JPH0225102B2 - - Google Patents

Description

[Detailed description of the invention] field of invention TECHNICAL FIELD This invention relates to microwave ovens.

BACKGROUND OF THE INVENTION Microwave ovens can cook, defrost, or reheat food extremely quickly, but because the heat energy is generated within the food itself by stirring the food molecules, the outer edges of the food may brown. does not reach the required temperature. This drawback has been addressed by providing known microwave ovens with some kind of heating means that is different from the microwave generator. For example, UK patent application no. 1172918
No. 1 and No. 1332122 describe ovens that have a thermal heating element in addition to a microwave generator.

Known microwave ovens employ different methods of using two forms of energy: microwave energy and thermal energy. One known oven generates thermal energy only during a first cooking period and subsequently generates microwave energy only during a second cooking period, and the conversion from thermal energy to microwave energy is automatic. It is done. During the first period, the food is not internally cooked by the thermal energy;
The surface is baked to a crispy or golden brown color. During the second period, when only microwave energy is applied to the oven, the core of the food is heated, resulting in the generation of steam, which is passed through the periphery of the already crispy and browned food to the outside. I have to run away. As a result, the outer periphery of the food contains steam and becomes soft and unpalatable. To disperse the steam, the oven is vented during the second period, reducing the temperature within the cooking chamber and reducing quality, especially in foods such as pies.

A second known microwave oven is characterized in that only microwave energy is generated during the first cooking period;
Subsequently, only thermal energy is generated within a second cooking period, operating in the opposite order to the first one. 1st
During this period, the oven cooking chamber is vented to disperse steam by forced air flow. At the beginning of the second period the vent is closed,
Thermal energy is added to bake the food.

Both of these known microwave ovens are
Since the vapor dispersion occurs during the generation period of the microwave energy, the problems associated with vapor dispersion cannot be successfully addressed. Excessive steam condenses on cold oven surfaces and also makes food soft or mushy. Adding more airflow to disperse the steam will reduce the temperature of the oven, while adding more heat energy will cause the outside of the food to burn before the center is cooked.

The present invention provides a microwave oven and method of cooking food in which sufficient heat is provided within the cooking chamber of the oven to dispose of steam emanating from the food when the food is cooked by microwave energy. purpose. To achieve this objective, thermal energy is continuously applied simultaneously with the microwave energy.

Microwave ovens are known in which microwave energy is applied simultaneously with thermal energy. Primarily, however, such known ovens have been large commercial or industrial ovens for high power applications. This means that the power required for microwave generators and thermal heating elements for various cooking applications has been severely limited by the power input level to the oven. In contrast, the present invention is a compact, home-use designed
It relates to ovens that can be connected to household electrical outlets, which have specific power limitations that vary from country to country. The invention relates to providing an oven designed to operate with a maximum power input of 1800 (suitable for the United States) and an oven designed to operate with a maximum power input of 3000 Watts (suitable for the United Kingdom). .

Microwave ovens are also known which have a fan so that hot air heated by the thermal heating means is distributed over the food being cooked. The success of cooking in such a microwave oven depends on the precise selection of many factors, such as the air convection pattern within the oven cooking chamber. One commercially available oven introduces heated air into the cooking chamber from a central portion of the back wall of the cooking chamber, where the air is directed forward and then split into two streams, which pass through the side wall of the oven cooking chamber. , and then exits the cooking chamber at two locations on the back wall of the cooking chamber. This airflow pattern does not always satisfactorily disperse the steam generated from the food as it is being cooked by microwave energy. If the steam produced as a result of cooking is not dispersed by a flow of hot air, this is a problem, especially in pies and the like, which become soft or mushy.

