GB2255001A

GB2255001A - Portable heating appliance

Info

Publication number: GB2255001A
Application number: GB9205680A
Authority: GB
Inventors: Herbert Huss; Martin Sonnek; Reinhard Kersten
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1991-03-18
Filing date: 1992-03-16
Publication date: 1992-10-28
Anticipated expiration: 2012-03-16
Also published as: ES1020588Y; IT226348Z2; GB9205680D0; GB2255001B; AT399979B; ITMI920235V0; ATA60391A; DE9203459U1; ES1020588U; ITMI920235U1; FR2674318B3; FR2674318A3

Abstract

A portable heating appliance (1) has a housing (2) with a heat-withstanding radiant energy transmissive support surface such as a glass-ceramic plate (24) underneath which is provided a heating device (28) for emitting radiant energy which is reflected towards the support surface (24) by a reflector (31). Temperature control within the housing is preferably provided by means of a cooling fan (49), controlled by a temperature sensor, which provides an air stream for cooling the reflector (31) and power-control circuit (44) within the housing (2). <IMAGE>

Description

PORTABLE HEATING APPLIANCE The invention relates to a portable heating appliance for heating a substance such as a foodstuff.

Portable heating appliances or cookers using resistive heating devices have been known for a long time. These cookers often have a housing with a circular upper wall as well as a circular bottom wall and a hollow cylindrical connecting wall. The upper wall is made of a heat-proof material, for example a clay-like or ceramic-like material, in which a resistive heating wire is embedded. These cookers generally only allow a coarse temperature setting and do not have accurate temperature control for maintaining the desired temperature setting. In addition because of the inertia of the resistive heating device, such cookers respond comparatively slowly to changes of the temperature setting.For example, if such a cooker is set from its off-state to its maximum temperature for rapidly heating a substance, this heating process will nevertheless take a comparatively long time as a result of the inertia of the resistive heating. Conversely, when switching from a high temperature setting to a lower temperature, for example to finish cooking of a vehemently boiling substance such as a soup at a lower temperature, the inertia of the resistive heating, although the temperature setting has been reduced already, results in continued excessive heating, which frequently leads to boiling over. Moreover, it is to be noted that with cookers using resistive heating a comparatively large mass has to be heated during heating up, so that these cookers have a comparatively low efficiency during heating up.Also the efficiency of heat transfer depends on the flatness of the bottom of the container receiving the substance to be heated and on the flatness of the cooker surface supporting the container. In addition, such cookers are not protected against overheating.

It is an object of the invention to mitigate the above disadvantages.

According to one aspect of the present invention, there is provided a portable heating appliance comprising a housing having a heat-withstanding radiant energy transmissive surface for supporting a substance to be heated, the housing containing a heating device for emitting radiant energy, a reflector for reflecting radiant energy from the heating device towards the support surface and means for controlling the temperature within the housing.

A portable heating appliance in accordance with the invention may be small, light-weight and easy-to-handle and the use of radiant heating should allow for fine temperature setting and accurate temperature control with rapid response to changes of the temperature setting. The reflector by reflecting more radiant energy through the support surface, should enable improved efficiency independent of the flatness of the bottom of the container. Also reliable overheating protection may be obtained.

In a second aspect, the present invention provides a portable heating appliance for heating a substance, preferably foodstuffs, comprising a slender housing having an upper wall, having a bottom wall and having at least one connecting wall interconnecting the upper wall and the bottom wall, a heating device accommodated in the housing and constructed to convert electric energy into thermal energy, by means of which heating device the substance to be heated can be heated to a desired temperature upon introduction into a heatable container for receiving said substance, in which appliance the upper wall of the housing is basically constituted by a glass-ceramic plate on which the heatable container can be placed, at least one rod-shaped radiator is provided as a heating device underneath the glass-ceramic plate, which radiator emits thermal energy of a radiation wavelength in a range between 0.4 and 5.0Zm, a reflector is provided between the radiator and the bottom wall of the housing and reflects radiation emitted to it by the radiator towards the glass-ceramic plate and protects the bottom wall against direct exposure to the radiation, the electric energy can be supplied to the radiator by means of power-control circuitry accommodated in the housing, and a cooling fan, which can be controlled by a temperature sensor, is arranged adjacent the reflector by means of which fan an air stream for cooling the reflector and the power-control circuitry can be produced between air inlet apertures formed in at least one housing wall and air outlet apertures formed in at least one housing wall.

