Microwave oven

Abstract

A microwave oven having a magnetron (12) which generates electromagnetic waves and directs them into a cooking cavity (2) formed in a casing (10) through a waveguide (6), the casing (10) together with the cooking cavity (2) defining a gap which accommodates the magnetron (12) and the waveguide (6), the waveguide (6) leading out through an opening (4) located substantially in the centre of the top wall of the cooking cavity (2), characterized in that a metal plate (8) is arranged on the top wall of the cooking cavity (2) at a distance of about 20-22 mm from the top wall and is positioned to cover partly said opening (4).

Description

Technical Field

[0001] This invention relates to a microwave oven. Background Technology

[0002] Microwave ovens are known, especially household microwave ovens, to heat and cook food using high-frequency electromagnetic waves generated by magnetrons, unlike traditional electric ovens that generate heat through resistance heating and transfer heat via conduction and radiation.

[0003] The cooking cavity is typically parallelepiped in shape, sized to accommodate one or more containers where food to be cooked, heated, or defrosted is placed. Within this cavity, electromagnetic waves generated by a magnetron are introduced via waveguides, which, depending on the microwave oven model, lead to the top, back, or side walls of the cavity. These waves cause water, fat, and sugar molecules within the food to vibrate, heating the food from the inside out, and at a much faster rate than with a conventional electric oven.

[0004] Because electromagnetic waves have a certain directionality, they do not act uniformly across the entire internal volume of the cooking cavity, but rather concentrate in areas where microwave energy is absorbed more effectively. Therefore, they cannot evenly transfer their energy to the food placed inside the cavity.

[0005] To eliminate this drawback, various solutions have been proposed. One of them involves installing a rotating disc at the bottom of the cooking cavity, on which the food container to be heated can be placed. By rotating the disc and the food container, their positions within the cooking cavity constantly change, thereby helping to achieve a more uniform heating effect using electromagnetic waves.

[0006] The solution has proven effective, but it adds complexity to the microwave oven's design due to the need for a support plate for the food container and an electric motor to rotate it. Furthermore, the motor must have sufficient power to move the rotating plate, the food container, and the food placed inside, resulting in additional power consumption.

[0007] Another known solution for achieving uniform cooking in a microwave oven involves placing a propeller in front of the waveguide outlet within the cooking cavity. This propeller is configured to rotate, and its motion helps to reflect at least a portion of the electromagnetic waves and distribute them throughout the cooking cavity.

[0008] This solution results in lower energy consumption because it eliminates the need to rotate food containers. However, it still requires an electric motor to turn the propeller, which adds complexity and cost to the microwave oven's construction and introduces a moving part that, like all moving parts, is prone to failure and damage.

[0009] Another known solution involves introducing electromagnetic waves into the microwave oven through multiple openings, thereby distributing the electromagnetic waves more evenly throughout the internal volume of the cooking cavity. While this method effectively solves the problem, it comes at the cost of increased manufacturing complexity, as it requires a waveguide system capable of reaching multiple openings in the walls of the cooking cavity.

[0010] JPS4879545U describes a microwave oven with static elements inside the cooking cavity configured to distribute waves within the cavity itself. However, this solution has limitations in terms of heating efficiency and temperature uniformity within the cooking cavity. Summary of the Invention

[0011] The purpose of this invention is to provide a microwave oven that eliminates all the above-mentioned disadvantages.

[0012] In particular, the object of the present invention is to provide a microwave oven that has a simpler construction compared to a conventional oven of the same power.

[0013] Another object of the present invention is to provide a microwave oven that, compared with a conventional oven of the same power, ensures that food placed in the cooking cavity is heated more evenly.

[0014] Another object of the present invention is to provide a microwave oven that requires fewer components compared to a conventional oven of the same power.

[0015] Another object of the present invention is to provide a microwave oven that has a lower cost compared to a conventional oven of the same power.

[0016] Another object of the present invention is to provide a microwave oven that, compared with a conventional oven of the same power, does not generate additional power consumption beyond that required for heating food.

[0017] All these objectives, and others that will become apparent from the following description, are achieved, according to the invention, together or individually, by the microwave oven as defined in claim 1. Attached Figure Description

[0018] The invention is further illustrated below with reference to the accompanying drawings, which are provided by way of example only and are not limiting, wherein: Figure 1 A schematic front view of a microwave oven according to the present invention is shown, without a front door; Figure 2 The microwave oven is shown along Figure 1 A horizontal cross-section taken from line II-II; Figure 3 The microwave oven is shown along Figure 1 The vertical cross-section taken from line III-III; Figure 4 A partial lower front perspective view of the microwave oven is shown; Figure 5 A perspective view of a static element disposed on the top wall of the microwave oven cooking cavity in the first embodiment of the present invention is shown, referred to as type A; Figure 6 A perspective view of the static element in the second embodiment is shown, referred to as type B; Figure 7 A perspective view of the static element in the third embodiment is shown, referred to as type C; Figure 8 A perspective view of the static element in the fourth embodiment is shown, referred to as type D; Figure 9 A perspective view of a static element, not belonging to the present invention, is shown, referred to as type E; Figure 10 A perspective view of the static element according to the invention in a variant of the type A static element is shown. Detailed Implementation

