CA1265831A - Thermally-sensitive controls - Google Patents
Thermally-sensitive controlsInfo
- Publication number
- CA1265831A CA1265831A CA000519701A CA519701A CA1265831A CA 1265831 A CA1265831 A CA 1265831A CA 000519701 A CA000519701 A CA 000519701A CA 519701 A CA519701 A CA 519701A CA 1265831 A CA1265831 A CA 1265831A
- Authority
- CA
- Canada
- Prior art keywords
- control
- spring
- thermally
- heater
- sensitive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H37/00—Thermally-actuated switches
- H01H37/002—Thermally-actuated switches combined with protective means
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H37/00—Thermally-actuated switches
- H01H37/74—Switches in which only the opening movement or only the closing movement of a contact is effected by heating or cooling
- H01H37/76—Contact member actuated by melting of fusible material, actuated due to burning of combustible material or due to explosion of explosive material
Landscapes
- Cookers (AREA)
- Thermally Actuated Switches (AREA)
- Control Of Resistance Heating (AREA)
- Control Of Temperature (AREA)
Abstract
ABSTRACT
Thermally-sensitive controls A thermally sensitive control 1 for an electric heater 2 comprises back-up protection means in the form of a pre-loaded spring mechanism comprising an actuating spring 25 which is held in normal use of the control in a pretensioned condition by retaining means in the form of push rod 27.
The push rod 27 is adapted to soften and deform in the event of serious overheating of the heater consequent upon failure of a primary protecter switch means of the control, whereby the spring 25 is released and moves an operating member 30 into engagement with a set switch contacts 15 to open the contacts and disable the heater.
Thermally-sensitive controls A thermally sensitive control 1 for an electric heater 2 comprises back-up protection means in the form of a pre-loaded spring mechanism comprising an actuating spring 25 which is held in normal use of the control in a pretensioned condition by retaining means in the form of push rod 27.
The push rod 27 is adapted to soften and deform in the event of serious overheating of the heater consequent upon failure of a primary protecter switch means of the control, whereby the spring 25 is released and moves an operating member 30 into engagement with a set switch contacts 15 to open the contacts and disable the heater.
Description
.5~3~
Thermally-Sensitive Controls This inven~ion relates to thermally-sellsitive controls for electric heaters of containers s-lch as electric kettles, ~ugs, urns, pans, coffee perco-lators, laboratory equipment and the like (hereinafter referred to as "containers of the kind described'l).
The electric heaters of such con~ainers are typica~ly either immersion heaters, or similarly constructed heaters mounted externally to the container in good thermal contact wi~h a wall thereof, for example by being brazed to the underside of the container base. Traditionally the heating elements of such heaters terminate in so-called "cold leads" by means of which electrical connections are made to the heater.
Thermally-sensitive controls for heaters of this t~rpe are well known which include electrical switch means operable to interrupt the power supply and thus deenergise the heater upon its element overheating, after for example having been switched on with insufficient liquid in the container to cover the element or having boiled dry. Such arrange-ments conventionally include a thermally responsive actuating means, typically a snap-acting bimetallic actuator, coupled mechanically to a set of breakable switch contacts wired in series with the element and operable to open the contacts upon the element overheating. Examples of such controls are descrîbed in British patent specifications Nos. 1,470,366 and 2,042,26g.
In such arrangements failure of the thermally responsive actuating means can represent a serious problem since if, for example, the container boils dry and the element overheats, the power supply ~5~
will not be automatically interrupted, and in the absence of manual intervention the element will become hotter and hotter until it eventually burns out. This not only leads to the expense of a replace-ment element but may also constitute a serioussafety hazard in the case o~ plastic containers or containers having plastic parts, since the over-heating can cause meltir.g and in the extreme burning of all or part of the container. The problem is of particular significance where the control is used with an appliance which is likely to be unattended, for example an automatic electric kettle or an early morning tea maker.
In an attemp~ to overcome this problem it has been proposed to provide back-up protection including means operable to interupt the power supply upon failure of the primary actuating means when the element overheats. One such arrangement is described in British patent specification No.
Thermally-Sensitive Controls This inven~ion relates to thermally-sellsitive controls for electric heaters of containers s-lch as electric kettles, ~ugs, urns, pans, coffee perco-lators, laboratory equipment and the like (hereinafter referred to as "containers of the kind described'l).
The electric heaters of such con~ainers are typica~ly either immersion heaters, or similarly constructed heaters mounted externally to the container in good thermal contact wi~h a wall thereof, for example by being brazed to the underside of the container base. Traditionally the heating elements of such heaters terminate in so-called "cold leads" by means of which electrical connections are made to the heater.
Thermally-sensitive controls for heaters of this t~rpe are well known which include electrical switch means operable to interrupt the power supply and thus deenergise the heater upon its element overheating, after for example having been switched on with insufficient liquid in the container to cover the element or having boiled dry. Such arrange-ments conventionally include a thermally responsive actuating means, typically a snap-acting bimetallic actuator, coupled mechanically to a set of breakable switch contacts wired in series with the element and operable to open the contacts upon the element overheating. Examples of such controls are descrîbed in British patent specifications Nos. 1,470,366 and 2,042,26g.
In such arrangements failure of the thermally responsive actuating means can represent a serious problem since if, for example, the container boils dry and the element overheats, the power supply ~5~
will not be automatically interrupted, and in the absence of manual intervention the element will become hotter and hotter until it eventually burns out. This not only leads to the expense of a replace-ment element but may also constitute a serioussafety hazard in the case o~ plastic containers or containers having plastic parts, since the over-heating can cause meltir.g and in the extreme burning of all or part of the container. The problem is of particular significance where the control is used with an appliance which is likely to be unattended, for example an automatic electric kettle or an early morning tea maker.
