Liquid heating appliance and heating device for liquid heating appliance

Abstract

A liquid heating appliance (2) and a heating device (15) for a liquid heating appliance (2) are provided. The heating device (15) comprises a substrate (18c) on which a resistive heater trace (18a) extending along a serpentine path is deposited. A bimetallic element (30a, 30b) extends over a portion (21a, 21b) of the heater trace and is arranged to operate at a predetermined temperature to open the switch (50), thereby interrupting the supply of power to the heater trace (18a). At least when the temperature of the bimetallic element (30a, 30b) is below a predetermined temperature, the contact portion of the bimetallic element (30a, 30b) is arranged in thermally conductive contact with the substrate (18c), but any component of the bimetallic element (30a, 30b) is arranged not in physical contact with the heater trace (18a).

Description

Technical Field

[0001] This utility model relates to a heating device for a liquid heater and an appliance including such a heating device. Background Technology

[0002] Liquid heating appliances, such as kettles, are common in many homes. A traditional kettle includes a power source arranged to supply electricity to an electric heater, which in turn heats the contents of the liquid container. The power source typically includes a switch that can cut off power to the electric heater in case of overheating, such as when the appliance has boiled dry or is turned on without any liquid inside. This switch is usually operated by a thermally responsive element, such as a bimetallic element, arranged to contact the electric heater.

[0003] Some existing liquid heating appliances include electric heaters that incorporate resistance heating traces. These heaters can reach very high temperatures and achieve boiling times much faster compared to other electric heaters, such as sheathed heating elements. However, the high operating temperatures of these heaters mean that the thermal response elements used to provide overheat protection may themselves need to operate at higher temperatures.

[0004] Designing thermally responsive components that can operate reliably at such high temperatures can increase the complexity of the design, testing, and manufacturing processes, potentially causing delays and increasing associated costs. Utility Model Content

[0005] This invention aims to solve or at least alleviate at least one of the above-mentioned problems.

[0006] From a first perspective, the present invention provides a heating device for a liquid heating appliance, the heating device comprising:

[0007] substrate;

[0008] The resistance heater track is deposited on the substrate;

[0009] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position; and

[0010] A thermal response element, arranged to operate at a predetermined temperature, to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0011] in:

[0012] The thermal response element extends at least partially over a portion of the resistance heater trace; and

[0013] At least when the temperature of the thermal response element is below the predetermined temperature:

[0014] Any component of the thermal response element is arranged so as not to be in direct physical contact with the traces of the resistance heater; and

[0015] The contact portion of the thermal response element is arranged to make thermally conductive contact with the substrate.

[0016] From a second perspective, this utility model provides a liquid heating appliance, comprising:

[0017] A liquid heating container for receiving a liquid to be heated; and

[0018] A heating device, arranged to heat the contents of a liquid heating container, includes:

[0019] substrate;

[0020] Resistance heater traces are deposited on a substrate;

[0021] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position;

[0022] A thermal response element, arranged to operate at a predetermined temperature, to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0023] in:

[0024] The thermal response element extends at least partially over a portion of the resistance heater trace; and

[0025] At least when the temperature of the thermal response element is below the predetermined temperature:

[0026] Any component of the thermal response element is arranged so as not to be in direct physical contact with the traces of the resistance heater; and

[0027] The contact portion of the thermal response element is arranged to make thermally conductive contact with the substrate.

[0028] The applicant has recognized that arranging the thermal response element in such a way that it is in thermally conductive contact with the substrate, but not in direct physical contact with the resistance heater traces, can advantageously reduce the rate of heat transfer from the resistance heater traces to the thermal response element. This means that when the temperature of the resistance heater traces becomes high enough to require overheat cutoff, the thermal response element is at a lower temperature. As a result, thermal response elements with lower operating temperatures can be used without increasing the risk of the thermal response element operating at excessively low temperatures (e.g., during normal operation of liquid heating appliances). This can save cost and time during the design and manufacturing process of the thermal response element.

[0029] Additionally, arranging the thermal response element such that it does not come into contact with the resistance heater trace at least when its temperature is below a predetermined temperature eliminates the need for electrical insulation between the thermal response element and the resistance heater trace. This reduces the cost of the heating device and, consequently, the cost of any appliance incorporating it.

[0030] Since the thermal response element extends at least partially over a portion of the resistance heater trace, it should be understood that the thermal response element can receive thermal energy from said portion of the resistance heater trace via thermal radiation, which can help ensure reliable operation of the thermal response element. By "extends over," it should be understood that when the heating device is viewed in a plan view along an axis perpendicular to the substrate, at least a portion of the coverage area / profile of the thermal response element covers a portion of the resistance heater trace over which the thermal response element extends. The coverage area / profile is the projection of the thermal response element in the plan view. The coverage area / profile may be defined by the projection of the outer edge of the thermal response element and the outer edges of one or more cutouts within the thermal response element.

[0031] Without direct physical contact with the resistance heater traces, the thermal response element may not exert any force on the resistance heater traces, either directly or indirectly. The thermal response element may lack any electrical insulation.

[0032] Resistance heater traces can be deposited on the lower surface of a substrate. In some embodiments, when the heating device is arranged to heat the contents of a liquid heating container, the substrate is arranged below the liquid heating container. It should be understood that "below" refers to the direction in which gravity acts on the liquid within the liquid heating container during operation of the appliance. In such embodiments, the thermally responsive element can be located below the resistance heater traces.

[0033] In some embodiments, at least when the temperature of the thermal response element is below a predetermined temperature, the contact portion of the thermal resistance element is arranged to make thermally conductive contact with the lower surface of the substrate.

[0034] In some embodiments, the heating device includes a control unit. The control unit may include a switch for a power supply circuit. In some embodiments, the control unit includes a mounting body for mounting the control unit to a substrate.

[0035] The control unit may include an electrical adapter component (sometimes called an electrical adapter) arranged to connect to a corresponding electrical connector component (sometimes called an electrical connector) to receive a power supply, such as mains power. The electrical adapter component may be a cordless electrical adapter component arranged to mate with a corresponding base electrical connector (e.g., a base electrical connector for a power base on which a liquid heating appliance is positioned). The cordless electrical adapter component and the corresponding base electrical connector component may be of the type that mate regardless of their relative angular orientation, i.e., a "360°" connector component and adapter component. The electrical adapter component and the corresponding electrical connector component may include any suitable number of poles, such as 3 poles or 5 poles.

[0036] In some embodiments, the thermal response element comprises a bimetallic element, such as a snap-action bimetallic element. In some embodiments, the heating device includes a second thermal response element arranged to operate at a corresponding predetermined temperature. It should be understood that any or all of the characteristics of the (first) thermal response element discussed above or below may be equally applicable to the second thermal response element where appropriate. In the event that the first thermal response element fails to operate, the second thermal response element may act as an automatic fail-safe device.

