GB2334190A - A carrier which secures a plurality of thermostatic devices to the surface of a planar heating element. - Google Patents

Abstract

A carrier which secures a plurality of thermal sensor devices to the surface of a planar heating element. The carrier comprises a plurality of limbs 6, 7, 8 and 9, each limb has the provision for the attachment thereto of one or more thermal sensors 10 where in the thermal sensor device 10 may be secured at selectable different positions on each respective limb. The carrier incorporates an electrical input connector 3 for the heating element, spring terminals 32 and 33 project from the connector for contacting terminations provided on heating element. The electrical input connector 1 is adaptable to enable engagement with a complementary output connector throughout 360‹ of relative orientation of the two connectors. The planar heating element may be a thick film element. The arrangement is suitable for use in a cordless appliance comprising an appliance proper and a base part.

Description

IMPROVEMENTS RELATING TO THERNIAL CONTROLS FOR ELECTRIC HEATING ELENIENTS Field of the Invention: This invention concerns improvements relating to thermal controls for electric heating elements and, more particularly, concerns the arrangements that are disclosed in our British Patent Application No. 9717144.1 filed 12 August 1997.

Background of the Invention: In our British Patent Application No. 9717144 1 abovementioned there are disclosed various different chassis or carrier members adapted for attachment to a planar heating element and having provision for the assembly therewith of a plurality of thermal sensor devices at selectably variable positions. The described embodiments comprise an appliance inlet connector based upon the Otter Controls CP7 inlet connector as presently manufactured, but with a plurality of limbs extending outwardly from the connector in different directions all in the same plane, each limb having provision for the mounting of one or more thermal sensors on the limb at a number of different positions. It is further proposed to employ simpie contactstat type thermal sensors as the sensors to be mounted on the limbs. The invention of British Patent Application No. 9717144. l has as its rationale the provision of flexibility as r regards the positioning of sensors on planar heating elements inter alia to accommodate the requirements of different manufacturers.

Summarv of the Invention: The present invention applies the teachings of our British Patent Application No. 9710096.0 filed 19 May 1997 to the disclosure of British Patent Application No 9717 144. 1 abovementioned and provides for the appliance inlet connector to have spring connections for contacting terminal portions of the planar heating element. Additionally, the thermal sensor(s) mounted on the limbs of the appliance inlet connector can have spring connections For contacting respective contact portions of the planar heating element at the location(s) whereat the element temperature is required to be sensed.

The present invention further provides a convenient form of thermal sensor for use with an arrangement as abovedescribed.

Embodiments of the above and further features of the present invention are hereinafter described. by way of example only, with reference to the accompanying drawings.

Description of the Drawins: Figure 1 is a perspective view similar to Figure I of the drawings of British Patent Application No. 9717144. but with the terminals of the appliance inlet connector nnodified so as to form spring terminals and the terminals of the sensor likewise modified, Figure 2 shows the Figure 1 embodiment viewed from the other side thereof; Figure 3 is a perspective view of an exemplary sensor device; Figure 4 shows the device of Figure 3 as viewed from the other (bottom) end thereof; Figure 5 is a view similar to Figure 3 but with a top end cap of the sensor shown removed; Figure 6 is a view similar to Figure 4 but with a bottom end moulding of the sensor removed; and Figure 7 is a view similar to Figure 6 and showing one of the sensor terminals removed so as to show the internal arrangement of the device.

Detailed Description ofthe Embodiments: Referring first to Figures 1 and 2, these show a modified form of the currently manufactured Otter Controls CP7 3600 appliance inlet connector which is adapted to be used with an Otter Controls CS4 outlet connector in a cordless appliance, the CP7 inlet connector being fitted to the appliance proper, a hot water jug or electric kettle for example, and the CS4 outlet connector being fitted to the base part of the cordless appliance. As shown, the modified CP7 connector comprises a generally cylindrical moulded plastics matenal cup-shaped body portion 1 having a centrally-located hollow axial boss 9 which accommodates a central pin terminal ; and respective inwardly and outwardly facing spring terminals 4 and 5 which are adapted to make electrical contact with respective inner and outer cylindrical contact parts of a CS4 outlet connector when the two connectors are mated.

