Patent Publication Number: US-6713740-B2

Title: Microwave oven having heaters for cooking food

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Application No. 2002-49034, filed Aug. 19, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a microwave oven, and more particularly, to a microwave oven which is designed such that an upper heater and one or more middle heaters are installed at upper and middle portions in a cooking cavity, respectively, and food holding members are slidably provided between the upper and middle heaters and between the middle heaters and a bottom of the cooking cavity, respectively, thus heating the upper and lower parts of the food at the same time, and cooking one or more foods at the same time. 
     2. Description of the Related Art 
     A microwave oven is an appliance which cooks and/or heats food laid in a cooking cavity using high-frequency electromagnetic waves generated by an oscillation of a magnetron installed in a machine room. That is, the high-frequency electromagnetic waves penetrate food laid in the cooking cavity so as to repeatedly change a molecular arrangement of moisture in the food. The food is cooked by frictional heat generated by molecules. 
     However, when food is cooked using only the high-frequency electromagnetic waves, the high-frequency electromagnetic waves do not uniformly penetrate the food. Instead penetration of the food is according to content or distribution of the moisture of the food and a size of the food. Thus, the food is not satisfactorily cooked when using only the high-frequency electromagnetic waves and to cook the food in a variety of manners may not be possible. In order to solve such problems, a microwave oven is provided with a heater at an upper portion in a cooking cavity thereof, thus cooking the food by high-frequency electromagnetic waves, and rapidly and uniformly cooking the food by heat generated from the heater, as well as browning a surface of the food by heat of a high temperature generated from the heater. 
     FIG. 1 schematically shows a conventional microwave oven having a heater at an upper portion of a cooking cavity. As shown in FIG. 1, the conventional microwave oven comprises a cooking cavity  1  and a machine room  2 . The cooking cavity  1  defines a space for cooking food. Several electrical devices, including a magnetron  3  to generate high-frequency electromagnetic waves, are installed in the machine room  2 . 
     A heater  4  heating the food to be cooked is installed at the upper portion of the cooking cavity  1 . A turntable-type cooking tray  5  is installed at a lower portion of the cooking cavity  1 . A motor  6  to rotate the turntable-type cooking tray  5  is installed under a bottom of the cooking cavity  1 . The food to be cooked is laid on the turntable-type cooking tray  5 , and the motor  6  rotates the turntable-type cooking tray  5 . 
     The method of cooking the food using a conventional microwave oven constructed, as above described, is as follows. As the magnetron  3  and the motor  6  are operated, the cooking tray  5  on which the food is laid is rotated at a low speed. At this time, high-frequency electromagnetic waves penetrate the food to cook the food. Further, when the heater  4  installed at the upper portion in the cooking cavity  1  is operated, the food is cooked by heat generated from the heater  4 . As such, when the heater  4  and the magnetron  3  are operated at the same time, the food is rapidly cooked by the heat of the heater  4  and the high-frequency electromagnetic waves. 
     However, since the conventional microwave oven is provided at the upper portion in the cooking cavity with only one heater, the distance between the heater and the food is large in the case of cooking small-sized food, so heat generated from the heater is not effectively transmitted to the food. Moreover, since heat is not sufficiently transmitted to a lower part of the food, the food must be turned upside down during a cooking process so as to desirably cook and brown the lower part of the food, thereby making cooking the food inconvenient using the conventional microwave oven. 
     Further, since the conventional microwave oven is designed such that the cooking cavity forms a single cooking space to cook the food, which is laid on the cooking tray, cooking several foods at one time, is not possible so cooking the food takes a long time. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an aspect of the present invention to provide a microwave oven, which is designed to heat upper and lower parts of food at a same time so that turning the food upside down during a cooking process is not needed. 
     Another aspect is to provide a microwave oven, which is designed to removably mount one or more food holding members in a cooking cavity, thus cooking several foods at a same time. 
     Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In order to accomplish the above and other aspects, a microwave oven, comprising a cooking cavity defined by a rear wall, sidewalls, an upper wall and a bottom wall, and a cooking tray installed on the bottom wall of the cooking cavity, wherein an upper heater is installed at a position adjacent to the upper wall of the cooking cavity, and one or more middle heaters are rotatably installed on the rear wall at positions between the upper heater and the cooking tray, upper supports are provided between the upper heater and the middle heaters so as to horizontally protrude from each of the sidewalls, and lower supports are provided between the middle heaters and the cooking tray so as to horizontally protrude from each of the sidewalls, whereby a food holding unit is removably mounted on the upper and lower supports. 
