Patent Application
20140263270
1. Technical Field
This invention relates to controls for controlling a liquid heating apparatus, e.g. to switch the apparatus off when water is boiling or to prevent overheating, and to assemblies and appliances incorporating such controls.
2. Background Information
A traditional electric kettle or hot water jug is equipped with a boiling control which, when liquid in the vessel boils, operates to disconnect the power supply to the heater of the vessel and so to discontinue boiling. Similarly an overheat control can be provided which disconnects the power supply when the heater exceeds a safe operating temperature.
Commonly such controls employ copper alloy leaf springs as moveable contacts to make or break the electrical power circuit with the leaf springs carrying current as part of the circuit. Typically the leaf springs are acted on via a push-rod by a thermally sensitive bimetallic actuator which operates when the liquid in the vessel boils or the heater overheats.
It is an object of the present invention to provide an improved and/or more cost-effective control for a liquid heating apparatus.
When viewed from a first aspect the present invention provides a control assembly for a cordless liquid heating apparatus comprising: a control for mounting to the liquid heating apparatus; and a cordless base connector adapted to supply electrical power to the control, wherein the control assembly comprises a switch arrangement for making or breaking an electrical circuit for supplying power to the liquid heating apparatus, the switch arrangement comprising: a fixed contact member provided on the cordless base connector, a moveable contact member mounted on a switch lever provided on the control, and resilient means, separate from and acting on the switch lever, so as to bias the moveable contact member into electrical contact with the fixed contact member.
This aspect of the invention extends to a control for a cordless liquid heating apparatus, comprising a switch arrangement for making or breaking an electrical circuit for supplying power to the liquid heating apparatus, the switch arrangement comprising: a moveable contact member mounted on a switch lever, and resilient means, separate from and acting on the switch lever, so as to bias the moveable contact member into electrical contact with a fixed contact member provided on a cordless base connector.
It will thus be appreciated that unlike in arrangements employing leaf springs, such a control decouples the mechanical and electrical properties of the structure carrying the moveable contact member, as the contact member is mounted on a lever which may be stiff (i.e. does not itself need to be resilient) and may include complex geometric features not easily provided in simple springs or conductors, whilst the biasing force necessary for good electrical contact is provided by separate resilient means, e.g. a spring. This enables the most appropriate material for each component to be chosen. Previously, as the biasing force and the electrical conductivity of the moveable electrical contact were provided by the same component in the control, e.g. a leaf spring, a compromise had to be made between the necessary functional properties of the two different operational requirements when choosing the material to use. It is advantageous to be able to use a stiff switch lever since this allows its movement, and thus movement of the contact member, to be predictable and reliable.
Furthermore, by having the moving contact member in the control and the fixed contact member in the cordless base connector, a considerable advantage can be achieved in that fewer current-carrying contact pairs are required overall than in more conventional arrangements where there are contacts between the two cordless connector parts and also in the control of the appliance for switching power—e.g. to prevent the element overheating. Instead the switch arrangement recited herein can also carry out the function of the necessary separable electrical connection between the control unit on the liquid heating apparatus and the cordless base connector. This is advantageous as such contact pairs typically require silver on each side and this gives rise to a significant proportion of the manufacturing cost of the control. The elimination of a set of contacts is also beneficial in reducing the number of moving parts in the control which improves reliability. Moreover, since the switch lever in the control of the invention is resiliently biased to give the necessary contact pressure, it is not necessary to provide a resiliently biased contact in the cordless base connector which makes it more robust as well as allowing more cost-effective manufacture.
The switch lever could be made of metal, and thereby could be arranged to carry current to the moveable contact member itself, but in a set of embodiments the lever comprises an electrically insulating material, e.g. plastic which can be molded easily into the desired shape and avoids the need to isolate the lever electrically from other parts of the control. A plastic lever can also help to reduce the cost of the control as it reduces the amount of expensive metals, e.g. copper, which have to be used. To further increase the safety of the control, in a set of embodiments the electrical conductor, e.g. a wire, leading to the moveable electrical contact is carried within the insulating switch lever. The insulating lever therefore acts as a sheath for the electrical conductor, providing a safe and convenient route for delivering current to the moveable electrical contact member.
Taking this further, in a set of embodiments the control comprises a sealed conductor connecting the movable contact member with a terminal, preferably a sealed terminal, of a heating element for the liquid heating apparatus, e.g. a cold tail of a sheathed heating element. Providing sealed electrical parts allows the control to be exposed to water without the risk of short-circuiting—e.g. to allow it to be made such that appliances incorporating it can be washed. The sealed conductor could be integrated with the switch lever, e.g. an insulated lever where one is provided, to further improve the safety of the control against water ingress.
This is considered novel and inventive in its own right and thus when viewed from a second aspect the present invention provides a liquid heating apparatus having an electrical heating element and a control which comprises a switch arrangement for making or breaking an electrical circuit for supplying power to the heating element, the switch arrangement comprising a moveable contact member mounted on a switch lever, and resilient means, separate from and acting on the switch lever, so as to bias the moveable contact member into electrical contact with a fixed contact member, the control further comprising a sealed conductor connecting the movable contact member with a sealed terminal of the heating element.
This aspect of the invention also extends to a control for mounting to a liquid heating apparatus having an electrical heating element, the control comprising a switch arrangement for making or breaking an electrical circuit for supplying power to said heating element, the switch arrangement comprising a moveable contact member mounted on a switch lever, and resilient means, separate from and acting on the switch lever, so as to bias the moveable contact member into electrical contact with a fixed contact member, the control further comprising a sealed conductor connecting the movable contact member with a sealed terminal of the heating element.
The fixed contact member could be provided inside the control but preferably, as in accordance with the first aspect of the invention, it is provided by a cordless base connector.
As in the first aspect of the invention, the switch lever is preferably of an electrically insulating material.
