CA1147001A - Thermally-sensitive electrical controls for electric heaters - Google Patents
Thermally-sensitive electrical controls for electric heatersInfo
- Publication number
- CA1147001A CA1147001A CA000343704A CA343704A CA1147001A CA 1147001 A CA1147001 A CA 1147001A CA 000343704 A CA000343704 A CA 000343704A CA 343704 A CA343704 A CA 343704A CA 1147001 A CA1147001 A CA 1147001A
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- steam
- control
- thermally
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- container
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Abstract
ABSTRACT OF THE DISCLOSURE
A thermally-responsive electrical control is disclosed for an electric heater of a water boiling container. The control includes a switch-on-dry protector switch unit adapted to make electrical connection with the cold leads of the heating element and includes thermally sensi-tive switch means effective, in use, to interrupt the electrical supply to the heater should the element overheat through being switched on when the container is dry. The control further includes a steam-sensitive unit adapted to be mounted on the protector switch unit, the steam-sensitive unit including an overcentre spring mechanism and a thermally-responsive actuator for that mechanism. The control is adapted for the impingement on the actuator of the steam-sensitive unit of vapour or steam issuing from the outlet of a tube or passage leading to the interior of the container. Electrical parts of the control are shielded from such vapour or steam, a mechanical link being provided between the overcentre spring mechanism and the switch means of the protector switch unit so that, on the overcentre spring mechanism being tripped by the actuator, the link serves mechanically to operate the switch means of the protector switch unit.
A thermally-responsive electrical control is disclosed for an electric heater of a water boiling container. The control includes a switch-on-dry protector switch unit adapted to make electrical connection with the cold leads of the heating element and includes thermally sensi-tive switch means effective, in use, to interrupt the electrical supply to the heater should the element overheat through being switched on when the container is dry. The control further includes a steam-sensitive unit adapted to be mounted on the protector switch unit, the steam-sensitive unit including an overcentre spring mechanism and a thermally-responsive actuator for that mechanism. The control is adapted for the impingement on the actuator of the steam-sensitive unit of vapour or steam issuing from the outlet of a tube or passage leading to the interior of the container. Electrical parts of the control are shielded from such vapour or steam, a mechanical link being provided between the overcentre spring mechanism and the switch means of the protector switch unit so that, on the overcentre spring mechanism being tripped by the actuator, the link serves mechanically to operate the switch means of the protector switch unit.
Description
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Thermally-sensitive electrical controls for electric heaters This invention relates to thermally-sensitive electrical controls for electric heaters of water boiling 5 containers such as electric kettles~ jugs, urns, pans, coffee perculators, laboratory equipment and the like , (hereinafter termed containers o the kind re~erred to) '~herein the electric heaters are either immersion heaters or ~imilarly ,constructed heaters mounted externally of the container in good thermal contact with a container wall thereof e.g. as by being brazed to the underside of the '' bottom of the container. The heating elements of such electric heaters as aforesaid terminate in so-called cold leads by means of which electrical connections are made to .
the heater.
Electric immersion heaters (héreinafter termed electric ~' immersion heaters of the first kind described) conventionally comprise a heating element carried by a head which is ' adapted to be secured in a water-tight manner in or adjacent , an opening in the container wall. In use said,h~ad mounts externally of said contàiner a thermally-sensitive electrical control (hereinafter termed a thermally-sensitive electrical control,' of the first kind described) in the form of a switch-on-dry ~rotector switch unit which makes electrical ~til47~)6;1:P
~ 1 .
.
Thermally-sensitive electrical controls for electric heaters This invention relates to thermally-sensitive electrical controls for electric heaters of water boiling 5 containers such as electric kettles~ jugs, urns, pans, coffee perculators, laboratory equipment and the like , (hereinafter termed containers o the kind re~erred to) '~herein the electric heaters are either immersion heaters or ~imilarly ,constructed heaters mounted externally of the container in good thermal contact with a container wall thereof e.g. as by being brazed to the underside of the '' bottom of the container. The heating elements of such electric heaters as aforesaid terminate in so-called cold leads by means of which electrical connections are made to .
the heater.
Electric immersion heaters (héreinafter termed electric ~' immersion heaters of the first kind described) conventionally comprise a heating element carried by a head which is ' adapted to be secured in a water-tight manner in or adjacent , an opening in the container wall. In use said,h~ad mounts externally of said contàiner a thermally-sensitive electrical control (hereinafter termed a thermally-sensitive electrical control,' of the first kind described) in the form of a switch-on-dry ~rotector switch unit which makes electrical ~til47~)6;1:P
- 2 -connection with said cold leads and includes thermally-sensitive switch means effective to interrupt the electrical supply to the heater should the element~ovex heat through being switched on dry. Switch-on-dry protector switch units per se are well known and are described in,for example, British Patent Specifications 1401954 and 1064643.
Electric immersion heaters (hereinafter termed electric ir~nersion heaters of the second kind described) o the first kind described are also known which additionally carry a tube for egress o vapour or steam from the interior of the container via the head of the heater, the tube being arranged, in use, so as to extend above the water level in the container.
In this case the head mounts a thermally-sensitive electrical control (hereinafter termed a thermally-sensitive electrical control of the second kind described) of the fi.rst kind described which is additi.onally ef~ective to interrupt the electrical supply to the heater in response to vapour or steam issuing from said tube upon the water in the container boilingO Such a thermally-sensitive electrical control of the second kind described together with an electric imrnersion heater of the second kind described is disclosed in British Patent Specification NoO 1316436.
: In the preferred embodiment of the invention described ` in Specification 1316436 there is connected to the head firstly a protector switch unit (shown in Figures 3 to 5) which incorporates a thermally-sensitive switch for cutting off the power supply to the heating element if the kettle is switched on dry, and also a vapour or steam sensitive switch unit (shown in Figures 6 to 8) which incorporates a further 30 thermally-sensitive switch for cutting o~f the power supply _ . . . . ... .. ... .. . .
1~L470~l r~ - 3 -when vapour or steam issueg through said tubeO
The steam-sensitive switch unit mounts on the protector switch unit and cooperates therewith to provide a line terminal connection to the heater element via the protector 5 switch and the steam-sensitive switch connected in seriesO
The provision of two separate thermally-sensitive switches and their connection in series results in a control which although-effective is complicated and hence expensive. Moreover although switch-on-dry protector switch units per se are well 10 known for use in non-automatic kettles (see British Patent Specifications 1401954 and 1064643) the construction described in Specification 1316436 necessarily involves substantial modification of a standard protector switch unit thus increasing costs..
. More generally lt is known from British Patent Specificati NoO 1274552 to provide a steam or vapour tube or passage either within or along an outer surface o a water boiling container for the flow of vapour or steam from within the container to an outlet in or adjacent the container floor 20 for the purpose of controlling a thermally-sensitive electrical control associated with an electric heater which heater may or may not be integral with the containerO
Speci~ically described in Speci~ication NoO 1274552 is an i~nersion heater of the first kind described in association 25 with a thermally-sensitive electrical control which as with that described in Specification 1316~36 comprises two switch units namely a dry-switch-on protector unit and a steam or vapour sensitive unit mounted one on the other with the attendant disadvantages mentioned above in relation to the control of Specification 1316436.
