Thermal control device

Abstract

The control unit for the liquid heating appliance includes a leaf spring 44 having 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 has a bent portion 54 between the fixed end 44a and the movable portion 44b. A movable electrical contact 50 is attached to the movable portion 44b and connects to a corresponding fixed electrical contact 52 of a power supply circuit when the leaf spring 44 is in the closed position. The control unit also includes a thermal actuator that is activated at a predetermined temperature to move the leaf spring 44 to the open position and separate the movable contact 50 from the fixed contact 52.

Description

[Technical Field]

[0001] The present invention relates to a thermal control device for a liquid heating appliance, a liquid heating appliance, a leaf spring, and a method for manufacturing a leaf spring. [Background technology]

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

[0003] Such control units often include a switch for disconnecting the electric heater from the power source when a predetermined temperature is sensed within the appliance. For example, the control unit may be configured to turn off the electric heater when the liquid in the liquid heating vessel reaches a boil (or some other selected temperature) or when an overheating condition is sensed. Typically, the control unit includes a heat-sensitive actuator (such as a snap-action bimetallic actuator) that activates at the predetermined temperature to move a switch and disconnect the power source.

[0004] In some conventional control units, the switch includes a leaf spring supporting a movable electrical contact configured to connect to a corresponding fixed electrical contact in the heater's power supply circuit. When the thermal actuator is activated at a predetermined temperature, the leaf spring deflects, separating the electrical contacts, thereby interrupting the supply of electrical energy to the heater. The electrical contacts are typically required to be separated with a minimum contact gap to avoid electrical arcing between the contacts when they are separated by activation of the thermal actuator. Summary of the Invention [Problem to be solved by the invention]

[0005] A smaller control unit may be desirable because it can provide beneficial savings in manufacturing time and cost, as well as greater freedom in the design phase of the liquid heating appliance. Typically, a smaller control unit would require correspondingly smaller components within the control unit, such as leaf springs. However, the minimum contact gap between the electrical contacts typically remains the same even when the control unit is smaller.

[0006] When the leaf spring length is reduced, deflecting the leaf spring to ensure a predetermined required contact gap increases bending stresses in the leaf spring (compared to the stresses experienced in longer leaf springs). This increased stress, combined with repeated deflection of the leaf spring during use of the device, can cause stress relaxation in the leaf spring.

[0007] This stress relaxation can reduce the contact force between the electrical contacts and increase the electrical resistance between the contacts, which exacerbates the self-heating effects caused by current flow through the leaf springs. This can lead to further stress relaxation, a further increase in electrical resistance, and thermal runaway, characterized by issues such as contact fizzing and control glitches.

[0008] As a result, existing small control units are only suitable for fixtures that operate at low currents and cannot be safely used with higher power fixtures (e.g., 13-15 amps).

[0009] SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved control unit that can be made smaller than conventional control units, yet is usable in devices that are not necessarily limited to low power appliances. [Means for solving the problem]

[0010] According to a first aspect, the present invention provides a control unit for controlling a power supply circuit to an electric heater in a liquid heating appliance, comprising: a leaf spring having a fixed end and a movable portion that is movable relative to the fixed end between a closed position and an open position; a movable electrical contact attached to a movable portion of the leaf spring for connecting to a corresponding fixed electrical contact in the power supply circuit when the leaf spring is in the closed position; a thermal actuator that operates at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position at which the movable electrical contact is separated from the fixed electrical contact to interrupt the power supply circuit; The leaf spring provides a control unit having a bent portion between the fixed end and the movable portion.

[0011] According to a second aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: a liquid heating vessel; an electric heater for heating the liquid contained in the liquid heating container, the electric heater being supplied with power by a power supply circuit; A control unit, a leaf spring having a fixed end and a movable portion that is movable relative to the fixed end between a closed position and an open position; a movable electrical contact attached to a movable portion of the leaf spring for connecting to a corresponding fixed electrical contact in the power supply circuit when the leaf spring is in the closed position; a control unit including a thermal actuator that is activated at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position at which the movable electrical contact is separated from the fixed electrical contact to interrupt the power supply circuit; A liquid heating appliance comprising: The leaf spring provides a liquid heating device having a bent portion between the fixed end and the movable portion.

[0012] It will be understood that the leaf spring has flexibility such that the bends and the movable portion flex relative to the fixed end as the movable portion moves between the closed and open positions. It will further be appreciated that because leaf springs are by definition substantially planar, the bends may be understood as deviations from the original planar shape of the leaf spring.

[0013] Therefore, the leaf springs provided by the embodiments of the present invention have an increased effective bending length due to the presence of the bends, which helps prevent the stress in the leaf spring from exceeding the yield stress of the leaf spring material while allowing the footprint length of the leaf spring to be shortened, thereby enabling the overall control unit to be made smaller, which reduces the manufacturing cost of the control unit and makes the liquid heating appliance equipped with the control unit more visually appealing.

[0014] Because the stresses within the bent leaf springs of the present invention can be reduced compared to conventional, unbent leaf springs of the same footprint length, the leaf springs of the present invention can, in some embodiments, carry higher currents (e.g., 13-15 amps). As noted above, leaf springs operating at high currents can experience poor stress relaxation due to increased temperatures in the leaf springs as a result of self-heating caused by the current flowing through them. The introduction of bends into the leaf springs of the present invention allows for a reduction in the maximum bending stress within the leaf spring, thereby mitigating the effects of stress relaxation at high currents and helping to facilitate safe operation of the leaf spring below its yield stress.

[0015] 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, of a corresponding power base stand, to receive power from the power supply circuit. The cordless electrical adapter component preferably includes one or more mating conductors for connection to a live or neutral pole (respectively) of the corresponding base electrical connector component.

[0016] In some embodiments, the control unit includes a control body defining a cordless electrical adapter component. The control body may be a unitary (e.g., molded) plastic body. The cordless electrical adapter component and its corresponding base electrical connector component may be matable regardless of relative angular orientation, or at least over a wide angular range (e.g., at least 340°, preferably up to 360°). Suitable cordless connectors of this "360° type" are described in WO 95 / 08024 and WO 01 / 28294 and are available as Strix P72 or P76 connector components.

[0017] In some embodiments, the liquid heating appliance is configured to seat on a power base stand, the power base stand including a corresponding base electrical connector assembly, which may include tabs for electrical connection to a mains power cable, or the mains power cable may be integrated into the connector assembly, and preferably the base electrical connector assembly is centrally mounted on the power base stand.

[0018] The cordless electrical adapter assembly located in the control unit may have at least two mating conductors for connecting to the live and neutral poles of the power circuit. An additional ground connection may also be present. In some embodiments, the cordless electrical adapter assembly is a three-prong connector assembly (e.g., for mating with a Strix P72). In other embodiments, the cordless electrical adapter assembly is a five-prong connector assembly (e.g., for mating with a Strix P76). Such a five-prong connector assembly allows for electrical signal connections as well as power connections. Preferably, the power supply circuit of the liquid heating appliance is configured to receive 13 to 15 amps of current (e.g., from the base electrical connector assembly).

[0019] Preferably, the fixed end of the leaf spring is secured to the mating conductor of the cordless electrical adapter component. The control unit preferably includes two leaf springs, a first leaf spring connected to or secured to the live conductor of the cordless electrical adapter component and a second leaf spring connected to or secured to the neutral conductor of the electrical adapter component. When first and second leaf springs are provided, any or all of the features of the leaf springs described herein may be applied (and preferably are applied) to either or both of the first and second leaf springs.

[0020] For example, the second leaf spring preferably has a fixed end and a movable portion 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 the neutral mating conductor of the electrical adapter component. Preferably, the second leaf spring extends substantially in a plane and has a bent portion disposed between the fixed end and the movable portion. The bent portion protrudes from the plane and then reverses back to substantially the same plane. The thickness of the second leaf spring is preferably 0.05 mm to 0.18 mm, for example, approximately 0.15 mm.