In a set of embodiments of either of the foregoing aspects of the invention the control is arranged such that the switch lever moves the moveable contact member away from the fixed contact member when the liquid heating apparatus reaches a predetermined temperature condition. This could be that the liquid in the apparatus reaches a predetermined temperature, e.g. boiling, or that the electric heating element reaches a predetermined temperature, e.g. to indicate boiling or overheating. In a set of embodiments the control comprises a temperature-sensitive actuator, e.g. a bimetallic actuator, arranged to act on the switch lever.
In a preferred set of embodiments a temperature-sensitive actuator is mounted on the control such that when the control is mounted on the liquid heating apparatus the temperature-sensitive actuator makes thermal contact with and is sensitive to the temperature of the liquid heating apparatus, the temperature-sensitive actuator being arranged to act on the switch lever such that the switch lever moves the moveable contact member away from the fixed contact member when the liquid heating apparatus reaches a predetermined temperature condition.
This is novel and inventive in its own right and thus when viewed from another aspect the invention provides a control for a liquid heating apparatus, comprising a switch arrangement for making or breaking an electrical circuit for supplying power to the liquid heating apparatus, the switch arrangement comprising: a fixed contact member, a moveable contact member mounted on a switch lever, a temperature-sensitive actuator mounted on the control such that when the control is mounted on the liquid heating apparatus the temperature-sensitive actuator makes thermal contact with and is sensitive to the temperature of the liquid heating apparatus, the temperature-sensitive actuator being arranged to act on the switch lever such that the switch lever moves the moveable contact member away from the fixed contact member when the liquid heating apparatus reaches a predetermined temperature condition, and resilient means, separate from and acting on the switch lever, so as to bias the moveable contact member into electrical contact with the fixed contact member.
In a set of embodiments the fixed contact member is provided in a cordless base connector, the advantages of which have been described above in relation to the first aspect of the invention.
Preferably the temperature-sensitive actuator provided in accordance with any foregoing aspect of the invention is mounted on an outer face of the control. The control could comprise more than one actuator, e.g. one to sense boiling and one to sense overheating. In one set of embodiments the control comprises a temperature sensitive actuator to detect boiling of the liquid in the liquid heating apparatus, e.g. a steam switch which could comprise a bimetallic actuator, arranged to act on the switch lever so as to separate the moveable and fixed contact members. In another, not mutually exclusive, set of embodiments, the control comprises a temperature-sensitive actuator to detect overheating of the liquid heating apparatus, e.g. which could comprise a bimetallic actuator mounted on or against the electric heating element, arranged to act on the switch lever so as to separate the moveable and fixed contact members.
Thus it can be seen that in preferred embodiments a temperature-sensitive actuator, such as a snap-acting bimetallic actuator, acts on the switch lever to separate the contacts. Here the nature of a lever can be exploited, e.g. by arranging the ratios of the lever such that the pivot is closer to the actuator than to the moveable contact member—i.e. so that the movement of the actuator is amplified by the lever. The lever can also be exploited to allow the relatively small force exerted by the actuator to be amplified in order to open the moveable contact member against its relatively high bias force, which is required when a higher contact pressure is desired. This creates a safer control as the relatively small distance of travel of an actuator such as a snap-acting bimetallic actuator can be amplified into a larger distance of travel of the moveable contact member, ensuring that there is adequate separation from the fixed contact member to meet safety standards.
In the set of embodiments in which two moveable switch arrangements are provided, e.g. for the live and neutral poles, preferably the control comprises independent temperature-sensitive actuators arranged to act on each respective switch lever. Alternatively or in addition, the control could comprise both boiling and overheat actuators arranged to act on the same switch lever. In a set of embodiments the control comprises independent temperature sensitive actuators for detecting overheating of the liquid heating apparatus which are arranged to act on the switch levers associated with the live and neutral poles respectively, and an actuator to detect boiling of the liquid in the liquid heating apparatus also arranged to act on the switch lever associated with the live pole. The actuators could act directly on the respective levers or by means of an intermediate mechanism—e.g. another lever. In a set of embodiments, for example, the boiling actuator is arranged to act on an on/off slider which in turn acts on the live switch lever. This arrangement is advantageous as it allows in some embodiments for the “on” mechanism to over-ride the action of the boiling actuator and thus permits the user to re-boil when desired.
As mentioned previously, in a set of embodiments where overheat actuators are provided to act on both the live and neutral poles, the actuator associated with the live pole is arranged preferentially to act first in normal use (primary)—e.g. because this allows only the live contact member to have a silver contact surface, or else a thicker layer of silver on its contact surface. This can be done by, for example, arranging the overheat temperature-sensitive actuator associated with the live pole to be closer to a sheathed heating element than the overheat temperature-sensitive actuator associated with the neutral pole (secondary). In one set of embodiments the overheat temperature-sensitive actuator associated with the live pole comprises a bimetallic actuator mounted on or adjacent the sheathed heating element. In one set of embodiments the overheat temperature-sensitive actuator associated with the neutral pole comprises a bimetallic actuator mounted more thermally remote from a sheathed heating element, e.g. between the cold tails of the sheathed element mounted beneath the base of a liquid heating chamber (i.e. an underfloor heater).
In one set of embodiments this neutral pole or secondary overheat actuator is arranged not to be able to be reset if it operates, i.e. it permanently holds the associated contact open. This provides an additional level of safety. A latching mechanism associated with this secondary actuator could be provided to hold open the respective contacts and/or to retain the actuator in an operated state. However, the Applicant has observed that even a remotely located secondary actuator can operate after the live pole or primary actuator, i.e. the actuator mounted closer to the sheathed heating element, has operated owing to the residual thermal energy dissipating through the heater, e.g. via a heater or diffuser plate (thermal overshoot). To prevent this happening, in a set of embodiments the control is mounted in a liquid heating apparatus comprising a heater or diffuser plate which comprises means to disrupt the direct thermal path from the sheathed heating element to the secondary overheat actuator. The disrupting means could comprise holes, gaps, slots, walls, baffles, etc., formed in the heater or diffuser plate, or additional thermal masses in thermal contact with the heater or diffuser plate.
