DE3001236A1 - COMBINED MICROWAVE OVEN WITH CONVECTION HEATING - Google Patents

Description

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R.TrR. 37 ROOO ΓΛ0Ν5ΟΗΞΝ 2 TKt. O O9 / SS Θ7 84

Munich, the lh. January 1980 / J Lawyer file: 27 - Pat. 27 * 1

Raytheon Company, lAl Spring Street, Lexington, Mass. Ο2173ι United States of America

Combined microwave oven with convection heating.

The invention relates to a combined microwave oven with convection heating. Recently, household stoves have been used or stoves with convection heating developed, in which the combustion products of a gas burner through a furnace chamber can be circulated by mixing these products of combustion with vapors emanating from the furnace chamber to the inlet of a Ventilation system, which is used to circulate the vapors serves. If the output of the burner is increased, the length of the burner flame also increases to a point at which the combustion is not complete before the flame enters the area between the inlet of the fan and the relative Microwave-shielded outlet of the furnace chamber enters. The vapors can thus be ionized and partly as a conductor act in the shielded outlet area, so that microwave energy can exit from the interior of the furnace chamber into the area of the fan assigned to the burner. It can then become a Absorption of microwave energy and to a corresponding

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Decrease in what is available in the oven for cooking or cooking Micro-shaft power come. The microwave energy can also be released into the environment through the burner system and / or the fan system step out.

The object is to be achieved by the invention, the devices to circulate the vapors through the furnace chamber of a household stove or cooker so that they are better on the operation of the device in question is coordinated with microwave energy are.

This object is achieved according to the invention by the features of the attached Claim 1 solved. Appropriate configurations and further training are the subject of the remaining claims, the content of which is hereby expressly made part of the description without repeating the wording at this point.

In particular, a combined microwave oven with convection heating is used proposed in which a multi-hole gas burner is arranged near a perforated steam outlet area of a furnace shell is, which can be applied with microwave energy, the height of the burner flame by an excess Secondary air is limited, which is near each burner opening is supplied and sucked in by a fan system to circulate the vapors through the furnace chamber into a combustion chamber will.

The burner is preferably composed of a number of sheet metal strips together, which are corrugated in the transverse direction over their length, so that the individual waves as burner channels or » can act as burner openings. The sheet metal strips have expediently measured from those with the primary fuel-air mixture acted upon chambers to the combustion chamber, a width which is sufficient to cause a flashback in the to prevent mixed-pressurized chambers, even if a proportionate rich primary fuel-air mixture of 50%

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up to 8θ % is used. Furthermore, since each of the burner openings is separated from a secondary air source by a maximum of three intermediate burner openings and an excess of air in the order of magnitude of 50 5 ^ to 150 % is provided, the height of the flame can be significantly reduced, so that for power densities of the burner of over 15 ^ BTlT per hour

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and cm of the burner surface a flame size of less than 2.5 cm is achieved. The combustion products of the burner can therefore be mixed with the vapors drawn off from the furnace space in the area of the perforated outlet area without the microwave energy escaping from the furnace space via the perforations.

The burner is preferably operated so that the negative pressure generated at the inlet of a fan is used to the primary Fuel-air mixture through at one speed pulling the burner, causing the burner flame to lift off causes the burner openings, so that the heating of the area the burner openings and the likelihood of kickback through the burner channels is reduced.

Use a fan system for suction, as suggested here of the combustion products from the burner into a combustion chamber which is both near the inlet of the fan system and also near the steam outlet of the microwaved energy Furnace is located, a heating system is obtained which enables most of the bottom of the furnace shell for generating and supplying the microwave energy to the Oven space can be used.