[0021] Preferably, the fixed end of the leaf spring (e.g., each leaf spring) is secured directly to the mating conductor (e.g., each respective mating conductor) of the cordless electrical adapter component. The leaf spring may be joined to the mating conductor by, for example, welding or soldering. The leaf spring may be secured to the mating conductor by friction. The leaf spring may be secured to the mating conductor by cooperation between a pair of fastening elements (e.g., a tab or hook and a corresponding opening).

[0022] In some other embodiments, the liquid heating appliance comprises a power socket for receiving a power cord for connection to a mains power source. In some embodiments, the liquid heating appliance comprises an integral power cord.

[0023] In various embodiments, the liquid heating appliance may include a heat spreader plate configured to be in thermal communication with the electric heater. Preferably, the control unit is configured to be attached to a lower surface of the heat spreader plate. In some embodiments, the control unit includes a mounting plate for mounting the control unit to the lower surface of the heat spreader plate. Preferably, the mounting plate is metal. Preferably, the mounting plate is substantially flat.

[0024] Preferably, the thermal actuator is configured to sense a temperature within the liquid heating appliance, which may be representative of the temperature of the liquid within the liquid heating vessel, the temperature may be the temperature of an electric heater, or the temperature may be the temperature of a heat spreader plate.

[0025] The predetermined temperature may be variable (e.g., adjustable). The predetermined temperature may correspond to a desired heating temperature of the liquid in the liquid heating space. The predetermined temperature may correspond to a desired state (e.g., boiling) of the liquid in the liquid heating space. In some embodiments, the predetermined temperature may correspond to a temperature within the appliance (e.g., the temperature of a heat spreader plate) during an overheated (e.g., "dry-fired") condition.

[0026] In some embodiments, the control unit comprises an "overheat" thermal actuator and a "liquid temperature condition" thermal actuator. The overheat thermal actuator is preferably configured 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 configured to operate at a predetermined temperature corresponding to a desired state of the liquid within the liquid heating space (e.g., boiling).

[0027] Preferably, both the overheat thermal actuator and the liquid temperature condition thermal actuator are configured 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 and the power supply circuit is interrupted.

[0028] In such an embodiment, where the control unit includes both an "overheat" thermal actuator and a liquid temperature condition thermal actuator, the control unit may be considered an "integrated" controller.

[0029] In some embodiments, the control unit does not include a liquid temperature condition thermal actuator. Instead, the control unit may include only an overheating thermal actuator. A control unit according to such embodiments may be suitable for use in a liquid heating appliance that includes an electrical switching arrangement that is physically separate from, but electrically connected to, the control unit. The electrical switching arrangement preferably includes a liquid temperature condition thermal actuator for opening a switch to cut off power to the heater. The liquid temperature condition thermal actuator is preferably configured to open the switch when a predetermined temperature corresponding to a desired state (e.g., boiling) of the liquid in the liquid heating space is detected.

[0030] Such a liquid heating appliance may be considered a "split switch" appliance because it has separate switches for cutting off power to the heater in an overheating condition and for cutting off power to the heater when a certain liquid temperature condition (e.g., boiling) is detected. In contrast, in an integrated controller, the same switch (i.e., the same set of contacts in the control unit) is opened in both cases. The thermal actuator for the liquid temperature condition may comprise a thermomechanical (e.g., bimetallic) switch. In some embodiments, the electrical switching arrangement comprises an electronic switching arrangement, e.g., a controller connected to a thermistor. The electrical switching arrangement is preferably located in a different portion of the liquid heating appliance from the controller. This allows for greater design flexibility of the liquid heating appliance. In some embodiments, the control unit is located in the base of the appliance and the electrical switching arrangement is located in the top portion of the appliance (e.g., the handle of the appliance). The electrical switching arrangement is preferably in series with a switch comprising a movable electrical contact and a fixed electrical contact of the control unit.

[0031] In some embodiments (e.g., embodiments in which the control unit is an integrated control unit), the control unit comprises a trip lever. The trip lever is preferably movable (e.g., pivotable). The trip lever is preferably movable to act on a movable portion of the leaf spring to move the movable portion from a closed position to an open position in which the movable electrical contact is separated from the fixed electrical contact, thereby interrupting the power supply circuit. The liquid temperature condition thermal actuator is preferably configured to move the trip lever at a predetermined temperature. The liquid temperature condition thermal actuator is preferably configured to move the trip lever, thereby moving 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, thereby interrupting the power supply circuit.

[0032] Preferably, the thermal actuator (e.g., for overheating) is mounted on the upper surface of the control unit. Preferably, the thermal actuator is mounted on the upper surface of the mounting plate. That is, if the control unit is mounted on the lower surface of the heat spreader plate, the thermal actuator can be positioned in good thermal communication with the heat spreader plate. As a result, the thermal actuator may be able to more reliably detect a predetermined temperature by, for example, accurately detecting the temperature of the heat spreader plate (and thus, for example, the temperature of the liquid in the appliance). This allows the thermal actuator to more reliably operate at a predetermined temperature.

[0033] The thermal actuator may include a bimetallic element, which is preferably a snap-action bimetallic actuator, and is preferably configured to activate (e.g., snap) when a predetermined temperature is detected.

[0034] The bimetallic element may act directly on the leaf spring. However, preferably the control unit (e.g. a thermal actuator) comprises an intermediate member 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 configured to act on the intermediate member to move it. Preferably, the intermediate member moves a distance equal to the distance the actuating portion of the bimetallic element deflects.

[0035] In a preferred embodiment, the intermediate member includes a push rod that is operated by an actuator (e.g., a 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 downward from the thermal actuator toward the movable portion of the leaf spring.

[0036] In some embodiments, the thermal actuator (e.g., its push rod) is configured to press against a contact point on 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 located at a point on the leaf spring distal to the fixed end and the movable electrical contact. Preferably, the movable electrical contact is attached to the movable portion of the leaf spring between the bent portion and the contact point.

[0037] Preferably, the distance travelled by the movable portion of the leaf spring at the point of contact is substantially equal to the deflection of the actuating portion of the bimetallic element.

[0038] To reduce costs and minimize design effort, it may be beneficial for manufacturers to use the same thermal actuator in smaller control units as in other (larger) sized control units. However, due to the shorter leaf spring lengths in conventional smaller control devices, this is often not feasible because the force exerted by the thermal actuator on the short leaf springs would cause the stress in the leaf springs to exceed the yield stress. However, as described herein, the leaf springs of the present invention include bends that reduce the maximum stress in the leaf springs. Therefore, in some embodiments, the thermal actuators provided in the control units to act on the leaf springs can be advantageously the same size as the type used in the larger control devices.

[0039] Furthermore, by positioning the thermal actuator (e.g., its push rod) so 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, the vertical distance at the location of the electrical contact (i.e., the location where the contact gap is formed) caused by vertical displacement of the thermal actuator (e.g., its push rod) at the contact point can be reduced. The location of the contact point between the thermal actuator (e.g., its push rod) and the movable part of the leaf spring can be selected during the design phase so that a desired separation distance is ensured between the movable electrical contact and the fixed electrical contact for a given vertical displacement of the thermal actuator when the movable part of the leaf spring is moved to the open position.

[0040] In some embodiments, the leaf spring defines an opening in which the movable electrical contact is disposed. The movable electrical contact may be disposed within the opening by an interference fit. Preferably, the leaf spring has (e.g., integrally formed) protrusions that protrude from the plane of the leaf spring around the periphery of the opening. This means that the contact area between the leaf spring and the movable electrical contact is greater than it would be if the leaf spring did not have the protrusions. This improves the bond (e.g., cold bond) between the movable electrical contact and the leaf spring, thereby helping to reduce self-heating (and resulting stress) in the leaf spring.

[0041] This movable electrical contact attachment configuration can be particularly beneficial for leaf springs that are thinner than conventional leaf springs (i.e., less than 0.2 mm thick) because conventional techniques for attaching electrical contacts to leaf springs (e.g., welding or riveting) are difficult to apply to such thin leaf springs.