However the Applicant has also devised a further approach which addresses the thermal overshoot issue in the control itself (i.e. without requiring any particular measures on a heating element diffuser plate etc.). Thus in a set of embodiments the control comprises a primary overheat temperature-sensitive actuator for interrupting the supply of power to a heating element in the liquid heating apparatus by opening a first (primary) switch arrangement in the event of said heating element overheating and a secondary overheat temperature-sensitive actuator for interrupting the supply of power to the heating element by opening a second (secondary) switch arrangement in the event of said primary actuator failing to operate, wherein the primary actuator is arranged in normal use to operate before the secondary actuator in the event of said heating element overheating and wherein the first and second switch arrangements have a relationship which is such that if the second switch arrangement independently opens before the first switch arrangement a latch is engaged which prevents one or both of said first and second switch arrangements from reclosing to supply power to the heating element but, if said first switch arrangement opens before the second switch arrangement, said latch is not engaged.
The first (primary) switch arrangement is conveniently the switch arrangement recited in accordance with the first or subsequent aspects of the invention—i.e. comprising a moveable contact member mounted on a resiliently biased switch lever etc.
To further improve the safety of the control and the apparatus, in a set of embodiments the control is arranged so that the switch arrangement cannot be re-closed once the switch lever has been acted on by an overheat temperature sensitive actuator before a further predetermined temperature condition is reached. Thus once overheating has been detected, the temperature-sensitive actuator has to cool down to a certain temperature before operation of the apparatus is possible again. This protects the apparatus and/or the heating element from being re-energized too soon after overheating has been detected. Furthermore it is not possible for this safety function to be overridden by a user attempting to re-energize the apparatus. The apparatus and/or the heating element therefore has to cool down to a safe temperature before a repeat operation is possible.
In contrast, in a set of embodiments the control is arranged so that the switch arrangement can be reclosed manually—e.g. with an ‘on’ button—after the switch lever has been acted on by a boiling temperature sensitive actuator. This allows for liquid to be re-boiled shortly after boiling has previously been reached.
The moveable contact member could contact the fixed contact member in any direction—e.g. vertically or horizontally (i.e. a side-swipe action), the switch lever could therefore be arranged to move the moveable contact member in one of these particular directions. This may require the switch lever to have a particular shape, depending on the direction in which the end remote from the moveable contact member is moved.
The cordless base connector is preferably of the type which allows electrical connection to be made substantially irrespective of the relative angular orientation between it and the control—i.e. a so-called 360° connector. However in some embodiments the connector may not allow full 360° relative to the orientation of the control, but while still allowing electrical connection to be made substantially irrespective of this orientation, e.g. through a range of 345° or greater.
In a control in accordance with any aspect of the invention, a single switch arrangement of the type described could be provided, e.g. for switching the live side of the power supply only, with the other electrical contacts, e.g. for connection to the neutral and earth terminals (where provided), connected differently, e.g. hard wired. However in a set of embodiments the control comprises at least two such switch arrangements, e.g. for switching the live and neutral poles.
Where two switch arrangements are provided, the resilient means providing the biasing force on the respective contacts could comprise a single spring. However, in a set of embodiments separate springs are provided. This makes it easier for the respective switching arrangements to be operated independently, for example by being acted upon by independent temperature-sensitive actuators, e.g. bimetals.
The moveable contact member preferably comprises a material which is a good electrical conductor, e.g. copper. In a set of embodiments the moveable contact member comprises a silver coating or tip. Silver is chosen for its high electrical conductivity which reduces the tendency for deterioration of the contact surface through oxidation, but it is only provided as a coating or at the tip, i.e. where the physical contact with the fixed contact member is made, in order to reduce the cost of the contact while maximizing the effectiveness of the silver. It is similarly preferred that the contact surface of the fixed contact member comprises silver. However the Applicant has found that using silver on one side only, i.e. on either the moveable contact member or the fixed contact member, when the opposing side is copper, provides an adequate performance. This is because the plasma generated during arcing, as the contacts open, causes the silver on the one contact to melt, resulting in a layer of silver being deposited on the opposite contact.
In the set of embodiments in which two moveable contact members are provided, e.g. for switching separate poles, it may be that only one of them comprises a silver coating or tip, preferably that used to switch the live (primary) pole. The control can advantageously be arranged such that in normal use the contact member with the silver contact surface preferentially makes or breaks contact first. This maximizes the benefit of the small amount of silver whilst allowing other contact pairs to be unsilvered or less silvered.
The resilient means for biasing the switch lever could comprise a coil spring or a leaf spring, but in a set of embodiments the resilient means comprises a wire spring, i.e. a length of wire displaced along its length from its natural position to exert a force in the direction opposite to its displacement. A wire spring is simple and cheap to manufacture and can be chosen from a material which has all the desired properties, e.g. high strength, high elastic limit, low Young's modulus and high cycle fatigue. For example, the wire spring could comprise steel, as this possesses all the desired properties.
As will be appreciated, the properties desired from the spring are not necessarily compatible with those desired from the moveable contact member or the lever carrying it, particularly not from a material which is cheap and easy to obtain. Furthermore, it is not necessary to require the spring to have any electrical conductivity, i.e. it could be formed from an insulator, as it is not required to carry any current. Likewise, it is not necessary to require the moveable contact member to have any specific mechanical properties, e.g. strength, that are necessary for the spring. Therefore the contact member can be formed from a relatively weak material, e.g. one which is ductile to facilitate forming it into the required shape; it can be chosen simply for its electrical conduction properties.
In a set of embodiments the switch lever is resiliently biased against a surface on which it pivots. This simplifies design and construction of a lever arrangement from relatively inexpensive plastics. The resilient bias could be provided by independent spring means, but in a set of preferred embodiments it is provided by the same resilient means biasing the moveable contact member towards the fixed contact member.
