GB2186166A

GB2186166A - Electric hobs and heating units therefor

Info

Publication number: GB2186166A
Application number: GB08628244A
Authority: GB
Inventors: Alan Wilfred Welsh; David Good
Original assignee: Redring Electric Ltd
Current assignee: Redring Electric Ltd
Priority date: 1986-01-24
Filing date: 1986-11-26
Publication date: 1987-08-05
Also published as: GB8628244D0; GB8601790D0

Abstract

The heating means for a glass ceramic hob comprises at least two spaced infrared emitting tungsten halogen lamps 3, and at least two coiled wire heating elements with the latter disposed in an intercalated spiral arrangement, and means for selectively energising the lamps and heating elements to provide a plurality of different power outputs. The arrangement of the wire elements ensures that a substantially circular area of the hob is heated on different power settings. <IMAGE>

Description

SPECIFICATION Electric hobs and heating units therefor This invention relates to electric hobs of the kind in which at least one heating unit is disposed beneath a glass ceramic plate. In such hobs as constructed hitherto the or each heating unit has commonly incorporated one or more electric heating elements of coiled wire form mounted on an insulating support and spaced from the lower surface of the plate. More recently there has come onto the market a glass ceramic hob of the kind referred to, having one or more heating units provided with a plurality of tubular, infra-red emitting tungsten halogen lamps, in place of the coiled wire heating elements.

It has also been proposed to utilise a combination of such lamps and at least one coiled wire heating element, the lamps and the limbs of the heating element or elements being disposed in parallel straight lines.

An object of the present invention is to provide a form of heating unit incorporating a combination of coiled wire heating elements and tungsten halogen lamps which has certain advantages over the prior art arrangement referred to above.

According to the invention a hob of the kind referred to incorporates a heating unit comprising at least two spaced infra-red emitting tungsten halogen lamps, and at least two coiled wire heating elements, with the latter disposed in an intercalated spiral arrangement, and means for selectively energising the lamps, and the heating elements to provide a plurality of different power outputs.

By disposing the heating elements in an intercalated spiral it can be arranged that even at heat output involving only oen of the elements, a substantially circular area of the ceramic plate associated with the heating unit is heated.

Preferably in order to provide the highest heat output the lamps and the heating elements are arranged to be connected to the electrical supply in parallel with each other, the second highest heat output being provided by energising only the heating elements in parallel with the lamps switched off. Other heat outputs may be achieved by operating the heating elements either individually or in series.

Preferably a hob unit in accordance with the invention comprises two spaced lamps, and three heating elements, and is associated with a selector switch operable to give six different heat outputs. Thus with the lamps each arranged to dissipate 350W under normal operating conditions, and the elements having a rating of 500W, 400W and 200W respectively, a power output of 1800W can be achieved by operating the two lamps and all the heating elements in parallel, and a power output of 1100W by operating only the heating elements in parallel.

Conveniently the lowest power output is obtained by operating the heating elements in series with each other and with a diode. With three heating elements having the ratings referred to above the power output can in this way be reduced to approximately 75W.

One hob incorporating a heating unit in accordance with the invention, and an operating circuit therefor, will now be described by way of example with reference to Figs. 1 to 3 of the accompanying schematic drawings, in which Figure 1 illustrates a cross section of part of the hob incorporating the heating unit, Figure 2 represents a plan view of the heating element itself, and Figure 3 illustrates diagrammatically a control circuit for the unit.

Referring first to Fig. 1, this shows a glass ceramic plate 1 having mounted beneath it, in any convenient manner, a heating unit 2 comprising two straight tubular halogen tungsten lamps 3 and three coiled wire electric heating elements 4, 5, 6 carried by a circular ceramic support 7 having a flat base 8 and surrounding side wall 9 and located within a sheet metal housing 10.

The lamps 3 are disposed parallel to each other on opposite sides of, and equidistant from, the centre of the support 7, with their ends extending through openings in the side wall 9 of the support 7, and through cut-outs 11 in the wall of the casing 10. Connectors 12 are fitted to the protruding ends of the lamps, which each have a power rating of 350W.

