Patent Publication Number: US-7915568-B2

Title: Multifunction microwave oven with superheated steam and the control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from CN Patent Application No. 200620053579.9 filed on Jan. 11, 2006, entitled “Multifunction Microwave Oven with Superheated Steam”. 
     TECHNICAL FIELD 
     The present invention relates to an electric kitchen appliance, particularly to a multifunction microwave oven with superheated steam and the control method thereof. 
     BACKGROUND OF THE INVENTION 
     The conventional microwave oven existing in the market does not have a steam heating function. Although it has a high cooking speed and high cooking efficiency, but the cooked food is often lack of water, not fresh nor tender, therefore the conventional microwave oven is only suitable for limited types of food. On the other hand, the steam cookers existing in the market include steamers, electric saucepans, pressure cookers, even microwave steamers. However, all of these commercial available steam cookers can not generate superheated steam, and have defects such as low heating efficiency, low steam temperature, small amount of steam, large steam loss, low cooking speed, inconvenient operation, unsafe for use and unsatisfactory cooking effect. In a Chinese patent application publication CN1829882A, a steam cooker which can generate superheated steam is disclosed, wherein a sub cavity incorporating a steam heating heater is formed at the center of the ceiling part of a heating chamber. Steam in the heating chamber is sucked into an air blow device through a suction port and force-fed into the sub cavity through an external circulating passage. Gas passed through the external circulation passage sucks steam from a steam generator midway in the external circulation passage and enters from the external circulation passage into the sub cavity. The steam heated by the steam heating heater until it is brought into an superheated state is jetted downward from a plurality of upper gas jetting holes formed in the bottom panel of the sub cavity by such a force that makes the steam reach the bottom of the heating chamber so that the steam can be collided with a heated matter. The steam is raised on the outside of downward air flow and the convection of steam occurs in the heating chamber. However, in this patent application, an axial fan is adopted, and the circulation passage is very complicated, therefore a large space is needed; meanwhile, since the gas jetting holes are formed on the top of the heating chamber, the steam with higher temperature and pressure from the sub cavity blows downwards directly to the food from the top of the heating chamber, which causes the temperature of the top part of the food to increase rapidly, while the lateral part and bottom part of the food does not contact directly with the high temperature gas and the temperature thereof increases slowly. Therefore, during the whole heating process, the temperature within the heating chamber is not uniform, and the food can not be heated uniformly, causing some part of the food to be overheated but some part to be underheated, which affects the cooking quality. 
     SUMMARY OF THE INVENTION 
     The present invention aims to solve the above-mentioned shortcomings of the prior art, and to provide a multifunction microwave oven with superheated steam and the control method thereof, so as to heat the food uniformly and to provide versatile heating modes. 
     The above-mentioned object of the present invention is realized by the technical solution as described below: 
     A multifunction microwave oven with superheated steam, comprising a casing, a cooking chamber for accommodating food to be cooked, a microwave generating assembly for generating microwave for cooking food, a steam generating assembly, a steam heating assembly and a control circuit. 
     Wherein the steam generating assembly for generating ordinary steam of approximately 100° C. is located at the bottom or beside of the casing; said steam generating assembly includes a water tank, a water pump, water pipes, a boiler and an ordinary steam pipe, and wherein the water tank is located at the bottom or beside of the cooking chamber, and the boiler incorporates a heating means and a water level sensing means. 
     Wherein the steam heating assembly for generating superheated steam up to 400° C. is located at the top or beside of the cooking chamber; said steam heating assembly includes a convection heating cavity incorporating a centrifugal impeller and its driving means, and a heating means. 
     Wherein the ordinary steam pipe is connected with the convection heating cavity, and the ordinary steam from the boiler enters the convection heating cavity through this ordinary steam pipe; upper gas outlets and upper gas suction ports are disposed on the convection heating cavity, so that the superheated steam passes through the upper gas outlets of the convection heating cavity and blows outwardly and downwardly into the cooking chamber, while the backflowing gas is sucked from the central area of the cooking chamber and enters the convection heating cavity through the upper gas suction ports. 