SUMMARY OF THE INVENTION In accordance with one aspect of the invention, a compact microwave oven designed to be powered from a household electrical plug in the range not exceeding 1500 watts is provided which supplies microwave energy to the cooking chamber of the oven. a rotatable turntable at the bottom of the cooking chamber and a thermal heating means capable of heating the air inside the oven cooking chamber and simultaneously supplying thermal energy to the oven cooking chamber. control means operative to continuously supply microwave energy to the cooking chamber, whereby the microwave energy heats the interior of the food;
The thermal energy also disperses the resulting steam and browns the external surface of the food, and the thermal heating means includes an electrical heating element and fan means for circulating air through the element and through the cooking chamber; A forced stream or air heated by the heating means enters the cooking chamber from one side of the cooking chamber, passes over the turntable and exits the cooking chamber from the other side of the cooking chamber. .

Preferably, the oven cooking chamber has a back wall, the rear side of which is a chamber containing an electrical heating element;
The back wall has an opening at said one side, the opening allowing heated air to be forced by a fan into the cooking chamber over the substantial height of the cooking chamber, and at the other end of the back wall. A fan constituting the fan means is provided near the bottom corner.

Preferably, the oven power rating does not exceed 1620 watts, which is the limit for US power restrictions.

In accordance with another aspect of the invention, a small microwave oven designed to be powered from a domestic electrical outlet at a rate not exceeding 3000 watts comprises:
a microwave generator for supplying microwave energy to the cooking chamber of the oven; a rotatable turntable provided at the bottom of the cooking chamber; and thermal heating means capable of heating air within the oven cooking chamber; and control means operative to supply continuous microwave energy to the oven chamber simultaneously with the supply of thermal energy to the oven chamber, whereby the microwave energy heats the interior of the food product and also provides thermal energy to the oven chamber. for dispersing the resulting steam and browning the external surface of the food, the thermal heating means comprising an electrical heating element and fan means for circulating air through the element and through the cooking chamber; A flow of air heated by the thermal heating means is forced into the cooking chamber from one side of the cooking chamber, across the turntable, and out of the cooking chamber from the other side of the cooking chamber.

Preferably, the power rating of said other aspect oven does not exceed 2650 or 2700 watts, this value being the limit for UK power restrictions.

In accordance with yet another aspect of the invention, food preparation in a small microwave oven designed to be powered from a domestic electrical outlet at a rate of either not more than 1800 watts or not more than 3000 watts. The method comprises the step of continuously supplying microwave energy to the cooking chamber of the oven into which the food is placed, while simultaneously supplying thermal energy to the cooking chamber, whereby the microwave energy heats the interior of the food and The thermal energy disperses the resulting steam and browns the external surface of the food product, the thermal energy being supplied by circulating convection of air forced by a fan to pass through the electrical heating element; Convection currents enter the oven chamber from one side of the oven chamber, pass over the food being rotated on the turntable, and exit the oven chamber from the other side of the oven chamber.

For a low power oven limited to a total input power of 1620 watts for the UK market, it has been found that 1250 watts of thermal energy and 200 watts of microwave energy into the cooking chamber give good results. A typical source of microwave energy is approximately
50% or somewhat better efficiency, so
A power input into the cooking chamber of 200 watts requires a power input into the microwave source of approximately 360 watts. Preferably, the oven has one thermal convection or heating element that produces thermal energy, which is sufficient so that preheating of the oven is not required, the microwave source (i.e. a magnetron) is , may be selected to operate at higher power to provide more energy into the cooking chamber, and the magnetron is set to lower power whenever the heating element is activated (i.e. 200 volts into the cooking chamber). watts supply).

Higher power ovens limited to 2650 watts for the UK market have more power available and fewer restrictions. For example 200 into the galley,
Low, medium, and high power levels exist for magnetrons corresponding to 300 and 600 watts, and one thermal heating element has a power rating of approximately 1450 watts.
For each of the low power and high power ovens, cooking preferably begins with a cold oven.

BRIEF DESCRIPTION OF THE DRAWINGS Two microwave ovens according to the invention will now be described by way of example with reference to the accompanying drawings.

