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WO1998001874A1 - Ameliorations apportees a des commutateurs a commande electrique receptifs a la chaleur - Google Patents

Ameliorations apportees a des commutateurs a commande electrique receptifs a la chaleur Download PDF

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Publication number
WO1998001874A1
WO1998001874A1 PCT/GB1997/001856 GB9701856W WO9801874A1 WO 1998001874 A1 WO1998001874 A1 WO 1998001874A1 GB 9701856 W GB9701856 W GB 9701856W WO 9801874 A1 WO9801874 A1 WO 9801874A1
Authority
WO
WIPO (PCT)
Prior art keywords
switch
electrical switch
electrical
control
housing part
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.)
Ceased
Application number
PCT/GB1997/001856
Other languages
English (en)
Inventor
Robert Andrew O'neill
Antonio Martin Gaeta
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Otter Controls Ltd
Original Assignee
Otter Controls Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Otter Controls Ltd filed Critical Otter Controls Ltd
Priority to AU34542/97A priority Critical patent/AU3454297A/en
Publication of WO1998001874A1 publication Critical patent/WO1998001874A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00

Definitions

  • This invention concerns improvements relating to thermally-responsive electric switches, and has particular though not exclusive application to the field of thermally-responsive electric switches for use in electrically heated vessels such as kettles, jugs, urns, pans, laboratory equipment and the like for switching off or reducing the supply of power to an electric heating element of the vessel when water or another liquid boils in the vessel and the hot vapour that is generated impinges upon a thermally-responsive switch-actuating element.
  • an element protector control such as our X-type control is to protect the heating element of an electrically powered water boiling vessel such as a kettle or hot water jug against overheating caused for example by switching the vessel on without first filling it with water, the element protector control responding rapidly to the element temperature rising above its normal operating level and switching off the electrical supply to the element.
  • An alternative exemplary form of the J-type steam sensor is shown in Figures 9A and 9B of
  • GB-A-2 212 664 The disclosures of GB-A-2 212 664 and
  • the thermally responsive element of the control is commonly constituted by a bimetal, often a snap-acting bimetal, which is arranged to change condition upon exposure to a predetermined temperature change, for example the change that occurs when it is exposed to steam generated when water boils in the respective vessel.
  • a bimetal often a snap-acting bimetal, which is arranged to change condition upon exposure to a predetermined temperature change, for example the change that occurs when it is exposed to steam generated when water boils in the respective vessel.
  • shape memory effect technology has been proposed and has been utilized. See in this connection our British Patent Application No. 9507386.2 and British Patent Specification No. GB-A-2 150 759 which both describe steam sensors for water boiling vessels which make use of coils of shape memory metal which elongate upon exposure to steam.
  • the present invention is not restricted to any particular form of thermally responsive actuator.
  • the J-type control that is described in GB-A-2 212 664 with reference, for example, to Figures 9A and 9B of the drawings thereof, comprises a main synthetic plastics moulding which defines spaced-apart abutments for an in-line combination consisting of a so-called trip lever, to which an ON-OFF operating knob of the vessel can be attached, and a creep acting bimetallic blade, the trip lever/bimetallic blade combination being arranged to move over-centre in response to impingement of steam onto the bimetallic blade.
  • the main moulding has a chamber which accommodates a switch sub-assembly consisting of two contact-carrying leaf springs, and the trip lever has a projection which co-operates with one of the leaf springs so that when the trip lever/bimetallic blade combustion moves to its hot condition the projection bears upon the respective leaf spring and moves it out of electrical contact with the other leaf spring. Having responded in this manner to the generation of steam within an associated vessel, the arrangement remains in this contacts-open condition until such time as it is manually reset.
  • the main plastics material moulding is designated 44
  • the trip lever is designated 45
  • the bimetallic blade is designated 46
  • the switch sub-assembly consists of leaf springs designated 41 and 42 which are affixed to a moulded plastics carrier 43.
  • the J-type control unavoidably gets wet as a result of steam condensing on the relatively cold control.
  • the control carries the electrical supply voltage of the associated vessel since the powering of the vessel heating element is arranged to be dependent upon the status of the steam control.
  • the moulded plastics parts of the control are thus subject to the normal operating voltages arising between the electrical parts of the control, namely between the leaf springs of the switch assembly, and, given that the control may get wet in operation, this can lead to arcing across wet moulded plastics surfaces of the control. This in turn can degrade the plastics material of the control and give rise to carbon tracks which progressively degrade the electrical insulation properties of the plastics mouldings. Failure of the control can result.
