GB2229899A

GB2229899A - Toaster heating element

Info

Publication number: GB2229899A
Application number: GB8830038A
Authority: GB
Inventors: Edward Charles Barnett; Jeremy Simmons
Original assignee: Kenwood Ltd
Current assignee: Kenwood Ltd
Priority date: 1988-12-22
Filing date: 1988-12-22
Publication date: 1990-10-03
Also published as: GB8830038D0

Abstract

A tubular heating element (1) for a toaster including a timer control circuit, comprises two separate electrically conductive coils (4 and 11), acts as a heating elements and one coil (4) supplies power to the timer control circuit by "tapping" a small amount of power from an external power supply and the other coil (11) is a larger coil of greater resistance which acts as the primary heating means of the element. Preferably the coils are surrounded by quartz tube 2 and coil 4 is wound on a ceramic insulating tube 4 with bores for the output end 5 of coil 4 and the input end 12 of coil 11. <IMAGE>

Description

TOASTER HEATING ELEMENT This invention relates to heating elements, and in particular to heating elements for domestic toasters.

A type of heating element commonly used in domestic toasters is a 'flat supported' element which comprises a resistance wire wound on a mica based former. Such heating elements are usually provided with low voltage tappings to supply power to the toaster's timer control circuit.

However, a disadvantage of a heating element of this kind is that the resistance wire is exposed, posing a potential hazard to a user. Accordingly in a domestic toaster, there is normally provided a protective outer covering or casing for the heating element so that the user cannot come directly into contact with the resistance wire of the heating element. To this end many toasters are now provided with tubular heating elements which comprise an outer silica glass tube with a spirally wound resistance wire element located inside the bore of the tube.

While such tubular heating elements are much safer to use than conventional flat elements, they have the disadvantage that they cannot be tapped to provide a power supply for the toaster's timer control circuit.

It is therefore an object of the invention to provide a tubular heating element for a toaster which is safe to use and which can be tapped to provide a power supply for the toaster's timer control circuit.

According to the present invention there is provided a tubular heating element for a toaster having a timer control circuit, said tubular heating element comprising means to effect tapping of the tubular heating element in order to supply power to the timer control circuit.

Preferably the means to effect tapping of the tubular heating element is provided by an arrangement comprising: a first electrically conductive coil wound to a predetermined value of resistance and connectable to the timer circuit of the toaster; a second, separate, electrically conductive coil wound to a predetermined value of resistance of substantially greater magnitude than that of said first coilt and a hollow tube of refractory dielectric material to encase the said first and second coils, the arrangement being such that the first and second coils are both provided with input and output means which are connectable to an external power supply.

Thus there is provided a tubular heating element for a toaster, the said element having two separate coils, one of which supplies power to the timer control circuit of the toaster by 'tapping' a small amount of power from the external power supply, the other, a larger coil of greater resistance, which acts as the primary heating means for the element.

In a preferred embodiment of the invention the first coil comprises a substantially solid non-conductive tube around which a piece of electrical resistance wire is wound to form a coil of the required predetermined resistance, which tube is provided with at least one bore along its length through which the unwound part of the resistance wire is threaded so that it passes back through the centre of the wound coil to provide the output means of the coil.

The use of such a non-conductive tube around which the first coil is formed into a coil and through the centre of which the output means is fed enables a very compact coil to be provided.

Without such a tube the output means could not easily be passed back through the centre of the coil without coming into electrical contact with it.

In a further preferred embodiment the said non-conductive tube is provided with an additional bore along its length through which the input means of the second coil is passed.

This effectively enables the input means of the second winding to be fed through the centre of the first coil without coming into electrical contact with it.

It is preferred that a second non-conductive tube be provided, the said tube having a bore along its length through which the output means of the second coil may be passed.

A specific embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings of which: Figure 1 shows a part cross-sectional view of a device embodying the invention; Figure 2 shows an enlarged view of part of the crosssectional view of Figure 1; Figure 3 shows a perspective view of the internal components of a device embodying the invention.