Figures 1 and 2 show an oven designed for use in the United States, where home use cannot have a power rating of more than about 1650 watts. Referring to FIG. 1, the microwave oven has a casing 1 fitted with a hinged door 2 sealing off a cooking chamber 3. A turntable 5 is provided at the bottom of the cooking chamber for rotating the food during cooking. A shelf guide 6 is provided on the side wall of the cooking chamber 3.
A fan 7 is provided on the back wall of the fan 7 for circulating air through a heat convection element 8 (FIG. 2) and through a perforated plate 9.

Control board 10 has control knobs and dials for the cook.

FIG. 2 shows the components of the oven's electrical circuit. Power from mains to 15 amp fuse 1
2, magnetron cutout 13, and mains on/off switch 14. When switch 14 is closed, 115V, 60Hz power is supplied to galley lamp 15 and fan motor 16 for cooking magnetron 17. The thermal convection timer switch has interlocking contacts 18, 18a. The contacts 18 are connected to a motor 19 for the fan 7, a galley thermostat 20 in series with a thermal convection element 8 of approximately 1250 watts, a first relay coil 22, and a second relay coil 22.
It is connected to the relay coil 33 of.

Door switch 24, microwave timer switch 25 and cooking start switch 26 are connected in series in a power supply line 27 which supplies power to magnetron 17 which supplies microwave energy to the cooking chamber. Contact 18a and thermal convection timer motor 36 are connected between power line 27 and neutral line 32. A thermal convection "on" lamp 30 is connected in parallel across the timer motor 36. A microwave timer motor 37 and a microwave "on" lamp 38 are connected between power line 27 and neutral line 32 at the locations shown. A turntable motor 39 for the turntable 5 is connected between the center contact of the relay contact 34 and the neutral line 32. The relay coil 33 is connected to the microwave energy switching switch 42 and the relay coil 35.
It also controls a normally closed relay contact 40 connected between the power supply line 27 and the neutral line 32. The transformer 44 takes out power to the magnetron 17. Switch 45 isolates one of the two parallel-connected capacitors 46, so that the magnetron draws low power. When the relay switch 45 is closed, both capacitors 4
6 is a circuit, and a magnetron 17 derives high power. At low power, the magnetron outputs approximately 200 watts into the cooking chamber 3, and at high power, the magnetron outputs approximately 650 watts into the cooking chamber 3.
Magnetrons are approximately 50% efficient, so the power consumed by the magnetron is approximately twice the energy delivered to the galley, both at low power and high power. For 200 watts of output energy into the cooking chamber, the magnetron requires approx.
Requires 360 watts input.

Returning to FIG. 1, the control board 10 controls the following:
a switch 42 for selecting high or low microwave energy; a rotation timer 50 for controlling the motor 37 and thus setting the time up to 60 minutes that the magnetron is operated; microwave "on";
a lamp 38, a thermal convection "on" lamp 30, a main switch 14, a rotary knob 52 that changes the setting of the thermostat 20 between 50°C and 250°C, which controls the motor 36 and thus thermal energy is generated. A separate rotary timer 53 is provided to set the time up to a maximum of 120 minutes, and a push button 54 controls the switch 26.

The oven is used from a cold start in a "mixed facility" mode, ie thermal and microwave energy modes, as follows.

(a) The microwave timer 50 is set to the desired cooking time.

(b) Knob 52 is rotated to set the temperature of thermostat 20.

(c) The convection timer 53 is set to the desired cooking time.

(d) Door 2 is closed, cooking button 54 is pressed and switch 26 is closed.

The turntable 5 rotates and both timers run simultaneously so that microwave energy and thermal energy are generated simultaneously.

As long as relay coil 33 is activated (i.e. as long as contact 18 is closed), contact 40
is open, so the magnetron produces low power regardless of the position of switch 42.

When the convection timer 53 reaches zero, the switch contacts 18, 18a open, the convection heating element 8 is disabled and the cooking period ends. Also, coil 2
2 and 33 are disabled. When coil 33 is disabled, contacts 34 are changed. Turntable motor 39 is thereby activated through switches 25 and 26 or through contact 18a. Lamp 38 (preferably green) is lit as long as microwave energy is being generated, and lamp 30 (preferably orange) is lit as long as thermal energy is being generated. When microwave timer 50 reaches zero, switch 25 opens, thereby isolating magnetron 17.
When the oven door 2 opens, the switch 24 opens,
This cuts off the power supply to the magnetron. Normal shorting switch 47 is line 2
7 and 32, the magnetron 17
short circuit.