~4~a~;a It is an object of the present invention to provide an improved and simplified thermally-sensitive dry-switch-on and water boiling control.
Thus according to the present invention there is provided a thermally-responsive electrical control for an electric heater of a water boiling container comprising a heating element terminating in cold leads, said control including a switch-on-dry protector switch unit adapted to make electrical connection with the cold leads of the heating element and including thermally sensitive switch : means effectiveJ in use, to interrupt the electrical supply to the heater should the element overheat through being switched on when the container is dry, said control further including a steam-sensitive unit adapted to be mounted on said protector switch unit, said steam-sensitive unit including an overcentre spring mechanism and a thermally-responsive actuator for said mechanism, the control being adapted for the impingement on said actuator of said steam-sensitive unit of vapour or steam issuing from the outlet of a tube or passage leading to the interior of said container, electrical parts of said control being shielded from such vapour or steam, a mechanical link being provided between said over-centre spring mechanism and the switch means o:E said protector switch unit so that on said overcentre spring mechanism being tripped by said actuator, said link serves mechanically to operate said switch means of the protector switch 2Q unit, said protector switch unit being separable from said steam-sensitive unit and able to be mounted on said container in the absence of said steam-sensitive unit.
It will thus be seen that with a control according to the present invention there is only one electrical switch means, namely that of the switch-on-dry protector switch unit which as is conventional may incorporate terminal pins whereby connection to a mains supply via a female socket connector may _~ _ ~4~700:~
be made. Consequently no electrical connections have to be made between the protector switch unit and the steam-sensitive unit from which it follows that the protector switch unit can be made to be used alone as a switch-on-dry'protector and yet in such a form as to be compatible for use with a simple non-electrical steam-sensitive unit when a control is required for automatic kettles or other water-Doiling containers of the kind describedO Thus not only is a great simplification achieved as compared with the control as described in Specification 1274552 and 1316436 but the protector switch unit may serve two functions, one by itself as a dry-switch-on protector and another as part of the composite switch-on-dry and boiling control according to the-present invention.
The manner of adaptation of the control for the impingement of steam or vapour on said actuator can take various formsO Thus for use with immersion heaters of the second kind described, the switch-on-dry protector switch unit will be adapted to engage said tube for steam or vapour so that steam o~ vapour~passes through the protector unit to reach said steam sensitive unitO Alternativèly provision may be made for steam,or vapour to be fed directly to the steam sensitive unit e.g. laterally and from above as vi`ewed when the control is fitted to the side and adjacent the base of a water-boiling container of the kind referred toO
'In order to provide a versatile control provision may be made both for the tube of an immersion heater of the second kind described and for steam or vapour to be fed directly to the steam sensitive unitO The control may be provided in a form in which for use with an immersion heater of the second .. . . ~
~ ~ 7 f-~ - 6 -kind described there is provided rangible me~ns defining an opening to receive said steam or vapour carrying tubeO
Alternatively whilst the control may be adapted to receive said tube7the path for steam or vapour to said steam sensitive unit may be made readily blockable off by the user as, depending on the design of the control, might be necessary to prevent steam or vapour fed directly to the steam sensitive unit passing via.said path into the elect~ics of the protector switch unitO
A control according to the invention adapted or the direct introduction of steam or vapour to the steam-sensitive unit from above as mentioned previously can conveniently receive steam or vapour via a tube or passage running down the outside of the container and communicating with a steam or vapour aperture in the upper wall of the containerO
Such a tube can be concealed or formed within a handle structure of the container. Likewise a steam or vapour passage can readily be defined between the container wall and a handle structureO With such arrangements an electric immersion heater of the Eirst kind described, which is simpler to manufacture and install than one of the second kind described, is all that is requiredO
The control according to the present invention is not however restricted to immersion heaters but is applicable to containers with external heatersO In such case, there being conventionally no head associated with the heater element~
it will be necessary to provide a ~ounting plate for said protector switch unit and to arrange the cold leads of said heater element in relation to said plate so that in mounting said protector switch unit on said plate, electrical .. . . . . . ~ .
~47~
f_~ - 7 -connections can be made with the cold leadsO The plate will also need to be mounted so that, as with the head of an immersion heater, its temperature will rise with that of the heater element should a dry-switch-on condition ariseO Thus the mounting plate may conveniently be in the form of a bracket mounted on the heater element.or on the base of the container adjacent the heater element. In this way the dry-switch-on control function can readily be exercised particularly as the temperature rise of an element in good thermal contact with the container wall is much less rapid than with an immersion heater since the container acts as a heat sink.
Steam or vapour may be led to the control via a steam tube exiting from said container, which tube may engage the protector switch unit in like manner as with controls for use with electric immersion heaters of the second k:ind described. Alternatively the arrangement may be as described above with the tube or passage nlnning down the outside o~ the container directly to communicate wlth the steam sensitive unit~
In a preferred embodiment, the thermally-responsive actuator of the steam-sensitive Lmit comprises a bimetallic elementO The bimetallic element pre~erably comprises a member of sheet bimetal having an aperture with an outer perimeter and an inner perimeter defining a ton~ue free at one end intermediate two lobe portions of said aperture, said inner perimeter and arcuate portions of said outer perimeter smoothly merging at rounded ends of the aperture adjacent the tongue root, the tongue being, at least in part, generally centrally disposed with respect to the member, the member having ... . . . . . . .. . .. ...... . .
. .
.~470 been defonned in a die presslng operation to conform in shape to a die o domed configuration, said domed area being such as to reverse its curvature with a snap action with change in temperature9 the width of the domed are being greatast ~, the region of the tongue root. Such an actuator is describ~d in German Offenlegungsschrift 2,556,062 and British Patent- Specification No. 1,542,252.
Preferably7 the over-centre mechanism comprises a lever pivotably mounted on a body member of the steam-sensitive unit so as to be movable between first and second positions through an unstable dead-centre positionO The pivotal mounting is preferably by meanS of at least one knife edge resting in a notch or bearing, the knife edge being retained in the notch by means of at least one C-spring extending between the lever and the body member. In such an arrangement, the dead-centre position occurs when the two ends of the C-spring lie in a common plane with the fulcrum o~ the lever.
The mechanical link preferably comprises a movable member which is acted on directly or indirectly by a lever of the over-centre mechanism and by a thermally responsive actuator of the switch unit. The movable member is preferably an elongate member movable in the direction of its axis, the lever comprising a portion extending through an aperture in the elongate member so as to engage therewith to operate said switch meansO
There is further provided the combination of a thermally-sensitive electrical control according to the invention and an electric immersion heater of the second kind described, wherein a hot return of the heating element is in thermal contact with the head in a position which, in use, i`s below the cold leads ... . .. ..... _ . .. . .. ..
~1~L7~9~
9 _ o~ the heatin~ element, a thermall~-sensitive actuator of the thermally-sensitive switch means being in thermal con-tact with the head in the vicinity o~ said position.
A preferred form of thermally-sensitive electrical con-trol according to the invention for an electric heater ofthe second kind described will now be described with reference to Figs l to 7 of the accompanying drawings.
