GB2242322A - Delayed operation of an indicator or cooling fan in a cooking appliance - Google Patents

Abstract

Energisation of an oven or grill produces a mains voltage signal at a terminal 2 or 3 whereby a resistor R1 is heated to close a heat-responsive switch S resulting in delayed turn on of a cooling fan F or an indicator. Switch S does not open until resistor R1 cools following turn off of the oven or grill whereby turn off of the fan F or indicator is delayed. Such an arrangement may be used to indicate that a hot plate is still warm after de-energisation of halogen lamp type heaters. A resistor R2 normally cooled by the fan F heats up if the fan fails resulting in opening of a switch or fuse FL, in response to which a fan failure indication is given and the cooling appliance is shut down. The appliance may be heated by gas and/or electrically. <IMAGE>

Description

Cooking Appliances This invention relates to cooking appliances.

It is becoming usual in some types of cookers, especially cooking ovens, to incorporate a cooling fan to ensure that the temperature of various parts of the cooker does not exceed acceptable limits. In such cookers it is usual to provide an outlet grill or vent, usually in the front of the appliance, through which the cooling air is vented. Conventionally, the cooling fan is energised as soon as the oven is turned on and when the oven is still cold, with the result that cold air is blown out of the venting grill which can be disconcerting and uncomfortable for a user. Similarly, the cooking fan is turned off when the oven is turned off so that the cooling effect of the fan ceases.

However, it can happen that even though the oven has been turned off, it can still be at a very high temperature and can cause parts of the oven which are accessible to a user and which would otherwise be cooled by the cooling fan to increase in temperature to a dangerous or unacceptable level.

It has been appreciated that both of these problems can be alleviated by providing a delay circuit which delays the turning on of the cooling fan relative to the time the oven is turned on and also a delay circuit which delays the turning off of the cooling fan relative to the time the oven is turned off.

Another problem arises in cookers which incorporate infra-red e.g. halogen type hotplates in that when such a hotplate is energised, it glows brightly and it is visibly apparent that the hotplate will be hot. However, when the hotplate is turned off, the visible indication soon disappears and yet the hotplate can remain dangerously hot for a considerable period of time. In order to provide an indication that the hotplate is still hot it is known to provide a warning indicator light which is lit when the hotplate is energised and which is provided with an electronic delay circuit for keeping the indicator light lit after the hotplate has been turned off and until the temperature of the hotplate has reduced to an acceptable level. The electronic delay device required to effect this is relatively expensive.

It is an object of the present invention to provide a cooking appliance with one or more electrical delay devices which are easy and cheap to implement and which enable the aforesaid disadvantages to be alleviated.

According to the present invention there is provided a cooking appliance including an electrical delay device comprising an electrical resistance which is caused to be heated when a first part of said appliance is energised, and a heat responsive switch, typically a bi-metallic switch, which is caused to be operated by the heat from said electrical resistance, said switch being used to effect the delayed operation of a further part of said appliance.

In one arrangement for carrying out the invention the cooking appliance may comprise a cooling fan which is energised when said heat responsive switch is operated.

In a preferred arrangement the cooking appliance may comprise an oven with heating means for heating said oven and/or a grill, means being provided for causing said electrical resistance to be heated when said heating means and/or said grill is energised.

In another arrangement for carrying out the invention the cooking appliance may comprise a cooling fan which is energised in response to said first part of said appliance being energised, said electrical resistance being positioned in the path of cooling air from said fan whereby it is cooled when said fan is operating but which is heated when said first part is energised and said fan is not operating so as to cause said heat responsive switch to operate, said heat responsive switch when operated being used to effect an indication that the cooling fan is not operating.

Conveniently, an electrical timer may be provided for controlling the operation of said appliance, said heat responsive switch taking the form of a fusible link or bi-metallic switch which is connected in the energising circuit of said timer, said fusible link being caused to be melted or said bi-metallic switch being caused to become open-circuit when it is heated thereby disabling said timer.

In yet another arrangement for carrying out the invention the cooking appliance may comprise at least one hotplate, e.g. a halogen type hotplate, means for energising said hotplate, and a visual indicator for affording an indication of the temperature of said hotplate, said electrical resistance being energised when said hotplate is energised and said visual indicator being energised when said heat responsive switch is operated.

