EP0782406A1

EP0782406A1 - Oven

Info

Publication number: EP0782406A1
Application number: EP96924065A
Authority: EP
Inventors: Stuart David Brown
Original assignee: Hasbro International Inc
Current assignee: Hasbro International Inc
Priority date: 1995-07-12
Filing date: 1996-07-11
Publication date: 1997-07-09
Also published as: GB9514188D0; NZ312745A; WO1997002777A1; AU6464696A

Abstract

An oven comprises an enclosure (1) having upper and lower sections (2, 3); an electrical heating element (9) mounted in the lower section (3) of the enclosure (1); and an open mesh support (8) positioned over the heating element (9) on which food to be cooked is located. The enclosure (1) is formed as a double wall structure to retain heat. The upper section (2) of the enclosure (1) is domed to enable heat to be converted from the heating element (9), through the open mesh support (8), onto the top of the food on the support. The upper and lower sections (2, 3) can be closed to define a sealed volume within the enclosure during cooking.

Description

OVEN

The invention relates to an oven.

There is a need in the field of toys and games for an oven which is capable of cooking food such as cakes and the like but which is safe for children to use. A primary requirement of such an oven, and one that is laid down in European regulations, is that the power source for such an oven should operate at relatively low voltage, typically no more than 12 volts. However, to achieve cooking of cake mixes and the like, air temperatures of around 200°C are required and cooking times must be comparable to those for conventional ovens. In practice, this makes it very difficult to construct an oven capable of cooking food in sufficient quantities.

Conventional ovens are not suitable for use by children since they do not satisfy the strict safety requirements now prevailing. In general, conventional ovens utilise high power heat sources and require significant power inputs. An example of a conventional oven is shown in EP-A-0082972, the oven being defined by a double walled enclosure in which is mounted a heat source. This will require a significant power input and is unsuitable for use by children. US-A-5315922 illustrates a table-top baking oven in which a pizza to be baked is positioned on a solid carrier plate beneath which, in one embodiment, is positioned an electrical heating element. A second electrical heating element is provided above the carrier plate. A domed cover having side apertures to allow access to the pizza can be placed over the carrier plate. Once again, this will require significant power input in view of the degree of heat loss through the apertures and the amount of heat needed to heat up the carrier plate for cooking purposes. In accordance with the present invention, an oven comprises an enclosure having upper and lower sections; an electrical heating element mounted in the lower section of the enclosure; and an open mesh support positioned over the heating element on which food to be cooked is located, wherein the enclosure is formed as a double wall structure to retain heat, wherein the upper section of the enclosure is domed to enable heat which has passed from the heating element through the open mesh support to be convected onto the top of food on the support, and wherein the upper and lower sections can be closed to define a sealed volume within the enclosure during cooking. We have designed a new form of oven which optimises the use of heat generated by the heating element so that food can be cooked even though the heating element is only powered from a low voltage source. This is achieved firstly by constructing the enclosure as a sealed double wall structure, secondly by forming the upper section of the enclosure in a domed manner, and thirdly by utilising an open mesh support over the heating element. The double wall structure minimises heat loss by radiation, while sealing the enclosure for cooking prevents heat loss by convection and radiation. Using an open mesh support avoids the need for the heating element to heat the support itself. Instead, heat from the heating element can be radiated or convected directly through the support to the food. All these features in combination maximise the efficiency of use of heat generated by the heating element and thus minimise the power requirements leading to the construction of an oven which is very well suited for use by children.

Further advantages of the use of a domed structure are that it reduces the volume of air to be heated and thus the energy requirements of the oven and also increases the rate at which heat is convected to the top surface of the food.

We have monitored the temperature distribution within this structure and this indicates that the dome produces a convection effect which gives an air temperature adjacent the food, in the centre of the oven, which is higher than at the outer edge. The use of a double wall structure primarily achieves an insulating layer but also acts, in conjunction with the use of a sealed enclosure, to decrease the heating up time and increase the final temperature for a given size of enclosure. A further benefit is that the outer wall is insulated from the inner wall and therefore does not allow heat to radiate into the outer oven structure. This is important because if heat can radiate into the outer structure, toy regulations can be breached. Typically, the upper section which is domed extends from the region of the support.

Conveniently, the upper section is movable relative to the lower section of the enclosure and preferably is hinged to it. In this way, the upper section can be pivoted away from the lower section to enable access to be obtained to the inside of the enclosure.

