CH639807A5 - Combined oven for microwave and resistance heating. - Google Patents

Description

639 807

2nd

The present invention relates to a combined

1. Combined cooker for microwave heating and counter-cooker for microwave heating and resistance heating with independent heating with a cooking space for heating a food, a cooking space for heating a food.

characterized in that by a microwave generator for a common use of microwave (16) microwave fields with a direction essentially parallel to a 5 gie and supplied via conventional resistance heating by a radiant heat energy in a cooker, it has been proposed a 1er ( 14) are emitted with a plurality of openings (32) to rotate rotating emitter for the microwave energy, the openings (32) turning from the axis of the emitter (14) and the resistance heating elements around them having different distances and the emitter (14) one to arrange. Such a stove is, however, manufactured in the feed chamber (28) into which a microwave oven is relatively expensive, since the abstractor is set in rotation by means of a belt guide line (22, 26) as a coaxial line with central and external drive and there protrudes specifically through conductors (22 or 26), and that a resistance heater made from machine processing, the transition body from (58, 60) in the cooking space (10) must be inserted into the coaxial conductor at a distance from the abstractor (14). Is set. moreover is caused by considerable energy radiation between

2. Cooker according to claim 1, characterized in that the rotating abstractor and the adjacent wall-the microwave source (16) is a magnetron which transmits the amount of energy directly to the waveguide (18) with the coaxial line via the one of the cooking chamber (22,26) is connected. Material to be heated is emitted is reduced.

3. Stove according to claim 1 or 2, characterized, It is therefore the object of the invention

that the dimensions of the openings (32) are essentially beyond the limits of the masses 20 which block the microwave transmission and which are used to heat the goods to be heated by microwave energy and thermal energy. auxiliary heating operated stove with cheaper mechanical

4. Stove according to claim 3, characterized in that the structure and improved energy efficiency to create the openings (32) with a microwave permeable This task is covered according to the invention with the marking material (34). nenden features of claim 1 solved.

5. Cooker according to claim 1, characterized in that 25 According to the invention, therefore, a microwave oven of the central conductor (22) of the coaxial line (22, 26) is created, which carries with the help of a plurality of simultaneously emitted (14). ter fields more effective than previously the microwave energy in

6. Stove according to claim 5, characterized in that the material to be heated releases.

the feed chamber (28) forms waveguide sections (50) from the output of a magnetron as a source for the micro of different lengths. 30 wave energy can be adapted to a co-

7. Cooker according to one of claims 1 to 6, characterized in that the axial line is coupled in such a way that the standing wave is characterized in that the outer conductor (26) of the coaxial line passes through the cooking chamber floor on the line for a plurality of dispensing openings in (22, 26) . is essentially one. This is particularly because of this

8. Stove according to one of claims 1 to 7, characterized in that a waveguide is provided, by which the characterized in that for all rotational positions of the emitter 35 output power of the magnet stron on the coaxial conductor with egg (14) the standing wave ratio is substantially the same . nem impedance transition body of essentially conical

9. Stove according to claim 8, characterized in that a blunt shape is transferred, this waveguide from the coaxial line (22, 26) to the waveguide (18) being made of punched or embossed sheet metal and the transition part (40) connected, which surrounds as a frustoconical center conductor of the coaxial line section. Sheet metal element surrounds the center conductor (22) and from the ends 40 The transition from the waveguide to (44, 46) of the waveguide (28) should expediently have a distance which is greater than the coaxial conductor in the course of the waveguide from the output of half the wavelength of the in the waveguide (18) occurring magnetrons have a distance and is from the ends of the microwave energy. Waveguide a greater distance than half the waveguide

10. Cooker according to one of claims 1 to 9, thereby comply with the length of the microwaves.

characterized in that the leads of the resistance heater 45 Furthermore, the outer conductor of the coaxial (58, 60) can pass through the cooking chamber wall and can be surrounded by throttle elements (64) on the transmission line and in the passage points, feed chamber of the rotating radiator -which are electrically connected to the cooking space wall. ken, which has a plurality of openings through which