  • the principal object of the present invention is to provide a solution to the problem aforementioned of carbon tracking on the moulded plastics parts of steam sensors for water boiling vessels, without need for relatively expensive sealing arrangements incorporating silicone rubber diaphragm seals.
  • the above object is at least substantially attained by an arrangement wherein moulded plastics materials continue to be utilized for the major components of the control, despite their susceptibility as hydrocarbon materials to degradation and the formation of carbon tracks under the influence of electrical arcing over wet surfaces, but the electrical terminal parts of the control are insulated from each other by means of ceramics material parts that are incorporated into the control, preferably as push-fit components which engage with appropriately formed apertures in the control. Ceramics materials, which generally speaking contain little or no carbon, are not susceptible to carbon tracking when wet.
  • a main chassis moulding, a trip lever and a switch carrier member are all formed of synthetic plastics material as has heretofore been customary in J-type controls.
  • the switch carrier member has a portion defining a rectangular frame, and first and second contact carrying leaf springs are retained in the frame by means of non-conductive ceramics material spacers which assemble together and with the leaf springs to form a generally rectangular block which fits closely into the frame.
  • a single preformed block may be provided having recesses formed therein for receiving the ends of the leaf springs.
  • the main chassis moulding is replaced by a pressed metal or die-cast metal housing.
  • a plastics material switch housing affixes to the metal housing in push-fit manner and contact carrying leaf springs are retained in the plastics material switch housing by means of ceramics material spacers.
  • the metal chassis can serve as a mounting for an in-line bimetal and trip lever overcentre combination as in the J-type control, or can mount a different kind of thermally-responsive switch actuator such as a creep-acting or snap-acting bimetal or a shape memory effect actuator.
  • Figures 1A and IB are perspective views from different directions of a J-type steam sensor embodying the present invention, but with the bimetal and trip lever omitted.
  • Figure 1C is a perspective view showing first and second leaf springs and associated ceramics material spacers
  • Figure ID is a perspective view showing how the assembled leaf springs and ceramics material spacers are retained in a switch carrier
  • Figure IE shows how the switch carrier with its retained leaf springs and ceramics material spacers is retained in the chassis moulding of the embodiment
  • FIG. 2A shows an alternative J-type steam sensor embodying the present invention with its component parts disassembled and Figure 2B is a perspective view of the assembled steam sensor;
  • FIG. 3 shows yet another steam sensor embodying the present invention.
  • the steam sensor control of Figures 1A to IE comprises a plastics material chassis or main body moulding 1 which defines spaced-apart abutments 2 and
  • the moulding 1 has a chamber 4 formed therein for receiving a switch sub-assembly 5 which is shown in Figure IE in assembled condition and in progressively disassembled condition in Figures ID and lC.
  • the switch sub-assembly 5 consists of a moulded plastics material carrier 6 which has a first part 7 which serves as a side wall closure for the chamber 4 of the main chassis moulding 1 and a second part 8 which defines a rectangular open frame, first and second contact-carrying leaf springs 9 and 10, and first and second non-conductive ceramics material spacers 11 and 12.
  • the leaf springs 9 and 10 are formed with tab receptacles 13 at their rear ends and the spacers 11 and 12 are formed with recesses 14 substantially complementary to the tab receptacles 13. Formations 15 are provided on the tab receptacles 13 and project from opposite sides thereof in the manner of ears, and complementary recesses 16 are provided in the spacers 11 and 12 for accommodating the ears 15.
  • the receptacles 13 at the ends of the leaf springs nest in and are retained by the recesses 14 of the ceramics material spacers 11 and 12 in the manner shown in Figure ID.
  • the spacer 12 has an extended end portion which, in the assembled arrangement, increases the electrical creepage distance between the tab receptacles and reduces the risk of tab terminations received in the receptacles accidentally contacting each other.
  • the assembled leaf springs 9 and 10 and ceramics material spacers 11 and 12 define a generally rectangular block structure 17 which is dimensioned to fit tightly into the frame defined by the part 8 of the carrier member 6 so as to constitute the switch sub-assembly 5 shown in Figure IE.
  • Co-operating dovetail slide features 18 are provided on respective edges of the frame part 8 of the leaf spring carrier 6 and on the chassis moulding 1, and click features 19 are provided on these parts to retain the switch sub-assembly 5 in the chassis moulding 1.