In an attemp~ to overcome this problem it has been proposed to provide back-up protection including means operable to interupt the power supply upon failure of the primary actuating means when the element overheats. One such arrangement is described in British patent specification No.
2,149,217, wherein back-up protection is provided by a further thermally responsive actuating means operable independently of the primary actuating means to open a set of switch contacts and thus deenergise the heater in the event of serious over-heating consequent upon failure of the primaryactuating means. In the arrangement described in British patent specification No. 2,149,217 the primary actuating means comprises a snap-acting bimetallic actuator whilst the back-up protection is provided by a slow acting creep bimetal, although it has also been proposed to include two snap-acting bimetallic actuators coupled to respective sets of switch contacts and calibrated to provide primary and back-up protection.
whilst in many applications the use of a thermally responsive actuating means such as a bimetallic actuator coupled to a suitable switch ~2~5~
means provides adequate back-up protection, in certain circumstances, particularly in the case of high wat~ge density heaters, experience has shown that reliable operation may not be achieved.
For example, problems can be caused by the effects of the ~over-shoot" heating which results from the residual heat in the element after the heater is deenergised. Such heating can cause melting and deformation of plastic parts of the control and this in turn can render the known type of back-up protection means ineffective, and in certain circumstances a secondary bimetallic actuator may operate initially to open the swi~ch contacts but shortly thereafter distortion of the control consequent upon the over-shoot heating is such that the contacts reclose. Under such circumstances current is thus allowed to flow once more to the element and this clearly represents a serious hazard.
An alternative approach to providing back-up protection is ~he provision of an electricalfuse wired in series with the element. Whilst a suitably callibrated fuse can provide adequate protection and avoid problems discussed above concerning possible re-closing of switch contacts, the provision of a fusable link can undesirably increase manufacturing costs.
Viewed ~rom one aspect the invention provides a thermally-sensitive control for an electric heater of a container of the kind described, said control including a thermally-sensitive actuating means arrange~ in use in good thermal contact with a part of the element and coupled to a set of switch contacts of electrical switch means of the control so that the actuating means is operable to open the contacts and deenergise the heater upon over heatinq of the element, wherein back-up protection for the control is provided by a pre-loaded spring
whilst in many applications the use of a thermally responsive actuating means such as a bimetallic actuator coupled to a suitable switch ~2~5~
means provides adequate back-up protection, in certain circumstances, particularly in the case of high wat~ge density heaters, experience has shown that reliable operation may not be achieved.
For example, problems can be caused by the effects of the ~over-shoot" heating which results from the residual heat in the element after the heater is deenergised. Such heating can cause melting and deformation of plastic parts of the control and this in turn can render the known type of back-up protection means ineffective, and in certain circumstances a secondary bimetallic actuator may operate initially to open the swi~ch contacts but shortly thereafter distortion of the control consequent upon the over-shoot heating is such that the contacts reclose. Under such circumstances current is thus allowed to flow once more to the element and this clearly represents a serious hazard.
An alternative approach to providing back-up protection is ~he provision of an electricalfuse wired in series with the element. Whilst a suitably callibrated fuse can provide adequate protection and avoid problems discussed above concerning possible re-closing of switch contacts, the provision of a fusable link can undesirably increase manufacturing costs.
Viewed ~rom one aspect the invention provides a thermally-sensitive control for an electric heater of a container of the kind described, said control including a thermally-sensitive actuating means arrange~ in use in good thermal contact with a part of the element and coupled to a set of switch contacts of electrical switch means of the control so that the actuating means is operable to open the contacts and deenergise the heater upon over heatinq of the element, wherein back-up protection for the control is provided by a pre-loaded spring
3'~
mechanism associated with the same or a further set of swi~ch contacts of the control and comprising an actuating sprin~ which in normal use of the control is held in a pretensioned condition by a retaining means and an opera~ing member coupled ~o the spring, said re~aining means being adapted and arranged ~o release the spring in the event of serious over-heating of the control consequent upon failure of said thermally-sensitive.actuating means, whereupon the operating member is moved under the force of the spring and co-operates with the switch contacts so as ~o open the contacts and deener~ise the heater.
The provision in accordance with the invention of a pre-loaded spri.ng mechanism adap~ed and arranged to be released in the event of serious over-heating consequent upon failure of the actuating means providing primary protection is advantageous to the extent that reliable operation may be achieved despite deformation of plastic parts of the control due ~o over-shoot heating. Thus, a spring loaded mechanism can provide a stronger, more positive action for opening the contacts than is possible with bimetallic actuators used in the prior art proposals, and the possibility in extreme conditions of the contacts reclosing may be avoi~ed~
In the design of thermally-sensitive controls of this type there are generally size constraints or the various components having regard to the desired overall compactness of the control~ and a preloaded sprîng mechanism is also advantageous in this respect since such a mechanism can be designed relatively com~actly. Moreover~ such a spring mechanism can be incorporated in a control without substantially increasing the manufacturing costs.
The preloaded spring mechanism make take any convenient form, and it could for example comprise a tension spring normally held in an extended condition by the retaining means and adapted to be released in the event of serious over-heating so that the switch contacts are opened. However, since it is desirable to provide a relatively strong biasing force generally within relatively narrow size constraints the preferred preloa~ed spring mechanism comprises a compression spring which in normal use is held in a compressed state by the retaining means.
The form of the retaining means may vary depending on the general configuration of the control and on the nature of the actuating spring provided.