[0019] like Figures 1 to 5 As shown, the microwave oven according to the invention belongs to a type similar to conventional microwave ovens, i.e., it does not require moving parts for distributing electromagnetic waves within the cooking cavity 2. However, this microwave oven can advantageously be equipped with a conventional heating resistor 6 and a static element 8 at the waveguide outlet opening 4, through which electromagnetic waves are introduced into the cooking cavity. The static element 8 is designed to partially interfere with the electromagnetic wave flow to alter the distribution of electromagnetic waves within the cavity 2.

[0020] The static element 8 is essentially composed of a small metal plate, preferably made of steel, and is installed at the opening 4 on the inner side of the top wall of the cooking cavity 2. The opening is roughly located in the center of the wall, is rectangular, with its shorter side parallel to the front wall of the microwave oven and measuring approximately 40-45 mm, and its longer side perpendicular to the front wall of the oven and measuring approximately 80-90 mm.

[0021] The cooking cavity 2 has a generally parallelepiped shape and is housed within the casing 10, separated from the casing 10 on all sides by air gaps. These air gaps house all the components necessary for the proper operation of the microwave oven, and in particular, the magnetron 12, which is located at its upper part. The magnetron generates electromagnetic waves, which are then directed through waveguides into the cooking cavity 2 via openings 4 located in the top wall of the cooking cavity.

[0022] The plate 8 has an overall elongated rectangular shape, measuring approximately 130-140 mm × 16-20 mm, and extends into two ends 14, which are generally bent at 90° to ensure that the plate maintains a gap of approximately 20-22 mm with the top wall of the cooking cavity. These ends 14 are further bent outward at 90° and are provided with holes 16 for screws to facilitate installation and removal for possible maintenance operations.

[0023] Near each of the two ends of the main body of plate 8, an opening 17 can be advantageously formed, preferably circular, with a diameter of about 11-13 mm.

[0024] The plate 8 is preferably mounted on the top wall of the cooking cavity 2, with its longer side parallel to the front opening of the cooking cavity 2, and positioned to cover about 25-50%, preferably 30-35%, of the opening 4. The uncovered portion of the opening may be sealed with a mica plate or other suitable known material to protect the antenna of the magnetron 12 from the steam inevitably generated during the heating or cooking of food.

[0025] All the dimensions described above refer to a standard microwave oven with a cooking cavity 2 of approximately 410 × 230 × 380 mm. These dimensions were determined through experimental testing designed to evaluate the microwave oven's performance in terms of the highest achievable temperature and temperature distribution within the cooking cavity 2.

[0026] In order to evaluate the influence of various characteristics of plate 8 on electromagnetic wave flow, and thus on heating efficiency and heating uniformity, the present invention includes other different types of plates 8 in addition to the plate 8 described above (referred to as type A for simplicity).

[0027] Specifically, a second type of board 8 (Type B) is provided, such as Figure 6 As shown. The plate is also constructed with two bent ends, as with the aforementioned A-type plate, to maintain a distance from the top wall of the cooking cavity 2. However, it differs in that it has a larger width of approximately 24-26 mm, and a central portion 18 that is further widened toward the microwave oven opening, reaching a total width of approximately 34-37 mm in this widened central portion 18. Furthermore, in this widened central portion 18, the plate 8 may advantageously include two elongated and aligned openings 20, which are approximately rectangular in shape and measure approximately 24-26 mm × 11-13 mm. From one of the two longer sides of each rectangular opening 20, specifically the side away from the oven door, an inwardly extending fin 22 extends into the cooking cavity 2. This fin 22 has a curved profile with its concave surface facing inward and extends to cover slightly less than half of the corresponding opening 20. In addition, at the end of the free long side of the widened central portion 18, two lugs 24 extend into the cooking cavity 2. These lugs 24 are coplanar with the rest of the plate 8, and are approximately semi-circular in shape with a diameter of 14-16 mm.

[0028] The invention also includes a third type of plate (Type C), such as Figure 7 As shown. Similar to the aforementioned type, it is designed to be positioned on the top wall of the cooking cavity 2 while maintaining a distance from the top wall. However, it differs from the B-type plate in that its central portion 18 has a constant width, equal to the width of the B-type plate at the lug 24 position.