For the combination of convection heating and microwave heating a dual control system is provided, with a temperature probe serving to measure the temperature of a proximal centerpiece to determine, while another temperature sensor is used to the temperature of the circulated through the furnace, heated Measure fumes. Primarily the temperature probe

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used to provide an indication of when the temperature of the piece of food or the item to be heated has reached a certain temperature value and one of the probe generated signal is then evaluated in such a way that the microwave energy is switched on and off in order to reduce the Probe detected temperature of the piece of food at or to keep it above a temperature value which has been preset by a manually operated temperature selector. Instead of this measure or at the same time takes place a temperature measurement of the vapors, which between a heat source, for example a gas burner arranged outside the furnace chamber and the furnace chamber are circulated and this temperature is used to turn the gas burner on and off, so that a certain Temperature of the circulated vapors is maintained, which ellvorrihtung with a manually operated Temperatureinst has been chosen.

The temperature probe is connected to the wall of the furnace chamber preferably via a cable of the usual type, for example a flexible one Coaxial line connected, which runs between the temperature probe and a plug that plugs into a socket or socket can be plugged into the wall of the furnace chamber. In this way, the temperature probe can be removed from the furnace chamber, see above that the flexible cable and the probe itself can be made of materials that only the usual temperatures of the Must withstand vapors in the oven space during normal cooking and not be in the oven when the increased Temperatures up to 5 ^ 0 C during the self-cleaning process rule in the oven.

An exemplary embodiment is described below with reference to FIG the accompanying drawings explained in more detail. They represent:

Fig. 1 is a partially broken open and in section

drawn side view of a combined microwave oven with convection heating,

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Fig. 2 is a partial plan view of a detail of the

Furnace according to Figure 1 corresponding to the line 2-2 indicated in this figure,

FIG. 3 is a front view of that shown in FIG

Microwave oven,

4 shows an enlarged illustration of the burner of the microwave oven according to FIG. 1, corresponding to the boundary line kk and shown in FIG

5 shows a further enlarged partial view of the burner according to FIG. K corresponding to the line 5-5 drawn in this drawing.

In the drawings, a combined microwave oven 10 with gas convection heating is shown. The furnace 10 contains a furnace jacket 12 made of metal, for example made of enamelled sheet steel. The furnace jacket can be locked by a door lk while the furnace is in use.

A grate 22, which is made for example from steel rods, is supported on bulges 2.k of the side walls of the furnace shell 12, the position of the grate 22 m can be changed in a known manner and as can be readily seen from the drawing.

The upper part of the rear wall of the furnace shell 12 has an elongated steam inlet region l6, while in the middle Part of the furnace shell back wall has a pair of steam outlet areas l8 is provided. The vapors are sucked in via the areas 18 from the furnace shell 12 into a space 20. The areas l6 and 18 preferably have a perforation 3 ^ »where the largest dimensions of the openings of the perforation much smaller than half a wavelength, based on the free space, the microwave energy radiated into the furnace chamber. In particular, the largest dimensions of the perforations of the per-

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forations 3 ^ smaller than a tenth of the free space wavelength the microwave energy, which is radiated by a radiator 26 into the furnace jacket 12, so that the microwave energy cannot escape through areas l6 and l8.

The radiator 26 located below the grate 22 can rotate are offset and radiates microwave energy upwards through the openings of the grate 22, through a tray 28, which rests in the center of the grate 22 and through a bowl 30 through which a piece of food 32, for example a roast. The bowl 30 and the tray 28 are for microwave energy expediently substantially transparent, so that the lower part of the piece of food 32 and the inner parts are sufficiently heated by microwave energy will.

The radiator 26 can contain an introduction chimney JS , the upper wall 38 of which has a number of radiator openings kO , through which microwave energy can be radiated upwards into the furnace space of the furnace shell 1.2. A central conductor k2 of a coaxial line kk carries the introduction chamber 36 and is fixed in the center of the upper wall 38 of the introduction chamber. The center conductor 42 extends downward through the outer conductor 46 of the coaxial line 44 and through a waveguide section 48 to an arrangement 50 serving as a microwave choke and bearing. An extension of the center conductor is coupled to a motor 52 located below the waveguide section 48. The microwave energy generated by a magnetron 54 is fed to the radiator 26 via the waveguide section 48 and the coaxial line 44. A fan blows cooling air past the cooling fins 58 of the magnetron 54 to cool the magnetron, but the cooling air does not get into the waveguide section 48.