[0037] The thermal response element can be mounted on a mounting body of the control unit. In some embodiments, the thermal response element includes a support portion and an actuator portion. The support portion of the thermal response element can be mounted on the mounting body of the control unit. At least when the temperature of the thermal response element is below a predetermined temperature, the support portion can press against the surface of the mounting body.

[0038] The actuator portion can move relative to the support portion. In some embodiments, when the thermal response element operates at a predetermined temperature, the actuator portion of the thermal response element is arranged to move relative to the support portion to move the switch to the off position.

[0039] The actuator portion of a thermally responsive element may include a contact portion of the thermally responsive element. In some embodiments, the support portion of the thermally responsive element includes the contact portion. In some such embodiments, a particular contact portion may not be directly supported by the mounting body, but the contact portion may extend directly from a portion of the thermally responsive element that is directly supported by the mounting body. Arranging the support portion of the thermally responsive element in contact with the substrate can help ensure that the actuator portion moves more reliably to operate the switch. For example, arranging the support portion in contact with the substrate can help set the distance between the actuator portion and the push rod, which is arranged to act on the push rod when the thermally responsive element operates at a predetermined temperature to disconnect the switch.

[0040] In some embodiments, the contact portion of the thermal response element includes a protrusion of the thermal response element. The protrusion may extend from the support portion and / or actuator portion of the thermal response element. The contact portion may include a portion of an edge of the thermal response element, such as a corner. The edge of the thermal response element may be concave, at least when the temperature of the thermal response element is below a predetermined temperature. The concave edge may include two vertices. The contact portion may include one or both vertices of the concave edge.

[0041] In some embodiments, the thermally responsive element includes a ring that defines an internal cutout. In some embodiments, the ring is substantially circular. However, the ring can include any suitable shape (e.g., rectangular or elliptical). The ring can include a support portion and an actuator portion. The support portion and the actuator portion can be separated by the internal cutout. In some embodiments, the thermally responsive element includes a central tongue that extends from the support portion toward the actuator portion into the internal cutout.

[0042] A thermally responsive element may include a proximal edge and a distal edge. In some embodiments, the thermally responsive element includes a proximal end and a distal end. The proximal end may be defined (along the longitudinal axis of the thermally responsive element) between the proximal edge of the thermally responsive element and the midpoint of the thermally responsive element. The distal end may be defined (along the longitudinal axis of the thermally responsive element) between the distal edge of the thermally responsive element and the midpoint of the thermally responsive element.

[0043] At least when the temperature of the thermal response element is below a predetermined temperature, the thermal response element may include a curved portion between its proximal and distal edges. At least when the temperature of the thermal response element is below the predetermined temperature, the thermal response element may be arranged such that a gap is defined between the curved portion and the substrate. This gap may extend from an edge of the thermal response element (e.g., a side edge extending between the proximal and distal edges). It should be understood that this gap allows the thermal response element to extend over a portion of the resistive heater trace without contacting that portion of the resistive heater trace, because the path of the resistive heater trace can enter and exit the coverage area of ​​the thermal response element through this gap.

[0044] In some embodiments, the thermal response element includes two parallel sides. The parallel sides may extend from the proximal edge to the distal edge of the thermal response element. The thermal response element may be substantially rectangular (in a plan view). In some embodiments, a gap is formed between one or both of the parallel sides and the substrate (and therefore any resistance heater traces on the substrate) at least when the temperature of the thermal response element is below a predetermined temperature.

[0045] In some embodiments, the centroid of the thermal response element is located within the proximal end of the thermal response element, rather than within the distal end. In other words, the centroid of the thermal response element may be closer to the proximal edge than the distal edge. In some embodiments, the thermal response element includes a cutout located within the distal end of the thermal response element rather than within the proximal end, such that the centroid of the thermal response element is located within the proximal end of the thermal response element rather than within the distal end.

[0046] The volume of the proximal end can be larger than that of the distal end, so that the centroid of the thermal response element is located within the proximal end of the thermal response element, rather than within the distal end of the thermal response element.

[0047] The thickness of the proximal end (i.e., the dimension of the thermal response element in the direction in which it operates to move the switch to the off position) can be greater than the thickness of the distal end, such that the centroid of the thermal response element is closer to the proximal edge of the thermal response element than to the distal edge. This may result in the centroid being located within the proximal end rather than the distal end.

[0048] In some embodiments, the proximal end of the thermal response element includes a support portion of the thermal response element. In some embodiments, the distal end of the thermal response element includes an actuator portion of the thermal response element.

[0049] The proximal end of the thermal response element may include a contact portion. It should be understood that, due to heat conduction from the substrate through the contact portion, the contact portion of the thermal response element can reach a higher temperature than the rest of the thermal response element. Because the proximal end of the thermal response element (i.e., the end closer to the center of mass of the thermal response element compared to the rest of the thermal response element) is heated, the thermal response element can operate with greater force compared to whether the distal end of the thermal response element (i.e., the end farther from the center of mass of the thermal response element compared to the rest of the thermal response element) is heated. This can help ensure that the thermal response element reliably disconnects at a predetermined temperature.

[0050] In some embodiments, any component of the thermal response element is arranged not to be in direct physical contact with the resistance heater traces (even when the temperature of the thermal response element is above a predetermined temperature). This means that in some embodiments, the thermal response element may not require any electrical insulation, which can reduce manufacturing complexity and / or cost.

[0051] After the thermal response element operates at a predetermined temperature, the contact portion can remain in thermally conductive contact with the substrate. However, in some embodiments, the thermal response element is arranged such that when the thermal response element operates at the predetermined temperature, at least a portion of the contact portion of the thermal response element disengages from the thermally conductive contact with the substrate.

[0052] In some embodiments, at or above a predetermined temperature, another portion of the thermal response element may (e.g., additionally) be arranged in thermally conductive contact with the substrate. In some embodiments, the thermal response element is configured such that at or above a predetermined temperature, any component of the thermal response element is arranged not in thermally conductive contact with the substrate.

[0053] The thermal response element can be arranged to reset at a second predetermined temperature below a (first) predetermined temperature, which is the temperature at which the thermal response element operates to disconnect the switch. It should be understood that arranging the thermal response element such that when the thermal response element operates at the predetermined temperature, the contact portion (or, in some embodiments, the entire thermal response element) disengages from the thermally conductive contact with the substrate can help allow the thermal response element to cool to the second predetermined temperature.

[0054] In some embodiments, a portion of the periphery of the thermal response element includes a contact portion. When the thermal response element operates at a predetermined temperature, the periphery of the thermal response element can be arranged to move relative to the rest of the thermal response element. By arranging the thermal response element such that its periphery includes the contact portion, this contact portion can be positioned on the part of the thermal response element that moves the furthest during operation. Therefore, after operation, the contact portion can be substantially spaced from the substrate. This helps ensure that the thermal response element cools to a second predetermined temperature.