Although the oven of FIGS. 1 and 2 can be operated in a microwave only mode or a convection only mode, the best results are achieved in the mixed facility mode described.

Relay coil 22 also operates a shutter (or valve) 84 for venting oven cooking chamber 3 under certain conditions. The shutter 84 is arranged near the front upper end of the right side wall of the cooking chamber 3, as shown in FIG. When convective heating is being applied to the cooking chamber 3, the relay coil 22 is activated and the shutter 84 is closed to prevent the air flow carried by the blower motor 16 from reaching the cooking chamber 3. do. When convective heating is not being provided to the cooking chamber 3, the coil 22 is disabled, thereby opening the shutter 84 and venting the cooking chamber. During venting, air carried by motor 16 is forced into the cooking chamber and from there into the atmosphere to remove steam from the cooking chamber.

The oven shown in Figure 3 was designed to suit the UK market where up to approximately 3KW of power can be derived from a domestic electrical outlet.

In FIG. 3, the same parts as in FIG. 2 are given the same reference numerals. The microwave switch 42 can be set (in addition to the "off" position) to one, two,
Alternatively, there are low, medium, and high energy setting positions, each provided by three capacitors 46, in which the switch 42 is closed, directing power to the transformer 44.

An oven thermostat 60 is connected in series with the fuse 12.
will be disconnected if the temperature in the cooking chamber becomes too high. Magnetron thermostat 62 performs a similar function to magnetron 17. Switches 63 and 64 are connected to each other, and switch 6
4 is connected to the timer motor 65 as follows. The switch 63 is an on/off switch corresponding to the switch 14 in FIG.
opens when timer motor 65 reaches zero;
Two switches 63 and 64 are installed on the control board 10.
Controlled by two circuit timer knobs.

Convection switch 66 controls element 8 independently of the automatic timing provided by timer motor 65.
be activated. Therefore, in manual mode, when switch 66 is closed, element 8
is activated so that thermal energy is generated independent of time constraints and independent of microwave energy. For automatic or timer mode, the start cook switch 26 is closed and the timer motor is set to operate from that time. After this time has passed, the switch 46 opens,
Element 8 is disabled.

When microwave energy is required, switch 46 is set to the required microwave energy level, a timer switch controlling motor 65 is set to the desired time, and switch 26 is closed. When timer motor 65 reaches zero, switch 64 opens and magnetron 17 is disabled.

Switch 66 is connected to a thermostat switch 67 in the oven cooking chamber, and monitor switch 47 is mechanically connected to a turntable "off" switch 68.

Regarding the first embodiment, the oven typically operates with thermal energy and microwave energy generated simultaneously, and during the cooking period the oven is operated by opening switch 64 to stop the generation of heat and microwave energy. finish.

Relay coil 33 controls contact 34, as in the previous embodiment, and coil 33 is used to control shutter 84. coil 33
When the coil 33 is activated, the shutter 84 closes the air entry into the cooking chamber and directs the air to the atmosphere. turn towards

This invention enables microwave ovens to operate very effectively at maximum power inputs that meet US or UK requirements. Providing thermal energy and microwave energy simultaneously allows the steam to be dispersed by the thermal energy as it is generated from within the food being cooked by the microwave energy. . This has been found to be particularly effective for products such as pies which are particularly sensitive to excess steam during cooking.

Instead of the control board 10 described, the oven of FIG. 2 or 3 may be equipped with a panel 70 as shown in FIG. 4.

Panel 70 includes a touch sensitive pad and display 72. The pads include a combination pad 73, a microwave pad 74, a thermal convection pad 75, two timer pads, a temperature pad 77, a reset/off pad 78, and a start pad 79. Panel 70 is operated in three possible modes as follows.