For example, however, it is en~isaged that such means ma~ include a retaining element fixedly secured lS to or moulded integrally with a body portion of the control which is adapted to mount the spring, the element being formed of an appropriate material and being so arranged as to deform, melt or break so as to release the spring when hea~ing of the control has reached a predetermined level consequent upon ~ailure o~ the primary protector. In the case o~ a compression spring, such may be mounted during assembly of the control within a suitable recess in the body portion and held under tension therein by means of the retaining element located at one end of the recess from which end the spring thus projects when released upon deformation of the retaining element.
In a preferred embodiment, however, the retaining menas comprises a displaceable means cou~led to or carried by the spring and arranged to co-operate with part of an external element defining the mounting location for the control so as to be displaced in such a way as to pre-load the ac~ua~ing spring when the control is secured in place. Thus, the retaining element is resiliently urged bv the actuating spring against part of the mounting location for ~2~
the control, and such part is arranged in suitable thermal contact with the element so that upon serious over-heating consequent upon failure of the primary protector the end of the retaining element remote S from the sprin~ melts or deforms sufficiently to release the spring mechanism and open the contacts.
In a particularly preferred such embodiment where the spring mechanism includes a compression spring, ~he retaining elemen~ may conveniently comprise a slidable push rod which at one end is coupled to the spring and which at the other end pro~ects externally of the control for engagement with part of the mounting location therefor.
~he mounting location for the control will vary depending on the nature of the heater and the type of container. For example, the control may be adap~ed for use with an immersion heater having a hea~ing element carried by a head which is securable in a water tigh~ manner in or adjacent an opening in the container wall. In such an embodiment, the heater head may define the mounting location for the control, and in the arrangement discusse~ above wherein the retaining element comprises a slidable push rod, the push rod may convenien~ly be arranged for engagement with part of the head when the control is mounted thereto. Thus, the push rod an~ spring mechanism are advantageously arranged so that upon mounting of the control to the heater head the push rod engages the head and is displaced axiall~ so as to compress and pre-load the spring. In the even~ of failure of the primary protector, when the head reaches a certain temperature the end of the push rod softens sufficiently to be distorted un~er the force o~ the spring which is thus release~ to open the contacts.
The operating member which is adapted to be moved under the force of the spring into engagement ~ 3~
with the contacts may take any convenient form, and in a preferred embodiment where the spring mechanism comprises a compression spring such member make conveniently comprise an arm which extends laterally from one end of the spring~ In the case of a coil spring, such arm may conveniently ~e formed integrally therewith. The manner in which the operating member co-operates wi~h the contacts of such a control may vary depending on the configuration o~ the swi~ch means. Typically however, the switch contacts include interengaging contact members, at least one of which is carried by a resilient conducting strip or leaf spring 50 as to be displaceable away from the other contact member. In such an arrangement, the operating member may conveniently be arranged to engage the leaf spring carrying the movable contact member.
The general configuration of the switch means of the control may take any convenient form, and ~0 the pre-loaded sprin~ mechanism may be associatefl either with the switch con~acts which are adapted to be opened in response to op~ration of the thermally-responsive actuating means, or alternatively the control may comprise a further set of contacts arranged to be acted on by the spring mechanism.
In one embodiment, the control additionally comprises means whereby the heater is disabled upon boiling of li~uid within an associated container, such means including a further thermally-responsive actuating means exposed to steam or vapour emitting from the container and coupled to a set of switch contacts via an over centre spring mechanism.
In such an embodiment, the Pre-loaded spring mechanism can alternatively be associated with the contacts formins part of the steam sensitive switch mechanism.
The primary thermally-responsive actuatinq means and, if provided, the actuating means for .
~ 3~
the steam sensitive switch mechanism, may both comprise snap actln~ bimetallic actuators of any convenient form, for example a stressed sheet of bimetal having a generally domed configuration and a central tounge such as that described in British patent 1,542,257. The control may be fabri-cated from the suitable thermoplastics material, and in a preferred embodiment wherein the retaining element comprises a push rod which is arranged ~o be engaged and axially displaced by ~he heater head, the body part of the con~rol which confronts the head and moun~s the push rod may if necessary be formed a material having a higher heat resistance than other plastic parts of the control and than the push rod itself. This avoids the possibility of this body portion being distorted in the event of serious overheating before releas~ of the spring mechanism in such a way as to impair the movement of the push rod.
An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:
Figure 1 is a partlY schematic vertical cross-sectional illustrating a thermally-sensit;ve control secured to the head o~ an immersion heater; and Fi~ures 2a and 2b are respectively diagrammatic cross-sectional eleva~ional views illustrating in more detail a pre-loade~ spring mechanism.
Referring firstly to Figure 1, a therma]ly-sensitive control 1 is mounted to the head 2 ofan electric immersion heater, the control and heater head being interconnected by means of bolts (not shown) and thus being clamped within an aperture formed in the wall 3 of an associated container 35 such as a kettle or hot water ~ug. ~he general configuration of the heater will be well known to those skilled in the art, and as is conventional ~ '3~3 ~
g the heater includes a hea~ing element terminating in a pair of cold leads 4 which extend through the plate-like head 2 and having a so-called hot return part which is braze~ to the head in good thermal contact therewith. A resilient annular sealing ring 6 is tightly engaged between the head an~ the control so as to provide a waker-ti~ht seal with the container wall 3.
The control 1 includes first and second body portions 7,8 which interengage axially and are so shaped to define cavities therebetween within whlch electrical switch means of the control are mounted. The second body por~ion 8 include~ three terminal pins 9 arranged in a ~riangular configuration and adapted to be engaged with a separate female socket CQnneCtor for the supply of electrical power to the heater, as is conventional wi~h this type of control. The live and neutral ones of the terminal pins 9 are connected via electrical switch means to the respective cold leads 4 of the element, the free end portions of which extend through apertures 10 formed in the first body portion 7 of the control.
