EP1929211B1 - Lighting device for ovens, and oven - Google Patents

Description

The invention relates to a lighting device for ovens, in particular for illuminating the oven muffle, and an oven with at least one lighting device.

In the oven muffle or the cooking chamber of a baking oven prevail during operation of the oven high temperatures. Lighting devices that are to illuminate the oven muffle must therefore be able to withstand such temperatures. For this purpose, backlamps are provided with a temperature-resistant glass. To attach the back lamp to the oven muffle, a piece of the side wall or top wall of the oven muffle must be cut out. Over this cut it comes to heat losses in the oven muffle and therefore to a higher energy consumption.

In the DE 38 27 528 A1 In order to eliminate these problems, a device for the illumination of internal spaces of a baking oven is proposed in which the light source is integrated into the front flap of the oven. The introduction of the light rays in the oven muffle takes place here directly from the light source or reflectors. The disadvantage of this type of lighting is that it is only possible from one side, namely the front. Lighting from the viewing direction is also fundamentally disadvantageous for a good assessment of the texture and thus the properties of the viewed, here the food.

In addition, the reveals US 5,836,669 a remote lighting and a light distribution in devices.

The DE 103 18 859 A1 discloses a cooking appliance.

The DE 103 01 078 A1 discloses a lighting device for ovens.

Finally, the reveals EP 0 922 910 A1 a multi-level lighting device for a household oven.

Object of the present invention is to provide a way with the energy-saving illumination of the oven muffle can be guaranteed.

This object is achieved according to a first aspect of the invention by the features of claim 1. By providing an insulating material, which is also referred to below as insulating material, between the partition wall and the at least one light source, heat loss from the furnace muffle in the region of the lighting device can be prevented. Thus, it is possible to design the lighting device over a large area without causing an energy loss. Furthermore, by providing an insulating material separate from the partition wall, the materials of the partition wall and the insulating material can be selected according to the conditions prevailing at these components. For example, while the partition must withstand the attack of high temperatures and at the same time the attack of fumes or vapors, the insulating material can be selected for its thermal insulation capacity and its optical properties. The partition wall preferably constitutes a temperature-resistant glass pane. Since the insulating material is a solid material and not, as in the prior art, air, the insulating material can also assume a supporting function for supporting the partition wall. By supporting the partition, it is possible to design this large area. Bending due to thermal changes can not take place, so that the stability and lifetime are increased even with large lighting devices.

With the lighting device according to the invention, it is also possible to produce sufficient thermal insulation that even light sources can be used, which withstand only low ambient temperatures. A separate cooling of the light source, for example via a separate fan, which is also used to cool the entire muffle wall, can be omitted. Such cooling is necessary in conventional lighting devices with an arranged behind a temperature-resistant glass pane bulb.

As the insulating material, a transparent or translucent porous material is used. By means of a material having these properties, heat conduction by convection can be prevented on the one hand by the cavities in the porous structure, and the solid body heat conduction can be reduced by the low solids content. On the other hand, the passage of the light emitted by the light source can be ensured.

According to a preferred embodiment, the insulating material consists of silica, that is of a silicon dioxide. The silica can be pyrogenic silica, precipitated silica, electric arc silica or silica In a preferred embodiment, the insulating material consists of silica, that is, of a silicon dioxide. The silica may be fumed silica, precipitated silica, electric arc silica or silica airgel. These materials have a low thermal conductivity and can thus serve for thermal insulation. The particle size of these materials may range from 0.5 μm to 10 mm.

Particularly preferably, the insulating material consists of an airgel, in particular a silica airgel. Silica airgel is a highly porous nanostructured material from a SiO ₂ network that has many voids. Due to its high porosity, silica airgel has excellent thermal insulation properties. The high porosity in the nano range means that both the heat conduction is prevented by convection and the solid body heat conduction is reduced by the low solids content. In addition, silica airgel has a high transparency for visible light. Due to this combination of properties, silica airgel is particularly suitable as an insulating material for the lighting device according to the invention. Furthermore, silica airgel has a low density, so that the lighting device can be manufactured with a light weight, whereby the requirements for the attachment, via which the lighting device is attached to the inner wall of the oven muffle, are low, that is, the attachment be simple can. Finally, silica airgel has a high strength compared to other insulating materials, by which the resistance of the lighting device and thus its life can be increased even with a small wall thickness of the partition.