[0042] This arrangement is believed to be novel and inventive in itself. Thus, according to a further aspect, the present invention provides a method for manufacturing a semiconductor device comprising: a proximal end and a distal portion movable relative to the proximal end; an electrical contact attached to the distal portion for connecting to a corresponding electrical contact, The leaf spring defines an opening in which the electrical contact is disposed, the leaf spring having a protrusion protruding from the plane of the leaf spring around the periphery of the opening and surrounding the electrical contact.

[0043] According to a further aspect, the present invention provides a control unit for controlling a power supply circuit to an electric heater in a liquid heating appliance, comprising: a leaf spring having a fixed end and a movable portion that is movable relative to the fixed end between a closed position and an open position; a movable electrical contact attached to a movable portion of the leaf spring for connecting to a corresponding fixed electrical contact in the power supply circuit when the leaf spring is in the closed position; a thermal actuator that operates at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position at which the movable electrical contact is separated from the fixed electrical contact to interrupt the power supply circuit; A control unit is provided in which the leaf spring defines an opening in which the movable electrical contact is disposed, the leaf spring having a protrusion protruding from the plane of the leaf spring around a periphery of the opening.

[0044] According to a further aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising a liquid heating vessel; an electric heater for heating the liquid contained in the liquid heating container, the electric heater being supplied with power by a power supply circuit; A control unit, a leaf spring having a fixed end and a movable portion that is movable relative to the fixed end between a closed position and an open position; a movable electrical contact attached to a movable portion of the leaf spring for connecting to a corresponding fixed electrical contact in the power supply circuit when the leaf spring is in the closed position; a control unit including a thermal actuator that is activated at a predetermined temperature to move the movable portion of the leaf spring from the closed position to the open position at which the movable electrical contact is separated from the fixed electrical contact to interrupt the power supply circuit; A liquid heating appliance comprising: The liquid heating apparatus includes a leaf spring defining an opening in which the movable electrical contact is disposed, the leaf spring having a protrusion protruding from the plane of the leaf spring around a periphery of the opening.

[0045] According to a further aspect, the present invention provides a method of manufacturing a leaf spring having a proximal end and a distal portion movable relative to the proximal end, comprising: forming an opening through the distal portion of the leaf spring; and attaching an electrical contact to the distal portion of the leaf spring by inserting the electrical contact into the opening; The method further provides that the step of forming the opening includes forming a protrusion that protrudes from the plane of the leaf spring around a periphery of the opening.

[0046] As noted above, in some embodiments, the movable electrical contact may be disposed within the opening by an interference fit. Preferably, the leaf spring has (e.g., integrally formed) protrusions that protrude from the plane of the leaf spring around the periphery of the opening, such that the contact area between the leaf spring and the movable electrical contact is greater than the contact area would be if the leaf spring did not have the protrusions.

[0047] In some embodiments, the leaf spring has a bend (e.g., having features of any one or more embodiments of other aspects described herein). However, the leaf spring may be substantially flat (e.g., at least between the proximal and distal ends). Preferably, the leaf spring has a thickness of less than 0.2 mm. In some embodiments, the leaf spring has a thickness of 0.05 mm to 0.18 mm. In some embodiments, the leaf spring has a thickness of approximately 0.15 mm.

[0048] The leaf spring and the protrusions may be separate components. However, the leaf spring is preferably a unitary component including the protrusions. The protrusions are preferably formed from the same material as the leaf spring. The protrusions are preferably formed at the same time (e.g., in the same operation) as the openings. This can simplify the manufacturing process of the leaf spring and help ensure the formation of the beneficial geometric shapes of the openings and protrusions, as described above.

[0049] For example, the opening may be formed by a stamping operation, which preferably causes the leaf spring material to bend in the direction of the stamping to form a protrusion around the periphery of the opening. Thus, in some embodiments, the method may include stamping the leaf spring to form the opening to form the protrusion.

[0050] The protrusion may extend around a portion of the opening. Preferably, the protrusion extends around a majority (e.g., the entire periphery) of the periphery of the opening. The protrusion may be formed to surround the electrical contact.

[0051] In embodiments of any aspect disclosed herein, the movable portion of the leaf spring is preferably biased toward the closed position. The biasing force may be provided by a separate member, i.e., a biasing member. However, the biasing force is preferably provided by the shape of the leaf spring itself. The thermal actuator is preferably operable to move the movable portion against this biasing force when moving the movable portion from the closed position to the open position. After being actuated to move the movable portion from the closed position to the open position, the thermal actuator is preferably configured to reset to allow the movable portion to return to the closed position. The thermal actuator may be manually reset. However, the thermal actuator is preferably configured to reset automatically (e.g., when the temperature sensed by the thermal actuator falls sufficiently below a predetermined temperature).

[0052] In some embodiments, the control unit further includes a trip lever for allowing a user to manually move the movable portion of the leaf spring from the closed position to the open position and / or from the open position to the closed position. The trip lever may be movable between an "off" position and an "on" position. In the "on" position, the movable electrical contact is preferably in contact with the fixed electrical contact. In the "off" position, the movable electrical contact may or may not be in contact with the fixed electrical contact. However, the control unit is preferably configured to prevent current from flowing through these electrical contacts when the trip lever is in the "off" position. Thus, the provision of a trip lever may allow a user to manually interrupt and / or start the heating operation of the liquid heating appliance.

[0053] As mentioned above, the trip lever may be configured to be moved by a liquid temperature condition thermal actuator of the control unit (eg, when boiling is detected).

[0054] Preferably, the control unit includes a stopper for stopping the movement of the movable portion of the leaf spring after the movable portion moves from the closed position to the open position. The movable portion of the leaf spring is preferably configured to contact the stopper after moving from the closed position to the open position. In this manner, the stopper can be provided to limit the overshoot distance that the movable portion of the leaf spring moves. This can help prevent plastic deformation of the leaf spring due to (e.g., repeated) deflection during use.

[0055] In some embodiments, the stopper is located on the control body of the control unit. In some embodiments, the stopper is located on the trip lever of the control unit. When the stopper is located on the trip lever of the control unit, the position of the trip lever may be reset (e.g., to the "off" position) by the force that the movable portion of the leaf spring exerts on the stopper when the movable portion contacts the stopper. Thus, the stopper can act as a force transmission pad and perform the dual function of resetting the position of the trip lever and reducing overshoot of the leaf spring.

[0056] Preferably, the stop is located vertically below (e.g., directly below) the contact point (i.e., the point where the thermal actuator or its push rod contacts the leaf spring). Positioning the stop directly below the contact point allows the leaf spring to be stopped more quickly and without creating a bending moment on the leaf spring between the stop and the contact point, which could damage the leaf spring.

[0057] In some embodiments, the control unit includes a return stop for stopping the movable portion of the leaf spring from moving from the open position toward the closed position (e.g., after the movable portion has been moved to the open position by the thermal actuator or when the movable portion attempts to return to the closed position under its own biasing force). The return stop is preferably configured 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 located on a trip lever of the control unit.

[0058] In some embodiments, the trip lever includes a stopper (e.g., a force transmission pad) and a return stopper. The stopper (e.g., a force transmission pad) is preferably located below the movable portion of the leaf spring (i.e., in the direction of movement of the movable portion by the thermal actuator). The return stopper is preferably located above the movable portion of the leaf spring.

[0059] 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 lever is moved from the "on" position to the "off" position (e.g., by a user or by activation of a thermal actuator for liquid temperature conditions).