Those skilled in this art will be familiar wi~h the basic components of the illustrated control and will recognise that the general layout could be varied. Similar types of control are known, for example from British Patent Specifications Nos. 1470366, 2149217 and from our co-pending British Patent Applica~ion No.8502170. The improvement of the presen~ invention is applicable ~o all of these and other known controls.
The control illustrated in Figure 1 further comprises a primary overheat protector including a snap-acting bimetallic actuator 11 mounted in gOOa thermal contact with a dimple 12 ~ormed ;n the head ad;acent the hot return 5 of the element.
The actuator 11 is of the general type descr ibe~
~2~
-- ]~o in British Patent Specification No.1,542,257 and thus includes a central ton~ue 13 which is secured to the first body portion 7 of the control by means such as a hammer drive screw~ and an upper peripheral portion 14. The upper portion 14 is arranged for engaqement with an axially slidable push rod tnot shown) extending through an aperture in the first body portion 7 and co-operating with a set of switch contacts (not shown) wired in series between either the live or neutral terminal pin 9 and a res~ective cold leafl 4. The actuator 11 is calibrated with a nominal operating temperature of 140DC so as to undergo snap action when the element overheats, for example having been switched on with insufficient water in the container to cover the element or in the event that the container boils dry. Upon operation of the actuator 11 it reverses its curvature from the configuration shown in Figure 1 and the upper peripheral portion 14 thereof is moved right-wardly ie, away from the heater head, so as toengage the push-rod which in turn opens ~he switch contacts so as to interrupt the power supply to the elemen~. This general arran~ement of primary protector is well known, and the particular configura-tion illustrated is similar to that described inmore detail in our co-pending application no. 850217n.
The control illustrated in Figure 1 further comprises a second set of switch contac~s 15 arranc~ed in series between the other cold lead 4 of the element and a respective terminal pin 9. The contacts 15 include contact members 16 carried by conductive leaf spring elements 17, 18, one of which 17 is connected to the base portion of the respective terminal pin 9 and the other of wh~ch 18 is connecte~
via a further conductive strip element to the respective cold lead 4. Such a contact arrangement is of the same general type as described in our co-pendinc~
3~
application no. 8502170, but many other similar configurations are possible.
The second set of contacts 15 is arranged to engaged by a slidable push-rod 20 which in turn co-operates with a lever member 21 forming part of a steam-sensitive over-centre spring mechanism (not shown). The over-centre spring mechanism may take any convenient form, and conventionally comprises a second thermally-responsive ac~uating means, for example a further snap-ac~ing bimetallic actuator, which is exposed to steam or vapour emitting ~rom the container during boiling and which is adapted to trip the over-centre spring mechanism so as t~ de-energise the heater. Thus~ in the arrangement illustrate~ in Figure 1, upon boiling the lever 21 is tripped to a second position (not shown) wherein the push-rod ~0 is urged leftwardly, i.e. towards ~he head, and engages a free-end part 22 of the leaf sprin~ 18 whereby the contacts 15 ~0 are broken. As is conventional means (not shown~
are provi~e~ whereby the over centre mechanism may readily be manually reset.
The illustrated control further comprises a pre-loade~ spring mechanism associated with the second set of contacts 15 which is arranged to provide back-up protection in the event that the bimetallic actuator 11 should failO One form of spring mechanism is shown in more detail ;n Figures 2a and 2b, from which it will be seen that the mechanism comprises a coil spring 25 which is mounted within a recess 26 formed in the second body portion 8 and which in normal use is held under tension by means o~ a retainin~ element in the form of a push-rod 27. Push-rod 27 is formed for example from nylon and extends through and is axially moveable within a bore 28 formed in the first body portion 7. Thus, when the control is clamped to the heater ~Z~33~
head, the push-rod 27 engages the head and is urged rightwardly relative to the control so that the spring 25 is placed under tension.
As shown in Figure 2b the spring 25 includes an operating member in the form of an arm 30 formed integrally therewith which extends laterally and which is arranged for engagement with the leaf spring 18 adjacent the free end portion 22 thereof.
~owever, as shown in Figure 1 in normal use when the spring is pre-loaded by means of the push-rod 27, the operating member 30 of the spring is spaced axially from the leaf spring 18 so that normally the contacts 15 are free to open and close in response to operation of the lever member 21 forming part of the steam-sensitive over-cen~re spring mechanism.
~ owever, in event of failure of the actuator 11, the arrangement is such that the consequent overheating of the head causes the end of the push-rod 27 which engages the head to soften and deform under the ~0 force of the spring whereby the spring is releasea sufficiently to enable the operating arm 30 to engage the leaf spring 18 and open the contacts.
The heater ;s thus disabled, and since the contacts 15 are open under the positive action of the coil spring 25 the possibility of subsequent reclosing of the contacts as a result for example of distortion of part of the control caused by over-shoot heating is avoided.
Modifications of the control described and illustrated herein will be apparent to persons skilled in this art and the disclosure hereof is intended to encompass all such modifications.
mechanism associated with the same or a further set of swi~ch contacts of the control and comprising an actuating sprin~ which in normal use of the control is held in a pretensioned condition by a retaining means and an opera~ing member coupled ~o the spring, said re~aining means being adapted and arranged ~o release the spring in the event of serious over-heating of the control consequent upon failure of said thermally-sensitive.actuating means, whereupon the operating member is moved under the force of the spring and co-operates with the switch contacts so as ~o open the contacts and deener~ise the heater.