11. Oven according to claim 10, characterized in that the microwave energy is emitted into the oven space in a plurality of simultaneously grate (72) for the food to be cooked via the radiator (14), so occurring field patterns, the grate openings of which are substantially larger than openings whose axes are essentially parallel to the axis of rotation of the block the microwave passage. Radiators lie and different from the axis of rotation

12. Stove according to one of claims 1 to 11, thereby have distances.

characterized in that the center conductor (22) of the coaxial line according to a further embodiment of the invention

(22, 26) with the conductive surface (30) of the feed chamber 55, the material to be heated or cooked can be connected within the mer (28) in which the openings (32) arranged radiation fields, which are generated by the rotating radiator. are lying on a grate while the outer conductor (26) enters the feed line, so that a very important mer (28) protrudes. Share of microwave energy already absorbed by the good

13. Stove according to one of claims 1 to 12, is taken when the field is characterized for the first time by the good that the central conductor (22) and with it the 60 passes through before the field reflects on the walls exit openings (32) for microwave energy from the Ein. In this way, a heating of the surface (30) having the feed chamber (28) can be rotated by a good by means of microwave energy with a high efficiency drive device (24). achieve, even if the stove walls from a cheap

Material like enamelled steel are made. According to a further feature of the invention, the magnetron is firmly connected to the hearth via coupling devices such as waveguides and a coaxial transition, so that the conversion efficiency of electrical input power is thereby efficient

3rd

639 807

in the microwave energy that is used in the material for heating is improved. If there is only a slight load in the cooker when it is switched on, or if there is no material to be heated in the cooker chamber, the radiation emitted into the cooker chamber is reflected on the radiator equipped with several discharge openings from the opposite wall of the cooker chamber and arrives at a common location, for example the center conductor of the coaxial transition line, where the waves then have significantly different phase positions, so that only relatively small amounts of energy are fed back into the magnetron and large parts of the energy are reflected back into the oven space, where the energy is finally absorbed through the walls of the oven.

Further advantageous embodiments of the invention are the subject of the dependent claims. Using an exemplary embodiment, the invention is explained in more detail in connection with the drawing. Show it:

Figure 1 is a vertical section through a stove built according to the invention for microwave and conventional resistance heating operation with a section line according to 1-1 of Figure 2.

Fig. 2 is a front view of the cooker with the hearth hatch removed;

3 shows a sectional view in plan view according to line 3-3 in FIG. 2;

4 shows a section through the abstractor shown in FIG. 3 along the line 4-4 in FIG. 3.

First of all, the overall representations of FIGS. 1 and 2 are considered, which show an oven chamber 10 fed with microwave energy, which can be closed with a door 12 and to which the microwave energy is supplied via a rotating radiator 14 on the floor of the oven chamber. The abstractor 14 receives its microwave energy from a magnetron 16 via a waveguide 18 and a coaxial conductor 20, the central conductor 22 of which is rigidly connected to the rotating abstractor 14 and which extends through the waveguide 18 to a geared motor 24. The motor 24 sits on the underside of the waveguide 18 and rotates the central conductor 22 and with it the abstractor 14. The coaxial conductor 20 also has an outer conductor 26 which is fixedly connected to the upper wall of the waveguide 18 and penetrates the bottom wall of the oven space 10 into a collecting chamber or feed chamber 28 of the radiator 14. Figures 3 and 4 show more details about the feed chamber or collecting chamber; the feed chamber 28 has an upper plate 30 which is connected to the central conductor 22 and has a number of openings 32 which are at different distances from the axis of the central conductor 22. The microwave energy supplied to the feed chamber enters the oven space 10 through these openings 32, which are covered with ceramic disks 34 and are thus permeable to microwave energy, but are impermeable to dust and solid parts falling off during cooking. A lower cover 38 of the feed chamber of the emitter 14 prevents microwave energy from being radially radiated, but rather directs the microwave energy through the openings 32, the lower surface of the cover 38 maintaining a sufficient distance from the floor of the oven space 10 so that the emitter 14 is free can turn. With an opening in the cover 38, this surrounds the upper end of the outer coaxial conductor 26, which projects so slightly into the feed chamber 28, which practically prevents microwave energy from entering the oven space 10 via the gap below the radiator 14. The length of the outer conductor 26, with which it protrudes into the feed chamber 28, can be set for the purpose of impedance matching.