A glass-ceramic plate has a high transmission coefficent of, for example, over 70%, which is advantageous for a high efficiency. As a result of the provision of a reflector substantially all the radiation energy emitted by the radiator may be transmitted to the glass-ceramic plate and via this plate to the container for the substance to be heated, this transfer of the radiation to the container being independent of unevenness of the container bottom and of the glass-ceramic plate, which is also favourable for an optimum efficiency. Moreover, the reflector should protect the bottom wall of the housing of the heating appliance, which is arranged near the at least one radiator in order to obtain a small and compact appliance, against the direct exposure to the radiation emitted by the radiator and thus against excessive heating.The provision of at least one heater of this kind should ensure that a very rapid response to changes of the temperature setting is obtained because such a radiator should immediately respond to any change of the amount of electric energy applied to it. The provision of the power-control circuitry should enable a fine temperature setting and very accurate temperature control. Moreover, the use of the cooling fan which can be controlled by the temperature sensor should allow for a very reliable overheating protection, which is very important in such a portable heating appliance where the risk of overheating is comparatively large because of the compactness of the appliance and the comparatively high heating power obtained, despite this compact construction, by the provision of the at least one radiator.

Summarising, these combined features should allow the provision of a small, lightweight, easy-to-handle and powerful heating appliance having a fine temperature setting, an accurate temperature control, a rapid response to changes of the temperature setting, a high efficiency and a reliable overheating protection.

It should be noted that heating appliances comprising a glass-ceramic plate with radiators arranged underneath the glass-ceramic plate, and reflectors carrying the radiators and a temperature sensor and arranged to reflect the radiation emitted by the radiators towards the glass-ceramic plate are known per se.

However, these appliances are large kitchen appliances which are not portable and therefore cannot simply be carried to an arbitrary location. In addition in such large kitchen appliances the problem of overheating of the housing accommodating the radiators, the reflector and the power control circuitry is virtually non-existent.

It should also be noted that heating appliances with cooling fans are known. However, in such heating appliances the heating device is not constituted by at least one radiator cooperating with a reflector but by an electromagnetic inductive heating device which does not yield the advantages attainable, in accordance with the invention, by the provision of a radiator cooperating with a reflector in a heating appliance in accordance with the invention.

The reflector may be substantially tray-shaped with the at least one radiator and the temperature sensor arranged in the tray-shaped reflector, the tray-shaped reflector may comprise a flat rim which extends parallel to the glass-ceramic plate, and with its flat rim the reflector, together with the at least one radiator and the temperature sensor arranged therein, may be placed on and connected to a reflector holder, which in relation to the reflector is situated at the side which is remote from the glass-ceramic plate, to form a constructional unit. In this way the highly vulnerable parts of such an appliance can be assembled to form a pre-assembled unit prior to the final mounting in the appliance, which unit can be mounted without any problems after pre-assembly.

Springs may be arranged between the reflector holder and the bottom wall and act on the reflector holder at one end and on insulators at the other end, which insulators bear against the bottom wall so that the springs press the rim of the reflector against the glass-ceramic plate via the reflector holder. In this way the reflector may always be in snug engagement with the glass-ceramic plate. At the same time the provision of the insulators should guarantee an effective thermal insulation of the reflector and the reflector holder relative to the bottom wall of the housing.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded view showing a first embodiment of a heating appliance in accordance with the invention; and Figure 2 is a view similar to Figure 1 but showing a second embodiment of a heating appliance in accordance with the invention.

Referring now to the drawings, Figure 1 shows a portable heating appliance 1 for heating a substance, preferably foodstuffs. The appliance 1 is of very slim construction and consequently has a slender (that is thin or shallow) housing 2.

The housing 2 is thus of small height or depth in relation to its width. The housing 2 comprises a tray-like lower section 3, having a bottom wall 4 and four side-wall portions 5,6,7 and 8, and a frame-like upper section9, which mainly comprises four further side-wall portions 10,11,12 and 13 which at their sides remote from the lower section 3 adjoin respective narrow web portions 14,15,16 and 17 extending parallel to the bottom wall 4. The side-wall portion 10 is inclined and has an opening 18 in which a cover 19 provided with key symbols is mounted in a water-tight manner. In the assembled condition of the heating appliance 1 the lower section 3 and the upper section 9 are secured to one another by means of screws 21, four rubber feet 22 being mounted in the recesses for the screws 21 in the lower section 3 after the screws 21 have been fitted.The side-wall portions 5 and 10, 6 and 11, 7 and 12, and 8 and 13 then form four connecting walls connecting the bottom wall 4 to the web portions 14, 15, 16 and 17, which constitute part of an upper wall 23 of the heating appliance 1. However, the upper wall 23 of the heating appliance 1 is formed mainly by a glassceramic plate 24. The glass-ceramic plate 24 is mounted in a plate holder 25 of a heat-proof thermosetting plastics, a rubber seal 26 being arranged on the glass-ceramic plate 24 and a steel frame 27 being arranged on this seal and connected to the plate holder 25 with the seal 26 and the glass-ceramic plate 24 interposed.