  • the bimetal actuator and the trip lever of the embodiment of Figures 1A to IE are not shown in the drawings, the operation of the described steam sensor will be well understood from consideration of GB-A-2 212 664.
  • the trip lever has a finger portion which extends into the chamber 4 of the main chassis moulding where, depending on the state of the bimetal, it can abut the free end of the leaf spring 10 and depress it out of electrical contact with the other leaf spring 9.
  • the leaf springs 9 and 10 are electrically isolated from each other by the non-conductive ceramics material spacers 11 and 12.
  • the receptacle 13 at the end of leaf spring 10 is in fact surrounded by ceramics material on all sides, whereas the receptacle 13 at the end of leaf spring 9 is isolated on three sides by ceramics material and on the fourth side by the plastics material of the carrier member 6.
  • This arrangement ensures that the maximum possible amount of ceramics material surrounds the leaf spring 10 and isolates it from leaf spring 9 thereby ensuring optimum electrical separation between the two leaf springs. Since the leaf springs 9 and 10 are isolated from each other by non-conductive ceramics material which does not suffer from the tracking problems associated with synthetic plastics materials as described hereinbefore, an improved electrical performance of the embodiment as compared to conventional all plastics J-type controls will be achieved.
  • FIGS 2A and 2B show an alternative embodiment of the present invention which has much in common with the embodiment of Figures 1A to IE.
  • a main body moulding or chassis formed of synthetic plastics materials is designated 20 and defines spaced-apart abutments as in the above-described embodiment for the in-line combination of a trip lever 21 and a creep acting bimetal (not shown) .
  • a moulded plastics switch enclosure 22 is adapted to be welded or otherwise affixed to the main body moulding 20 as shown in Figure 2B and serves to accommodate a switch assembly comprising contact-carrying leaf springs 23 and 24 and one-piece ceramics material support block 25.
  • the block 25 has recesses 26 formed therein for receiving the ends of the leaf springs 23 and 24 and is sized to make a tight interference fit into the open end of enclosure 22.
  • a finger 27 on the trip lever 21 extends into the enclosure 22 through an aperture 28 in its upper wall and, within the enclosure 22, abuts the lowermost leaf spring 23 for urging the same into a contacts-open condition of the switch assembly when the bimetal responds to the impingement of steam thereupon.
  • the embodiment of Figures 2A and 2B is functionally the same as the embodiment of Figures 1A to IE.
  • FIG. 3 Yet another embodiment of the invention is illustrated in Figure 3 where a metal chassis 30, formed by pressing or by die casting for example, is adapted to carry a moulded plastics material switch housing 31 which accommodates a switch sub-assembly 32 formed of contact-carrying leaf springs 33 and 34 and ceramics material spacer elements 35 and 36.
  • the metal chassis 30 of the Figure 3 embodiment provides spaced-apart abutments 37 and 38 for an overcentre movement type thermally-responsive actuator such as the in-line bimetal and trip lever combination previously described herein and described more fully in GB-A-2 212 664 with reference for example to Figures 9A and 9B of the drawings thereof.
  • the moulded plastics switch housing 31 has formations 39 which engage with complementary formations 40 in the metal chassis 30 to retain the two parts together, and arcuate slots 41 and 42 that are provided respectively in contiguous walls of the switch housing 31 and the chassis 30 register with each other to permit a limb of the trip lever to extend into the switch housing for operating the switch sub-assembly 32.
  • a further formation 43 provided on the switch housing 31 extends through an opening 44 in the chassis 30 and provides a mounting for a rotary cam (not shown) which constitutes an adjustable abutment against which the bimetal of the bimetal/trip lever combination works when switching the overcentre arrangement from its cold to its hot condition (see in this connection the fixed abutment 62 in Figure 3J of GB-A-2 212 664 and the corresponding description at lines 19-22 of page 22) .
  • the ceramics material spacer elements 35 and 36 operate to secure the leaf springs 33 and 34 in the switch housing 31 substantially as in the first embodiment.
  • the two elements 35 and 36 are identical and are formed to stack positively one upon the other with projections 45 formed on the under sides of the spacers engaging in recesses 46 formed in their upper sides. Note also the rearwardly extended portions 47 of the spacers which protect against accidental short-circuiting of electrical tab terminals and attached conductors which are engaged with the tab receptacles of the leaf springs 33 and 34 in use.
  • the metal chassis 30 as shown in Figure 3 is adapted for use with a creep acting bimetal and trip lever combination as taught in GB-A-2 212 664 and it is to be appreciated that alternative thermally responsive switch actuators could be employed, the chassis then being redesigned as appropriate.
  • a snap-acting bimetal or a shape memory effect actuator could be utilized in place of the creep acting bimetal and trip lever combination.