There will further be described with reference to ~igures 8 to 14 of the accompanying drawings a ~lightly modified version of the first described control whereby steam or vapour may also be fed directly to the steam sensi-tive unit and the application of this modified control to a heater mounted externally of the container as well as to a kettle having an immersion heater of the-first kind des-cribed i.e. without a steam tube.
~ n the accompanying drawin~s wherein like parts bearthe same reference numerals;
Figure l is a perspective view from below and to one side of an embodiment of a thermally-sensitive ~20 eIectrical control according to the invention~ the housing of the control being removed;
Figure 2 is a side view of the control shown in Figure 1 r"ith the housing in place;
Figure 3 is a view corresponding to that of - 25 Figure 2~ but showing a cross-section;
Figure 4 is a front elevation of the control of Figures 2 and 3;
Figure 5 is a view corresponding to that of Figure 4~ but with the housing removed;
Figure 6 is a front elevation of a switch-on-dry protector switch unit forming part of the control shown in Figures l to 5; and Figure 7 is a side view of the switch unit shown in Figure 6.
~7~
Figure 8 is a side elevation partially in section of a water-boiling jug whose hea-ker is brazed to the underside of the base of the jug and fitted wlth a modified control accordiny to the invention wherein steam or vapour is intro-duced directly to the steam-sensitive unit of the control;
Figures 9 and 10 are side elevations in cross-section of the control as fitted in the jug;
Figure 11 is a perspective view from below and to one side of the control itself without its outer housing;
Figure lla is a perspective view of the body moulding of the switch-on-dry protector unit of the control;
Figures 12 and 13 are front elevations of the control respectively with and without an outer housing in place; and Figure 14 is a side elevation of an electric kettle fitted with a control as shown in Figs 8 to 13.
~ s shown in Figures 1 to 5 of the drawings, a thermally-sensitive electrical control is mounted on the head l~O~of an electrical immersion heater. The head is secured in a water-tight manner in an opening in the wall o~ a kettle 6. The head 10 carries a steam tube 5 for conducting steam from the interior of ~L~471;)~D:~
the kettle to the thermally-sensitive control. The tube ~ is arranged so as to extend in use above the water level in the kettle. The immersion heater comprises two cold leads 3 and a hot return ll which passes underneath the cold leads 3 and is brazed to the head lO so as to be in thermal contact therewith. By virtue of the pro~imity of the hot return to the base of the kettle, the kettle is capable of boiling a small quantity of water if desired.
The thermally-sensitive electrical control comprises a switch-on-dry protector switch unit 2 mounted on the head lO and a steam-sensitive unit 1 which is in turn mounted on the switch unit 2. The switch unit 2 is lS provided with three pins 4., including a line pin, a neutral pin and an earth pin, for connection to a female socket to supp~y mains electrical power to the heating element. The line pin is connected to one of the cold leads 3 vla a pair of electrical contacts including a movable contact 7 mounted on a resilient conductive strip 27 and a stationary contact 8 (Figure
Electric immersion heaters (hereinafter termed electric ir~nersion heaters of the second kind described) o the first kind described are also known which additionally carry a tube for egress o vapour or steam from the interior of the container via the head of the heater, the tube being arranged, in use, so as to extend above the water level in the container.
In this case the head mounts a thermally-sensitive electrical control (hereinafter termed a thermally-sensitive electrical control of the second kind described) of the fi.rst kind described which is additi.onally ef~ective to interrupt the electrical supply to the heater in response to vapour or steam issuing from said tube upon the water in the container boilingO Such a thermally-sensitive electrical control of the second kind described together with an electric imrnersion heater of the second kind described is disclosed in British Patent Specification NoO 1316436.
: In the preferred embodiment of the invention described ` in Specification 1316436 there is connected to the head firstly a protector switch unit (shown in Figures 3 to 5) which incorporates a thermally-sensitive switch for cutting off the power supply to the heating element if the kettle is switched on dry, and also a vapour or steam sensitive switch unit (shown in Figures 6 to 8) which incorporates a further 30 thermally-sensitive switch for cutting o~f the power supply _ . . . . ... .. ... .. . .
1~L470~l r~ - 3 -when vapour or steam issueg through said tubeO
The steam-sensitive switch unit mounts on the protector switch unit and cooperates therewith to provide a line terminal connection to the heater element via the protector 5 switch and the steam-sensitive switch connected in seriesO
The provision of two separate thermally-sensitive switches and their connection in series results in a control which although-effective is complicated and hence expensive. Moreover although switch-on-dry protector switch units per se are well 10 known for use in non-automatic kettles (see British Patent Specifications 1401954 and 1064643) the construction described in Specification 1316436 necessarily involves substantial modification of a standard protector switch unit thus increasing costs..
. More generally lt is known from British Patent Specificati NoO 1274552 to provide a steam or vapour tube or passage either within or along an outer surface o a water boiling container for the flow of vapour or steam from within the container to an outlet in or adjacent the container floor 20 for the purpose of controlling a thermally-sensitive electrical control associated with an electric heater which heater may or may not be integral with the containerO
Speci~ically described in Speci~ication NoO 1274552 is an i~nersion heater of the first kind described in association 25 with a thermally-sensitive electrical control which as with that described in Specification 1316~36 comprises two switch units namely a dry-switch-on protector unit and a steam or vapour sensitive unit mounted one on the other with the attendant disadvantages mentioned above in relation to the control of Specification 1316436.
~4~a~;a It is an object of the present invention to provide an improved and simplified thermally-sensitive dry-switch-on and water boiling control.
Thus according to the present invention there is provided a thermally-responsive electrical control for an electric heater of a water boiling container comprising a heating element terminating in cold leads, said control including a switch-on-dry protector switch unit adapted to make electrical connection with the cold leads of the heating element and including thermally sensitive switch : means effectiveJ in use, to interrupt the electrical supply to the heater should the element overheat through being switched on when the container is dry, said control further including a steam-sensitive unit adapted to be mounted on said protector switch unit, said steam-sensitive unit including an overcentre spring mechanism and a thermally-responsive actuator for said mechanism, the control being adapted for the impingement on said actuator of said steam-sensitive unit of vapour or steam issuing from the outlet of a tube or passage leading to the interior of said container, electrical parts of said control being shielded from such vapour or steam, a mechanical link being provided between said over-centre spring mechanism and the switch means o:E said protector switch unit so that on said overcentre spring mechanism being tripped by said actuator, said link serves mechanically to operate said switch means of the protector switch 2Q unit, said protector switch unit being separable from said steam-sensitive unit and able to be mounted on said container in the absence of said steam-sensitive unit.
It will thus be seen that with a control according to the present invention there is only one electrical switch means, namely that of the switch-on-dry protector switch unit which as is conventional may incorporate terminal pins whereby connection to a mains supply via a female socket connector may _~ _ ~4~700:~
be made. Consequently no electrical connections have to be made between the protector switch unit and the steam-sensitive unit from which it follows that the protector switch unit can be made to be used alone as a switch-on-dry'protector and yet in such a form as to be compatible for use with a simple non-electrical steam-sensitive unit when a control is required for automatic kettles or other water-Doiling containers of the kind describedO Thus not only is a great simplification achieved as compared with the control as described in Specification 1274552 and 1316436 but the protector switch unit may serve two functions, one by itself as a dry-switch-on protector and another as part of the composite switch-on-dry and boiling control according to the-present invention.