[0060] Preferably, the trip lever is configured such that, when moved from the "off" position to the "on" position, it releases the movable portion of the leaf spring, allowing the movable portion to move from the open position to the closed position (e.g., by the biasing force of the leaf spring). Preferably, movement of the trip lever from the "off" position to the "on" position does not directly move the movable portion of the leaf spring and cause the movable electrical contact to contact the fixed electrical contact. For example, the range of movement of the stopper (when the trip lever is moved) is preferably insufficient to allow the stopper to directly move the movable portion of the leaf spring, thereby causing the movable electrical contact to contact the fixed electrical contact. This configuration can help improve safety by preventing a user from manually closing the electrical contact and overriding the control unit before the thermal actuator resets. Preferably, the movable portion is moved from the open position to the closed position by the biasing force of the leaf spring alone.

[0061] The leaf spring is preferably a single homogeneous member, preferably including at least a fixed end, a movable portion, and a bending portion. Preferably, the leaf spring has an elongated shape. The leaf spring is preferably attached to the control unit as a cantilevered structure, i.e., the fixed end (proximal end) is fixed and the opposite end (distal end) is unsupported (and preferably movable). The bending portion may be spaced from the fixed end by a further movable portion of the leaf spring. However, preferably, the bending portion is located adjacent to the fixed end of the leaf spring. Preferably, the bending portion is located at the flexion point of the leaf spring. The flexion point is the point of the leaf spring closest to the fixed end but which flexes when the movable portion moves relative to the fixed end. Locating the bending portion at the flexion point of the leaf spring helps to reduce the stress in the leaf spring at the flexion point, where the leaf spring is usually most stressed. Reducing the stress in this region can increase the durability of the leaf spring.

[0062] The bends may be of any suitable or desired shape for increasing the effective bending length. Preferably, the bends extend out of the plane of the leaf spring and return to substantially the same plane. The bends may be arcuate. The bends may be substantially semicircular. The bends may be "U," "S," "V," "W," "M," or "C" shaped. The bends may be substantially sinusoidal. The bends may include a folded portion. Preferably, the bends are continuously curved. The bends may have a shape that approximates a normal (bell) curve. Preferably, the bends include an arcuate portion. Preferably, the leaf spring includes one or more continuously curved transition shapes (e.g., fillets) between the substantially planar leaf spring and the bends (e.g., their arcuate portions). This helps avoid high stress concentrations in the leaf spring, which may allow the leaf spring to be miniaturized without exceeding the yield stress of the leaf spring material.

[0063] As discussed above, by providing bends in the leaf spring to increase the effective bending length of the leaf spring, stresses within the leaf spring can be reduced for a given footprint length, allowing for smaller leaf springs without exceeding the yield stress of the leaf spring material.

[0064] The leaf spring of the present invention is believed to be novel and inventive in itself. Thus, according to a further aspect, the present invention provides: a proximal end and a distal portion movable relative to the proximal end; an electrical contact attached to the distal portion for connecting to a corresponding electrical contact, A leaf spring is provided having a bend between the proximal end and the distal portion.

[0065] According to a further aspect, the present invention provides a method of manufacturing a leaf spring having a proximal end and a distal portion movable relative to the proximal end, comprising: forming a bend between the proximal end and the distal portion of the leaf spring; and attaching an electrical contact to the distal portion of the leaf spring for connection to a corresponding electrical contact.

[0066] In some embodiments, the method for manufacturing the leaf spring includes forming an aperture through a distal portion of the leaf spring. Preferably, the method includes attaching the electrical contact to the distal portion of the leaf spring by inserting the electrical contact into the aperture. The electrical contact may be press-fit into the aperture. Forming the aperture may include stamping the aperture. Preferably, forming the aperture includes forming a protrusion that protrudes from the plane of the leaf spring around a periphery of the aperture. As explained 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.

[0067] The proximal end of the leaf spring is preferably suitable for attachment to a control unit of a (e.g., domestic) liquid heating appliance, and the electrical contacts are preferably suitable for connection with corresponding electrical contacts in the control unit of the (e.g., domestic) liquid heating appliance.

[0068] The leaf spring may include one or more fillets disposed adjacent to the bend to smoothly connect the geometry of the bend with the geometry of the remainder of the leaf spring. In some embodiments, the bend includes an arcuate portion disposed between two fillets. Preferably, the radius of curvature of the arcuate portion of the bend is between 0.3 mm and 1.5 mm, e.g., between 0.5 mm and 1.0 mm, e.g., about 0.8 mm. Preferably, the radius of curvature of the one or more fillets is between 0.1 mm and 1.35 mm, e.g., between 0.35 mm and 0.8 mm, e.g., about 0.65 mm.

[0069] The leaf spring may have any suitable or desired length. However, in a preferred embodiment, the footprint length of the leaf spring is less than 25 mm. This allows the leaf spring to be used in control units that are smaller than conventional control units. The (footprint) length of the leaf spring may be between 5 mm and 30 mm, such as between 15 mm and 25 mm, e.g., about 22 mm. The width of the leaf spring may be between 1.5 mm and 5 mm, such as between 2.0 mm and 4.0 mm, e.g., about 3.5 mm.

[0070] The leaf spring may have 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 reduces the cross-sectional area for current flow through the leaf spring, thereby enhancing the self-heating effect of the leaf spring. However, the applicant has determined that reducing the thickness of the leaf spring can also reduce the stress induced in the leaf spring. In other words, the leaf spring can be made even shorter before the yield stress of the material is exceeded. The thickness of the leaf spring may be 0.05 mm to 0.3 mm, for example, 0.1 mm to 0.2 mm, for example, about 0.15 mm. Preferably, the leaf spring has a cross-sectional area of ​​0.07 mm or less in a plane perpendicular to its largest dimension (i.e., length). 2 ~1.5mm 2 , e.g. 0.2 mm 2 ~0.8mm 2 , for example, about 0.5 mm 2 is.

[0071] In some embodiments, 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 about 0.15 mm.

[0072] 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 0.3 mm to 1.5 mm, e.g., 0.7 mm to 1.2 mm, e.g., about 0.9 mm. This separation distance may be the minimum distance necessary to avoid electrical arcing between the contacts when the movable portion moves between the closed and open positions. The leaf spring is preferably shaped so that when the leaf spring is disposed in a control device and the movable electrical contact is in the closed position, deflection of the leaf spring applies a preload force from 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 configured so that the movable electrical contact applies a preload of 10 grams to 30 grams, e.g., 15 grams to 25 grams, e.g., about 20 grams, to the fixed electrical contact.

[0073] The leaf springs may be made of any suitable or desired material. Preferably, the leaf springs are electrically conductive, e.g., made of metal. In a preferred embodiment, the leaf spring material is a (e.g., hardened) copper alloy, e.g., C7025.

[0074] It will be understood that any embodiment described herein may include (and preferably includes) one or more (e.g., all) of the optional and preferred features outlined herein. [Brief explanation of the drawings]

[0075] Certain preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0076] FIG. 1 shows a perspective view of a liquid heating appliance according to one embodiment of the present invention.

[0077] 2a and 2b show perspective views of the control unit of the liquid heating appliance of FIG.

[0078] FIG. 3 shows a cross-sectional front view of the control unit of FIGS. 2a and 2b.

[0079] FIG. 4 shows a perspective view of the various components of the control unit of FIGS. 2a and 2b.

[0080] Figures 5a, 5b and 5c show cross-sectional front views of the leaf spring of the control unit of Figures 2a and 2b when operated by the push rod of the control unit.

[0081] 6a and 6b show cross-sectional front views of the leaf spring of the control unit of FIGS. 2a and 2b when operated by the trip lever of the control unit.

[0082] FIG. 7 is a graph showing von Mises stress in conventional leaf springs of different lengths.

[0083] FIG. 8 shows a cross-sectional front view of a control unit of a liquid heating appliance according to another embodiment of the present invention.

[0084] 9a and 9b show cross-sectional front views of the leaf spring of the control unit of FIG.

[0085] FIG. 10 shows a perspective view of a "split switch" type liquid heating appliance according to one embodiment of the present invention.

[0086] FIG. 11a shows a front view of the leaf spring of the control unit of FIG.