(1) Combination cooking mode (i.e. microwave and thermal energy) Contact combination pad 73.

1 time for low microwave energy 2 times for medium microwave energy (Figure 3 only) 3 times for high microwave energy (3 times)
(Illustration only) Touch temperature pad 77 until the desired temperature is reached, as indicated by the illuminated numeral 80 on display 72.

Touch time pad 76 until the desired time is reached, as indicated by numeral 82 on display 72.

Contact start pad 79.

When cooking, display 72 shows the ongoing cooking time, selected temperature, and combination mode. Also for the British model of FIG. 3, the display 72 shows either level of combination.

(2) Microwave only cooking mode Microwave pad 74 is contacted.

Touch the time pad 76 once for high energy, twice for medium to low energy, and three times for low energy until the desired time is reached.

Contact start pad 79.

During cooking, display 72 shows the ongoing cooking time, medium mode and microwave energy level.

(3) Heat convection only cooking mode Convection pad 75 is contacted.

Contact temperature pad 77 until the desired temperature is reached.

Touch time pad 76 until the desired time is reached.

Contact start pad 76.

If preheating is required, the oven is set as described and heated for a set period of time or until that temperature is reached.

The temperature indicator on the display will flash to indicate that the temperature has been reached.

During cooking, display 72 shows the ongoing cooking time, selected temperature, and heat convection mode.

When the cooking time is over, a continuous beep sounds and the heat is automatically switched off.

Touch the pad 78 to turn off the continuous sound, and the time will be displayed. Pads 78 is
Alternatively, it may be a push switch.

Pad 70 may be connected to a microprocessor that provides the necessary control functions for the thermal heating elements, microwave generator, and other operating components of the oven.

A perforated plate 9 is provided at the right corner of the back wall 3a and is vertically elongated so that hot air enters the cooking chamber 3 over the substantial height of the cooking chamber. A fan 7 is provided near the lower left corner of the back wall 3a and is electrically driven to force a flow of hot air over the entire food product placed on the rotary turntable 5.

FIG. 5 shows the convection pattern of air within the oven. The hot air passes through the perforated plate 9 into the cooking chamber 3 (arrow 86), passes over the turntable 5 (arrow 88) and is drawn through the fan 7 into the chamber 92 behind the cooking chamber 3. (arrow 90). room 92
Therein is provided a thermal heating element 8 (shown electrically in FIG. 5) which heats the air before it enters the cooking chamber 3. The turntable 5 rotates counterclockwise as shown in FIG. 5 to maximize the relative velocity between the hot air entering the cooking chamber through the perforated plate 9 and the food rotating on the turntable 5.

Although the convection pattern described above is effective in heating food, the walls of the oven cavity remain cool compared to known air convection patterns in which hot air is blown along the walls of the oven cavity. be.

The back wall 3a is provided with a vent hole (not shown) above the fan 7 for venting steam out of the oven.

If the door is opened during cooking, the switch 24 is opened and the magnetron is disabled, but the thermal heating element 8 continues to be energized.
It will be understood from the circuit diagrams of FIGS. 2 and 3.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the first oven. FIG. 2 is an electrical circuit diagram of the first oven. FIG. 3 is an electrical circuit diagram of the second oven. FIG. 4 is an optional control board for the ovens of FIGS. 2 and 3. FIG. 5 is a schematic plan view of both embodiments of the oven showing the convection pattern of hot air within the oven. In the figure, 1 is a casing, 2 is a door, 3 is an oven cooking chamber, 3a is a back wall, 5 is a turntable, 6 is a shelf guide, 7 is a fan, 8 is a heat convection element, 9 is a perforated plate, 10 1 is a control board, 15 is a cooking chamber lamp, 16 is a blower motor, 17 is a cooking magnetron, 20 is a cooking chamber thermostat, 22,3
3 and 35 are relay coils, 24 is a door switch,
25 is a microwave timer switch, 26 is a start switch, 30 is a thermal convection on-ramp, 36 is a timer motor, 37 is a microwave timer motor, 38 is a microwave on-ramp, 39 is a turntable motor, 44 is a transformer, 65 is a timer motor ,6
6 is a heat convection switch, 68 is a turntable off switch, 70 is a plate, and 72 is a display.