The heating appliance 1 comprises a heating device 28 arranged in the housing 2, which device is constructed to convert electrical energy into thermal energy and by means of which a substance to be heated can be heated to a desired temperature upon introduction into a heatable container for receiving this substance, which container is not shown in Fig. 1. The heating device 28 of the heating appliance 1 comprises two rod-shaped radiators 29 and 30 emitting thermal energy in a wavelength range between 0.4 jim and 5.0 jim. In this case the two radiators are constituted by halogen lamps.

Between the two radiators 29 and 30 and the bottom wall 4 of the housing 2 a substantially tray-shaped reflector 31 is arranged. In accordance with the number of halogen lamps 29 and 30 the tray-shaped area of the reflector 31 is divided into two substantially parabolic reflector zones 32 and 33, each facing one of the two halogen lamps 29 and 30. The two halogen lamps 29 and 30 are mounted in the reflector 31 and are mechanically connected to this reflector. Moreover, a temperature sensor 34 is arranged in the reflector 31 and is also mechanically connected to the reflector 31. In this appliance the temperature sensor 34 is rod-shaped and is situated in the transition area 35 between the two reflector zones 32 and 33 but at the side of the reflector 31 which is remote from the glass-ceramic plate 24.The reflector 31 reflects the radiation emitted to it by the two radiators 29 and 30 towards the glass-ceramic plate 24. In addition, the reflector 31 protects the bottom wall 4 against direct exposure to the radiation emitted by the two radiators 29 and 30.

As can be seen in Fig. 1 the tray-shaped reflector 31 has a flat rim 36 which extends parallel to the glass-ceramic plate 24. With this flat rim 36 the reflector 31 together with the two radiators 29 and 30 and the temperature sensor 34 arranged therein is mounted on a reflector holder 38, which in relation to the reflector 31 is situated at the side which is remote from the glass-ceramic plate 24, to form a constructional unit 37. The reflector holder 38 is substantially annular and comprises a hollow cylindrical portion 39, which receives the tray-shaped portion of the reflector 31, and a further rim 40 which extends parallel to the rim 36 of the reflector 31 and engages against the rim 36 of the reflector 31. The two rims 36 and 40 are connected by means of embossed portions of the two rims 36 and 40 but this connection can also be made by means of separate rivets.Three springs 41 in the form of compression springs are arranged between the reflector holder 38 and the bottom wall 4. At one end the springs 41 act directly on the reflector holder 38, i.e. on the flat rim 40 thereof, and at the other end they act directly on insulators 42 of a suitable thermally insulating material, which insulators bear against the bottom wall 4 at the location of raised portions 43 which project from the bottom wall 4 into the interior of the appliance. The springs 41 press the rim 36 of the reflector 31 against the glass-ceramic plate 24 via the reflector holder 38, thereby ensuring that the rim 36 of the reflector 31 is always in contact with the glass-ceramic plate 24.

For the electrical power supply of the two halogen-lamp radiators 29 and 30,the housing 2 of the heating appliance 1 accommodates a power-control circuitry 44 on a printed circuit board 45 secured in the lower section 3. A mains cord 46 leads to the circuitry 44 to connect the heating appliance 1 electrically to a power-supply mains. The temperature sensor 34 is electrically connected to the power-control circuitry 44 in a manner not shown. At a given temperature in the area of the reflector 31 the temperature sensor 34, which basically comprises a bimetal element, supplies a control signal to the circuitry 44, the effects of this signal being described hereinafter.

The two halogen lamps 29 and 30 are also electrically connected to the circuitry 44 in order to apply the appropriate amount of electric energy to these lamps. For temperature selection the heating appliance 1 comprises a keyboard 47 which in the present appliance is arranged directly on the printed circuit board 45 and whose keys 48 are arranged underneath the cover 19 below the printed key symbols 20. Depending on the desired temperature selected by means of the keyboard 47 the halogen lamps 29 and 30 receive the corresponding amount of electric energy from the power-control circuitry 4A, causing the halogen lamps 29 and 30 to emit the radiation energy required to reach the desired temperature.