[0029] Furthermore, the present invention provides a fourth type of plate (Type D), such as Figure 8 As shown. This plate has the same shape as the B-type plate, but lacks the elongated opening 20 and the fin 22.

[0030] To evaluate the effectiveness of the various features of the aforementioned board 8, a fifth type of board (Type E) was also designed, such as... Figure 9 As shown. It has the same shape and size as the B-type plate, but the main difference is that it lacks the 90° bent end 14. Therefore, it is designed to be set on the top wall of the cooking cavity 2 in a basically coplanar manner.

[0031] To further evaluate the performance of the plate 8 according to the invention compared to known similar elements, a sixth type of plate (Type F) was also designed. This plate is completely similar to the plate described in prior art JPS4879545U, and like that plate, it is intended to be mounted on the top wall of the cooking cavity 2 in a substantially coplanar manner according to the mounting method shown in the prior art.

[0032] To compare the performance of the AF type plates, they were all subjected to the same test after being installed in the same manner on the top wall of the cooking cavity of the same microwave oven.

[0033] Specifically, type A panels are installed to cover approximately 30-35% of opening 4. Types B, C, and D panels, due to their larger size, cover an even larger proportion of opening 4, estimated at 40-45%.

[0034] To further evaluate the achievable temperature and temperature distribution within the cooking cavity, glasses were placed inside the cavity in the following different arrangements: a. A single glass containing 275 g of water is placed in the center of the bottom of the cooking cavity.

[0035] b. Four glasses, each containing 50 g of water, are positioned at the vertices of a square whose sides are parallel to the walls of the cooking cavity. A fifth glass, containing the same amount of water, is placed at the center of the square.

[0036] c. Four glasses, each containing 50 g of water, are positioned at the vertices of a square whose diagonals are parallel to the walls of the cooking cavity and whose length is equal to the side length of the square in arrangement (b). A fifth glass, containing the same amount of water, is placed at the center of the square.

[0037] d. Five glasses, each containing 50 g of water, are positioned at the vertices of a regular pentagon whose width is approximately equal to the width of the square in arrangement (b). A sixth glass, containing the same amount of water, is placed at the center of the pentagon.

[0038] e. Six glasses, each containing 50 g of water, are positioned at the vertices of a regular hexagon whose width is approximately equal to the width of the pentagon in arrangement (d). A seventh glass, containing the same amount of water, is placed at the center of the hexagon.

[0039] Then, various tests were conducted using different plates 8 and different glass arrangements. The microwave oven was powered by a 900 W magnetron 12. The first test lasted 120 seconds, and subsequent tests lasted 60 seconds.

[0040] The table, created based on the test data, reports the temperature values ​​and their respective standard deviations σ for different types of plates 8 and different glass arrangements within the cooking cavity. (x - )² / n – 1)]¹ / ² ). In addition, the sum of standard deviations σ is shown in the last line, indicating the overall performance of all glass arrangements in various tests.

[0041]

[0042] In various tests conducted using multiple water-filled glasses, the temperature value refers to the position of each glass in the corresponding test, indicated by the number recorded in the table itself.

[0043] The test results show that: - The gap between the A-plate 8 and the top wall of the cooking cavity 2 allows for an optimal average trade-off between the highest achievable temperature and greater heating uniformity within the cavity.

[0044] - Type B plate 8 is also spaced from the top wall of cooking cavity 2, but has a larger surface area and covers opening 4 to a greater extent. It allows for a slightly lower temperature compared to the temperature achieved with type A plate 8, but provides good temperature uniformity inside cooking cavity 2.

[0045] - The C-shaped plate 8 is also spaced from the top wall of the cooking cavity 2 and covers the opening 4 in a manner similar to the B-shaped plate 8, allowing for a slightly lower temperature and slightly lower heating uniformity inside the cooking cavity.

[0046] - The D-type plate 8 is also spaced from the top wall of the cooking cavity 2, allowing for a slightly higher temperature than that achieved with the A-type plate 8, but the temperature uniformity inside the cooking cavity 2 is between that of the B-type plate 8 and the C-type plate 8.

[0047] - The E-shaped plate 8 is flush with the top wall of the microwave oven. It is not part of this invention. It presents a basically uniform but rather low temperature inside the cooking cavity.

[0048] - The F-type plate, based on JPS4879545U, exhibits significantly higher temperatures inside the cooking cavity, but the temperature is quite uneven.

[0049] In summary, the tests show that the best results are achieved when the plate 8 is installed at a distance from the top wall of the cooking cavity 2 and partially covers the opening 4 formed in the top wall.