The modification of the CP7 connector that is effected in accordance with the teachings of the invention of British Patent Application No.

9717144.1 afiorementioned resides in the provision of four integrally formed limbs 6, 7. S and 9 extending radially outwardly from the body portion 1 all in the same plane perpendicular to the axis of the CP7 connector. The limbs 6 and S extend in opposite directions from opposite sides of the body portion 1, and the limbs 7 and 9 each extend in different directions which are not at 900 to each other and are not at 90 to either of the limbs 6 and 8.

The limbs 6, 7. S and 9 are each bifurcated and the two parts of each limb, for example the two pans 6' and 6" of limb 6, define therebetween an elongate slot or channel for accommodating a thermal sensor 10. The opposed surfaces of the channels are rippled so that a thermal sensor 10 introduced into the open end of a channel can be pushed therealong into a number of different positions where it will be positively located by the ripples. Only one sensor 10 is shown engaged with the limb 6 in Figures 1 and 2, but more or less sensors could be provided depending on the application and more than one sensor could be provided in any one or more of the limbs The limbs could be longer than in the illustrated embodiment and need not all be of the sane length, for use of the arrangement with a non-circular heating element for example, and the ripples 11 need not be uniformly spaced along the lengths of the limbs or along the length of any one or more of the limbs.

In the illustrated embodiment of Figures 1 and 2 it is contemplated that the arrangement will be attached to the underside of a planar heating element by engagement of depending studs that are provided on the heating element with separate clamping brackets 13, preferably formed of a relatively low thermal conductivity material such as stainless steel for example. By forming the braclcets 13 of a low thermal conductivity material, a degree of thermal isolation of the limbs from the heating element is provided. Since the brackets 13 are not part of the limbs, they can more readily accommodate variations in the positions of the studs, either as a resuit of tolerance variations in manufacture of the heating element, or resulting from different heating element designs from different manufacturers for example.

The embodiment of Figures 1 and 2 is substantially as described in our British Patent Application No. 9717144. l and differs principally therefrom in that the terminals 3', 4' and 5' of the appliance inlet connector, which connect to the conductors 3, 4 and 5 of the connector, are terminated as spring terminals rather than as spade terminals. Likewise the terminal conductors 32, 33 of the sensor(s) i 0 are formed as spring terminals. The rationale for this, as is explained in our British Patent Application No. 9710096.0 is that it reduces the task faced by the appliance manufacturer who no longer has to provide discrete conductor connections between terminals of the appliance inlet connector and of the appliance heating element, namely the assembly of the appliance inlet connector with the heating element makes the requisite electrical connections without necessitating additional wiring operations.

Furthermore. the spring terminals 3', 4' and 5' are readily able to accommodate positional tolerances, and additionally are readily able to accommodate movements of the heating element in use. We have found that planar heating elements coiprising a substrate having a resistance heating layer or track formed on one side thereof, with insulation as necessary is liable to bow in use and the spring terminals 3', 4' and 5 can readily accommodate this. The present invention contemplates that planar heating elements thus constructed might have pre-formed terminal locations adapted and arranged to mate with the spring terminals of such a device as has hereinbefore been described with reference to Figures 1 and 2.

Referring now to Figures z-7, shown therein is an exemplary contactstat type thermal sensor 10 adapted for use in the arrangement that is shown in Figures 1 and S. This sensor. as will be described hereinafter in detail. incorporates a snap-acting bimetallic disc in one end thereof to be held in close thermal contact with the surface whose temperature is to be monitored. The bimetallic disc is dished. as is well known, so as to be movable to an opposite curved configuration as the temperature changes through a certain predetermined level. The bimetal movement is transmitted by means of a push rod to a movabie switch component within the sensor and the status of the switch, contacts-open or contacts-closed. determines the status of the electrical conduction path through the sensor from one to the other of its external terminals. Contactstat devices of this general type are well known and only the principal features of the illustrated contactstat will be described in the following.

As shown in Figures 3 and 4, the contactstat 10 has a body portion 101 fonned of several plastics material mouldings as will be described hereinafter.