The manner of adaptation of the control for the impingement of steam or vapour on said actuator can take various formsO Thus for use with immersion heaters of the second kind described, the switch-on-dry protector switch unit will be adapted to engage said tube for steam or vapour so that steam o~ vapour~passes through the protector unit to reach said steam sensitive unitO Alternativèly provision may be made for steam,or vapour to be fed directly to the steam sensitive unit e.g. laterally and from above as vi`ewed when the control is fitted to the side and adjacent the base of a water-boiling container of the kind referred toO
'In order to provide a versatile control provision may be made both for the tube of an immersion heater of the second kind described and for steam or vapour to be fed directly to the steam sensitive unitO The control may be provided in a form in which for use with an immersion heater of the second .. . . ~
~ ~ 7 f-~ - 6 -kind described there is provided rangible me~ns defining an opening to receive said steam or vapour carrying tubeO
Alternatively whilst the control may be adapted to receive said tube7the path for steam or vapour to said steam sensitive unit may be made readily blockable off by the user as, depending on the design of the control, might be necessary to prevent steam or vapour fed directly to the steam sensitive unit passing via.said path into the elect~ics of the protector switch unitO
A control according to the invention adapted or the direct introduction of steam or vapour to the steam-sensitive unit from above as mentioned previously can conveniently receive steam or vapour via a tube or passage running down the outside of the container and communicating with a steam or vapour aperture in the upper wall of the containerO
Such a tube can be concealed or formed within a handle structure of the container. Likewise a steam or vapour passage can readily be defined between the container wall and a handle structureO With such arrangements an electric immersion heater of the Eirst kind described, which is simpler to manufacture and install than one of the second kind described, is all that is requiredO
The control according to the present invention is not however restricted to immersion heaters but is applicable to containers with external heatersO In such case, there being conventionally no head associated with the heater element~
it will be necessary to provide a ~ounting plate for said protector switch unit and to arrange the cold leads of said heater element in relation to said plate so that in mounting said protector switch unit on said plate, electrical .. . . . . . ~ .
~47~
f_~ - 7 -connections can be made with the cold leadsO The plate will also need to be mounted so that, as with the head of an immersion heater, its temperature will rise with that of the heater element should a dry-switch-on condition ariseO Thus the mounting plate may conveniently be in the form of a bracket mounted on the heater element.or on the base of the container adjacent the heater element. In this way the dry-switch-on control function can readily be exercised particularly as the temperature rise of an element in good thermal contact with the container wall is much less rapid than with an immersion heater since the container acts as a heat sink.
Steam or vapour may be led to the control via a steam tube exiting from said container, which tube may engage the protector switch unit in like manner as with controls for use with electric immersion heaters of the second k:ind described. Alternatively the arrangement may be as described above with the tube or passage nlnning down the outside o~ the container directly to communicate wlth the steam sensitive unit~
In a preferred embodiment, the thermally-responsive actuator of the steam-sensitive Lmit comprises a bimetallic elementO The bimetallic element pre~erably comprises a member of sheet bimetal having an aperture with an outer perimeter and an inner perimeter defining a ton~ue free at one end intermediate two lobe portions of said aperture, said inner perimeter and arcuate portions of said outer perimeter smoothly merging at rounded ends of the aperture adjacent the tongue root, the tongue being, at least in part, generally centrally disposed with respect to the member, the member having ... . . . . . . .. . .. ...... . .
. .
.~470 been defonned in a die presslng operation to conform in shape to a die o domed configuration, said domed area being such as to reverse its curvature with a snap action with change in temperature9 the width of the domed are being greatast ~, the region of the tongue root. Such an actuator is describ~d in German Offenlegungsschrift 2,556,062 and British Patent- Specification No. 1,542,252.
Preferably7 the over-centre mechanism comprises a lever pivotably mounted on a body member of the steam-sensitive unit so as to be movable between first and second positions through an unstable dead-centre positionO The pivotal mounting is preferably by meanS of at least one knife edge resting in a notch or bearing, the knife edge being retained in the notch by means of at least one C-spring extending between the lever and the body member. In such an arrangement, the dead-centre position occurs when the two ends of the C-spring lie in a common plane with the fulcrum o~ the lever.
The mechanical link preferably comprises a movable member which is acted on directly or indirectly by a lever of the over-centre mechanism and by a thermally responsive actuator of the switch unit. The movable member is preferably an elongate member movable in the direction of its axis, the lever comprising a portion extending through an aperture in the elongate member so as to engage therewith to operate said switch meansO
There is further provided the combination of a thermally-sensitive electrical control according to the invention and an electric immersion heater of the second kind described, wherein a hot return of the heating element is in thermal contact with the head in a position which, in use, i`s below the cold leads ... . .. ..... _ . .. . .. ..
~1~L7~9~
9 _ o~ the heatin~ element, a thermall~-sensitive actuator of the thermally-sensitive switch means being in thermal con-tact with the head in the vicinity o~ said position.
A preferred form of thermally-sensitive electrical con-trol according to the invention for an electric heater ofthe second kind described will now be described with reference to Figs l to 7 of the accompanying drawings.
There will further be described with reference to ~igures 8 to 14 of the accompanying drawings a ~lightly modified version of the first described control whereby steam or vapour may also be fed directly to the steam sensi-tive unit and the application of this modified control to a heater mounted externally of the container as well as to a kettle having an immersion heater of the-first kind des-cribed i.e. without a steam tube.
~ n the accompanying drawin~s wherein like parts bearthe same reference numerals;
Figure l is a perspective view from below and to one side of an embodiment of a thermally-sensitive ~20 eIectrical control according to the invention~ the housing of the control being removed;
Figure 2 is a side view of the control shown in Figure 1 r"ith the housing in place;
Figure 3 is a view corresponding to that of - 25 Figure 2~ but showing a cross-section;
Figure 4 is a front elevation of the control of Figures 2 and 3;
Figure 5 is a view corresponding to that of Figure 4~ but with the housing removed;
Figure 6 is a front elevation of a switch-on-dry protector switch unit forming part of the control shown in Figures l to 5; and Figure 7 is a side view of the switch unit shown in Figure 6.
~7~
Figure 8 is a side elevation partially in section of a water-boiling jug whose hea-ker is brazed to the underside of the base of the jug and fitted wlth a modified control accordiny to the invention wherein steam or vapour is intro-duced directly to the steam-sensitive unit of the control;
Figures 9 and 10 are side elevations in cross-section of the control as fitted in the jug;
Figure 11 is a perspective view from below and to one side of the control itself without its outer housing;
Figure lla is a perspective view of the body moulding of the switch-on-dry protector unit of the control;
Figures 12 and 13 are front elevations of the control respectively with and without an outer housing in place; and Figure 14 is a side elevation of an electric kettle fitted with a control as shown in Figs 8 to 13.
