trip bar 36 holds the leaf spring 44 in the 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 when it is operated. 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 when it is operated. The vertical movement of the movable electrical contact 50 depends on the relative distance between the flexure point 45, the movable electrical contact 50 and the push rod 40b. Since the push rod 40b is arranged to contact the leaf spring 44 at a point on the more distal side of the movable electrical contact 50 along the leaf spring 44, 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 utility model can be shorter than a conventional leaf spring, an existing thermal actuator can still be used with an embodiment of the utility model without the need to modify the thermal actuator to provide a shorter stroke distance.

[0158] Since the leaf spring 44 is thinner than a conventional leaf spring, it may also be less rigid, which means that the leaf spring 44 may over-travel after the thermal actuator 30b operates. This over-travel may cause the stress generated in the leaf spring to exceed the yield stress of the leaf spring material. When the leaf spring 44 is deflected by the thermal actuator 30b via the push rod 40b, the force transfer pad 48b prevents the leaf spring 44 from over-travel by the inertia of the tripping rod 36. The thermal actuator 30b can apply high dynamic mechanical loads on the leaf spring 44. However, by preventing the excessive travel of the leaf spring 44, the stress on the leaf spring 44 can be limited. As described above, when the force transfer pad 48b is arranged on the tripping rod 36, the impact between the leaf spring 44 and the force transfer pad 48b also causes the tripping rod 36 to pivot to the OFF position, thereby resetting the tripping rod 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 fillets on either side of the arc of the kink 54, thereby rounding the intersection of the sinusoidal kink 54 and the flat leaf spring 44 geometry.

[0160] Figure 7 The von Mises stress graphs for straight (ie conventional) leaf springs of different lengths with a thickness of 0.15 mm are shown, and a deflection of 0.9 mm is applied, 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 when deflected by 0.9 mm without exceeding the yield stress is 9 mm.

[0162] Figure 7 Also shown is a dot 200 which represents 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 shape of the leaf spring, a leaf spring having a footprint of 8 mm can be used without exceeding the yield stress of the material. This is because the kink can increase the effective bending length of the leaf spring, thereby helping to reduce the maximum induced stress without increasing the leaf spring footprint.

[0163] Figure 4 , Figures 5a to 5c and Figures 6a to 6bThe leaf spring 44 shown is about 22 mm long, about 3.5 mm wide, and about 0.15 mm thick. The material of the leaf spring 44 is C7025, a hardened copper alloy with a yield stress of about 540 MPa. The radius of curvature of the arc of the kink 54 is 0.8 mm, and the radius of curvature of the fillets 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 thermally sensitive actuator 30b is operated, the movable electrical contact 50 is separated from the fixed electrical contact 52 by 0.9 mm to cut off 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 2a to 6b An "integrated" control unit 16 is shown, wherein the control unit 16 itself includes means for interrupting the power circuit in an overheat condition (i.e., thermally sensitive actuators 30a, 30b), and means for disconnecting the power circuit when liquid temperature conditions (such as boiling) are reached (thermal sensitive actuator 30c).

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

[0167] Fig.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 switch device 103 includes a steam sensitive bimetallic element (not shown) which is located on top of the handle 108. The electric switch 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 switch 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 8The control unit 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. Figures 2a to 6b The control unit 16 is basically the same.

[0170] Figure 9a and Figure 9b Shows Figure 8 1. A front view of 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 in the push rod 140b has been moved downwardly toward the stopper 148b by the thermal actuator, the leaf spring 144 in the disconnected position. In the disconnected 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] Fig.11a Shows Figure 9a and Figure 9b A front view and an enlarged cross-sectional front view of a 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 in the hole 156 by a press fit. When the hole 156 is punched in the leaf spring 144, the peripheral edge 156a of the hole 156 is bent downwardly away from the plane of the leaf spring 144, which means that when the contact 150 is received in the hole 156, the surface area of ​​the leaf spring 144 at a high point contacts the movable electrical contact 150. This means that, although the leaf spring 144 is thinner than a conventional leaf spring, the contact surface area between the leaf spring 144 and the movable electrical contact 150 can remain the same, which means 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] In addition, the process also forms a rigid cylindrical structure within the leaf spring 144 at the contact point between the movable electrical contact 150 and the fixed electrical contact 152. This helps to offset any reduction in the stiffness of the leaf spring 144 due to the relative reduction in the thickness of the leaf spring 144 compared to known leaf springs, and helps to 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 and 152.