At one end of the body portion there is a bimetal retention cap 102 which is formed of a material having good thermal conductivity, copper for example, and makes a push fit onto the body portion. An aperture 103 is formed in the cap 103. At the other end. the body portion 101 has a grooved formation 104 which is adapted to cooperate with the limbs 6, 7, 8. 9 of the arrangement shown in Figures 1 and 2 and with the ripples 11 formed on the limbs. The bore 105 allows access to an internal adjusting screw ofthe contactstat.

Figures ; and 4 also show the external terminals 32 and 33 of the contactstat and it can be seen that, similarly to the terminals 3'. 4', 5' of the 360" inlet connector 1 that is built into the arrangement of Figures 1 and 2, the terminals 32 and 33 are formed as spring terminals for contacting terminal portions of a planar heating element.

Figure 5 shows a view similar to Figure 3, but with the end cap 102 removed from the body portion 101 so as to reveal the disc bimetal 106 and the push rod 107 which takes its movement from the edge of the bimetal. The push rod 107 transmits the movements of the bimetal 106 to the switch components which can be seen in Figure 6. which shows the contactstat with its lower cover moulding i OS removed, and in Figure 7, which shows a fixed contact mounting 109 removed, the mounting 109 being formed integrally with contactstat spring terminal 33 The lower cover moulding 108 defines with a main body moulding 110 an internal switch compartment 111 of the contactstat and the two external terminals 32, 33 extend into this compartment where they provide mollnts for a fixed contact 112, for a leaf spring 113 and for a moving contact 114. The terminal components 109 and 115 are secured to the main body moulding 110 by means of spigots 116 which are thermally deformed subsequent to installation of the components.

In operation of the contactstat. the end cap 102 is maintained in close thermal contact with the surface whose temperature is to be sensed and transfers heat to the bimetal 106. If the temperature rises above a predetermined level, the bimetal snaps to its oppositely dished configuration, namely from a convex configuration as viewed in Figure 5 to a concave configuration. which causes the push rod 107, which is normally depressed so as to push the leaf spring 113 so as to close the moving contact 1 14 with fixed contact 112, to resile so as to break this connection Referring back to Figures 1 and 2, it will be appreciated that with the illustrated arrangement clamped to the underside of a planar heating element with the spring terminals 3', 4' 5' of the inlet connector I contacting terminal portions of the heating element and the spring terminals 32, 33 of the or each contactstat 10 similarly contacting contact points of the heating element track, for example in the manner disclosed in Figure 3A of our British Patent Application No. 97904us.0 filed 25 September 1997, and with the bimetal retention cap of the contactstat also pressed firmly into thermal contact with a suirablv formed area of tlie heater track, the contactstat(s) will provide a protective function for the heating element and will switch off the heating, by opening the circuit of the heating element, in the event of an overtemperature situation.

The footprint' of the contactstat abovedescribed is such that the spring terminals 32, 33 are offset to one side of the bimetal retention cap 102.

By virtue of this arrangement and since the bimetal retention cap is electrically isolated from the spring terminals 32, 33 by the push rod 107 and by the plastics material of the contactstat body 101, the spring terminals 32, 33 could be arranged to contact spaced apalt points in one track of the heating element whilst the bimetal retention cap 109 was in physical and electrical contact with a section of an adjacent track, there being no need for electrical insulation between the heating element track and the bimetal retention cap. Such an arrangement. by dispensing with the need for electrical insulation between the heating element track and the thermal sensor which monitors its temperature, facilitates the obtaining of appropriate responsiveness of the sensor(s) to overheating of the heating element.

Whilst the accompanying drawings show only arrangements similar to Figures I and 2 of the drawings of our British Patent Application No.

