AU650523B2 - Electric toasters - Google Patents

Description

AUSRAio 0 2 P/00/011 28/5/91 Regulaion 3.2(2) Patents Act 1990

ORIGINAL

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*5*S S S S. S Invention Title: "ELECTRIC TOASTERS" The following statement Is a full description of this invention, Including the best method of performfing It known to Black Decker Inc.:- ELECTRIC TOASTERS The present invention relates to electric toators and in particular electric toasters that are intended primarily for domestic end use.

For convenience, many domestic toasters include radiant electric resistance heating elements on opposed sides of a toasting compartment with the heating elements in series in an electric circuit. In some toasters with side-by-side toasting compartments, three heating elements are provided with one central element between the toasting compartments and two outer heating elements, however, in such cases the three heating elements are connected in series in an electric circuit. Such toasters are arranged to radiant substantially equal heat levels to opposed surfaces of a product to be toasted such as a bread slice, however, when toasting food products such as crumpets, muffins, or 0920. buns, uniform radiant heat applied to opposed surfaces is unsatisfactory. Such products, 0 particularly crumpets, require differential heat levels applied to opposed surfaces for S•S satisfactory toasting. Such differential heat levels have conventionally been unable to be

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15 achieved with series arranged heating elements. The reason for this is of course that a control switch or element placed in a series circuit to control one heating element will also have a direct effect on the other heating element.

It is currently known in commercial type toasters adapted to toast bread or similar food products in hotel, cafeteria, or cafe kitchens to provide the radiant electric resistance heaters in a parallel electric circuit arrangement. In such arrangements it is known to provide switch means to selectively turn off one or other of the heating elements or to provide simmerstat control means to vary the radiant heat energy from one or both of the heating elements. Such arrangements are relativeiy simple to achieve with heating elements that are In a parallel circuit configuration.

German PatenW Specification No. DE 2950229 discloses circuit arrangements for use in toasters which will enable selectively one of the heatinrg elements to be turned off completely allowing toasting of one side only of a food product but not simultaneously both sides with differential heating effect. Australian Patent Specification No. 573,097 discloses a circuit arrangement for a domestic toaster wherein the heating elements are in series and the toaster can be selectively altered from a configuration for toasting bread to a configuration for toasting crumpets, muffins or the like. The disclosed circuit comprises two main resistance radiant heating elements arranged in series with an auxiliary electrical resistance also arranged in series with one of the main heating elements. An openable or closable switch is prtvided in a shunt on parallel circuit to the auxiliary resistance whereby when the switch is open, the total electrical resistance of the heating elements also includes the auxiliary resistance and when the switch is closed, the auxiliary resistance is removed from the total resistance of the heating elements.

The circuit arrangement works satisfactorily but has the effect of increasing the effective total resistance in the main heating element circuit and thereby decreases the current on this circuit with the consequent result of substantially lengthening the toasting cycle in the crumpet mode of toasting compared to when a bread slice is being toasted. It will of course be appreciated that crumpets often do take much longer to toast than bread slices and the result of the above described circuit is to further extend this toasting time.

The objective therefore of the present invention is to provide a domestic type toaster with heating elements arranged in series which will satisfactorily toast bread and .oG products such as crumpets and muffins but will do so without greatly affecting toasting time in either mode of operation.

see Accordingly the present invention provides an electric toaster including a toasting compartment, a first heating means adapted to supply radiant heat energy to one side of said toasting compartment, a second heating means adapted to supply radiant heat enorgy to an opposed side of said toasting compartment, said first and second heating means being electrically connected in series in a main electric circuit, control means electrically connected to said main electric circuit and arranged in parallel to one of said first or second heating means, said control means being activatable to modify said main S• electric circuit from a first configuration where said heating means radiate substantially o equal heat energy to a second configuration without increasing total electrical resistance 4 in said main electric circuit where said heating means radiate substantially unequal heat energy with both said heating means radiating heat energy.

By avoiding the need to include additional resistance in the main heating element series circuit, when transferring to the second configuration in crumpet mode of operation, there is no decrease of current in this circuit and therefore no deleterious effect on toasting time.

Advantageously, the first and second heating means are electrical resistance radiant heating elements. Conveniently, the toasting compartment may be a vertical slot with a product support carriage located therein for movement between wx ,wper product receiving position and a lowered product toasting position. In an alternative arrangement two said toasting compartments may be employed, each said toasting compartment comprising a vertical slot with said vertical slots being located in adjacent side-by-side arrangement and with one of said heating means being located between said vertical slots and adopted to radiate heat energy to both said toasting compartments.

Clearly any other conventional domestic toaster configuration could also be used with the present invention.