     In the microwave oven, a projection is provided on a sidewall of the cooking cavity at a position above the upper supports so as to protrude by a predetermined length toward a center of the cooking cavity, thus preventing the food holding unit from tilting downwards and falling to the floor when the food holding unit slides out of the cooking cavity. 
     In the cooking cavity, a vertical step is provided at a position between the upper and lower supports so as to be positioned at a front portion of a sidewall of the cooking cavity, thus preventing the food holding unit from colliding with the middle heaters when putting the food holding unit between the upper and lower supports. 
     The food holding unit comprises a first food holding member fabricated in a form of a wire rack and a second food holding member fabricated in a form of a tray. 
     A tube made of a nonconductive and heat-resistant material is fitted over each side end of the first food holding member so that the tube comes into contact with the upper supports or the lower supports when the first food holding member is mounted in the cooking cavity, thus preventing sparks from arcing between the first food holding member and the upper supports or the lower supports, and allowing the first food holding member to smoothly slide in and out of the cooking cavity. 
     A stopper having a predetermined length extends from a central portion of each of front and rear ends of the first food holding member, thus allowing the first food holding member to be spaced apart from the rear wall of the cooking cavity by a predetermined length. 
     A flange downwardly extends along an edge of the second food holding member to have a predetermined width so that the flange lays on the upper supports or the lower supports when the second food holding member slides in and out of the cooking cavity. 
     At least one tube made of a nonconductive and heat-resistant material is fitted over a lower end of the flange so that the tube comes into contact with the upper supports or the lower supports when the second food holding member is mounted in the cooking cavity, thus preventing sparks from arcing between the second food holding member and the upper supports or the lower supports, and allowing the second food holding member to smoothly slide in and out of the cooking cavity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a front sectional view showing a conventional microwave oven having a heater at an upper portion in a cooking cavity; 
     FIG. 2 is a front sectional view showing a microwave oven according to an embodiment of the present invention, the microwave oven provided such that an upper heater and one or more middle heaters are installed at an upper portion and a middle portion in a cooking cavity, respectively, and upper and lower supports are provided between the upper heater and the one or more middle heaters and between the one or more middle heaters and a bottom wall of the cooking cavity, respectively, to support a first food holding member and a second food holding member, respectively; 
     FIG. 3 is a perspective view of the first food holding member according to the embodiment of the present invention, the first food holding member being fabricated in a form of a wire rack; 
     FIG. 4A is a bottom perspective view of the second food holding member according to the embodiment of the present invention, the second food holding member being fabricated in a form of a tray; 
     FIG. 4B is an exploded view of the area A in FIG. 4A; 
     FIG. 5 is a view corresponding to FIG. 2, but showing the microwave oven the embodiment of the present invention, with the first food holding member and the second food holding member being seated on upper supports and lower supports, respectively; and 
     FIG. 6 is a partial perspective view showing the microwave oven of the embodiment of the present invention, with the first food holding member being stopped by a projection, which is provided above the upper support, when the food holding member tilts downward. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     FIG. 2 is a front sectional view showing a microwave oven according to an embodiment of the present invention, the microwave oven being provided such that an upper heater and one or more middle heaters are installed at an upper portion and a middle portion in a cooking cavity, respectively, and upper supports and lower supports are provided between the upper heater and the one or more middle heaters and between the one or more middle heaters and a bottom wall of the cooking cavity, respectively, to support a first food holding member and a second food holding member, respectively. 
     As shown in FIG. 2, the microwave oven comprises a machine room  10  and a cooking cavity  20 . Several electrical devices, including a magnetron  11 , are installed in the machine room  10  so as to generate high-frequency electromagnetic waves. The housing of the microwave oven is partitioned into the machine room  10  and the cooking cavity  20  which defines a space to cook the food. High-frequency electromagnetic waves generated by the magnetron  11  are transmitted to the cooking cavity  20  to cook the food, which is placed in the cooking cavity  20 . 