Typically, an air gap is provided between the walls of the enclosure but in some examples this gap could be filled completely or partially with further heat insulating material.

The support can be constructed in any convenient way but typically comprises a grille, which may be formed of plastics material or metal mesh. The use of metal enables heat to be conducted to food supported on the support in addition to the convected heat.

The food to be cooked may be placed directly on the mesh, but typically will be placed in a dish, tray or tin resting on the mesh.

The heating element can be any conventional form such as a heating coil but preferably comprises a halogen bulb. This is a relatively safe low power heat source. Indeed, heat sources delivering no more than 35W are preferred and can be used in this invention to achieve cooling temperatures relatively quickly. Typically, the oven further comprises a temperature sensor for monitoring the temperature within the enclosure. This enables the temperature to be displayed for example but in addition can be used, as will be explained in more detail below, to control access to the food.

The oven according to the invention can be used in a stand-alone form but preferably, particularly when the oven is to be used by children, further control means is provided to prevent access to the food until the temperature within the enclosure is below a predetermined threshold. For example, the control means could comprise a suitable locking system for locking the upper and lower sections of the enclosure together, the system being responsive to the temperature within the enclosure so as to be released when that temperature falls below a predetermined threshold.

In a particularly preferred arrangement, however, we provide a toy oven assembly comprising an oven according to the invention; and a protective structure within which the oven is positioned, the protective structure having at least one door through which access to the oven can be obtained, the door having a lock; and a control system responsive to the temperature within the oven to activate the lock when the temperature is less than a predetermined value.

The control system could be implemented in a variety of ways using a microprocessor or the like but conveniently, where the oven includes a temperature sensor for monitoring the temperature within the enclosure, the control system comprises an electrical circuit connecting a lock actuator and the temperature sensor whereby the temperature sensor acts as a switch which in one condition activates the lock actuator so that the lock is released and in the other condition deactivates the lock actuator. Activation occurs when the sensed temperature is less than the predetermined threshold.

Preferably, the oven further includes a closure sensor for sensing when the enclosure is closed and for providing a suitable output signal. Conveniently, this sensor can be used as a switch in an electrical circuit of the control system to control activation of the heating element only when the enclosure is closed.

Preferably, the protective structure includes a second access opening through which food to be cooked can be supplied by the user when the door is closed. As will be explained below, this enables food to be inserted into the enclosure after the oven has been heated up but without risk to the user.

Conveniently, a further access opening is provided to enable cooked food to be extracted from the protective structure.

An example of an oven and a protective structure in which the oven is mounted in accordance with the present invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a schematic, cross-section through the oven;

Figure 2 is a view similar to Figure 1 but with most of the inner parts omitted, showing the enclosure in its open position;

Figure 3 is an exploded view of the components making up the enclosure;

Figure 4 is a perspective view of a toy oven assembly from the front and right side incorporating an oven of the type shown in Figure 1;

Figure 5 is a perspective view of the oven assembly shown in Figure 4 from above, left side and front;

Figure 6 is a perspective view of the oven assembly shown in Figures 4 and 5 from the left side and front; Figure 7 is a block circuit diagram of the control system of the assembly shown in Figures 4-6; and,

Figures 8-13 are front elevations showing the oven assembly in different stages of use.

The construction of the oven is shown in Figure 1. The oven includes an enclosure 1 having an upper section 2 and a lower section 3 to which the upper section is hinged at 4. Each section 2,3 of the enclosure 1 has an outer. plastics skin 5 and an inner, reflective skin 6 made of a different material with a 10mm air gap 7 between them. The upper section 2 has a generally domed, hemispherical form and the lower section 3 is dish shaped with a circular periphery. A support plate 8 in the form of an aluminium grille with apertures 8A is mounted at the top of the lower section 3 and beneath this is positioned a heating element 9 in the form of a halogen bulb connected via support connectors 10 to a low voltage supply (not shown) . An aluminium tray 11 sits on the support 8 and contains a cake mixture to be baked.

In use, when a voltage is applied across the bulb 9, the bulb 9 will radiate heat which is partly conducted directly to the tray 11 through the support 8 as shown at 12 and is partly convected around the tin 11 and is guided by the domed form of the upper section 2 of the enclosure and impinges on the mix from above as shown at 13.