[0087] FIG. 11b shows a front view of a leaf spring of a control unit of a liquid heating appliance according to another embodiment of the present invention.

[0088] 12a, 12b, 12c, and 12d show alternative geometries for the flexures of the leaf spring. DETAILED DESCRIPTION OF THE INVENTION

[0089] Figure 1 shows a perspective view of a liquid heating appliance 2 (hereinafter referred to as appliance 2) according to one embodiment of the present invention. Appliance 2 includes a liquid heating container 4, a spout 6, and a handle 8. The top of appliance 2 is closed by a lid 10. Appliance 2 is configured to be placed on a power supply base 12, which has a 360-degree base-side electrical connector part 14 provided in the center for supplying electricity to the appliance.

[0090] The appliance 2 further includes an electric heater (not shown in FIG. 1 ) for heating the liquid contained within the liquid heating container 4. The heater includes an electric heating element attached to the underside of the heat spreader plate. The heating element is configured to be in thermally conductive communication with the base 23 of the liquid heating container 4 via the heat spreader plate when electrical energy is supplied to the heater, thereby heating the contents of the liquid heating container 4.

[0091] A control unit (not shown in FIG. 1) is also attached to the underside of the heat spreader plate and controls the power supply from the power supply base 12 to the electric heater.

[0092] FIG. 2a shows a perspective view of the control unit 16 of the device 2 of FIG.

[0093] The control unit 16 includes a molded plastic control body 26 having a cordless electrical adapter member 28 formed on its bottom surface. The cordless electrical adapter member 28 is configured to mate with the base electrical connector member 14 of the power base 12.

[0094] The control unit 16 includes a fixed electrical tab 29 electrically connected to a cordless electrical adapter component 28 via a power supply circuit, described in more detail below. Flying leads or other electrical connection means may be connected to the fixed electrical tab 29 to connect the power supply circuit to the electrical terminations of the electric heater, as is known in the art.

[0095] The control unit 16 further includes a first thermal actuator 30a and a second thermal actuator 30b supported by a metal mounting plate 32 fixed to the top surface of the control body 26. The thermal actuators 30a and 30b are snap-action bimetallic actuators that are each set to operate independently at a predetermined temperature.

[0096] The actuators 30a and 30b are positioned on the upper surface of the control unit 16 so that when the control unit 16 is attached to the lower surface of the heat spreader plate, the actuators 30a and 30b are in thermally conductive communication with the spreader plate, i.e., the actuators 30a and 30b are positioned to sense the temperature of the spreader plate.

[0097] As described in more detail below, thermal actuators 30a and 30b are configured to activate at a predetermined temperature, causing a switch in control unit 16 to open, thereby cutting off the supply of electrical energy to the heater. As is known in the art, this allows the heater to be turned off in the event of a "dry-fire" condition, where no liquid is present in liquid heating vessel 4.

[0098] The control unit 16 further includes a trip lever 36 pivotally mounted to the control body portion 26 of the control unit 16, the trip lever being manually operable to open or close electrical contacts in the power supply circuit, as described in more detail below.

[0099] FIG. 2b shows a perspective view of the underside of the control unit 16 of the instrument 2 of FIG.

[0100] The control unit 16 includes a third thermal actuator 30c mounted to the control body portion 26 just below the distal end of the trip lever 36. The proximal end of the trip lever is adjacent the electrical contacts of the first and second thermal actuators 30a and 30b and the power supply circuit.

[0101] The third thermal actuator 30c is in fluid communication with the liquid heating reservoir 4 of the appliance 2, in this example via a conduit (not shown) that extends through the handle 8 of the appliance 2, thereby directing vapor generated in the liquid heating reservoir 4 toward the third thermal actuator 30c. The thermal actuator 30c is a snap-action bimetallic actuator that is set to activate at a predetermined temperature indicating that the liquid in the liquid heating reservoir 4 has reached boiling temperature and converted to vapor.

[0102] As described in more detail below, the thermal actuator 30c is configured to activate at a predetermined temperature, exerting a force on the distal end of the trip lever 36 to pivot the trip lever 36 to an "off" position, thereby opening electrical contacts in the power supply circuit and interrupting the supply of electrical energy to the heater. As is known in the art, this allows the heater to be turned off when the liquid in the liquid heating vessel 4 reaches a boil.

[0103] Figure 3 shows a cross-sectional front view of the control unit 16 of Figures 2a and 2b as mounted on the underside of the heat spreader plate 18b of the electric heater 18. The electric heater 18 further comprises an electric heating element 18a surrounding the periphery of the control unit 16, also mounted on the underside of the heat spreader plate 18b.

[0104] 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 neutral ring 28c are concentrically arranged around the central ground pin 28a. The base electrical connector (not shown in FIG. 3) includes a central opening for receiving the ground pin 28a and coaxial annular openings for receiving both the live ring 28b and the neutral ring 28c.

[0105] When connector parts 14 and 28 are mated, the electrical contacts housed within the coaxial openings contact live ring 28b and neutral ring 28c, respectively, for connection with the live and neutral poles of the power supply circuit. The electrical contact housed in the central opening contacts ground pin 28a.

[0106] The control unit 16 includes a first push rod 40a and a second push rod 40b. The first push rod 40a is disposed directly below the first actuator 30a, and the second push rod 40b is disposed directly below the second actuator 30b. The first push rod 40a and the second push rod 40b are configured to move vertically downward when the first actuator 30a and the second actuator 30b, respectively, are actuated.

[0107] FIG. 4 shows a partial perspective view of the control unit of FIGS. 2a and 2b, with some elements of the control unit 16 removed for ease of illustration.

[0108] The control unit 16 includes a live-side leaf spring 42 and a neutral-side leaf spring 44. The live-side leaf spring 42 has a fixed end 42a attached to and electrically connected to the live ring 28b. The live-side leaf spring 42 also has a movable portion 42b extending from a deflection point of the live-side leaf spring 42. The first push rod 40a is positioned to contact the distal end of the movable portion 42b of the live-side leaf spring 42.

[0109] The neutral-side leaf spring 44 has a fixed end 44a attached to and electrically connected to the neutral ring 28c and a movable portion 44b extending from a flexure point 45 (shown in FIGS. 5a and 5b) of the neutral-side leaf spring 44. The second push rod 40b is positioned to contact the distal end of the movable portion 44b of the neutral-side leaf spring 44.

[0110] The live and neutral leaf springs 42 and 44 are directly secured to the live and neutral rings 28b and 28c, respectively, and have openings in them to receive corresponding tabs projecting from the live and neutral rings 28b and 28c, thereby facilitating this direct securing.

[0111] The control unit 16 further includes a live side fixing tab 29a positioned above the movable portion 42b of the live side leaf spring 42 and a neutral side fixing tab 29b positioned above the movable portion 44b of the neutral side leaf spring 44.

[0112] The leaf springs 42 and 44 are disposed below the push rods 40a and 40b, respectively. When the push rods 40a and 40b move downward due to the actuation of the actuators 30a and 30b, the movable portions 42b and 44b of the leaf springs 42 and 44 are deflected downward by the push rods 40a and 40b. The trip lever 36 of the control unit 16 includes a force transmission pad 48b disposed below the movable portion 44b of the neutral-side leaf spring 44. The force transmission pad 48b transmits the downward movement of the push rod 40b to the trip lever 36 via the movable portion 44b of the leaf spring 44, moving the trip lever 36 to the "off" position. This movement of the trip lever 36 subsequently holds the contacts in the open position via a stopper 48a. The force transmission pad 48b is disposed directly below the push rod 40b. The trip lever 36 also includes a force transmission pad (not shown in FIG. 4) disposed below the movable portion 42b of the live-side leaf spring 42 for the same purpose.