Where, as is preferred, the liquid heating apparatus is of the so-called cordless type, comprising a cordless base for connection to the mains supply and an appliance proper for mating therewith, the control of the invention could be provided in the cordless base, but in a set of preferred embodiments the control is mainly in the appliance proper—e.g. electrically connected to an electric heating element. However, as mentioned above, the fixed contact member of the switch arrangement may be provided in the cordless base connector while its other components are provided in the appliance part. The electric heating element will typically be arranged in good thermal contact with the liquid to be heated in the apparatus. The electric heating element could comprise a sheathed heating element, e.g. immersed or mounted on the underside of a heater plate on the liquid heating apparatus, or a thick film heating element.
In a set of embodiments the control comprises a user-operated actuator arranged to move the moveable contact member away from the fixed contact member against the biasing force of the resilient means, e.g. an “off” button to break the electrical power circuit. Preferably the user-operated actuator acts on the moveable contact member associated with the live (primary) pole of the electrical circuit, where provided. In a set of embodiments the actuator acts directly on the switch lever. In a set of embodiments the control comprises a latching mechanism arranged to hold the moveable contact member away from the fixed contact member, i.e. when it is acted on by the user-operated actuator. This may be necessary because in some embodiments the resilient means to bias the moveable contact could be monostable, i.e. when the user-operated actuator is released, the moveable contact member would be biased back towards the fixed contact member. In general, providing a resilient means which is monostable allows a simpler actuating mechanism to be used either for the user-operated actuator or the temperature-sensitive actuators in combination with a latching mechanism described below as a further movement is no longer needed, e.g. as would be for a bistable or over-center mechanism. A further user-operated actuator, e.g. an “on” button, could be provided to release the moveable contact member from the latching mechanism. In one set of embodiments the “on” and “off” buttons could comprise a linking mechanism, e.g. so that only one of them can be actuated at any one time. In a set of embodiments, only an “on” button is provided with the user able to switch the apparatus off in another way—e.g. by momentarily lifting it from its base. This reduces the number of components and so increases reliability.
In the set of embodiments in which a cordless appliance comprising the control is provided, preferably the control comprises a mechanism arranged to move the moveable contact member away from the fixed contact member against the biasing force of the resilient means when the appliance is placed on the cordless base. This prevents the appliance being inadvertently re-energized when it is placed on the base after being lifted off, e.g. to pour heated liquid out of the appliance. It also provides a mechanism whereby the apparatus can be switched off without having to provide an “off” switch. The moveable contact member could latch into place in its position away from the fixed contact member when acted on by the mechanism, or the mechanism itself could be latched by the action of placing the appliance on the cordless base thus holding the moveable contact member away from the fixed contact member. In a set of embodiments the mechanism comprises a physical blocking member arranged so that when the moveable contact member is separated from the fixed contact member, the blocking member moves automatically to a blocking position in which it prevents the moveable contact member from making electrical contact with the fixed contact member.
In a set of possible embodiments the mechanism—e.g. the blocking member—is biased by resilient means, e.g. a wire spring, into the position in which it holds the moveable contact member away from the fixed contact member when the appliance is placed on the cordless base. The resilient means biasing the mechanism need not necessarily act directly against the resilient means biasing the moveable contact member; the mechanism could be biased by the resilient means into a position in which it acts on the moveable contact member such that when the appliance is placed on the cordless base the moveable contact member is moved away from the fixed contact member. In another set of embodiments the mechanism, e.g. the blocking member, moves under gravity.
In either case, the action of placing the appliance on the cordless base could therefore provide the force necessary to overcome the biasing force on the moveable contact member, with the moveable contact member being moved by the mechanism. In a set of embodiments the control comprises a user-operated actuator, e.g. an “on” switch arranged to disengage the mechanism. This acts to release the moveable contact member from its position where it is held open by the mechanism, allowing it to remake contact with the fixed contact member (although not necessarily forcing it do so—e.g. in the case of a thermally sensitive actuator acting on the switch not yet having reset).
In one set of embodiments the control comprises a substantially planar vertical mounting member on which the switch arrangement, e.g. the switch lever(s), and/or the resilient means are mounted. It will be appreciated that a substantially planar vertical mounting member provides a robust and rigid support for a control. Typically such controls are arranged to be mounted on the underside of a heater or diffuser plate of a liquid heating appliance. This plate will flex when the heater is energized, but a substantially planar mounting member arranged in the vertical direction, i.e. perpendicular to the heater or diffuser plate, will not be susceptible to movement in this direction. Therefore the control will be held in the same position throughout the heating cycle, allowing its components, particularly those which move, to be accurately located.
In a set of embodiments the control comprises one or more thermally sensitive actuators, e.g. bimetallic actuators, mounted on the mounting member. Typically a control comprises three thermally sensitive actuators: two overheat or boil dry sensors and one boil detection sensor. Using the mounting member to position the thermally sensitive actuators allows them to be accurately positioned, e.g. up against the heater, and/or the heater or diffuser plate of the liquid heating apparatus. For example, this allows a bimetallic actuator to be positioned so that it just touches the relevant part of the liquid heating apparatus, thereby enabling only a small area of the bimetallic actuator to contact, e.g. the heating element. As the thermally sensitive actuators are generally the most important components to accurately position on the control relative to the liquid heating apparatus, preferably the control comprises means, e.g. rivets or screws, to attach the control to the liquid heating appliance in close proximity to the thermally sensitive actuators. Therefore even if there is some distortion in the heater or diffuser plate of the liquid heating apparatus, the thermally sensitive actuators will be kept in the same relative position.
In one set of embodiments the mounting member is arranged to limit the distance of travel of at least one part of the thermally sensitive actuator, e.g. by means of a stop on the mounting member. Preferably the thermally sensitive actuator is arranged to be in contact with the mounting member. For example, if a thermally sensitive bimetallic actuator is provided, and is mounted on the mounting member by its central tongue, the mounting member could also limit the distance of travel of the edge of the bimetallic actuator. This would result in an increased distance of travel for the opposite edge of the bimetallic actuator as the constraint in movement of one edge of the actuator will tend to tilt the plane of the actuator somewhat and so amplify the movement of the opposite edge. As will be appreciated, this becomes important in an arrangement in which the thermally sensitive actuator acts directly on the switch lever or moveable contact member, i.e. the movement of the thermally sensitive actuator is not amplified by an intermediate leaf spring.