Said electrical resistance may be constituted by a single electrical resistor, by two electrical resistors connected in parallel or by three or more electrical resistors connected in series/parallel configuration.

An exemplary embodiment will now be described reference being made to the accompanying single figure drawing which is a partially block schematic circuit diagram of an electrical delay circuit for use in a cooking appliance according to the present invention.

The electrical delay circuit shown in the drawing is designed for use in a cooking appliance comprising a single oven cavity and a separate grill cavity, a cooling fan being provided for cooling various parts of the appliance, especially the controls thereof. The electrical delay circuit may be used with any type of cooking appliance e.g. gas, electric or gas/electric combination, the only requirement being that when the oven is being operated an electrical signal, typically at mains voltage, indicative of same, is generated and similarly when the grill is operated, a further electrical signal indicative of same is generated.

The electrical delay circuit shown in the drawing comprises a common supply terminal 1, an "oven energised11 supply terminal 2, which has mains voltage applied to it when the oven (not shown) is energised, and a grill energised!' supply terminal 3 which has mains voltage applied to it when the grill (not shown) is energised. The supply terminals 2 and 3 are connected together via respective isolating diodes D1 and D2 which permit use of existing switches and separate grill and oven ignition functions and are connected to an electrical resistance R1 the other end of which is connected to the common supply terminal 1.

Thus, if either the oven or grill of the cooking appliance is operated, mains voltage will be applied across the resistance R1 and it will be caused to be heated. Situated closely adjacent the resistance R1 is a heat sensitive switch S, typically a bi-metallic element, which is normally open. As the resistance R1 is heated, which takes a finite time, a temperature is reached at which the heat sensitive switch S operates to a closed position. The heat sensitive switch S is connected in series with a cooling fan F between the junction of the diodes D1 and D2 and the common supply terminal 1 so that when the heat sensitive switch S operates the cooling fan 7 is energised.Due to the finite time that it takes for the electrical resistance R1 to heat up and thus for the heat sensitive switch S to operate, the energisation of the cooling fan F is delayed relative to the energisation of the appliance oven or grill. By suitably choosing the value of the electrical resistance, the delay may be typically set at approximately two minutes. In this way cold air is not circulated by the cooling fan F until some time after the oven or grill is operated, by which time the cooling air will be partially warmed due to the heating of the oven or grill.

When the oven or grill, whichever happens to be operating at any particular time, is turned off, the heating of the electrical resistance R1 ceases and it immediately starts to cool. However, it takes a finite time for it to cool to a temperature at which the heat sensitive switch S again operates to open-cireuit and therefore de-energise the cooling fan F. Thus the cooling fan F is operated for a finite period after the oven or grill is turned off and continues to cool any parts of the appliance which would otherwise increase in temperature, even with the oven or grill off.

In cooking appliances which incorporate a cooling fan, there is always the possibility that the fan could break down or otherwise fail to operate, and if this happens and the oven or grill, but especially the oven, continues to be used, then parts of the appliance, which would otherwise be cooled by the cooling air from the fan, can get dangerously hot and can cause an accident. In such cases it is necessary to provide a warning that the cooling fan is not working, and also, possibly, to shut down the oven so that it cannot be used until the fault in the cooling fan is rectified.

This is achieved in the electrical delay circuit shown in the drawing by providing a further electrical resistance R2 which is connected between the common supply terminal 1 and the oven and grill energised supply terminals 2 and 3 via respective isolating diodes D3 and D4, so that when either the oven or grill is operated, the electrical resistance R2 is caused to be heated. The electrical resistance is positioned in the path of the cooling air of the fan F so that when the fan F is operating, the electrical resistance R2 is cooled thereby. Immediately adjacent the electrical resistance R2 is a fusible link FL which is connected between terminals 4 and 5 of the delay circuit and it is arranged that these are used to afford an indication when the fan F is not operating correctly.In an especially envisaged arrangement, it is proposed that the terminals 4 and 5 would be connected in series with the energising circuit of an electrical timer which forms part of the cooking appliance. Should either the grill or oven be operated without the fan 7 operating, the electrical resistance R2 will be heated until a temperature is reached where the fusible link FL melts and becomes open-circuit, thereby disabling the electrical timer. The fact that the timer is disabled, e.g. unlit, makes it apparent to a user that a fault exists on the appliance, necessitating the fault on the cooling fan F to be corrected and replacement of the fusible link FL. It will be appreciated that the fusible link FL could be replaced by a bi-metallic switch which becomes open-circuit when heated.Other ways of indicating that the cooling fan is not operative and of shutting down the appliance could also be used.