The insulating material may be provided as a bed of granular material. As a result, the introduction of the insulating material between the partition wall and the at least one light source is simplified. In addition, in a bed, the bulk density and the distribution of a granule size in the bed can be adjusted so that the necessary for the light source used optical properties and temperature conditions can be adjusted. The granule size to be used in this case is preferably in the range of 0.1 mm to 8 mm. Particular preference is given to using a bed of granular silica airgel. In this bed, in particular with granules in the preferred Area can be achieved a good color rendering and thus a natural assessment of the food to be guaranteed.

Instead of in the form of a bed of granular material, the insulating material may also be present in the form of a powder, in particular a powder bed, or may be introduced between the dividing wall and the at least one light source. In this case, suitable as insulating material, for example, fumed silica, precipitated silica or electric arc silica. With this material too, the particle size, the particle size distribution and the type of insulating material can influence the transmission spectra of the insulating layer. The grain size of the powder can go down to 0.5 μm.

According to one embodiment, the insulating material is a monolith, in particular a silica airgel monolith.

According to one embodiment, an electroluminescent light source is used as the light source. This can be a luminescent film or a light emitting diode (LED). The advantage of these light sources is on the one hand in the simple production and on the other hand in the low energy consumption, which is caused by these light sources. The use of LEDs, which usually only withstand ambient temperatures up to 80 ° C, is made possible in the lighting device according to the invention, since the LED is largely decoupled by the insulating material from the interior of the furnace muffle and the prevailing temperatures there.

In particular, when using a bed of silica airgel as insulating material further advantages can be achieved in connection with the use of an LED as a light source. By scattering processes on the bed, the radiated light of the LEDs is redistributed, whereby the disadvantages that occur in the conventional use of LEDs can be prevented. Although light-emitting diodes allow a high luminous efficacy, they generally have a clear maximum in the blue spectral range. The cause is the generation of blue light in the semiconductor crystal. This is not desirable when lighting a baking oven. When using an insulating material made of nanostructured silica particles, it has been found that there is a red shift in the light emitted by the LED. This shift too longer wavelengths results from the Rayleigh scattering of the light emitted by the LED occurring in the insulating material. As a result, an overall natural color reproduction can be achieved.

Compared to incandescent bulbs used in conventional lighting devices, the luminous efficacy can be increased with the use of an LED, thus reducing the energy requirement for a given minimum illuminance in the oven muffle.

However, it is also possible according to the invention to use a halogen incandescent lamp as the light source. By using light emitting diodes as light sources or lamps with a superior layer of transparent nanostructured silica (silicon dioxide), a particularly energy-saving and color-neutral oven lighting can be realized.

Preferably, the partition wall is part of a receptacle for the insulating material. The receptacle may be a separate component from the oven, which is attached to or in the wall of the oven muffle or introduced. For example, the receptacle may consist of two panes of glass, which are held in a frame. In the receptacle, the at least one light source can be introduced. But it is also possible to introduce the light sources, for example via recesses in the rear wall of the receptacle in the region of the insulating material. By providing a receptacle whose one side is formed by the partition wall, optimum conditions for the insulating material can be set, which will be explained later in more detail. Furthermore, the manufacture and attachment of the lighting device in the oven muffle are simplified.

A condition that can be set in the receptacle, for example, is a negative pressure. To set the operating temperature at the light source or the lighting means, a corresponding thickness of the insulating layer or bulk density of the insulating material is usually necessary. However, such an increase in the layer thickness or the bulk density leads to a decrease in the transmission of the radiation emanating from the luminous means through the insulating material. By evacuating the receptacle, the Insulation amount and thus the thickness of the insulating layer or the bulk density can be reduced. By this reduction of the gas pressure, the gas heat pipe is suppressed in the cavities of the insulating material and the insulating material in the receptacle can take over a support function for the partition in this case, so that a large-scale partition can be used without having to increase the wall thickness of the partition.