971 7144. 1 and show only a single contactstat, any of the other arrangements shown In Application No 97 1 7144. 1 could be employed and more than one contactstat cold be employed. Similarly a steam sensor or simmer control (simmerstat) could be mounted to the arrangement in the same way. Whilst the arrangements described are best suited for use with planar heating elements of the type comprising a substrate having a resistive heating element track applied to one side thereof: the invention could be employed with other types of planar heating elements such as die cast elements incorporating a resistive heating wire into their structure or elements having a traditional metal sheathed, mineral insulated heating element proper clamped or clenched to the underside of a metal plate. so long as the necessary termination points to be contacted by the spring terminals of the appliance inlet connector and the contactstat(s) could be provided. One way of achieving this would be to provide a printed circuit board with the appropriate electrical connections and to clamp it to the underside of such heating elements.

It is an undesirable characteristic of thick film heating elements, namely heating elements conapllszn < ^ a substrate, commonly of stainless steel, with a resistive track or laver applied to one side thereof, that the elements distort significantly during thermal cycling. The problems of making reliable electrical connections to such elements can be relieved by use of spring connectors as contemplated by the instant disclosure. The spring connectors should be capable ofaccommodating several millimetres of movement and more complex spring terminals than those illustrated in the accompanying drawings might be employed for achieving this purpose.

Having thus described the present invention by reference to specific embodiments, it is to be appreciated that the embodiments described are exemplary only and that modifications and variations will occur to those possessed of reievant skills without departure from the spirit and scope of the invention.

Claims (1)

1. CLMMS: 1. A carrier for use in the securing of a plurality of thermal sensor devices at selectably different positions with respect to the surface of a planar electric heating element, said carrier incorporating an electrical input connector for said heating element and said connector having spring terminals projecting therefrom, for contacting terminations provided on said heating element.

   9. A carrier as claimed in claim 1 wherein said electrical input connector is adapted to enable mating engagement with a complementary output connector throughout 3600 of relative orientation of the two connectors.

   3. A carrier as claimed in claim 1 or 2 which includes a plurality of limbs each enabling the attachment thereto of one or more thermal sensor devices 4. A carrier as claimed in claim 3 including at least three said limbs, 5. A carrier as claimed in claim 3 to 4 wherein one or more of said limbs has provision for the attachment thereto of one or more thermal sensor devices at different positions of the respective limb.

   6. A carrier as claimed in claim 5 wherein said one or mc-re limbs are bifurcated so as to define opposed surfaces for engagement with a thermal sensor, and said opposed surfaces are formed so as to define a plurality of different engagement positions for a said thermal sensor.

   7. A carrier as claimed in any of the preceding claims including means for attachment of the same to a planar heating element.

   S. A carrier substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.

   9. A carrier as claimed in any of the preceding claims in combination with one or more thermal sensors.

   10. A combination as claimed in claim 9 wherein said thermal sensors comprise contact thermostats (contactstats).

   11. A combination as claimed in claim 9 or 10 wherein said one or more thermal sensors have spring terminals projecting therefrom for contacting terminations provided on said heating element.

   12. A combination as claimed in claim 9 or 10 or 11 wherein said one or more thermal sensors are substantially as herein described with reference to Figures 3 to 7 of the accompanying drawings.

   13. A carrier as claimed in any of claims 1 to 8 or a combination as claimed in claim 9 or 10 or 11 or 12 in combination with a planar heating element, said planar heating element having terminations contacted by the spnng terminals of the electrical input connector and of the one or more thermal sensors.

   14. A combination as claimed in claim 13 wherein said planar heating element is a thick film heating element.

   15. An appliance incorporating a combination as claimed in claim 13 or 14.

   16. A cordless appliance as claimed in claim 15 comprising an appliance proper and a base part.

   17. A thermal sensor for use with a carrier as claimed in any of claims 1 to 8 and wherein the thermal sensor has spring terminals projecting therefrom for contacting terminations provided on a planar heating element. is. Q thermal sensor substantially as herein described with reference to Figures 3 to 7 of the accompanying drawings.

   19. A planar electric heating element having a plurality of terminations provided thereon, a first pair of said terminations providing for the connection to the heating element of an electrical input connector having spring terminals for contacting said first pair of heating element terminations, and at least one second pair of said terminations providing for the connection to the heating element of a thermal sensor device having spring terminations for contacting said at least one second pair of heating element elements.

   20. A planar electric heating element as claimed in claim 19 wherein said heating element is a thick film heating element.