The heating appliance 1 comprises a cooling fan 49 arranged adjacent the reflector 31 and the reflector holder 38. The cooling fan 49 basically comprises a fan motor 50, which is accommodated in a motor holder 51 and secured to this motor holder 51 by means of two screws 52, and a fan wheel 54, which is rotationally locked on the shaft 53 if the fan motor 50. Three screws 55 secure the motor holder 51 to portions projecting from the bottom wall 4. The cooling fan 49 can be controlled by means of the temperature sensor 34, in such a way that, as already stated, the temperature sensor 34 supplies a control signal to the circuitry 44 at a specific temperature in the area of the reflector 31, the circuitry 44 processing this control signal and in response thereto switching on the fan motor 50.When the fan motor 50 is switched on the fan wheel 54 of the cooling fan 49 produces an air stream, the air flowing from air inlet apertures 56 in the bottom wall 4 underneath the fan 49, past the circuitry 44 on the printed circuit board 45 and past the bottom wall 4 and the reflector 31 to air outlet slots 57 provided both in the bottom wall 4 and in the side-wall portion 7 of the lower section 3. This air stream cools the bottom wall 4, the reflector 31 and the power-control circuitry 44.

As is apparent from Fig. 1 and the corresponding description the appliance described is a compact, light-weight and easy-to-handle heating appliance which can be carried with one hand. The construction of the heating appliance using halogen lamps has the advantage of a rapid response to variations in the temperature setting. By constructing the upper wall of the appliance as a glass-ceramic plate and providing the reflector, which ensures that substantially all the radiation emitted by the halogen lamps reaches the glass-ceramic plate and is consequently available for heating the substance to be heated, a high efficiency of the appliance is achieved. The provision of a power-control circuitry results in a sensitive temperature control.The provision of a cooling fan controlled by a temperature sensor has the essential advantage that despite the compact construction and small dimensions of the appliance overheating of the appliance, which could lead to damage to the appliance and to the area where it is located, is substantially excluded.

Fig. 2 shows a further portable heating appliance 1 for heating a substance, preferably foodstuffs. In this heating appliance 1 the glass-ceramic plate 24 has a circular area 58 which is transparent to visible light and a printed area 59 which is opaque to or hardly transmits visible light. In the present appliance 1 the glass-ceramic plate 24 is mounted in the upper section 9 from the top, the glass-ceramic plate 24 being surrounded by the narrow web portions 14, 15, 16 and 17 and the glass-ceramic plate 24 being connected to the upper section 9 in a water-tight manner by means of a silicone sealing 60, shown diagrammatically in Fig. 2.

In the heating appliance 1 shown in Fig. 2 a reflector 31 is arranged underneath the glass-ceramic plate 24 in which a heating device 28 is mounted comprising two radiators 29 and 30 formed by halogen lamps. Moreover, a temperature sensor 34 is connected to the reflector 31, which sensor is not rod-shaped but substantially block-shaped in the present appliance and is also arranged in the transition area 35 between the two reflector zones 32 and 33 at the side of the reflector 31 which is remote from the glass-ceramic plate 24. In this appliance the reflector 31 is also mounted in a reflector holder 38 to form a constructional unit 37, the flat rim 36 of the reflector 31 being connected to the flat rim 40 of the reflector holder 38 by means of, for example, rivets. In the present appliance the reflector holder 38 is tray-shaped and has a bottom wall 61.A shielding plate 62 is arranged underneath the bottom wall 61.

The provision of the bottom wall 61 and the shielding plate 62 in the present appliance assures a very effective thermal insulation between the radiators 29 and 30 and the bottom wall 4 of the heating appliance 1. The shielding plate 62 has three openings 63 through which the insulators 42 are passed with their tubular portions. In the present appliance the springs 41 act directly on the flat rim 40 of the reflector holder 38 the flat rim 40 and at the other end they act indirectly on the insulators 42 via the shielding plate 62, the springs 41 being positioned by the tubular portions of the insulators 42 which engage the springs.

In the heating appliance 1 shown in Fig. 2 the keyboard 47 is not arranged on the printed circuit board 45 accommodating the power-control circuitry 44 but on a separate printed circuit board 64 connected to a further printed circuit board 65 accommodating circuitry which is basically associated with the keyboard 47. This has the advantage that in order to construct appliance types which differ with respect to the keyboard, the keyboard and the associated circuitry can be exchanged simply without the necessity of replacing the complete printed circuit board 45 with the power-control circuitry 44.