It has been found that this structure maximises the use of heat generated by the heating element 9 firstly by minimising heat loss through the enclosure by using an air gap and different materials for inner and outer skins 5,6; secondly by forming the upper section 2 of the enclosure in a domed form so that the convected heat is guided back onto the cake mix; and thirdly by allowing heat to radiate directly through the apertures 8A to the tray 11.

Figure 2 illustrates the oven with the upper section 2 in its open position, with the tray 11 removed and omitting the bulb 9.

The manner of manufacturing the enclosure 1 can be seen more clearly in Figure 3. The outer and inner skins 5,6 of the upper section 2 are formed as separate, domed structures, the inner skin 6 having a radially outwardly extending flange 14 to which the outer skin 5 is welded or glued. The outer and inner skins 5,6 of the lower section 3 are also formed separately with the inner skin 6 having a radially outwardly extending flange 15 to which the outer skin 5 is welded or glued.

Typically, the diameter of the enclosure 1 is about 13cm. Figures 4-6 illustrate the oven shown in Figure 1 incorporated into a protective structure 20. The structure includes a main cavity 21 in which the oven 1 is located. The lower section 3 of the oven enclosure is embedded in a base 22 while the upper section 2 is visible. A transparent plastic fronted door 23 provides access to the cavity 21. The righthand side of the enclosure 20 has an inlet opening 24 while a hob 25 is provided on the top of the enclosure, the hob being controlled from a control switch 26. A power light is included at 27 and a heating light at 28. A control knob 29 is mounted to the left side of the structure (Figure 5) and is linked by a mechanical linkage (not shown) to the upper section 2 of the enclosure 1 of the oven to enable the upper section to be pivoted between open and closed positions. A digital clock display is provided at 40. An optional light (not shown) may be included to indicate when the door 23 is locked.

The control system is shown in block circuit diagram form in Figure 7. The system is connected at 41 to a 12 volt supply (not shown) positioned within the protective structure 20. The supply is connected to the switch 26 and the hob 25 which is fabricated in the form of a 5W, 12V heating lamp. In addition, the -12V pole is connected to a solenoid 31 which acts as a lock actuator/deactuator for controlling a lock (not shown) associated with the transparent plastic door 23. The circuit including the solenoid 31 is connected in series with two temperature sensors 32 mounted within the oven 1, the sensors 32 acting as a switch which closes when the temperature within the oven reaches 40°C. The sensors 32 are also connected to the +12V pole.

In parallel, the supply is connected to a circuit having a pair of switches 33,34 adapted to be closed when the door 23 and the upper section 2 of the oven 1 respectively are closed. The switches 33,34 are connected in series with a second sensor 35 mounted within the oven 1 for sensing when the temperature within the oven reaches 200°C. The sensor 35 acts as a switch and is connected in series with an LED constituting the heating light 28 and is also connected to the 35W, 12V bulb 9. The power supply is also connected in series with an LED constituting the power light 27. A typical sequence of operation will now be described with reference to Figure 7 and Figures 8-13.

Initially, the door 23 and the upper section 2 of the oven 1 are both closed (Figure 8) causing each of the switches 33,34 to close. Power is switched on causing the LED 27 to light indicating "power on" while the sensor 35 is closed (since the temperature is less than 200°C) so that the LED 28 is also on and the bulb 9 heats up. Initially, the sensors 32 will be open since the sensed temperature is less than 40°C and the solenoid 31 will therefore be energised so keeping the door lock (not shown) retracted.

After a while, the temperature within the oven exceeds 40°C which is sensed by the sensors 32 which close thus deactivating the solenoid 31 and allowing the lock to actuate so that the door 23 can no longer be opened. At this time, an LED 43 will illuminate indicating the locked condition.

After a further period (typically a total of 10 minutes from initiation) , the temperature within the oven 1 will reach about 200°C which is sensed by the sensor 35 which then opens. This deactivates the LED 28 and the bulb 9 and deactivation of the LED 28 will indicate to the user that the oven is ready for food to be inserted. The knob 29 is rotated to open the upper section 2 of the oven 1 (and thus opening the switch 34) and a tray 36 containing cake mix is inserted through the opening 24 and pushed using a plastics pusher 37 onto the grille 8 (Figures 9 and 10) . The pusher 37 is removed and the upper section 2 of the oven is then lowered by rotating the knob 29 (Figure 11) . The door 23 remains locked during this process.