The provision in accordance with the invention of a pre-loaded spri.ng mechanism adap~ed and arranged to be released in the event of serious over-heating consequent upon failure of the actuating means providing primary protection is advantageous to the extent that reliable operation may be achieved despite deformation of plastic parts of the control due ~o over-shoot heating. Thus, a spring loaded mechanism can provide a stronger, more positive action for opening the contacts than is possible with bimetallic actuators used in the prior art proposals, and the possibility in extreme conditions of the contacts reclosing may be avoi~ed~
In the design of thermally-sensitive controls of this type there are generally size constraints or the various components having regard to the desired overall compactness of the control~ and a preloaded sprîng mechanism is also advantageous in this respect since such a mechanism can be designed relatively com~actly. Moreover~ such a spring mechanism can be incorporated in a control without substantially increasing the manufacturing costs.
The preloaded spring mechanism make take any convenient form, and it could for example comprise a tension spring normally held in an extended condition by the retaining means and adapted to be released in the event of serious over-heating so that the switch contacts are opened. However, since it is desirable to provide a relatively strong biasing force generally within relatively narrow size constraints the preferred preloa~ed spring mechanism comprises a compression spring which in normal use is held in a compressed state by the retaining means.
The form of the retaining means may vary depending on the general configuration of the control and on the nature of the actuating spring provided.
For example, however, it is en~isaged that such means ma~ include a retaining element fixedly secured lS to or moulded integrally with a body portion of the control which is adapted to mount the spring, the element being formed of an appropriate material and being so arranged as to deform, melt or break so as to release the spring when hea~ing of the control has reached a predetermined level consequent upon ~ailure o~ the primary protector. In the case o~ a compression spring, such may be mounted during assembly of the control within a suitable recess in the body portion and held under tension therein by means of the retaining element located at one end of the recess from which end the spring thus projects when released upon deformation of the retaining element.
In a preferred embodiment, however, the retaining menas comprises a displaceable means cou~led to or carried by the spring and arranged to co-operate with part of an external element defining the mounting location for the control so as to be displaced in such a way as to pre-load the ac~ua~ing spring when the control is secured in place. Thus, the retaining element is resiliently urged bv the actuating spring against part of the mounting location for ~2~
the control, and such part is arranged in suitable thermal contact with the element so that upon serious over-heating consequent upon failure of the primary protector the end of the retaining element remote S from the sprin~ melts or deforms sufficiently to release the spring mechanism and open the contacts.
In a particularly preferred such embodiment where the spring mechanism includes a compression spring, ~he retaining elemen~ may conveniently comprise a slidable push rod which at one end is coupled to the spring and which at the other end pro~ects externally of the control for engagement with part of the mounting location therefor.
~he mounting location for the control will vary depending on the nature of the heater and the type of container. For example, the control may be adap~ed for use with an immersion heater having a hea~ing element carried by a head which is securable in a water tigh~ manner in or adjacent an opening in the container wall. In such an embodiment, the heater head may define the mounting location for the control, and in the arrangement discusse~ above wherein the retaining element comprises a slidable push rod, the push rod may convenien~ly be arranged for engagement with part of the head when the control is mounted thereto. Thus, the push rod an~ spring mechanism are advantageously arranged so that upon mounting of the control to the heater head the push rod engages the head and is displaced axiall~ so as to compress and pre-load the spring. In the even~ of failure of the primary protector, when the head reaches a certain temperature the end of the push rod softens sufficiently to be distorted un~er the force o~ the spring which is thus release~ to open the contacts.
The operating member which is adapted to be moved under the force of the spring into engagement ~ 3~
with the contacts may take any convenient form, and in a preferred embodiment where the spring mechanism comprises a compression spring such member make conveniently comprise an arm which extends laterally from one end of the spring~ In the case of a coil spring, such arm may conveniently ~e formed integrally therewith. The manner in which the operating member co-operates wi~h the contacts of such a control may vary depending on the configuration o~ the swi~ch means. Typically however, the switch contacts include interengaging contact members, at least one of which is carried by a resilient conducting strip or leaf spring 50 as to be displaceable away from the other contact member. In such an arrangement, the operating member may conveniently be arranged to engage the leaf spring carrying the movable contact member.
The general configuration of the switch means of the control may take any convenient form, and ~0 the pre-loaded sprin~ mechanism may be associatefl either with the switch con~acts which are adapted to be opened in response to op~ration of the thermally-responsive actuating means, or alternatively the control may comprise a further set of contacts arranged to be acted on by the spring mechanism.
In one embodiment, the control additionally comprises means whereby the heater is disabled upon boiling of li~uid within an associated container, such means including a further thermally-responsive actuating means exposed to steam or vapour emitting from the container and coupled to a set of switch contacts via an over centre spring mechanism.
In such an embodiment, the Pre-loaded spring mechanism can alternatively be associated with the contacts formins part of the steam sensitive switch mechanism.
The primary thermally-responsive actuatinq means and, if provided, the actuating means for .
~ 3~
the steam sensitive switch mechanism, may both comprise snap actln~ bimetallic actuators of any convenient form, for example a stressed sheet of bimetal having a generally domed configuration and a central tounge such as that described in British patent 1,542,257. The control may be fabri-cated from the suitable thermoplastics material, and in a preferred embodiment wherein the retaining element comprises a push rod which is arranged ~o be engaged and axially displaced by ~he heater head, the body part of the con~rol which confronts the head and moun~s the push rod may if necessary be formed a material having a higher heat resistance than other plastic parts of the control and than the push rod itself. This avoids the possibility of this body portion being distorted in the event of serious overheating before releas~ of the spring mechanism in such a way as to impair the movement of the push rod.
An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:
Figure 1 is a partlY schematic vertical cross-sectional illustrating a thermally-sensit;ve control secured to the head o~ an immersion heater; and Fi~ures 2a and 2b are respectively diagrammatic cross-sectional eleva~ional views illustrating in more detail a pre-loade~ spring mechanism.