~ s shown in Figures 1 to 5 of the drawings, a thermally-sensitive electrical control is mounted on the head l~O~of an electrical immersion heater. The head is secured in a water-tight manner in an opening in the wall o~ a kettle 6. The head 10 carries a steam tube 5 for conducting steam from the interior of ~L~471;)~D:~
the kettle to the thermally-sensitive control. The tube ~ is arranged so as to extend in use above the water level in the kettle. The immersion heater comprises two cold leads 3 and a hot return ll which passes underneath the cold leads 3 and is brazed to the head lO so as to be in thermal contact therewith. By virtue of the pro~imity of the hot return to the base of the kettle, the kettle is capable of boiling a small quantity of water if desired.
The thermally-sensitive electrical control comprises a switch-on-dry protector switch unit 2 mounted on the head lO and a steam-sensitive unit 1 which is in turn mounted on the switch unit 2. The switch unit 2 is lS provided with three pins 4., including a line pin, a neutral pin and an earth pin, for connection to a female socket to supp~y mains electrical power to the heating element. The line pin is connected to one of the cold leads 3 vla a pair of electrical contacts including a movable contact 7 mounted on a resilient conductive strip 27 and a stationary contact 8 (Figure
3). When the contacts are separated, the supply of electrical current to the heating element is cut off.
A bimetallic actuator 9 of the type disclosed in Offenleguhgsschrifc 2,556,062 is provided in the protector switch unit, the tongue of the actuator being riveted to a pillar of the unit~ and the main bod~
of the actuator being in thermal contact with the head lO in the'cold" position of the actuator. A
mechanical link in the forrn of an elongate member 12 ~:~L47(1~)~
r. - 1.2-is mounted in the protector switch unit 2 so as to be slidable in its axial direction, the member 12 including an upwardly extending stop 29 adapted to engage the lower end of the resilient strip 27. Thus, when the kettle is switched on dry, that is without the heating element being covered by water~ so that the temperature of the element rises above its normal working temperature to, say 120C, the actuator 9 reverses its curvature with a snap action, moving the member 12 'eftwardly as shown in Figure 3, thereby moving the movable contact 7 away from the fixed contact 8.
The steam-sensitive unit 1 comprises a body member 13 which seats over the switch unit 2. The body member 13 has apertures therethrough for the pins 4 and includes a shroud 14 which surrounds the pins and guides the female socket in use. An aperture 15 through the body member 13 receives the end of the steam tube 5 and is sealed thereto by an 0-ring seal 37. A lever member 16 ~` is pivotably mounted on the body member 13 by means of t~o knife edges 17 formed integrally with the member 16 resting in notches 18 formed integrally with the member 13. Two over-centre C-springs 19 e~tend between notches formed in the lever member and body member respectively and bias the knife edges into engagement with the notches. The lever member 16 is pivotable between a first position in which two stops 25 provided on the lever member 16 are in contact with the face of the body member 13 and a second position (as shown in the drawings)in which two portions 20 ~70~3~
r of the member 16 came into contact with two pillars 21 formed on the shroud 14. In passing from one to the other position, the lever passes through an unstable dead centre position in which the two ends of S each of the C-springs and the knife edge pivots are all in a common plane.
A bimetallic actuator 22 similar to the actuator 9 is mounted by means of the rim of its domed area on the lever member 16. The actuator is orientated so thatits tongue 23 bears against apillar 24 formed on the body member 13 in its "hot" position. When the kettle boils, steam issues from the steam tube 5 and impinges on the actuator 22. The actuator then reverses its curvature with a snap action, so that its tongue 23 bears against the pillar 24, thus moving the lever member 16 from its irst to its second position. A portion 26 of the lever extends through an aperture in the elongate mernber 12. Thus, when the lever moves from its ~irst to :its second position, the portion 26 of the lever engages the member 12 and slides it le~twardly as shown in Figure 3, thereby separatin~ the contacts 7,8 as described above. The effect is that when the kettle boils, the lever 16 is tr-pped by the actuator 22 from its first to its second position, thus interruptin~ the supply of electricity to the heating element. When the actuator 9 of~le protector switch unit separates the contacts 7, 8, the movement of the member 12 trips the lever 16 so that it moves from its first to its second positon thus retaining the contacts in their separated position.
~ 70 r~
A knob 28 is mounted on the lever member 16 and extends through an aperture 30 in a housing 31 surrounding the thermally-sensitive control, for manually resetting the control. I~hen the knob 28 is - 5 pressed downwardly, the lever member 16 is retured to its first position, thus allowing the resilient strip 27 to move the movable contact 7 into electrical contact with the fixed contact 8. The supply of current to the heating element can then be resumed.
At the same time, the resilient strip 27 shifts the member 12 in the rightward direction as shown in Figure 3.
Thus, the parts of the control which carry electricity in use are all carried by the dry-switch-on protector unit 2 and are shielded from the steam issuing from the steam tube 5 by the body of the steam-sensitive unit 1, a mechanical link being provided between the over-centre mechanism and the switch means of ,the protector switch unit.
Referring now to ~igures6 and 7 of the drawings there is shown ~he dry-switch-on protector switch unit of Figures l to 5, but used without the steam-sensitive switch. The element on which this unit is mounted will thus be protected if the kettle is switched on dry or allowed to boil dry, but will not be switched off automatically when the kettle boils. The unit 2 is mounted on the head 10 without modification and is enclosed by a housing 32 which includes a portion 33 forming a shroud for the pins 4. The housing 32 is secured to the head lO by means of an internally ~4~01~
_ 15 -thre`aded ring 24 and the switch unit is secured to the housing by two screws 35 which enter two pillars 36 formed on the switch unit 2, as is the housing of the control o~ Figures 1 to 5.
It will thus be seen that the mechanical steam-sensitive switch unit of the present invention enables the use of a protector switch unit ~hich can be used in either an automatic or non-automatic kettle without modification. The unit costs of the switch unit can thus be reduced.
As shown in Figure ~ of the drawings, the thermally-sensitive electrical control l,2 is fitted to a jug 38 having an electrical.heater 39 brazed to the underside of the bottom 40 of the jugo The conkrol 1,2 is mounted on a bracket 41 brazed to a heated portion of the heater element, the bracket being provided in like manner as the head of an immersion heater with a mounting stud whereby the control is mounted thereto. A detachable base 42 of the jug encloses ~he heater 39, an opening in the side of the base 42 being provided to receive the control l,2. A lid (not shown) is provided for the jug 38 and a steam or vapour venting aperture 43 is provided at the top of the side wallO This aperture 43 communicates with a passage 44 defined between a handle structure 45 and the jug wall. The passage ~4 leads directly to the control l,2 so that when water boils in the jug and ~he lid is in place steam or water vapour is directed to the control l,20 Referring addi-tionally to Eigs.~ to 13 the thermally- -sensitive electrical control comprises a switch-on-dry protector switch unit 2 mounted on the bracket 41 and a steam-sensitive unit l which is in turn mounted on the switch unit 20 The switch unit 2 îs provided with three pins 4, including a line pin, a neutral pin and an earth pin, for connection to a female socket to supply mains electrical power to the heating elementO The line pin is connected to one of the cold leads 3,which extend through the bracket 41, via a pair of electrical contacts ~ncluding a movable contact 7 mounted on a resilient conductive strip 27 and a statinnary contact 8 (Figures 9 and l~). When the contacts are separated, the supply of electrical current to the heating element is cut off. A bimetallic actuator 9 of the type disclosed in Specification No. 1,542~252 is provided in the protector switch unit, the ~ongue of`the actuator being riveted to a pillar of the unit, and the main body of the actuator being 15 in thermal contact with the bracket 41 in the "cold" position of the actuatorO A mechanical link in the form o~ an elongate member 12 is mounted in the protector switch unit 2 so as to be slidable in its axial direction, the member 12 including an upwardly extending stop 29 adapted to enga~e the lower end 20 of the resilient strip 270 Thus, when the jug is switched on dryJ that is without any water in the jug, so that the . temperature of the element rises above its normal working temperaturel the actuator 9 is heated above its operating temperature by ~onduction o~ heat through bracket 41 and 25 actuator 9 reverses its curvature with a snap action! moving the member 12 rightwardly as shown in Figures 9 and lo~thereby - moving the movable contact 7 away from the fixed contact 80 The steam-sensitive unit 1 includes a body member 13 which seats over the switch unit 20 The body member 13 has 30 apertures therethrough for the pins 4 and includes a shroud 700~
14 which surrounds the pins and guides a female socket in use.