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A cover 60 made of permeable for microwave energy material is supported on the floor of the furnace shell 12 at Zentrierungsvorsprüngen 62 through the radiator 26 and covering the radiator 26, so that juice or other materials from the food to be cooked not drip or the radiator 26 \ fall.

The door lk is sealed against the oven jacket 12 by a high temperature door steam seal, a microwave oven seal being located between the steam seal and the interior of the oven jacket 12, so that the microwave energy radiated into the oven chamber is prevented from being in the high temperature Vapor seal is absorbed. If, however, microwave energy should pass through the throttle seal, it will ultimately be completely absorbed by the high-temperature steam seal. If the door Ik closed, a locking mechanism is mechanically moved lk in the position for locking the door, and only then the magnetron ^ can be switched k. Further details and advantages of the microwave feed to the oven space and the use of a rotating radiator are suggested elsewhere. It should be noted, however, that other microwave feed devices and radiators and / or door seals can also be used in conjunction with the features specified here.

In the microwave oven described here, a slight negative pressure is generated in the room 20 by a fan system which contains two centrifugal fans 6k , which suck the steam out of the oven jacket 12 via the perforations Jk into the room 20 and via the rooms 66 surrounding the fans 6k convey to the inlet area l6. At the upper ends of the spaces 66 there is an opening through which a small part of the volume conveyed by the fans 64 flows to an outlet 68 in order to then be mixed with the air which is conveyed by a second set of fans 70. The fans 70 suck in cooling air from the rear of the device 10 in order to

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Ren 72 for the fan wheels 64 and 70 to cool, after which this cooling with. the vapors emerging from the outlet 68 is mixed and the result of the mixture exits through a barred opening Ik at the upper end of the device 10 above the level of the hotplates.

From Figures 1 and 2 it can be seen that via each of the perforated outlet areas 18 vapors reach a separate fan wheel Gk and each fan wheel Gk is driven together with one of the fan wheels 70 by a separate drive motor 72 attached to the rear wall 78 of the furnace 10 (is noted. A partition 80 between the two fan wheels Gk prevents tangential interaction of the steam outlet flow of the fans Gk. The fans 64 preferably rotate in opposite directions , so that the air between the fan wheels near the partition 80 moves upwards It should be noted that a single fan wheel could be used in place of the two fan wheels 64 and that the space 66 could be provided with separate guide means for introducing the vapors into the furnace through a plurality of inlet areas 16 However, it turned out that the system of two counter-rotating fan wheels resulted in an improved glide The shape of the convection heating in the furnace leads.

A burner system 90 is located in the rear of the Furnace 10 behind and under the furnace shell 12. The burner system includes a strip burner 92 which extends over the largest Part of the width of the furnace extends and from one side with a primary fuel-air mixture via a vertical tube 9 ^ is fed. The open lower end of the vertical tube 9 ^ is acted upon by means of a gas nozzle 96 with fuel gas, which is from a Solenoid operated valve 98 is obtained, the latter being fed via a gas line 102 and a pressure regulator.

As can be seen from FIG. 5, the strip burner 92 two burner sections 104 and IO6, which each consist of

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ben sheet metal strips 108 with a width of 12.7 mm and a thickness are composed of 0.1 mm. The sheet metal strips extend extend over the length of the burner and are corrugated, for example, by means of a suitable shape. The waves run over the Width of the metal strips and measure from vertex to vertex: of the shaft, for example, 4.8 mm. Between the corrugated sheet metal strips 108 are flat sheet metal strips 110 of the same width, which also extend over the length of the burner, so that the spaces between the shafts act as burner channels are effective, through which a primary fuel-air mixture, which is fed through the vertical pipe 94 flow can. The burner sections 104 and 106 are through. Each separate chambers 112 and 114 are fed, both of which are connected at their ends to the vertical tube 94.