A tubular heating element shown generally at 1 in Figure 1, comprises an outer casing 2, made of silica quartz and an insulating ceramic inner tube 3 shown in more detail in Figures 2 and 3. A first coil 4 is formed from resistance wire wound spirally around the tube 3; output end 5 of the coil 4 is passed through a first bore 6 in the tube 3 and is provided with a silicon rubber fly lead 7. An input end 8 of the coil 4 is similarly provided with a silicon rubber fly lead 9. Thus the input end 8 and output end 5 are conveniently positioned at the same end 10 of the casing 2. The ceramic tube 3 insulates the output end 5 from the rest of the coil 4.

A second coil 11 is provided with an input end 12 which is passed through a second bore in the ceramic tube 3 and a corresponding bore 13 in a locating ceramic disc spacer 19 and is insulated from both coil 4 and its output end 5 by the ceramic tube 3 and the spacer 19. On passing out of the casing 2, the output end 5 of the first coil 4 and the input end 12 of the second coil 11 are crimped together at A and covered by the fly lead 7.

The coil 11 is formed by a piece of a resistance wire wound into a spiral. The coil 11 has an output end 14 at end 15 of casing 2. The output end 14 of coil 11 is provided with a silicone rubber insulated fly lead 17.

The casing 2 is provided with end caps 18.

A power supply external to the toaster is connected across input 8 and output 14.

The coil 4 is connected into the timer control circuit of the toaster and acts as a 'tapping' coil, providing sufficient power to operate that circuit. As well as providing power to the timer control circuit, the coil 4 also contributes to the overall heat output of the element.

The coil 11 is however the main heating coil of the element.

The resistance values and hence power ratings of the coils 4 and 11 are predetermined and the coils are provided with requisite number of windings to achieve those respective values. Obviously the number of windings of the tapping coil 4 is much less than in the heating coil 11 since the coil 4 is required to have a voltage of preferably 12V whereas coil 11 must preferably have a voltage of 108V.

It is envisaged that a toaster embodying the tubular heating element of the invention should be provided with one such element and several conventional elements.

Thus the present invention provides a tubular heating element for a toaster which is safe to use and which can be tapped to provide power for the toaster's timer control circuit.

Claims

CT.zS

1. A tubular heating element for a toaster having a timer control circuit, said tubular heating element comprising means to effect tapping of the tubular heating element in order to supply power to the timer control circuit.

2. A tubular heating element as claimed in claim 1, wherein said element comprises two separate coils, one of said coils being arranged to supply power to the timer control circuit of the toaster by tapping a small amount of power from an external power supply, and the other of said coils comprising a larger coil of greater resistance and being arranged to act as a primary heating means of the element.

3. A tubular heating element as claimed in claim 2, wherein said one coil comprises a first electrically conductive coil wound to a predetermined value of resistance and connectable to the timer circuit of the toaster; and the other coil comprises a second, separate, electrically conductive coil wound to a predetermined value of resistance of substantially greater magnitude than that of said first coil, said first and second coils being encased within a hollow tube of refractory dielectric material and both being provided with input and output means which are connectable to an external power supply.

4. A tubular heating element as claimed in claim 3, wherein the first coil comprises an electrically nonconductive cylindrical member having a bore extending along its length, and a length of electrical resistance wire, one portion of which is wound around the cylindrical member to form a coil of the predetermined resistance and another portion of which extends through said bore such that both ends of said wire are located adjacent one end of said cylindrical member.

5. A tubular heating element, as claimed in claim 4, wherein said non-conductive cylindrical member is provided with an additional bore extending along its length through which one end of the second coil is passed.

6. A tubular heating element as claimed in claim 5, wherein a non-conductive spacer element is located within the hollow tube between said first and second coils, said spacer element being formed with an aperture through which said one end of said second coil is passed.

7. A tubular heating element as claimed in any one of claims 3 to 6, wherein said hollow tube is closed at its ends by end caps, through which the input and output means of the two coils extend.

8. A tubular heating element for a toaster, said heating element being substantially as herein described with reference to the accompanying drawings.

9. A toaster including a timer control circuit and a tubular heating element as claimed in any preceding claim.

10. A toaster substantially as herein described with reference to the accompanying drawings.