An aperture 15 is provided through the body member 13 capable of receiving a steam tube leading frorn the interior of the jug but in this case is blocked off by a plug 46. A lever member 16 of unit 1 is pivotably mounted on the body member 13 by mean of two knife edges 17 formed integrally with the member 16 resting in notches 18 formed integrally~with the member 130 Two over-centre C-springs 19 e~tend between notches formed in the lever member and body member respectively and bias the knife edges ~7 into engagement with the notches 180 The lever member 16 is pivotable between a first position in which two stops 25 provided on the lever member 16 are in contact with the face of the body member 13 and a second position (as shown in the drawings) in which two portions 20 of the member 16 15 c~me into contact with two pillars 21 formed on the shrou ~ 140 The stops 25 are provided on the lever member in the proxi-mity of the notches on the lever member for the two C-springs 19. Thus, a certain degree of warping or inaccurate formation of the lever member 16 does not affect the opertion of the over-centre mechanism in view of the fact tllat any change in the distance between the knife edges 17 and the stops 25 owing to warping of the lev~r member is taken up by a similar change in the distance between the notch for the C-spring and the knife edge fulcrum. In passing from one to the other position~ the lever passes through an unstable dead centre position in which the two ends of each of the C~springs and the knife edge pivots are all in a common plane.
A bimetallic actuator 22 similar to the actuator 9 is mounted by means of the rim of its domed area on the lever o~
member 160 The actuator is orientated so that its tongue 23bears against a pillar 24 formed on the body member 13 in its "hot" positionO When the water in the jug boils, steam or vapour issues ~rom the aperture 43 passes along passage 44 and imDin~es on the actuator 22 as described hereinafterO The.
actuator then reverses its curvature with a snap action, so that its tongue 23 bears agai~st the pillar 2~j thus mo~-ing the lever member.16 ~rom its first (Figo 9) to its second position (~igoI0) A portion 26 of the lever 16 extends through an aperture in the elongate member 120 Thus, when the lever moves from its first to its second position, the portion 26 of the lever engages the member 12 and slides it rightwardl~
as shown in Figures 9 and lO,thereby separating the contacts 7,8 as described above~ The ~f~ect is that when the water boils, the lever 16 is tripped by the actuator 22 from its first to its second position, thus interrupting the supply of electricity to the heating elementO When the actuator 9 of the protector ~witch unit separates the contacts 7,8, the movement o~ the member 12 also trips the lever 16 so that it 20 moves from its first to its second position thus retaining the contacts in their separated position ~see Flg.10).
A knob 28 is mounted on the lever member 16 and extends through an aperture 30 in a housing 31 surrounding the thermally-sensitive control, for manually resetting the 25 controlO When the knob 28 is pressed dowrlwardly, the lever member 16 isreturned to its ~irst position, thus allowing the resilient strip 27 to move the movable contact 7 into electrical contact with the fixed contact 80 The supply of current to the heating element can then be resumedO At the 30 same time, the resilient strip 27 shifts the membèr 12 in the ~7010~.
left-~ard direction as shown in Figures lo and 11.
As shown in Figs 10 to 13 the upper part of the body member 13 is adapted to provide a steam or vapour channel 47 open upwardly to co~municate with passage 44 and laterally to S direct steam or vapour toward actuator 220 Plug 46 prevents passage of steam or vapour into the dry-switch-on protector unit 2 and pins~ 4 are shielded from the steam issuing from the channel 47 by the shroud of the steam-sensitive unit 1, a mechanical link being provided between the over-centre mechanism and the switch means of the protector switch unit.
Housing 31 is secured to the unit 2 by screws 35 which engage internally threaded pillars 48 on the unit ~ (FigOlla), these pillars extending through apertures in body member 13~
thus securing steam-sensit:ive unit 1 on unit 20 Fig. l]a also shows clearly the integral protective guides 50 for the link member 120 Referring to Fig.14 there is shown the control of ~igso 8 to 13 fi~ted to an electric kettle having an immersion 20 heater 49, the control being mounted in conventional manner on the heater head 10, the head likewise being secured in conventional manner in a water-tight fashion in an opening in the wall of the kettleO An aperture 43 is provided in the kettle wall and a passage 44 is defined between the handle 25 structure 45 and the kettle wall whereby steam or vapour issuing from aperture 43 is led to the stec~m unit 7 in like manner as with the water ~oiling JUg.
A bimetallic actuator 9 of the type disclosed in Offenleguhgsschrifc 2,556,062 is provided in the protector switch unit, the tongue of the actuator being riveted to a pillar of the unit~ and the main bod~
of the actuator being in thermal contact with the head lO in the'cold" position of the actuator. A
mechanical link in the forrn of an elongate member 12 ~:~L47(1~)~
r. - 1.2-is mounted in the protector switch unit 2 so as to be slidable in its axial direction, the member 12 including an upwardly extending stop 29 adapted to engage the lower end of the resilient strip 27. Thus, when the kettle is switched on dry, that is without the heating element being covered by water~ so that the temperature of the element rises above its normal working temperature to, say 120C, the actuator 9 reverses its curvature with a snap action, moving the member 12 'eftwardly as shown in Figure 3, thereby moving the movable contact 7 away from the fixed contact 8.
The steam-sensitive unit 1 comprises a body member 13 which seats over the switch unit 2. The body member 13 has apertures therethrough for the pins 4 and includes a shroud 14 which surrounds the pins and guides the female socket in use. An aperture 15 through the body member 13 receives the end of the steam tube 5 and is sealed thereto by an 0-ring seal 37. A lever member 16 ~` is pivotably mounted on the body member 13 by means of t~o knife edges 17 formed integrally with the member 16 resting in notches 18 formed integrally with the member 13. Two over-centre C-springs 19 e~tend between notches formed in the lever member and body member respectively and bias the knife edges into engagement with the notches. The lever member 16 is pivotable between a first position in which two stops 25 provided on the lever member 16 are in contact with the face of the body member 13 and a second position (as shown in the drawings)in which two portions 20 ~70~3~
r of the member 16 came into contact with two pillars 21 formed on the shroud 14. In passing from one to the other position, the lever passes through an unstable dead centre position in which the two ends of S each of the C-springs and the knife edge pivots are all in a common plane.