[0055] In some embodiments, the thermal response element includes one or more additional contact portions, which are arranged to make thermally conductive contact with the substrate at least when the temperature of the thermal response element is below a predetermined temperature. At least one of the contact portions may be arranged at a distal end of the thermal response element. At least one of the contact portions is arranged at a proximal end of the thermal response element. Distributing the contact portions across the thermal response element can help to uniformly distribute the heat supplied to the thermal response element, which can help ensure reliable operation of the thermal response element at the predetermined temperature.

[0056] In some embodiments, the resistance heater trace includes a thick-film printed element. In some embodiments, the resistance heater trace includes a sprayed element. Such a heating element can operate at high temperatures, for example, above 200°C, which can allow the heating device to heat the contents of a liquid heating appliance at a faster rate (e.g., compared to a sheathed electric heater). The heating device can be arranged to heat a liquid (e.g., water) to boiling.

[0057] In some embodiments, the rated power of the resistance heater trace is between 700W and 3000W, for example between 1000W and 2500W, such as approximately 2000W. This may be particularly suitable for embodiments in which the container of the liquid heating appliance is arranged to hold 1 to 2 liters of water, such as a household kettle. In some embodiments, the rated power of the resistance heater trace is between 300W and 700W, for example between 400W and 600W, such as approximately 500W. This may be particularly suitable for embodiments in which the container of the liquid heating appliance is arranged to hold between 100ml and 600ml, such as portable (e.g., handheld) beverage containers.

[0058] In some embodiments, the thermally responsive element is arranged such that, at least when the temperature of the thermally responsive element is below a predetermined temperature, the thermally responsive element elastically deforms upon contact with a substrate, causing the contact portion to exert a force on the substrate. This can help improve the contact between the contact portion and the substrate, thereby helping to improve the thermal conductivity between the thermally responsive element and the substrate. This elastic deformation can be achieved, for example, by suitably positioning a mounting device relative to the substrate, such as causing the thermally responsive element to deform when it presses against the substrate.

[0059] In some embodiments, resistance heater traces are deposited on a substrate such that they extend along a serpentine path on the substrate. This can help increase the total heating power of the substrate and the resistance heater traces, thereby reducing the time required for the heating device to heat the contents of the liquid heating appliance. In some embodiments, the total power density of the substrate is 7 W / cm². 2 With 18W / cm 2 Between, for example, at 9W / cm 2 With 15W / cm2 Between, for example, at 12W / cm 2 With 14W / cm 2 Between, for example, approximately 13 W / cm 2 Power density should be understood as power per unit area. The power density of the substrate can be roughly equated to the power density of the resistance heater traces.

[0060] It should be understood that the total power density of the substrate is the total heating power of the resistance heater traces per unit area of ​​the substrate (including the area of ​​the substrate on which the resistance heater traces are deposited) (when viewed in a plan view).

[0061] In some embodiments, the thermally responsive element is arranged such that its periphery extends over a portion of the resistive heater trace thereon. This portion of the resistive heater trace may extend along the periphery of the thermally responsive element. This portion of the resistive heater trace may be deposited to define a portion of the substrate on which the resistive heater trace is not deposited. The control unit may include a mounting device on which the thermally responsive element is mounted. The portion of the substrate on which the resistive heater trace is not deposited may surround but not physically contact the mounting device. This helps to prevent the control unit from being heated by the resistive heater trace and helps to avoid the requirement for electrical insulation of the mounting device.

[0062] In some embodiments, a portion of the resistive heater trace extending thereon of the thermal response element may occupy between 30% and 100% of the coverage area of ​​the thermal response element (i.e., the total area of ​​the substrate on which the thermal response element extends), for example between 40% and 80%, such as about 60%.

[0063] In some embodiments, the resistive heater trace includes a first portion having a first power density and a second portion having a second power density. In some embodiments, the second power density is lower than the first power density. The lower power density can be achieved in any suitable manner. For example, the second portion of the resistive heater trace can be wider than the first portion. Furthermore, or alternatively, the second portion of the resistive trace can be deeper than the first portion. The width of the first portion of the resistive heater trace can be between 1 mm and 2 mm, for example, between 1.2 mm and 1.8 mm, such as approximately 1.5 mm. The width of the second portion of the resistive heater trace can be between 1.5 mm and 2.5 mm, for example, between 1.7 mm and 2.2 mm, such as approximately 2 mm. The second portion of the resistive heater trace can include a material that is more conductive than the first portion of the resistive heater trace, such as silver. This can also help to reduce the second power density compared to the first power density.

[0064] In some embodiments, the second portion includes a portion of a resistance heater trace over which the thermal response element extends at least partially. It should be understood that, due to its lower power density, the second portion of the resistance heater trace can have a lower operating temperature than the first portion. Arranging the thermal response element on the second portion of the resistance heater trace means that the thermal response element can be exposed to a lower temperature than if it were arranged on the first portion. This means that the predetermined operating temperature of the thermal response element can be lower than the temperature when it is arranged on the first portion of the resistance heater trace, which can reduce the complexity and cost of manufacturing the thermal response element.

[0065] In some embodiments, the local power density of the first portion is 30 W / cm². 2 With 70W / cm 2 Between, for example, at 40W / cm 2 With 55W / cm 2 Between, for example, approximately 45 W / cm 2 In some embodiments, the local power density of the second portion is 15 W / cm². 2 With 25W / cm 2 Between, for example, at 17 W / cm 2 With 23W / cm 2 Between, for example, approximately 20 W / cm 2 It should be understood that the power density of the resistance heater trace is the heating power of the resistance heater trace per unit area (where the area of ​​the resistance heater trace is the area of ​​contact between the resistance heater trace and the substrate).

[0066] As discussed above, in some embodiments, the centroid of the thermal response element is located within the proximal end of the thermal response element, rather than within the distal end of the thermal response element.

[0067] In some embodiments, the resistance heater traces are arranged on the substrate such that the total heating power applied to the proximal end of the thermal response element is greater than or equal to the total heating power applied to the distal end of the thermal response element. This takes into account the heat transferred to the thermal response element by conduction and radiation. Arranging the resistance heater traces such that the total heating power applied to the proximal end (i.e., the end where the centroid of the thermal response element is located) is greater than or equal to the total heating power applied to the distal end can help prevent creep in the thermal response element, which can help prevent the thermal response element from disconnecting at temperatures below a predetermined temperature.

[0068] In some embodiments, the resistance heater traces are arranged on a substrate such that the total heating power output from a portion of the resistance heater traces below the proximal end of the thermal response element is greater than or equal to the total power output from a portion of the resistance heater traces below the distal end of the thermal response element.

[0069] The total heating power applied to the distal end can be zero. In some embodiments, the distal end of the thermal response element does not extend over any part of the resistance heater trace.