In one set of embodiments the control comprises a moveable contact member mounted on a switch lever, wherein the switch lever is pivotally mounted on the mounting member. Mounting the switch lever as well as the thermally sensitive actuator (which acts on the switch lever) on the mounting member provides a fixed relative position for these two components. Therefore even if the mounting member is moved when the liquid heating apparatus is in operation, e.g. by distortion of the heater plate, the switch lever does not move relative to the thermally sensitive actuator. This fixed positioning of these components independent of thermal movements of the base is beneficial as it allows a very small lost motion to be designed in between them which in turn allows as much of the movement of the actuator as possible to be translated into movement of the moveable contact member (via the switch lever) where there is a direct coupling between the two as in preferred embodiments of the invention.
Preferably the mounting member comprises an integral earth connection. Providing an integrated mount and earth connection made from the same material dispenses of the need to provide these as separate components and therefore increases the reliability of the control. Preferably the earth connection is annular to suit it for use with a substantially 360 degree cordless connector. However in some embodiments the connector may not allow full 360° relative to the orientation of the control, but while still allowing electrical connection to be made substantially irrespective of this orientation, e.g. through a range of 345° or greater.
It will be appreciated of course that this indicates that the substantially planar vertical mounting member could be part of a larger component which is not all planar.
As is mentioned above, the control is particularly well-suited for use with a cordless electrical appliance comprising a connector part of the 360°-type, that is, an appliance connector part that can be brought into engagement with a corresponding base connector provided by a power base unit regardless, or substantially regardless, of the relative angular orientation of the two parts. The cordless connector system may include two or three electrical terminals (e.g. live, neutral and optionally earth) for basic power connection, such as the Strix P72, or a larger number of terminals for additional electrical/data connections, such as the Strix P76. Examples of suitable cordless connector systems are described in the Applicant's published applications WO 95/08204 and WO 01/28294. In particular, the appliance connector part may be in the form of a male connector part comprising one or more annular terminals and the base connector may be in the form of a female connector part comprising one or more corresponding annular recesses.
In a typical cordless connector system there are two sets of silver-coated or silver-tipped contacts, one set of contacts provided between a control unit and the electrical terminals of the appliance connector part, and another set of contacts in the base connector part. As is discussed above, one of the objects of the present invention is to make the electrical connections in an appliance more robust and one way of achieving this, together with a material saving, is to reduce the number of contacts by providing a moveable contact member mounted on a switch lever to make electrical contact with a fixed contact member. When the control is part of a cordless appliance then this object also applies to the contacts in the base connector. One or more electrical contacts in the base connector may be mounted on leaf springs which are themselves connected to the power supply for the base unit, as is conventional (i.e. contacts other than the fixed contact member recited hereinabove). Mains electrical power is usually supplied by a cable e.g. led to the base connector by a cable guide in the power base unit.
However the Applicant has recognized a benefit in reducing the number of separate parts comprised in the power base unit and in integrating the base connector with its power supply cable. Thus according to a preferred set of embodiments the connector part comprises a sub-assembly comprising a mains power supply cable and at least one electrical contact, in which the electrical contact is permanently attached to a respective conductor in the mains power supply cable. An integrated sub-assembly comprising the electrical contact(s) permanently attached to the conductor(s) of a mains power supply cable can ensure that the contact(s), or at least a contact surface thereof, have an appropriate current rating regardless of the design of the rest of the connector or further manufacturing steps involved. As is mentioned above, the electrical contact(s) may provide electrical contact for the live and/or neutral poles of the power supply.
It will be appreciated that such a sub-assembly provides a new approach to making cordless connectors for mains electrical power supply. Previously the cordless connector, or at least the base connector part thereof, would be manufactured as a generic item that has its contacts removably attached, e.g. via “Faston” tab connectors, to a mains power supply cable rated for the expected current when used in a particular country. However, this approach requires the electrical contacts in the connector to be over-designed for many applications just so that they can safely switch high currents e.g. in appliances connected to the Japanese or US mains power supply. By integrating the mains power supply cable with the electrical contact(s) in a sub-assembly before assembling the connector part, the materials used for the electrical contact(s), or at least a contact surface thereof, can be matched to the current to be supplied by the mains power cable. To take advantage of the contact(s) being matched to a mains power supply cable, it is preferable that the thickness of a silver layer at least on the contact surface of the live electrical contact member is selected depending on the current rating of the power supply cable.
In one set of embodiments each electrical contact comprises an integral contact member having a contact surface and a body that is permanently attached to a conductor in the power supply cable. The attachment point may, for example, be at one end of the contact member distal from the contact surface. This can make it easier to separate the point of attachment from the point of electrical connection. Preferably the electrical contacts in the connector part are end-point contacts—i.e. providing an end-point contact surface adapted to engage with a corresponding contact on a distal end of a conductor rather than an extended surface contact such as an annular ring. Preferably the connector part comprises end-point contacts for both the live and neutral poles.
The electrical contact(s) may be permanently attached to respective conductor(s) in the power supply cable by any suitable means. In one set of embodiments the contacts may, for example, be welded, soldered, or brazed to the conductor(s). The contact(s) may even be adhesively attached to the conductors. In a preferred set of embodiments the contact(s), or contact members thereof, are permanently attached to the conductor(s) by mechanical deformation e.g. by crimping to form a gas-tight connection. Such a permanent connection may then be protected by an integral molding e.g. a plastics overmolding that covers the point of attachment. The overmolding can help to avoid oxidation at the attachment point when a copper member is attached to a copper conductor. In one set of embodiments the attachment point of the electrical contact(s) may be integrally molded with the power supply cable, for example with the plastic sheathing of the cable being molded around at least part of the conductor(s) and a part of the contact(s), or contact member(s), while the contact surfaces are left exposed. Such a molded sub-assembly may then be incorporated into a connector part that provides a housing for the contact(s), preferably preventing direct access to the contact surfaces. The housing may be molded from different plastics. However, in at least some embodiments the power supply cable may be integrally molded with a connector part (or portion thereof) so that the integral molding comprises a single plastics part that houses the contact(s).