     The cooking cavity  20  is defined by a rear wall  21 , left sidewall  22  and right sidewall  23 , an upper wall  24  and a bottom wall  25 , and is open at a front of the cooking cavity  20 . A door (not shown) is mounted to the open front so as to selectively open the cooking cavity  20 . A turntable-type cooking tray  26  and a motor  27  are installed at positions above and under the bottom wall  25  of the cooking cavity  20 , respectively. The food to be cooked is placed on the turntable-type cooking tray  26 . 
     An upper heater  31  is installed at a position adjacent to the upper wall  24  of the cooking cavity  20  and emits heat of a high temperature downwardly in the cooking cavity  20 . One or more middle heaters  32  are installed between the upper heater  31  and the turntable-type cooking tray  26  and emit heat of a high temperature upwardly and downwardly in the cooking cavity  20 . That is, the upper heater  31  is positioned at an upper portion in the cooking cavity  20 , and the one or more middle heaters  32  are positioned between the upper heater  31  and the turntable-type cooking tray  26 . Thus, heat is transmitted to upper and lower parts of the food placed between the upper heater  31  and the one or more middle heaters  32 . Further, heat is transmitted to the upper part of the food placed between the one or more middle heaters  32  and the turntable-type cooking tray  26 . 
     Each of the one or more middle heaters  32  is fixed to one rotating member of a pair of rotating members  33  which are rotatably installed on the rear wall  21  of the cooking cavity  20 . As the rotating members  33  are rotated by a drive unit (not shown) which is installed outside the cooking cavity  20 , the one or more middle heaters  32  may be rotated between vertical closed positions, respectively, for which the one or more heaters  32  face the side walls  22  and  23 , as shown in FIG. 2, and horizontal open positions, respectively, for which the one or more heaters  32  are directed to a center of the cooking cavity  20  as shown in FIG.  5 . 
     A pair of upper supports  34  is provided between the upper heater  31  and the one or more middle heaters  32  so as to horizontally and inwardly protrude from the left and right sidewalls  22  and  23 , respectively. The pair of upper supports  34  supports a first food holding member  50  or a second food holding member  60  described hereinafter (see FIGS. 3,  4 A and  4 B) so as to slide in and out of the cooking cavity  20 . In the similar manner as the upper supports  34 , a pair of lower supports  35  are provided between the one or more middle heaters  32  and the turntable-type cooking tray  26  so as to horizontally and inwardly protrude from the left and right sidewalls  22  and  23 , respectively. The pair of lower supports  35  support the first food holding member  50  or the second food holding member  60  so as to allow the first food holding member  50  or the second food holding member  60  to slide in and out of the cooking cavity  20 . 
     The first and second food holding members  50  and  60  are removably seated on the upper and lower supports  34  and  35 , thus allowing one or more food items to be cooked in the cooking cavity  20 . 
     A projection  36  is provided on a front portion of the left sidewall of the cooking cavity  20  at a position above one of the upper supports  34  and is spaced apart from the one upper support  34  by a predetermined interval. The projection  36  horizontally protrudes by a predetermined length toward the center of the cooking cavity  20 . When the first food holding member  50  or the second food holding member  60 , which is seated on the upper supports  34 , slides out of the cooking cavity  20 , the projection  36  prevents the first food holding member  50  or the second food holding member  60  from tilting excessively downward and falling to the floor due to the weight of the food (see FIG.  6 ). The projection  36  may be installed on the right sidewall  23  in place of the left sidewall  22  or two projections  36  may be installed on the left and right sidewalls  22  and  23 , respectively. 
     A vertical step  37  is provided at a position between the upper and lower supports  34  and  35  so as to be positioned at the front portion of the left sidewall  22 , and prevents the first food holding member  50  or second food holding member  60  from interfering with the one or more middle heaters  32  which are positioned between the upper and lower supports  34  and  35 . As shown in FIG. 2, the vertical step  37  is designed to be slightly longer than each middle heater  32 , in a vertical length, when each middle heater  32  is placed at closed positions at which the one or more middle heaters  32  face the left sidewall  22  or the right sidewall  23 , so that the first holding member  50  or second food holding member  60  is prevented from being undesirably in contact with the one or more middle heaters  32 , thus preventing damage to the first and second food holding members  50  and  60 . 