     Preferably, the heating means of the boiler includes a first boiler heating tube and a second boiler heating tube which can be controlled separately. And the heating means of the convection heating cavity includes a first upper heating tube and a second upper heating tube which can be controlled separately. So that these four heating tubes can be controlled to work in different modes to generate at least superheated steam between 100° C. to 400° C., ordinary steam of approximately 100° C. and convective hot flow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further explained by a preferred embodiment in combination with the accompanying drawings. 
         FIG. 1  is a schematic front view of the multifunction microwave oven with superheated steam according to one embodiment of the present invention; 
         FIG. 2  is a schematic side view of the multifunction microwave oven with superheated steam as shown in  FIG. 1 ; 
         FIG. 3  is a schematic top view of the multifunction microwave oven with superheated steam as shown in  FIG. 1 ; 
         FIG. 4  is a schematic diagram of the control circuit of the multifunction microwave oven with superheated steam as shown in  FIG. 1 . 
     
    
    
     Wherein the numerals for the parts are listed as below:
           1 : motor for the rotating disc     2 : glass rotating disc;     3 : cooking chamber     4 : high voltage transformer;     5 : magnetron;     6 : water tank;     7 : water pump;     8 : water pipe;     9 : boiler;     10 : big boiler heating tube;     11 : small boiler heating tube;     12 : water lever sensing bar;     13 : ordinary steam pipe;     14 : convection heating chamber;     15 : centrifugal impeller;     16 : upper big heating tube;     17 : upper small heating tube;     18 : belt;     19 : motor;     20 : cooling impeller;     21 : thermistor;     22 : upper gas outlets;     23 : upper gas suction ports;     24 : lower gas outlets.       

     DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be illustrated in details referring to the embodiments as described below: 
     As shown in  FIG. 1  to  FIG. 3 , according to one embodiment of the present invention, the multifunction microwave oven with superheated steam is comprised of a casing, a cooking chamber  3 , a microwave generating assembly, a steam generating assembly, a steam heating assembly and a control circuit. 
     The cooking chamber  3  incorporates a glass rotating disc  2  driven by a motor  1 , for accommodating food to be cooked. 
     The microwave generating assembly includes a high voltage transformer  4  and a magnetron  5 , for generating microwave for cooking food. 
     The steam generating assembly for generating ordinary steam of approximately c is located at the bottom or beside of the casing, including a water tank  6 , a pump  7 , water pipes  8 , a boiler  9  and an ordinary steam pipe  13 . The water tank  6  is located at the bottom of the cooking chamber  3 . The boiler  9  incorporates a big boiler heating tube  10 , a small boiler heating tube  11  and a water lever sensing bar  12 . The water lever sensing bar  12  is installed within the water tank  6 , whose resistance value varies with the water level, so that the control unit of the control circuit will acquire the information of the water level and send instructions to the water pump  7 . 
     The steam heating assembly for generating superheated steam up to 400° C. is located at the top or beside the cooking chamber. The steam heating assembly includes a convection heating cavity  14  incorporating a centrifugal impeller  15 , a driving means for the centrifugal impeller  15 , an upper big heating tube  16 , and an upper small heating tube  17 . The driving means for the centrifugal impeller  15  comprises a belt  18 , a motor  19  and a impeller  20  for cooling the motor  19 . 
     In addition to heating tubes, the heating means in the steam generating assembly or in the steam heating assembly may include other types of heating means such as electric-heated diaphragms, semiconductor heating means, etc. 
     The ordinary steam pipe  13  is connected with the convection heating cavity  14 , and the ordinary steam from the boiler  9  enters the convection heating cavity  14  through this ordinary steam pipe  13 . 
     Upper gas outlets  22  and upper gas suction ports  23  are disposed at the bottom panel of the convection heating cavity  14 . The upper gas suction ports  23  include plurality of through holes distributed within an inner circular region at the bottom panel of the convection heating cavity  14 , and the upper gas outlets  22  include plurality of through holes distributed within an outer circular ring at the bottom panel of the convection heating cavity  14 . 
     The inner circular region, the outer circular ring and the impeller  15  are concentric. And the inner circular region and the outer circular ring are positioned to conform to the radial dimension of blades of the centrifugal impeller  15 , i.e., the blades are substantially located within the separation between the inner circular region and the outer circular ring. 