According to a further aspect, the invention relates to an oven with at least one lighting device for illuminating the oven muffle. The oven is characterized in that the at least one lighting device comprises a partition wall facing the furnace muffle and an insulating material provided behind the partition wall, which is provided between the at least one light source and the partition wall.

The size of the lighting devices is not limited due to the design of the lighting devices. It can also be provided a variety of lighting devices.

According to one embodiment, the oven has at least two lighting devices, which are each provided above each of two superimposed baking levels. This makes it possible to illuminate several baking trays simultaneously. By using the lighting device according to the invention, this illumination can be done with significantly reduced energy losses at the partitions and with a lower energy consumption of the entire lighting device.

Preferably, the lighting devices are provided on the side walls of the muffle space of the oven muffle. The lighting devices are preferably introduced into the side walls. For this purpose, depressions are provided in the side walls of the muffle space. By the illumination devices are provided in recesses, on the one hand, the surface over which heat could escape from the Muffelraum be minimized and on the other hand, the lighting devices do not reduce the interior of the oven muffle, so that this in its entire size for holding Gar Dough is available.

Due to the lateral arrangement, the illumination of the baking levels can be optimized. In particular, an illumination of all levels can be ensured even with several introduced into the different baking levels Gargutträgern, such as baking trays. Also on the upper jaw level, a more uniform illumination of the baking plane can be achieved with the lateral illumination according to the invention, as is possible with a lighting by a light bulb from above the baking plane.

The oven preferably has a lighting device according to the invention.

Advantages and features that are described with respect to the lighting device apply - as far as applicable - according to the oven according to the invention and vice versa.

• Figur 1: eine schematische perspektivische Ansicht der Ofenmuffel eines erfindungsgemäßen Backofens; und
• Figur 2: eine schematische Schnittansicht einer Ausführungsform einer erfindungsgemäßen Beleuchtungsvorrichtung.

The invention will be explained again below with reference to the accompanying drawings. Show it:

• FIG. 1 a schematic perspective view of the oven muffle of a baking oven according to the invention; and
• FIG. 2 : A schematic sectional view of an embodiment of a lighting device according to the invention.

In the FIG. 1 Furnace muffle 1 shown is configured cuboid and shown without oven door or front flap. The muffle space 2 is bounded by a bottom-side muffle wall 3, two lateral, vertical muffle walls 4 and 5, an upper, muffle-side muffle wall 6 and a rear Muffelwand 7. In five superimposed baking levels 8 to 12 are on the side muffle walls 4 and 5 slide rails 13th 17 attached to the holder of retractable Gargutträgern, such as the illustrated baking tray 18th

Between the slide rails 13 to 17, which define the baking levels 8 to 12, and above the upper baking level 8 lighting devices 19 are provided on the side walls 4 and 5 of the muffle space. The lighting devices 19 are in the form of lighting rails and extend in the horizontal direction along the side walls 4 and 5 from the region of the front of the muffle space 2 to the vicinity of the rear muffle 7. The lighting devices 19 are received in recesses 20 in the side walls 4 and 5 of the oven muffle 1 and fixed there. Preferably, the lighting devices 19 are completely received in the recesses 20, that is, do not stand in the muffle space 2 inside.

The construction of an embodiment of the lighting device according to the invention will be described below with reference to FIGS FIG. 2 explained.

The lighting device 19 comprises in the illustrated embodiment a receptacle 21 which consists of a partition wall 22, a rear wall 23 and a frame 24 carrying these two walls 22 and 23. The frame 24 defines the side walls of the rectangular cross-section of the receptacle 21.

On the rear wall 23, the partition 22 of the receptacle 21 facing light sources 25 are provided, which are indicated only schematically in the figure and can represent LEDs, for example. In this embodiment, the receptacle 21 thus serves not only to receive the insulating material 26 but also to receive the light sources 25. In the figure, three light sources 25 are provided in the receptacle 21. These may, in addition to the actual bulbs include a corresponding holder, which in the FIG. 2 not shown. The receptacle 21 is filled with an insulating material 26. The insulating material 26 preferably represents a bed of silica airgel. On the rear wall 23 in the illustrated embodiment on the partition wall 22 side facing a reflective layer 27, in particular a mirror coating, applied via the re-coupling of incident on the rear wall 23 light he follows.