[0070] This in itself is considered novel and inventive. Therefore, viewed from a third aspect, this invention provides a heating device for a liquid heating appliance, the heating device comprising:

[0071] substrate;

[0072] Resistance heater traces are deposited on a substrate;

[0073] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position; and

[0074] A thermal response element, arranged to operate at a predetermined temperature, to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0075] in:

[0076] The thermal response element includes a proximal end and a distal end, wherein the centroid of the thermal response element is located within the proximal end of the thermal response element, rather than within the distal end of the thermal response element;

[0077] The thermal response element extends at least partially over a portion of the resistance heater trace; and

[0078] The resistance heater traces are arranged on the substrate such that the total heating power applied to the proximal end of the thermal response element is greater than or equal to the total heating power applied to the distal end of the thermal response element.

[0079] From a fourth perspective, this utility model provides a liquid heating appliance, comprising:

[0080] A liquid heating container for receiving a liquid to be heated; and

[0081] A heating device, arranged to heat the contents of a liquid heating container, includes:

[0082] substrate;

[0083] Resistance heater traces are deposited on a substrate;

[0084] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position; and

[0085] A thermal response element, arranged to operate at a predetermined temperature, to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0086] in:

[0087] The thermal response element includes a proximal end and a distal end, wherein the centroid of the thermal response element is located within the proximal end of the thermal response element, rather than within the distal end of the thermal response element;

[0088] The thermal response element extends at least partially over a portion of the resistance heater trace; and

[0089] The resistance heater traces are arranged on the substrate such that the total heating power applied to the proximal end of the thermal response element is greater than or equal to the total heating power applied to the distal end of the thermal response element.

[0090] As discussed above, arranging the resistance heater traces such that the total heating power applied to the proximal end of the thermal response element (i.e., the end where the centroid of the thermal response element is located) is greater than or equal to the total heating power applied to the distal end of the thermal response element can help improve the reliability of the thermal response element operating at a predetermined temperature to disconnect the switch.

[0091] The features of the first and second aspects of this utility model, including any embodiments thereof, can be applied to the third and fourth aspects discussed above.

[0092] The following features may be applied to any suitable embodiments discussed herein, including embodiments of the first, second, third, and fourth aspects of this invention.

[0093] In some embodiments, the total heating power applied to the proximal end of the thermal response element is greater than the total heating power applied to the distal end. Arranging the resistance heater traces such that the total heating power applied to the proximal end is greater than (but not equal to) the total heating power applied to the distal end may be particularly advantageous for avoiding creep effects in the thermal response element. In some embodiments, the resistance heater traces are arranged on a substrate such that the total heating power applied to the proximal end of the thermal response element is equal to the total heating power applied to the distal end. This can help provide a uniform heat distribution in the thermal response element, thereby improving the reliability of the thermal response element operating at a predetermined temperature.

[0094] Variations in the total heating power applied to different ends of the thermal response element can be achieved in any suitable manner. In some embodiments, the average power density of the resistive heater trace below the proximal end is greater than that of the resistive heater trace below the distal end. In some embodiments, the cross-sectional area of ​​the resistive heater trace below the distal end of the thermal response element is greater than that of the resistive heater trace below the proximal end in a plane perpendicular to the length of the resistive heater trace. For example, the resistive heater trace below the distal end may be wider than that below the proximal end (assuming the resistive heater trace has a constant depth). Locally reducing the cross-sectional area of ​​the resistive heater trace can increase the local resistance of the resistive heater trace, which can increase the local heating power output. In some embodiments (e.g., when the resistive heater trace has a substantially uniform cross-sectional area), the proportion of the substrate area on which the resistive heater trace is deposited (compared to the total area of ​​the substrate overlapped by the thermal response element) is greater below the proximal end than below the distal end. In other words, more substrate area can be exposed below the distal end compared to below the proximal end. It should be noted that this may result in the heating power applied to the proximal end being greater than the heating power applied to the distal end.

[0095] As discussed above with reference to the first and second aspects, the thermal response element can be mounted on the mounting body of the control unit. The thermal response element can be mounted on the mounting body via its proximal end. The thermal response element can be mounted on the mounting body via a portion of the thermal response element between its proximal and distal edges, which can overlap both the proximal and distal ends (e.g., a central tongue).

[0096] In some embodiments, as described above, the proximal end of the thermal response element includes a support portion of the thermal response element. In some embodiments, as described above, the distal end of the thermal response element includes an actuator portion of the thermal response element. The proximal end may include an actuator portion. The distal end may include a support portion.

[0097] In some embodiments, as discussed above, the proximal end of the thermal response element includes a contact portion of the thermal response element. The distal end of the thermal response element may include a contact portion.

[0098] In some embodiments, the path of the resistive heater trace extends from outside the coverage area of ​​the thermal response element into the coverage area of ​​the thermal response element. It should be understood that the coverage area of ​​the thermal response element is defined by the projection of the outer edge of the thermal response element into a plan view. In some embodiments, the path of the resistive heater trace extends into the coverage area of ​​the thermal response element below the distal end of the thermal response element (e.g., at or near the distal edge). The path of the resistive heater trace may (e.g., additionally) extend beyond the coverage area of ​​the thermal response element. In some embodiments, the path of the resistive heater trace extends beyond the coverage area of ​​the resistive heater trace below the distal end of the thermal response element (e.g., at or near the distal edge). Arranging the path of the resistive heater trace such that it enters and exits the coverage area of ​​the thermal response element below the distal end of the thermal response element (e.g., at or near the distal edge) can help reduce the power density at the distal end of the thermal response element, which can help reduce the total heating power applied to the distal end of the thermal response element.

[0099] In any of the embodiments described above, the substrate may comprise stainless steel, such as 400 series stainless steel, such as martensitic stainless steel. In some embodiments, the substrate comprises a first layer and a second layer. The first layer may be formed of stainless steel. The second layer may comprise an electrically insulating material deposited on the substrate. The resistance heater traces may be deposited on the second layer. The electrical insulation may be formed of any suitable material, such as polyester, polyimide, acrylate, polyurethane, acetate, or cellulose. The material of the substrate may have a similar coefficient of thermal expansion to the insulating material. This can help prevent damage to the heating device during use due to the components expanding at different rates with respect to temperature. For this reason, forming the substrate from martensitic stainless steel may be particularly advantageous, as its coefficient of thermal expansion may be similar to that of the material used for insulation.

[0100] From a fifth perspective, this utility model provides a heating device for a liquid heating appliance, the heating device comprising:

[0101] substrate;

[0102] A resistance heater trace is deposited on a substrate such that at least a portion of the resistance heater trace extends along a serpentine path.

[0103] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position; and

[0104] A bimetallic element arranged to operate at a predetermined temperature to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0105] in:

[0106] The bimetallic element extends at least partially over a portion of the resistance heater trace; and

[0107] At least when the temperature of the bimetallic element is below a predetermined temperature:

[0108] All components of the bimetallic element are arranged to avoid direct physical contact with the traces of the resistance heater; and

[0109] The contact portion of the bimetallic element is arranged to make thermally conductive contact with the substrate.