[0113] As will be described in more detail below, the trip lever 36 also includes return stops 49a and 49b disposed above the movable portions 42b and 44b of the live-side leaf spring 42 and the neutral-side leaf spring 44, respectively, for limiting the upward movement of the movable portions 42b and 44b. The return stops 49a and 49b are configured to contact and depress the movable portions 42b and 44b of the leaf springs 42 and 44 when the trip lever 36 is pivoted to the “off” position, for example, by manual operation of the trip lever 36 or as a result of steam being detected and the third thermal actuator 30c being activated.

[0114] Figures 5a, 5b, and 5c show cross-sectional front views of the neutral-side leaf spring 44 of the control unit 16 of Figures 2a and 2b. In Figure 5a, the leaf spring 44 is in a closed position. Figure 5b shows the leaf spring 44 after the push rod 40b has moved downward. Figure 5c shows the leaf spring 44 in an open position.

[0115] The leaf spring 44 includes a movable electrical contact 50 attached to the movable portion 44b of the leaf spring 44 between the fixed end 44a and the portion of the leaf spring 44 that is configured to come into contact with the push rod 40b. As shown in Figure 5a, in the closed position, the movable electrical contact 50 contacts the fixed electrical contact 52 of the neutral side fixed tab 29b.

[0116] The leaf spring 44 is biased to a closed position (shown in FIG. 5 a ), i.e., the movable electrical contact 50 is biased by the leaf spring 44 into contact with the fixed electrical contact 52 .

[0117] As described above, when the second thermal actuator 30b is actuated, the push rod 40b moves vertically downward, thereby deflecting the movable portion 44b downward relative to the fixed end 44a and bending the leaf spring 44. As can be seen in Figure 5b, the force applied by the push rod 40b to the movable portion 44b causes the movable portion 44b of the leaf spring 44 to continue to deflect downward even after the push rod 40b reaches the end of its range of movement. As shown in Figure 5b, the deflection of the movable portion 44b is stopped by the force transfer pad 48b of the trip lever 36.

[0118] This deflection separates the movable electrical contact 50 from the fixed electrical contact 52. Thus, actuation of the actuator 30b moves the leaf spring 44 to the open position (shown in FIGS. 5b and 5c). The leaf spring 44 depresses the force transfer pad 48b, which pivots the trip lever 36 to the "off" position. FIG. 5b shows the positions of the force transfer pad 48b and stop 49b of the trip lever 36 before the trip lever moves to the "off" position. FIG. 5c shows the positions of the force transfer pad 48b and stop 49b with the trip lever 36 in the "off" position.

[0119] The restoring force of the leaf spring 44 then causes the movable portion 44b of the leaf spring 44 to move 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 again contact the end of the push rod 40b and the return stop 49b of the trip lever 36 (now in the "off" position). In this manner, the return stop 49b and the push rod 40b hold the leaf spring 44 in the open position, in which the movable electrical contact 50 is separated from the fixed electrical contact 52, as shown in FIG. 5c.

[0120] The leaf spring 44 can return to the closed position only after the thermal actuator 30b has cooled sufficiently to reset (allowing the push rod 40b to move upward) and 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 (shown in FIG. 5a). The force required to pivot the trip lever 36 is greater than the upward force that the movable portion 44b of the leaf spring 44 exerts on the return stop 49b due to the restoring force of the leaf spring 44.

[0121] In addition to being movable to the open position by push rod 40b after activation of thermal actuator 30b, leaf spring 44 is also movable to the open position by manual operation of trip lever 36 or as a result of the detection of steam causing a third thermal actuator 30c to actuate and pivot trip lever 36. This is shown in Figures 6a and 6b.

[0122] Figure 6a shows the same view of the neutral side leaf spring 44 as shown in Figure 5a, with the leaf spring 44 in the closed position. Figure 6b shows the leaf spring 44 after the trip lever 36 has pivoted to the "off" position. As mentioned above, the trip lever 36 includes a return stop 49b and a force transfer pad 48b, both of which are shown in Figures 6a and 6b.

[0123] As can be seen in Figure 6b, as the push rod 40b moves vertically downward, instead of contacting and moving the leaf spring 44, the trip lever 36 pivots, causing the return stop 49b of the trip lever 36 to move downward and contact the distal end of the movable portion 44b of the leaf spring 44, deflecting the movable portion 44b against the fixed end 44a and separating the movable electrical contact 50 from the fixed electrical contact 52. The return stop 49b of the trip lever 36 holds the leaf spring 44 in this open position. To allow the leaf spring 44 to return to the closed position (shown in 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.

[0124] The vertical movement of the push rod 40b is substantially equal to the vertical distance traveled by the thermal actuator 30b upon actuation. At the point where the push rod 40b contacts the leaf spring 44 (i.e., the "contact point"), the vertical movement of the movable portion 44b of the leaf spring 44 is substantially equal to the distance traveled by the flexible portion of the thermal actuator 30b upon actuation. The vertical movement of the movable electrical contact 50 depends on the relative distances between the flexible point 45, the movable electrical contact 50, and the push rod 40b. Because the push rod 40b is positioned to contact the leaf spring 44 at a point distal to 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. Thus, while the leaf spring of the present invention can be shorter than conventional leaf springs, existing thermal actuators can still be used in combination with embodiments of the present invention, and those thermal actuators do not need to be modified to achieve the shorter travel distance.

[0125] Because the leaf spring 44 is thinner than conventional leaf springs, it may also be less stiff. This means that the leaf spring 44 may move excessively after the thermal actuator 30b is activated. This excessive movement may cause stress in the leaf spring to exceed the yield stress of the leaf spring material. The force transfer pad 48b prevents the leaf spring 44 from moving excessively due to the inertia of the trip lever 36 when the thermal actuator 30b deflects the leaf spring 44 via the push rod 40b. The thermal actuator 30b may impose a high dynamic mechanical load on the leaf spring 44. However, by preventing the leaf spring 44 from moving excessively, the stress on the leaf spring 44 can be limited. As described above, if the force transfer pad 48b is disposed on the trip lever 36, the collision between the leaf spring 44 and the force transfer pad 48b also pivots the trip lever 36 to the OFF position, thereby resetting the trip lever 36.

[0126] The leaf spring 44 has a bend 54 located adjacent to the flexure point 45 between the fixed end 44a and the movable portion 44b of the leaf spring 44. The bend 54 is substantially sinusoidal in cross section, extending from the plane of the leaf spring 44 in an arc and returning to substantially the same plane (i.e., approximately halfway through a sine wave). The curved cross section of the leaf spring 44 includes fillets on either side of the arc of the bend 54, thereby rounding the intersection of the sinusoidal bend 54 and the flat leaf spring 44 geometry.

[0127] Figure 7 is a graph showing the von Mises stress generated in straight (i.e., conventional) leaf springs of different lengths and thicknesses of 0.15 mm when a 0.9 mm deflection, which corresponds to the amount of deflection caused by a push rod, is applied to each leaf spring.

[0128] From the figure, it can be seen that for a conventional leaf spring with a yield stress of 540 MPa, the minimum length at which the yield stress can be not exceeded when the leaf spring is deflected by 0.9 mm is 9 mm.

[0129] 7 also shows points 200 representing the von Mises stress for a 0.15 mm thick leaf spring with a bend in accordance with the present invention. As can be seen, incorporating a bend into the leaf spring geometry allows for the use of a leaf spring with an 8 mm footprint length without exceeding the yield stress of the material. This is because the bend helps increase the effective bending length of the leaf spring, thereby reducing the maximum stress generated without increasing the footprint length of the leaf spring.

[0130] The leaf spring 44 shown in Figures 4, 5, and 6 is approximately 22 mm long, 3.5 mm wide, and 0.15 mm thick. The material of the leaf spring 44 is C7025, a hardened copper alloy with a yield stress of approximately 540 MPa. The radius of curvature of the arc of the bent portion 54 is 0.8 mm, and the radius of curvature of the fillets on both sides of the bent portion 54 is 0.65 mm.