When installed, the partition wall 22, which in particular represents a temperature-resistant glass pane, faces the muffle space 2. The frame 24 and the rear wall 23 are received in the recess 20 in the side wall 4 or 5 of the oven muffle 1. The rear wall 23 of the receptacle 21 may be made of glass or other temperature resistant material. The frame 24 is made of metal, for example.

In the receptacle 21, there is preferably a reduced gas pressure. For this reason, the transitions between the partition wall 22 and the frame 24 or the frame 24 and the rear wall 23 are designed gas-tight accordingly. For example, a separate sealant (not shown) may be used. Alternatively, the rear wall 23 and the frame 24 may be configured in one piece.

The light emitted from the light sources 25 is scattered on the insulating material 26. As a result of this Rayleigh scattering on the insulating material 26, the color impression of the light entering the muffle space 2 is shifted to reddish.

With this warm white light, an illumination of the oven interior can be achieved, which meets the highest requirements for the visual assessment of food, in particular ensures a good, natural color reproduction.

By using a silica airgel or other silica, a sufficient illuminance of 300 Ix can be achieved. In addition to the mean value of illuminance, the distribution of lighting is important. In this case, uniform lighting at a low level is preferable to uneven lighting at a high level. Equally important is the balance between diffused and directed illumination, which is also referred to as modeling below. The general appearance improves when objects are illuminated in such a way that shape and surface structures are clearly and pleasantly recognizable. This is achieved when the light has a preferential direction; This creates the clear shadows that are important for good modeling. The lighting should not be too strong, otherwise hard shadows will form. It should also not be too diffuse, otherwise the modeling effect is lost and results in an unattractive light climate. These requirements can be met by the use of an airgel, in particular a silica airgel, in conjunction with an LED as a light source and at the same time the other advantages that can be achieved with the airgel, in particular the good thermal insulation, are used.

With the present invention, it is possible to ensure a uniform illumination of the oven interior even with the use of all baking trays in the different baking levels. In addition, a good assessment of the food can be made possible. With the lighting according to the invention a sufficient average illuminance, an acceptable lighting climate, a good color rendering, a low-energy operation of the lighting system and due to the good thermal insulation and a low-energy operation of the oven can be ensured.

Claims (12)

1. Lighting device for an oven, which comprises at least one light source (25) and at least one partition (22) for separating the at least one light source (25) from the muffle chamber (2) of an oven muffle (1), wherein an insulation material (26) is introduced between the at least one partition (22) and the at least one light source (25) and said insulation material (26) is a transparent or translucent heat insulation material, characterised in that the heat insulation material is porous.
2. Lighting device according to one of claims 1, characterised in that the insulation material (26) consists of silica.
3. Lighting device according to claim 1 to 2, characterised in that the insulation material (26) is a silica aerogel.
4. Lighting device according to one of claims 1 to 3, characterised in that the insulation material (26) is a loose fill of granular material.
5. Lighting device according to one of claims 1 to 3, characterised in that the insulation material (26) is a powder fill.
6. Lighting device according to one of claims 1 to 3, characterised in that the insulation material (26) is a monolith.
7. Lighting device according to one of claims 1 to 6, characterised in that the at least one light source (25) is an electroluminescence light source, especially a light-emitting diode (LED).
8. Lighting device according to one of claims 1 to 7, characterised in that the at least one partition (22) is part of a receptacle (21) for the insulation material (26).
9. Lighting device according to claim 8, characterised in that a reduced gas pressure prevails in the receptacle (21).
10. Oven with at least one lighting device according to one of claims 1 to 9.
11. Oven according to claim 10, characterised in that this features at least two lighting devices (19) and that these devices are provided above two oven levels lying one above the other (8-12) in each case.
12. Oven according to one of claims 10 or 11, characterised in that the at least one lighting device (19) is provided on the side wall (4, 5) of the oven muffle (1).

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