Landscapes

  • Thermally Actuated Switches (AREA)

Abstract

La présente invention porte sur une commande de détecteur de vapeur pour appareils chauffe-eau électriques, de type chopes ou bouilloires électriques, qui coupe l'alimentation en énergie de l'élément chauffant de l'appareil lorsque l'eau bout à l'intérieur de celui-ci. La commande fonctionne dans un milieu dont l'humidité est due à la condensation de la vapeur sur des parties relativement froides du dispositif de commande, ce qui peut entraîner un arc électrique rejoignant les surfaces humides dudit dispositif. Le dispositif de commande est habituellement constitué de pièces en plastique moulé (20, 21, 22) que cet amorçage d'arc électrique peut dégrader en donnant lieu à des pistes de carbone qui dégradent peu à peu les propriétés d'isolation électrique des moulages plastiques et risquent de provoquer une défaillance du dispositif de commande. Pour résoudre ce problème tout en évitant un travail d'étanchéité onéreux, il est proposé, dans le cadre de la présente invention, de continuer à utiliser des matières plastiques moulées pour les pièces les plus importantes (20, 21, 22) du dispositif de commande, mais d'isoler une extrémité électrique (23) de la commande de l'autre extrémité (24) en insérant dans la commande des pièces en céramique (25). Ces pièces sont de préférence des éléments qui s'emboîtent, prévus pour s'engager dans des ouvertures formées dans les éléments plastiques de la commande, les éléments à emboîter épousant la forme de ces ouvertures. En effet, les matières céramiques ne sont généralement pas sensibles aux pistes de carbone lorsqu'elles sont mouillées.
PCT/GB1997/001856 1996-07-10 1997-07-10 Ameliorations apportees a des commutateurs a commande electrique receptifs a la chaleur Ceased WO1998001874A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU34542/97A AU3454297A (en) 1996-07-10 1997-07-10 Improvements relating to thermally responsive electric switches

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9614437.3 1996-07-10
GB9614437A GB2315161B (en) 1996-07-10 1996-07-10 Improvements relating to thermally responsive electric switches

Publications (1)

Publication Number Publication Date
WO1998001874A1 true WO1998001874A1 (fr) 1998-01-15

Family

ID=10796636

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1997/001856 Ceased WO1998001874A1 (fr) 1996-07-10 1997-07-10 Ameliorations apportees a des commutateurs a commande electrique receptifs a la chaleur

Country Status (3)

Country Link
AU (1) AU3454297A (fr)
GB (1) GB2315161B (fr)
WO (1) WO1998001874A1 (fr)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1476995A (fr) * 1965-04-26 1967-04-14 Texas Instruments Inc Perfectionnements aux interrupteurs électriques étanches et à leurs dispositifs d'étanchéité
US3624323A (en) * 1969-01-07 1971-11-30 Borgmann Kg W Microswitch
FR2158396A1 (fr) * 1971-11-05 1973-06-15 Dreefs E Gmbh
EP0189593A2 (fr) * 1985-01-29 1986-08-06 EMERSON ELECTRIC GmbH & Co. Dispositif à fiche pour un appareil électrique, en particulier un régleur thermostatique
GB2212664A (en) * 1987-11-23 1989-07-26 Otter Controls Ltd Thermal sensors

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB355047A (en) * 1930-09-04 1931-08-20 John Ashworth Crabtree Improvements in, or relating to, electrical tumbler and other switches, bell-pushes,and the like

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1476995A (fr) * 1965-04-26 1967-04-14 Texas Instruments Inc Perfectionnements aux interrupteurs électriques étanches et à leurs dispositifs d'étanchéité
US3624323A (en) * 1969-01-07 1971-11-30 Borgmann Kg W Microswitch
FR2158396A1 (fr) * 1971-11-05 1973-06-15 Dreefs E Gmbh
EP0189593A2 (fr) * 1985-01-29 1986-08-06 EMERSON ELECTRIC GmbH & Co. Dispositif à fiche pour un appareil électrique, en particulier un régleur thermostatique
GB2212664A (en) * 1987-11-23 1989-07-26 Otter Controls Ltd Thermal sensors

Also Published As

Publication number Publication date
GB2315161B (en) 2000-10-11
AU3454297A (en) 1998-02-02
GB9614437D0 (en) 1996-09-04
GB2315161A (en) 1998-01-21

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