The chambers 112 and 11 ^ have the shape of a rectangular cross-section, box-shaped components 124, which by bracket Il6 on Bottom of a combustion chamber 1l8 are held, which connection to the inlet of the fan 64 via the space 20. The two burner sections 104 and 106 are supported by spacers 120 separated from each other and the burner sections are held together by rivets 122 which extend through the spacers 120 as well as all of the sheet metal strips 108 and HO and also through the walls of the box-shaped components 124 extend so that a gap is created between the box-shaped components 124, Via the secondary air can be sucked into the combustion chamber Il8. In addition, secondary air is longitudinally via the gap spaces 126 the outer edges of the burner sections 104 and 106 sucked into the combustion chamber Il8. It turns out that none of the burner openings is separated from a secondary air source by more than three intermediate burner openings.

It has been shown that the fact that the secondary air sources are close to the burner openings and an excess of air of 100 % is effective, for example, makes the height of the burner flame smaller than the total width of the burner section.

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can if the fuel-air mixture is sufficient is pulled through the burner channels in order to lift the burner flame from the mouths of the burner channels, for example 1.6 mm to 3 | 2 mm can be achieved. This releasing the burner flame reduces the heating of the sheet metal strips used to form the burner channels, so that a backfire of the primary Prevents fuel-air mixture into the chambers 112 and Il4 even if a relatively rich primary fuel-air mixture is used. By reducing the The length of the burner flame can be the length of the combustion chamber in the transverse direction the rear lower edge of the furnace shell are arranged immediately below the outlet areas l8 of the furnace shell and the axis the furnace chamber via the outlet areas l8 extracted vapors nevertheless remain essentially deionized, so that the microwave shielding carried out through the perforation 3 ^ is effective remains and the escape of microwave energy from the furnace shell 12 is connected into room 20, even if the The microwave source and the burner are in operation at the same time.

The microwave oven specified here has a safety control device, which has an air flow sensor l48 with a switch operated by a flag, which is in the Outlet of the fan 70 is arranged. A manually operated selector switch l68 causes the fan motors 72 to switch on when one of the convection heating modes is set, in which microwave heating can also be provided. The output flow of the fans causes the switch to close of the air flow sensor 1 ^ 8 in terms of activation a customary resistance heating igniter 132 which protrudes into the heating space 118. After a delay time of, for example 30 seconds the solenoid operated valve 98 becomes actuated, which then allows gas to flow to the nozzle 96. As soon the fuel-air mixture formed in this way the combustion chamber 118 has reached through the openings of the burner 92, is it ignited by the igniter 132 and the products of combustion

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are sucked in by the fan 6k and conveyed into the furnace space of the furnace shell 12 via the inlet area. Part of the output volume of the fan 6k is blown out via the outlet 7k , so that a slight negative pressure in the combustion chamber Il8 and in the furnace ^! jacket 12 arises, which determines the amount of primary air that is sucked in through the vertical tube 9k and also the amount of secondary air that is sucked in around the edges of the burner sections 104 and 106, after the vertical tube 9 ^ as a constriction opening to form the primary Fuel-air mixture, changes in the fan speed and the air temperature or steam temperature, which change the amount of primary air and secondary air sucked into the combustion chamber Il8, have the effect that corresponding changes in the flow of the gaseous fuel through the controller also occur, whereby the possibility of an excessive fuel-air mixture and the generation of noxious smoke and noxious gases which could escape through the grille 7k at the upper end of the device can be avoided. The burner shown here can, for example, have a thermal output of 20,000 to 30,000 BTU per hour. The thermal output line is selected by choosing the size of the vertical tube 9 ^ and the gas nozzle 96 and by setting the fuel pressure regulator. The amount of secondary air is determined by choosing the width of the gap spaces between the box-shaped components 124 and the gap spaces along the outer edges of the burner sections 104 and IO6, the secondary air entering the combustion chamber II8 through these gap spaces.