     The convection heating cavity  14  has a side passage connected to the cooking chamber  3 , and the interface between the convection heating cavity  14  and the cooking chamber  3  is a wall with plurality of through holes thereon, namely the lower gas outlets  24 . The lower gas outlets  24  are distributed within a rectangular region at the bottom of the cooking chamber  3 . 
     Some of the superheated steam passes through the upper gas outlets  22  of the convection heating cavity  14  and blows outwardly and downwardly into the cooking chamber, while some of the superheated steam passes through the lower gas outlets  24  and blows forwardly and horizontally to the lower region of the cooking chamber  3 . The backflowing gas is sucked from the central area of the cooking chamber  3  and enters the convection heating cavity  14  through the upper gas suction ports  23 . 
     The blades of the centrifugal impeller  15  rotate in a high speed by the driving means, which produce a gas flow in the cooking chamber  3 . The gas within the convection heating cavity  14  rotates in a high speed around the periphery of the blades of the centrifugal impeller  15 , and spreads away from the convection heating cavity  14  through the upper gas outlets  22 . Meanwhile, under the centrifugal effect, the gas at the lower region of the cooking chamber  3  is sucked towards the convection heating cavity  14  through the upper gas suction ports  23 . Thus, a convection and circulating passage for the steam and hot air is formed. 
     During the high speed rotation of the blades of the centrifugal impeller  15 , some of the superheated steam passes through the lower gas outlets  24  and enters the cooking chamber  3 , so as to heat the bottom of the food loaded on the glass rotating disc  2 . The lower gas outlets  24  may be positioned at the left side, right side or back side of the cooking chamber  3 . However, the lower gas outlets  24  are not necessarily needed for this invention. 
     As shown in  FIG. 4 , the control circuit of the present invention includes a control unit  24  incorporating a microprocessor and a memory, by which the multifunction microwave oven works according to a preset program. Connected with the control unit  24  are the centrifugal impeller  15 , the water pump  7 , the motor  19 , a lock detection means  33 , a temperature sensing means  25 , a gas release and water discharging control circuit  26 , a water tank detection circuit  27 , switches  28 , a motor  29  for water discharging valve, a control circuit  30  for the gas release valve, a lighting control circuit  31 , a power switch  32 , the water level sensing bar  12 , a control circuit for the steam generating assembly and a control circuit for the steam heating assembly. 
     Since the big boiler heating tube  10  and the small boiler heating tube  11  of the steam generating assembly can be controlled separately, and the upper big heating tube  16  and the upper small heating tube  17  of the steam heating assembly can be controlled separately, so that these four heating tubes can be controlled to work in different modes to generate at least superheated steam between 100° C. to 400° C., ordinary steam of approximately 100° C. and convective hot flow. 
     Under the control circuit, the superheated steam cooking mode is programmed as follows: 
     Step 1: after the oven is started, the water level sensing bar  12  detects whether water exists in the boiler  9 , and sends the signal to the control unit  24 ; 
     Step 2: if no water is detected, the control unit  24  sends instructions to start the water pump  7 , and the water pump  7  supplies prescribed amount of water to the boiler  9  via water pipes  8  within a preset time duration; 
     Step 3: After water enters the boiler  9 , the big boiler heating tube  10  and a small boiler heating tube  11  are energized to heat the water to turn into ordinary steam of approximately 100° C.; 
     Step 4: the ordinary steam enters the convection heating cavity  14  through the ordinary steam pipe  13 . Under the effect of the centrifugal impeller  15 , ordinary steam from the boiler  9  and the gas coming from the cooking chamber  3  through the upper gas suction ports  23  are fed to be heated by the upper big heating tube  16  and the upper small heating tube  17 . The gas is further heated up to 400° C. within the convection heating cavity  14 . 
     Step 5: by the effect of the centrifugal impeller  15 , the mixed gas with higher temperature enters the cooking chamber  3  through the upper gas outlets  22  and the lower gas outlets  24 . 
     Wherein either the ordinary steam of about 100° generated by the steam generating assembly or the superheated steam between 100° and 400° generated by the steam heating assembly may have a pressure of 1 atm or above 1 atm (Standard atmosphere). 
     Thus, the ordinary steam from the boiler  9  and the gas from the cooking chamber  3  are heated and circulated by the effect of the centrifugal impeller  15 , so as to increase the temperature of the gas within the cooking chamber  3  to approximately between 100° C. to 250° C. 
