WO1988000808A1

WO1988000808A1 - Electric toasters

Info

Publication number: WO1988000808A1
Application number: PCT/GB1987/000495
Authority: WO
Inventors: Brian Sinclair Wolfe
Original assignee: Dreamland Electrical Appliances PLC
Current assignee: Dreamland Electrical Appliances PLC
Priority date: 1986-07-29
Filing date: 1987-07-14
Publication date: 1988-02-11
Anticipated expiration: 1989-01-29
Also published as: GB2193086A; AU7693687A; GB8618464D0

Abstract

A toaster comprises at least one heating element (18, 20) for effecting toasting, control means (26) responsive to a desired extent of toasting having been achieved to de-energise the heating element, and sensor means (30) directly or indirectly responsive to a temperature within the toaster reaching a value higher than a value or maximum value which should be achieved during toasting. The sensor means (30) may be operative to activate an alarm (34) and/or to de-energise the heating element (18, 20).

Description

ELECTRIC TOASTERS

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This invention relates to electric toasters, that is devices for toasting slices of bread or other toastable items of food.

Electric toasters generally are provided with a control means or device which is responsive to a parameter, which varies with the extent of 5 toasting, reaching a value indicating that a desired extent of toasting has been achieved to de-energise one or more electrical heating elements that effect the toasting by cutting off a supply of electricity thereto. The control means may, for example, comprise a bimetallic switch or other temperature responsive device which is responsive to a temperature within

10 the toaster reaching a predetermined value to cut off the supply of electricity to the electrical heating element or elements, in which case the predetermined (temperature) value is chosen to correspond to the temperature having risen by an amount sufficient to have achieved a desired extent of toasting. Usually, the predetermined value of the temperature or

15 other parameter is manually adjustable, so that the user can control the extent of toasting. Sometimes, in more sophisticated toasters, a compensation device may be provided to ensure at least approximate uniformity of the extent of toasting as between first use (switching on from cold) and subsequent use (switching on with toaster already warm).

20 The control means should, of course, normally ensure that the supply of electricity to the heating element or elements is cut off well before the bread or other toastable item is burnt. However, should the control means fail to accomplish this function, an excessive amount of heating may occur, which can give rise to several unfortunate consequences. Firstly, the bread

25 or the like may be burnt and therefore become inedible. Secondly, burning of the bread or the like can give rise to unpleasant smoke and odour. Thirdly, overheating can result in damage to the toaster and/or a fire hazard; possibly, in extreme cases, an electrical fault caused by overheating can even give rise to an electrical (electrocution) hazard. The risk of

30 damage/fire hazard/electrical hazard can be particularly severe if, in accordance with a modern design tendency, a casing of the toaster is constructed wholly or partially of a low melting point material, in particular a plastics material, rather than of metal.

According to the present invention there is provided an electric toaster comprising: at least one electrical heating element for effecting toasting; control means responsive to a desired extent of toasting having been achieved to de -energise the heating element; and sensor means responsive to a temperature within the toaster reaching a value higher than a value or maximum value which should be achieved during toasting.

The sensor means may be operative to activate an alarm (e.g. audible and/or visual) so that the user will be made aware of the excessive temperature and can take appropriate corrective action, for instance switching off the toaster or unplugging the toaster from an electrical supply. Additionally or alternatively, the sensor means may be operative to de-energise the heating element, thereby automatically taking appropriate corrective action.

The invention will now be further described, by way of illustrative and non- limiting example, with reference to the accompanying drawing, in which like references indicate like items throughout, and in which:-

Figure 1 is a schematic representation of an electric toaster embodying the invention;

Figure 2 is a schematic electrical circuit diagram of the toaster of

Figure 1; and Figures 3 and 4 are schematic electrical circuit diagrams of respective modifications of the toaster of Figure 1.

The electric toaster illustrated in the drawing comprises a casing 10, which may for example be constructed wholly or partially of a thermoplastic or other plastics material, having therein a slot 12 through which a slice of bread 14 (or other toastable item of food) can be inserted into the toaster.

When inserted within the toaster, the bread 14 is supported by a grille 16 or the like in such a position that its opposite sides face respective electrical heating elements 18, 20. In a manner well known per se in the art, insertion of the bread 14 causes closure of an ON/OFF switch 22 (Figure 2) whereby the heating elements 18, 20 are connected to an electrical supply 24. The heating elements 18, 20 thus generate heat and start to toast the bread 14. An extent of toasting control means or device, which may be in the form of or which may include a switch 26, is arranged within the casing 10. As shown in Figure 2, the switch 26 is connected in series with the ON/OFF

_*\ switch 22 between the heating elements 18, 20 and the electrical supply 24 5 and is normally closed so that it permits energisation of the heating elements. The control means is responsive to a parameter, which is indicative of the extent of toasting.- reaching a predetermined value indicative of a desired extent of toastirsg having been achieved to open the switch 26 to de-energise the heating elements 18,20. The above-mentioned 10 parameter may be a temperature, in which case the control means may comprise a temperature responsive device, e.g. a semiconductor device or a bimetallic switch. In this case, when the temperature in the vicinity of the control means or a temperature-sensitive part thereof (e.g. the temperature in the vicinity of the bimetallic switch 26) reaches a predetermined value 15 which is selected such that the bread 14 will have been (or at least ought to have been) toasted to a desired extent, the switch 26 will open whereby the heating elements 18, 20 are de-energised. However, other parameters than temperature may be employed. The parameter may, for example, be an optical parameter directly indicative of the extent of toasting, in which 20 case the control means may comprise an optical device.

In a manner known per se in the art, the toaster may be provided with a sprung latch arrangement (not shown) which provides a spring force which resists slightly the insertion of the bread 14 and latches the bread in the illustrated position when it is fully inserted. When the switch 26 is opened, 25 the latch is released so that the spring force at least partially ejects the toasted bread 14 through the slot 12 ready for withdrawal.