     FIG. 3 is a perspective view of the first food holding member  50  according to the present invention. As shown in the FIG. 3, the first food holding member  50  is fabricated in a form of a wire rack, which has spaces, opened to a top and a bottom. The first food holding member  50  comprises front and rear bars  51 , two side bars  52 , and a plurality of support bars  53  formed into a single structure with a rectangular shape. In this case, the support bars  53  are arranged at regular intervals in a space defined by the front and rear bars  51  and the two side bars  52  which form edges of the first food holding member  50 . The first food holding member  50  having such a construction may be used to cook some kinds of food, such as fish or meat, which are placed on the support bars  53 , by heat of the upper heater  31  and the one or more middle heaters  32  or the high-frequency electromagnetic waves. 
     A stopper  54  having a semi-circular cross-section is provided at a central portion of each of front and rear bars  51  so as to horizontally extend from the front and rear bars  51  by a predetermined length. The stopper  54  makes one of the front or rear bars  51  be spaced apart from the rear wall  21  of the cooking cavity  20  by a predetermined length when the first food holding member  50  is installed in the cooking cavity  20 , to prevent sparks from arcing between one of the front or rear bars  51  and the rear wall  21  and to effectively transmit heat from the upper heater  31  and the one or more middle heaters  32  to the food placed on the first food holding member  50 . 
     A tube  55  made of a nonconductive and heat-resistant material is fitted over each of the side bars  52  of the first food holding member  50 . The tubes  55  allow the first food holding member  50  to come into contact with the upper supports  34  or the lower supports  35  when the first food holding member  50  is seated on the upper supports  34  or lower supports  35 , respectively, thus preventing sparks from arcing between the first food holding member  50  and the upper supports  34  or lower supports  35 , and allowing the first food holding member  50  to smoothly slide in and out of the cooking cavity  20  without wearing out the upper supports  34  or lower supports  35 . 
     The tubes  55  are made of a nonconductive and heat-resistant material and may be made of Teflon. 
     Since each of the stoppers  54  provided at the front and rear bars  51  is in spot-contact with the rear wall  21 , there are few sparks and little abrasion between the rear wall  21  of the cooking cavity  20  and the stopper  54 . But, when the tubes  55  are fitted over the stoppers  54 , sparks and abrasion are more effectively prevented. 
     The first food holding member  50  is constructed with open spaces between the bars  51 ,  52  and  53 , thus uniformly cooking and browning the upper and lower surfaces of the food and effectively removing grease when cooking some kinds of food, such as fish or meat. 
     FIG. 4A is a bottom perspective view showing a second food holding member  60  according to the embodiment of the present invention. As shown in the FIG. 4A, a food reception part  61  is concavely and downwardly provided on the second food holding member  60  to create a rectangular tray structure, and receives food to be cooked. The second food holding member  60  has front and rear flanges  62  and two side flanges  63 , which downwardly extend from an edge of the second food holding member  60 . That is, the side flanges  63  of the second food holding member  60  are primarily seated on the upper supports  34  or lower supports  35  provided in the cooking cavity  20  and then slide in and out of the cooking cavity  20  so that the second food holding member  60  is installed in and removed from the cooking cavity  20 . 
     As shown in FIG. 4B, in the same manner as the first food holding member  50 , tubes  66 , which are made of a nonconductive and heat-resistant material, are fitted over front and rear portions of the side flanges  63  at predetermined positions so as to prevent sparks from being produced when cooking food placed on the second food holding member  60  seated on the upper supports  34  or the lower supports  35 . Each of the tubes  66  is held on a side flange  63  of the second food holding member  60  as the sidewall of each of the tubes  66  is inserted into a respective longitudinal hole  64  which is formed at a predetermined position of the front and rear portions of the side flange  63  of the second food holding member  60 . A lug  65  horizontally and inwardly projects from an edge of each of the side flanges  63  at a position around each longitudinal hole  64  so that the sidewall of each of the tubes  66  is inserted into the respective longitudinal hole  64  as an inner surface of each of the tubes  66  is locked to the lug  65 , thus locking the tubes  66  to each of the respective longitudinal holes  64  without allowing an unexpected movement of each of the respective tubes  66 . Each of the tubes  66  may be made of Teflon which is heat-resistant and non-conductive in the same manner as the tubes  55  of the first food holding member  50 . 