The burner system described above is expediently arranged in the lower rear part of the furnace 10 based on the knowledge that when the outlet areas l8 are at a distance of less than the size of the diameter of a fan wheel 6k from the associated inlet, the burner system 90 with the Strip burner 92 can be arranged immediately below the outlet areas 18 and any remaining

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ionized parts of the combustion products directly into the Fan sucked in and not whirl around in the areas of the perforations 3 **. The burner system can therefore be practical be placed in substantially the same general area as the steam outlet and ventilation system, thereby making the entire The bottom of the oven jacket remains free and for the installation of the rotating microwave heater and the transparent cover is available.

Since the steam outlet areas l8 of the oven jacket are preferably above the apex of the cover 6O transparent to microwaves, it is not necessary to cool the cover 6O by blowing air into the oven and via the radiator 26, even if during the self-cleaning process via the inlet area l6 near the top wall of the furnace shell 12 vapors at a temperature close to ^ kQ C are blown into the furnace, since the vapors cool considerably before they finally reach the cover 60. The cover 6O can therefore be made of conventional material, as it is also used for the production of dishes, such as heat-resistant glass dishes »

A temperature probe 150 can be inserted into a piece of food 32 and is via an electrical connection cable 152 connected to a socket 15 ^ in the wall of the furnace shell 12, so that the temperature probe can be removed. Located on the display panel in the upper part of the cooker or oven 10 a temperature display device I56, which the Probe I50 displays the measured temperature. The temperature can be determined, for example, in that a pointer 158 of the display device I56 points to a desired temperature of the piece of food to be treated is set «When the probe I5O is inserted into the piece of food, and the When the set temperature is reached, an indicator light 160 lights up or an acoustic alarm is given. The temperature probe 150 can also be used to supply microwave energy to control the oven chamber, where the microwaves =

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energy is always switched on when the from the probe 150 measured temperature of the piece of food below the desired temperature set by means of the pointer I58 lies while the microwave energy is switched off, when the said temperature exceeds the preset temperature value. The microwave energy can be a predetermined Time can be switched on, this time being selected by means of a control button l62, during the duration of the Exposure of Mi krowel 1 erienergie by setting a timer button l64 is determined. The mean microwave power is selected by means of a control knob I66, so that the mean Microwave power, which reaches the furnace chamber, can be varied from about 100 watts to 700 watts.

The gas burner 92 is controlled by rotating a Selector button I68 on a convection heating signaling Marking area and by setting a temperature selector knob 170 to a temperature of the circulated vapors. A timer, for example a digital clock 172, is equipped with switch-on and switch-off control means 17 ^ and 176 are provided to to be able to set the time during which convection heating should be effective in the oven.

In operation, a temperature sensor I78 speaks, which is connected to a Tab is mounted in the furnace jacket 12 immediately below the inlet area l6, to the temperature of the circulated in the furnace jacket Vapors and if this temperature is below the temperature set on the control button I70, the burner system will 90 put into operation.

The oven proposed here is therefore a combined microwave oven with convection heating, where the microwave energy is used to thaw a piece of food or for rapid preheating of a piece of food can be used while convection heating is used to keep the essentials

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Provide thermal energy for the final heating and / or for cooking the piece of food as well as for determining the surface quality and the browning. After each separate control systems are provided for this, a considerable variety of temperature combinations can be selected so that a variety of size, shape and type of food pieces can be handled and an optimal program can be set in each case to ensure the food preparation is quick and flawless in terms of taste perform.

The browning of the piece of food, such as a roast, can be achieved by using vapors heated via the inlet area 16 are blown in and at the same time the furnace chamber is subjected to full microwave power. The rapidly flowing hot air dries moisture from the surface of the food piece, so that the microwave energy is more easily removed from the dry surface of the piece of food is absorbed and this surface can brown. An additional heating element for tanning or a tanning grill is therefore not necessary.