The appliance 2 shown in Figure 2 is also a small, lightweight and easy-to-handle heating appliance which can be carried with one hand and which also has the advantages mentioned for the appliance shown in Figure 1. Another advantage of the appliance shown in Figure 2 is that it guarantees a very effective thermal insulation relative to the bottom wall of the appliance and a simple replacement of the control keyboard of the appliance.

With respect to the actual size of the two heating appliances described above it is to be noted that in each case the housing may be, for example, approximately 315mm (millimetres) by approximately 340mm with a height of only approximately 55mm. The weight of each of the two appliances may be, for example, approximately 2.5kg.

The two halogen lamps of both appliances may be, for example, dimensioned to provide together a maximum power of 2000 W. As is apparent, the heating appliances are small, light-weight and therefore easy-to-handle in spite of a very high power rating.

Of course, it will be appreciated by the person skilled in the art that the dimensions of the housing of the appliance may differ from those given above and that, moreover, the nature and number of the radiators may vary.

From reading the present disclosure, other modifications and variations will be apparent to persons skilled in the art. Such modifications and variations may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

CLAIM(S)

1. A portable heating appliance comprising a housing having a heat-withstanding radiant energy transmissive surface for supporting a substance to be heated, the housing containing a heating device for emitting radiant energy, a reflector for reflecting radiant energy from the heating device towards the support surface and means for controlling the temperature within the housing.

2. An appliance according to Claim 1, wherein the temperature controlling means comprises means for providing an air stream for cooling the reflector and control circuitry provided within the housing.

3. An appliance according to Claim 2, wherein the air-stream providing means comprises a fan, a temperature sensor for controlling operation of the fan, and air inlet and outlet apertures provided in the housing.

4. An appliance according to Claim 1,2 or 3, wherein the support surface comprises a glass-ceramic plate.

5. An appliance according to Claim 1,2,3 or 4, wherein the heating device comprises at least one rod shaped radiator for emitting radiant energy having a wavelength in the range of from about 0.4 micrometres (gum) to about 0.5 micrometres.

6. An appliance according to any one of Claims 1 to 5, wherein the reflector is supported within the housing by resilient support means.

7. An appliance according to any one of Claims 1 to 6, wherein a thermal shielding plate is provided, remote from the heating device, between the reflector and the housing.

8. A portable heating appliance for heating a substance, preferably foodstuffs, comprising a slender housing having an upper wall, having a bottom wall and having at least one connecting wall interconnecting the upper wall and the bottom wall, a heating device accommodated in the housing and constructed to convert electric energy into thermal energy, by means of which heating device the substance to be heated can be heated to a desired temperature upon introduction into a heatable container for receiving said substance, in which appliance the upper wall of the housing is basically constituted by a glass-ceramic plate on which the heatable container can be placed, at least one rod-shaped radiator is provided as a heating device underneath the glass-ceramic plate, which radiator emits thermal energy of a radiation wavelength in a range between 0.4 and 5.0cm, a reflector is provided between the radiator and the bottom wall of the housing and reflects radiation emitted to it by the radiator towards the glass-ceramic plate and protects the bottom wall against direct exposure to the radiation, the electric energy can be supplied to the radiator by means of power-control circuitry accommodated in the housing, and a cooling fan, which can be controlled by a temperature sensor, is arranged adjacent the reflector by means of which fan an air stream for cooling the reflector and the power-control circuitry can be produced between air inlet apertures formed in at least one housing wall and air outlet apertures formed in at least one housing wall.

9. An appliance according to Claim 8, wherein the reflector is substantially tray-shaped, the at least one radiator and the temperature sensor are arranged in the tray-shaped reflector, the tray-shaped reflector comprises a flat rim which extends parallel to the glass-ceramic plate, and with its flat rim the reflector, together with the at least one radiator and the temperature sensor arranged therein, is placed on and connected to a reflector holder, which in relation to the reflector is situated at the side which is remote from the glass-ceramic plate, to form a constructional unit.

10. An appliance according to Claim 9, wherein springs are arranged between the reflector holder and the bottom wall and act on the reflector holder at one end and on insulators at the other end, which insulators bear against the bottom wall, said springs pressing the rim of the reflector against the glass-ceramic plate via the reflector holder.

11. A portable heating appliance substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.