[0110] From a sixth perspective, this utility model provides a liquid heating appliance, comprising:

[0111] A liquid heating container for receiving a liquid to be heated; and

[0112] A heating device, arranged to heat the contents of a liquid heating container, includes:

[0113] substrate;

[0114] A resistance heater trace is deposited on a substrate such that at least a portion of the resistance heater trace extends along a serpentine path.

[0115] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position;

[0116] A bimetallic element arranged to operate at a predetermined temperature to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0117] in:

[0118] The bimetallic element extends at least partially over a portion of the resistance heater trace; and

[0119] At least when the temperature of the bimetallic element is below a predetermined temperature:

[0120] Any component of the bimetallic element is arranged to be in direct physical contact with the traces of the resistance heater; and

[0121] The contact portion of the bimetallic element is arranged to make thermally conductive contact with the substrate.

[0122] From a seventh perspective, the present invention provides a heating device for a liquid heating appliance, the heating device comprising:

[0123] substrate;

[0124] A resistance heater trace is deposited on a substrate such that at least a portion of the resistance heater trace extends along a serpentine path.

[0125] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position; and

[0126] A bimetallic element arranged to operate at a predetermined temperature to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0127] in:

[0128] The bimetallic element includes a proximal end and a distal end, wherein the centroid of the bimetallic element is located within the proximal end of the bimetallic element, rather than within the distal end of the bimetallic element;

[0129] The bimetallic element extends at least partially over a portion of the resistance heater trace; and

[0130] The resistance heater traces are arranged on the substrate such that the total heating power applied to the proximal end of the bimetallic element is greater than or equal to the total heating power applied to the distal end of the bimetallic element.

[0131] From an eighth perspective, this utility model provides a liquid heating appliance, comprising:

[0132] A liquid heating container for receiving a liquid to be heated; and

[0133] A heating device, arranged to heat the contents of a liquid heating container, includes:

[0134] substrate;

[0135] A resistance heater trace is deposited on a substrate such that at least a portion of the resistance heater trace extends along a serpentine path.

[0136] A power supply circuit for supplying power to the traces of a resistance heater, the circuit including a switch movable between a closed position and an open position; and

[0137] A bimetallic element arranged to operate at a predetermined temperature to move a switch to the off position, thereby interrupting the power supply to the resistance heater trace;

[0138] in:

[0139] The bimetallic element includes a proximal end and a distal end, wherein the centroid of the bimetallic element is located within the proximal end of the bimetallic element, rather than within the distal end of the bimetallic element;

[0140] The bimetallic element extends at least partially over a portion of the resistance heater trace; and

[0141] The resistance heater traces are arranged on the substrate such that the total heating power applied to the proximal end of the bimetallic element is greater than or equal to the total heating power applied to the distal end of the bimetallic element.

[0142] Features of any embodiment of the first, second, third, fourth, fifth, sixth, seventh, or eighth aspect of this invention may include any one or more of the optional features outlined herein with respect to any aspect of the first, second, third, fourth, fifth, sixth, seventh, or eighth aspect. It should be understood that the optional features of the thermally responsive element described with respect to the first, second, third, or fourth aspect of this invention may be applied to the bimetallic element of the fifth, sixth, seventh, and eighth aspects of this invention. Attached Figure Description

[0143] Some embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0144] Figure 1 A perspective view of a liquid heater according to an embodiment of the present invention is shown;

[0145] Figure 2a This shows what happens when the bimetallic element is below a predetermined temperature. Figure 1 A cross-sectional view of the power supply base and control unit of the liquid heating appliance;

[0146] Figure 2b This shows what happens when the thermal response element is above a predetermined temperature. Figure 1 A cross-sectional view of the power supply base and control unit of the liquid heating appliance;

[0147] Figure 3a A perspective view of the individual thermal response element is shown when the temperature is below a predetermined level;

[0148] Figure 3b A perspective view of the individual thermal response element is shown when the temperature is above a predetermined value;

[0149] Figure 4a It shows Figure 1 A perspective view of the resistance heater trace on the lower surface of the substrate below the first thermal response element of the liquid heater.

[0150] Figure 4b It shows Figure 1 A perspective view of the resistance heater trace on the lower surface of the substrate below the second thermal response element of the liquid heater; and

[0151] Figure 5 It shows Figure 1 Bottom side view of the substrate of the liquid heating appliance. Detailed Implementation

[0152] Figure 1 A perspective view of a liquid heating appliance 2 (hereinafter referred to as appliance 2) according to an embodiment of the present invention is shown. Appliance 2 includes a liquid heating container 4, a container spout 6, and a handle 8. The top of the liquid heating container 4 is closed with a cap 10. In the depicted embodiment, the liquid heating container 4 is arranged to rest on a power base 12, which includes a central 360° base electrical connector component 14 for supplying power to appliance 2. The power base 12 includes a plug 13 for receiving mains power. However, it should be understood that in other embodiments, appliance 2 may be powered in a corded manner.

[0153] Figure 2a A cross-sectional view is shown passing through the lower portion of the liquid heating container 4 and through the power supply base 12. For ease of illustration, Figure 2a and Figure 2b The base electrical connector component 14 and the cordless electrical adapter component 28 are shown in a detached state. Figure 2a As shown in the figure, according to an embodiment of the present invention, the appliance 2 includes a heating device 15 for heating a certain volume of liquid contained in the liquid heating container 4.

[0154] The heating device 15 includes resistance heater traces 18a deposited on the underside of a substrate 18c. The resistance heater traces 18a can be printed or sprayed. The substrate 18c is mounted below the liquid heating container 4 and can form the base of the liquid heating container 4. The resistance heater traces 18a are arranged to be in thermal communication with the liquid heating container 4 via the substrate 18c. When electrical energy is supplied to the resistance heater traces 18a, the resistance heater traces 18a generate heat, thereby heating the substrate 18c, which in turn heats the contents of the liquid heating container 4.

[0155] The heating device 15 also includes a control unit 16 mounted to the bottom side of the substrate 18c. When the liquid heating container 4 is seated on the power base 12, the control unit 16 controls the power supply from the power base 12 to the resistance heater trace 18a. The control unit 16 includes a cordless power adapter component 28, which is arranged to mate with the base electrical connector component 14 of the power base 12 when the liquid heating appliance 2 is received on the power base 12.

[0156] In the depicted embodiment, the cordless power adapter component 28 is a 3-pole adapter, comprising a charged post conductor 28a, a neutral loop conductor 28b, and a ground loop conductor 28c. The base electrical connector component 14 is a 3-pole connector, comprising a central hole in which a charged electrical contact 14a is disposed, a first coaxial hole in which a neutral electrical contact 14b is disposed, and a second coaxial hole in which a ground electrical contact 14c is disposed. The charged post conductor 28a is arranged to be received within the central hole, the neutral loop conductor 28b is received within the first coaxial hole, and the ground loop conductor 28c is received within the second coaxial hole, such that when the power adapter component 28 mates with the base electrical connector component 14, the corresponding charged conductor, neutral conductor, and ground conductor, as well as the contacts, are brought together to form a power supply circuit.

