Electrical cooking unit and electrical cooking apparatus provided with this unit

The electrical cooking unit has a housing (1) accommodating an electrical IR lamp (10). The lamp (10) has a lamp vessel (11) which is bent according to an n-gon with several bent portions (14) interconnected by straight portions (15). End portions (12) of the lamp vessel (11) are passed through openings (4) in the side walls (3) of the housing (1) to the exterior.

FIELD OF THE INVENTION 
The invention relates to an electrical cooking unit comprising: 
a housng provided with a base wall and side walls extending from said base 
wall and having at least one opening; 
an electrical IR lamp provided with a tubular lamp vessel sealed in a 
vacuum-tight manner, having first and second end portions extending beside 
each other and provided with a respective seal, which lamp vessel extends 
from its first to its second end portion along a circle, 
which lamp is arranged in the housing so that its end portions are passed 
through the at least one opening in its side walls to the exterior. The 
invention also relates to a electrical cooking apparatus provided with 
such as electrical cooking unit. 
BACKGROUND OF THE INVENTION 
Such a cooking apparatus and such a cooking unit are known from GB 1 273 
023. 
In the known cooking unit, the lamp vessel of the IR lamp is bent 
circularly but for the end portions extending parallel to each other. The 
advantage of such a lamp vessel is that a hot plate under which the unit 
is arranged is heated during operation over a surface area of the size of 
a cooking position more uniformly than with a linear tubular lamp. 
A disadvantage of the known IR lamp is that the lamp is fairly expensive 
due to a time-consuming manufacturing step, in which the lamp vessel or a 
tube from which the lamp vessel is to be formed is bent. When bending a 
finished lamp having a lamp vessel sealed in a vacuum-tight manner, there 
is a risk that the lamp vessel is unintentionally deformed due to the fact 
that the gas pressure in the lamp vessel increases as a result of 
temperature increase. The increased temperature required for bending the 
lamp vessel must therefore be brought about only in the short zone 
traversing slowly the whole lamp vessel, while the already bent part is 
being cooled. Since for IR lamps mostly glass is used having a 
comparatively high softening temperature, for example glass having an 
SiO.sub.2 content of at least 95% by weight, such as, for example, quartz 
glass, the step of bending the lamp vessel is time-consuming. 
Also if a glass tube from which a lamp vessel is to be formed is 
circurlarly bent before the lamp is assembled, the bending step is 
time-consuming, though to a smaller extent than if a finished lamp vessel 
is bent. The tube can be brought in one step to the required high 
temperature throughout its length between the end portions. A disadvantage 
of a bent still open lamp vessel, however, is that a filament provided 
with supports to keep the filament in a centered position in the lamp 
vessel at a certain distance from its wall can be introduced only with 
difficulty into such a lamp vessel. The supports then in fact act as 
barbed hooks, which impede the introduction of the filament. 
SUMMARY OF THE INVENTION 
The invention has for its object the provision of an electrical cooking 
unit and a cooking apparatus provided with such a unit of the described in 
the opening paragraph, having an electrical IR lamp of a shape that can be 
readily manufactured. 
According to the invention, this object is achieved in an electrical 
cooking unit of the kind described in that the lamp vessel is bent between 
the end portions according to an n-gon with substantially equal angles, 
where n.gtoreq.6, while bent portions are interconnected by straight 
portions. 
The lamp vessel of the unit according to the invention need be heated and 
bent during its manufacture, only at several areas. The straight portions 
can remain untreated. As a result, this unit can be manufactured more 
readily and more rapidly, while nevertheless the advantage of a more 
uniform heating of an area above the cooking unit is maintained due to the 
face that the lamp vessel extends between its end portions along a circle. 
Due to the fact that the angles are at least substantially equal, they can 
be made in the same bending arrangement. A lamp vessel bent into the form 
of a regular octagon is particularly suitable. Also the angles the end 
portions of the lamp vessel enclose with the adjacent straight portion of 
the polygonal lamp vessel part are then equally large as the angle 
adjacent straight portions enclose with each other. All bending steps can 
then be carried out in the same bending arrangement. A lamp vessel bent 
according to a decagon is also attractive because of its ease of 
manufacture and its heating uniformity. 
On the condition that a helically wound filament has an operating 
temperature of at most about 1500.degree. C., for example a temperature in 
the range of about 1200 to about 1500.degree. C., it is advantageous to 
arrange the filament in the lamp vessel without using supports. The 
filament then bears on the wall of the lamp vessel. Due to the absence of 
supports, the filament in fact is readily slipped into an already bent 
tube. 
Depending upon the nominal operating voltage and the power consumption, the 
filament may be a wire, consisting, for example, of tungsten, wound as a 
single or a double helix. The lamp vessel may contain besides an inert gas 
a halogen or a halogen compound. 
In order to adjust the power consumed by a cooking unit, an electrical 
cooking apparatus can comprise an electronic power regulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, the electrical cooking unit has a housing 1, which has a base 
wall 2 and side walls 3 extending from this wall and having at least one 
opening 4. In the embodiment shown, the wall are covered with a thermally 
insulating material 5. An electrical IR lamp 10 has a tubular lamp vessel 
11 sealed in a vacuum-tight manner, and having first and second end 
portions 12 extending beside each other and provided with a respective 
seal 13, which lamp vessel extends from its first to its second end 
portion along a circle. The lamp vessel consists, for example, of a glass 
having an SiO.sub.2 content of at least 95% by weight. A respective metal 
foil 16 is embedded in the seals 13 and a respective outer current 
conductor 17 and a respective inner current conductor 18 to a tungsten 
filament 19 arranged in the lamp vessel 11 are connected to this 
respective metal foil. The filament 19 is kept in a centered position by 
supports 20. The electrical IR lamp 10 is arranged in the housing 1 so 
that its end portions 12 are passed through the at least one opening 4 in 
its side walls 3 to the exterior. The lamp vessel 10 is bent between the 
end portions 12 according to an n-gon with substantially equal angles 
(180-.alpha..degree.), where n.gtoreq.6 and has been portions 14, which 
are interconnected by straight portions 15. In the Figure, the lamp vessel 
11 is bent in a flat plane into the form of a regular octagon. Not only 
are the angles .alpha. equal to each other, but because of the octagon 
also the angles .beta. of the bent portions 24 are equal to the angle 
.alpha. since the end portions extend parallel to each other. In the 
Figure, the straight portions 15 are equally long, but if it should be 
necessary for the end portion 12 to be located close to each other or 
farther remote from each other, for example, the straight portions 15 
adjoining the bent portions 24 may be longer and shorter, respectively. 
The lamp 10 is filled up to a pressure of 1 bar with argon, to which 0.2% 
by volume of CH.sub.2 Br.sub.2 and 0.15% by volume of CH.sub.3 I may be 
added. 
In FIG. 2, the electrical cooking apparatus 30 has a hot plate 31 of a 
material transparent to IR radiation, for example glass ceramic, with two 
cooking positions 32, 33 under which a respective cooking unit according 
to the invention comprising an electrical IR lamp 10 is situated.