[0131] The leaf spring 44 is shaped to apply a 20 gram preload against the fixed electrical contact 52. When the thermal actuator 30b is actuated, the movable electrical contact 50 is separated from the fixed electrical contact 52 by 0.9 mm, breaking the electrical connection between the contacts 50 and 52.

[0132] Figure 8 shows a cross-sectional front view of a control unit 116 according to another embodiment of the present invention. The control unit 16 shown in Figures 2-6 is an "integrated" control unit 16, which itself includes a mechanism for shutting off the power circuit in an overheating condition (i.e., thermal actuators 30a and 30b) and a mechanism for shutting off the power circuit when a certain liquid temperature condition (e.g., boiling) is reached (i.e., thermal actuator 30c).

[0133] However, the control unit 116 of Figure 8 only includes an "overheat" protection mechanism. Whereas in the integrated control unit 16 of Figures 2-5, the thermal actuators 30a and 30b that detect "overheat" and the thermal actuator 30c that detects "liquid temperature condition" are configured to open the same sets of electrical contacts 50 and 52, the control unit 116 of Figure 8 is suitable for use in an appliance in which the "overheat" detection mechanism and the "liquid temperature condition" mechanism are configured to open different sets of electrical contacts.

[0134] Figure 10 shows an example of such an appliance 102 with the control unit 116 of Figure 8. The appliance 102 is a "split switch" type appliance, with a separate electrical switching arrangement 103 for interrupting the power circuit when a certain liquid temperature condition is reached. The electrical switching arrangement 103 is located separately from the control unit 116, which includes an "overheat" detection mechanism.

[0135] The separate electrical switching arrangement 103 comprises a vapor-sensitive bimetallic element (not shown) located on top of the handle 108. The electrical switching arrangement 103 is electrically connected to the control unit 116 by an electrical cable 105 that extends through the handle 108 of the instrument 102. The separate electrical switching arrangement 103, the electric heater (not shown), and the control unit 116 are electrically connected in series.

[0136] The control unit 116 does not have a trip lever, and therefore the control unit 116 of FIG. 8 has, instead of force transmission pads 48a and 48b, stoppers 148a and 148b that prevent overshoot deflection of the live side leaf spring 142 and the neutral side leaf spring 144, respectively, disposed on the molded control body portion 126 of the control unit 116. The other components of the control unit 116 are essentially the same as those of the control unit 16 of FIGS. 2 to 6.

[0137] 9a and 9b show front views of components of the control unit 116 of FIG.

[0138] Figure 9a shows the neutral leaf spring 144 in the closed position, with the movable electrical contact 150 in contact with the fixed electrical contact 152. Figure 9b shows the leaf spring 144 in the open position after the thermal actuator has moved the push rod 140b downward toward the stopper 148b. In the open position, the movable electrical contact 150 is separated from the fixed electrical contact 152 by 0.9 mm, breaking the electrical connection between the contacts 150 and 152.

[0139] Figure 11a shows a front view and an enlarged cross-sectional front view of the leaf spring 144 shown in Figures 9a and 9b in a mounting configuration for the movable electrical contact 150. The leaf spring 144 includes a bent portion 154 as previously described.

[0140] The leaf spring 144 defines a stamped opening 156 for receiving the movable electrical contact 150. The movable electrical contact 150 is positioned within the opening 156 by a press fit. Because the opening 156 is formed by stamping in the leaf spring 144, a peripheral edge 156a of the opening 156 is bent downward from the plane of the leaf spring 144. This means that the leaf spring 144 has a large surface area that contacts the movable electrical contact 150 when the contact 150 is positioned within the opening 156. This means that the leaf spring 144 is thinner than conventional leaf springs, yet the contact surface area between the leaf spring 144 and the movable electrical contact 150 can be maintained the same, meaning that the flow of electrical current between the leaf spring 144 and the movable electrical contact 150 is not substantially affected by the thinning of the leaf spring.

[0141] Additionally, this process also creates 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 the reduced stiffness of the leaf spring 144 due to its relatively thin thickness compared to known leaf springs and helps ensure a strong cold bond can be formed between the movable electrical contact 150 and the leaf spring 144. As a result, more of the force imparted by the leaf spring 144 is transferred to the electrical contacts 150 and 152, allowing them to close.

[0142] It will be appreciated that the mounting arrangement for the movable electrical contact 150 shown in FIG. 11a and described above is equally applicable to either of the leaf springs 42 and 44 of the embodiments shown in FIGS.

[0143] In accordance with another aspect of the invention, the above mounting configuration can also be applied to leaf springs that do not include bends. Figure 11b shows one example of such a configuration, in which a substantially planar leaf spring 644 defines an opening 656 in which an electrical contact 650 is disposed. A peripheral edge 656a of opening 656 bends downwardly out of the plane of leaf spring 644.

[0144] While the embodiments described above and illustrated in Figures 2-11a feature leaf springs with bends that correspond to approximately half a sine wave, many alternative bend geometries can be used to achieve the same effect of increasing the effective bending length of the leaf spring. Some examples of alternative geometries are shown in Figures 12a, 12b, 12c, and 12d.

[0145] FIG. 12a shows an alternative leaf spring 244 with an S-shaped or sinusoidal bend 254, ie, a bend that corresponds to one period of a sine wave.

[0146] 12b shows an alternative leaf spring 344 with an inverted "V" shaped bend 354. The bend 354 projects diagonally out of the plane of the leaf spring 344 in a straight line to an apex, then symmetrically returns to the plane of the leaf spring 344.

[0147] Figure 12c shows an alternative leaf spring 444 with a generally "M" shaped bend 454. This "M" shaped bend is similar to the inverted "V" shaped bend 354 of Figure 12b, except that the peak is inverted on itself, thereby forming two peaks separated by a valley.

[0148] 12d shows an alternative leaf spring 544 with a folded bend 554. The bend 554 curves upward from the plane of the leaf spring 544 at an angle of approximately 180°, then extends distally again beyond the crest of the bend and back into the plane of the leaf spring 544. Thus, the folded bend 554 substantially resembles the shape of a breaking wave.

[0149] Those skilled in the art will appreciate that many additional alternative bend shapes may be suitable in addition to those shown and described herein.

Claims

1. 1. A control unit for controlling a power supply circuit to an electric heater in a liquid heating appliance, comprising: a leaf spring having a fixed end and a movable portion that is movable relative to the fixed end between a closed position and an open position; a movable electrical contact attached to the movable portion of the leaf spring for connecting to a corresponding fixed electrical contact in the power supply circuit when the leaf spring is in the closed position; a thermal actuator that operates 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 supply circuit; The control unit, wherein the leaf spring has a bent portion between the fixed end and the movable portion.

2. 2. The control unit of claim 1, further comprising a cordless electrical adapter component for mating with a corresponding base-side electrical connector component to receive power, the cordless electrical adapter component having a mating conductor for connecting to a live pole or a neutral pole of the corresponding base-side electrical connector component, the fixed end of the leaf spring being directly fixed to the mating conductor of the cordless electrical adapter component.

3. 3. The control unit of claim 2, wherein said cordless electrical adapter component and said corresponding base electrical connector component are of a type that allows mating regardless of relative angular orientation.

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

5. 10. A control unit according to any one of the preceding claims, wherein the bend is continuously curved.

6. The control unit of claim 5 , wherein the bend includes an arcuate portion disposed between two fillets.

7. 10. A control unit according to any one of the preceding claims, wherein the bends project out of the plane of the leaf spring and return to substantially the same plane.

8. 10. A control unit according to any one of the preceding claims, wherein the thermal actuator is configured to press a contact point on the movable part of the leaf spring to move the movable part from the closed position to the open position, and the movable electrical contact is attached to the movable part of the leaf spring between the bent part and the contact point.

9. 10. A control unit according to any one of the preceding claims, wherein the leaf spring defines an opening in which the movable electrical contact is located, the leaf spring having a protrusion that protrudes out of the plane of the leaf spring around a periphery of the opening.

10. 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. 11. The control unit of claim 10, wherein the leaf spring has a thickness of about 0.15 mm.