Referring firstly to Figure 1, a therma]ly-sensitive control 1 is mounted to the head 2 ofan electric immersion heater, the control and heater head being interconnected by means of bolts (not shown) and thus being clamped within an aperture formed in the wall 3 of an associated container 35 such as a kettle or hot water ~ug. ~he general configuration of the heater will be well known to those skilled in the art, and as is conventional ~ '3~3 ~
g the heater includes a hea~ing element terminating in a pair of cold leads 4 which extend through the plate-like head 2 and having a so-called hot return part which is braze~ to the head in good thermal contact therewith. A resilient annular sealing ring 6 is tightly engaged between the head an~ the control so as to provide a waker-ti~ht seal with the container wall 3.
The control 1 includes first and second body portions 7,8 which interengage axially and are so shaped to define cavities therebetween within whlch electrical switch means of the control are mounted. The second body por~ion 8 include~ three terminal pins 9 arranged in a ~riangular configuration and adapted to be engaged with a separate female socket CQnneCtor for the supply of electrical power to the heater, as is conventional wi~h this type of control. The live and neutral ones of the terminal pins 9 are connected via electrical switch means to the respective cold leads 4 of the element, the free end portions of which extend through apertures 10 formed in the first body portion 7 of the control.
Those skilled in this art will be familiar wi~h the basic components of the illustrated control and will recognise that the general layout could be varied. Similar types of control are known, for example from British Patent Specifications Nos. 1470366, 2149217 and from our co-pending British Patent Applica~ion No.8502170. The improvement of the presen~ invention is applicable ~o all of these and other known controls.
The control illustrated in Figure 1 further comprises a primary overheat protector including a snap-acting bimetallic actuator 11 mounted in gOOa thermal contact with a dimple 12 ~ormed ;n the head ad;acent the hot return 5 of the element.
The actuator 11 is of the general type descr ibe~
~2~
-- ]~o in British Patent Specification No.1,542,257 and thus includes a central ton~ue 13 which is secured to the first body portion 7 of the control by means such as a hammer drive screw~ and an upper peripheral portion 14. The upper portion 14 is arranged for engaqement with an axially slidable push rod tnot shown) extending through an aperture in the first body portion 7 and co-operating with a set of switch contacts (not shown) wired in series between either the live or neutral terminal pin 9 and a res~ective cold leafl 4. The actuator 11 is calibrated with a nominal operating temperature of 140DC so as to undergo snap action when the element overheats, for example having been switched on with insufficient water in the container to cover the element or in the event that the container boils dry. Upon operation of the actuator 11 it reverses its curvature from the configuration shown in Figure 1 and the upper peripheral portion 14 thereof is moved right-wardly ie, away from the heater head, so as toengage the push-rod which in turn opens ~he switch contacts so as to interrupt the power supply to the elemen~. This general arran~ement of primary protector is well known, and the particular configura-tion illustrated is similar to that described inmore detail in our co-pending application no. 850217n.
The control illustrated in Figure 1 further comprises a second set of switch contac~s 15 arranc~ed in series between the other cold lead 4 of the element and a respective terminal pin 9. The contacts 15 include contact members 16 carried by conductive leaf spring elements 17, 18, one of which 17 is connected to the base portion of the respective terminal pin 9 and the other of wh~ch 18 is connecte~
via a further conductive strip element to the respective cold lead 4. Such a contact arrangement is of the same general type as described in our co-pendinc~
3~
application no. 8502170, but many other similar configurations are possible.
The second set of contacts 15 is arranged to engaged by a slidable push-rod 20 which in turn co-operates with a lever member 21 forming part of a steam-sensitive over-centre spring mechanism (not shown). The over-centre spring mechanism may take any convenient form, and conventionally comprises a second thermally-responsive ac~uating means, for example a further snap-ac~ing bimetallic actuator, which is exposed to steam or vapour emitting ~rom the container during boiling and which is adapted to trip the over-centre spring mechanism so as t~ de-energise the heater. Thus~ in the arrangement illustrate~ in Figure 1, upon boiling the lever 21 is tripped to a second position (not shown) wherein the push-rod ~0 is urged leftwardly, i.e. towards ~he head, and engages a free-end part 22 of the leaf sprin~ 18 whereby the contacts 15 ~0 are broken. As is conventional means (not shown~
are provi~e~ whereby the over centre mechanism may readily be manually reset.
The illustrated control further comprises a pre-loade~ spring mechanism associated with the second set of contacts 15 which is arranged to provide back-up protection in the event that the bimetallic actuator 11 should failO One form of spring mechanism is shown in more detail ;n Figures 2a and 2b, from which it will be seen that the mechanism comprises a coil spring 25 which is mounted within a recess 26 formed in the second body portion 8 and which in normal use is held under tension by means o~ a retainin~ element in the form of a push-rod 27. Push-rod 27 is formed for example from nylon and extends through and is axially moveable within a bore 28 formed in the first body portion 7. Thus, when the control is clamped to the heater ~Z~33~
head, the push-rod 27 engages the head and is urged rightwardly relative to the control so that the spring 25 is placed under tension.
As shown in Figure 2b the spring 25 includes an operating member in the form of an arm 30 formed integrally therewith which extends laterally and which is arranged for engagement with the leaf spring 18 adjacent the free end portion 22 thereof.
~owever, as shown in Figure 1 in normal use when the spring is pre-loaded by means of the push-rod 27, the operating member 30 of the spring is spaced axially from the leaf spring 18 so that normally the contacts 15 are free to open and close in response to operation of the lever member 21 forming part of the steam-sensitive over-cen~re spring mechanism.
