EP0556892B1 - Radiant element for a cooking apparatus - Google Patents

Abstract

The invention relates to a radiant element (10) for a cooking apparatus, having a cooking plate (16) constructed in particular as a glass ceramic plate, and having at least one trough-shaped reflector (14, 15), which has a radiator (12, 13) and is divided by a raised break edge (19, 20) which extends below the radiator into two curved reflector segments (14a, b; 15a, b), the reflector segment (14a, 15a) extending outwards from the break edge (19, 20) being subdivided into an adjacent inner sub-region (26), a central sub-region (27) and an outer sub-region (28) and being formed in such a way a) that the direct radiation (31) impinging in the inner sub-region (26) is directed essentially into the outer region of the cooking plate after double reflection (31'') in the inner and outer sub-regions (26, 28), b) that the direct radiation (33) impinging in the central sub-region (27) is directed essentially into the region of the cooking plate (16) situated above this sub-region after single reflection (31'), and c) that the direct radiation (32) impinging in the outer sub-region (28) is directed essentially into the outer region of the cooking plate (16) after single reflection (32'). <IMAGE>

Description

The invention relates to a radiant heater for a cooking appliance with a hotplate designed in particular as a glass ceramic plate, with at least one trough-shaped reflector having a radiator, which is divided into two reflector sections by a raised edge running below the radiator.

From DE-OS 38 42 033 a radiant heater has become known, in which two trough-shaped reflectors which merge into one another are designed as a circular, all-round cooking hob. In this case, two mutually abutting partial parabolic surfaces or reflector sections with raised outer edges are formed in each reflector by the folded edge. The fold edges lying in a plane parallel to the hob are curved outwards in such a way that the projection of a fold edge and the associated radiator onto the hob results in two interfaces in the region of the radiator. Such a design enables a good distribution of the power density in the plane of the hob. Due to the curved design of the folding edges, places with an undesirable high or low power density are avoided compared to a straight design. In this known design, the beams are divided by single reflection to the left and right of a kink edge so that the decreasing intensity of the direct radiation increases towards the edge and towards the center the simply reflected parts are added. However, it has turned out to be a disadvantage that the side wall loading of components which adjoin the hotplate can become too high, so that the permissible limit values are exceeded. This means that, when using the known type, binding installation regulations for an enlarged side wall spacing must currently be observed or this problem is otherwise, for. B. must be solved by pot detection sensors. It has also been found that such an arrangement with a known parabola-like reflector profile is less fault-tolerant than misalignments of the spotlights from a target position. Inhomogeneities and focal lines with too high irradiance easily occur in the plane of the pot base or on the side wall. One reason for an excessive side wall load is that a substantial part of the reflected rays are relatively flat (approx. 40 °) with respect to the plane of the hotplate, so that the rays hit the side wall at a short distance and with high irradiance. Another reason is that a large part of the reflector profile allows the beams to emerge in one direction.

The invention has for its object to improve a radiant heater of the type mentioned in such a way that the load in the region of the side walls of the radiant heater is reduced while maintaining a uniform radiation distribution in the plane of the hotplate.

• a) daß die im inneren Teilbereich auftreffende Direktstrahlung nach Doppelreflexion im inneren und äußeren Teilbereich im wesentlichen in den Außenbereich der Kochplatte gelenkt wird,
• b) daß die im mittleren Teilbereich auftreffende Direktstrahlung nach Einfachreflexion im wesentlichen in den oberhalb dieses Teilbereiches liegenden Plattenbereich gelenkt wird und
• c) daß die im äußeren Teilbereich auftreffende Direktstrahlung im wesentlichen in den Außenbereich der Kochplatte gelenkt wird.

This object is achieved according to the invention in a radiant heater of the type mentioned in that the reflector sections extending outward from the folded edge are each subdivided into an inner partial area adjacent to the folded edge, into a subsequent central partial area and into an adjoining outer partial area and is shaped

• a) that the direct radiation impinging in the inner partial area after double reflection in the inner and outer partial area is directed essentially into the outer area of the hotplate,
• b) that the direct radiation impinging in the central section after single reflection is directed essentially into the plate area above this section and
• c) that the direct radiation incident in the outer partial region is directed essentially into the outer region of the hotplate.

In the case of a design with only one reflector forming a cooktop and a rod-shaped radiator above a straight folding edge drawn up from the center of the reflector, the identically designed reflector sections lying on both sides of the folding edge are each subdivided into the sub-areas mentioned.

Another advantageous type of construction of the invention is characterized by two trough-shaped reflectors forming a cooktop and merging into one another via a straight, raised central edge, with two rod-shaped, parallel emitters and with two raised from the reflectors below the emitters, outward curved fold edges. The reflector sections located outside the buckling edges are each subdivided into the named partial areas.

Halogen lamps are preferably provided as emitters.