A bimetallic actuator 22 similar to the actuator 9 is mounted by means of the rim of its domed area on the lever member 16. The actuator is orientated so thatits tongue 23 bears against apillar 24 formed on the body member 13 in its "hot" position. When the kettle boils, steam issues from the steam tube 5 and impinges on the actuator 22. The actuator then reverses its curvature with a snap action, so that its tongue 23 bears against the pillar 24, thus moving the lever member 16 from its irst to its second position. A portion 26 of the lever extends through an aperture in the elongate mernber 12. Thus, when the lever moves from its ~irst to :its second position, the portion 26 of the lever engages the member 12 and slides it le~twardly as shown in Figure 3, thereby separatin~ the contacts 7,8 as described above. The effect is that when the kettle boils, the lever 16 is tr-pped by the actuator 22 from its first to its second position, thus interruptin~ the supply of electricity to the heating element. When the actuator 9 of~le protector switch unit separates the contacts 7, 8, the movement of the member 12 trips the lever 16 so that it moves from its first to its second positon thus retaining the contacts in their separated position.
~ 70 r~
A knob 28 is mounted on the lever member 16 and extends through an aperture 30 in a housing 31 surrounding the thermally-sensitive control, for manually resetting the control. I~hen the knob 28 is - 5 pressed downwardly, the lever member 16 is retured to its first position, thus allowing the resilient strip 27 to move the movable contact 7 into electrical contact with the fixed contact 8. The supply of current to the heating element can then be resumed.
At the same time, the resilient strip 27 shifts the member 12 in the rightward direction as shown in Figure 3.
Thus, the parts of the control which carry electricity in use are all carried by the dry-switch-on protector unit 2 and are shielded from the steam issuing from the steam tube 5 by the body of the steam-sensitive unit 1, a mechanical link being provided between the over-centre mechanism and the switch means of ,the protector switch unit.
Referring now to ~igures6 and 7 of the drawings there is shown ~he dry-switch-on protector switch unit of Figures l to 5, but used without the steam-sensitive switch. The element on which this unit is mounted will thus be protected if the kettle is switched on dry or allowed to boil dry, but will not be switched off automatically when the kettle boils. The unit 2 is mounted on the head 10 without modification and is enclosed by a housing 32 which includes a portion 33 forming a shroud for the pins 4. The housing 32 is secured to the head lO by means of an internally ~4~01~
_ 15 -thre`aded ring 24 and the switch unit is secured to the housing by two screws 35 which enter two pillars 36 formed on the switch unit 2, as is the housing of the control o~ Figures 1 to 5.
It will thus be seen that the mechanical steam-sensitive switch unit of the present invention enables the use of a protector switch unit ~hich can be used in either an automatic or non-automatic kettle without modification. The unit costs of the switch unit can thus be reduced.
As shown in Figure ~ of the drawings, the thermally-sensitive electrical control l,2 is fitted to a jug 38 having an electrical.heater 39 brazed to the underside of the bottom 40 of the jugo The conkrol 1,2 is mounted on a bracket 41 brazed to a heated portion of the heater element, the bracket being provided in like manner as the head of an immersion heater with a mounting stud whereby the control is mounted thereto. A detachable base 42 of the jug encloses ~he heater 39, an opening in the side of the base 42 being provided to receive the control l,2. A lid (not shown) is provided for the jug 38 and a steam or vapour venting aperture 43 is provided at the top of the side wallO This aperture 43 communicates with a passage 44 defined between a handle structure 45 and the jug wall. The passage ~4 leads directly to the control l,2 so that when water boils in the jug and ~he lid is in place steam or water vapour is directed to the control l,20 Referring addi-tionally to Eigs.~ to 13 the thermally- -sensitive electrical control comprises a switch-on-dry protector switch unit 2 mounted on the bracket 41 and a steam-sensitive unit l which is in turn mounted on the switch unit 20 The switch unit 2 îs provided with three pins 4, including a line pin, a neutral pin and an earth pin, for connection to a female socket to supply mains electrical power to the heating elementO The line pin is connected to one of the cold leads 3,which extend through the bracket 41, via a pair of electrical contacts ~ncluding a movable contact 7 mounted on a resilient conductive strip 27 and a statinnary contact 8 (Figures 9 and l~). When the contacts are separated, the supply of electrical current to the heating element is cut off. A bimetallic actuator 9 of the type disclosed in Specification No. 1,542~252 is provided in the protector switch unit, the ~ongue of`the actuator being riveted to a pillar of the unit, and the main body of the actuator being 15 in thermal contact with the bracket 41 in the "cold" position of the actuatorO A mechanical link in the form o~ an elongate member 12 is mounted in the protector switch unit 2 so as to be slidable in its axial direction, the member 12 including an upwardly extending stop 29 adapted to enga~e the lower end 20 of the resilient strip 270 Thus, when the jug is switched on dryJ that is without any water in the jug, so that the . temperature of the element rises above its normal working temperaturel the actuator 9 is heated above its operating temperature by ~onduction o~ heat through bracket 41 and 25 actuator 9 reverses its curvature with a snap action! moving the member 12 rightwardly as shown in Figures 9 and lo~thereby - moving the movable contact 7 away from the fixed contact 80 The steam-sensitive unit 1 includes a body member 13 which seats over the switch unit 20 The body member 13 has 30 apertures therethrough for the pins 4 and includes a shroud 700~
14 which surrounds the pins and guides a female socket in use.
An aperture 15 is provided through the body member 13 capable of receiving a steam tube leading frorn the interior of the jug but in this case is blocked off by a plug 46. A lever member 16 of unit 1 is pivotably mounted on the body member 13 by mean of two knife edges 17 formed integrally with the member 16 resting in notches 18 formed integrally~with the member 130 Two over-centre C-springs 19 e~tend between notches formed in the lever member and body member respectively and bias the knife edges ~7 into engagement with the notches 180 The lever member 16 is pivotable between a first position in which two stops 25 provided on the lever member 16 are in contact with the face of the body member 13 and a second position (as shown in the drawings) in which two portions 20 of the member 16 15 c~me into contact with two pillars 21 formed on the shrou ~ 140 The stops 25 are provided on the lever member in the proxi-mity of the notches on the lever member for the two C-springs 19. Thus, a certain degree of warping or inaccurate formation of the lever member 16 does not affect the opertion of the over-centre mechanism in view of the fact tllat any change in the distance between the knife edges 17 and the stops 25 owing to warping of the lev~r member is taken up by a similar change in the distance between the notch for the C-spring and the knife edge fulcrum. In passing from one to the other position~ the lever passes through an unstable dead centre position in which the two ends of each of the C~springs and the knife edge pivots are all in a common plane.