~ owever, in event of failure of the actuator 11, the arrangement is such that the consequent overheating of the head causes the end of the push-rod 27 which engages the head to soften and deform under the ~0 force of the spring whereby the spring is releasea sufficiently to enable the operating arm 30 to engage the leaf spring 18 and open the contacts.
The heater ;s thus disabled, and since the contacts 15 are open under the positive action of the coil spring 25 the possibility of subsequent reclosing of the contacts as a result for example of distortion of part of the control caused by over-shoot heating is avoided.
Modifications of the control described and illustrated herein will be apparent to persons skilled in this art and the disclosure hereof is intended to encompass all such modifications.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A thermally-sensitive control for an electric heater for a container, said heater having an element, and said control including a thermally-sensitive actuating means arranged in use in good thermal contact with a part of the element and coupled to a set of switch contacts of electrical switch means of the control so that the actuating means is operable to open the contacts and deenergise the heater upon over-heating of the element, wherein back-up protection for the control is provided by a pre-loaded spring mechanism associated with the same or a further set of switch contacts of the control and comprising an actuating spring which in normal use of the control is held in a pretensioned condition by a retaining means and an operating member coupled to the spring, said retaining means being adapted and arranged to release the spring in the event of serious over-heating of the control consequent upon failure of said thermally-sensitive actuating means, whereupon the operating member is moved under the force of the spring and co-operates with the switch contacts so as to open the contacts and deenergise the heater.
2. A thermally-sensitive control as claimed in claim 1 wherein said pre-loaded spring mechanism comprises a compression spring.
3. A thermally-sensitive control as claimed in claim 1 or 2 wherein the retaining means comprises a displaceable means coupled 13a to or carried by the spring and arranged to co-operate with part of an external element defining the mounting location for the control so as to be displaced in such a way as to pre-load the actuating spring when the control is secured in place.
4. A thermally-sensitive control as claimed in claim 2 wherein the retaining means comprises a slidable push rod which at one end is coupled to the spring and which at the other end projects externally of the control for engagement with part of the mounting location therefor.
5. A thermally-sensitive control as claimed in claim 4 adapted for mounting to the head of an associated electric heater, the push rod and spring mechanism being arranged so that upon mounting of the control to the heater head the push rod engages the head and is displaced axially so as to compress and pre-load the spring.
6. A thermally-sensitive control as claimed in claim 5 wherein a plastics body part of the control which confronts the heater head and mounts the push rod is formed of a material having a higher heat resistance than other plastic parts of the control than the push rod itself.
7. A thermally-sensitive control as claimed in claim 1 wherein the operating member comprises an arm which extends laterally from one end of the spring.
8. A thermally-sensitive control as claimed in claim 6 wherein said arm is arranged for engagement with a leaf spring carrying a movable contact of switch means of the control.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8524487 | 1985-10-04 | ||
| GB858524487A GB8524487D0 (en) | 1985-10-04 | 1985-10-04 | Thermally-sensitive controls |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1265831A true CA1265831A (en) | 1990-02-13 |
Family
ID=10586170
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000519701A Expired - Lifetime CA1265831A (en) | 1985-10-04 | 1986-10-03 | Thermally-sensitive controls |
Country Status (8)
| Country | Link |
|---|---|
| AU (1) | AU582470B2 (en) |
| BE (1) | BE905550A (en) |
| CA (1) | CA1265831A (en) |
| DE (1) | DE3633759C2 (en) |
| GB (2) | GB8524487D0 (en) |
| HK (1) | HK37992A (en) |
| SG (1) | SG21490G (en) |
| ZA (1) | ZA867457B (en) |
Families Citing this family (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2204450B (en) * | 1987-05-07 | 1991-06-05 | Strix Ltd | Thermally-sensitive switch |
| GB2206734B (en) * | 1987-06-27 | 1991-04-24 | Haden D H Ltd | Thermally responsive electrical device |
| DE3904463C2 (en) * | 1989-02-15 | 1996-10-31 | Stiebel Eltron Gmbh & Co Kg | Electric water heater |
| AT397374B (en) * | 1990-01-16 | 1994-03-25 | Kiepe Electric Gmbh | OVER TEMPERATURE LIMIT PROTECTION FOR ELECTRIC RADIATORS |
| GB9117415D0 (en) | 1991-08-12 | 1991-09-25 | Strix Ltd | Liquid heating vessels |
| DE4233676A1 (en) * | 1992-10-07 | 1994-04-14 | Ego Elektro Blanc & Fischer | Electric radiator for media, especially flow heaters |
| GB9302965D0 (en) * | 1993-02-15 | 1993-03-31 | Strix Ltd | Immersion heaters |
| GB9319159D0 (en) * | 1993-09-16 | 1993-11-03 | Strix Ltd | Cordless electrical appliances and connectors therefor |