In a first preferred embodiment, the control means includes switch means operable by a user of the toaster to alter the configuration of the toaster between said first and second configurations. Conveniently the control means may also include an auxiliary electrical resistance. In a preferred embodiment, the auxiliary resistance element is arranged physically adjacent the other of said resistance heating means to increase the heating effect of said other resistance heating element. In these arrangements, with the control switch open, the resistance heating elements act normally to radiate substantially equal heat levels for toasting a bread slice or the like.

With the control switch closed, current flows through the auxiliary resistance 15 element as well as the other two or main resistance heating elements. In such an arrangement the parallel circuit consisting of one resistance heating means and the auxiliary resistance element has an effective resistance in the series circuit less than the other of the heating means with the resultant effect that the other of the heating means radiates more energy than the heating means forming part of the parallel circuit.

Moreover, locating the auxiliary element adjacent the main heating means that radiates higher energy levels tends to augment this heat radiation and thereby increases the Simbalance.

It will of course be apparent that the overall resistance of the series circuit in this configuration is decreased thereby increasing the current level and decreasing the toasting cycle time, In a second preferred embodiment said control means comprises a switch means to make said at least one heating means conductive for only part of the toasting cycle.

Conveniently, the control means may comprise a Triac adapted to successively remove half cycles of power from said one heating means with the effect of said one heating means radiating less energy that said other heating means without increasing the overall resistance of said series circuit and thereby lengthening the toasting cycle.

Several preferred circuit arrangements have been described hereinafter with reference to the accompanying drawings, in which Figure 1 is a schematic circuit arrangement drawing for a first preferred embodiment; Figure 2 is a schematic circuit arrangement drawing for a second preferred embodiment; Figure 2A is a voltage v time graph for one of the heating elements in the arrangement of Figure 2; Figure 2B is a voltage v time graph for the other heating element in the arrangement of Figure 2; and Figure 3 is a schematic circuit arrangement drawing for a still further embodiment.

Referring first to Figure 1, the toaster comprises a toasting chamber 10 and a product 11 to be toasted, as shown, carried on a movable carriage 12 within the toasting chamber. Such elements may be in accordance with any currently known toaster arrangement. Radiant energy electric resistance elements 13 and 14 are provided which are arranged so that in normal bread toasting, they supply substantially the same radiant *fee energy to toast the product evenly on both sides. The elements 13 and 14 together with 15 appropriate conductors form a series circuit 15 which is in itself a conventional arrangement. The elements 13 and 14 may, in s -ingle slot toaster, have nominally equal resistance levels R 1 and R 2 The arrangement further includes an auxiliary resistance element 16 having a resistance R 3 arranged in parallel to one of the main heating elements 13, 14 and in the 20 illustrated version it forms a parallel circuit 17 with the heating element 14. A simple 4 O0 open or closed switch 18 is provided in series with the auxiliary element 16 and acts to alter the mode of operation of the toaster from a normal bread toasting situation to a crumpet or muffin toasting situation depending on whether the switch is open or closed.

As is illustrated, the auxiliary resistance element 16 is arranged physically adjacent the main heating element 13 so that any heat generated in the element 16 augments the radiant heat levels of the main element 13. It will of course be appreciated that any heat levels generated by the element 16 might be dissipated elsewhere, If desired.

With the switch 18 open, no current passes through the auxiliary element 16 and the main elements 13, 14 radiate effectively equal heat levels. In this contiguraton the total resistance RO of the series circuit 15 may be considered as effectively R1 1 2 If the switch 18 is closed, current then flows through all elements 13, 14 and 16 and the effective total resistance Rc of the circuit is

R

1

R

2

R

3

R

2

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3 where R1 R 2 Thus R. is necessarily less than Ro and the current level in the series circuit 15 is in fact increased so that toasting of crumpets and muffins or the like would occur more quickly. Moreover, the effective resistance of the element 13 in the series circuit would remain as R 1 whereas the effective resistance of the element 14 in the series circuit would be

R

2

R

3

R

1

R

3

R

3

R

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1 S• thereby causing the element 14 to radiate heat levels less than those of the element 13.

a 01 It will of course be appreciated that the wattage expended by the circuit would be l2R. As the current increases in the circuit when the switch 18 is closed, relative to when the switch is open, the total watts expended with the switch closed also increases despite the ••slight drop in effective resistance. As a result, not only is an imbalance created between elements 13 and 14 but also the total wattage used is increased. Furthermore, by locating the element 16 as illustrated increases this level of imbalance.