     Under the control circuit, the strong steam cooking mode is programmed as follows: 
     Step 1: after the oven is started, the water level sensing bar  12  detects whether water exists in the boiler  9 , and sends the signal to the control unit  24 ; 
     Step 2: if no water is detected, the control unit  24  sends instructions to start the water pump  7 , and the water pump  7  supplies prescribed amount of water to the boiler  9  via water pipes  8  within a preset time duration; 
     Step 3: After water enters the boiler  9 , the big boiler heating tube  10  and a small boiler heating tube  11  are energized to heat the water to turn into ordinary steam of approximately 100° C.; 
     Step 4: the ordinary steam enters the convection heating cavity  14  through the ordinary steam pipe  13 . Under the effect of the centrifugal impeller  15 , ordinary steam from the boiler  9  and the gas coming from the cooking chamber  3  through the upper gas suction ports  23  are fed to be heated by one of the upper big heating tube  16  and the upper small heating tube  17 , while the other one of the upper big heating tube  16  and the upper small heating tube  17  is not energized. The gas is further heated up to 200-300° C. within the convection heating cavity  14 . 
     Step 5: by the effect of the centrifugal impeller  15 , the mixed gas with higher temperature enters the cooking chamber  3  through the upper gas outlets  22  and the lower gas outlets  24 . 
     Under the control circuit, the ordinary steam cooking mode is programmed as follows: 
     Step 1: after the oven is started, the water level sensing bar  12  detects whether water exists in the boiler  9 , and sends the signal to the control unit  24 ; 
     Step 2: if no water is detected, the control unit  24  sends instructions to start the water pump  7 , and the water pump  7  supplies prescribed amount of water to the boiler  9  via water pipes  8  within a preset time duration; 
     Step 3: After water enters the boiler  9 , the big boiler heating tube  10  and a small boiler heating tube  11  are energized to heat the water to turn into ordinary steam of approximately 100° C.; 
     Step 4: the ordinary steam enters the convection heating cavity  14  through the ordinary steam pipe  13 . Under the effect of the centrifugal impeller  15 , ordinary steam from the boiler  9  and the gas coming from the cooking chamber  3  through the upper gas suction ports  23  are fed to the convection heating cavity  14 . While neither of the upper big heating tube  16  and the upper small heating tube  17  is energized. 
     Step 5: by the effect of the centrifugal impeller  15 , the mixed gas with higher temperature enters the cooking chamber  3  through the upper gas outlets  22  and the lower gas outlets  24 . 
     Under the control circuit, the convective hot flow cooking mode is programmed as follows: 
     Step 1: after the oven is started, neither of the water level sensing bar  12  and the water pump  7  works. 
     Step 2: by the effect of the centrifugal impeller  15 , the gas from the cooking chamber  3  enters the convection heating cavity  14 ; both of the upper big heating tube  16  and the upper small heating tube  17  are energized to heat the dry gas, and the hot gas flow enters the cooking chamber  3  through the upper gas outlets  22  and the lower gas outlets  24 . 
     Since the superheated steam, ordinary steam and convective hot flow can enter the cooking chamber  3  through both of the upper gas outlets  22  and the lower gas outlets  24 , the food loaded on the glass rotating disc  2  driven by the motor  1  will be cooked uniformly. 
     With the multifunction microwave oven of the present invention, one can cook food with a high speed, high quality and versatile modes. The water in the food is preserved during cooking, the food cooked is fresh and tender, with its original taste and color. And what is more important, the superfluous fat and salt in the food is removed, vitamins and minerals are preserved, the food cooked has low calorie and is more healthy. 
     The various cooking functions include baking, air convective baking, water baking, steaming, microwave cooking, thaw and zymolysis, etc. And the multifunction microwave oven of the present invention can be used to cook daily food such as meat, fowl, seafood, vegetable, cake and biscuit, etc. 
     According to the present invention, convective superheated steam can be generated when the oven has not been loaded with food so as to clean the dirt on the walls of the cooking chamber. 
     According to the present invention, after lemon scour is added to the water tank, the water tank operates when the oven has not been loaded with food so as to remove the scale inside by the recycling of the lemon water in the system.