The coiled wire electric heating elements 4, 5, 6 are disposed in spiral grooves formed in the upper surface of the base 7 of the support, and have power ratings of 500W, 400W and 200W respectively.

The element terminals 13 and the lamp connectors 12 are connected to a rotary switch (not shown) having a series of positions arranged to connect the lamps and heating elements in parallel with each other to the supply, or alternatively to connect the heating elements to the supply individually or in various parallel or series combinations to give six different power outputs as follows:: Switch Position Power Output 1) Both lamps and all three 1800W heating elements in parallel 2) Three heating elements in 1100W parallel (lamps switched off) 3) Elements 1 and 3 in parallel 700W 4) Element 3 alone 200W 5) All elements in series 105W 6) All elements in series and 75W also in series with a diode D The circuit arrangement for obtaining the required operation of the lamps and heating elements is illustrated in diagrammatic form in Fig. 3, Switch Position Switch terminals Switch Terminals connected to one connected to supply Terminal other supply Terminal 1 (with Contacts S1 S2 S5 S3 S4 C1 across diode D closed) 2 " " S1 S2 S3 S4 3 " " S1 S2 S4 4 " " S2 S4 5 " " S1 S3 6 (with Contacts S1 S3 C1 open) It will, however, be appreciated that heating elements of different power ratings and different switching sequences could be used if desired.

The heating unit conveniently includes a thermal limiter (not shown), for reducing the heat output from the unit in the event that it attains an excessively high temperature so as to avoid damage to the glass ceramic plate. Such a thermal limiter may be of the kind in corporating a heat sensitive rod extending across the unit and designed to actuate switching means attached to the side of the casing, so as to reduce or cut-off the supply of current to the unit at a predetermined high temperature.

In a hob in accordance with the invention a glass ceramic plate may be common to a plurality of heating units, each mounted in a respective position beneath the plate. Alternatively the hob may be in the form of a metal supporting surface with a plurality of openings formed in it, each of which has a glass ceramic plate extending across it, and an associated heating unit being disposed beneath each ofthe plates.

Claims

1. An electric hob incorporating at least one heating unit disposed beneath a glass ceramic plate, wherein the heating unit comprises at least two spaced infra-red emitting tungsten halogen lamps, and at least two coiled wire heating elements, said coiled heating elements being disposed in an intercalated spiral arrangement, mounted on an insulating support and spaced from the lower surface of the plate, and means for selectively energising the lamps and heating elements, to provide a plurality of different power outputs.

2. A hob as claimed in Claim 1 wherein the highest heat output from the heating unit is provided by connecting the lamps and the heating elements to an electrical supply, in parallel with each other.

3. A hob as claimed in Claim 2 wherein the second highest heat output from the heating unit is provided by energising only the heating unit is provided by energising only the heating elements in parallel, with the lamps switched off.

4. A hob as claimed in Claim 1 wherein the heating elements are energisable either individually or in series to achieve different heat outputs.

5. A hob as claimed in any preceding Claim, wherein the heating unit comprises two spaced lamps, and three heating elements, and is associated with a selector switch operable to give six different heat outputs.

6. A hob as claimed in Claim 5, wherein the lamps are each arranged to dissipate 350 W under normal operating conditions, and the elements have ratings of 500 W, 400 W and 200 W.

7. A hob as claimed in any preceding Claim, wherein the heating elements are operated in series with each other and with a diode, to provide the lowest power output.

8. A hob as claimed in any preceding Claim, wherein the heating unit has a thermal limiter which reduces the heat output from the heating unit when the temperature of the unit becomes excessively high, but below that which would result in damage to the glass ceramic plate.

9. A hob as claimed in Claim 8, wherein the thermal limiter incorporates a heat sensitive rod extending across the unit and designed to actuate switching means attached to the side of the casing, so as to reduce the supply of current to the unit when it reaches said excessively high temperature.

10. A hob as claimed in any preceding Claim, wherein the glass ceramic plate is common to a plurality of heating units, each of which is mounted in a respective position beneath the plate.

11. A hob as claimed in any preceding Claim, wherein the hob is in the form of a metal supporting surface with a plurality of openings formed in it, each of which has a glass ceramic plate extending across it, and an associated heating unit being disposed beneath each of the plates.

12. A hob substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.