The functions of the three areas mentioned have different meanings. In comparison to the known type, the design of the reflectors according to the invention results in a considerable reduction in the side wall load. This is due to the fact that the corresponding reflected rays now emerge steeper from the reflector troughs in the middle section and thus hit the side walls at a greater distance from the hotplate and also at a flatter radiation angle. This measure alone would result in an excessively high irradiance in the area of the radiators and an insufficient irradiance on the outside. The fact that both a single and a double reflection takes place in the outer partial area results in a good homogeneous radiation distribution over the entire hotplate. The invention thus enables both a homogeneous radiation distribution on the bottom of the pot and a reduction in the load on the side wall.

Another advantage according to the invention is that almost all reflected rays go past the emitters themselves. In practice, this has the effect that when using a lamp, for. B. a halogen lamp, as the lamp of the lamp bulb is less heated due to reduced reabsorption. The The design of the reflectors according to the invention further means an improvement in that the reflected rays now hit the hotplate or the pan base on average at a steeper angle than before. This increases the efficiency of the arrangement.

A further reduction in the side wall load can be achieved in that, in an embodiment of the invention, at least part of the surface of the reflectors is facet-shaped with flat elements. This faceting enables the beams of rays corresponding to the size of the facets to be aligned in a targeted manner on the hotplate on the one hand and the side wall on the other. A glass-like bundling is not possible with a faceted design of the reflectors. At the same time, a sufficiently uniform distribution of the radiation on the hotplate can be achieved. The fewer facet elements are used for the entire reflector area (always in accordance with sufficient homogeneity on the bottom of the pot), the more fluid the distribution outside the hotplate. The faceting causes a wider and thus also lower side wall load.

An advantageous design of a facet-like reflector results from the fact that the facet elements follow the trough-shaped curvature, two adjacent facet elements each forming an obtuse angle, that the facet elements extend in the longitudinal extent approximately parallel to the crease edge and that the radius of curvature of the individual is on the hotplate projected facet elements, starting from the crease edge, increases towards the outside. This the The design of the individual facet elements, which resembles a banana, ensures great homogeneity of the rays in the hotplate.

Another particular advantage of faceting is that a greater fault tolerance can be achieved with respect to misalignment of the radiator. The faceted system is also more fault-tolerant compared to an inevitable spiral sag.

In an embodiment of the invention, the distribution of the direct radiation within the partial areas is achieved in that the width and inclination of the facet elements and also the diameter of the radiator and its distance from the facet elements are correspondingly coordinated with one another.

In a further embodiment of the invention it is provided that the outer portion of the reflector trough is constructed from a single reflector element. This prevents focal lines in the outer area of the pot base and inhomogeneities in the area in which the middle and outer partial area of the reflector collide.

Finally, in a further embodiment, the inner and the middle partial area of the reflector are each made up of several facet elements. The inner partial region adjacent to the fold edge is preferably constructed from four reflector elements. This ensures that the major part (approx. 90%) of the radiation for double reflection to the outer part of the reflector is directed.

• Fig. 1 zeigt eine Draufsicht auf einen Strahlheizkörper,
• Fig. 2 zeigt einen Querschnitt A-A gemäß Fig. 1,
• Fig. 3 zeigt einen Querschnitt B-B gemäß Fig. 1,
• Fig. 4 zeigt den Strahlungsverlauf und die Strahlungsverteilung, dargestellt am vergrößerten rechten Teil gemäß Fig. 2 im Schnitt A-A,
• Fig. 4a zeigt einen vergrößerten Ausschnitt aus Fig. 4,
• Fig. 5 zeigt den Strahlungsverlauf und die Strahlungsverteilung auf einer Seitenwand, dargestellt an dem um 90° gedrehten linken Teil der Fig. 2 im Schnitt A-A,
• Fig. 6 zeigt im Vergleich zu Fig. 5 den entsprechenden Strahlungsverlauf und die Strahlungsverteilung auf einer Seitenwand bei einer Bauart gemäß dem Stand der Technik,
• Fig. 7 zeigt im Vergleich zu Fig. 4 den entsprechenden Strahlungsverlauf und die Strahlungsverteilung bei einer Bauart gemäß dem Stand der Technik,
• Fig. 8 und 9 zeigen den Strahlungsverlauf und die Strahlungsverteilung bei einem Strahlheizkörper mit einem Reflektor und einem Strahler, und zwar einmal bei einer Herdplatte und einmal bei einer Seitenwand.

In the drawing, a first embodiment according to the invention is shown schematically in FIGS. 1 to 5 and an associated embodiment according to the prior art is shown schematically in FIGS. 6 and 7. 8 and 9 show a further embodiment according to the invention.