[0175] It should be understood that Fig.11a The mounting arrangement of the movable electrical contact 150 shown and described above may also be applied to Figures 2a to 6b Either of the leaf springs 42, 44 of the illustrated embodiment.

[0176] According to another aspect of the present invention, the mounting arrangement may also be applied to leaf springs that do not include kinking. Fig.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 Figures 2a to 11a The illustrated embodiment features a leaf spring having a kink corresponding to approximately a half 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. Fig.12a , Figure 12b , Fig.12c and Fig.12d Some examples of alternative geometries are shown.

[0178] Fig.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 returns symmetrically to the plane of the leaf spring 344.

[0180] Fig.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. 1 is different in that the peak itself is inverted so as to form two peaks and a valley between the peaks.

[0181] Fig.12d An alternative leaf spring 544 is shown that includes a folded kink 554. The kink 554 bends upward at an angle of approximately 180° away from the plane of the leaf spring 544 and then continues again in a distal direction 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 device, characterized in that: The control unit comprises: 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; a movable electrical contact mounted on the movable portion of the leaf spring for mating with a corresponding fixed electrical contact in the power circuit when the leaf spring is in the closed position; and a bimetallic element operable at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position in which the movable electrical contact is separated from the fixed electrical contact to interrupt the power circuit; Wherein the leaf spring defines a hole 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 hole.

2. The control unit according to claim 1, wherein: The leaf spring extends in a plane and includes a kink, disposed between the fixed end and the movable portion, which extends out of the plane and reverses to return to the same plane.

3. The control unit according to claim 2, wherein: The kink is arranged adjacent to the fixed end at a flexure point of the leaf spring.

4. The control unit according to claim 2 or 3, wherein: The kink is a continuous turn.

5. The control unit according to claim 4, wherein: The kink includes an arcuate portion disposed between two rounded corners.

6. The control unit according to claim 2 or 3, wherein: The bimetallic element 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.

7. The control unit according to claim 1 or 2, characterized in that: The control unit further includes a stopper for preventing movement of the movable portion of the leaf spring after the movable portion has been moved from the closed position to the open position.

8. The control unit according to claim 7, characterized in that The control unit further comprises a trip lever 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.

9. The control unit according to claim 8, characterized in that The stopper is arranged on the trip rod.

10. The control unit according to claim 1 or 2, characterized in that: The thickness of the leaf spring is between 0.05 mm and 0.18 mm.

11. The control unit according to claim 10, characterized in that The leaf spring is 0.15 mm thick.

12. The control unit according to claim 1 or 2, characterized in that: The movable electrical contact is disposed in the hole by an interference fit.

13. The control unit according to claim 1 or 2, characterized in that: The leaf spring is an integral component including the protrusion.

14. A liquid heating device, characterized in that: The liquid heating device comprises: 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; and A control unit as claimed in claim 1 or 2.

15. A leaf spring, characterized in that: include: 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.

16. The leaf spring according to claim 15, wherein The leaf spring extends in a plane and includes a kink disposed between the proximal end and the distal portion that extends out of the plane and reverses direction to return to the same plane.

17. The leaf spring according to claim 16, wherein: The kink is disposed adjacent the proximal end at a flexure point of the leaf spring.

18. The leaf spring according to claim 16 or 17, wherein: The kink is a continuous turn.

19. The leaf spring according to claim 18, wherein The kink includes an arcuate portion disposed between two rounded corners.

20. The leaf spring according to claim 15 or 16, characterized in that The thickness of the leaf spring is between 0.05 mm and 0.18 mm.

21. The leaf spring according to claim 20, characterized in that The leaf spring is 0.15 mm thick.

22. The leaf spring according to claim 15 or 16, characterized in that The electrical contact of the leaf spring is arranged in the hole by interference fit.

23. The leaf spring according to claim 15 or 16, characterized in that The leaf spring is an integral component including the protrusion.

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