It will be appreciated that integrally molding the power supply cable with the base connector, or at least a main part of that connector, can make the electrical connections more robust with the protection provided by the molded plastic part. Assembly of the power base unit may also be simplified as the single plastic molded part can be fitted to the base unit without the need for any separate fasteners for the power supply cable. The integrally molded part can conveniently be snap fitted to the base unit in a single assembly step. Any further components of the base connector, such as a cover or the like, may also be attached to the main molded part, e.g. with a snap-fit. A cover can provide a safety feature, preventing access to the (exposed) live parts.
When the base connector is integrally molded with the power supply cable it may be possible for the electrical contact(s) to connect to the conductor(s) in the power supply cable via conventional leaf springs, but this would likely complicate the molding as it would have to be formed with internal spaces to accommodate the movement of the contact member(s) when mounted on leaf springs. Therefore, it is further preferred that the contact(s), or rather the body of the contact members, have a static connection with the conductor(s) in the power supply. Such a static connection may be encapsulated by the plastic molding without interfering with the operation of the connector, i.e. switching current at the contact surface, and with the benefit of making the connection more durable. Such static or fixed contact(s) may be ideally suited for engagement with the electrical terminals of an appliance that comprises a moveable contact member mounted on a switch lever, as described above. To reduce the number of parts and increase reliability, preferably the contact(s), or rather the body of the contact members, are directly connected with the conductor(s) in the power supply. The integrity of the electrical connections in the base unit are thereby further improved.
In one set of embodiments the live and neutral contacts may comprise a static connection, while the earth contact comprises a leaf spring. Preferably, at least the live and neutral contacts are housed by the integrally molded part. Although the earth contact could also be within the integrally molded housing, in a set of embodiments the earth contact projects from the integrally molded housing. The projecting earth contact may be connected by a leaf spring without complicating the molding operation, because the outside periphery of the housing can be accessible for shut-off features in the mold tool.
Another aspect of the invention provides a control for a liquid heating apparatus, comprising a switch arrangement for making or breaking an electrical circuit for supplying power to the liquid heating apparatus, the switch arrangement comprising: a fixed contact member, a moveable contact member mounted on a switch lever; and resilient means, separate from and acting on the switch lever, so as to bias the moveable contact member into electrical contact with the fixed contact member.
Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
a is a partial perspective view of the main chassis of the control seen in
a is a close-up of the connector part seen in
b is a cross-sectional view taken through the close-up of
a is a partial cross-sectional view of the configuration seen in
a shows the configuration of the control before it is turned on,
a shows the configuration of the control after operation of a primary actuator;
a is a partial perspective view of the latch mechanism in the control,
There is seen in
As can be better seen in
From
Each of the switch levers 10, 12 is acted on by a respective wire spring 11, 13 that biases the respective moveable contact member 6, 8 downwards, i.e. towards the corresponding fixed contacts in the base electrical connector part 4, 102. The live contact member 6 comprises a silver contact surface for contact with the silver contact surface on the live contact 112 in the base electrical connector part 4, 102. The neutral contact member 8 is gently curved for passing through an annular channel in the base electrical connector part 4, 102 and making contact with a ring shaped neutral contact 114 therein.
Referring now to
The spine 24 of the vertical mount plate 18 includes three tabs 28, 30, 32 onto which respective thermally sensitive snap-acting bimetallic actuators 33, 37, 41 are mounted. The bimetallic actuators 33, 37, 41 are shown in their low temperature configurations, i.e. each is designed to snap into a reverse curvature configuration (relative to that shown) above a certain temperature. The two bimetallic actuators 33, 37 on the upper side of the vertical mount plate 18, i.e. an outer face of the control, are arranged to be in thermal contact with the heater plate and/or the heating element (not shown) of the liquid heating apparatus when the control is mounted to the underside of the heater plate, and to act as overheat sensors. The bimetallic actuator 41 on the lower side of the vertical mount plate 18 is arranged to be in fluid communication with the end of a steam tube (not shown) from the liquid heating apparatus, and acts as a boiling sensor. The bimetallic actuators 33, 37, 41 are each mounted on the vertical mount plate 18 through holes in their respective central tongues 34, 38, 42, but they also contact the vertical mount plate at their bases 35, 39, 43 such that when they snap at their actuating temperature, only the hoop 36, 40, 44 of the actuator moves.
The vertical mount plate 18 also provides a structure on which a plastic chassis 46 is mounted (see e.g.
The control 1 further comprises an “on” button 48 and an “off” button 50. As can be seen in
As is seen in
When the reset lever 56 is in its biased position, a sideways projection on the tab 64 at the distal end 62 fits underneath a lip 66 of the live switch lever 10 (see
Also provided on the live switch lever 10, rotatably attached to the beam 47 at its pivot point, is a steam override lever 55 which acts on the lower bimetallic actuator 41. The other end of the steam override lever 55 engages with a notch 53 on the arm of the “on” button which enables the steam bimetallic actuator 41 to be overridden or reset (see
There is seen in
The components making up the base connector part 102 will be described with reference to
It can be seen from
Operation of this control will now be described with reference to
The electrical base connector part 4, 102 is mounted in a cordless connector base 104, one example of which is described above with reference to
Therefore, when the upper part 2 of the control 1 is placed on top of the electrical base connector part 4, 102, the tab 64 on the reset lever 56 comes into contact with the plastic molding of the base connector part 4, 102, lifting upwards the distal end 62 and the live switch lever 10. The neutral contact member 8 comes into contact with the fixed neutral contact 114 in the base connector part 4, 102, but the circuit is not completed as the live contact member 6 has been lifted clear of the fixed live contact 112 in the base connector part 4, 102, and so the heating element in the apparatus is not energized. Also, the earth connector ring 26 comes into contact with the earth contact 116 in the base connector part 4, 102.