• 1 shows a top view of a radiant heater,
• FIG. 2 shows a cross section AA according to FIG. 1,
• 3 shows a cross section BB according to FIG. 1,
• 4 shows the radiation course and the radiation distribution, shown on the enlarged right part according to FIG. 2 in section AA,
• 4a shows an enlarged detail from FIG. 4,
• 5 shows the radiation course and the radiation distribution on a side wall, shown on the left part of FIG. 2 rotated by 90 ° in section AA,
• 6 shows, in comparison to FIG. 5, the corresponding radiation profile and the radiation distribution on a side wall in the case of a design according to the prior art,
• FIG. 7 shows, in comparison to FIG. 4, the corresponding radiation profile and the radiation distribution in a construction according to the prior art,
• 8 and 9 show the radiation course and the radiation distribution in a radiant heater with a reflector and a radiator, once for a hotplate and once for a side wall.

1 to 3 show a radiant heater 10 with a housing 11 and two halogen lamps 12, 13 which are arranged between two trough-shaped reflectors 14, 15 and a hotplate 16. The two reflectors meet at an edge 17 in the central region or merge into one another. The reflectors 14, 15 each have an outwardly curved, extending in a common plane 18 under the hotplate 16, raised in the direction of the halogen lamps 12, 13 bent edge 19, 20. The circular-shaped bent edges form, seen from above, two each fictitious interfaces 21 with the halogen lamps 12, 13. The reflectors 14, 15 are designed in the form of facets. The individual facet elements are indicated in the right part of FIG. 1 and designated 22. They form an obtuse angle with one another, their radius of curvature 22 ', 22 "etc. increases towards the outside. The bent edges 19, 20 cause a beam splitting to the left and right around the lamps. FIGS. 2 and 3 show schematically in two sectional images the Formation of the reflectors 14, 15 and the position and course of the halogen lamps 12, 13 and the folding edges 19, 20. Each reflector 14, 15 has two formed by the folding edges 19, 20 Reflector sections 14a, b and 15a, b.

FIG. 4 shows a radiation course belonging to FIG. 2 with the associated radiation distribution corresponding to section A-A in FIG. 1. The right part of the radiant heater is shown, i. H. the area with the reflector 15. The left edge of the image in FIG. 4 represents the plane of symmetry 23 of the two reflectors 14, 15. It is to be understood as a mirror in order to evaluate the rays of the other halogen lamp 12 of the reflector 14. The radiation distribution 24 is plotted above the hotplate 16. The area from the plane of symmetry 23 to the crease edge 20 is designated by 25, while the outer area beyond the crease edge is divided into three partial areas 26, 27 and 28.

The direct radiation emanating from the lamp 13 and hitting the hotplate 16 without reflection is designated by 29. The direct radiation 30 which strikes the reflector sub-area 15b in the region 25 is directed onto the hotplate 16 after single reflection 30 '. The direct radiation 31 incident in the partial region 26 is first directed into the partial region 28 and then reflected again, so that this radiation 31 is only directed into the outer region of the hotplate 16 after a double reflection 31 ′, 31 ″. In this partial area 28 there is also a single reflection 32 'of direct rays 32, which are likewise directed into the outer area of the hotplate 16. In the partial area 27, the direct beams 33 are directed into the central area of the hotplate 16 after single reflection 33 ′ and strike the hotplate 16 relatively steeply. On the one hand, the Efficiency increased, on the other hand, this has the consequence that these direct rays 33 after single reflection 33 'on a side wall 34 (Fig. 5) hit relatively flat and far above and can therefore no longer cause damage. An overall homogeneous radiation distribution 24 results over the entire hotplate 16.

4a shows schematically and enlarged the transition from the partial area 27 to the partial area 28 of the reflector section 15a, in which here a total of four facet elements 22 are shown, each of which forms the obtuse angles 22a to 22c with one another.

FIG. 5 shows the load that occurs on the left side wall 34 in the region of the reflector 14 according to FIG. 2. For illustration, the cross section of the reflector 14 is shown rotated by 90 ° in FIG. 5. The side wall 34, which is represented in FIG. 5 by the upper horizontal irradiation surface, is located at a distance 35 from the center of the hotplate. As can be seen, the side wall load represented by 36 has a maximum at a height 37 above the hotplate 16. As a direct comparison with FIG. 6 according to the prior art shows, with otherwise comparable data and radiation numbers, the maximum of the side wall loading in the prior art is 38, ie at a considerably smaller distance from the hotplate 16 than in the invention. As can be seen, the rays from the reflector 39 do not emerge as steeply in FIG. 6 and therefore hit the side wall at an unfavorable angle than in the case of the construction according to the invention. In the design according to the invention, the side wall load has become considerably smaller, such as shows the height of the maximum. The radiation units per unit area are approximately one third lower.

FIG. 7 shows, in comparison to FIG. 4, the known reflector 39 with a raised, outwardly curved fold edge 40. The area beyond the fold edge 40 is not divided into partial regions. There is no double reflection with this design. The rays to the right of the lamp 41 do not emerge as steeply here as in the construction according to the invention. The radiation distribution 42 is also relatively uniform here.