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

13. 13. The control unit of claim 12, further comprising a trip lever for enabling a user to manually move the movable portion of the leaf spring from the closed position to the open position and / or from the open position to the closed position, the stopper being located on the trip lever.

14. a liquid heating vessel; an electric heater for heating the liquid contained in the liquid heating container, the electric heater being powered by a power supply circuit; A liquid heating appliance comprising a control unit according to any one of the preceding claims.

15. further comprising an electrical switching arrangement physically separate from but electrically connected to said control unit; the electrical switching arrangement comprises a liquid temperature condition thermal actuator configured to open a switch to cut off power to the heater when a predetermined temperature corresponding to a desired state of the liquid in the liquid heating space is sensed; 15. The liquid heating appliance of claim 14, wherein the thermal actuator of the control unit includes an overheating thermal actuator, and the predetermined temperature at which the overheating thermal actuator is configured to operate corresponds to the temperature within the liquid heating appliance when it is in an overheated state.

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

17. the thermal actuator of the control unit includes an overheating thermal actuator, and the predetermined temperature at which the overheating thermal actuator is configured to operate corresponds to a temperature within the liquid heating appliance during an overheating condition; 14. A control unit as described in any one of claims 1 to 13, further comprising a liquid temperature condition thermal actuator configured to separate the movable electrical contact from the fixed electrical contact to interrupt the power supply circuit when a predetermined temperature corresponding to a desired state of the liquid in the liquid heating space is detected.

18. 18. The control unit of claim 17, further comprising a trip lever movable to act on the movable portion of the leaf spring to move it from the closed position to the open position, wherein the liquid temperature condition thermal actuator is configured to move the trip lever at a predetermined temperature, thereby moving 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 supply circuit.

19. a liquid heating vessel; an electric heater for heating the liquid contained in the liquid heating container, the electric heater being powered by a power supply circuit; A liquid heating appliance comprising: a control unit according to claim 17 or 18.

20. a proximal end and a distal portion movable relative to the proximal end; an electrical contact attached to the distal portion for connecting to a corresponding electrical contact, A leaf spring having a bend between the proximal end and the distal portion.

21. 21. The leaf spring of claim 20, wherein the bend is continuously curved.

22. 22. The leaf spring of claim 21, wherein the bend includes an arcuate portion disposed between two fillets.

23. 23. A leaf spring as claimed in any one of claims 20 to 22, wherein the bends project out of the plane of the leaf spring and return to substantially the same plane.

24. 24. The leaf spring of any one of claims 20 to 23, wherein the leaf spring defines an opening in which the electrical contact of the leaf spring is located, the leaf spring having a protrusion that protrudes from the plane of the leaf spring around a periphery of the opening.

25. 25. The leaf spring according to any one of claims 20 to 24, having a thickness of 0.05 mm to 0.18 mm.

26. 26. The leaf spring of any one of claims 20 to 25, having a thickness of about 0.15 mm.

27. A method for manufacturing a leaf spring having a proximal end and a distal portion movable relative to the proximal end, comprising: forming a bend between the proximal end and the distal portion of the leaf spring; and attaching an electrical contact to the distal portion of the leaf spring for connection to a corresponding electrical contact.

28. forming an opening through the distal portion of the leaf spring; and attaching the electrical contact to the distal portion of the leaf spring by inserting the electrical contact into the opening.

29. 30. The method of claim 28, wherein forming the opening includes forming a protrusion that protrudes out of the plane of the leaf spring around a periphery of the opening.

30. 1. A control unit for controlling a power supply circuit to an electric heater in a liquid heating appliance, comprising: a leaf spring having a fixed end and a movable portion that is movable relative to the fixed end between a closed position and an open position; a movable electrical contact attached to the movable portion of the leaf spring for connecting to a corresponding fixed electrical contact in the power supply circuit when the leaf spring is in the closed position; a thermal actuator that operates 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 supply circuit; The control unit, wherein the leaf spring defines an opening in which the movable electrical contact is disposed, the leaf spring having a protrusion that protrudes from a plane of the leaf spring around a periphery of the opening.

31. A 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 about 0.15 mm.

32. 32. A control unit according to claim 30 or claim 31, wherein the movable electrical contact is located in the opening by an interference fit.

33. 33. A control unit according to any one of claims 30 to 32, wherein the leaf spring is a unitary member including the protrusion.

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

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

36. 36. The control unit of claim 35, further comprising a trip lever for enabling a user to manually move the movable portion of the leaf spring from the closed position to the open position and / or from the open position to the closed position, the stopper being located on the trip lever.

37. 37. The control unit of claim 30, further comprising a cordless electrical adapter part for mating with a corresponding base electrical connector part to receive power, the cordless electrical adapter part having mating conductors for connecting to live or neutral poles of the corresponding base electrical connector part, the fixed end of the leaf spring being directly fixed to the mating conductors of the cordless electrical adapter part.

38. 38. The control unit of claim 37, wherein the cordless electrical adapter component and the corresponding base electrical connector component are of a type that are mateable regardless of relative angular orientation.

39. a liquid heating vessel; an electric heater for heating the liquid contained in the liquid heating container, the electric heater being powered by a power supply circuit; A liquid heating appliance comprising a control unit according to any one of claims 30 to 38.

40. further comprising an electrical switching arrangement physically separate from but electrically connected to said control unit; the electrical switching arrangement comprises a liquid temperature condition thermal actuator configured to open a switch to cut off power to the heater when a predetermined temperature corresponding to a desired state of the liquid in the liquid heating space is sensed; 40. A liquid heating appliance as described in claim 39, wherein the thermal actuator of the control unit includes an overheating thermal actuator, and the predetermined temperature at which the overheating thermal actuator is configured to operate corresponds to the temperature within the liquid heating appliance when in an overheated state.

41. 41. A liquid heating appliance according to claim 40, wherein the electrical switching arrangement is located in a different part of the liquid heating appliance than the control unit.

42. the thermal actuator of the control unit includes an overheating thermal actuator, and the predetermined temperature at which the overheating thermal actuator is configured to operate corresponds to a temperature within the liquid heating appliance during an overheating condition; 39. A control unit as described in any one of claims 30 to 38, further comprising a liquid temperature condition thermal actuator configured to separate the movable electrical contact from the fixed electrical contact to interrupt the power supply circuit when a predetermined temperature corresponding to a desired state of the liquid in the liquid heating space is detected.

43. 43. The control unit of claim 42, further comprising a trip lever movable to act on the movable portion of the leaf spring to move it from the closed position to the open position, wherein the liquid temperature condition thermal actuator is configured to move the trip lever at a predetermined temperature, thereby moving 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 and the power supply circuit is interrupted.

44. a liquid heating vessel; an electric heater for heating the liquid contained in the liquid heating container, the electric heater being powered by a power supply circuit; A liquid heating appliance comprising a control unit according to claim 42 or claim 43.

45. a proximal end and a distal portion movable relative to the proximal end; an electrical contact attached to the distal portion for connecting to a corresponding electrical contact, The leaf spring defines an opening in which the electrical contact of the leaf spring is located, the leaf spring having a protrusion protruding from a plane of the leaf spring around a periphery of the opening and surrounding the electrical contact.

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

47. 47. The leaf spring of claim 46, having a thickness of about 0.15 mm.

48. 48. A leaf spring according to any one of claims 45 to 47, wherein the electrical contacts of the leaf spring are disposed in the openings by an interference fit.

49. 49. A leaf spring as claimed in any one of claims 45 to 48, which is a unitary member including the protrusion.

50. A method for manufacturing a leaf spring having a proximal end and a distal portion movable relative to the proximal end, comprising: forming an opening through the distal portion of the leaf spring; and attaching an electrical contact to the distal portion of the leaf spring by inserting the electrical contact into the opening; The method wherein forming the opening includes forming a protrusion that protrudes from the plane of the leaf spring around a periphery of the opening.

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