A bimetallic actuator 22 similar to the actuator 9 is mounted by means of the rim of its domed area on the lever o~
member 160 The actuator is orientated so that its tongue 23bears against a pillar 24 formed on the body member 13 in its "hot" positionO When the water in the jug boils, steam or vapour issues ~rom the aperture 43 passes along passage 44 and imDin~es on the actuator 22 as described hereinafterO The.
actuator then reverses its curvature with a snap action, so that its tongue 23 bears agai~st the pillar 2~j thus mo~-ing the lever member.16 ~rom its first (Figo 9) to its second position (~igoI0) A portion 26 of the lever 16 extends through an aperture in the elongate member 120 Thus, when the lever moves from its first to its second position, the portion 26 of the lever engages the member 12 and slides it rightwardl~
as shown in Figures 9 and lO,thereby separating the contacts 7,8 as described above~ The ~f~ect is that when the water boils, the lever 16 is tripped by the actuator 22 from its first to its second position, thus interrupting the supply of electricity to the heating elementO When the actuator 9 of the protector ~witch unit separates the contacts 7,8, the movement o~ the member 12 also trips the lever 16 so that it 20 moves from its first to its second position thus retaining the contacts in their separated position ~see Flg.10).
A knob 28 is mounted on the lever member 16 and extends through an aperture 30 in a housing 31 surrounding the thermally-sensitive control, for manually resetting the 25 controlO When the knob 28 is pressed dowrlwardly, the lever member 16 isreturned to its ~irst position, thus allowing the resilient strip 27 to move the movable contact 7 into electrical contact with the fixed contact 80 The supply of current to the heating element can then be resumedO At the 30 same time, the resilient strip 27 shifts the membèr 12 in the ~7010~.
left-~ard direction as shown in Figures lo and 11.
As shown in Figs 10 to 13 the upper part of the body member 13 is adapted to provide a steam or vapour channel 47 open upwardly to co~municate with passage 44 and laterally to S direct steam or vapour toward actuator 220 Plug 46 prevents passage of steam or vapour into the dry-switch-on protector unit 2 and pins~ 4 are shielded from the steam issuing from the channel 47 by the shroud of the steam-sensitive unit 1, a mechanical link being provided between the over-centre mechanism and the switch means of the protector switch unit.
Housing 31 is secured to the unit 2 by screws 35 which engage internally threaded pillars 48 on the unit ~ (FigOlla), these pillars extending through apertures in body member 13~
thus securing steam-sensit:ive unit 1 on unit 20 Fig. l]a also shows clearly the integral protective guides 50 for the link member 120 Referring to Fig.14 there is shown the control of ~igso 8 to 13 fi~ted to an electric kettle having an immersion 20 heater 49, the control being mounted in conventional manner on the heater head 10, the head likewise being secured in conventional manner in a water-tight fashion in an opening in the wall of the kettleO An aperture 43 is provided in the kettle wall and a passage 44 is defined between the handle 25 structure 45 and the kettle wall whereby steam or vapour issuing from aperture 43 is led to the stec~m unit 7 in like manner as with the water ~oiling JUg.
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A thermally-responsive electrical control for an electric heater of a water boiling container comprising a heating element terminating in cold leads, said control including a switch-on-dry protector switch unit adapted to make electrical connection with the cold leads of the heating element and including thermally sensitive switch means effective, in use, to interrupt the electrical supply to the heater should the element overheat through being switched on when the container is dry, said control further including a steam-sensitive unit adapted to be mounted on said protector switch unit, said steam-sensitive unit including an overcentre spring mechanism and a thermally-responsive actuator for said mechanism, the control being adapted for the impingement on said actuator of said steam-sensitive unit of vapour or steam issuing from the outlet of a tube or passage leading to the interior of said container, electrical parts of said control being shielded from such vapour or steam, a mechanical link being provided between said overcentre spring mechanism and the switch means of said protector switch unit so that on said overcentre spring mechanism being tripped by said actuator, said link serves mechanically to operate said switch means of the protector switch unit, said protector switch unit being separable from said steam-sensitive unit and able to be mounted on said container in the absence of said steam-sensitive unit.
2. A control as claimed in claim 1, wherein the thermally-responsive actuator of the steam-sensitive unit comprises a bimetallic element, the bi-metallic element comprising a member of sheet bimetal having an aperture with two lobe portions and an outer perimeter and an inner perimeter defining a tongus free at one end intermediate the two lobe portions of said aperture, said inner perimeter and arcuate portions of said outer perimeter smoothly merging at rounded ends of the aperture adjacent a root of the tongue, the tongue being, at least in part, generally centrally disposed with respect to the member, the member having been deformed in a die pressing operation to conform in shape to a die of domed configuration, said domed area being such as to reverse its curvature with a snap action with change in temperature, the width of the domed area being greatest in the region of the tongue root.
3. A control as claimed in claim 1, wherein the over-centre mechanism comprises a lever mounted on a body member of the steam-sensitive unit by means of a pivotal mounting so as to be movable between first and second positions through an unstable dead-centre position.
4. A control as claimed in claim 3, wherein the pivotal mounting com-prises at least one knife edge resting in a notch, the knife edge being retained in the notch by means of at least one C-spring extending between the lever and the body member.
5. A control as claimed in claim 3, wherein the mechanical link comprises a movable member which is acted on directly or indirectly by said lever and by a thermally responsive actuator of the protector switch unit.
6. A control as claimed in claim 5, wherein the movable member is an elongate member movable in the direction of its length.
7. A control as claimed in claim 6, wherein the lever comprises a portion which extends through an aperture in the elongate member.
8. A control as claimed in claim 5, wherein the switch means comprises a stationary electrical contact and a movable electrical contact, the movable electrical contact being mounted on a resilient member engageable by the movable member.
9. A control as claimed in claim 8, wherein movement of the movable member by the thermally responsive actuator of the protector switch unit so as to separate the contacts moves said lever to its second position thus retaining the contacts in their separated position.
10. A control as claimed in claim 1 in combination with a heating element, the heating element being in thermal contact with the thermally sensitive switch means of the protector switch unit.
11. The invention as claimed in claim 10, in a water boiling container, wherein the heater is an immersion heater, the control is mounted on a head secured in water-tight manner in or adjacent an opening in the container wall, and a tube for conducting vapour or steam from the interior of the container to the thermally-responsive actuator passes through the head and through a body member of the steam-sensitive unit.
12. The invention as claimed in claim 10, in a water boiling container, wherein the heater is in thermal contact with the exterior of the container, the control is mounted on a mounting plate in direct or indirect thermal contact with the heater, and a tube or passage for conducting vapour or steam from the interior of the container to the thermally-responsive actuator extends along the outside of the container.
13. The invention as claimed in claim 12, wherein the steam tube or passage enters the steam-sensitive unit without passing through the switch-on-dry protector unit.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7901289A GB2012288B (en) | 1978-01-12 | 1979-01-12 | Polyesteramides and process for producing the same |
| GB7901400 | 1979-01-15 | ||
| GB7901400 | 1979-01-15 | ||
| GB7901289 | 1979-03-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1147001A true CA1147001A (en) | 1983-05-24 |
Family
ID=26270216
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000343704A Expired CA1147001A (en) | 1979-01-12 | 1980-01-15 | Thermally-sensitive electrical controls for electric heaters |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1147001A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5968393A (en) * | 1995-09-12 | 1999-10-19 | Demaline; John Tracey | Hot water controller |
-
1980
- 1980-01-15 CA CA000343704A patent/CA1147001A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5968393A (en) * | 1995-09-12 | 1999-10-19 | Demaline; John Tracey | Hot water controller |
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