The faceted design of the reflectors makes it possible to have the light beams diverge outside the reflectors while avoiding focal lines. This means that the side wall load can also be reduced as a result.

8 and 9, a radiant heater with a single reflector and a single rod-shaped radiator 43 is shown. The reflector is faceted. 8, the reflector 44 is divided by a raised folding edge 45 into two identical sections 44a and 44b, both of which are each divided into three partial areas 26, 27, 28. As in FIG. 4, there is also a single or double reflection in the individual partial areas, so that in this example there is a similarly uniform and good distribution. The load on the side wall according to FIG. 9 is correspondingly favorable. From FIG. 8 it follows that the folded edge 45 is at a relatively large distance from the radiator 43. This large distance leads to Combination with double reflection for a particularly low side wall load according to FIG. 9.

In general, it applies to all constructions that increasing the distance between the emitter and the folded edge leads to a greater overall depth and thus to a narrowing of the beam. With all constructions of the present type, this would always tend to result in a lower side wall load. The structural depth of radiant heaters of the present type, however, are subject to certain limits for design and construction reasons, which cannot be exceeded.

With small distances, the result regarding the side wall load is always worse than with larger distances.

Regarding the size of the distance between the radiator and the kink edge, it must be said that experience shows that the relationship between the emitter and kink edge distance to the proportional reflector opening is important. The proportional reflector opening is formed from the sum of the sections 26 to 28. In this sense, there is a small distance if the ratio is of the order of magnitude less than about 0.1, and there is a large distance if the ratio of the order of magnitude is greater than is about 0.1.

Claims (8)

1. A radiant heater (10) for a cooking apparatus including a cook-top (16), particularly constructed as a glass-ceramic plate, which heater comprises at least one trough-shaped reflector (14, 15; 44) provided with a radiator (12, 13) and divided into two curved reflector sections (14a, b; 15a, b; 44a, b) by a ridge (19, 20; 45) which extends underneath the radiator (12, 13; 43), characterized in that the reflector sections (14a, 15a; 44a, b), which extend from the ridge (19, 20; 45) towards the periphery, have each been divided into an inner segment (26) adjacent the ridge, a central segment (27) and an outer segment (28) and have such a shape

   a) that the direct radiation (31) impinging in the inner segment (26) is substantially deflected into the peripheral area of the cook-top (16) after double reflection (31") in the inner and the outer segment (26, 28),

   b) that the direct radiation (33) impinging in the central segment (27) is substantially deflected into the area of the cook-top (16) situated above this segment after single reflection (33'), and

   c) that the direct radiation (32) impinging in the outer segment (28) is substantially deflected into the peripheral area of the cook-top (16) after single reflection (32').
2. A radiant heater as claimed in Claim 1, characterized by a reflector (44) forming a cooking cavity and having one rod-shaped radiator (43) above a straight ridge (45) which projects from the centre of the reflector (44), the similarly shaped reflector sections (44a, b) at both sides of the ridge (45) each being divided into segments (26, 27, 28).
3. A radiant heater as claimed in Claim 1, characterized by two trough-shaped reflectors (14, 15) forming a cooking cavity and adjoined by a projecting straight central edge (45), having two rod-shaped mutually parallel radiators (12, 13) and having two outwardly curved ridges (19, 20) which extend in one plane (18) underneath the radiators, the reflector sections (14a, 15a) situated outside the two ridges (19, 20) each being divided into segments (26, 27, 28).
4. A radiant heater as claimed in any one of the Claims 1 to 3, characterized in that at least a part of the area of the reflectors (14, 15, 44) has been formed with flat elements (22) in a facet-like manner.
5. A radiant heater as claimed in Claim 4, characterized in that the facet elements (22) follow the trough-shaped curvature, two adjacent facet elements each time forming an obtuse angle (22a, 22b, 22c) with one another, the longitudinal directions of the facet elements extend substantially parallel to the ridge (19, 20; 45), and the radius of curvature (22) of the individual facet elements (22), projected on the cook-top (16), increases from the ridge towards the periphery.
6. A radiant heater as claimed in Claim 4 or 5, characterized in that the desired distribution of the direct radiation (31, 32, 33) within the segments (26 to 28) is obtained in that the width and the inclination of the facet elements (22) and their distances from the radiator (12, 13; 43) have been adapted to one another accordingly.
7. A radiant heater as claimed in any one of the Claims 4 to 6, characterized in that the outer segment (28) of each reflector (14, 15; 44) is formed by a single facet element.
8. A radiant heater as claimed in any one of the Claims 4 to 6, characterized in that the inner and the central segment (26, 27) of each reflector (14, 15; 44) are each formed by a plurality of facet elements (22).

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