Claims (1)

[Scope of Claims] 1. A microwave oven designed to receive power from a household power outlet, comprising: a microwave generator for supplying microwave energy to a cooking chamber of the oven; and the microwave generator. a blower motor for the oven; and thermal heating means for supplying thermal energy capable of heating the air in the oven cooking chamber, the thermal heating means comprising an electric heating element and a fan means for circulating air through the cooking chamber, said cooking chamber having a back wall, behind said back wall being a chamber in which said electrical heating element is provided, said back wall being one side of said cooking chamber. an inlet opening on one side for allowing heated air to be forced into the cooking chamber by the fan means, and the back wall having an inlet opening on the other side of the cooking chamber for allowing heated air to be forced into the cooking chamber by the fan means; and an outlet opening for drawing the air out of the cooking chamber, the fan means forcing a flow of air heated by the thermal heating means so that the air is drawn to one side of the cooking chamber. A microwave oven that enters the cooking chamber from the side, passes over a turntable, and exits the cooking chamber from the other side of the cooking chamber, comprising: a rotatable turntable provided at the bottom of the cooking chamber; and a first control means operative to supply the continuous microwave energy to the oven cooking chamber simultaneously with the supply of thermal energy to the cooking chamber, whereby the microwave energy is supplied to the food preparation chamber. heating the interior of the food product, and said thermal energy dispersing the resulting steam and browning the exterior surface of the food product, further comprising a shutter on a side wall of said cooking chamber, said shutter being configured to blow air by said blower motor. movable between an open position in which air is blown into the cooking chamber and a closed position in which the shutter prevents air supplied by the blower motor from reaching the cooking chamber; a second control disposed in the closed position when the electrical heating element is energized and in the open position when the electrical heating element is deenergized to ventilate the cooking chamber; A microwave oven further comprising means. 2 further comprising timing means for maintaining the supply of power to the microwave generator and the heating element for a preset cooking time, and upon expiration of the cooking time, the microwave generator and the heating element are activated. The microwave according to claim 1, wherein the microwave is deenergized to finish cooking, and the shutter moves from the closed position to the open position to blow air into the cooking chamber by the blower motor. oven. 3. The microwave generator is capable of operating at a high or low level, and the microwave generator is at the low energy level whenever the electrical heating element is activated. The microwave oven according to item 1 or 2. 4. A microwave oven according to claim 1 or 2, wherein the microwave generator comprises low, medium and high energy levels. 5. The direction of rotation of the turntable is such that a forced air flow passes through the front face of the turntable in a direction opposite to the direction of movement of the front face of the turntable. The microwave oven according to any one of the ranges 1 to 4. 6 comprising a door for closing the cooking chamber and an electrical door switch operable according to the position of the door, the microwave generator being supplied with power via the door switch, while the electrical The heating element is powered independently of the door switch, so that when the door is opened during operation of the oven, the supply of power to the microwave generator is interrupted by the door switch. 6. A microwave oven according to any one of claims 1 to 5, wherein the heating element is heated and the supply of power to the heating element is maintained. 7. The first control means includes a first touchpad that simultaneously selects microwave and thermal energy to the cooking chamber, a second touchpad that selects only the microwave energy to the cooking chamber, and a second touchpad that selects only the microwave energy to the cooking chamber. a control panel with a third touchpad for selecting only the heat energy to be fed, a fourth touchpad for setting the cooking time, a fifth touchpad for setting the maximum temperature, and a sixth touchpad for starting the cooking. With this, users who desire microwave and thermal energy at the same time can use the first
Select the combination mode by touching the fourth touch pad, set the cooking time by touching the fourth touch pad, select the maximum temperature by touching the fifth touch pad, and select the maximum temperature by touching the sixth touch pad. 7. The microwave oven according to claim 1, wherein cooking can be started by touching the microwave oven.