In cooking appliances which incorporate one or more infra-red hotplates, e.g. of the halogen type, an electrical delay circuit similar to that used for operating the cooling fan F may be used to operate a warning indicator which indicates when the hotplate is still warm even though the hotplate has been turned off. In this case a "hotplate energised" mains signal would be applied to supply terminal 2 in the electrical delay circuit shown in the drawing, and the heat sensitive switch S would be used to energise the visual indicator instead of the fan F. In this case, when the hotplate was energised, the electrical resistance R2 would be energised and would heat the heat sensitive switch S. After a finite time, a temperature would be reached where the heat sensitive switch operates to energise the visual indicator, indicating that the hotplate was hot.When the hotplate is turned off, the energisation to the electrical resistance R1 is terminated and it starts to cool until, after a finite time, a temperature is reached where the switch S again operates to its normally open position, thereby de-energising the visual indicator. In this way the visual indicator remains lit for a period after the hotplate has been turned off, thereby indicating that the hotplate is still hot.

Although in the electrical delay device which has been described, use has been made of a single electrical resistance R1 or R2 which is heated when a particular part of the cooking appliance is energised, it should be appreciated that the use of such a single resistance does not afford a fail-safe capability should the resistance malfunction for some reason. It is therefore envisaged that the electrical resistance R1 or R2 could be constituted by, for example, a single resistor, by two resistors connected in parallel or by three or more resistors connected in series/parallel configuration.

It will be appreciated that the electrical delay circuit which has been described may be used in a cooking appliance for functions other than those specifically described.

Claims (13)

1. A cooking appliance comprising an electrical delay device comprising an electrical resistance which is caused to be heated when a first part of said appliance is energised, and a heat responsive switch which is caused to be operated by the heat from said resistance, said switch being used to effect the delayed operation of a further part of said appliance.

2. A cooking appliance as claimed in claim 1, comprising a cooling fan which is energised when said heat responsive switch is operated.

3. A cooking appliance as claimed in claim 2, comprising an oven, and heating means for heating said oven, means being provided for causing said electrical resistance to be heated when said heating means is energised.

4. A cooking appliance as claimed in claim 2 or claim 3, comprising a grill, means being provided for causing said electrical resistance to be heated when said grill is energised.

5. A cooking appliance as claimed in claim 1, comprising a cooling fan which is energised in response to said first part of said appliance being energised, said electrical resistance being positioned in the path of cooling air of said fan whereby it is cooled when said fan is operating but which is heated when said first part is energised and said fan is not operating so as to cause said heat responsive switch to operate, said heat responsive switch when operated being used to effect an indication that said cooling fan is not operating.

6. A cooking appliance as claimed in claim 5, comprising an electrical timer for controlling the operation of said appliance, said heat responsive switch taking the form of a fusible link or bi-metallic switch which is connected in the energising circuit of said timer, said fusible link being caused to be melted or said bi-metallic switch being caused to become opencircuit when it is heated thereby disabling said timer.

7. A cooking appliance as claimed in claim 1, comprising at least one hotplate, means for energising said hotplate, and a visual indicator for affording an indication of the temperature of said hotplate, said electrical resistance being energised when said hotplate is energised and said visual indicator being energised when said heat responsive switch is operated.

8. A cooking appliance as claimed in claim 7, in which said at least one hotplate takes the form of a halogen type hotplate.

9. A cooking appliance as claimed in any preceding claim, in which said heat responsive switch takes the form of a bi-metallic switch.

10. A cooking appliance as claimed in any preceding claim, in which said electrical resistance is constituted by a single electrical resistor.

11. A cooking appliance as claimed in any of claims 1 to 9, in which said electrical resistance is constituted by two electrical resistors connected in parallel.

12. A cooking appliance as claimed in any of claims 1 to 9, in which said electrical resistance is constituted by three or more electrical resistors connected in series/parallel configuration.

13. A cooking appliance comprising an electrical delay circuit substantially as hereinbefore described with reference to the accompanying drawing.