It can be seen from FIG. 1 that a frustoconical

ges transition element 40 is used between the waveguide and coaxial line, which consists of sheet metal and is attached to the bottom wall of the waveguide 18, enclosing the center conductor 22. The transition element 40 extends upward from the bottom wall on the central conductor 22 over a length which is equal to an effective electrical quarter wavelength of the frequency of the magnetron 16, thereby forming a choke which dampens the energy and prevents it from flowing out of the waveguide 18 escapes in the direction of the motor 24. A bearing 42 made of dielectric material is inserted between the transition element 40 and the waveguide 22, so that no spark or glow discharge can occur in the bearing.

The ends of the waveguide 18 are closed by short-circuit elements 44 and 46, which ensure a relatively reflection-free standing wave ratio between the output 48 of the magnetron 16 and the center conductor 22.

FIGS. 3 and 4 show that each radiation opening 32 receives its microwave energy via a special waveguide section 50, which is offset by an angle of 120 ° with respect to the adjacent one, the inner ends of the axes being at a common point on the central conductor 22 to meet. A conical impedance matching element 54 sits on the central conductor 22 and thus increases its radius as it approaches the upper plate 30 of the feed chamber 28. The side walls of the waveguide sections 50 form the sides of the feed chamber 28 and have different lengths, the maximum length difference being of the order of magnitude of X / 3 or less, so that energy radiated into the feed chamber by the central conductor 22 arrives at the openings 32 with the corresponding phase differences . While the width of the waveguide sections 50 is selected to be between 2/3 X and X, the waveguide sections 50 are mainly excited in the TE, _0 vibration type, and since the openings 32 are formed in a slit shape transverse to the waveguide sections 50 the emitted field patterns of each individual opening have a different polarization.

Energy reflected from, for example, the top wall of the oven space 10 to the openings 32 is coupled into the openings 32 depending on the polarization and directed towards the common point on the central conductor 22. As a result of the different distances through which the waves have passed and which are twice the length of the waveguide length differences, these waves arrive at the center conductor 22 with different phase positions, which is preferably chosen such that the field vectors largely cancel each other out with the consequence that that the common point of the waveguide sections 50 on the central conductor 22 reflects the energy back through the openings 32 into the hearth space. In this way, the magnetron is very well shielded against reflected waves. In addition, since this effect is particularly maximized on the condition when the oven space is unoccupied, and since the geometry of the oven is fixed, if there are only small amounts of items to be heated in the oven space, the microwave energy will be low when it first passes through the block to be heated absorb this mutual abolition to a considerable extent. Under these conditions, the magnetron 16 can therefore be coupled as tightly as possible to the oven space 10, so that the magnetron can operate close to its maximum efficiency in converting electrical input energy into microwave energy, while maintaining low microwave energy field gradients and thus low wall losses occur in the waveguide 18. Such an adjustment is made primarily with the help of the position selection for the end closure element 44 of the hollow 5

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reached conductor, which should be on the order of an eighth of the wavelength away from the axis of the magnetron output 48, so that the energy radiated from the output antenna 48 in the direction of the terminating element 44 is reflected back onto the antenna 48 with a phase position: with which it the directional radiation energy can be added directly in order to form the directional radiation from the antenna 48 through the waveguide 18 to the center conductor 22. In the same way, the end element 46 is arranged

that the energy passing by the magnetron output 48 at the central conductor 22 is out of phase with the energy reflected back by the central conductor 22 from the magnetron output 48 and thus these reflected energies cancel each other out, as a result of which the impedance matching between the coaxial conductor 20 and the waveguide 18 is improved. In this way, the standing wave ratio in these zones can almost reach the value one and for most rotary positions of the emitter 14 can be within a range of 20% below one. Peak voltage gradients caused by resonance are thus avoided, and high efficiency levels of the heat yield can be achieved in the oven.