     Although the tubes  66  are fitted over only the side flanges  63  of the second food holding member  60 , the tubes  66  may be fitted over the front and rear flanges  62 , as well as the side flanges  63 , so as to effectively prevent sparks from arcing between the second food holding member  60  and the rear wall  21  of the cooking cavity  20 . 
     The second food holding member  60  may be made of a metal, and further may be made of aluminum which is light and has excellent heat-conductivity. 
     FIG. 5 is a view showing the microwave oven of the embodiment of the present invention, when the first and second food holding members  50  and  60  are seated on the upper and lower supports  34  and  35 , respectively. As shown in the FIG. 5, the first and second food holding members  50  and  60  are mounted in or removed from the cooking cavity  20  by sliding the first and second food holding members  50  and  60  in or out of the cooking cavity  20 , as the tubes  55  and  66  directly come into contact with the upper and lower supports  34  and  35 . 
     As shown in FIG. 5, when the first food holding member  50  is seated on the upper supports  34  and the second food holding member  60  is seated on the lower supports  35 , the upper heater  31  and the two middle heaters  32  are operated to uniformly cook upper and lower parts of greasy food, such as meat, while browning a surface of the food. At this time, grease from the food, such as meat, which is placed on the first food holding member  50 , falls to the second food holding member  60  which is fabricated in a form of a tray. 
     Further, the second food holding member  60 , which may be made of aluminum, reflects radiant heat transmitted from the upper heater  31  and one or more middle heaters  32 , to the first food holding member  50 , so the heat generated from the heaters  31  and  32  is more effectively used. 
     As shown in FIG. 5, when both the first and second food holding members  50  and  60  are mounted in the cooking cavity  20 , many pieces of bread can be browned at one time, thus rapidly making many pieces of toast. 
     Further, when cooking food, such as cookies, pizza, or cake, a user may put the second food holding member  60  fabricated in the form of a tray on one of the upper and lower supports  34  and  35  and operate the upper heater  31  and one or more middle heaters  32 . 
     When high-frequency electromagnetic waves generated by the magnetron  11  are transmitted to the cooking cavity  20 , in addition to an operation of the heaters  31  and  32 , food placed on the first and second food holding members  50  and  60  is more rapidly cooked. 
     FIG. 6 is a partial perspective view showing the microwave oven of the embodiment of the present invention, with the first food holding member  50  being stopped by the projection  36  which is provided above one of the upper supports  34 . As shown in the FIG. 6, the projection  36  is provided at a front portion of the left sidewall  22  of the cooking cavity  20  so as to project toward a center of the cooking cavity  20  by a predetermined length, and is positioned above the one upper support  34  of the left sidewall  22  and the projection  36  is spaced apart from the one upper support  34  by a predetermined length. When the first food holding member  50  slides out of the cooking cavity  20  to be removed from the cooking cavity  20 , the front portion of the first food holding member  50  may be tilted downward by a weight of the food or carelessness of the user. At this time, one of the side bars  52  is stopped by the projection  36  so as to prevent the first food holding member  50  from falling to the floor, thus preventing food placed on the first food holding member  50  from spilling. 
     As described above, a microwave oven is provided, which is designed such that an upper heater is provided at a position adjacent to the upper wall of a cooking cavity and one or more middle heaters is provided between a turntable-type cooking tray and the upper heater so that upper and lower surfaces of the food, which is placed on a food holding member, face the upper heater and the one or more middle heaters, respectively, so that heat generated from the heaters is effectively transmitted to the food, therefore rapidly and uniformly cooking the food. 
     The microwave oven is provided having sidewalls of the cooking cavity with upper and lower supports so that one or more food holding members are mounted in the cooking cavity, thus cooking a large quantity of food at one time, therefore reducing overall cooking time. 
     Further, the microwave oven is designed to prevent sparks from arcing between the food holding members and the rear wall of the cooking cavity and to prevent sidewalls of the cooking cavity from being worn, thus safely cooking the food and lengthening a life span of the microwave oven. 
     Further, the microwave oven is provided with a projection on a sidewall so as to prevent a food holding member from undesirably falling down from the microwave oven when pulling the food holding member from the cooking cavity, thus safely allowing the food to be taken out of the cooking cavity. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.