Microwave oven

Abstract

Microwave oven with a magnetron (12), which generates electromagnetic waves and, through a waveguide (6), directs them into a cooking chamber (2) formed inside a chassis (10), which delimits, together with said cooking chamber (2), a gap in which said magnetron (12) and said waveguide (6) are housed, which waveguide (6) exits through an opening (4) located substantially centrally in the upper wall of said cooking chamber (2), characterized in that a metal plate (8) is applied to the upper wall of said cooking chamber( )2, kept spaced about 20-22 mm from said upper wall and positioned in such a way as to partially cover said opening (4).

Description

[0001] MICROWAVE OVEN.

[0002] The present invention relates to a microwave oven.

[0003] Microwave ovens are known, particularly household ovens which, unlike conventional electric ovens, where heating and cooking of food are carried out by heat generated by electric resistances and transmitted through conduction and radiation, perform the heating and cooking of food using high-frequency electromagnetic waves generated by a magnetron.

[0004] The cooking chamber generally has a parallelepiped shape and dimensions suitable for containing one or more containers, in which the food to be cooked, heated, or defrosted is placed. In this cooking chamber, the electromagnetic waves generated by the magnetron are introduced through a waveguide, which opens into the upper wall, rear wall, or a lateral wall of the cooking chamber itself, depending on the oven model. These waves cause the vibration of water, fat, and sugar molecules within the food, heating them from the inside out and at a much faster rate compared to conventional electric ovens.

[0005] Since electromagnetic waves have a certain directionality, they do not evenly affect the entire internal volume of the cooking chamber but concentrate in areas that absorb microwave energy more effectively. As a result, they fail to uniformly transmit their energy to the food placed inside.

[0006] To eliminate this drawback, various solutions have been proposed. One of these consists of positioning a rotating plate on the floor of the cooking chamber, on which the food container or containers to be heated can be placed. By rotating the plate and the food container(s), their position within the cooking chamber continuously changes, contributing to a more uniform heating effect due to the electromagnetic waves.

[0007] This solution has proven effective but has led to a certain complexity in the construction of the microwave oven due to the need for a support plate for the food container and an electric motor to rotate it. Moreover, the electric motor, in order to move the rotating plate, the food container, and the food placed inside it, must have a certain power, resulting in additional electricity consumption.

[0008] Another known solution to achieve uniform cooking in a microwave oven consists of placing a sort of propeller in front of the waveguide outlet in the cooking chamber. This propeller is set in rotation, and its movement helps to reflect at least part of the electromagnetic waves and to distribute them within the cooking chamber.

[0009] This solution results in lower energy consumption since it does not require the rotation of the food container. However, it still requires a motor to rotate the propeller, which adds a certain complexity to the oven’s construction, increases costs, and introduces a moving component that, like all moving parts, is susceptible to failures and breakages.

[0010] Another known solution consists of introducing electromagnetic waves into the oven through multiple openings, thereby distributing them more evenly throughout the entire internal volume of the cooking chamber. While this approach has effectively solved the problem, it has done so at the expense of increased manufacturing complexity due to the need for a system of waveguides capable of reaching multiple openings in the walls of the cooking chamber.

[0011] JPS4879545U describes a microwave oven featuring a static element inside the cooking chamber, configured to distribute the waves within the chamber itself. However, this solution has shown limitations in terms of heating efficiency and temperature uniformity within the cooking chamber.

[0012] The objective of the invention is to provide a microwave oven that eliminates all the aforementioned drawbacks.

[0013] In particular, the objective of the invention is to propose a microwave oven that, compared to conventional ovens of equal power, has a simpler construction.

[0014] Another objective of the invention is to propose a microwave oven that, compared to conventional ovens of equal power, ensures greater uniformity in the heating of food placed inside the cooking chamber.

[0015] Another objective of the invention is to propose a microwave oven that, compared to conventional ovens of equal power, requires fewer components.

[0016] Another objective of the invention is to propose a microwave oven that, compared to conventional ovens of equal power, has a lower cost.

[0017] Another objective of the invention is to propose a microwave oven that, compared to conventional ovens of equal power, does not result in additional electricity consumption beyond what is necessary for heating the food.

[0018] All these objectives, as well as others that will become apparent from the following description, are achieved jointly or separately, according to the invention, by a microwave oven as defined in claim 1.

[0019] The present invention is further clarified below in some of its preferred embodiments, provided purely by way of example and without limitation, with reference to the attached drawing sheets, in which: figure 1 shows a schematic front view of a microwave oven according to the invention, without the front door. figure 2 shows it in a horizontal section along II - II of Fig. 1. figure 3 shows it in a vertical section along III - III of Fig. 1. figure 4 shows it in a partial perspective front-bottom view, figure 5 shows a perspective view of the static element applied to the upper wall of the cooking chamber of the oven in a first embodiment of the invention, referred to as Type A. figure 6 shows it in a perspective view in a second embodiment of the invention, referred to as Type B. figure 7 shows it in a perspective view in a third embodiment of the invention, referred to as Type C. figure 8 shows it in a perspective view in a fourth embodiment of the invention, referred to as Type D. figure 9 shows it in a perspective view in a configuration not belonging to the invention, referred to as Type E. figure 10 shows a perspective view of a static element according to the invention in a variant of the static element of Type A.

[0020] As seen in Figures 1-5, the microwave oven according to the invention is of a type similar to that of a traditional microwave oven without moving parts for distributing electromagnetic waves inside a cooking chamber 2. However, it may advantageously be provided, at the waveguide outlet opening 4, through which the electromagnetic waves are introduced into the cooking chamber, with a traditional electric resistance 6 and a static element 8 designed to partially interfere with the electromagnetic wave flow in order to modify their distribution within the chamber 2.

[0021] This static element 8 essentially consists of a little metal plate, preferably made of steel, applied inside the upper wall of the cooking chamber 2 at the opening 4. This opening is located approximately at the center of the wall, has a rectangular shape, with its shorter side parallel to the front wall of the oven and measuring approximately 40-45 mm, and its longer side orthogonal to the front wall of the oven, measuring approximately 80-90 mm.

[0022] The cooking chamber 2 has a generally parallelepiped shape and is housed within a chassis 10, from which it is separated on all sides by an air gap. This air gap accommodates all the necessary components for the correct operation of the oven and, in particular, houses the magnetron 12 in its upper section. The magnetron generates electromagnetic waves and directs them through the waveguide into the cooking chamber 2 via the opening 4 located in its upper wall. The plate 8 has an overall elongated rectangular shape, measuring approximately 130- 140 mm x 16-20 mm, and extends into two end sections 14 substantially bent at 90°, ensuring that the plate remains spaced from the upper wall of the cooking chamber by approximately 20-22 mm. These end sections 14 are further bent 90° outward and feature holes 16 for screws, facilitating both installation and removal for potential maintenance operations.

[0023] Near each of the two ends of the main section of the plate 8, an opening 17, preferably circular, with a diameter of approximately 11-13 mm, can advantageously be created. The plate 8 is preferably installed on the upper wall of the cooking chamber 2 with its longer side parallel to the front opening of the same chamber 2 and positioned to cover approximately 25-50% of the opening 4, preferably 30 -35%. The uncovered portion of the opening can be closed with a mica plate or another suitable known material, serving to protect the antenna of the magnetron 12 from the vapors inevitably produced by food during heating or cooking.

[0024] All the above dimensions refer to a conventional microwave oven with a standard-sized cooking chamber 2 of approximately 410 x 230 x 380 mm. These dimensions were determined experimentally through tests aimed at evaluating the oven’s performance in terms of maximum achievable temperatures and temperature distribution within the cooking chamber 2.

[0025] To assess the effect of various characteristics of the plate 8 on the electromagnetic wave flow, and consequently on heating efficiency and uniformity, the invention includes, in addition to the described plate 8 (referred to as Type A for brevity), other plates 8 of different types.

[0026] Specifically, a second type of plate 8 (Type B) is provided, as illustrated in Fig. 6. This plate is also configured with two bent ends, like the previously described Type A plate, to remain spaced from the upper wall of the cooking chamber 2. However, it differs in having a greater width of approximately 24-26 mm and a central section 18 that is further widened toward the oven opening, reaching an overall width of approximately 34-37 mm in this widened central section 18. Additionally, in this widened central section 18, the plate 8 may advantageously include two elongated and aligned openings 20, which are approximately rectangular in shape, measuring about 24-26 mm x 11-13 mm. From one of the two longer sides of each of these rectangular openings 20, specifically the side farther from the oven door, an inwardly extending wing 22 protrudes into the cooking chamber 2. This wing 22 has a curved profile with its concavity facing inward and extends to cover slightly less than half of the corresponding opening 20. Furthermore, at the ends of the free longer edge of the widened central section 18, two lobes 24 project into the cooking chamber 2. These lobes 22 are coplanar with the rest of the plate 8 and are approximately semicircular in shape, with a diameter of 14-16 mm.

[0027] The invention also includes a third type of plate (Type C), illustrated in Fig. 7. Similar to the previous types, it is designed to be applied to the upper wall of the cooking chamber 2 while remaining spaced from it. However, it differs from the Type B plate in that its central section 18 has a constant width, equal to the width that the Type B plate exhibits at the location of the lobes 24.

[0028] Additionally, the invention provides for a fourth type of plate (Type D), illustrated in Fig. 8. This plate has the same shape as the Type B plate but lacks the elongated openings 20 and the wings 22.

[0029] T o assess the effect of the various features of the plates 8 described above, a fifth type of plate (Type E) was also created, as illustrated in Fig. 9. It essentially has the same shape and dimensions as the Type B plate but differs primarily in that it lacks the 90°- bent end sections 14. As a result, it is intended to be applied in a substantially coplanar manner to the upper wall of the cooking chamber 2.

[0030] For further evaluation of the performance of the plate 8 according to the invention compared to a known similar element, a sixth type of plate (Type F) was also created. This plate is entirely similar to the one described in prior document JPS4879545U and, like that one, is intended to be applied in a substantially coplanar manner to the upper wall of the cooking chamber 2, following the installation method indicated in the prior document.

[0031] To compare the performance of the Type A-F plates, they were all subjected to the same tests after being installed in the same manner on the upper wall of the cooking chamber of the same microwave oven.

[0032] In particular, the Type A plate was mounted to cover approximately 30-35% of the opening 4. The Type B, C, and D plates, given their larger size, covered a greater portion of opening 4, estimated to be 40-45%.

[0033] To further evaluate the achievable temperatures within the cooking chamber and their distribution, glasses were placed inside the chamber in the following different arrangements: a. a single glass containing 275 g of water placed at the center of the floor of the cooking chamber. b. four glasses, each containing 50 g of water, positioned at the vertices of a square with sides parallel to the walls of the cooking chamber, plus a fifth glass with the same amount of water placed at the center of the square. c. four glasses, each containing 50 g of water, positioned at the vertices of a square whose diagonal is parallel to the walls of the cooking chamber and has a length equal to the side length of the square in arrangement (b), plus a fifth glass with the same amount of water placed at the center of the square. d. five glasses, each containing 50 g of water, positioned at the vertices of a regular pentagon with a width approximately equal to that of the square in arrangement (b), plus a sixth glass with the same amount of water placed at the center of the pentagon. e. six glasses, each containing 50 g of water, positioned at the vertices of a regular hexagon with a width approximately equal to that of the pentagon in arrangement (d), plus a seventh glass with the same amount of water placed at the center of the hexagon.

[0034] With the different plates 8 and with the different glass arrangements, various tests were then conducted, powering the microwave with a magnetron 12 of 900 W for 120 seconds for the first test and for 60 seconds for the subsequent tests.

[0035] In the table created with the data obtained from the tests, the temperature values and their respective standard deviations o (o = [Z(x - x)2 / n - 1)]1 / 2) for the different types of plate 8 used and for the different glass arrangements inside the cooking chamber are reported. Additionally, the sum of the standard deviations Zo is indicated in the last row, which is indicative of the global behavior of all the glass arrangements in the various tests. In the various tests carried out with multiple glasses of water, the temperature values were referred to the position that each glass had in the corresponding test, which was marked with a number reported in the table itself.

[0036] From the results of the tests, it was observed that: the plate 8 of type A, which is spaced from the upper wall of the cooking chamber 2, allows the best average compromise between maximum reachable temperature and greater heating uniformity inside it. the plate 8 of type B, which is also spaced from the upper wall of the cooking chamber 2 but has a larger surface area and covers the opening 4 to a greater extent, allows slightly lower temperatures compared to those reached with the plate 8 of type A, but with a good temperature uniformity inside the cooking chamber 2. the plate 8 of type C, which is also spaced from the upper wall of the cooking chamber 2 and covers the opening 4 in a manner similar to plate 8 of type B, allows slightly lower temperatures with slightly lower heating uniformity inside the cooking chamber. the plate 8 of type D, which is also spaced from the upper wall of the cooking chamber 2, allows slightly higher temperatures than those reached with plate 8 of type A, but with a temperature uniformity inside the cooking chamber 2 that is intermediate between those of plates 8 of type B and C.

[0037] - the plate 8 of type E, which is applied flush to the upper wall of the oven and does not belong to the invention, exhibited substantially uniform temperatures inside the cooking chamber, but rather low ones.

[0038] - the plate of type F, which is made according to JPS4879545U, exhibited significantly higher temperatures inside the cooking chamber but rather uneven ones.

[0039] In conclusion, the tests carried out revealed the best effects with a plate 8 applied in a spaced condition from the upper wall of the cooking chamber 2 and positioned in such a way as to partially cover the opening 4 formed in it.

[0040] Finally, a plate, illustrated in figure 10, was also created, which is essentially similar to the plate of type A, but unlike it, is devoid of openings 17. The experimental tests revealed that this plate performed better in certain loading conditions of the cooking chamber 2 compared to a plate 8 without openings 17, but in other situations, it showed slightly worse performance. However, it was still better than both the performance of a plate applied flush to the upper wall of the cooking chamber 2 (plate of type E) and the performance of a plate according to JPS4879545U (plate of type F). Therefore, the openings 17 should be considered preferential but not essential. In figures 1-4, the cooking chamber 2 of the oven has been illustrated with an electric resistor 6 applied to its upper wall to integrate, where necessary, microwave cooking with traditional radiant cooking. However, the invention also includes microwave ovens without an electric resistor or with multiple electric resistors, which can be applied to the upper wall of the cooking chamber 2, or even to a different wall of it, or also in the gap between it and the chassis 10, along with a possible fan capable of generating a flow of hot air to be introduced into the cooking chamber 2 through openings formed in its walls.

[0041] If multiple electric resistors are provided, the oven also includes means for controlling the activation of one or the other, or multiple resistors simultaneously, depending on the desired type of cooking.

Claims

C L A I M S1 . Microwave oven with a magnetron (12), which generates electromagnetic waves and, through a waveguide (6), directs them into a cooking chamber (2) formed inside a chassis (10), which delimits, together with said cooking chamber (2), a gap in which said magnetron (12) and said waveguide (6) are housed, which waveguide (6) exits through an opening (4) located substantially centrally in the upper wall of said cooking chamber (2), characterized in that a metal plate (8) is applied to the upper wall of said cooking chamber( )2, kept spaced about 20-22 mm from said upper wall and positioned in such a way as to partially cover said opening (4).

2. Microwave oven according to claim 1 , characterized in that said plate (8) is positioned in such a way as to cover from 30% to 35% of said opening (4).

3. Oven according to claim 1 and / or 2, characterized in that said plate (8) is provided with two folded terminal portions (14) for its mounting distanced from the upper wall of said cooking chamber (2).

4. Oven according to claim 3, characterized in that said plate is provided, near each of said terminal portions (14), with an opening (17) preferably circular in shape.

5. Oven according to claim 4, characterized in that each circular opening (17) made in said plate (8) has a diameter of approximately 11 - 13 mm.

6. Microwave oven according to one or more of the preceding claims, characterized in that said plate (8) has a length of approximately 130 - 140 mm, and in the mounted condition this dimension is parallel to the front opening of said cooking chamber (2).

7. Microwave oven according to one or more of the preceding claims, characterized in that said plate (8) has a width of approximately 16 - 20 mm measured in the anteroposterior direction of said cooking chamber (2).

8. Microwave oven according to one or more of claims 1 to 6, characterized in that said plate (8) has a width between 16 and 53 mm measured in the anteroposterior direction of said cooking chamber (2).

9. Microwave oven according to one or more of the preceding claims, characterized in that said plate (8) has a width of approximately 34 - 37 mm measured in the anteroposterior direction of said cooking chamber (2) and is provided with a pair of elongated apertures (20), aligned in the direction of the longitudinal development of the plate itself and having dimensions of 24 - 26 x 11 - 13 mm.

10. Microwave oven according to claim 9, characterized in that said plate (8) has a width of 34 - 37 mm and is provided, on the side facing the oven opening, with two lobes (24) coplanar with the plate itself and directed towards the front opening of said cooking chamber (2).

11. Microwave oven according to claim 10, characterized in that said lobes (24) are positioned at the ends of the major side of the plate (8), have a substantially semicircular shape, and a diameter of 14 - 16 mm.

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

13. Microwave oven according to claim 12, characterized in that said wing (22) has a concavity facing the interior of said cooking chamber 2.

14. Microwave oven according to one or more of the preceding claims, characterized in that the portion of said opening (4) of said waveguide (6) not covered by said plate (8) is provided with a protective plate element for shielding the antenna of said magnetron (12) from cooking vapors.

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

16. Microwave oven according to one or more of the preceding claims, characterized in that it further comprises at least one electric resistance (6) aimed at integrating microwave cooking with radiant cooking.

17. Microwave oven according to one or more of the preceding claims, characterized in that it houses at least one electric resistance (6) in the gap delimited by said chassis (10) and said cooking chamber (2), and optionally a fan to generate a flow of hot air to be introduced into said cooking chamber (2) through holes provided in at least one wall of it.

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