[0157] The charged column conductor 28a and the neutral ring conductor 28b are electrically connected to the corresponding terminals of the resistance heater trace 18a. Figure 2a and Figure 2b This electrical connection is schematically illustrated in the diagram.

[0158] Although Figure 2a The embodiment shown includes a 3-pole cordless power adapter component 28 and a base electrical connector component 14, but it should be understood that the adapter component 28 and the connector component 14 may include any suitable number of poles, such as 5 poles.

[0159] The control unit 16 also includes a mounting body 16a and a first thermal response element 30a mounted to the upper surface of the mounting body 16a. In this embodiment, the thermal response element 30a is in the form of a snap-action bimetallic element 30a, but it should be understood that any suitable type of thermal response element can be used. The bimetallic element 30a is configured to operate at a predetermined temperature, i.e., snap / change its physical shape. Figure 2a The configuration of the bimetallic element 30a when its temperature is below its predetermined temperature is shown. For example... Figure 3a As depicted, the bimetallic element 30a is arranged such that no part of the bimetallic element 30a is in direct physical contact with the resistance heater trace 18a. However, as depicted, the bimetallic element 30a does contact the substrate 18c, as will be discussed further below. The control unit 16 also includes a second thermal response element (also a snap-on bimetallic element in this embodiment) 30b (as shown in the image). Figure 4b As shown in the diagram, the second thermally responsive element is also mounted to the upper surface of the mounting body 16a and is configured to operate at a predetermined temperature, which may be the same as or different from the predetermined temperature of the first bimetallic element 30a. Unless otherwise stated, the characteristics of the first bimetallic element 30a described herein also apply to the second bimetallic element 30b.

[0160] like Figure 2a As shown, when the temperature of the bimetallic element 30a is below a predetermined temperature, the bimetallic element 30a can take a concave shape (i.e., the surface of the bimetallic element 30a facing the resistance heater trace 18a is concave). Figure 2b As shown, when the temperature of the bimetallic element 30a reaches a predetermined temperature, the bimetallic element 30a can suddenly jump into a convex shape (that is, the surface of the bimetallic element 30a facing the resistance heater trace 18a is convex).

[0161] Figure 2b A cross-sectional view of the power base 12 and control unit 16 is shown when the bimetallic element 30a is above a predetermined temperature. As can be seen, the bimetallic element 30a has abruptly changed from its initial concave configuration to a convex configuration, in which the bimetallic element 30b is no longer in contact with the substrate 18c. The movement of the bimetallic element 30a causes it to exert a force on the push rod 40, which moves downward to disconnect the switch 50 within the control unit 16, thereby interrupting the power supply to the resistance heater trace 18a.

[0162] As is known in the prior art, this allows the resistance heater trace 18a to be cut off in the case of "dry burning" in the absence of liquid in the liquid heating container 4. The second bimetallic element 30b is arranged to disconnect the switch 50 via a separate push rod (not shown) when the second bimetallic element 30b is operating at its predetermined temperature (or, optionally, a separate switch).

[0163] exist Figure 3a and Figure 3b The bimetallic element 30a is shown in more detail and separately in an isometric side view. The bimetallic element is... Figure 3a It is shown in its concave form (i.e., the form when its temperature is below a predetermined temperature), while... Figure 3b It is shown in its convex form (i.e., the form when its temperature is above a predetermined temperature).

[0164] In the depicted embodiment, the bimetallic element 30a is substantially rectangular and includes a pair of parallel sides 35 connecting the distal edge 27 and the proximal edge 29 of the bimetallic element 30a. The parallel sides 35 are parallel to the central longitudinal axis 41 of the bimetallic element 30a, and the plan view of the bimetallic element 30a is substantially a mirror image of the longitudinal axis 41 (e.g., Figure 4a and Figure 4b (As shown). The distal end 37 of the bimetallic element 30a is defined between the distal edge 27 of the bimetallic element 30a and the midpoint 25 of the bimetallic element 30a (in the direction of the longitudinal axis 41). The proximal end 39 of the bimetallic element 30a is defined between the proximal edge 29 of the bimetallic element 30a and the midpoint 25 of the bimetallic element 30a.

[0165] Return to reference Figure 2a As can be seen, when the bimetallic element 30a is below a predetermined temperature, a gap 53 is defined between the bimetallic element 30a and the substrate 18c. The gap 53 is defined between the distal edge 27 and the proximal edge 29 of the bimetallic element 30a and allows the resistance heater trace 18a to extend beneath the bimetallic element 30a, such that the bimetallic element 30a covers a portion of the resistance heater trace 18a. The gap 53 allows the bimetallic element 30a (i.e., the thermally responsive element) to extend over the resistance heater trace 18a without touching it. As previously discussed, this may advantageously mean that the bimetallic element 30a does not require electrical insulation thereon, as it does not contact the resistance heater trace 18a.

[0166] Return to reference Figure 3a The bimetallic element 30a includes a ring 51 defining an internal cutout 47. The internal cutout 47 is located closer to the distal edge 27 of the bimetallic element 30a than to its proximal edge 29. As a result, the centroid 59 of the bimetallic element 30a is located within the proximal end 39, rather than the distal end 37. In other words, the centroid 59 is closer to the proximal edge 29 than to the distal edge 27.

[0167] The bimetallic element 30a includes a central tongue 45 that extends parallel to a central longitudinal axis 41 into an internal cutout 47 defined between the distal edge 27 and the proximal edge 29 of the bimetallic element 30a. The bimetallic element 30a can be mounted to the control unit 16 via the central tongue 45. The proximal end 39 of the bimetallic element 30a is also supported by the control unit 16, for example, it can press against the surface of the control unit 16 when mounted to the control unit 16. Thus, the proximal end 39 and the central tongue 45 together constitute a support portion of the bimetallic element 30a. When the bimetallic element 30a operates at a predetermined temperature, the distal edge 27 and the proximal edge 29 of the bimetallic element 30a move relative to the central tongue 45, respectively. The distal end 37 is arranged to contact a push rod 40 for disconnecting the switch 50, and therefore the distal end 37 includes the actuator portion of the bimetallic element 30a.

[0168] The proximal end portion 39 includes a pair of protrusions 31a, 31b, wherein a corresponding one of the protrusions 31a, 31b is positioned on each side of the central longitudinal axis of the bimetallic element 30a. The protrusions 31a, 31b extend from the proximal edge 29 of the bimetallic element 30a in a direction parallel to the central longitudinal axis 41 of the bimetallic element 30a. The distal end portion 37 includes two additional protrusions 31c, 31d, which extend coaxially from the distal edge 27 with the proximal end protrusions 31a, 31b, respectively.