Figure 2, 2A and 2B illustrate a still further embodiment. Like features having been given the same reference numerals as in Figure 1. In this embodiment, the parallel circuit 17' provided around the main heating element 14 include a Triac 19 rather than Sa. a switch and auxiliary resistance element. The Triac 19 is select~bly externally activated so that periodic half cycles (such as every third half cycle shown in Figure 2A) are removed from the power supply to the heating element 14. When activated, the Triac 19 thereby causes the element 14 to have no power for repeated discrete periods of time during a toasting cycle to effectively lower the heat levels radiated by the element 14 relative to the element 13 without increasing the resistance level of the series circuit During each of these discrete periods the voltage level across the other element 13 increases as shown in Figure 2B. Clearly any number of repeated half cycles might be removed as desired to vary the degree of imbalance between elements 13 and 14 as desired when toasting crumpets, muffins or the like. When the Triac is deactivated, the elements 13 and 14 act normally to radiate substantially equal heat levels for uniformly toasting bread or similar products.

6 Figure 3 illustrates a still further embodiment similar to Figure 2 employing a Triac 19'. In this embodiment the Triac 19' selectively forms a parallel circuit 17" with either of the main elem its 13 or 14 via operation of a control switch 20. In this manner, it is possible to vary either of the elements 13, 14 relative to the other.

In addition, the Triac 19' may be controlled from a printed circuit board on which two potentiometers may be arranged ganged or formed together with a central control switch. The external control might be via a slider knob or rotary knob with a central position where the heating elements 13 and 14 are essentially balanced. When the control is moved either side of centre, it would make the front hotter and the rear cooler 1 0 or vice versa. The arrangement would select which side to be hotter by switching the Triac 19' across either the element 13 or the clement 14. The amount of travel from the o, central position would dictate how many half waves would be shorted out. Again, in this arrangement, tl'e toasting cycle time is not adversely affected by increasing the effective resistance in the series circuit 0 0 00 C 00 *Ir

Claims (11)

1. An electric toaster including a toasting compartment, a first heating means adapted to supply radiant heat energy to one side of said toasting compartment, a second heating means adapted to supply radiant heat energy to an opposed side of said toasting compartment, said first and second heating means being electrically connected in series in a main electric circuit, control means electrically connected to said main electric circuit and arranged in parallel to att4e at-one of said first or second heating means, said control means being activatable to modify said main electric circuit from a first configuration where said heating means radiate substantially equal heat energy to a second configuration without increasing total electrical resistance in said main electric circuit where said heating means radiate substantially unequal heat energy with both said heating means radiating heat energy. O"

2. An electric toaster according to claim 1 wherein said first and second heating ,means are electrical resistance radiant heating elements. 0

3. An electric toaster according to claim 1 or claim 2 wherein said toasting compartment is a vertical slot with a product support carriage located therein for movement between an upper product receiving position and a lowered product toasting position. 6V*°

4. An electric toaster according to claim 1 or claim 2 wherein two said toasting compartments are provided, each said toasting compartment comprising a vertical slot with said vertical slots being located In adjacent side-by-side arrangement and with one of said heating means being located between said vertical slots and adopted to radiate heat energy to both said toasting compartments.

An electric toaster according to any one of claims 1 to 4 wherein said control means includes switch means operable by a user of the toaster to alter the configuration of said toaster between said first and said second configurations.

6. An electric toaster according to claim 5 wherein said control means includes an auxiliary electric resistance.

7. An electric toaster according to claim 6 wherein said control means is electrically located in parallel to said first heating means and said auxiliary electric resistance is located adjacent to said second heating means.

8. An electric toaster according to claim 5 wherein said switch means includes an electronic switch which is non-conductive when said toaster is in said first configuration and which is non-conductive during a toasting cycle when said toaster is in said second configuration except for at least one period of time when said switch is conductive.

9. An electric toaster according to claim 8 wherein said electronic switch in said second configuration is conductive for repeated discrete periods of time during the toasting cycle.

10. An electric toaster according to claim 8 or claim 9, wherein said electronic e switch includes a Triac.

11. An electric toaster according to any one of claims 8 to 10, further including auxiliary switch means to enable said electronic switch to be selectably located in parallel to either of said first or said second heating means. D ATED this 11th day of March, 1992 *e BLACK DECKER INC. WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRAUA AU000PK5439.WPC(DOC.010) SKP:EK le f A ABSTRACT An electric domestic toaster is disclosed herein which is configurable to toast bread slices by supplying equal heat energy levels to opposed sides of the bread slide or to toast crumpets or the like by supplying unequal heat energy levels to opposed sides of the crumpet, the toaster having a main electrical series circuit comprising a first heating element (13) and a second heating element (14) on opposed sides of a toasting compartment (10) control means separate from service main electrical series circuit located parallel to one of the two heating elements (13, 14), said control means (17, 17', 17") being either non-conductive in a first mode of operation or conductive at least for one or more periods of time during a toasting cycle in a second mode of operation whereby in said second mode of operation unequal heat energy is supplied by said heating elements without increasing the effective resistance of the main electrical series circuit or the toasting cycle time in said second mode of operation. s o *0 I*