Examples of the services to be set for effective browning of a piece of food are set Microwave power from 500 watts to 80Ö watts corresponding to approximately 2000 to 3000 BTU / hour and a gas burner output of about 500 to 15,000 BTU / hour. With these performance values can baking and / or browning of a cake can be achieved in a few minutes. In the context of the here given thoughts a multitude of further training and modification possibilities. For example, the perforations and the openings can also be in other places instead of in the rear wall of the furnace shell be provided. Other electrical control devices and other means of supplying the Microwave energy can be provided in the oven space. Also the special means for generating the circulation and the burner construction can be varied.

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Claims (12)

Patent claims 1 «Combined microwave oven with convection heating, characterized in that means (6k) are provided for circulating heated vapors through the oven space (12) which can be impacted with microwave energy, which vapors from the oven space via a device (18) preventing the escape of microwave energy Suck off combustion chamber (118), which is located near the inlet of an air system for the circulation means and in which a burner (92) also delivers its combustion products. 2. Microwave oven according to claim 1, characterized in that the fan system (6k) is located outside of the oven shell (12). 3. Microwave oven according to claim 1 or 2, dadxirch characterized, that the burner has at least one multi-hole strip burner section (104, IO6). k. Microwave oven according to one of Claims 1 to 3i, characterized in that secondary air supply openings (126, 128) are assigned to the burner (92) and are separated from each individual burner opening by no more than three burner openings in between. 5. Microwave oven according to one of claims 1 to 4, characterized characterized in that the burner has a plurality of strip burner sections (104, IO6) with a plurality of burner channels, wherein the burner sections from one another by a secondary air duct (128) are separated. 03CQ30 / 080S
BATH ORIGINAL 6. Microwave oven according to one of claims 1 to 5, characterized characterized in that at the bottom of the furnace shell (12) a rotatable radiator (26) for introducing microwave energy into the Oven space is arranged. 7 · Microwave oven according to one of claims 1 to 6, characterized characterized in that a temperature sensor probe (I50) which is located inside the furnace shell (12), with a circuit located outside the furnace shell for determining d »-r Temperature of a Nahrurijcsmi tt el piece (32) is connected. 8. Microwave oven according to claim 7 »characterized in that the (152, 15 * 0 Circuit feeds a display device, which feeds a display delivers, as soon as the temperature of the middle piece (32) has reached a manually preset temperature. 9. Microwave oven according to claim 7 or 8, characterized in that that the one coupled to the temperature sensor probe (150) Switching the supply of microwave energy to the oven space as a function controls from the recorded temperature. 10. Microwave oven, in particular according to one of claims 1 to 9i, characterized in that devices (I78) for determination the temperature of the circulating vapors and for controlling the means located outside the furnace shell (12) are provided for heating these vapors or the burner (92) depending on the temperature. 11. Microwave oven according to one of claims 1 to 10, characterized characterized in that the rear wall of the furnace shell (12) has at least one perforated steam exhaust area (l8), the maximum dimensions of the perforations is much smaller than half the wavelength of the microwave energy, that further the gas burner (92) below the level of the outlet area .- j "JU / 0 8 (.1 '
BATH ORIGINAL is arranged so that a flow of combustion products past the outlet area to the generation of the steam circulation serving means comes about and that the height of the flame above the gas burner to prevent ionization of the Vapors in front of the vapor outlet area is restricted by secondary air sources near the mouths of the Πι enii erkanäl e provided which of the secondary air sources by a maximum of three intermediate focal ducts must be separated. 12. Microwave oven according to one of claims 1 to 11, characterized characterized in that the means for circulating the vapors contain a plurality of fan wheels (64, 70) rotating in opposite directions. C:. "Mi / ο ρ ^r ■ BATH; QRlGIl ^ lAb