[0169] When the temperature of the bimetallic element 30a is lower than the predetermined temperature (e.g.) Figure 2a and Figure 3a As shown, the distal edge 27 of the bimetallic element 30a is concave, with the lowest point of the distal edge 27 located at the midpoint of the distal edge 27, and the highest point of the distal edge 27 located at the edge where the distal edge 27 intersects with the two parallel sides 35 of the bimetallic element 30a. Therefore, the highest point of the distal edge 27 defines the two distal vertices 37a and 37b of the bimetallic element 30a.

[0170] In this configuration of the bimetallic element 30a, the parallel side 35 is also concave, wherein the highest point of the parallel side 35 (i.e., the point farthest from the control unit 16 when the bimetallic element 30a is mounted on the control unit 16) is located at the far edge 27 and the near edge 29 of the parallel side 35.

[0171] In this configuration (i.e., when the temperature of the bimetallic element 30a is below a predetermined temperature), the protrusions 31a and 31b at the distal vertices 37a and 37b and the proximal edge 29 are the highest points of the bimetallic element 30a, that is, when the bimetallic element 30a is mounted on the control unit 16, they are furthest from the control unit 16. For illustrative purposes, in Figure 3a The distal vertices 37a and 37b and the protrusions 31a and 31b at the proximal ends are indicated by shading. When the bimetallic element 30a is mounted below the substrate 18c, the portions of the bimetallic element 30a that contact the substrate 18c are only the distal vertices 37a and 37b and the protrusions 31a and 31b. The distal vertices 37a and 37b and the protrusions 31a and 31b may be referred to herein as the contact portions of the bimetallic element 30a.

[0172] When the temperature of the bimetallic element 30a is below a predetermined temperature, the protrusions 31a, 31b and the distal vertices 37a, 37b (i.e., the contact portions at this temperature) are in thermal communication with the substrate 18c, meaning that the bimetallic element 30a is arranged to be sensitive to the temperature of the substrate 18c. However, no part of the bimetallic element 30a is in direct physical contact with the resistance heater trace 18a.

[0173] When the temperature of the bimetallic element 30a is higher than the predetermined temperature (e.g.) Figure 2b and Figure 3b As shown, the distal edge 27 and proximal edge 29 of the bimetallic element 30a are moved relative to the central tongue 45, causing the parallel side 35 of the bimetallic element 30a to become convex, wherein the lowest point of the parallel side 35 (i.e., the point closest to the control unit 16 when the bimetallic element 30a is mounted on the control unit 16) is located at the distal edge 27 and proximal edge 29 of the parallel side 35, respectively. As a result, the protrusions 31a, 31b and the distal vertices 37a, 37b (i.e., the contact portions) of the bimetallic element 30a no longer contact the substrate 18c. In this configuration, no part of the bimetallic element 30a contacts the substrate 18c. This allows the bimetallic element 30a to cool to a temperature that resets it to its concave configuration.

[0174] Figure 4a and Figure 4b A perspective view of the resistance heater trace 18a on the lower surface of the substrate 18c and the corresponding first bimetallic element 30a and second bimetallic element 30b is shown. Figure 4a The image shows a first bimetallic element 30a arranged on the left-hand side of the substrate 18c, while... Figure 4b The image shows a second bimetallic element 30b arranged on the right-hand side of the substrate 18c. The bimetallic elements 30a and 30b are shown transparently, so that the arrangement of the resistance heater trace 18a above each bimetallic element 30a and 30b can be seen.

[0175] Figure 5 A bottom side view of a substrate 18c on which resistance heater traces 18a are deposited is shown. The resistance heater traces 18a meander along the lower surface of the substrate 18c in a serpentine path from a first electrical terminal 19a to a second electrical terminal 19b. Except for wider regions 21a, 21b below the first bimetallic element 30a and the second bimetallic element 30b, respectively, the width of the resistance heater traces 18a is substantially uniform, for example, 1.5 mm along most of its length. The first wider region 21a and the second wider region 21b may, for example, have a width of 2 mm. The first wider region 21a and the second wider region 21a, 21b do not need to have the same width, but can have different corresponding widths; for example, the first wider region 21a may have a width of 1.7 mm, and the second wider region 21b may have a width of 2 mm.

[0176] The local widening of the resistance heater trace 18a above the bimetallic elements 30a and 30b reduces the resistance of the resistance heater trace 18a in these wider regions 21a and 21b. This, in turn, reduces the local power density and normal operating temperature. While the non-widened region of the resistance heater trace 18a can reach a maximum temperature of approximately 200°C during normal heating operation (i.e., in the presence of liquid in a liquid heating vessel), the widened regions 21a and 21b can reach an average temperature of approximately 125°C during the same operation. This means that bimetallic elements 30a and 30b, configured to operate at relatively low temperatures (e.g., between 125°C and 155°C), can be advantageously used.

[0177] refer to Figure 4a and Figure 4b In some embodiments, the path of the resistance heater trace 18a extends both into the coverage area of ​​the bimetallic element 30a near its distal edge 27 and exits the coverage area of ​​the bimetallic element 30a near its distal edge 27. Similarly, the path of the resistance heater trace 18a also extends into the coverage area of ​​the second bimetallic element 30b near its distal edge 55a and exits the coverage area of ​​the second bimetallic element 30b near its distal edge 55a. The total heating power applied to the distal end 37 of the first bimetallic element 30a is less than the total heating power applied to the proximal end 39 of the first bimetallic element 30a. Likewise, the total heating power applied to the distal end 55 of the second bimetallic element 30b is less than the total heating power applied to the proximal end 57 of the second bimetallic element 30b.

[0178] When bimetallic elements 30a and 30b are installed on control unit 16, such as when they are in Figure 4a and Figure 4bAs shown, the distal vertices 37a, 37b and protrusions 31a, 31b of the first bimetallic element 30a, and the distal vertices 43a, 43b and protrusions 33a, 33b of the second bimetallic element 30b are arranged above the portion of the substrate 18c where the resistive heater trace 18a is absent. When the first bimetallic element 30a and the second bimetallic element 30b are below their respective predetermined temperatures, the distal vertices 37a, 37b, 43a, 43b and protrusions 31a, 31b, 33a, 33b of the first bimetallic element 30a and the second bimetallic element 30b are in direct thermal contact with the substrate 18c. No part of the first bimetallic element 30a and the second bimetallic element 30b is in direct physical contact with the resistance heater trace 18a, and no part of the first bimetallic element 30a and the second bimetallic element 30b is in direct physical contact with the substrate 18c except for the distal vertices 37a, 37b, 43a, 43b and the protrusions 31a, 31b, 33a, 33b.