In connection with the invention, the oven space 10 can be made from a relatively heavily lossy or energy absorbing material which, for example, can absorb and also reflect a few percent of the microwave energy that strikes the wall. For example, ordinary steel sheet such as that used in conventional stoves can be used, and this can be enamelled in the usual way so that known manufacturing methods can be used. In addition, conventional grill or heating units 58, 60 can be attached near the upper and lower wall of the cooking space 10 by means of ordinary supports or supports 62. However, if a heating element 60 is used, it should preferably be bent so that it is at a distance from the outer edge of the 35th

Radiator 14 surrounds and does not interfere with the microwave fields.

The heating elements 58 and 60 extend from the rear wall of the oven space 10 to the front. The outer coating of the heating rods is conductively connected to the stove wall by means of tabs 66 and is thus grounded, these tabs being screwed tight with 40 screws 68. Sleeves 64, which are preferably a quarter wavelength of the microwave energy prevailing in the oven 10, surround the heating rods at a distance caused by an enamel coating on the sleeve elements 64. In this way, the microwave energy cannot escape from the oven space 10 via the gaps between the heating elements 58, 60 and the inner surfaces of the sleeves 64. The electrical connections for the heating and grill rods are conventional.

A piece 70 of a foodstuff to be heated is arranged, for example, on a grate 72 above the abstractor 14 in a bowl 74 which is permeable to microwave energy on a plate 76 which likewise consists of a microwave 25

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energy-permeable material, such as refractory ceramic. The grate 72 can be a wire grate, the gaps between the individual wire rods are larger than X / 2 and which can be used at different heights in the oven space 10 with the aid of guide grooves 78 in the side walls.

The abstractor 14 can have any desired shape. For example, at a microwave frequency of 2.45 GHz, waveguide sections 50 with a width of 10 cm and a height of 2.5 cm are used, which are fed via a central conductor 22 of 1.25 cm in diameter, which is supplied by a coaxial outer conductor 26 of FIG. 5 cm diameter is surrounded. The lengths of the waveguide sections 50 are 2.5 cm, 8.3 cm and 5 cm from the axis of the central conductor 22 to the discharge openings 32, the width of which is 1.25 cm, 0.6 cm and 2.5 cm, respectively. In this case, the waveguide 18 can be 10 cm wide and 5 cm high, and the distances from the terminating element 44 to the center of the magnetron antenna 48 are 1.8 cm, to the axis of the central conductor 22 12.5 cm and to the opposite terminating plate 46 26 cm.

A fan (not shown) blows in a conventional manner over the cooling fins of the magnetron 16 and guides this hot air to the oven space 10, for example through the waveguide 18 via opening 80 in the end plates 46 and 44, the transmission line 20 and the gap between the outer conductor 26 and the breakthrough in the plate 38, where the air then flows around the resistance heating elements 30 and passes the food 70 to be heated during the cooking process. The air then exits through a pipe 82 at the top of the cooker midway between the hot plates 84.

During the self-cleaning cycle of the cooker, in which no food is used, the cooker temperature is increased to 400 to 550 ° C, whereby both heating rod units 58 and 60 are fed, so that food residues adhering to the inner wall of the cooker chamber burn and the resulting gases then are blown out through the exhaust pipe 82, in which a catalyst can be contained in a conventional manner for a complete oxidation of the gases.

The door 12 is provided with a heat seal 86, such as a tube made of glass fiber fabric over a spring steel fabric tube, which surrounds the entire opening of the oven, so that no hot gases can escape. A slot throttle device 88 on the door 12 prevents microwave energy from escaping from the oven space along the entire edge of the door. The hearth space 10 is surrounded by thermal insulation 90 and a metal foil 92 surrounding it. The oven space can be illuminated with a lamp 94 through a metal plate 96 provided with openings and covered with heat-resistant glass 98. Within the scope of the invention, the person skilled in the art is able to make modifications to the example described. For example, the number of openings 32 can be chosen differently.

2 sheets of drawings