To energize the heating element in the apparatus the “on” button 48 is pushed in. The “on” button's distal end 70 pushes against the wedge shaped projection 68 on the reset lever 56 (see
Once the heating element has been energized, liquid in the apparatus is heated to boiling, though if for any reason heating is to be stopped, the off button 50 can be depressed. Depressing the “off” button causes the spigot 54 on the live switch lever to be moved downwards by means of the wedge 52 on the “off” button 50. This lifts the moveable neutral contact member 8 away from the fixed neutral contact 114, and breaks the electrical circuit thus de-energizing the heating element. Otherwise, heating proceeds to boiling, which produces steam in the apparatus. The increasing pressure of the increasing volume of steam forces the steam into the steam tube and down to impinge on the steam bimetal 41. The snap acting temperature of the bimetal 41 does not need to be arranged at 100° C., i.e. boiling, but can be lower, e.g. 75° C., as it is merely the presence of steam which indicates boiling in the apparatus. This enables reliable boil detection. When the steam bimetal 41 snaps, because the base 43 of the bimetal 41 is touching the vertical mount plate 18, all the movement of the bimetal 41 occurs in the hoop section 44. The steam bimetal 41 pushes down on the hook shaped tab 45 on the live switch lever 10, thus pivoting the live switch lever 10 which lifts the moveable live contact member 6 clear of the fixed live contact 112 in the base connector part 4, 102. This breaks the circuit and de-energizes the heating element. If the liquid is desired to be boiled shortly after the heating element has been de-energized, the “on” button 48 can be depressed which rotates the steam override lever 55 via the notch 53 on the arm of the “on” button 48. The steam override lever 55 pushes the steam bimetallic actuator 41 away from the hook shaped tab 45 on the live switch lever 10 and thus allows the live contact 6 to remake, energizing the heating element again.
In the event of overheating of the heating element, e.g. if the apparatus is turned on without any water in the vessel, the overheat bimetallic actuator 33, snaps to act on the live switch lever 10, thus moving the moveable live contact member 6 away from the fixed live contact 112 in the connector base part 4, 102. The live bimetal 33 will snap first as this is in closer thermal contact with the sheathed heating element as opposed to the neutral bimetal 37 which is positioned between the cold tails of the sheathed heating element. If, for some reason the live overheat bimetal 33 does not snap, the neutral bimetal 37 will subsequently snap, lifting the neutral contact lever 12 and thus the moveable neutral contact member 8 away from the fixed neutral contact 114 in the connector base part 4, 102 and de-energizing the heating element.
As for the steam bimetal 41, when the live and neutral overheat bimetals 33, 37 snap, because their bases 35, 39 are touching the vertical mount plate 18, all the movement of the bimetals 33, 37 occurs in the respective hoop section 36, 40. Again, the heating element is de-energized, which in this situation prevents any damage to the heating element and/or the apparatus. With the live switch lever 10 having been lifted up by the overheat bimetal 33, the reset lever 56, which is biased towards the center of the control 1 by its wire spring 60, moves underneath the live switch lever 10, preventing the moveable live contact 6 from remaking the circuit. Although the “on” button 48 can be used to release the live switch lever 10, the lever will not move back down to remake the circuit until the live overheat bimetal 33 cools and resets. This is different to the operation of the steam bimetallic actuator 41 which can be reset using the steam override lever 55. For safety reasons no override mechanism is provided for the overheat bimetallic actuators 33, 37.
There is seen in
There is seen in
In
Each of the contact members 206, 208 is carried by a respective moveable switch lever 210, 212. The two switch levers 210, 212 are each pivotally mounted on the main chassis molding 246 of the control 200. Furthermore, the lever 210 carrying the live contact member 206 and the lever 212 carrying the neutral contact member 208 are each moveable independently of the other in normal use. Also pivotally mounted on the control chassis 246 is an on/off slider 252 arranged to interact with the live contact lever 210. Movement of the on/off slider 252 is actuated by a rocking pivot member 254 which is itself moved by the on/off switch 250.
From the view in
As can be better seen from the exploded view in
As is best seen from
Similar to the first embodiment described above, the upper surface of the spine 224 of the vertical mount plate 218 provides locations for the overheat actuators 233, 237 (seen in
In
As will be understood with reference to
The rating stops 229, 231 are designed to be slightly ‘proud’ of the nominal position achieved when the control 200 is fully engaged with a heater in order to prevent excessive force being applied to the actuators 233, 237 located on the steps 229a, 231a. Such an arrangement enables the actuators 233, 237 to be held in precise alignment with the heater surface without any risk of imposing stresses which could affect their thermal switching or snap action point. If the actuators 233, 237 were to be pressed against the heater surface and overly stressed then their operating temperature would be affected. The rating stops 229, 231 prevent this from happening.
In this embodiment a third thermally sensitive snap acting bimetallic actuator 241 is mounted vertically at one end of the control chassis 246, as is seen most clearly in
In the exploded view of
Returning to the control assembly shown in
Although the live and neutral switch levers 210, 212 do move independently of one another in normal use, they are arranged in the control 200 so as to ensure that the live contact pin 206 always makes or breaks the electrical circuit before the neutral contact ring 208 is moved in or out of electrical contact. This is achieved by having the live contact pin 206 at a higher position relative to the control chassis 246, and hence relative to any apparatus and its heater to which the control 200 is mounted, as compared to the neutral contact ring 208. There is also a relationship between the two switch levers 210, 212 by virtue of a latching mechanism seen in detail in
As can be seen in
It can also be seen, especially from
The wire spring 211 tends to bias the live lever 210 with its contact pin 206 into a downwards position, i.e. into contact with the corresponding contact 112′ in the base connector part 204. However, downwards movement of the live pin 206 can be blocked by a blocking member 260 that is seen to be pivotably mounted towards the front end of the live lever 210. The blocking member 260 is sized and shaped so as to interact with one or more upper surfaces of the base connector part 204 when the upper part of the control 202 is placed thereon. The blocking member 260 can be swung out of a blocking position by a push member 262 provided at the distal end of the on/off slider 252. Forwards movement of the on/off slider 252, for example when the on/off switch 250 is flicked down, can press the push member 262 against the blocking member 260. However, forwards movement of the on/off slider 252 is limited by another wire spring 264 (seen in
a-20b show details of another base connector part 204 that could be used with the base stand 104 seen in
It will be appreciated that the amount of material used for the integral molding 110′ may be minimized as it does not act to house the contacts 112′, 114′, 116 but only to protect the point of permanent attachment to the power cord 106. The housing 124′ can be molded as a separate piece. The integral molding 110′ is formed around the proximal end of the power cable 106 after the adjacent ends of the contact pins 112′, 114′ and earth spring 116 have been permanently attached to the ends of respective leads 120, 122, 118, for example by a mechanical deformation operation such as crimping. In some connectors only the live contact 112′ may have a silvered surface, if this is the only contact intended to make or break electrical connection. However the neutral contact 114′ may also have a silver coating.