Once the upper section 2 has closed, the switch 34 is again closed and since the temperature will have dropped during this process, the sensor 35 will have also have closed so that the bulb 9 is reactivated and cooking continues, typically for about 15 minutes as the user wishes. At the end of the desired cooking time, the user rotates the knob 29 to open the upper section 2 thus opening the switch 34 and terminating the supply of power to the bulb 9 (Figure 12) . This allows the interior σf the oven to cool and once the temperature has dropped below 40°C as detected by the sensor 32, the switch constituted by the sensor opens, activating the solenoid 31 which releases the lock to enable the door 23 to be opened (Figure 13) . The cooked cake can now be removed.

It will be appreciated that the cake and cake mix have been omitted from the drawings, for clarity.

It will also be appreciated that this sequence of controls ensures that the user does not risk being burnt by the high temperatures which are reached during the cooking process. If the user wishes to use the hob, he closes the switch 26 which then enables power to be supplied to the heating lamp 25. A temperature sensor 44 is positioned adjacent the heating lamp 25 and is normally closed at temperatures less than 40°C. Once the temperature exceeds that value, the sensor 44 will open thus breaking the circuit through the heating lamp 25 and allowing the lamp to cool. When the temperature drops below 40°C, the sensor 44 closes again and the lamp 25 is reactivated.

The display 40 is connected to a timing circuit 45 which allows the user to simulate the setting of cooking times although the timer does not in fact control the cooking process. Thus, an oscillator 46 is provided connected via a microprocessor 50 to three switches 47-49 constituting a timer start/stop switch, a minute setting switch and an hour setting switch respectively. Times are displayed on the display 40 which is typically an LCD. The microprocessor 50 responds to suitable inputs via the switches 47-49 to set start and stop times and to simulate the appearance of a conventional oven providing such a feature.

Claims

1. An oven comprising an enclosure having upper and lower sections; an electrical heating element mounted in the lower section of the enclosure; and an open mesh support positioned over the heating element on which food to be cooked is located, wherein the enclosure is formed as a double wall structure to retain heat, wherein the upper section of the enclosure is domed to enable heat which has passed from the heating element through the open mesh support to be convected onto the top of food on the support, and wherein the upper and lower sections can be closed to define a sealed volume within the enclosure during cooking.

2. An oven according to claim 1, wherein the upper section of the enclosure is hinged to the lower section.

3. An oven according to claim 1 or claim 2, wherein the domed upper section extends from the vicinity of the support.

4. An oven according to any of the preceding claims, wherein an air gap is provided between the walls of the enclosure.

5. An oven according to any of the preceding claims, wherein the support comprises a grille.

6. An oven according to any of the preceding claims, wherein the heating element comprises a halogen bulb.

7. An oven according to any of the preceding claims, wherein the heating element delivers heat at no more than 35W.

8. An oven according to any of the preceding claims, further comprising at least one sensor for monitoring the temperature within the enclosure.

9. An oven according to any of the preceding claims, wherein the heating element is connected to an electrical supply which generates a voltage of not more than 12 volts.

10. A toy oven assembly comprising an oven according to any of the preceding claims; and a protective structure within which the oven is positioned, the protective structure having at least one door through which access to the oven can be obtained, the door having a lock; and a control system responsive to the temperature within the oven to deactivate the lock only when the temperature is less than a predetermined value.

11. A toy oven assembly according to claim 10, when dependent on claim 8, wherein the control system includes an electrical circuit connecting a lock actuator for operating the lock and the temperature sensor within the oven enclosure which acts as a switch, and which in one condition activates the lock actuator so that the lock is released and in the other condition deactivates the lock actuator.

12. An assembly according to claim 10 or claim 11, wherein the oven further includes a closure sensor for sensing when the enclosure is closed and for providing a suitable output signal, and wherein the control system is responsive to the output signal from the closure sensor to control activation of the heating element only when the enclosure is closed.

13. An assembly according to any of claims 10 to 12, wherein the protective structure includes a second access opening through which food to be cooked can be supplied by the user when the door is closed.

14. An assembly according to any of claims 10 to 13, wherein the protective structure includes an actuator accessible from outside the protective structure, the actuator being connected to the upper section of the oven to enable the upper section to be opened and closed without exposing the user to heat from within the enclosure.