[0050] Finally, it was also designed Figure 10 The plate shown is essentially similar to the Type A plate, but unlike the Type A plate, it lacks the opening 17. Experimental tests revealed that this plate performs better under certain load conditions in the cooking cavity 2 compared to plate 8 without opening 17, but exhibits slightly inferior performance under other conditions. However, it still outperforms the plate flush with the top wall of the cooking cavity 2 (Type E plate) and the plate according to JPS4879545U (Type F plate). Therefore, opening 17 should be considered preferred but not essential.

[0051] exist Figures 1 to 4 The invention illustrates a microwave oven cooking cavity 2 with an electrothermal resistor 6 applied to its top wall to combine microwave cooking with conventional radiant cooking when necessary. However, the invention also includes microwave ovens without electrothermal resistors or with multiple electrothermal resistors, which may be disposed on the top wall of the cooking cavity 2, or even on different walls thereon, or in the gap between the cavity and the housing 10, and an optional fan capable of generating a hot airflow introduced into the cooking cavity 2 through openings formed in its walls.

[0052] If multiple heating resistors are provided, the microwave oven also includes a device for controlling the simultaneous activation of one or more heating resistors depending on the desired cooking type.

Claims

1. A microwave oven having a magnetron (12) that generates electromagnetic waves and guides the electromagnetic waves through a waveguide (6) into a cooking cavity (2) formed inside a housing (10), the housing (10) and the cooking cavity (2) defining a gap, the magnetron (12) and the waveguide (6) being housed in the gap, the waveguide (6) being led out through an opening (4) substantially located at the center of the top wall of the cooking cavity (2), characterized in that, A metal plate (8) is disposed on the top wall of the cooking cavity (2), maintaining a distance of about 20-22 mm from the top wall, and positioned to partially cover the opening (4).

2. The microwave oven according to claim 1, characterized in that, The plate (8) is positioned to cover 30% to 35% of the opening (4).

3. The microwave oven according to claim 1 and / or 2, characterized in that, The plate (8) is provided with two folded ends (14) for mounting the plate to be spaced apart from the top wall of the cooking cavity (2).

4. The microwave oven according to claim 3, characterized in that, The plate has an opening (17) near each of the ends (14), and the opening is preferably circular in shape.

5. The microwave oven according to claim 4, characterized in that, Each circular opening (17) formed in the plate (8) has a diameter of approximately 11-13 mm.

6. The microwave oven according to one or more of the preceding claims, characterized in that, The plate (8) is approximately 130-140 mm long, and in the installed state, this dimension is parallel to the front opening of the cooking cavity (2).

7. The microwave oven according to one or more of the preceding claims, characterized in that, The width of the plate (8) measured in the front-back direction of the cooking cavity (2) is approximately 16-20 mm.

8. The microwave oven according to one or more of claims 1 to 6, characterized in that, The width of the plate (8) in the front-back direction of the cooking cavity (2) is between 16 and 53 mm.

9. A microwave oven according to one or more of the preceding claims, characterized in that, The plate (8) has a width of approximately 34-37 mm measured in the front-back direction of the cooking cavity (2) and is provided with a pair of elongated orifices (20) aligned along the longitudinal extension direction of the plate itself. The size of the elongated orifices (20) is 24-26 × 11-13 mm.

10. The microwave oven according to claim 9, characterized in that, The plate (8) is 34-37 mm wide and has two lugs (24) on the side facing the microwave oven opening. The lugs (24) are coplanar with the plate itself and face the front opening of the cooking cavity (2).

11. The microwave oven according to claim 10, characterized in that, The lug (24) is located at the end of the long side of the plate (8), has a basically semi-circular shape, and has a diameter of 14-16 mm.

12. The microwave oven according to one or more of the preceding claims, characterized in that, Each elongated opening (20) formed in the plate (8) is provided with a wing (22) on the longitudinal side away from the oven door, the wing (22) facing the interior of the cooking cavity (2) and configured to partially cover the elongated opening (20).

13. The microwave oven according to claim 12, characterized in that, The wing (22) has a concave surface facing the interior of the cooking cavity 2.

14. The microwave oven according to one or more of the preceding claims, characterized in that, The portion of the opening (4) of the waveguide (6) not covered by the plate (8) is provided with a protective plate element to shield the effect of cooking steam on the magnetron (12) antenna.

15. The microwave oven according to claim 14, characterized in that, The protective plate element is made of mica.

16. The microwave oven according to one or more of the preceding claims, characterized in that, The microwave oven also includes at least one heating resistor (6) designed to combine microwave cooking with radiation cooking.

17. The microwave oven according to one or more of the preceding claims, characterized in that, The microwave oven houses at least one heating resistor (6) and optionally a fan in the gap defined by the housing (10) and the cooking cavity (2) to generate a hot airflow that is introduced into the cooking cavity (2) through a hole provided on at least one wall of the cooking cavity (2).

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