The predetermined value of the above-mentioned parameter (e.g. the operating temperature of the bimetallic switch 26) preferably is manually adjustable, for example by means of a knob 28 or the like, so that the user 30 _can select the desired degree of toasting (stepwise or continuously) over a range of values extending from a lightest value (minimum extent of toasting) to a darkest value (maximum extent of toasting).

The construction of the electric toaster, as so far described, is known. 35 The electric toaster is additionally provided with an overtemperature sensor device, which may be in the form of or include another normally closed switch 30. As shown in Figure 2, the switch 30 is connected in series with the ON/OFF switch 22 and the switch 26. The overtemperature sensor device is responsive to an excessive temperature having been attained within the casing to open the switch 30. The sensor device need not sense temperature directly, but could for example comprise an optical device which senses by monitoring a parameter representative of the extent of toasting that the parameter has reached a value indicating that the toast has been excessively toasted, which will, of course, occur only when the temperature within the casing 10 is excessive. The sensor device 30 may, however, sense temperature directly, in which case it may, for example, comprise a temperature sensitive device such as a semiconductor device or bimetallic switch which is operative to sense the temperature at a location within the casing 10. Although that location is shown as being remote from the location of the switch 26, the switches 26, 30, if they are in themselves temperature sensitive, or temperature sensitive parts of the control means and the sensor means, if disposed remote from the switches 26, 30, could in fact be located adjacent one another. A predetermined temperature at which the switch 30 will become open is so chrsen as to be higher than the temperature that will be achieved in the vicinity of the switch 30 (or in the vicinity of a temperature sensitive part of the sensor means) when the switch 26 is set for the maximum extent of toasting. Thus, during normal operation, the switch 30 will always be closed. However, in the event of the switch 26 failing to become open when maximum toasting has been achieved, the switch 30 will become open and cut off the heating elements 18, 20 from the electrical supply 24, thereby preventing any substantial overheating and avoiding the above-described possibly unfortunate consequences of overheating. The toaster may be so designed that opening of the switch 30 may, as is the case for opening of the switch 26, release the latch to cause at least partial ejection of the bread 14 through the slot 12. Preferably, the toaster is operative to provide an alarm signal in the event of operation of the overtemperature sensor device (opening of the switch 30) so that the user will be aware that a fault has occurred. For example, as shown in Figure 2, the switch 30 may be provided with an auxiliary, normally open contact set 32 which is closed on opening of the switch 30 to energise an alarm lamp 34 to provide a visual alarm. Electrical latching means (not shown) could be provided to maintain energisation of the lamp 34 cause of its energisation has been removed, for example (if the switch 30 is temperature sensitive) after the switch 30 has cooled down.

Instead of or as well as a visual alarm, the toaster could be designed to provide an audible alarm. This could be achieved, for example, by connecting a buzzer or the like (not shown) in parallel with the lamp 34 or by replacing the lamp with a buzzer or the like.

In a modification shown in Figure 3, the toaster provides only an alarm in the event of overheating, leaving it to the user to de -energise the heating elements 18, 20 by switching off the toaster or unplugging the toaster from the electrical supply. According to the modification, the switch 30 is replaced by a switch 30'. The switch 30' is the same as the switch 30, except that it is normally open rather than normally closed. Further, the switch 30' is not connected in series with the switch 26, but is connected simply between the supply 24 and the lamp 34 (and/or buzzer or the like) so as to provide an alarm in the event of closure of the switch 30' due to overheating. Again, electrical latching means could be provided to maintain energisation of the lamp 34 (and/or buzzer or the like) after the cause of its energisation has been removed, for example (if the switch 30 is temperature sensitive) after the switch 30 has cooled down. In another modification shown in Figure 4, the switch 30 (30') that constitutes or forms part of the overtemperature sensor means is a changeover-type switch 30" located where shown in Figure 4 so that, in the event of an overtemperature, the contacts of the switch 30" change over from the position shown so as to energise the alarm lamp 34 and de-energise all other components. The switch 30" could be designed so as to be capable of being manually reset.

The invention can, of course, be embodied in other ways than those described above by way of illustrative and non- limiting example. For instance, the extent of toasting control means and the overtemperature sensor means could comprise a common device for sensing a parameter (such as temperature) and operative to produce outputs for opening the switches 26,30 (30',30") at respective different predetermined parameter values.

Claims

1. A toaster comprising: at least one electrical heating element for effecting toasting; control means responsive to a desired extent of toasting having been achieved to de-energise the heating element; and sensor means responsive to a temperature within the toaster reaching a value higher than a value or maximum value which should be achieved during toasting.

2. A toaster according to claim 1, wherein the control means comprises a temperature sensitive device which is responsive to a temperature within the housing having attained a predetermined value to de-energise the heating element.

3. A toaster according to claim 1, wherein the control means is operative to sense a parameter directly indicative of the extent of toasting and is responsive to that parameter having attained a predetermined value to de-energise the heating element.

4. A toaster according to claim 1, claim 2 or claim 3, wherein the sensor means comprises a temperature sensitive device whereby the sensor means is operative to sense temperature directly.

5. A toaster according to claim 1, claim 2 or claim 3, wherein the sensor means is operative to sense temperature indirectly by sensing a parameter representative of the extent of toasting.

6. A toaster according to any one of the preceding claims, wherein the sensor means is operative to activate an alarm when the sensed temperature within the toaster has reached a value higher than the value or maximum value which should be achieved during toasting.

7. A toaster according to any one of the preceding claims, wherein the sensor means is operative to de-energise the heating element when the sensed temperature within the toaster has reached a value higher than the value or maximum value which should be achieved during toasting.