Referring back to
As can be seen from
Operation of the control 200 will now be described with reference to
The detail in
a-23c show how the configuration of the control 200 changes when a user switches on the liquid heating apparatus using the on/off switch 250 (not shown) and its rocker 254 and then the apparatus is switched off, either manually or by operation of the steam sensor. In
The control 200 provides for automatic switch off upon detecting that liquid being heated in the apparatus has reached boiling. Steam delivered to the bimetallic actuator 241 causes it to reach its operating temperature. The snap action of the actuator 241 results in it pulling on the projection 255 to move the on/off slider 252 backwards so that its cam surface 256 engages against the follower 258 carried by the live switch lever 210, as is seen in
If a user decides to switch off the apparatus before boiling has been detected, upwards movement of the on/off switch 250 acts on the rocker 254 to pull the on/off lever backwards 252 and break the live connection in the same way. Even once the on/off slider 252 is returned to its neutral position by its centralizing spring 264, the blocking member 260 ensures that the live lever 210 is blocked in a raised position. Thus a user must manually turn on the control 200 again using the on/off switch 250. It is envisaged that the on/off switch 250 may not be bi-stable as described herein, but may instead function only to switch on the control 200 while a user can manually switch off the apparatus simply by separating it from the cordless base connector part 204.
If the apparatus is lifted during operation so that the upper connector part 202 is lifted away from the base connector part 204, the electrical circuit is broken between the live contact pin 206 and its associated contact member 112′ before the neutral ring 208 breaks its contact. This means that only the live contact members 206, 112′ may be provided with a layer of silver, or with a relatively thick layer of silver. Furthermore, it may only be necessary to provide one of the live contact members, such as the pin 206, with a layer of silver as the plasma generated during arcing causes the silver to melt and deposit a layer of silver on the surface of the other contact member 112′ in use. During normal use of the appliance i.e. in the absence of an overheat position, the neutral switch lever 212 does not move relative to the chassis molding 246 of the control 200. The neutral contacts are therefore always made/broken, respectively, after/before the live contacts.
The safety back-up operation of the bimetallic actuators 233, 237 will now be described with reference to
b shows the configuration of the control 200 in the event that overheating takes place very rapidly and/or the apparatus continues to heat up even after operation of the primary actuator 233. In this situation the secondary actuator 237 may independently operate as well, albeit upon sensing a higher temperature, and its hoop 240 can be seen to have moved downwardly to contact the protrusion 225 on the neutral switch lever 212. The lever 212 is pivoted against the force of the spring 213 so that the neutral contact ring 208 breaks electrical contact with the corresponding pin 114′ in the base connector part 204. By setting the two overheat sensors 233, 237 to operate at different predetermined temperature conditions it can be ensured that the neutral contacts (which may not be provided with a silver coating) are broken after the live contacts and re-made before the live contacts.
In a fault situation the secondary bimetallic actuator 237 may operate before the primary bimetallic actuator 233, for example due to a failure of the primary actuator 233. In an abnormal overheat condition the latch mechanism that links the two switch levers 210, 212 comes into effect and the control 200 has a configuration as seen in
In an abnormal situation where the primary actuator 233 fails to operate and only the secondary actuator 237 operates, the live lever 210 is down when the neutral lever 212 is raised, and the latch member 270 that is pivotally connected to the neutral switch lever 212 swings down under gravity and engages the keeper 268 on the live lever 210, as is seen in
There is shown in
The upper part of the control is mounted to a heater in the cordless liquid heating vessel 101. It was described above that the upper part of the control 202 includes a datum point 266 on a lower surface thereof which is arranged to bear on the base connector part 204 when the two parts are engaged, i.e. when the heating vessel 101 is placed on the power base unit 100 to receive electrical power from the mains. So that the cordless liquid heating vessel 101 is not unstable when placed on the power base 100, its lower housing 101a has three resilient feet 103 arranged to bear on the base unit 100 in addition to the datum point 266, thereby providing a tripod arrangement to support the vessel 101. The feet 103 comprise portions of the lower housing 101a which have been relieved from the rest of the surface to provide sprung cantilevered tongues. Of course, in other embodiments the resilient feet 103 may be replaced by resilient support portions provided on an upper surface of the power base unit 100 instead.
It will be appreciated that the control arrangements described herein may find use in many different kinds of liquid heating apparatus, including electric kettles and water boilers, hot water dispensers, beverage makers and steam irons, of both the corded and cordless varieties. Where reference is made to a sheathed heating element e.g. in an underfloor heater, this could equally apply to a heating track provided by a thick film heating element, as in both cases the sheathed heating element or thick film heating track may be mounted to a heater and/or diffuser plate to provide a planar heater.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1113780.9 | Aug 2011 | GB | national |
| 1203954.1 | Mar 2012 | GB | national |
This application is entitled to the benefit of, and incorporates by reference essential subject matter disclosed in PCT Application No. PCT/GB2012/051958 filed on Aug. 10, 2012, which claims priority to GB1113780.9 filed Aug. 10, 2011 and GB1203954.1 filed Mar. 6, 2012.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2012/051958 | 8/10/2012 | WO | 00 | 6/6/2014 |