[0179] Arranging the bimetallic element 30a such that it extends over but does not contact the resistance heater trace 18a advantageously means that no electrical insulation is required between the bimetallic element 30a and the resistance heater trace 18a. Arranging the bimetallic element 30a in a thermally conductive contact with the substrate 18c, but not in direct physical contact with the resistance heater trace 18a, advantageously reduces the rate of heat transfer from the resistance heater trace 18a to the bimetal. This means that when the temperature of the resistance heater trace 18a is high enough to require overheat cutoff, for example, when the liquid heating vessel 4 has been dry-burned, the bimetallic element 30a is at a lower temperature than the resistance heater trace 18a. As a result, a bimetallic element 30a with a lower operating temperature can be used without increasing the risk of the bimetallic element 30a operating at excessively low temperatures (e.g., during normal operation of the liquid heating appliance 2). This can save cost and time during the design and manufacturing process of the bimetallic element 30a.

[0180] Although the present invention has been described in detail with reference to only a limited number of embodiments, it should be readily understood that the present invention is not limited to these disclosed embodiments. Rather, the present invention can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not previously described but equivalent to the scope of the present invention. Furthermore, while various embodiments of the present invention have been described, it should be understood that aspects of the present invention may include only some of the described embodiments. Therefore, the present invention should not be considered as limited to the foregoing description, but only to the scope of the appended claims.

Claims

1. A heating device for a liquid heating appliance, characterised in that, The heating device includes: substrate; A resistance heater trace is deposited on the substrate such that at least a portion of the resistance heater trace extends along a serpentine path; A power supply circuit for supplying power to the resistance heater trace, the circuit including a switch movable between a closed position and an open position; and A bimetallic element arranged to operate at a predetermined temperature to move the switch to the off position, thereby interrupting the power supply to the resistance heater trace; in: The bimetallic element extends at least partially over a portion of the trace of the resistance heater; and At least when the temperature of the bimetallic element is below the predetermined temperature: Any component of the bimetallic element is arranged to avoid direct physical contact with the traces of the resistance heater; and The contact portion of the bimetallic element is arranged to make thermally conductive contact with the substrate.

2. The heating device of claim 1, wherein, The resistance heater trace includes a first portion having a first power density and a second portion having a second power density, wherein the second power density is lower than the first power density, and wherein the second portion includes a portion of the resistance heater trace over which the bimetallic element extends at least partially.

3. The heating device according to claim 1 or 2, wherein The heating device further includes a control unit, which includes: The switch of the power supply circuit; and Mounting body, the mounting body being used to mount the control unit to the base plate; And wherein the bimetallic element includes: A support portion, said support portion being mounted on the mounting body of the control unit, wherein said support portion includes the contact portion; and An actuator portion that is movable relative to the support portion when the bimetallic element operates at the predetermined temperature, so as to move the switch to the off position.

4. The heating device according to claim 3, wherein: The control unit includes a mounting device, and the bimetallic element is mounted on the mounting device; A portion of the resistive heater trace extending thereon from the bimetallic element is deposited on the substrate so as to extend along the periphery of the bimetallic element to define a portion of the substrate on which no resistive heater trace is deposited. as well as The substrate has a portion of the resistive heater traces deposited on it surrounding but not physically contacting the mounting device.

5. The heating device of claim 1 or 2, wherein, The bimetallic element includes a proximal edge and a distal edge, and wherein, at least when the temperature of the bimetallic element is below the predetermined temperature: The bimetallic element includes a curved portion between the proximal edge and the distal edge; and The bimetallic element is arranged such that it defines a gap between the curved portion and the substrate, wherein the gap extends from the edge of the bimetallic element.

6. The heating device of claim 1 or 2, wherein, The bimetallic element includes: Proximal edge and distal edge; The proximal end portion is defined between the proximal edge of the bimetallic element and the midpoint of the bimetallic element; and The distal end is defined between the distal edge of the bimetallic element and the midpoint of the bimetallic element; The centroid of the bimetallic element is located within the proximal end of the bimetallic element, rather than within the distal end of the bimetallic element.

7. The heating device of claim 6, wherein, The proximal end of the bimetallic element includes the contact portion.

8. The heating device of claim 6, wherein, The resistance heater traces are arranged on the substrate such that the total heating power applied to the proximal end of the bimetallic element is greater than or equal to the total heating power applied to the distal end of the bimetallic element.

9. The heating device of claim 1 or 2, wherein, The bimetallic element is configured such that at or above the predetermined temperature, any component of the bimetallic element is arranged not to have thermal contact with the substrate.

10. The heating device of claim 1 or 2, wherein, The contact portion is included in a portion of the periphery of the bimetallic element.

11. The heating device of claim 1 or 2, wherein, The bimetallic element includes one or more additional contact portions, which are arranged to make thermally conductive contact with the substrate at least when the temperature of the bimetallic element is below the predetermined temperature, wherein at least one of the contact portions is arranged at a distal end of the bimetallic element and at least one of the contact portions is arranged at a proximal end of the bimetallic element.

12. The heating device of claim 1 or 2, wherein, The resistance heater traces include thick-film printed elements or sprayed elements.

13. The heating device of claim 1 or 2, wherein, The bimetallic element is arranged such that, at least when the temperature of the bimetallic element is below the predetermined temperature, the bimetallic element elastically deforms by contacting the substrate, such that the contact portion applies a force to the substrate.

14. A liquid heating appliance characterised in that, include: A liquid heating container for receiving a liquid to be heated; as well as The heating device according to claim 1 or 2.

15. A heating device for a liquid heating appliance, characterised in that, The heating device includes: substrate; A resistance heater trace is deposited on the substrate such that at least a portion of the resistance heater trace extends along a serpentine path; A power supply circuit for supplying power to the resistance heater trace, the circuit including a switch movable between a closed position and an open position; and A bimetallic element arranged to operate at a predetermined temperature to move the switch to the off position, thereby interrupting the power supply to the resistance heater trace; in: The bimetallic element includes a proximal end and a distal end, wherein the centroid of the bimetallic element is located within the proximal end of the bimetallic element, rather than within the distal end of the bimetallic element; The bimetallic element extends at least partially over a portion of the trace of the resistance heater; and The resistance heater traces are arranged on the substrate such that the total heating power applied to the proximal end of the bimetallic element is greater than or equal to the total heating power applied to the distal end of the bimetallic element.

16. The heating device of claim 15, wherein, The resistance heater trace below the distal end of the bimetallic element is wider than the resistance heater trace below the proximal end of the bimetallic element.

17. The heating device of claim 15 or 16, wherein, The serpentine path extends from outside the footprint of the bimetallic element to within the footprint of the bimetallic element under the distal end of the bimetallic element, and / or wherein the path extends from within the footprint of the bimetallic element out of the footprint of the bimetallic element under the distal end of the bimetallic element.

18. A liquid heating appliance comprising: Comprising: a liquid heating vessel for receiving a liquid to be heated; and a heating arrangement according to claim 15 or 16.

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