| GB2296847B (en) | 1994-11-30 | 1999-03-24 | Strix Ltd | Electric heaters |
| GB9707789D0 (en) * | 1997-04-17 | 1997-06-04 | Strix Ltd | Terminal pins for eletrical appliances |
| CN2504753Y (en) * | 2001-10-25 | 2002-08-07 | 邵志成 | Socket with improved temp induction control structure |
| CN1186703C (en) * | 2002-01-14 | 2005-01-26 | 邵志成 | Temp controller, electric connector and electric water heater |
| CN1374490A (en) * | 2002-01-29 | 2002-10-16 | 刘鑫浩 | Temperature controller for electrical liquid heater |
| GB0302537D0 (en) | 2003-02-04 | 2003-03-12 | Strix Ltd | Electric heaters |
| GB2472631B (en) | 2009-08-13 | 2014-10-08 | Otter Controls Ltd | Electrical appliances |
| JP2013515233A (en) | 2009-12-21 | 2013-05-02 | ストリックス リミテッド | Flow heater |
| CN104779118B (en) * | 2015-04-30 | 2017-03-15 | 佛山市川东磁电股份有限公司 | A kind of fuse protection structure |
| CN112656264B (en) * | 2020-12-16 | 2022-04-15 | 董丽萍 | Pediatric nursing cleaning device capable of preheating |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB686800A (en) * | 1950-08-25 | 1953-01-28 | R E Thompson & Company Sunbury | Improvements in temperature-sensitive safety cut-outs for electric heaters |
| GB1055581A (en) * | 1961-11-15 | 1967-01-18 | Arnot Alfred E R | Improvements in or relating to heating controls |
| BE683652A (en) * | 1965-07-06 | 1966-12-16 | ||
| GB1408387A (en) * | 1971-11-26 | 1975-10-01 | Hobbs R Ltd | Electric kettles and other electrically heated beverage makers |
| FR2212629B3 (en) * | 1972-12-29 | 1976-06-18 | Morgan John | |
| GB1470366A (en) * | 1973-06-28 | 1977-04-14 | Otter Controls L D | Electric immersion heaters |
| BE818448A (en) * | 1973-08-04 | 1975-02-03 | COMBINED TEMPERATURE REGULATOR | |
| DE7421749U (en) * | 1974-06-26 | 1974-11-21 | Morgan J | Electric thermal switch |
| GB1542252A (en) * | 1975-10-30 | 1979-03-14 | Taylor J | Snap-acting thermally responsive bimetallic actuators |
| US4145654A (en) * | 1977-07-21 | 1979-03-20 | Minnesota Mining And Manufacturing Company | Thermal switch |
| DE2826205C2 (en) * | 1978-06-15 | 1986-11-20 | Inter Control Hermann Köhler Elektrik GmbH & Co KG, 8500 Nürnberg | Thermal fuse for electrical devices |
| GB2042269B (en) * | 1979-01-15 | 1983-04-13 | Taylor J C | Thermally-sensitive electrical controls for electric heaters |
| GB8329055D0 (en) * | 1983-10-31 | 1983-11-30 | Strix Ltd | Thermally-sensitive controls |
| GB8508051D0 (en) * | 1985-03-28 | 1985-05-01 | Otter Controlls Ltd | Heating elements |
-
1985
- 1985-10-04 GB GB858524487A patent/GB8524487D0/en active Pending
-
1986
- 1986-09-30 AU AU63402/86A patent/AU582470B2/en not_active Expired
- 1986-09-30 ZA ZA867457A patent/ZA867457B/en unknown
- 1986-10-02 GB GB8623704A patent/GB2181598C/en not_active Expired - Lifetime
- 1986-10-03 CA CA000519701A patent/CA1265831A/en not_active Expired - Lifetime
- 1986-10-03 DE DE3633759A patent/DE3633759C2/en not_active Expired - Lifetime
- 1986-10-03 BE BE0/217253A patent/BE905550A/en not_active IP Right Cessation
-
1990
- 1990-03-16 SG SG214/90A patent/SG21490G/en unknown
-
1992
- 1992-05-28 HK HK379/92A patent/HK37992A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| AU582470B2 (en) | 1989-03-23 |
| DE3633759A1 (en) | 1987-04-09 |
| GB8524487D0 (en) | 1985-11-06 |
| GB2181598A (en) | 1987-04-23 |
| ZA867457B (en) | 1987-05-27 |
| GB8623704D0 (en) | 1986-11-05 |
| SG21490G (en) | 1990-07-06 |
| GB2181598C (en) | 1994-08-17 |
| GB2181598B (en) | 1989-09-13 |
| AU6340286A (en) | 1987-04-09 |
| DE3633759C2 (en) | 1998-04-09 |
| HK37992A (en) | 1992-06-04 |
| BE905550A (en) | 1987-02-02 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1265831A (en) | Thermally-sensitive controls | |
| US4288686A (en) | Thermostat for popcorn cooking containers or the like | |
| US4295114A (en) | Thermo-switch | |
| EP0564150A1 (en) | Overcurrent protection device | |
| GB2208336A (en) | Hot water jug | |
| EP0255347B1 (en) | Improvements relating to thermal control units | |
| EP1075701B1 (en) | Improvements relating to the control of electric heating elements | |
| EP0510863A2 (en) | Controls for water heating appliances | |
| EP1312289B1 (en) | A temperature controller for a liquid heater | |
| EP1586102B1 (en) | Improvements relating to the control of electric heating elements | |
| EP0458873B1 (en) | Immersion heaters | |
| WO1998030066A1 (en) | Liquid heating apparatus | |
| EP1223790B1 (en) | Liquid heating vessels | |
| EP1072048B1 (en) | Improvements relating to thermal controls for electric heating elements | |
| GB2204450A (en) | Hydraulic power assisted vehicle steering system | |
| CA1247173A (en) | Thermal cutout | |
| GB2381385A (en) | Thermal control | |
| GB2217160A (en) | Electric immersion heaters and thermally-sensitive controls therefor | |
| EP1249851B1 (en) | Improvements relating to the control of electric heating elements | |
| EP1642309B1 (en) | Improvements relating to thermal control units | |
| EP0846329B1 (en) | Heat transfer element for thermal controls | |
| GB2173045A (en) | Electric heating elements | |
| WO1993016569A1 (en) | Immersion heaters | |
| GB2220547A (en) | Electric immersion heaters | |
| GB2372159A (en) | Cordless kettle connector with bimetallic overtemperature controls |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |