EP3090604A1

EP3090604A1 - Improved microwave leakproof door for combination convection/microwave oven

Info

Publication number: EP3090604A1
Application number: EP13823958.7A
Authority: EP
Inventors: Metin Gur; Mehmet Baris Gocer; Yalcin Yaman
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2013-12-30
Filing date: 2013-12-30
Publication date: 2016-11-09
Anticipated expiration: 2033-12-30
Also published as: WO2015101396A1; EP3090604B1; CN105850227A

Abstract

The present invention relates to a door (1) suitable for use in a combination convection/ microwave oven (2) comprising a cooking cavity (3) enclosed by a cavity wall (4) which is formed from a first metal lining (5), wherein the cooking cavity (3) has an opening (6) and a front wall (7) which is formed from a second metal lining (8), wherein the first metal lining (5) and the second metal lining (8) respectively have an inwardly bent first segment (9) and an inwardly bent second segment (10) which abut each other outside the cooking cavity (3) circumferentially around the opening (6).

Description

IMPROVED MICROWAVE LEAKPROOF DOOR FOR COMBINATION CONVECTION/MICROWAVE OVEN

The present invention relates to a door for use in a domestic cooking oven which has a microwave facility. The present invention particularly relates to a door for use in a combination convection/microwave oven.
The microwave cooking technology enables rapid and energy efficient cooking of food. In the microwave cooking technology the food is subjected to microwave radiation which causes polarized molecules in the food to vibrate and produce heat. As the microwave radiation easily penetrates into the food, the entire food can be instantly and uniformly heated. Thereby the food can be quickly and uniformly cooked.
A drawback of the microwave cooking technology is that the oven must be properly sealed to prevent the microwave radiation from leaking to an outside. The cooking cavity acts as a Faraday cage. However, a small fraction of the microwave radiation typically leaks through the apertures between the door and the cooking cavity. The microwave radiation which leaks to an outside poses severe risks to the health of users and can cause burns and permanent damages. Therefore, compliance with the maximum permissible leakage limit is of utmost importance. This leakage limit is generally prescribed by the competent authorities.
A commonly known technique is to seal the aperture between the door and the cooking cavity by utilizing a microwave sealing choke which is usually mounted on a periphery of the door so as to oppose a metal front wall around the opening of the cooking cavity. The microwave sealing choke includes a plurality of resonant cavities which receive the microwave radiation which propagates along the metal front wall to an outside. The radiation is attenuated by the resonant cavities.
EP1333703A2 discloses a microwave oven which has a microwave sealing choke. The microwave sealing choke is arranged onto the periphery of the door so as to oppose the metal front wall.
Another drawback of the microwave cooking technology is that it is not possible to obtain gastronomic results that can be typically obtained by conventional cooking ovens which utilize convective heat transfer. Therefore, the so called “combination ovens” have devised which allow cooking by convective heat transfer and/or microwave radiation. Thereby, the user can selectively apply any of the above-mentioned cooking technologies to the food to achieve the best cooking results.
In general, the temperatures reached during microwave cooking are relatively lower than the temperatures reached during cooking by convective heat transfer. Therefore, in a combination convection/microwave oven, when the food is cooked by convective heat transfer, the temperature reached inside the cooking cavity reaches relatively high levels in particular during baking, grilling or the like in comparison to sole microwave cooking. The heat produced in the cooking cavity is radiated off by conductive heat transfer to the front metal wall, and therefrom to the critical electrical components like the user-interface, the control unit or the like which are typically installed into the front wall. Certain temperature limits must be observed for the proper operation of these electrical components. Therefore, the electrical components parts must be suffiently cooled. However, the cooling process increases the energy consumption of the oven.
To reduce the demand for cooling, the front wall could be modified to become less heat conductive. However this impairs electrical conductivity of the front wall and, in turn, the microwave sealing performance degrades. Thus, it becomes difficult to comply with the standard requirements on the maximum permissible microwave leakage limits.
An objective of the present invention is to provide a door suitable for use in a combination convection/microwave oven and a combination convection/microwave oven which overcome the aforementioned drawbacks of the prior art and which is improved both in thermal and microwave leakproofing.
This objective has been achieved by the door according to the present invention as defined in claim 1, and the combination convection/microwave oven according to the present invention as defined in claim 10. Further achievements have been attained by the subject-matters respectively defined in the dependent claims.
The door of the present invention is suitable for use in a combination convection/ microwave oven which has a front wall and a cooking cavity enclosed by a cavity wall. In the combination convection/ microwave oven of the present invention, a first metal lining which forms the cavity wall and a second metal lining which forms the front wall respectively have an inwardly bent first segment and an inwardly bent second segment which abut each other outside the cooking cavity circumferentially around an opening of the cooking cavity. Thus, the heat transfer from the cavity wall to the front wall has been diminished through the discontinuously abutting segments. The door of the present invention has an inner metal wall which includes a straight portion and an inwardly bent portion. In the door of the present invention, the straight portion is configured to circumferentially oppose directly the inwardly bent first segment and the inwardly bent second segment through a gap whereas the inwardly bent portion is configured to circumferentially protrude into the cooking cavity along an edge of the opening so as to directly oppose the first metal lining through a gap. The inwardly bent portion contributes via the straight portion to the sealing performance of a microwave sealing choke formed on the lateral metal walls of the door which is configured to circumferentially oppose the front wall through a gap. Thus, the inwardly bent portion, the straight portion and microwave sealing choke arranged on the lateral metal walls effectively act as a single microwave sealing choke. Thereby, the reduction in the sealing performance of the microwave sealing choke arranged on the lateral metal walls due to the deterioration of the thermal and the electrical conductivity across the abutting segments has been compensated by the inwardly bent portion.
In an embodiment, the overall shape of the inwardly bent portion is convex or alternatively concavo-convex.
In another embodiment, a penetration depth of the inwardly bent portion which protrudes into the cooking cavity is equal to or less than a critical value where the inwardly bent portion starts to function like a waveguide. This is determined with respect to a cut-off frequency of the inwardly bent portion. The critical value largely depends, among others, on a main frequency of the magnetron which is typically around 2.45 GHz. In a version of this embodiment, the critical value is about eight millimeters, and an optimum sealing performance is attained the when the penetration depth ranges from two millimeters to eight millimeters.
In another embodiment, the inwardly bent first segment and the inwardly bent second segment are spot welded at predetermined intervals circumferentially around the opening of the cooking cavity. Thereby the heat conductivity is effectively reduced. In an alternative embodiment, the inwardly bent first segment and the inwardly bent second segment are connected by mechanical means such as screws, snap-fittings, claws, or the like.
In another embodiment, the door has a monolithic metal frame. Thereby a manufacturing of the door has been simplified. In addition, this improves the overall microwave sealing performance.
By the present invention, a combined convection/microwave cooking oven has been provided in which the front wall has been protected from excessive thermal radiation of the cooking cavity. By the present invention, a microwave sealing choke has been provided which reduces microwave leakage below a maximum permissible leakage limit. Thereby, optimum operation conditions for the electrical components have been established without compromising the microwave sealing performance.
Additional advantages of the door according to the present invention and the combination convection/microwave oven of the present invention will become apparent with the detailed description of the embodiments with reference to the accompanying drawing in which:
Figure 1 - is a schematic cross sectional partial side view of a combination convection/microwave oven which has a door according to an embodiment of the present invention, taken along a vertical direction.
The reference signs appearing on the drawings relate to the following technical features.

Door
Oven
Cooking cavity
Cavity wall
First metal lining
Opening
Front wall
Second metal lining
First segment
Second segment
Lateral metal wall
Sealing choke
First gap
Inner metal wall
Straight portion
Second gap
portion
Edge
Third gap
Third metal lining
Door frame
Screen portion
Tapered shoulder
Arc-shaped shoulder
LC resonant cavity
Slot

The door (1) is suitable for use in a combination convection/microwave oven (2). The combination convection/microwave oven (2) comprises a cooking cavity (3) which is enclosed by a cavity wall (4), wherein the cooking cavity (3) has an opening (6), and wherein the cavity wall (4) is formed from a first metal lining (5), the door (1) which is pivotably arranged to open/close the opening (6) of the cooking cavity (3), a front wall (7) which is formed from a second metal lining (8), one or more than one electrical resistance (not shown) for convectively heating food inside the cooking cavity (3), a microwave magnetron (not shown) for radiative heating of food inside the cooking cavity (3), a user interface (not shown) for receiving user inputs and for audibly and/or visually outputting information and a control unit (not shown) for controlling the electrical resistance, the magnetron and the user interface .
In the combination convection/microwave oven (2) according to the present invention the first metal lining (5) and the second metal lining (8) respectively have an inwardly bent first segment (9) and an inwardly bent second segment (10) which abut each other outside of the cooking cavity (3) and circumferentially around the opening (6). Thereby, the heat conductivity from the cavity wall (4) to the front wall (7) is effectively reduced and the heat dissipation from the cooking cavity (3) to the front wall (7) is improved.
The door (1) comprises lateral metal walls (11) which include a microwave sealing choke (12) configured to circumferentially oppose the front wall (7) through a first gap (13).
The door (1) of the present invention further comprises an inner metal wall (14) which includes a straight portion (15) and an inwardly bent portion (17). The straight portion (15) is configured to circumferentially oppose directly the inwardly bent first segment (9) and the inwardly bent second segment (10) through a second gap (16). The inwardly bent portion (17) is configured to circumferentially protrude into the cooking cavity (3) along an edge (18) of the opening (6) so as to directly oppose the first metal lining (5) through a third gap (19).
In an embodiment, the overall shape of the inwardly bent portion (17) is convex. In an alternative embodiment, the overall shape of the inwardly bent portion (17) is concavo-convex.
In another embodiment, the lateral metal walls (11) and the inner metal wall (14) are integrally formed from a third metal lining (20). In this embodiment, the microwave sealing choke (12), the straight portion (15), and the inwardly bent portion (17) constitute a monolithic metal door frame (21). In a version of this embodiment, the monolithic door frame (21) is formed by pressing and bending. Thereby, a manufacturing process of the door (1) becomes simple and cost effective.
In another embodiment, the inner metal wall (14) further includes a perforated metal screen portion (22). The preformation is suffiently large to enable a user to observe the cooking cavity (3) and sufficiently small to keep the microwave leakage below permissible limits i.e., maximum 1.4 mW/cm^2. In this embodiment, the perforated metal screen portion (22) is circumferentially surrounded by the inwardly bent portion (17).
In another embodiment, the perforated metal screen portion (22) is outwardly offset relative to the inwardly bent portion (17) by a predetermined distance. Thereby an inner volume of the cooking cavity (4) is increased, and a microwave sealing performance of the inwardly bent portion is increased.
In another embodiment, the perforated metal screen portion (22) and the straight portion (15) lie in a same plane.
In another embodiment, the inwardly bent portion (17) includes one or more than one tapered shoulder (23) and an arc-shaped shoulder (24). In this embodiment, the tapered shoulders (23) adjoin the perforated metal screen portion (22) whereas an arc-shaped shoulder (24) joins the straight portion (15). In this embodiment, the overall shape of the inwardly bent portion (17) is concavo-convex. In a version of this embodiment, the arc-shaped shoulder (24) and the edge (18) have matching outlines in order to improve the microwave sealing performance.
In another embodiment, a penetration depth (D) of the inwardly bent portion (17) which protrudes into the cooking cavity (3) ranges between two millimeters to eight millimeters. This specific range largely depends, among others, on a size and shape of the cooking cavity (3). Above eight millimeters, the inwardly bent portion (17) may start functioning like a waveguide, and thus the sealing performance may degrade. Similarly below 2 millimeters the sealing performance may be insufficient. Thus an optimum sealing performance is attained the when the penetration depth (D) ranges from two millimeters to eight millimeters.
In another embodiment, the microwave sealing choke (12) includes a plurality of LC resonant cavities (25) which are successively formed at predetermined intervals along a circumferential direction on the lateral walls. Each LC resonant cavity has one or more than one slot (26) which opposes the front wall (7). The resonant frequency is adjusted in accordance with a main frequency of the magnetron. A typical value for the magnetron frequency is 2.45 GHz.
The present invention also provides a combination convection/microwave oven (2) which has the door (1).
In another embodiment, the inwardly bent first segment (9) and the inwardly bent second segment (10) are spot welded at predetermined intervals circumferentially around the opening (6) of the cooking cavity (3). Throughout the predetermined interval, the first/second segments (9, 10) are not continually welded. Thereby, the conductive heat transfer can be considerably reduced. The predetermined interval largely depends on the size of the front wall (7), the cavity wall and the wattage of the oven (2).
In another embodiment, the predetermined interval which separates two successive spot-welding is equal to or less than four centimeters.
In another embodiment, the predetermined interval is about three centimeters. In a version of this embodiment the predetermined interval is exactly three centimeters.
In another embodiment, the control unit and the user interface are arranged on the front wall (7). By virtue of the improved thermal dissipation, the electrical components of the control unit and the user interface can be operated within optimum temperature limits.
In another embodiment, the control unit has a plurality of modes including at least three modes. The first mode is suitable for cooking food by convective heat transfer only. The second mode is suitable for cooking food by microwave radiation only. The third mode is suitable for cooking food by convective heat transfer and microwave radiation in combination.
By the present invention, a combined convection/microwave cooking oven has been provided in which the front wall has been protected from excessive thermal radiation of the cooking cavity. By the present invention, a microwave sealing choke has been provided which reduces microwave leakage below a maximum permissible leakage limit. Thereby, optimum operation conditions for the electrical components have been established without compromising microwave sealing. By the present invention, the oven can be reliably operated even at the highest designated operation temperatures. Hence the temperature of the exposed parts and the internal parts can be safely kept below critical threshold values.

Claims

A door (1) suitable for use in a combination convection/microwave oven (2) comprising a cooking cavity (3) enclosed by a cavity wall (4) which is formed from a first metal lining (5), wherein the cooking cavity (3) has an opening (6) and a front wall (7) which is formed from a second metal lining (8), wherein the first metal lining (5) and the second metal lining (8) respectively have an inwardly bent first segment (9) and an inwardly bent second segment (10) which abut each other outside the cooking cavity (3) circumferentially around the opening (6), the door (1) comprising lateral metal walls (11) which include a microwave sealing choke (12) configured to circumferentially oppose the front wall (7) through a first gap (13), the door (1) being characterized by further comprising an inner metal wall (14) which includes

- a straight portion (15) configured to circumferentially oppose directly the inwardly bent first segment (9) and the inwardly bent second segment (10) through a second gap (16) and

- an inwardly bent portion (17) configured to circumferentially protrude into the cooking cavity (3) along an edge (18) of the opening (6) so as to directly oppose the first metal lining (5) through a third gap (19).
The door (1) according to claim 1, characterized in that the lateral metal walls (11) and the inner metal wall (14) are integrally formed from a third metal lining (20) such that the microwave sealing choke (12), the straight portion (15), and inwardly bent portion (17) constitute a monolithic metal door frame (21).
The door (1) according to claim 1 or 2, characterized in that the inner metal wall (14) further includes a perforated metal screen portion (22), wherein the perforated metal screen portion (22) is circumferentially surrounded by the inwardly bent portion (17).
The door (1) according to claim 3, characterized in that the perforated metal screen portion (22) is outwardly offset relative to the inwardly bent portion (17) by a predetermined distance.
The door (1) according to claim 3 or 4, characterized in that the perforated metal screen portion (22) and the straight portion (15) lie in a same plane.
The door (1) according to any one of claims 3 to 5, characterized in that the inwardly bent portion (17) includes one or more than one tapered shoulder (23) which adjoins the perforated metal screen portion (22) and an arc-shaped shoulder (24) which joins the straight portion (15).
The door (1) according to any one of claims 1 to 6, characterized in that a penetration depth (D) of the inwardly bent portion (17) which protrudes into the cooking cavity (3) ranges between two millimeters to eight millimeters.
The door (1) according to any one of claims 1 to 7, characterized in that the microwave sealing choke (12) includes a plurality of LC resonant cavities (25) which are successively formed at predetermined intervals along a circumferential direction onto the lateral walls, wherein each LC resonant cavity has one or more than one slot (26) which opposes the front wall (7).
The door (1) according to any one of claims 2 to 7, characterized in that the monolithic door frame (21) is formed by pressing and bending.
A combination convection/microwave oven (2) comprising a cooking cavity (3) enclosed by a cavity wall (4) which is formed from a first metal lining (5), wherein the cooking cavity (3) has an opening (6), a front wall (7) which is formed from a second metal lining (8), one or more than one electrical resistance for convectively heating food inside the cooking cavity (3), a microwave magnetron for radiative heating of food inside the cooking cavity (3), a user interface for receiving user inputs and for audibly and/or visually outputting information and a control unit for controlling the electrical resistance, the magnetron and the user interface, the combination convection/microwave oven (2) being characterized by further comprising a door (1) as defined in any one of claims 1 to 9, which is pivotably arranged to open/close the cooking cavity (3), wherein the first metal lining (5) and the second metal lining (8) respectively have an inwardly bent first segment (9) and an inwardly bent second segment (10) which abut each other outside of the cooking cavity (3) and circumferentially around the opening (6).
The combination convection/microwave oven (2) according to claim 10, characterized in that the inwardly bent first segment (9) and the inwardly bent second segment (10) are spot welded at predetermined intervals circumferentially around the opening (6) of the cooking cavity (3).
The combination convection/microwave oven (2) according to claim 11, characterized in that said predetermined interval is equal to or less than four centimeters.
The combination convection/microwave oven (2) according to claim 11 or 12, characterized in that said predetermined interval is about three centimeters.
The combination convection/microwave oven (2) according to any one of claims 10 to 13, characterized in that the control unit and the user interface are installed into the front wall (7).
The combination convection/microwave oven (2) according to claim 14, characterized in that the control unit has a plurality of modes including a first mode for cooking food by convective heat transfer only, a second mode for cooking food by microwave radiation only and a third mode for cooking food by convective heat transfer and microwave radiation in combination.